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Crystal Structure and Optical Properties of the [Ag62S12(SBu(t))32](2+) Nanocluster with a Complete Face-Centered Cubic Kernel.
J. Am. Chem. Soc.
PUBLISHED: 10-24-2014
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The crystal structure of the [Ag62S12(SBu(t))32](2+) nanocluster (denoted as NC-I) has been successfully determined, and it shows a complete face-centered-cubic (FCC) Ag14 core structure with a Ag48(SBu(t))32 shell configuration interconnected by 12 sulfide ions, which is similar to the [Ag62S13(SBu(t))32](4+) structure (denoted as NC-II for short) reported by Wang. Interestingly, NC-I exhibits prominent differences in the optical properties in comparison with the case of the NC-II nanocluster. We employed femtosecond transient absorption spectroscopy to further identify the differences between the two nanoclusters. The results show that the quenching of photoluminescence in NC-I in comparison to that of NC-II is caused by the free valence electrons, which dramatically change the ligand to metal charge transfer (LMCT, S 3p ? Ag 5s). To get further insight into these, we carried out time-dependent density functional theory (TDDFT) calculations on the electronic structure and optical absorption spectra of NC-I and NC-II. These findings offer a new insight into the structure and property evolution of silver cluster materials.
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Crystal structure of Au25(SePh)18 nanoclusters and insights into their electronic, optical and catalytic properties.
Nanoscale
PUBLISHED: 10-16-2014
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The crystal structure of selenolate-capped Au25(SePh)18(-) nanoclusters has been unambiguously determined for the first time, and provides a solid basis for a deeper understanding of the structure-property relationships. The selenolate-capped Au25 cluster shows noticeable differences from the previously reported Au25(SCH2CH2Ph)18(-) counterpart, albeit both share the icosahedral Au13 core and semi-ring Au2(SeR)3 or Au2(SR)3 motifs. Distinct differences in the electronic structure and optical, catalytic and electrochemical properties are revealed by the coupling experiments with density functional theory (TD-DFT) calculations. Overall, the successful determination of the Au25(SePh)18(-) structure removes any ambiguity about its structure, and comparison with the thiolated Au25 counterpart helps us to further understand how the ligands affect the properties of the nanocluster.
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Heterobimetallic dinuclear lanthanide alkoxide complexes as acid-base difunctional catalysts for transesterification.
J. Org. Chem.
PUBLISHED: 09-23-2014
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A practical lanthanide(III)-catalyzed transesterification of carboxylic esters, weakly reactive carbonates, and much less-reactive ethyl silicate with primary and secondary alcohols was developed. Heterobimetallic dinuclear lanthanide alkoxide complexes [Ln2Na8{(OCH2CH2NMe2)}12(OH)2] (Ln = Nd (I), Sm (II), and Yb (III)) were used as highly active catalysts for this reaction. The mild reaction conditions enabled the transesterification of various substrates to proceed in good to high yield. Efficient activation of transesterification may be endowed by the above complexes as cooperative acid-base difunctional catalysts, which is proposed to be responsible for the higher reactivity in comparison with simple acid/base catalysts.
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A simple model for understanding the fluorescence behavior of Au25 nanoclusters.
Nanoscale
PUBLISHED: 04-16-2014
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In this work, we synthesized Au25 nanoclusters protected by 2-(naphthalen-2-yl)ethanethiolate. Our experiments revealed that the luminescence of this nanocluster consists of two bands, namely, band I centered at 740 nm and band II centered at 680 nm. Compared with 2-phenylethanethiolate protected Au25 nanoclusters, this new nanocluster has a much higher QY (quantum yield) value (6.5 times higher). Fluorescence lifetime measurements showed multiple components, i.e. 0.15 ns, ?20 ns and ?150 ns. With an increase in the electropositivity of the nanocluster, the fluorescence intensity of the nanocluster exhibits a significant enhancement. Since the 2-(naphthalen-2-yl)ethanethiolate protected Au25 nanocluster shares the same Au13/Au12 core-shell structure as the 2-phenylethanethiolate protected nanocluster, the band II fluorescence implies that the surface ligands play a major role in the origin of the fluorescence.
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Crystal structure of selenolate-protected Au24(SeR)20 nanocluster.
J. Am. Chem. Soc.
PUBLISHED: 02-18-2014
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We report the X-ray structure of a selenolate-capped Au24(SeR)20 nanocluster (R = C6H5). It exhibits a prolate Au8 kernel, which can be viewed as two tetrahedral Au4 units cross-joined together without sharing any Au atoms. The kernel is protected by two trimeric Au3(SeR)4 staple-like motifs as well as two pentameric Au5(SeR)6 staple motifs. Compared to the reported gold-thiolate nanocluster structures, the features of the Au8 kernel and pentameric Au5(SeR)6 staple motif are unprecedented and provide a structural basis for understanding the gold-selenolate nanoclusters.
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A 200-fold quantum yield boost in the photoluminescence of silver-doped Ag(x)Au(25-x) nanoclusters: the 13th silver atom matters.
Angew. Chem. Int. Ed. Engl.
PUBLISHED: 01-28-2014
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The rod-shaped Au25 nanocluster possesses a low photoluminescence quantum yield (QY=0.1%) and hence is not of practical use in bioimaging and related applications. Herein, we show that substituting silver atoms for gold in the 25-atom matrix can drastically enhance the photoluminescence. The obtained Ag(x)Au(25-x) (x=1-13) nanoclusters exhibit high quantum yield (QY=40.1%), which is in striking contrast with the normally weakly luminescent Ag(x)Au(25-x) species (x=1-12, QY=0.21%). X-ray crystallography further determines the substitution sites of Ag?atoms in the Ag(x)Au(25-x) cluster through partial occupancy analysis, which provides further insight into the mechanism of photoluminescence enhancement.
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Intramolecular charge transfer and solvation dynamics of thiolate-protected Au20(SR)16 clusters studied by ultrafast measurement.
J Phys Chem A
PUBLISHED: 09-30-2013
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It is accepted that the monolayer ligand shell in monolayer-protected gold nanoclusters (MPCs) plays an important role in stabilizing the metal core structure. Previous reports have shown that the core and shell do not interact chemically, and very few studies investigating the intramolecular charge transfer (ICT) between the core and ligand shell in clusters have been reported. The underlying excited state relaxation mechanisms about the influence of solvents, the optically excited vibration, and the roles of the core and shell in charge transfer remain unknown to a large extent. Here we report a femtosecond transient absorption study of a Au20(SR)16 (R = CH2CH2Ph) cluster in toluene and tetrahydrofuran. The ICT from the outside shell to the inside core upon excitation in Au20(SR)16 is identified. The observed solvation-dependent oscillations in different solvents further confirm the photoinduced ICT formation in Au20(SR)16. The results provide a fundamental understanding of the structure-property relationships about the solvation-dependent core-shell interaction in Au MPCs.
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A rhodamine-based fluorescent probe for detecting Hg(2+) in a fully aqueous environment.
Dalton Trans
PUBLISHED: 08-30-2013
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A water-soluble fluorescent probe for Hg(2+) based on a rhodamine B derivative was designed and synthesized. The new probe showed reversible colorimetric and fluorescent response to Hg(2+) in a fully aqueous solution. The probe exhibited real-time detection of Hg(2+) with high selectivity in media containing less than 1% organic cosolvent. Furthermore, bioimaging studies indicated that the new probe was cell permeable and suitable for the real-time imaging of Hg(2+) in living cells by confocal microscopy.
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Chiral 38-Gold-Atom Nanoclusters: Synthesis and Chiroptical Properties.
Small
PUBLISHED: 07-25-2013
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Enantioselective synthesis of chiral Au38 nanoclusters is achieved with chiral 2-phenylpropane-1-thiol (abbreviated as R/S-PET, organic soluble), captopril and glutathione (water soluble) as the respective ligand. The circular dichroism (CD) spectra of Au38 (R-PET)24 and Au38 (S-PET)24 show multiple bands which are precisely mirror-imaged, while their normal optical absorption spectra are identical with each other and also superimposable with that of the racemic Au38 (SCH2 CH2 Ph)24 nanoclusters. The observed CD signals are not from the chiral ligands themselves (which only give rise to CD signals in the UV (<250 nm), rather than in the visible wavelength region). Chiral Au38 nanoclusters with different types of ligands are further compared. Although the Au38 core is intrinsically chiral, different chiral ligands are found to largely influence the chiroptical response of the overall nanocluster. Thus, the chiral response of ligand-protected nanoclusters has both contributions from the metal core and the ligand shell around it. These optically active nanoclusters hold promise in future applications such as chiral sensing and catalysis.
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Design of an ultrasmall Au nanocluster-CeO2 mesoporous nanocomposite catalyst for nitrobenzene reduction.
Nanoscale
PUBLISHED: 07-11-2013
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In this work we are inspired to explore gold nanoclusters supported on mesoporous CeO2 nanospheres as nanocatalysts for the reduction of nitrobenzene. Ultrasmall Au nanoclusters (NCs) and mesoporous CeO2 nanospheres were readily synthesized and well characterized. Due to their ultrasmall size, the as-prepared Au clusters can be easily absorbed into the mesopores of the mesoporous CeO2 nanospheres. Owing to the unique mesoporous structure of the CeO2 support, Au nanoclusters in the Au@CeO2 may effectively prevent the aggregation which usually results in a rapid decay of the catalytic activity. It is notable that the ultrasmall gold nanoclusters possess uniform size distribution and good dispersibility on the mesoporous CeO2 supports. Compared to other catalyst systems with different oxide supports, the as-prepared Au nanocluster-CeO2 nanocomposite nanocatalysts showed efficient catalytic performance in transforming nitrobenzene into azoxybenzene. In addition, a plausible mechanism was deeply investigated to explain the transforming process. Au@CeO2 exhibited efficient catalytic activity for reduction of nitrobenzene. This strategy may be easily extended to fabricate many other heterogeneous catalysts including ultrasmall metal nanoclusters and mesoporous oxides.
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A comparison of the chiral counterion, solvent, and ligand used to induce a chiroptical response from Au25(-) nanoclusters.
Nanoscale
PUBLISHED: 07-10-2013
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A 25-atom gold nanocluster capped with an achiral thiolate exhibits no chiroptical signals in circular dichroism (CD) measurements. Herein, we report a systematic study on the effects of the chiral environment on the CD response from the Au25 metal core. We found that Au25(SC2H4Ph)18(-)TOA(+) dissolved in a chiral solvent did not give rise to a CD response, nor did Au25(SC2H4Ph)18(-) when associated with a chiral counterion (e.g., (-)-N-dodecyl-N-methylephedrinium, DME(+)). Both scenarios imply that the interaction of the chiral counterion (or chiral solvent molecules) with the achiral Au25(SC2H4Ph)18(-) nanocluster is not strong enough to induce CD signals from the metal core. In contrast, when the metal core is capped with chiral ligands (i.e., Au25(SCH2C*H(NH2)CH2Ph)18), strong CD signals in the visible wavelength range were observed. Thus, the induction of CD signals by surface chiral ligands is much stronger than that by the external chiral environment (including the chiral solvent or counterion). This work reveals some further insight into the origin of the chiroptical response of the Au nanoclusters. These chiral nanoclusters hold potential for practical applications in bioconjugation, sensing, and chiral catalysis.
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Au25 clusters as electron-transfer catalysts induced the intramolecular cascade reaction of 2-nitrobenzonitrile.
Sci Rep
PUBLISHED: 05-31-2013
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Design of atomically precise metal nanocluster catalysts is of great importance in understanding the essence of the catalytic reactions at the atomic level. Here, for the first time, Au25(z) nanoslusters were employed as electron transfer catalysts to induce an intramolecular cascade reaction at ambient conditions and gave rise to high conversion (87%) and selectivity (96%). Electron spin-resonance spectra indeed confirmed the consecutive electron transfer process and the formation of N radical. UV-vis absorption spectra also verified Au25(z) was intact after the catalytic circle. Our research may open up wide opportunities for extensive organic reactions catalyzed by Au25(z).
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High yield synthesis of Au25 nanoclusters by controlling the reduction process.
J Nanosci Nanotechnol
PUBLISHED: 05-08-2013
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The syntheses of gold nanoclusters, namely, the 25-gold-atom nanocluster (Au25(SR)18) and 38-gold-atom nanocluster (Au38(SR)24), with SR representing the thiol ligand, were described in previously reported studies. The synthesis was via a fast reduction process using sodium borohydride. The ratio of Au:HSR:NaBH4 was 1:3:10. Herein we report that the Au25 nanocluster can also be synthesized via a slow reduction process through a dropwise addition of an aqueous solution of sodium borohydride. The ratio of Au:S:NaBH4 is also changed to 1:3:5. This method synthesized Au25 nanoclusters at a high yield (47%). Pure Au25 nanoclusters were obtained after extraction, and the product was fully characterized by UV-vis spectroscopy, thermogravimetric analysis (TGA) and Matrix-Assisted Laser Desorption/Ionization (MALDI) mass spectrometry. The possible formation mechanism is discussed in this paper. This work contributes to a better understanding of the mechanism of Au25 formation and provides a basis for further study of gold nanoclusters.
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One-pot synthesis of phenylmethanethiolate-protected Au20(SR)16 and Au24(SR)20 nanoclusters and insight into the kinetic control.
Chem Asian J
PUBLISHED: 03-26-2013
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We report two synthetic routes for concurrent formation of phenylmethanethiolate (-SCH2Ph)-protected Au20(SR)16 and Au24(SR)24 nanoclusters in one-pot by kinetic control. Unlike the previously reported methods for thiolate-protected gold nanoclusters, which typically involve rapid reduction of the gold precursor by excess NaBH4 and subsequent size focusing into atomically monodisperse clusters of a specific size, the present work reveals some insight into the kinetic control in gold-thiolate cluster synthesis. We demonstrate that the synthesis of -SCH2Ph-protected Au20 and Au24 nanoclusters can be obtained through two different, kinetically controlled methods. Specifically, route 1 employs slow addition of a relatively large amount of NaBH4 under slow stirring of the reaction mixture, while route 2 employs rapid addition of a small amount of NaBH4 under rapid stirring of the reaction mixture. At first glance, these two methods apparently possess quite different reaction kinetics, but interestingly they give rise to exactly the same product (i.e., the coproduction of Au20(SCH2Ph)16 and Au24(SCH2Ph)20 clusters). Our results explicitly demonstrate the complex interplay between the kinetic factors that include the addition speed and amount of NaBH4 solution as well as the stirring speed of the reaction mixture. Such insight is important for devising synthetic routes for different sized nanoclusters. We also compared the photoluminescence and electrochemical properties of PhCH2S-protected Au20 and Au24 nanoclusters with the PhC2H4S-protected counterparts. A surprising 2.5 times photoluminescence enhancement was observed for the PhCH2S-capped nanoclusters when compared to the PhC2H4S-capped analogues, thereby indicating a drastic effect of the ligand that is merely one carbon shorter.
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Synthesis of selenolate-protected Au18(SeC6H5)14 nanoclusters.
Nanoscale
PUBLISHED: 01-04-2013
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This work reports the first synthesis of selenophenolate-protected Au(18)(SePh)(14) nanoclusters. This cluster exhibits distinct differences from its thiolate analogue in terms of optical absorption properties. The Au(18)(SePh)(14) nanoclusters were obtained via a controlled reaction of Au(25)(SCH(2)CH(2)Ph)(18) with selenophenol. Electrospray ionization time-of-flight mass spectrometry (ESI-TOF-MS) revealed the crude product to contain predominantly Au(18)(SePh)(14) nanoclusters, and side products include Au(15)(SePh)(13), Au(19)(SePh)(15) and Au(20)(SePh)(16). High-performance liquid chromatography (HPLC) was employed to isolate Au(18)(SePh)(14) nanoclusters. The results of thermogravimetric analysis (TGA), elemental analysis (EA), and (1)H/(13)C NMR spectroscopy confirmed the cluster composition. To the best of our knowledge, this is the first report of selenolate-protected Au(18) nanoclusters. Future theoretical and X-ray crystallographic work will reveal the geometric structure and the nature of selenolate-gold bonding in the nanocluster.
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Chirality in gold nanoclusters probed by NMR spectroscopy.
ACS Nano
PUBLISHED: 10-07-2011
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We report the analysis of chirality in atomically precise gold nanoclusters by nuclear magnetic resonance (NMR) spectroscopic probing of the surface ligands. The Au(38)(SR)(24) and Au(25)(SR)(18) (where, R = CH(2)CH(2)Ph) are used as representative models for chiral and nonchiral nanoclusters, respectively. Interestingly, different (1)H signals for the two germinal protons in each CH(2) of the ligands on the chiral Au(38)(SR)(24) nanocluster were observed, so-called diastereotopicity. For ?-CH(2) (closest to the chiral metal core), a chemical shift difference of up to ~0.8 ppm was observed. As for the nonchiral Au(25)(SCH(2)CH(2)Ph)(18)(-)TOA(+) nanocluster, no diastereotopicity was detected (i.e., no chemical shift difference for the two protons in the CH(2)), confirming the Au(25) core being nonchiral. These two typical examples demonstrate that NMR spectroscopy can be a useful tool for investigating chirality in Au nanoclusters. Since the diastereotopicity induced on the methylene protons by chiral nanoclusters is independent of the enantiomeric composition of the chiral particles, NMR can probe the chirality of the nanoclusters even in the case of a racemic mixture, while circular dichroism spectroscopy is not useful for racemic mixtures.
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Chiral Au?? nanospheres and nanorods: synthesis and insight into the origin of chirality.
Nano Lett.
PUBLISHED: 08-11-2011
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Chirality in nanoparticles is an intriguing phenomenon. Herein, we have devised a well-defined gold nanoparticle system for investigating the origin of chirality in nanoparticles. We have designed chiral thiols (R- and S-isomers) and synthesized chiral gold nanoparticles composed of 25 gold atoms and 18 ligands, referred to as Au(25)(pet)(18), where pet represents chirally modified phenylethylthiolate -SCH(2)CH(CH(3))Ph at the 2-position. These optically active nanoparticles are close analogues of the optically nonactive phenylethylthioalte-capped Au(25)(pet)(18) nanoparticles, and the latters crystal structure is known. On the basis of the atomic and electronic structures of these well-defined Au(25) nanoparticles, we have explicitly revealed that the ligands and surface gold atoms of Au(25)(pet)(18) play a critical role in effecting the circular dichroism responses from the nanoparticles. Similar effects are also observed in chiral Au(25) rods. The mixing of electronic states of ligands with those of surface gold atoms constitutes the fundamental origin of chirality in such nanoparticles.
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Unexpected reactivity of Au25(SCH2CH2Ph)18 nanoclusters with salts.
Nanoscale
PUBLISHED: 02-14-2011
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We report some interesting results of the chemical reactivity of thiolate-protected [Au(25)(SCH(2)CH(2)Ph)(18)](0) nanoclusters with two types of salts, including tetraoctylammonium halide (TOAX) and NaX. At the early stage of the reaction, [Au(25)(SCH(2)CH(2)Ph)(18)](0) was found to spontaneously convert to its anionic form ([Au(25)(SCH(2)CH(2)Ph)(18)](-)) in the presence of either type of salt. However, a large difference was observed in the second stage of the reaction. With NaX, we observed decomposition of anionic clusters, while with TOAX, the clusters show excellent stability. We have gained some insight into the reaction mechanism. The X(-) ions seem to attack [Au(25)(SCH(2)CH(2)Ph)(18)](q) surface and displace some thiolates, evidenced by the observation of halide-bound clusters such as Au(25)(SCH(2)CH(2)Ph)(18-x)Br(x) in mass spectrometry analysis. These halide-bound clusters show a reduced stability, and their decomposition into Au(I) complexes leads to the release of gold valence electrons of the clusters; concurrently, the non-halide-bound [Au(25)(SCH(2)CH(2)Ph)(18)](0) clusters are reduced into [Au(25)(SCH(2)CH(2)Ph)(18)](-). For the second stage of reaction with organic salts such as TOA-Br, after [Au(25)(SCH(2)CH(2)Ph)(18)](0) clusters are converted to [Au(25)(SCH(2)CH(2)Ph)(18)](-)) the TOA(+) counterions surprisingly protect the anionic clusters from further attack by halide ions, hence, TOA(+) cations can stabilize [Au(25)(SCH(2)CH(2)Ph)(18)](-) clusters. In contrast, with NaX salts the Na(+) ions do not provide any steric stabilization of the [Au(25)(SCH(2)CH(2)Ph)(18)](-) clusters, hence, degradation occurs when being further attacked by halide ions, especially Br(-) and I(-).
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Thiolate-protected Au(20) clusters with a large energy gap of 2.1 eV.
J. Am. Chem. Soc.
PUBLISHED: 05-13-2009
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We report a kinetically controlled approach to synthesizing thiolate-capped 20-atom gold clusters. ESI mass spectrometry analysis in combination with other methods, including elemental analysis, XPS, NMR, and thermogravimetric analysis, determines the cluster composition to be Au(20)(SCH(2)CH(2)Ph)(16). The Au(20)(SCH(2)CH(2)Ph)(16) clusters exhibit a stepwise, multiple-band optical absorption spectrum, reminiscent of quantum confinement behavior. The optical energy gap is determined to be E(g) approximately 2.15 eV; this HOMO-LUMO gap is remarkably larger than that of Au(25)(SR)(18) (1.3 eV). The Au(20)(SCH(2)CH(2)Ph)(16) clusters were also found to be particularly robust again excess thiol etching, in contrast to the previous report on the thiol etching stability of a series of glutathione-capped Au(n)(SG)(m) (n < 25) clusters. This stability difference might indicate some structural differences between Au(20)(SCH(2)CH(2)Ph)(16) and Au(n)(SG)(m) (n < 25). The crystal structure of the Au(20)(SCH(2)CH(2)Ph)(16) cluster remains to be unraveled in future work.
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Facile, large-scale synthesis of dodecanethiol-stabilized Au38 clusters.
J Phys Chem A
PUBLISHED: 02-14-2009
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It has long been a major challenge to achieve synthetic control over size and monodispersity of gold thiolate nanoclusters. Among the reported Aun thiolate clusters, Au38 has been shown to be particularly stable but was only obtained as a minor product in previous syntheses. In this work, we report a bulk solution synthetic method that permits large-scale, facile synthesis of truly monodisperse Au38 nanoclusters. This new method explores a two-phase ligand exchange process utilizing glutathione-capped Aun clusters as the starting material. The ligand exchange process with neat dodecanethiols causes gold core etching and secondary growth of clusters, and eventually leads to monodisperse Au38 clusters in high purity, which eliminates nontrivial postsynthetic separation steps. This method can be readily scaled up to synthesize Au38(SC12H25)24 in large quantities and thus makes the approach and Au38 nanoclusters of broad utility.
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Reversible switching of magnetism in thiolate-protected Au25 superatoms.
J. Am. Chem. Soc.
PUBLISHED: 01-31-2009
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We report reversible switching of paramagnetism in a well-defined gold nanoparticle system consisting of atomically monodisperse nanoparticles containing 25 gold atoms protected by 18 thiolates [abbreviated as Au(25)(SR)(18)]. The magnetism in these nanoparticles can be switched on or off by precisely controlling the charge state of the nanoparticle, that is, the magnetic state of the Au(25)(SR)(18) nanoparticles is charge-neutral while the nonmagnetic state is an anionic form of the particle. Electron paramagnetic resonance (EPR) spectroscopy measurements establish that the magnetic state of the Au(25)(SR)(18) nanoparticles possess one unpaired spin per particle. EPR studies also imply an unusual electronic structure of the Au(25)(SR)(18) nanoparticle. Density functional theory calculations coupled with the experiments successfully explain the origin of the observed magnetism in a Au(25)(SR)(18) nanoparticle as arising from one unpaired spin having distinct P-like character and delocalized among the icosahedral Au(13) core of the particle in the highest occupied molecular orbital. The results suggest that the Au(25)(SR)(18) nanoparticles are best considered as ligand-protected superatoms.
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Quantum sized gold nanoclusters with atomic precision.
Acc. Chem. Res.
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Gold nanoparticles typically have a metallic core, and the electronic conduction band consists of quasicontinuous energy levels (i.e. spacing ? ? k(B)T, where k(B)T is the thermal energy at temperature T (typically room temperature) and k(B) is the Boltzmann constant). Electrons in the conduction band roam throughout the metal core, and light can collectively excite these electrons to give rise to plasmonic responses. This plasmon resonance accounts for the beautiful ruby-red color of colloidal gold first observed by Faraday back in 1857. On the other hand, when gold nanoparticles become extremely small (<2 nm in diameter), significant quantization occurs to the conduction band. These quantum-sized nanoparticles constitute a new class of nanomaterial and have received much attention in recent years. To differentiate quantum-sized nanoparticles from conventional plasmonic gold nanoparticles, researchers often refer to the ultrasmall nanoparticles as nanoclusters. In this Account, we chose several typical sizes of gold nanoclusters, including Au(25)(SR)(18), Au(38)(SR)(24), Au(102)(SR)(44), and Au(144)(SR)(60), to illustrate the novel properties of metal nanoclusters imparted by quantum size effects. In the nanocluster size regime, many of the physical and chemical properties of gold nanoparticles are fundamentally altered. Gold nanoclusters have discrete electronic energy levels as opposed to the continuous band in plasmonic nanoparticles. Quantum-sized nanoparticles also show multiple optical absorption peaks in the optical spectrum versus a single surface plasmon resonance (SPR) peak at 520 nm for spherical gold nanocrystals. Although larger nanocrystals show an fcc structure, nanoclusters often have non-fcc atomic packing structures. Nanoclusters also have unique fluorescent, chiral, and magnetic properties. Due to the strong quantum confinement effect, adding or removing one gold atom significantly changes the structure and the electronic and optical properties of the nanocluster. Therefore, precise atomic control of nanoclusters is critically important: the nanometer precision typical of conventional nanoparticles is not sufficient. Atomically precise nanoclusters are represented by molecular formulas (e.g. Au(n)(SR)(m) for thiolate-protected ones, where n and m denote the respective number of gold atoms and ligands). Recently, major advances in the synthesis and structural characterization of molecular purity gold nanoclusters have made in-depth investigations of the size evolution of metal nanoclusters possible. Metal nanoclusters lie in the intermediate regime between localized atomic states and delocalized band structure in terms of electronic properties. We anticipate that future research on quantum-sized nanoclusters will stimulate broad scientific and technological interests in this special type of metal nanomaterial.
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Controlled reduction for size selective synthesis of thiolate-protected gold nanoclusters Aun(n?=?20, 24, 39, 40).
Nanoscale Res Lett
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This work presents a controlled reduction method for the selective synthesis of different sized gold nanoclusters protected by thiolate (SR?=?SC2H4Ph). Starting with Au(III) salt, all the syntheses of Aun(SR)m nanoclusters with (n, m)?=?(20, 16), (24, 20), (39, 29), and (40, 30) necessitate experimental conditions of slow stirring and slow reduction of Au(I) intermediate species. By controlling the reaction kinetics for the reduction of Au(I) into clusters by NaBH4, different sized gold nanoclusters are selectively obtained. Two factors are identified to be important for the selective growth of Au20, Au24, and Au39/40 nanoclusters, including the stirring speed of the Au(I) solution and the NaBH4 addition speed during the step of Au(I) reduction to clusters. When comparing with the synthesis of Au25(SC2H4Ph)18 nanoclusters, we further identified that the reduction degree of Au(I) by NaBH4 also plays an important role in controlling cluster size. Overall, our results demonstrate the feasibility of attaining new sizes of gold nanoclusters via a controlled reduction route.
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Ligand-exchange synthesis of selenophenolate-capped Au25 nanoclusters.
Nanoscale
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We report the synthesis and characterization of selenophenolate-capped 25-gold-atom nanoclusters via a ligand-exchange approach. In this method, phenylethanethiolate (PhCH(2)CH(2)S) capped Au(25) nanoclusters are utilized as the starting material, which is subject to ligand-exchange with selenophenol (PhSeH). The as-obtained cluster product is confirmed to be selenophenolate-protected Au(25) nanoclusters through characterization by electrospray ionization (ESI) and matrix-assisted laser desorption ionization mass spectrometry (MALDI-MS), thermogravimetric analysis (TGA), elemental analysis (EA), UV-Vis and (1)H/(13)C NMR spectroscopies. The ligand-exchange synthesis of [Au(25)(SePh)(18)](-)[(C(8)H(17))(4)N](+) nanoclusters demonstrates that the core size of gold nanoclusters is retained in the thiolate-to-selenolate exchange process and that the 18 surface thiolate ligands can be completely exchanged by selenophenolate, rather than giving rise to a mixed ligand shell on the cluster. The two types of Au(25)L(18) (L = thiolate or selenolate) nanoclusters also show some differences in stability and optical properties.
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A novel quinoline-based two-photon fluorescent probe for detecting Cd2+ in vitro and in vivo.
Dalton Trans
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A new two-photon fluorescent Cd(2+) probe APQ is developed by introducing a N(1),N(1)-dimethyl-N(2)-(pyridin-2-ylmethyl)ethane-1,2-diamine binding group and a 4-methoxyphenylvinyl conjugation-enhancing group to the 2- and 6-positions of quinoline. This probe shows a large red shift and good emission enhancement under Cd(2+) binding. It also exhibits a high ion selectivity for Cd(2+) (especially over Zn(2+)) and a large two-photon absorption cross section at 710 nm. Two-photon microscopy imaging studies reveal that the new probe is non-toxic and cell-permeable and can be used to detect intracellular Cd(2+) under two-photon excitation.
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6-Substituted quinoline-based ratiometric two-photon fluorescent probes for biological Zn2+ detection.
Chem. Commun. (Camb.)
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New ratiometric two-photon fluorescent probes are developed from 6-substituted quinolines for biological Zn(2+) detection. They show large red shifts and good ratiometric responses upon Zn(2+) binding. They also exhibit high ion selectivities and large two-photon absorption cross sections at nearly 720 nm. Because the new probes are cell-permeable, they can be used to detect intracellular zinc flux under two-photon excitation.
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What is Visualize?

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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We use abstracts found on PubMed and match them to JoVE videos to create a list of 10 to 30 related methods videos.

Video X seems to be unrelated to Abstract Y...

In developing our video relationships, we compare around 5 million PubMed articles to our library of over 4,500 methods videos. In some cases the language used in the PubMed abstracts makes matching that content to a JoVE video difficult. In other cases, there happens not to be any content in our video library that is relevant to the topic of a given abstract. In these cases, our algorithms are trying their best to display videos with relevant content, which can sometimes result in matched videos with only a slight relation.