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Why is sulfuric acid a much stronger acid than ethanol? Determination of the contributions by inductive/field effects and electron-delocalization effects.
Phys Chem Chem Phys
PUBLISHED: 10-16-2014
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Two different and complementary computational methods were used to determine the contributions by inductive/field effects and by electron-delocalization effects toward the enhancement of the gas-phase deprotonation enthalpy of sulfuric acid over ethanol. Our alkylogue extrapolation method employed density functional theory calculations to determine the deprotonation enthalpy of the alkylogues of sulfuric acid, HOSO2-(CH2CH2)n-OH, and of ethanol, CH3CH2-(CH2CH2)n-OH. The inductive/field effect imparted by the HOSO2 group for a given alkylogue of sulfuric acid was taken to be the difference in deprotonation enthalpy between corresponding (i.e., same n) alkylogues of sulfuric acid and ethanol. Extrapolating the inductive/field effect values for the n = 1-6 alkylogues, we obtained a value of 51.0 ± 6.4 kcal mol(-1) for the inductive/field effect for n = 0, sulfuric acid, leaving 15.4 kcal mol(-1) as the contribution by electron-delocalization effects. Our block-localized wavefunction method was employed to calculate the deprotonation enthalpies of sulfuric acid and ethanol using the electron-localized acid and anion species, which were compared to the values calculated using the electron-delocalized species. The contribution from electron delocalization was thus determined to be 18.2 kcal mol(-1), which is similar to the value obtained from the alkylogue extrapolation method. The two methods, therefore, unambiguously agree that both inductive/field effects and electron-delocalization effects have significant contributions to the enhancement of the deprotonation enthalpy of sulfuric acid compared with ethanol, and that the inductive/field effects are the dominant contributor.
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[Analysis on GJB2 gene mutations with nonsyndromic hearing impairment in Kazak patients of Xinjiang].
Lin Chung Er Bi Yan Hou Tou Jing Wai Ke Za Zhi
PUBLISHED: 08-19-2014
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To study mutations in the GJB2 gene in Kazak patients with nonsyndromic hearing impairment from Xinjiang.
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Liquid/Liquid interfacial fabrication of thermosensitive and catalytically active Ag nanoparticle-doped block copolymer composite foam films.
Langmuir
PUBLISHED: 08-19-2014
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An aqueous solution of AgNO3 (upper phase) and a DMF/CHCl3 solution of polystyrene-b-poly(acryl acid)-b-polystyrene (PS-b-PAA-b-PS) or PS-b-PAA-b-PS/1,6-diaminohexane (DAH) (lower phase) constituted a planar liquid/liquid interface. The lower phase gradually transformed to a water-in-oil (W/O) emulsion via spontaneous emulsification due to the "ouzo effect". Polymer molecules, DAH molecules, and Ag(+) ions assembled into microcapsules around emulsion droplets that adsorbed at the planar liquid/liquid interface, resulting in formation of a foam film. DAH acted as a cross-linker during this process. Transmission electron microscopic observations indicated that Ag nanoclusters that were generated through reduction of Ag(+) ions by DMF were homogeneously dispersed in the walls of the foam structure. X-ray photoelectron spectroscopic investigations revealed that Ag(I) and Ag(0) coexisted in the film, and Ag(I) transformed to Ag(0) after further treatment. The film formed without DAH was not stable, while the film formed with DAH was very stable due to intermolecular attraction between PAA and DAH and formation of amides, as revealed by FTIR spectra. The film formed with DAH exhibited high and durable catalytic activity for hydrogenation of nitro compounds and, very interestingly, exhibited thermoresponsive catalytic behavior.
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On the nature of blueshifting hydrogen bonds.
Chemistry
PUBLISHED: 02-14-2014
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The block-localized wave function (BLW) method can derive the energetic, geometrical, and spectral changes with the deactivation of electron delocalization, and thus provide a unique way to elucidate the origin of improper, blueshifting hydrogen bonds versus proper, redshifting hydrogen bonds. A detailed analysis of the interactions of F(3)CH with NH(3) and OH(2) shows that blueshifting is a long-range phenomenon. Since among the various energy components contributing to hydrogen bonds, only the electrostatic interaction has long-range characteristics, we conclude that the contraction and blueshifting of a hydrogen bond is largely caused by electrostatic interactions. On the other hand, lengthening and redshifting is primarily due to the short-range n(Y)??*(X-H) hyperconjugation. The competition between these two opposing factors determines the final frequency change direction, for example, redshifting in F(3)CH???NH(3) and blueshifting in F(3)CH???OH(2). This mechanism works well in the series F(n)Cl(3)-n CH???Y (n=0-3, Y=NH(3), OH(2), SH(2)) and other systems. One exception is the complex of water and benzene. We observe the lengthening and redshifting of the O-H bond of water even with the electron transfer between benzene and water completely quenched. A distance-dependent analysis for this system reveals that the long-range electrostatic interaction is again responsible for the initial lengthening and redshifting.
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How solvent influences the anomeric effect: roles of hyperconjugative versus steric interactions on the conformational preference.
J. Org. Chem.
PUBLISHED: 01-31-2014
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The block-localized wave function (BLW) method, which can derive optimal electron-localized state with intramolecular electron delocalization completely deactivated, has been combined with the polarizable continuum model (PCM) to probe the variation of the anomeric effect in solution. Currently both the hyperconjugation and electrostatic models have been called to interpret the anomeric effect in carbohydrate molecules. Here we employed the BLW-PCM scheme to analyze the energy differences between ? and ? anomers of substituted tetrahydropyran C5OH9Y (Y = F, Cl, OH, NH2, and CH3) and tetrahydrothiopyran C5SH9Y (Y = F, Cl, OH, and CH3) in solvents including chloroform, acetone, and water. In accord with literature, our computations show that for anomeric systems the conformational preference is reduced in solution and the magnitude of reduction increases as the solvent polarity increases. Significantly, on one hand the solute-solvent interaction diminishes the intramolecular electron delocalization in ? anomers more than in ? anomers, thus destabilizing ? anomers relatively. But on the other hand, it reduces the steric effect in ? anomers much more than ? anomers and thus stabilizes ? anomers relatively more, leading to the overall reduction of the anomeric effect in anomeric systems in solutions.
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On the large ?-hyperconjugation in alkanes and alkenes.
J Mol Model
PUBLISHED: 01-22-2014
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The conventional view that the ?CC and ?CH bonds in alkanes and unsaturated hydrocarbons are so highly localized that their non-steric interactions are negligible is scrutinized by the block-localized wavefunction (BLW) method. Even molecules considered conventionally to be "strain free" and "unperturbed" have surprisingly large and quite significant total ?-BLW-delocalization energies (DEs) due to their geminal and vicinal hyperconjugative interactions. Thus, the computed BLW-DEs (in kcal mol(-1)) for the antiperiplanar conformations of the n-alkanes (C(N)H(2N+2), N = 1-10) range from 11.6 for ethane to 82.2 for?n-decane and are 50.9 for cyclohexane and 91.0 for adamantane. Although ?-electron delocalization in unsaturated hydrocarbons usually is ignored, the ?-BLW-DEs (in kcal mol(-1)) are substantial, as exemplified by D2h ethylene (9.0), triplet D2d ethylene (16.4), allene (19.3), butadiene (19.0), hexatriene (28.3), benzene (28.1), and cyclobutadiene (21.1). While each individual geminal and vicinal hyperconjugative interaction between hydrocarbon ?-bonding and ?-antibonding orbitals tends to be smaller than an individual ? conjugative interaction (e.g., 10.2 kcal mol(-1) in anti-1,3-butadiene, the presence of many ?-hyperconjugative interactions (e.g., a total of 12 in anti-1,3-butadiene, see text), result in substantial total ?-stabilization energies (e.g., 19.0 kcal mol(-1) for butadiene), which may surpass those from the ? interactions. Although large in magnitude, ?-electron delocalization energies often are obscured by cancellation when two hydrocarbons are compared. Rather than being strain-free, cyclohexane, adamantane, and diamantane suffer from their increasing number of intramolecular 1,4-C…C repulsions resulting in elongated C-C bond lengths and reduced ?-hyperconjugation, compared to the (skew-free) antiperiplanar n-alkane conformers. Instead of being inconsequential, ?-bond interactions are important and merit consideration.
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Enhanced power conversion efficiencies in bulk heterojunction solar cells based on conjugated polymer with isoindigo side chain.
Chem. Commun. (Camb.)
PUBLISHED: 04-03-2013
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A novel conjugated side-chain polymer (PBDT-TID), based on benzo[1,2-b:4,5-b]dithiophene (BDT) and isoindigo (ID) moieties, was designed and synthesized. The new polymer exhibited excellent microphase separation in active layers. Bulk heterojunction polymer solar cells fabricated from PBDT-TID and PC61BM showed promising power conversion efficiencies of 5.25% and 6.51% using conventional and inverted device structures, respectively.
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Sensing or no sensing: can the anomeric effect be probed by a sensing molecule?
J. Am. Chem. Soc.
PUBLISHED: 08-10-2011
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The anomeric effect plays a central role in carbohydrate chemistry, but its origin is controversial, and both the hyperconjugation model and the electrostatic model have been proposed to explain this phenomenon. Recently, Cocinero et al. designed a peptide sensor, which can bind to a sugar molecule methyl D-galactose, and claimed that the anomeric effect can be sensed by the spectral changes from the ?- to the ?-complex, which are ultimately attributed to the lone pair electron density change on the endocyclic oxygen atom [Nature 2011, 469, 76; J. Am. Chem. Soc. 2011, 133, 4548]. Here, we provide strong computational evidence showing that the observed spectral changes simply come from the conformational differences between the ?- and ?-anomers, as the replacement of the endocyclic oxygen atom with a methylene group, which disables both the endo- and the exo-anomeric effects in methyl D-galactose, leads to similar spectral shifts. In other words, the "sensor" cannot probe the anomeric effect as claimed. We further conducted detailed energetic and structural analyses to support our arguments.
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[Analysis of mtDNA 12SrRNA A1555G mutations of Uigur patients with nonsyndromic hereditary hearing loss in Xinjiang].
Lin Chung Er Bi Yan Hou Tou Jing Wai Ke Za Zhi
PUBLISHED: 07-31-2010
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To explore the incidence of Uigur patients with nonsyndromic hereditary hearing loss in Xinjiang, and to provide the basis for preventing deafness caused by aminoglycoside antibiotics.
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Passive interferometric array optimization based on redundant spacing calibration.
Opt Express
PUBLISHED: 12-10-2009
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An optimization of passive interferometric circular arrays for redundant spacing calibration (RSC) is advanced to eliminate phase errors of the array system. The principle of RSC is presented to solve corresponded constraints for passive interferometric circular arrays. The simulated annealing algorithm (SAA) is introduced to settle the array optimization with a criterion of maximizing the distance between u-v points. The optimized circular arrays with element numbers of 8 to 16 antennas are laid out, and RSC is used for the optimized ten-element passive interferometric circular array.
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The Third Dimension of a More OFerrall-Jencks Diagram for Hydrogen Atom Transfer in the Isoelectronic Hydrogen Exchange Reactions of (PhX)(2)H(•) with X = O, NH, and CH(2).
J Chem Theory Comput
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A critical element in theoretical characterization of the mechanism of proton-coupled electron transfer (PCET) reactions, including hydrogen atom transfer (HAT), is the formulation of the electron and proton localized diabatic states, based on which a More OFerrall-Jencks diagram can be represented to determine the step-wise and concerted nature of the reaction. Although the More OFerrall-Jencks diabatic states have often been used empirically to develop theoretical models for PCET reactions, the potential energy surfaces for these states have never been determined directly based on first principles calculations using electronic structure theory. The difficulty is due to a lack of practical method to constrain electron and proton localized diabatic states in wave function or density functional theory calculations. Employing a multistate density functional theory (MSDFT), in which the electron and proton localized diabatic configurations are constructed through block-localization of Kohn-Sham orbitals, we show that distinction between concerted proton-electron transfer (CPET) and HAT, which are not distinguishable experimentally from phenomenological kinetic data, can be made by examining the third dimension of a More OFerrall-Jencks diagram that includes both the ground and excited state potential surfaces. In addition, we formulate a pair of effective two-state valence bond models to represent the CPET and HAT mechanisms. We found that the lower energy of the CPET and HAT effective diabatic states at the intersection point can be used as an energetic criterion to distinguish the two mechanisms. In the isoelectronic series of hydrogen exchange reaction in (PhX)(2)H(•), where X = O, NH, and CH(2), there is a continuous transition from a CPET mechanism for the phenoxy radical-phenol pair to a HAT process for benzyl radical and toluene, while the reaction between PhNH(2) and PhNH(•) has a mechanism intermediate of CPET and HAT. The electronically nonadiabatic nature of the CPET mechanism in the phenol system can be attributed to the overlap interactions between the ground and excited state surfaces, resulting in roughly orthogonal minimum energy paths on the adiabatic ground and excited state potential energy surfaces. On the other hand, the minimum energy path on the adiabatic ground state for the HAT mechanism coincides with that on the excited state, producing a large electronic coupling that separates the two surfaces by more than 120 kcal/mol.
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How the generalized anomeric effect influences the conformational preference.
Chemistry
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The generalized anomeric effect refers to the conformational preference of a gauche structure over an anti structure for molecules with a R-X-C-Y moiety. Whereas there are conflicting reports regarding the origin of this ubiquitous effect, a general consensus is that both the steric (more specifically electrostatic) and hyperconjugative interactions contribute. Here we employed the block-localized wavefunction (BLW) method, which is the simplest variant of ab initio valence bond (VB) theory and can define reference electron-localized states self-consistently, to evaluate the magnitude of the hyperconjugation effect in a number of acyclic molecules exhibiting the generalized anomeric effect. The BLW-based energy decomposition analysis revealed that both the steric and hyperconjugation effects contribute to the conformational preferences of methoxymethyl fluoride and methoxymethyl chlorides. But for the other systems under investigation, including methanediol, methanediamine, aminomethanol and dimethoxymethane, the hyperconjugative interactions play a negative role in the conformational preferences and the steric effect is solely responsible for the generalized anomeric effect.
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JoVE Visualize is a tool created to match the last 5 years of PubMed publications to methods in JoVE's video library.

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