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At least 199 records · Page 11Linked to original sources
PubMed1999

Complexes with S-Donor Ligands. 7. New 1,1-Ethylenedithiolato Complexes of Thallium(I), Gold(I), and Gold(III): Syntheses, Structure, and Molecular Cubic Hyperpolarizabilities.

beta-Diketonato complexes [Tl{CH{C(O)R}(2)}] or PPN[Au{CH{C(O)R}(2)}(2)] [where PPN = (Ph(3)P)(2)N] react with an excess of CS(2) to give, respectively, [Tl(2){S(2)C=C{C(O)R}(2)}](n)() [R = Me (1) or Ph (2)] or (PPN)(2)[Au(2){&mgr;-kappa(2)-S(2)C=C{C(O)R}(2)}(2)] [R = Me (3.PPN) or Ph (4.PPN)]. The gold complexes 3.PPN and 4.PPN can also be obtained from PPN[AuCl(2)] and the corresponding thallium 1,1-ethylenedithiolate. PPN[AuCl(4)] reacts with 1 to give PPN[Au{kappa(2)-S(2)C=C{C(O)Me}(2)}(2)] (5) which, in turn, reacts with PhICl(2), Br(2) or I(2) (1:1) to give PPN[AuX(2){kappa(2)-S(2)C=C{C(O)Me}(2)}] [X = Cl (6), Br (7), or I (8)]. By reacting 6 with TlCF(3)SO(3) and 1,10-phenanthroline (phen) in 1:2:1 molar ratio, the cationic complex [Au{kappa(2)-S(2)C=C{C(O)Me}(2)}(phen)]CF(3)SO(3) (9) can be obtained. The crystal structures of 5 and 6.0.5Me(2)CO have been determined. Third-order nonlinearities of 3.PPN, 3.Pr(4)N, 5, and 6 have been evaluated by the Z-scan technique; an increase in nonlinearity upon extending the pi-system is observed, with the anionic dimetallacycle containing two gold and four sulfur atoms in 3 responsible for the largest nonlinearities (approximately 100 x 10(-36) esu).

Journal Article↗
PubMed2002

The fate of sulfur-bound hydrogen on formation of self-assembled thiol monolayers on gold: (1)H NMR spectroscopic evidence from solutions of gold clusters.

It is demonstrated that thiols can adsorb to gold without losing hydrogen. Dodecyl sulfide-capped gold clusters have been prepared and subjected to ligand exchange reactions in perdeuterated benzene by addition of dodecanethiol and subsequently dodecyl disulfide. It is shown by 1H NMR spectroscopy that dodecanethiol molecules are readily taken up as ligands producing characteristic broad signals corresponding to the alpha-methylene and S-H protons, with chemical shifts close to those found for thiol in solution; these signals are absent in spectra of thiolate-capped clusters. Addition of excess disulfide to such clusters capped with both dialkyl sulfides and thiols leads to the appearance of sharp signals for free dialkyl sulfide and intact thiol. Amounts of thiols up to 50% of the ligand shell are, however, taken up by the clusters under rapid and irreversible loss of hydrogen.

Journal Article↗
PubMed2005

Synthesis of gold nanoparticles from gold(I)-alkanethiolate complexes with supramolecular structures through electron beam irradiation in TEM.

Monodisperse gold nanoparticles were prepared via electron beam irradiation of Au(I)-SR (R = -CnH2n+1) polymers with highly ordered supramolecular structures in transmission electron microscopy. The Au(I)-SR polymers were synthesized simply by mixing LiAuCl4 and an excess amount of alkanethiol in tetrahydrofuran. The sizes of the gold nanoparticles were controlled by changing the length of the alkyl group or by adjusting the energy of the electron beam.

Journal Article↗
PubMed2005

Gold cluster carbonyls: saturated adsorption of CO on gold cluster cations, vibrational spectroscopy, and implications for their structures.

We report on the interaction of carbon monoxide with cationic gold clusters in the gas phase. Successive adsorption of CO molecules on the Au(n)(+) clusters proceeds until a cluster size specific saturation coverage is reached. Structural information for the bare gold clusters is obtained by comparing the saturation stoichiometry with the number of available equivalent sites presented by candidate structures of Au(n)(+). Our findings are in agreement with the planar structures of the Au(n)(+) cluster cations with n < or = 7 that are suggested by ion mobility experiments [Gilb, S.; Weis, P.; Furche, F.; Ahlrichs, R.; Kappes, M. M. J. Chem. Phys. 2001, 116, 4094]. By inference we also establish the structure of the saturated Au(n)(CO)(m)(+) complexes. In certain cases we find evidence suggesting that successive adsorption of CO can distort the metal cluster framework. In addition, the vibrational spectra of the Au(n)(CO)(m)(+) complexes in both the CO stretching region and in the region of the Au-C stretch and the Au-C-O bend are measured using infrared photodepletion spectroscopy. The spectra further aid in the structure determination of Au(n)(+), provide information on the structure of the Au(n)(+)-CO complexes, and can be compared with spectra of CO adsorbates on deposited clusters or surfaces.

Journal Article↗
PubMed2005

Laser-induced gold deposition on p+-Si from liquid precursors: a study on the reduction of gold ions through competing Dember and Seebeck effects.

Gold micropatterns are deposited from aqueous solutions of NaAuCl(4) on boron-doped Si(100) surfaces (rho = 1.5 x 10(-4) Omega m) using a focused Ar(+) laser beam (TEM(00), lambda = 488 nm, w(0) = 1.5 mum, P = 20-80 mW). The finite-element method employed for computing the surface temperature profiles reveals that the maximum temperature at the precursor/silicon interface increases only to the range 316-372 K, which is not high enough for chemical reactions with formaldehyde in the precursor. This suggests a different mechanism to be responsible for the reduction of gold ions, namely, changes in the surface potential of Si caused by the Dember and Seebeck effects.

Journal Article↗
PubMed2006

Chemisorption-induced spin symmetry breaking in gold clusters and the onset of paramagnetism in capped gold nanoparticles.

We present a simple model to describe the induction of magnetic behavior on gold clusters upon chemisorption of one organic molecule with different chemical linkers. In particular, we address the problem of stability of the lowest lying singlet and show that for some linkers there exists a spin symmetry-breaking that lowers the energy and leads to preferential spin density localization on the gold atoms neighboring the chemisorption site. The model is basically an adaptation of the Stoner model for itinerant electron ferromagnetism to finite clusters and it may have important implications for our understanding of surface magnetism in larger nanosystems and its relevance to electronic transport in electrode-molecule interfaces.

Journal Article↗
PubMed2004

Directly monitoring the growth of gold nanoparticle seeds into gold nanorods.

This paper describes the use of atomic force microscopy to directly image surface-attached 3-5 nm diameter gold nanoparticle seeds before and after seed-mediated growth into gold nanorods (Au NRs) and other shapes (spheres, triangles, and hexagons). Results show that Au NRs form from seeds growing in either one or two directions. A direct correlation exists between seed diameter and NR diameter; small diameter seeds form small diameter NRs. However, correlation between seed diameter and nanostructure shape or NR length is less evident. We describe our results in terms of growth mechanisms proposed in the literature and discuss possible reasons for the large size dispersity observed for surface-grown Au NRs. A better understanding of Au NR and other metal and semiconductor one-dimensional (1D) growth processes is necessary to improve synthesis, tailor their properties, and utilize 1D nanostructures for useful technological applications.

Journal Article↗
PubMed2004

Reaction of gold(III) oxo complexes with alkenes. Synthesis of unprecedented gold alkene complexes, [Au(N,N)(alkene)][PF6]. Crystal structure of [Au(bipy(ip))(eta2-CH2=CHPh)][PF6] (bipy(ip) = 6-isopropyl-2,2'-bipyridine).

Gold alkene complexes [Au(bipyR)(eta2-alkene)][PF6] (bipyR = 6-alkyl-2,2'-bipyridine) have been obtained by reaction of gold(III) oxo complexes [Au2(bipyR)2(mu-O)2][PF6]2 with alkenes. The crystal structure of the styrene adduct [Au(bipy(ip))(eta2-CH2=CHPh)][PF6] (bipy(ip) = 6-isopropyl-2,2'-bipyridine) has been solved by X-ray analysis.

Journal Article↗
PubMed2006

Secondary interactions in gold(I) complexes with thione ligands. 5. Two ionic compounds of the form bis(thione)gold(I) bis(4-halobenzenesulfonyl)amide.

Bis(1,3-thiazolidine-2-thione-kappaS2)gold(I) bis(4-chlorobenzenesulfonyl)amide, [Au(C3H5NS2)2](C12H8Cl2NS2O4), has no imposed symmetry. Classical N-H...N and N-H...O hydrogen bonds link the residues to form chains parallel to the b axis. Weaker interactions involve C-H...O, C-H...Au and a number of X...Cl contacts (X = Cl, S or Au) clustered in the region y approximately equal to 1/4}. In bis(1-methylimidazolidine-2-thione-kappaS2)gold(I) bis(4-iodobenzenesulfonyl)amide, [Au(C4H8N2S)2](C12H8I2NS2O4), the Au atom of the cation and the N atom of the anion lie on the twofold axis (0, y, 1/4}) in the space group C2/c. The formula unit forms a self-contained ring with two symmetry-equivalent N-H...O hydrogen bonds, and weak C-H...X (X = O, I or S), Au...I and I...I contacts are observed. In both compounds, the anions display extended conformations.

Journal Article↗
PubMed2001

Electrochemical characteristics of thin nickel hexacyanoferrate films formed on gold and thiol self-assembled monolayers modified gold electrodes.

Nickel hexacyanoferrate (NiHCF) film was prepared and characterized on gold and thiol self-assembled monolayers (SAMs)-modified gold electrodes. It was found that the film exhibited some different electrochemical characteristics compared with that found on a carbon electrode. In the presence of K+, the film exhibited a redox peak at about 0.5 V. The peak potential shifted linearly with the K+ concentration over the range of about 0.1 mM - 0.1 M with slopes of 54 - 60 mV per log[K+]. However, in solutions containing Na+, Li+ or NH4+ ion the film did not generate well-defined peaks, or even a visible redox peak. Therefore, the film showed a selective potential response to K+. The voltammetric behavior of NiHCF film varied with thiols, the preparation procedure and the solution pH. Under certain conditions, the characteristics of the film could be improved to some extent.

Journal Article↗
PubMed1992

Ultrastructural localization of hyaluronan in myelin sheaths of the rat central and rat and human peripheral nervous systems using hyaluronan-binding protein-gold and link protein-gold.

Neural tissue of central (rat spinal cord) and peripheral origin (rat sciatic nerve, nerve fascicles of rat skin and iris and of human conjunctiva) was processed by osmium tetroxide/microwave fixation and embedded in epoxy resin. Hyaluronan-binding proteins and link proteins coupled to 15-20-nm gold particles were used as markers in a one-step post-embedding procedure for identifying hyaluronan (hyaluronic acid) at the ultrastructural level. All myelin sheaths in both rat and human material were found to be intensely labelled. The specificity of the hyaluronan-binding probes was demonstrated by the total loss of labelling following treatment of sections with hyaluronidase or by preincubating either the probes with hyaluronan oligosaccharides or the sections with unlabelled hyaluronan-binding protein. The identified hyaluronan appears to be located extracellularly, but is precise role here remains to be elucidated.

Animals↗
PubMed1993

The (8-thiotheophyllinate) (triphenylphosphine) gold (I), (tTAuP): a new gold complex as an anticancer agent.

In continuous Friend leukemia cell exposure to tTAuP, the IC50 was 0.2 microM whereas in cells exposed 15 or 60 min to tTAuP followed by 72 h in drug-free medium the IC50 was 2.2 and 1.3 microM respectively. A combination of tTAuP and cisplatin (CDDP) is shown to be more active than either agent alone. Intracellular accumulation studies analysed by SXRF have shown that to achieve a cytotoxic effect, large concentrations of gold are necessary to accumulate in both the nuclear and cytoplasmic fraction. However, at cytostatic doses (1 microM), tTAuP has no effect on the cell cycle but does affect DNA synthesis. At a higher dose, greater than that necessary to induce cytotoxicity, it produces DNA damage, as observed by alkaline elution method. When cells were exposed to toxic doses of tTAuP (10 microM) in the presence of albumin, cytotoxicity was significantly reduced. Similar results were obtained when cells were co-treated with L-cysteine, dithiothreitol or reduced gluthatione. Reduced cytotoxic effect can be related to the interaction with free thiol groups. According to these data it is concluded that tTAuP is highly effective in vitro; whether it is active in vivo remains to be determined.

Antineoplastic Agents↗
PubMed2005

Structural studies of lanthanide ion complexes of pure gold, pure silver and mixed metal (gold-silver) dicyanides.

Crystal structures of four lanthanide complexes of La[Au(CN)2](3).3H2O, La[Ag(CN)2](3).3H2O, La[Ag(0.83)Au(0.17)(CN)2](3).3H2O, and La[Ag(0.39)Au(0.61)(CN)2](3).3H2O are reported. Studies reveal that all the structures reported are isostructural. All systems were found to be in the hexagonal crystal system, space group P6(3)/mcm. The metal-metal distance for the pure gold system is 3.332 (1) A versus 3.359(1) A for the pure silver system. The mixed-metal systems have shown no distinct differences in the location of the metal atoms, with the La[Ag(0.83)Au(0.17)(CN)2](3).3H2O complex having a metal-metal Ag-Au separation of 3.346(1) A, and 3.344(1) A for the La[Ag(0.39)Au(0.61)(CN)2](3).3H2O complex. The crystal structures of the pure and mixed La complexes have been solved to provide evidence of Ag-Au heterometallic interactions and as a basis for understanding the interesting optical properties of the systems.

Crystallography, X-Ray↗
PubMed1986

An ultrastructural study of gold thioglucose lesion formation in the ventromedial hypothalamus: subnecrotic gold thioglucose dose.

In an ultrastructural study of gold thioglucose (GTG) lesion formation in the mouse ventromedial hypothalamus (VMH), a single intraperitoneal subnecrotic dose of GTG (100 mg/kg) was used to induce a VMH microlesion, visible only by electron microscopy. Definitive neuronal alterations were not evident until eight hours after GTG injection. Large pericapillary processes, probably dendrites, displayed a loss of cytoplasmic density and distention, while the capillary endothelium appeared normal. Some intercellular distention also was apparent. By 24 hours after GTG administration, degenerating neurons were visible. Swollen and disrupted synaptic profiles were seen. However, no vascular damage was evident. These results support the evidence that GTG is a neurotoxin for structures in the mouse VMH.

Animals↗