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Find video protocols related to scientific articles indexed in Pubmed.
Phosphorescence within benzotellurophenes and color tunable tellurophenes under ambient conditions.
Chem. Commun. (Camb.)
PUBLISHED: 11-01-2014
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The zirconium-mediated syntheses of pinacolboronate (BPin) appended benzo[b]tellurophenes and two phenyl/BPin substituted tellurophene isomers with different colors of emission have been achieved. These species are new additions to an emerging class of inorganic heterocycles that display visible phosphorescence in the solid state under ambient conditions.
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To Bend or Not To Bend: Experimental and Computational Studies of Structural Preference in Ln(Tp(iPr)2)2 (Ln = Sm, Tm).
Inorg Chem
PUBLISHED: 10-27-2014
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The synthesis and characterization of Ln(Tp(iPr2))2 (Ln = Sm, 3Sm; Tm, 3Tm) are reported. While the simple (1)H NMR spectra of the compounds indicate a symmetrical solution structure, with equivalent pyrazolyl groups, the solid-state structure revealed an unexpected, "bent sandwich-like" geometry. By contrast, the structure of the less sterically congested Tm(Tp(Me2,4Et))2 (4) adopts the expected symmetrical structure with a linear B-Tm-B arrangement. Computational studies to investigate the origin of the unexpected bent structure of the former compounds indicate that steric repulsion between the isopropyl groups forces the Tp ligands apart and permits the development of unusual interligand C-H···N hydrogen-bonding interactions that help stabilize the structure. These results find support in the similar geometry of the Tm(III) analogue [Tm(Tp(iPr2))2]I, 3Tm(+), and confirm that the low symmetry is not the result of a metal-ligand interaction. The relevance of these results to the general question of the coordination geometry of MX2 and M(C5R5)2 (M = heavy alkaline earth and Ln(II), X = halide, and C5R5 = bulky persubstituted cyclopentadienyl) complexes and the importance of secondary H-bonding and nonbonding interactions on the structure are highlighted.
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Experimental and Computational Studies on Interrupted Nazarov Reactions: Exploration of Umpolung Reactivity at the ?-Carbon of Cyclopentanones.
J. Am. Chem. Soc.
PUBLISHED: 10-13-2014
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A set of densely substituted, ?-functionalized cyclopentanones can be generated by a two-component, domino reaction sequence entailing the Nazarov electrocyclization of divinyl ketones and nucleophilic addition of the resulting 2-oxidocyclopentenyl cations by selected trapping modalities. Bypassing the typical eliminative termination, Nazarov oxyallyl species can react with carbon ?-nucleophiles through cycloadditions (or formal cycloadditions), in which bridged bicyclic systems are established, or nucleophilic trappings whereby one terminal carbon of the oxyallyl intermediate is subjected to carbon-carbon bond formation. A detailed investigation of reaction parameters to explicitly control the course of the "interrupted" Nazarov reactions is described. This methodology allows for facile installation of ?-quaternary centers bearing allyl, alkynyl, and heteroaryl groups in an umpolung fashion. In addition, the trapping event of a Nazarov intermediate with furan was studied by DFT computations, in conjunction with experimental data, offering a rationale for the observed reaction pattern and diastereoselectivity.
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Comparative effectiveness of carotid revascularization therapies: evidence from a national hospital discharge database.
Stroke
PUBLISHED: 10-09-2014
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Clinical equipoise of carotid revascularization therapies remains controversial. We sought to determine whether adverse outcomes after carotid endarterectomy (CEA) or carotid angioplasty and stenting (CAS) were similar using propensity score-matched analysis of retrospective data from a large hospital discharge database.
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Donor- and/or Acceptor-Substituted Expanded Radialenes: Theory, Synthesis, and Properties.
J. Org. Chem.
PUBLISHED: 09-27-2014
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The synthesis of donor- (D) and/or acceptor (A)-expanded [4]radialenes has been developed on the basis of readily available dibromoolefin (7), tetraethynylethene (10 and 20), and vinyl triflate (12) building blocks. The successful formation of D/A radialenes relies especially on (1) effective use of a series alkynyl protecting groups, (2) Sonogashira cross-coupling reactions, and (3) the development of ring closing reactions to form the desired macrocyclic products. The expanded [4]radialene products have been investigated by spectroscopic (UV-vis absorption and emission) and quantum chemical computational methods (density functional theory and time dependent DFT). The combined use of theory and experiment provides a basis to evaluate the extent of D/A interactions via the cross-conjugated radialene framework as well as an interpretation of the origin of D/A interactions at an orbital level.
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Synthesis and photophysics of thioindigo diimines and related compounds.
J. Org. Chem.
PUBLISHED: 09-23-2014
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We report the synthesis and comprehensive characterization of diamine and diimine derivatives of the fluorescent compound thioindigo. Diamines 1 were obtained by metal-mediated amine condensation reaction with thioindigo. Oxidation of the products of the coupling reaction provided the diimines 2. X-ray crystal structures, cyclic voltammetry, and spectral and photophysical data of the compounds are presented. X-ray crystal structures demonstrate a planar structure for the diimine derivatives and a twisted conformation for the diamines. The diamine compounds 1 absorb in the UV (?max 324-328 nm), significantly blue-shifted from the absorption spectrum of thioindigo. Diamines 1 exhibit moderate fluorescence (?F = 0.25, 0.045). A transient triplet state is observed in laser flash photolysis (LFP) experiments of 1, with lifetimes 1 order of magnitude longer than those of thioindigo. The diimine compounds 2 absorb at longer wavelengths (?max 495-510 nm) than the diamines but are still slightly blue-shifted from thioindigo, with molar extinction coefficients 17-70% higher compared to thioindigo. The diimine compounds are not emissive, and LFP studies indicate transient species with microsecond lifetimes. Quenching experiments and transient absorption spectra are consistent with trans-cis isomerization.
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Intravenous Contrast Material Exposure Is Not an Independent Risk Factor for Dialysis or Mortality.
Radiology
PUBLISHED: 09-09-2014
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Purpose To determine the risk of emergent dialysis and short-term mortality following intravenous iodinated contrast material exposure. Materials and Methods This single-center retrospective study was HIPAA compliant and institutional review board approved. All contrast material-enhanced (contrast group) and unenhanced (noncontrast group) abdominal, pelvic, and thoracic computed tomography scans from 2000-2010 were identified. Patients in the contrast and noncontrast groups were compared following propensity score-based 1:1 matching to reduce intergroup selection bias. Patients with preexisting diabetes mellitus, congestive heart failure, or chronic or acute renal failure were identified as high-risk patient subgroups for nephrotoxicity. The effects of contrast material exposure on the rate of acute kidney injury (AKI) (serum creatinine level ? 0.5 mg/dL [44.2 ?mol/L] above baseline within 24-72 hours of exposure) and dialysis or death within 30 days of exposure were determined by using odds ratios (ORs) and covariate-adjusted Cox proportional hazards models. Results were validated with a bootstrapped sensitivity analysis. Results The 1:1 matching on the basis of the propensity score yielded a cohort of 21 346 patients (10 673 in the contrast group, 10 673 in the noncontrast group). Within this cohort, the risks of AKI (OR, 0.94; 95% confidence interval [CI]: 0.83, 1.07; P = .38), emergent dialysis (OR, 0.96; 95% CI: 0.54, 1.60; P = .89), and 30-day mortality (hazard ratio [HR], 0.97; 95% CI: 0.87, 1.06; P = .45) were not significantly different between the contrast group and the noncontrast group. Although patients who developed AKI had higher rates of dialysis and mortality, contrast material exposure was not an independent risk factor for either outcome for dialysis (OR, 0.89; 95% CI: 0.40, 2.01; P = .78) or for mortality (HR, 1.03; 95% CI: 0.82, 1.32; P = .63), even among patients with compromised renal function or predisposing comorbidities. Conclusion Intravenous contrast material administration was not associated with excess risk of AKI, dialysis, or death, even among patients with comorbidities reported to predispose them to nephrotoxicity. © RSNA, 2014 Online supplemental material is available for this article.
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Metal coordination, and metal-ligand redox non-innocence, modulates allosteric C-N bond homolysis in an N-benzyl tetrazine.
Chem. Commun. (Camb.)
PUBLISHED: 09-09-2014
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Remote coordination of a Ru(hfac)2 moiety to a chelating N-benzyl tetrazine lowers the C-N homolytic bond dissociation enthalpy by approximately 20 kJ mol(-1). The significant bond strength perturbation is believed to arise as a consequence of metal-ligand redox non-innocence.
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Classical and non-classical redox reactions of Pd(II) complexes containing redox-active ligands.
Chem. Commun. (Camb.)
PUBLISHED: 08-21-2014
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Reactivity studies of a Pd(II)-verdazyl complex reveal novel ligand-centred reduction processes which trigger pseudo-reductive elimination at Pd. Reaction of the complex with water induces a ligand-centred redox disproportionation. The reduced verdazyl ligands can also be reversibly protonated.
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Application of the donor-acceptor concept to intercept low oxidation state group 14 element hydrides using a Wittig reagent as a Lewis base.
Inorg Chem
PUBLISHED: 07-30-2014
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This article outlines our attempts to stabilize the Group 14 element dihydrides, GeH2 and SnH2, using commonly employed phosphine and pyridine donors; in each case, elemental Ge and Sn extrusion was noted. However, when these phosphorus and nitrogen donors were replaced with the ylidic Wittig ligand Ph3P?CMe2, stable inorganic methylene complexes (EH2) were obtained, demonstrating the utility of this under-explored ligand class in advancing main group element coordination chemistry.
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Twenty-year follow-up of a randomized prospective clinical trial of excimer laser photorefractive keratectomy.
Am. J. Ophthalmol.
PUBLISHED: 06-15-2014
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To investigate the 20-year efficacy and safety of photorefractive keratectomy (PRK).
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Prototypical phosphine complexes of antimony(III).
Inorg Chem
PUBLISHED: 04-28-2014
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Complexes of the generic formula [Cln(PR3)mSb]((3-n)+) (n = 1, 2, 3, or 4 and m = 1 or 2) have been prepared featuring [ClSb](2+), [Cl2Sb](1+), Cl3Sb, or [Cl4Sb](1-) as acceptors with one or two phosphine ligands {PMe3, PPh3, PCy3 (Cy = C6H11)}. The solid-state structures of the complexes reveal foundational features that define the coordination chemistry of a lone pair bearing stibine acceptor site. The experimental observations are interpreted with dispersion-corrected density functional theory calculations to develop an understanding of the bonding and structural diversity.
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?-Hydroxycyclopentanones via one-pot oxidation of the trimethylaluminum-mediated Nazarov reaction with triplet oxygen.
Chem. Commun. (Camb.)
PUBLISHED: 04-24-2014
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Trimethylaluminum and molecular oxygen are used in tandem to interrupt the Nazarov cyclization. ?-Hydroxycyclopentanones are produced in moderate to good yield as a mixture of epimers. This sequence is the first example of combined nucleophilic/electrophilic trapping of the Nazarov oxyallyl intermediate.
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Accessing zinc monohydride cations through coordinative interactions.
Angew. Chem. Int. Ed. Engl.
PUBLISHED: 04-23-2014
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We present isolable examples of formal zinc hydride cations supported by N-heterocyclic carbene (NHC) donors, and investigate the dual electrophilic and nucleophilic (hydridic) character of the encapsulated [ZnH](+) units by computational methods and preliminary hydrosilylation catalysis.
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Endothelial apoptosis in pulmonary hypertension is controlled by a microRNA/programmed cell death 4/caspase-3 axis.
Hypertension
PUBLISHED: 04-14-2014
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Pulmonary endothelial cell apoptosis is a transient, yet defining pathogenic event integral to the onset of many pulmonary vascular diseases such as pulmonary hypertension (PH). However, there is a paucity of information concerning the molecular pathway(s) that control pulmonary arterial endothelial cell apoptosis. Here, we introduce a molecular axis that when functionally active seems to induce pulmonary arterial endothelial cell apoptosis in vitro and PH in vivo. In response to apoptotic stimuli, human pulmonary arterial endothelial cells exhibited robust induction of a programmed cell death 4 (PDCD4)/caspase-3/apoptotic pathway that was reversible by direct PDCD4 silencing. Indirectly, this pathway was also repressed by delivery of a microRNA-21 mimic. In vivo, genetic deletion of microRNA-21 in mice (miR-21(-/-) mice) resulted in functional activation of the PDCD4/caspase-3 axis in the pulmonary tissues, leading to the onset of progressive PH. Conversely, microRNA-21-overexpressing mice (CAG-microRNA-21 mice) exhibited reduced PDCD4 expression in pulmonary tissues and were partially resistant to PH in response to chronic hypoxia plus SU 5416 injury. Furthermore, direct PDCD4 knockout in mice (PDCD4(-/-) mice) potently blocked pulmonary caspase-3 activation and the development of chronic hypoxia plus SU 5416 PH, confirming its importance in disease onset. Broadly, these findings support the existence of a microRNA-21-responsive PDCD4/caspase-3 pathway in the pulmonary tissues that when active serves to promote endothelial apoptosis in vitro and PH in vivo.
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Comorbid Rat Model of Ischemia and ?-Amyloid Toxicity: Striatal and Cortical Degeneration.
Brain Pathol.
PUBLISHED: 04-02-2014
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Levels of cerebral amyloid, presumably ?-amyloid (Abeta), toxicity and the incidence of cortical and subcortical ischemia increases with age. However, little is known about the severe pathological condition and dementia that occur as a result of the comorbid occurrence of this vascular risk factor and Abeta toxicity. Clinical studies have indicated that small ischemic lesions in the striatum are particularly important in generating dementia in combination with minor amyloid lesions. These cognitive deficits are highly likely to be caused by changes in the cortex. In this study, we examined the viability and morphological changes in microglial and neuronal cells, gap junction proteins (connexin43) and neuritic/axonal retraction (Fer Kinase) in the striatum and cerebral cortex using a comorbid rat model of striatal injections of endothelin-1 (ET1) and Abeta toxicity. The results demonstrated ventricular enlargement, striatal atrophy, substantial increases in ?-amyloid, ramified microglia and increases in neuritic retraction in the combined models of stroke and Abeta toxicity. Changes in connexin43 occurred equally in both groups of Abeta-treated rats, with and without focal ischemia. Although previous behavioral tests demonstrated impairment in memory and learning, the visual discrimination radial maze task did not show significant difference, suggesting the cognitive impairment in these models is not related to damage to the dorsolateral striatum. These results suggest an insight into the relationship between cortical/striatal atrophy, pathology and functional impairment.
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Evidence of dihydrogen bonding of a chiral amine-borane complex in solution by VCD spectroscopy.
Angew. Chem. Int. Ed. Engl.
PUBLISHED: 03-25-2014
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IR and vibrational circular dichroism (VCD) spectra of a chiral amine-borane in solution are investigated. By comparison of experimental and calculated spectra, unique VCD spectral signatures, which can be attributed to the formation of dihydrogen-bonded dimers in solution, are identified for the first time. These VCD features are highly sensitive to the specific dihydrogen-bonding topologies utilized by the chiral amine-borane subunits and thus provide direct structural information of these dihydrogen-bonded species in solution. Differences in the dihydrogen binding arrangements in solution and in solid state are also revealed.
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Strong solvent-dependent preference of ? and ? stereoisomers of a tris(diamine)nickel(II) complex revealed by vibrational circular dichroism spectroscopy.
Inorg Chem
PUBLISHED: 03-06-2014
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In the present study, we use vibrational circular dichroism (VCD) spectroscopy to investigate the metal-centered ? and ? chirality of a tris(diamine)nickel(II) complex. Chiral diphenylethylenediamine is chosen as the ligand, which puts the ? and ? isomers of the complex in a diastereomeric relationship. X-ray crystallography indicates an equal preference of both stereoisomers in the solid state. This equal preference is also supported by the related density functional theory calculations. A comparison between the experimental and calculated VCD spectra also proves the existence of both isomers in an acetonitrile solution. However, a significant shift of the equilibrium toward the ? diastereomer is found for the complex in dimethyl sulfoxide. This solvent-induced preference for a particular absolute configuration is hypothesized to arise from a stronger and more effective solvation of the ? isomer. The observation that the solvent can significantly influence and shift an equilibrium between two diastereomeric forms is expected to have important implications on structural analysis and on how reaction mechanisms are rationalized.
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The effects of chronic photoperiod shifting on the physiology of female Long-Evans rats.
Brain Res. Bull.
PUBLISHED: 02-16-2014
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As the prevalence of shift work is increasing, it is important to elucidate the impact that shift work has on health. Because of the alternating work schedules present in rotating shift work and working at night, shift workers are in a chronic state of circadian disruption. Animal models of circadian disruption are useful because they offer more experimental control than the largely correlational human shift work studies. The effects of chronic circadian disruption on food preference, glucose tolerance, corticosterone secretion, and performance in a stress-inducing task were investigated in female Long-Evans rats. A 64-day photoperiod shifting paradigm was used to induce circadian disruption. Surprisingly, neither the photoperiod shifted animals, nor the control animals demonstrated a preference for either an unhealthy or healthy diet. Nor was there a difference between the groups in weight gained during photoperiod shifting. However, the photoperiod shifted rats gained significantly more weight than control animals, without eating more food during discriminative fear conditioning to context (DFCTC). Surprisingly, chronic photoperiod shifting appeared to facilitate retention in the DFCTC task. The photoperiod shifted animals also had increased serum glucose values during fasting and after a glucose challenge test. The photoperiod shifted animals only had elevated corticosterone during the final two phases of photoperiod shifting. This study demonstrates that chronic photoperiod shifting elicits weight gain when exposed to a stressful event and impairs glucose tolerance in the same individual.
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Coaxing solid-state phosphorescence from tellurophenes.
Angew. Chem. Int. Ed. Engl.
PUBLISHED: 01-31-2014
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The synthesis of the first examples of tellurophenes exhibiting phosphorescence in the solid state and under ambient conditions (room temperature and in air) is reported. Each of these main-group-element-based emitters feature pinacolboronates (BPin) as ring-appended side groups. The nature of the luminescence observed was also investigated using computational methods.
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Coordination complexes of Ph?Sb²? and Ph?Bi²?: beyond pnictonium cations.
Angew. Chem. Int. Ed. Engl.
PUBLISHED: 01-23-2014
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The syntheses of salts containing ligand-stabilized Ph3Sb(2+) and Ph3Bi(2+) dications have been realized by in?situ formation of Ph3Pn(OTf)2 (Pn=Sb or Bi) and subsequent reaction with OPPh3, dmap and bipy. The solid-state structures demonstrate diversity imposed by the steric demands and nature of the ligands. The synthetic method has the potential for broad application enabling widespread development of the coordination chemistry for Pn(V) acceptors.
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Lesions of dorsal striatum eliminate lose-switch responding but not mixed-response strategies in rats.
Eur. J. Neurosci.
PUBLISHED: 01-18-2014
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We used focal brain lesions in rats to examine how dorsomedial (DMS) and dorsolateral (DLS) regions of the striatum differently contribute to response adaptation driven by the delivery or omission of rewards. Rats performed a binary choice task under two modes: one in which responses were rewarded on half of the trials regardless of choice; and another 'competitive' one in which only unpredictable choices were rewarded. In both modes, control animals were more likely to use a predictable lose-switch strategy than animals with lesions of either DMS or DLS. Animals with lesions of DMS presumably relied more on DLS for behavioural control, and generated repetitive responses in the first mode. These animals then shifted to a random response strategy in the competitive mode, thereby performing better than controls or animals with DLS lesions. Analysis using computational models of reinforcement learning indicated that animals with striatal lesions, particularly of the DLS, had blunted reward sensitivity and less stochasticity in the choice mechanism. These results provide further evidence that the rodent DLS is involved in rapid response adaptation that is more sophisticated than that embodied by the classic notion of habit formation driven by gradual stimulus-response learning.
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Risk of intravenous contrast material-mediated acute kidney injury: a propensity score-matched study stratified by baseline-estimated glomerular filtration rate.
Radiology
PUBLISHED: 01-16-2014
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To determine the effect of baseline estimated glomerular filtration rate (eGFR) on the causal association between intravenous iodinated contrast material exposure and subsequent development of acute kidney injury (AKI) in propensity score-matched groups of patients who underwent contrast material-enhanced or unenhanced computed tomography (CT).
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Synthesis and luminescent properties of Lewis base-appended borafluorenes.
Inorg Chem
PUBLISHED: 01-15-2014
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A series of Lewis base adducts of 9-bromo-9-borafluorene (BrBFl-LB, LB = IPr, IPrCH2, PPh3, and PCy3), parent borafluorenes (HBFl-IPr and HBFl-IPrCH2), and the bisadduct [(DMAP)2BFl]Br were prepared and structurally characterized (IPr = [(HCNDipp)2C:], IPrCH2 = [(HCNDipp)2C?CH2], Dipp = 2,6-i-Pr2C6H3, and DMAP = N,N-dimethylaminopyridine). The adducts BrBFl-IPr, BrBFl-PPh3, BrBFl-PCy3, [(DMAP)2BFl]Br, BrBFl-IPrCH2, and HBFl-IPrCH2 were found to exhibit bright blue luminescence with low to moderately high quantum efficiencies (19 to 63%). Selective irradiation at different excitation wavelengths revealed the presence of two distinct emission processes in the adducts BrBFl-LB, leading to a ligand-independent, presumably borafluorene-based, blue light emission at 435 nm and another less intense emission band in the ultraviolet region (315-324 nm); [(DMAP)2BFl]Br exhibits an emission profile that tails into the visible region. Time-dependent density functional theory studies are also included for representative borafluorene adducts. With a judicious choice of functional groups at boron, one can envisage the future generation of a whole library of 4-coordinate borafluorene-based luminogens that complement the efficient light-emitting behavior known for the widely studied boron-dipyrromethene analogues.
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A trinuclear palladium(II) complex containing N,S-coordinating 2-(benzylsulfanyl)anilinide and 1,3-benzothiazole-2-thiolate ligands with a central square-planar PdN4 motif.
Acta Crystallogr C Struct Chem
PUBLISHED: 01-09-2014
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The reaction of dichlorido(cod)palladium(II) (cod = 1,5-cyclooctadiene) with 2-(benzylsulfanyl)aniline followed by heating in N,N-dimethylformamide (DMF) produces the linear trinuclear Pd3 complex bis(?2-1,3-benzothiazole-2-thiolato)bis[?2-2-(benzylsulfanyl)anilinido]dichloridotripalladium(II) N,N-dimethylformamide disolvate, [Pd3(C7H4NS2)2(C13H12NS)2Cl2]·2C3H7NO. The molecule has -1 symmetry and a Pd...Pd separation of 3.2012?(4)?Å. The outer Pd(II) atoms have a square-planar geometry formed by an N,S-chelating 2-(benzylsulfanyl)anilinide ligand, a chloride ligand and the thiolate S atom of a bridging 1,3-benzothiazole-2-thiolate ligand, while the central Pd(II) core shows an all N-coordinated square-planar geometry. The geometry is perfectly planar within the PdN4 core and the N-Pd-N bond angles differ significantly [84.72?(15)° for the N atoms of ligands coordinated to the same outer Pd atom and 95.28?(15)° for the N atoms of ligands coordinated to different outer Pd atoms]. This trinuclear Pd3 complex is the first example of one in which 1,3-benzothiazole-2-thiolate ligands are only N-coordinated to one Pd centre. The 1,3-benzothiazole-2-thiolate ligands were formed in situ from 2-(benzylsulfanyl)aniline.
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The trouble with circadian clock dysfunction: multiple deleterious effects on the brain and body.
Neurosci Biobehav Rev
PUBLISHED: 01-07-2014
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This review consolidates research employing human correlational and experimental work across brain and body with experimental animal models to provide a more complete representation of how circadian rhythms influence almost all aspects of life. In doing so, we will cover the morphological and biochemical pathways responsible for rhythm generation as well as interactions between these systems and others (e.g., stress, feeding, reproduction). The effects of circadian disruption on the health of humans, including time of day effects, cognitive sequelae, dementia, Alzheimer's disease, diet, obesity, food preferences, mood disorders, and cancer will also be discussed. Subsequently, experimental support for these largely correlational human studies conducted in non-human animal models will be described.
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Comorbid A? toxicity and stroke: hippocampal atrophy, pathology, and cognitive deficit.
Neurobiol. Aging
PUBLISHED: 01-04-2014
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Numerous clinical and epidemiological reports indicate that patients with history of vascular illness such as stroke are more likely to develop dementia as the clinical manifestation of Alzheimer's disease. However, there are little data regarding the pathologic mechanisms that link vascular risk factors to the factors associated with dementia onset. We provide evidence that suggests intriguing detrimental interactions between stroke and ?-amyloid (A?) toxicity in the hippocampus. Stroke was induced by unilateral striatal injection of endothelin-1, the potent vasoconstrictor. A? toxicity was modeled by bilateral intracerebroventricular injections of the toxic fragment A?. Gross morphologic changes in comorbid A? and stroke rats were enlargement of the lateral ventricles with concomitant shrinkage of the hippocampus. The hippocampus displayed a series of synergistic biochemical alterations, including microgliosis, deposition of A? precursor protein fragments, and cellular degeneration. In addition, there was bilateral induction of connexin43, reduced neuronal survival, and impaired dendritic development of adult-born immature neurons in the dentate gyrus of these rats compared with either rats alone. Behaviorally, there was impairment in the hippocampal-based discriminative fear-conditioning to context task indicating learning and memory deficit. These results suggest an insight into the relationship between hippocampal atrophy, pathology, and functional impairment. Our work not only highlights the exacerbated pathology that emerges when A? toxicity and stroke occur comorbidly but also demonstrates that this comorbid rat model exhibits physiopathology that is highly characteristic of the human condition.
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A triple dissociation of memory systems: Hippocampus, amygdala, and dorsal striatum.
Behav. Neurosci.
PUBLISHED: 12-18-2013
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This reprinted article originally appeared in Behavioral Neuroscience, 1993(Feb), 107 (1), 3-22 (see record 1993-24696-001). This study investigated the respective roles of the hippocampus, the amygdala, and the dorsal striatum in learning and memory. A standard set of experimental conditions for studying the effects of lesions to the three brain areas using an 8-arm radial maze was used: a win-shift version, a conditioned cue preference (CCP) version, and a win-stay version. Damage to the hippocampal system impaired acquisition of the win-shift task but not the CCP or win-stay tasks. Damage to the lateral amygdala impaired acquisition of the CCP task but not the win-shift or win-stay tasks. Damage to the dorsal striatum impaired acquisition of the win-stay task but not the win-shift or CCP tasks. These results are consistent with the hypothesis that the mammalian brain may be capable of acquiring different kinds of information with different, more-or-less independent neural systems. A neural system that includes the hippocampus may acquire information about the relationships among stimuli and events. A neural system that includes the amygdala may mediate the rapid acquisition of behaviors based on biologically significant events with affective properties. A neural system that includes the dorsal striatum may mediate the formation of reinforced stimulus-response associations. (PsycINFO Database Record (c) 2013 APA, all rights reserved).
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Dissociation of memory systems: The story unfolds.
Behav. Neurosci.
PUBLISHED: 12-18-2013
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In this article we describe the ideas and circumstances that led to the experiment demonstrating a triple dissociation of memory systems. We then move on to discuss the results of 20 years of investigation of those ideas. First, evidence is described from animal studies consistent with the ideas that memory for different kinds of information is stored in different brain systems, and that the hippocampus, amygdala, and dorsal striatum are each central structures in one of the systems. We then focus on the 3 tasks used in the original triple dissociation: win-stay learning, conditioned cue preference, and win-shift learning. Each of these tasks is specific to behavior resulting from the type of information stored in one of the systems, but the use of other behavioral tests that are sensitive to the types of information stored in other systems has revealed that, in each case, other types of information are acquired in parallel. Next, evidence consistent with the idea that the outputs of the systems compete for control of behavior is discussed together with alternative forms of more direct interactions among the systems. Finally, some evidence that many of these ideas about multiple parallel memory systems may apply to humans is reviewed. (PsycINFO Database Record (c) 2013 APA, all rights reserved).
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Behind the numbers: propensity score analysis-a primer for the diagnostic radiologist.
Radiology
PUBLISHED: 11-23-2013
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Researchers frequently use observational studies to compare outcomes of patients who undergo different treatments. However, as patients in these observational studies are not randomly assigned to a particular treatment group, unknown confounding variables may be present. Specifically, there may be major differences in numerous clinical variables between the treatment groups that may affect the outcomes being examined. Propensity score adjustment is an increasingly popular statistical method used to simultaneously balance these clinical variables and control for this confounder bias. Propensity score analysis can minimize the limitations of retrospective or prospective observational studies by simulating the randomization process of randomized controlled trials. In this review, an introduction to propensity score adjustment is provided by using the Takuma et al study published in this issue of Radiology as an example.
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Synthesis and characterization of heterobimetallic (Pd/B) Nindigo complexes and comparisons to their homobimetallic (Pd2, B2) analogues.
Inorg Chem
PUBLISHED: 09-20-2013
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Reactions of Nindigo-BF2 complexes with Pd(hfac)2 produced mixed complexes with Nindigo binding to both a BF2 and a Pd(hfac) unit. These complexes are the first in which the Nindigo ligand binds two different substrates, and provide a conceptual link between previously reported bis(BF2) and bis(Pd(hfac)) complexes. The new Pd/B complexes have intense near IR absorption near 820 nm, and they undergo multiple reversible oxidations and reductions as probed by cyclic voltammetry experiments. The spectral, redox, and structural properties of these complexes are compared against those of the corresponding B2 and Pd2 complexes with the aid of time-dependent density functional calculations. In all cases the low-energy electronic transitions are ligand-centered ?-?* transitions, but the highest occupied molecular orbital (HOMO) and lowest unoccupied molecular orbital (LUMO) energies--and hence the absorption wavelength as well as the oxidation and reduction potentials--are significantly modulated by the moieties bound to the Nindigo ligand.
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How does a specific learning and memory system in the mammalian brain gain control of behavior?
Hippocampus
PUBLISHED: 07-17-2013
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This review addresses a fundamental, yet poorly understood set of issues in systems neuroscience. The issues revolve around conceptualizations of the organization of learning and memory in the mammalian brain. One intriguing, and somewhat popular, conceptualization is the idea that there are multiple learning and memory systems in the mammalian brain and they interact in different ways to influence and/or control behavior. This approach has generated interesting empirical and theoretical work supporting this view. One issue that needs to be addressed is how these systems influence or gain control of voluntary behavior. To address this issue, we clearly specify what we mean by a learning and memory system. We then review two types of processes that might influence which memory system gains control of behavior. One set of processes are external factors that can affect which system controls behavior in a given situation including task parameters like the kind of information available to the subject, types of training experience, and amount of training. The second set of processes are brain mechanisms that might influence what memory system controls behavior in a given situation including executive functions mediated by the prefrontal cortex; switching mechanisms mediated by ascending neurotransmitter systems, the unique role of the hippocampus during learning. The issue of trait differences in control of different learning and memory systems will also be considered in which trait differences in learning and memory function are thought to potentially emerge from differences in level of prefrontal influence, differences in plasticity processes, differences in ascending neurotransmitter control, differential access to effector systems like motivational and motor systems. Finally, we present scenarios in which different mechanisms might interact. This review was conceived to become a jumping off point for new work directed at understanding these issues. The outcome of this work, in combination with other approaches, might improve understanding of the mechanisms of volition in human and non-human animals.
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Synthesis and derivatization of expanded [n]radialenes (n=3, 4).
Chemistry
PUBLISHED: 06-25-2013
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Versatile, iterative synthetic protocols to form expanded [n]radialenes have been developed (n=3 and 4), which allow for a variety of groups to be placed around the periphery of the macrocyclic framework. The successful use of the Sonogashira cross-coupling reaction to complete the final ring closure demonstrates the ability of this reaction to tolerate significant ring strain while producing moderate to excellent product yields. The resulting radialenes show good stability under normal laboratory conditions in spite of their strained, cyclic structures. The physical and electronic characteristics of the macrocycles have been documented by UV-visible spectroscopy, electrochemical methods, and X-ray crystallography (four derivatives), and these studies provide insight into the properties of these compounds as a function of pendent substitution in terms of conjugation and donor/acceptor functionalization.
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Persistent impairments in hippocampal function following a brief series of photoperiod shifts in rats.
Anim Cogn
PUBLISHED: 05-16-2013
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The impact of an acute circadian disruption on learning and memory in male and female rats was examined. Circadian disruption was elicited using a brief series of photoperiod shifts. Previous research using male rats showed that acute circadian disruption during acquisition of a spatial navigation task impaired long-term retention and that chronic circadian disruption impaired acquisition of the same task. However, the long-term effects of acute circadian disruption following circadian re-entrainment and whether sex differences in response to circadian disruption exist are still unknown. For the present study, rats were trained on the standard, spatial version of the Morris water task (MWT) and a visual discrimination task developed for the eight-arm radial maze. After reaching asymptotic performance, behavioural training was terminated and the experimental group experienced a series of photoperiod shifts followed by circadian re-entrainment. Following circadian re-entrainment, the subjects were given retention tests on the MWT and visual discrimination task. Following retention testing, an extra-dimensional shift using the eight-arm radial maze was also performed. An acute episode of circadian disruption elicited via photoperiod shifts negatively impacted retention of spatial memory in male and female rats. Retention of the visual discrimination task and the ability to detect extra-dimensional shifts were not impaired. The observed impairments on the MWT indicate that hippocampal representations are susceptible to a small number of photoperiod shifts even if the association is acquired prior to rhythm manipulation and retention is assessed following rhythm stabilization. Effects were limited to a hippocampus-dependent task, indicating that impairments are specific, not global.
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Assessment of a novel, capsid-modified adenovirus with an improved vascular gene transfer profile.
J Cardiothorac Surg
PUBLISHED: 04-26-2013
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Cardiovascular disorders, including coronary artery bypass graft failure and in-stent restenosis remain significant opportunities for the advancement of novel therapeutics that target neointimal hyperplasia, a characteristic of both pathologies. Gene therapy may provide a successful approach to improve the clinical outcome of these conditions, but would benefit from the development of more efficient vectors for vascular gene delivery. The aim of this study was to assess whether a novel genetically engineered Adenovirus could be utilised to produce enhanced levels of vascular gene expression.
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Synthesis and Mössbauer spectroscopy of formal tin(II) dichloride and dihydride species supported by Lewis acids and bases.
Inorg Chem
PUBLISHED: 04-25-2013
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(119)Sn Mössbauer spectroscopy was performed on a series of formal Sn(II) dichloride and dihydride adducts bound by either carbon- or phosphorus-based electron pair donors. Upon binding electron-withdrawing metal pentacarbonyl units to the tin centers in LB·SnCl2·M(CO)5 (LB = Lewis base; M = Cr or W), a significant decrease in isomer shift (IS) was noted relative to the unbound Sn(II) complexes, LB·SnCl2, consistent with removal of nonbonding s-electron density from tin upon forming Sn-M linkages (M = Cr and W). Interestingly, when the nature of the Lewis base in the series LB·SnCl2·W(CO)5 was altered, very little change in the IS values was noted, implying that the LB-Sn bonds were constructed with tin-based orbitals of large p-character (as supported by prior theoretical studies). In addition, variable temperature Mössbauer measurements were used to determine the mean displacement of the tin atoms in the solid state, a parameter that can be correlated with the degree of covalent bonding involving tin in these species.
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Multiple effects of circadian dysfunction induced by photoperiod shifts: alterations in context memory and food metabolism in the same subjects.
Physiol. Behav.
PUBLISHED: 04-20-2013
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Humans exposed to shiftwork conditions have been reported to have increased susceptibility to various health problems including various forms of dementia, cancer, heart disease, and metabolic disorders related to obesity. The present experiments assessed the effects of circadian disruption on learning and memory function and various food related processes including diet consumption rates, food metabolism, and changes in body weight. These experiments utilized a novel variant of the conditioned place preference task (CPP) that is normally used to assess Pavlovian associative learning and memory processes produced via repeated context-reward pairings. For the present experiments, the standard CPP paradigm was modified in that both contexts were paired with food, but the dietary constituents of the food were different. In particular, we were interested in whether rats could differentiate between two types of carbohydrates, simple (dextrose) and complex (starch). Consumption rates for each type of carbohydrate were measured throughout training. A test of context preference without the food present was also conducted. At the end of behavioral testing, a fasting glucose test and a glucose challenge test were administered. Chronic photoperiod shifting resulted in impaired context learning and memory processes thought to be mediated by a neural circuit centered on the hippocampus. The results also showed that preferences for the different carbohydrate diets were altered in rats experiencing photoperiod shifting in that they maintained an initial preference for the simple carbohydrate throughout training. Lastly, photoperiod shifting resulted in changes in fasting blood glucose levels and elicited weight gain. These results show that chronic photoperiod shifting, which likely resulted in circadian dysfunction, impairs multiple functions of the brain and/or body in the same individual.
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Azide alkyne cycloaddition facilitated by hexanuclear rhenium chalcogenide cluster complexes.
Dalton Trans
PUBLISHED: 04-15-2013
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Two hexanuclear rhenium clusters containing azide ligands, [Re6Se8(PEt3)5(N3)]BF4 and [Re6Se8(PEt3)4(N3)2], were synthesized from the analogous pyridine complexes and fully characterized. Studies show that [Re6Se8(PEt3)5(N3)]BF4 reacts with activated alkynes, dimethyl acetylenedicarboxylate and methyl 4-hydroxyhex-2-yneoate, to form the triazolate cluster complexes [Re6Se8(PEt3)5(L1 or L2)]BF4 (where L1 = 4,5-bis(methoxycarbonyl)-1,2,3-triazol-2-yl and L2 = 4-methoxycarbonyl-5-(1-propanol)-1,2,3-triazol-2-yl). The bis-triazolato complex, cis-[Re6Se8(PEt3)4(L1)2] was also prepared via a similar reaction starting with cis-[Re6Se8(PEt3)4(N3)2] demonstrating that these clusters can promote two azide moieties to undergo heterocyclic ring formation. The structures of [Re6Se8(PEt3)5(N3)]BF4, [Re6Se8(PEt3)4(N3)2], and [Re6Se8(PEt3)5(L1)](BF4), were determined by single-crystal X-ray diffraction analysis. In addition, studies involving the alkylation of [Re6Se8(PEt3)5(L1)]BF4 with benzyl bromide and methyl iodide are reported.
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Utilizing a novel tool for the comprehensive assessment of resident operative performance.
J Surg Educ
PUBLISHED: 04-12-2013
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A mechanism for more effective and comprehensive assessment of surgical residents performance in the operating room (OR) is needed, especially in light of the new requirements issued by the American Board of Surgery. Furthermore, there is an increased awareness that assessments need to be more meaningful by including not only procedure-specific and general technical skills, but also nontechnical skills (NOTECHS), such as teamwork and communication skills. Our aims were to develop a methodology and create a tool that comprehensively assesses residents operative performance.
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Global chromatin profiling reveals NSD2 mutations in pediatric acute lymphoblastic leukemia.
Nat. Genet.
PUBLISHED: 03-29-2013
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Epigenetic dysregulation is an emerging hallmark of cancers. We developed a high-information-content mass spectrometry approach to profile global histone modifications in human cancers. When applied to 115 lines from the Cancer Cell Line Encyclopedia, this approach identified distinct molecular chromatin signatures. One signature was characterized by increased histone 3 lysine 36 (H3K36) dimethylation, exhibited by several lines harboring translocations in NSD2, which encodes a methyltransferase. A previously unknown NSD2 p.Glu1099Lys (p.E1099K) variant was identified in nontranslocated acute lymphoblastic leukemia (ALL) cell lines sharing this signature. Ectopic expression of the variant induced a chromatin signature characteristic of NSD2 hyperactivation and promoted transformation. NSD2 knockdown selectively inhibited the proliferation of NSD2-mutant lines and impaired the in vivo growth of an NSD2-mutant ALL xenograft. Sequencing analysis of >1,000 pediatric cancer genomes identified the NSD2 p.E1099K alteration in 14% of t(12;21) ETV6-RUNX1-containing ALLs. These findings identify NSD2 as a potential therapeutic target for pediatric ALL and provide a general framework for the functional annotation of cancer epigenomes.
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The marriage of metallacycle transfer chemistry with Suzuki-Miyaura cross-coupling to give main group element-containing conjugated polymers.
J. Am. Chem. Soc.
PUBLISHED: 03-27-2013
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A versatile and general synthetic route for the synthesis of conjugated main group element-based polymers, previously inaccessible by conventional means, is reported. These polymers contain five-membered chalcogenophene rings based on S, Se, and Te, and we demonstrate that optoelectronic properties can be readily tuned via controlled atom substitution chemistry. In addition, regioregular hybrid thiophene-selenophene-tellurophene and selenophene-fluorene copolymers were synthesized to provide a further illustration of the scope of the presented metallacycle transfer/cross-coupling polymerization method.
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miRNA-21 is dysregulated in response to vein grafting in multiple models and genetic ablation in mice attenuates neointima formation.
Eur. Heart J.
PUBLISHED: 03-25-2013
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The long-term failure of autologous saphenous vein bypass grafts due to neointimal thickening is a major clinical burden. Identifying novel strategies to prevent neointimal thickening is important. Thus, this study aimed to identify microRNAs (miRNAs) that are dysregulated during neointimal formation and determine their pathophysiological relevance following miRNA manipulation.
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Percutaneous renal cryoablation in obese and morbidly obese patients.
Urology
PUBLISHED: 03-05-2013
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To compare percutaneous renal cryoablation complications and outcomes in obese and morbidly obese vs nonobese patients.
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Comparative effectiveness of unruptured cerebral aneurysm therapies: propensity score analysis of clipping versus coiling.
Stroke
PUBLISHED: 02-28-2013
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Endovascular therapy has increasingly become the most common treatment for unruptured cerebral aneurysms in the United States. We evaluated a national, multi-hospital database to examine recent utilization trends and compare periprocedural outcomes between clipping and coiling treatments of unruptured aneurysms.
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Laterality errors in radiology reports generated with and without voice recognition software: frequency and clinical significance.
J Am Coll Radiol
PUBLISHED: 02-15-2013
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The aim of this study was to determine the incidence, types, and clinical implications of laterality errors and the effect of voice recognition software on the frequency of laterality errors.
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Management of Fusarium keratitis and its associated fungal iris nodule with intracameral voriconazole and amphotericin B.
Clin Exp Optom
PUBLISHED: 02-07-2013
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A retrospective case report on the management of a 56-year-old man who was diagnosed with Fusarium keratitis with an associated iris fungal nodule. He presented with persistent right ocular pain, redness, photophobia and reduced vision following an injury six weeks earlier. Conservative management with topical antibiotics and intracameral injections was successfully used to treat a rare case of Fusarium keratitis with an associated fungal iris nodule. The patient had complete resolution of his vision. Therefore, conservative management of the fungal nodule is a successful therapy without the risk of anterior chamber dissemination, which may occur with surgical resection.
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Long-term follow-up of riboflavin/ultraviolet A (370 nm) corneal collagen cross-linking to halt the progression of keratoconus.
Br J Ophthalmol
PUBLISHED: 02-05-2013
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To determine long-term efficacy of riboflavin/ultraviolet A corneal cross-linking (CXL).
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Metal-free dehydrogenation of amine-boranes by an N-heterocyclic carbene.
Dalton Trans
PUBLISHED: 01-30-2013
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The dehydrogenation of primary and secondary amine-boranes (RNH(2)·BH(3) and R(2)NH·BH(3); R = alkyl groups) was studied using the bulky N-heterocyclic carbene IPr (IPr = [(HCNDipp)C:]; Dipp = 2,6-(i)Pr(2)C(6)H(3)) as a stoichiometric dehydrogenation agent. In the case of primary amine-boranes, carbene-bound adducts IPr·BH(2)-NH(R)-BH(3) were obtained in place of the desired polymers [RNH-BH(2)](n). The secondary amine-borane (i)Pr(2)NH·BH(3) participated in dehydrogenation chemistry with IPr to afford the aminoborane [(i)Pr(2)N=BH(2)] and the dihydroaminal IPrH(2) as products. Attempts to induce H(2) elimination from the arylamine-borane DippNH(2)·BH(3) yielded a reaction mixture containing the known species IPr·BH(2)NHDipp, IPr·BH(2)NH(Dipp)-BH(3), free DippNH(2) and IPrH(2). The new hindered aryl-amine borane adduct Ar*NH(2)·BH(3) [Ar* = 2,6-(Ph(2)CH)(2)-4-MeC(6)H(2)] underwent a reaction with IPr to give IPr·BH(3) and free Ar*NH(2), consistent with the presence of a weaker N-B dative bond in Ar*NH(2)·BH(3) relative to its less hindered amine-borane analogues.
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Intravenous contrast material-induced nephropathy: causal or coincident phenomenon?
Radiology
PUBLISHED: 01-29-2013
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To determine the causal association and effect of intravenous iodinated contrast material exposure on the incidence of acute kidney injury (AKI), also known as contrast material-induced nephropathy (CIN).
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Vasculitis resulting from a superficial femoral artery angioplasty with a paclitaxel-eluting balloon.
J. Vasc. Surg.
PUBLISHED: 01-24-2013
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Drug-eluting balloons (DEBs) coated with the antiproliferative agent paclitaxel may improve primary patency by reducing recurrent luminal stenosis. A proportion of the active drug and excipient coating are known to embolize distally, but until now, there have been no reports of adverse events resulting from their use. We report an unusual case of a painful nodular, biopsy specimen-proven vasculitic rash that afflicted the ipsilateral lower limb of a patient after superficial femoral artery treatment with a DEB. This adverse event may have implications for the use of DEB in this and other vascular territories.
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Frequency of acute kidney injury following intravenous contrast medium administration: a systematic review and meta-analysis.
Radiology
PUBLISHED: 01-14-2013
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To perform a systematic review and meta-analysis of controlled studies examining the incidence of acute kidney injury (AKI) and other outcomes in patients exposed to intravenous (i.v.) contrast medium compared with patients who underwent an imaging examination without contrast medium or were otherwise unexposed (control group).
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An investigation of 1:1 adducts of gallium trihalides with triarylphosphines by solid-state (69/71)Ga and 31P NMR spectroscopy.
Chemistry
PUBLISHED: 01-10-2013
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Several 1:1 adducts of gallium trihalides with triarylphosphines, X(3)Ga(PR(3)) (X=Cl, Br, and I; PR(3)=triarylphosphine ligand), were investigated by using solid-state (69/71)Ga and (31)P NMR spectroscopy at different magnetic-field strengths. The (69/71)Ga nuclear quadrupolar coupling parameters, as well as the gallium and phosphorus magnetic shielding tensors, were determined. The magnitude of the (71)Ga quadrupolar coupling constants (C(Q)((71)Ga)) range from approximately 0.9 to 11.0 MHz. The spans of the gallium magnetic shielding tensors for these complexes, ?(11)-?(33), range from approximately 30 to 380 ppm; those determined for phosphorus range from 10 to 40 ppm. For any given phosphine ligand, the gallium nuclei are most shielded for X=I and least shielded for X=Cl, a trend previously observed for In(III)-phosphine complexes. This experimental trend, attributed to spin-orbit effects of the halogen ligands, is reproduced by DFT calculations. The signs of C(Q)((69/71)Ga) for some of the adducts were determined from the analysis of the (31)P NMR spectra acquired with magic angle spinning (MAS). The (1)J((69/71)Ga,(31)P) and ?J((69/71)Ga, (31)P) values, as well as their signs, were also determined; values of (1)J((71)Ga,(31)P) range from approximately 380 to 1590 Hz. Values of (1)J((69/71)Ga,(31)P) and ?J((69/71)Ga,(31)P) calculated by using DFT have comparable magnitudes and generally reproduce experimental trends. Both the Fermi-contact and spin-dipolar Fermi-contact mechanisms make important contributions to the (1)J((69/71)Ga,(31)P) tensors. The (31)P NMR spectra of several adducts in solution, obtained as a function of temperature, are contrasted with those obtained in the solid state. Finally, to complement the analysis of NMR spectra for these adducts, single-crystal X-ray diffraction data for Br(3)Ga[P(p-Anis)(3)] and I(3)Ga[P(p-Anis)(3)] were obtained.
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An examination of the palladium/Mor-DalPhos catalyst system in the context of selective ammonia monoarylation at room temperature.
Chemistry
PUBLISHED: 01-04-2013
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An examination of the [{Pd(cinnamyl)Cl}(2)]/Mor-DalPhos (Mor-DalPhos = di(1-adamantyl)-2-morpholinophenylphosphine) catalyst system in Buchwald-Hartwig aminations employing ammonia was conducted to better understand the catalyst formation process and to guide the development of precatalysts for otherwise challenging room-temperature ammonia monoarylations. The combination of [{Pd(cinnamyl)Cl}(2)] and Mor-DalPhos afforded [(?(2)-P,N-Mor-DalPhos)Pd(?(1)-cinnamyl)Cl] (2), which, in the presence of a base and chlorobenzene, generated [(?(2)-P,N-Mor-DalPhos)Pd(Ph)Cl] (1?a). Halide abstraction from 1?a afforded [(?(3)-P,N,O-Mor-DalPhos)Pd(Ph)]OTf (5), bringing to light a potential stabilizing interaction that is offered by Mor-DalPhos. An examination of [(?(2)-P,N-Mor-DalPhos)Pd(aryl)Cl] (1?b-f) and related precatalysts for the coupling of ammonia and chlorobenzene at room temperature established the suitability of 1?a in such challenging applications. The scope of reactivity for the use of 1?a (5?mol?%) encompassed a range of (hetero)aryl (pseudo)halides (X = Cl, Br, I, OTs) with diverse substituents (alkyl, aryl, ether, thioether, ketone, amine, fluoro, trifluoromethyl, and nitrile), including chemoselective arylations.
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Two challenges for U.S. irrigation due to climate change: increasing irrigated area in wet states and increasing irrigation rates in dry states.
PLoS ONE
PUBLISHED: 01-01-2013
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Agricultural irrigation practices will likely be affected by climate change. In this paper, we use a statistical model relating observed water use by U.S. producers to the moisture deficit, and then use this statistical model to project climate changes impact on both the fraction of agricultural land irrigated and the irrigation rate (m³ ha?¹). Data on water withdrawals for US states (1985-2005) show that both quantities are highly positively correlated with moisture deficit (precipitation--PET). If current trends hold, climate change would increase agricultural demand for irrigation in 2090 by 4.5-21.9 million ha (B1 scenario demand: 4.5-8.7 million ha, A2 scenario demand: 9.1-21.9 million ha). Much of this new irrigated area would occur in states that currently have a wet climate and a small fraction of their agricultural land currently irrigated, posing a challenge to policymakers in states with less experience with strict regulation of agriculture water use. Moreover, most of this expansion will occur in states where current agricultural production has relatively low market value per hectare, which may make installation of irrigation uneconomical without significant changes in crops or practices by producers. Without significant increases in irrigation efficiency, climate change would also increase the average irrigation rate from 7,963 to 8,400-10,415 m³ ha?¹ (B1 rate: 8,400-9,145 m³ ha?¹, A2 rate: 9,380-10,415 m³ ha?¹). The irrigation rate will increase the most in states that already have dry climates and large irrigation rates, posing a challenge for water supply systems in these states. Accounting for both the increase in irrigated area and irrigation rate, total withdrawals might increase by 47.7-283.4 billion m³ (B1 withdrawal: 47.7-106.0 billion m³, A2 withdrawal: 117.4-283.4 billion m³). Increases in irrigation water-use efficiency, particularly by reducing the prevalence of surface irrigation, could eliminate the increase in total irrigation withdrawals in many states.
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Rational and predictable chemoselective synthesis of oligoamines via Buchwald-Hartwig amination of (hetero)aryl chlorides employing Mor-DalPhos.
J. Org. Chem.
PUBLISHED: 12-23-2011
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We report a diverse demonstration of synthetically useful chemoselectivity in the synthesis of di-, tri-, and tetraamines (62 examples) by use of Buchwald-Hartwig amination employing a single catalyst system ([Pd(cinnamyl)Cl](2)/L1; L1 = N-(2-(di(1-adamantyl)phosphino)phenyl)morpholine, Mor-DalPhos). Competition reactions established the following relative preference of this catalyst system for amine coupling partners: linear primary alkylamines and imines > unhindered electron-rich primary anilines, primary hydrazones, N,N-dialkylhydrazines, and cyclic primary alkylamines > unhindered electron-deficient primary anilines, ?-branched acyclic primary alkylamines, hindered electron-rich primary anilines ? cyclic and acyclic secondary dialkylamines, secondary alkyl/aryl and diarylamines, ?,?-branched primary alkylamines, and primary amides. The new isomeric ligand N-(4-(di(1-adamantyl)phosphino)phenyl)morpholine (p-Mor-DalPhos, L2) was prepared in 63% yield and was crystallographically characterized; the [Pd(cinnamyl)Cl](2)/L2 catalyst system exhibited divergent reactivity. Application of the reactivity trends established for [Pd(cinnamyl)Cl](2)/L1 toward the chemoselective synthesis of di-, tri-, and tetraamines was achieved. Preferential arylation was observed at the primary alkylamine position within 2-(4-aminophenyl)ethylamine with [Pd(cinnamyl)Cl](2)/L1 and 4-chlorotoluene (affording 5a); the alternative regioisomer (5a) was obtained when using [Pd(cinnamyl)Cl](2)/L2. These observations are in keeping with coordination chemistry studies, whereby binding of 2-(4-aminophenyl)ethylamine to the in situ generated [(L1)Pd(p-tolyl)](+) fragment occurred via the primary amine moiety, affording the crystallographically characterized adduct [(L1)Pd(p-tolyl)(NH(2)CH(2)CH(2)(4-C(6)H(4)NH(2))](+)OTf(-) (7) in 72% yield.
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Efficient generation of stable adducts of Si(II) dihydride using a donor-acceptor approach.
Chem. Commun. (Camb.)
PUBLISHED: 12-19-2011
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A stable Si(II) dihydride complex, IPr·SiH(2)·BH(3) (IPr = [(HCNDipp)(2)C:]; Dipp = 2,6-(i)Pr(2)C(6)H(3)), was synthesized and preliminary reactivity involving this source of encapsulated silylene is reported.
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Hemilabile silyl pincer ligation: platinum group PSiN complexes and triple C-H activation to form a (PSiC)Ru carbene complex.
Chem. Commun. (Camb.)
PUBLISHED: 12-12-2011
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The first example of PSiN mixed-donor silyl pincer ligation is described. Studies involving platinum group metal complexes of [(2-(t)Bu(2)PC(6)H(4))(2-Me(2)NC(6)H(4))SiMe](-) ((t)Bu-PSiN-Me) confirmed that the ligand amino donor is labile. Within the coordination sphere of Ru, (t)Bu-PSiN-Me is transformed into a PSiC ligand via multiple C-H bond activation events.
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Synthesis and properties of isomerically pure anthrabisbenzothiophenes.
Org. Lett.
PUBLISHED: 11-29-2011
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The synthesis of three heptacyclic heteroacenes is described, namely anthra[2,3-b:7,6-b]bis[1]benzothiophenes (ABBTs). A stepwise sequence of aldol reactions provides regiochemical control, affording only the syn-isomer. The ABBTs are characterized by X-ray crystallography, UV-vis absorption, and emission spectroscopy, as well as cyclic voltammetry. Field effect transistors based on solution-cast thin films of ABBT derivatives exhibit charge-carrier mobilities of as high as 0.013 cm(2)/(V s).
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MicroRNA and vascular remodelling in acute vascular injury and pulmonary vascular remodelling.
Cardiovasc. Res.
PUBLISHED: 11-07-2011
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Vascular remodelling is an integral pathological process central to a number of cardiovascular diseases. The complex interplay between distinct cell populations in the vessel wall following vascular injury leads to inflammation, cellular dysfunction, pro-growth signals in the smooth muscle cell (SMC) compartment, and the acquisition of a synthetic phenotype. Although the signals for vascular remodelling are diverse in different pathological contexts, SMC proliferation and migration are consistently observed. It is therefore critical to elucidate key mechanisms central to these processes. MicroRNAs (miRNAs) are small non-coding sequences of RNA that have the capacity to regulate many genes, pathways, and complex biological networks within cells, acting either alone or in concert with one another. In diseases such as cancer and cardiac disease, the role of miRNA in disease pathogenesis has been documented in detail. In contrast, despite a great deal of interest in miRNA, relatively few studies have directly assessed the role of miRNA in vascular remodelling. The potential for modulation of miRNA to achieve therapeutic benefits in this setting is attractive. Here, we focus on the role of miRNA in vascular inflammation and remodelling associated with acute vascular injury (vein graft disease, angioplasty restenosis, and in-stent restenosis) as well as in vascular remodelling associated with the development of pulmonary arterial hypertension.
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Structural diversity for phosphine complexes of stibenium and stibinidenium cations.
Chem. Commun. (Camb.)
PUBLISHED: 10-20-2011
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Reactions of trimethylphosphine or diphosphines with SbCl(3) in the presence of AlCl(3) or Me(3)SiSO(3)CF(3) give ligand stabilized stibenium and stibinidenium cations. The geometry at each antimony center reveals a variety of environments for antimony that describes new bonding and highlights new directions in the chemistry of the pnictogen elements.
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Impact of admission month and hospital teaching status on outcomes in subarachnoid hemorrhage: evidence against the July effect.
J. Neurosurg.
PUBLISHED: 09-23-2011
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The authors sought to identify the presence of a "July effect," a transient increase in adverse outcomes during July, among a cohort of spontaneous subarachnoid hemorrhage (SAH) admissions recorded in the National Inpatient Sample (NIS).
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Global urban growth and the geography of water availability, quality, and delivery.
Ambio
PUBLISHED: 08-19-2011
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Globally, urban growth will add 1.5 billion people to cities by 2030, making the difficult task of urban water provisions even more challenging. In this article, we develop a conceptual framework of urban water provision as composed of three axes: water availability, water quality, and water delivery. For each axis, we calculate quantitative proxy measures for all cities with more than 50,000 residents, and then briefly discuss the strategies cities are using in response if they are deficient on one of the axes. We show that 523 million people are in cities where water availability may be an issue, 890 million people are in cities where water quality may be an issue, and 1.3 billion people are in cities where water delivery may be an issue. Tapping into groundwater is a widespread response, regardless of the management challenge, with many cities unsustainably using this resource. The strategies used by cities deficient on the water delivery axis are different than for cities deficient on the water quantity or water quality axis, as lack of financial resources pushes cities toward a different and potentially less effective set of strategies.
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A reactive Ru-binaphtholate building block with self-tuning hapticity.
J. Am. Chem. Soc.
PUBLISHED: 08-15-2011
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A versatile Ru-BINO building block is reported, which offers a straightforward entry point into the chemistry of atropisomeric binaphtholate complexes of ruthenium. Reaction of RuCl(2)(PPh(3))(3)6a with Tl(2)((S)-BINO) affords Ru((S)-BINO)(PPh(3))(2)7 as a mixture of isomers: in 7, the BINO ligand is bound via ?(3)-CCO,?(1)-O donors, and in symmetrical 7?, via ?(3)-CCO,?(3)-OCC interactions. The bis(enolate) BINO bonding mode in the latter, not previously observed for any metal, underscores the remarkable geometric and electronic flexibility of the binaphtholate moiety. The BINO ligand proves able to stabilize complexes containing as few as two, and as many as four, additional ligands in 7 and its derivatives, enabling a synthetic versatility that contrasts with that of the superficially similar o-catecholate complex Ru(o-cat)(PPh(3))(3). As with the important achiral Ru precursor 6a, complex 7 undergoes facile transformation into a range of products under mild conditions, including acetonitrile, pyridine, and vinylidene derivatives. Single-crystal X-ray structures are reported for three of these complexes: Ru(?(3),?(3)-(S)-BINO)(PPh(3))(2)7?, Ru(?(3),?(1)-(S)-BINO)(PPh(3))(2)(MeCN) 9, and Ru(?(3),?(1)-(S)-BINO)(PPh(3))(py)(2)11. (13)C{(1)H} NMR signatures are proposed for new and known BINO coordination modes (?(1)-O,?(1)-O; ?(1)-C1,?(1)-O; ?(3)-CCO,?(3)-OCC; ?(3)-CCO,?(1)-O; ?(6)-C(6),?(1)-O), as a potential aid to further developments in late-metal BINO chemistry.
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Intracranial hemorrhage is much more common after carotid stenting than after endarterectomy: evidence from the National Inpatient Sample.
Stroke
PUBLISHED: 08-11-2011
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Intracranial hemorrhage (ICH) is a rare and devastating complication of carotid revascularization. We sought to determine the prevalence of, type of, and risk factors associated with ICH among recipients of carotid endarterectomy (CEA) and carotid angioplasty and stenting (CAS) within the National Inpatient Sample (NIS).
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Four-coordinate, 14-electron Ru(II) complexes: unusual trigonal pyramidal geometry enforced by bis(phosphino)silyl ligation.
J. Am. Chem. Soc.
PUBLISHED: 08-10-2011
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Unprecedented diamagnetic, four-coordinate, formally 14-electron (Cy-PSiP)RuX (Cy-PSiP = [?(3)-(2-R(2)PC(6)H(4))(2)SiMe](-); X = amido, alkoxo) complexes that do not require agostic stabilization and that adopt a highly unusual trigonal pyramidal coordination geometry are reported. The tertiary silane [(2-Cy(2)PC(6)H(4))(2)SiMe]H ((Cy-PSiP)H) reacted with 0.5 [(p-cymene)RuCl(2)](2) in the presence of Et(3)N and PCy(3) to afford [(Cy-PSiP)RuCl](2) (1) in 74% yield. Treatment of 1 with KO(t)Bu led to the formation of (Cy-PSiP)RuO(t)Bu (2, 97% yield), which was crystallographically characterized and shown to adopt a trigonal pyramidal coordination geometry in the solid state. Treatment of 1 with NaN(SiMe(3))(2) led to the formation of (Cy-PSiP)RuN(SiMe(3))(2) (3, 70% yield), which was also found to adopt a trigonal pyramidal coordination geometry in the solid state. The related anilido complexes (Cy-PSiP)RuNH(2,6-R(2)C(6)H(3)) (4, R = H; 5, R = Me) were also prepared in >90% yields by treating 1 with LiNH(2,6-R(2)C(6)H(3)) (R = H, Me) reagents. The solid state structure of 5 indicates a monomeric trigonal pyramidal complex that features a C-H agostic interaction. Complexes 2 and 3 were found to react readily with 1 equiv of H(2)O to form the dimeric hydroxo-bridged complex [(Cy-PSiP)RuOH](2) (6, 94% yield), which was crystallographically characterized. Complexes 2 and 3 also reacted with 1 equiv of PhOH to form the new 18-electron ?(5)-oxocyclohexadienyl complex (Cy-PSiP)Ru(?(5)-C(6)H(5)O) (7, 84% yield). Both amido and alkoxo (Cy-PSiP)RuX complexes reacted with H(3)B·NHRR reagents to form bis(?-B-H) complexes of the type (Cy-PSiP)RuH(?(2):?(2)-H(2)BNRR) (8, R = R = H; 9, R = R = Me; 10, R = H, R = (t)Bu), which illustrates that such four-coordinate (Cy-PSiP)RuX (X = amido, alkoxo) complexes are able to undergo multiple E-H (E = main group element) bond activation steps. Computational methods were used to investigate structurally related PCP, PPP, PNP, and PSiP four-coordinate Ru complexes and confirmed the key role of the strongly ?-donating silyl group of the PSiP ligand set in enforcing the unusual trigonal pyramidal coordination geometry featured in complexes 2-5, thus substantiating a new strategy for the synthesis of low-coordinate Ru species. The mechanism of the activation of ammonia-borane by such low-coordinate (R-PSiP)RuX (X = amido, alkoxo) species was also studied computationally and was determined to proceed most likely in a stepwise fashion via intramolecular deprotonation of ammonia and subsequent borane B-H bond oxidative addition steps.
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Homologous Mukaiyama reactions via trapping of the Nazarov intermediate with silyloxyalkenes.
Org. Lett.
PUBLISHED: 06-23-2011
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Treatment of 1,4-pentadien-3-ones and silyloxyalkenes with BF(3)·OEt(2) at room temperature or lower initiates a domino process consisting of sequential 4? electrocyclization and capture of the resulting cyclopentenyl cation by the electron-rich trap. The overall process furnishes 1,4-dicarbonyl products containing highly substituted cyclopentanones in good yields and with the establishment of up to five new stereocenters.
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Redox-active bridging ligands based on indigo diimine ("Nindigo") derivatives.
Inorg Chem
PUBLISHED: 06-20-2011
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Reactions of indigo with a variety of substituted anilines produce the corresponding indigo diimines ("Nindigos") in good yields. Nindigo coordination complexes are subsequently prepared by reactions of the Nindigo ligands with Pd(hfac)(2). In most cases, binuclear complexes are obtained in which the deprotonated Nindigo bridges two Pd(hfac) moieties in the expected bis-bidentate binding mode. When the Nindigo possesses bulky substituents on the imine (mesityl, 2,6-dimethylphenyl, 2,6-diisopropylphenyl, etc.), mononuclear Pf(hfac) complexes are obtained in which the Nindigo core has isomerized from a trans- to a cis-alkene; in these structures, the palladium is bound to the cis-Nindigo ligand at the two indole nitrogen atoms; the remaining proton is bound between the imine nitrogen atoms. The palladium complexes possess intense electronic absorption bands [near 920 nm for the binuclear complexes and 820 nm for the mononuclear cis-Nindigo complexes; extinction coefficients are (1.0-2.0) × 10(4) M(-1) cm(-1)] that are ligand-centered (?-?*) transitions. Cyclic voltammetry investigations reveal multiple redox events that are also ligand-centered in origin. All of the palladium complexes can be reversibly oxidized in two sequential one-electron steps; the binuclear complexes are reduced in a two-electron process whose reversibility depends on the Nindigo ligand substituent; the mononuclear palladium species show two one-electron reductions, only the first of which is quasi-reversible.
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Actinide metals with multiple bonds to carbon: synthesis, characterization, and reactivity of U(IV) and Th(IV) bis(iminophosphorano)methandiide pincer carbene complexes.
Inorg Chem
PUBLISHED: 06-13-2011
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Treatment of ThCl(4)(DME)(2) or UCl(4) with 1 equiv of dilithiumbis(iminophosphorano) methandiide, [Li(2)C(Ph(2)P?NSiMe(3))(2)] (1), afforded the chloro actinide carbene complexes [Cl(2)M(C(Ph(2)P?NSiMe(3))(2))] (2 (M = Th) and 3 (M = U)) in situ. Stable PCP metal-carbene complexes [Cp(2)Th(C(Ph(2)P?NSiMe(3))(2))] (4), [Cp(2)U(C(Ph(2)P?NSiMe(3))(2))] (5), [TpTh(C(Ph(2)P?NSiMe(3))(2))Cl] (6), and [TpU(C(Ph(2)P?NSiMe(3))(2))Cl] (7) were generated from 2 or 3 by further reaction with 2 equiv of thallium(I) cyclopentadienide (CpTl) in THF to yield 4 or 5 or with 1 equiv of potassium hydrotris(pyrazol-1-yl) borate (TpK) also in THF to give 6 or 7, respectively. The derivative complexes were isolated, and their crystal structures were determined by X-ray diffraction. All of these U (or Th)-carbene complexes (4-7) possess a very short M (Th or U)?carbene bond with evidence for multiple bond character. Gaussian 03 DFT calculations indicate that the M?C double bond is constructed by interaction of the 5f and 6d orbitals of the actinide metal with carbene 2p orbitals of both ? and ? character. Complex 3 reacted with acetonitrile or benzonitrile to cyclo-add C?N to the U?carbon double bond, thereby forming a new C-C bond in a new chelated quadridentate ligand in the bridged dimetallic complexes (9 and 10). A single carbon-U bond is retained. The newly coordinated uranium complex dimerizes with one equivalent of unconverted 3 using two chlorides and the newly formed imine derived from the nitrile as three connecting bridges. In addition, a new crystal structure of [CpUCl(3)(THF)(2)] (8) was determined by X-ray diffraction.
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A DNA damage response screen identifies RHINO, a 9-1-1 and TopBP1 interacting protein required for ATR signaling.
Science
PUBLISHED: 06-11-2011
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The DNA damage response (DDR) is brought about by a protein kinase cascade that orchestrates DNA repair through transcriptional and posttranslational mechanisms. Cell cycle arrest is a hallmark of the DDR. We screened for cells that lacked damage-induced cell cycle arrest and uncovered a critical role for Fanconi anemia and homologous recombination proteins in ATR (ataxia telangiectasia and Rad3-related) signaling. Three DDR candidates, the RNA processing protein INTS7, the circadian transcription factor CLOCK, and a previously uncharacterized protein RHINO, were recruited to sites of DNA damage. RHINO independently bound the Rad9-Rad1-Hus1 complex (9-1-1) and the ATR activator TopBP1. RHINO was recruited to sites of DNA damage by the 9-1-1 complex to promote Chk1 activation. We suggest that RHINO functions together with the 9-1-1 complex and TopBP1 to fully activate ATR.
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