Metal cluster topology. 2. Gold clusters

Previously developed methods for the treatment of polyhedral boranes, carboranes, and metal clusters are extended to the treatment of gold clusters, which present a variety of new problems. In most cases gold atoms in such cluster compounds do not employ the usual 9-orbital sp³d⁵ spherical bonding orbital manifold. Instead almost all non-tetrahedral gold clusters consist of a center gold atom surrounded by a puckered polygonal belt of peripheral gold atoms generally with one or more additional peripheral gold atoms in distal positions above and/or below the belt. The peripheral gold atoms in such clusters use a 7-orbital spd⁵ cylindrical bonding orbital manifold, but their residual two orthogonal anti- bonding p orbitals can receive electron density from the filled d orbitals of adjacent peripheral gold atoms through dσ → pσ^* and/or dπ → pπ^* backbonding leading to bonding distances between adjacent peripheral gold atoms. Centered gold clusters can be classified into either spherical or toroidal clusters depending upon whether the center gold atom uses a 9-orbital sp³d⁵ spherical bonding orbital manifold or an 8-orbital sp²d⁵ toroidal bonding orbital manifold, respectively. The topology of the core bonding in gold clusters is generally not that of the K_n complete graph found in other clusters but instead mimics the topology of the polyhedron formed by the surface atoms. This apparently is a consequence of the poor lateral overlap of the cylindrical spd⁵ manifolds of the peripheral gold atoms. Examples of non-centered gold clusters treated in this paper include the squashed pentagonal bipyramidal Au₇(PPh₃)₇⁺ and the edge-fused bitetrahedral (Ph₃P)₄Au₆[Co(CO)₄]₂ which may be regarded as a ‘perauraethylene’ in which the six cluster gold atoms correspond to the six atoms of ethylene including a double bond between the two gold atoms corresponding to the two ethylene carbon atoms.     

Radioactive gold cluster immunoconjugates: Potential agents for cancer therapy

An 11 gold atom (undecagold) cluster was covalently attached to specific sites on Fab′, F(ab′)₂ and whole IgG molecules such that each carried 11–33 gold atoms without significant loss of native immunospecificity. Gold cluster labeled 17-1A monoclonal F(ab′)₂ antibody fragments showed 80% immunoreactivity compared to native antibody fragments in binding to human colon carcinoma cells in vitro. Radioactive gold in vivo biodistributions in nude mice with human tumors are also reported. By using clusters, potentially a larger destructive payload can be carried per antibody.     

A systematic search for the structures,stabilities, and electronic properties of bimetallic Ca<Subscript>2</Subscript>-doped gold clusters: comparison with pure gold clusters

The local meta-GGA exchange correlation density functional (TPSS) with a relativistic effective core potential was employed to systematically investigate the geometric structures, stabilities, and electronic properties of bimetallic Ca₂Au _n (n = 1–9) and pure gold Au _n (n ≤ 11) clusters. The optimized geometries show that the most stable isomers for Ca₂Au _n clusters have 3D structure when n > 2, and that one Au atom capping the Ca₂Au _n−1 structure for different-sized Ca₂Au _n (n = 1–9) clusters is the dominant growth pattern. The average atomic binding energies and second-order difference in energies show that the Ca₂Au₄ isomer is the most stable among the Ca₂Au _n clusters. The same pronounced even–odd alternations are found in the HOMO–LUMO gaps, VIPs, and hardnesses. The polarizabilities of the Ca₂Au _n clusters show an obvious local minimum at n = 4. Moreover, the inverse corrections to the polarizabilities versus the ionization potential and hardness were found for the gold clusters.     

All-electron scalar relativistic calculation of water molecule adsorption onto small gold clusters

An all-electron scalar relativistic calculation was performed on Au _n H₂O (n = 1–13) clusters using density functional theory (DFT) with the generalized gradient approximation at PW91 level. The calculation results reveal that, after adsorption, the small gold cluster would like to bond with oxygen and the H₂O molecule prefers to occupy the single fold coordination site. Reflecting the strong scalar relativistic effect, Au _n geometries are distorted slightly but still maintain a planar structure. The Au–Au bond is strengthened and the H–O bond is weakened, as manifested by the shortening of the Au–Au bond-length and the lengthening of the H–O bond-length. The H–O–H bond angle becomes slightly larger. The enhancement of reactivity of the H₂O molecule is obvious. The Au–O bond-lengths, adsorption energies, VIPs, HLGs, HOMO (LUMO) energy levels, charge transfers and the highest vibrational frequencies of the Au–O mode for Au _n H₂O clusters exhibit an obvious odd-even oscillation. The most favorable adsorption between small gold clusters and the H₂O molecule takes place when the H₂O molecule is adsorbed onto an even-numbered Au _n cluster and becomes an Au _n H₂O cluster with an even number of valence electrons. The odd–even alteration of magnetic moments is observed in Au _n H₂O clusters and may serve as material with a tunable code capacity of “0” and “1” by adsorbing a H₂O molecule onto an odd or even-numbered small gold cluster.     

Highly sensitive electrochemiluminescence biosensors for cholesterol detection based on mesoporous magnetic core–shell microspheres

A sensitive electrochemiluminescence (ECL) biosensor for cholesterol detection based on multifunctional core–shell structured microspheres (Fe₃O₄@SiO₂–Au@mpSiO₂) is reported. This microsphere consisted of a core of silica-coated magnetite nanoparticle, an active transition layer of gold nanoparticles and a mesoporous silica shell. Scanning electron microscopy was employed to observe the morphology of the nanomaterials and transmission electron microscopy was used to further confirm the subtle structure of Fe₃O₄@SiO₂–Au@mpSiO₂. The microspheres possessed a large surface area that increased enzyme loading, and an active transition layer gold nanoparticles enhanced the ECL signal. They were used to immobilize cholesterol oxidase for cholesterol detection with a high sensitivity, low detection limit and wide linear range. The linear range was from 0.83 to 2.62 mM with a detection limit of 0.28 µM (S/N = 3). Moreover, the reproducibility, stability and selectivity of the biosensor were established.     

A Simple and Sensitive SPRS Method for Trace H2O2 Based on the TiO2+ Complex and Gold Nanoparticles Aggregation Reactions

In the medium of H₂SO₄ and in the presence of TiO²⁺, gold nanoparticles in size of 10 nm exhibited a weak surface plasmon resonance scattering (SPRS) peak at 775 nm. Upon addition of trace H₂O₂, the yellow complex [TiO(H₂O₂)]²⁺ formed that cause the gold nanoparticles aggregations to form bigger gold nanoparticle clusters in size of about 900 nm, and the SPRS intensity at 775 nm (I) enhanced greatly. The enhanced intensity ΔI was linear to the H₂O₂ concentration in the range of 0.025–48.7 μg/mL, with a detection limit of 0.014 μg/mL H₂O₂. This SPRS method was applied to determining H₂O₂ in water samples with satisfactory results.     

Stabilization of gold nanowires inside nanoaggregates of cyclo[8]thiophene, cyclo[8]selenophene, and cyclo[8]tellurophene: a theoretical study

The stabilities and electronic properties of gold clusters containing up to six atoms trapped inside cyclo[8]thiophene (CS8), cyclo[8]selenophene (CSe8), and cyclo[8]tellurophene (CTe8) nanoaggregates have been studied using the M06 functional. The 6-31G(d) basis set was used for all atoms except Au and Te, for which the LANL2DZ(d,p) pseudopotential basis set was applied. Single-point energy calculations were performed with the 6-311G(d,p) basis set for all atoms except for Au and Te, for which the cc-TZVP-pp pseudopotential basis set was used. Among the three studied macrocycles, only CS8 and CSe8 were found to be capable of nanoaggregate formation. In the lowest-energy conformer of CTe8, the tellurophene fragments adopt an anti orientation, thus impeding a tubular arrangement of the macrocycles. The formation of gold clusters inside the CS8 and CSe8 nanoaggregates is a thermodynamically favorable process, and could represent a potentially useful method of stabilizing metal nanowires. The binding energy between the nanoaggregate and the gold cluster is always higher for selenium-containing complexes than for sulfur-containing ones because Se has a higher affinity than S for Au in such complexes. Interactions of the gold cluster with the nanoaggregate walls can change the geometry of the most stable isomer for the cluster. The relative energies of different isomers are rather similar, suggesting that they coexist. For nanoaggregates containing Au₆ clusters, the cluster geometry when it is inside a nanoaggregate is different from the geometry of the cluster when it is not inside the nanoaggregate, due to the geometric restrictions imposed by the nanoaggregate cavity. The reorganization energy needed to change the geometry leads to lower binding energies for these complexes compared to those of some smaller systems, although the formation of a complex between Au₆ and a nanoaggregate with six CS8 or CSe8 macrocycles is still thermodynamically viable.     

Catalytic mechanisms of Au<Subscript>11</Subscript> and Au<Subscript>11-n</Subscript>Pt<Subscript>n</Subscript> (<Emphasis Type="Italic">n</Emphasis>=1–2) clusters: a DFT investigation on the oxidation of CO by O<Subscript>2</Subscript>

The oxidation of CO catalyzed by clusters of Au₁₁, Au₁₀Pt and Au₉Pt₂ was investigated using the M06 functional suite of the density functional theory. Au and Pt atoms were described with the double-ζ valence basis set Los Alamos National Laboratory 2-double-z (LanL2DZ), whereas the standard 6-311++G(d,p) basis set was employed for the C and O atoms. Our theoretical model showed that (1) after coordination to Au and Au-Pt cluster, O₂ and CO are apparently activated, and Mulliken charges show that the gold atoms in the active sites of Au11 are negatively charged; (2) Au-Pt clusters with 11 atoms can effectively catalyze the oxidation of CO by O₂; (3) Au₁₁ exhibits good catalytic performance for the oxidation of CO; (4) oxidation of CO occurs preferably on the Au–Pt active sites in Pt-doped clusters, and the single-center mechanisms are more favorable energetically than the two-center mechanisms; (5) after adsorption, an O₂ molecule oxidates two CO molecules via stepwise mechanisms; and (6) the catalytic processes are highly exothermic.     

Density functional study of bare gold clusters: the ten-vertex neutral system

Four novel Au₁₀ structures have been located by means of density functional methods and their geometry and electronic structure are discussed. Furthermore, the behavior of less extensive basis sets in conjunction with the B3PW91 functional is compared to a highly accurate and more extensive energy-consistent scalar-relativistic pseudopotential and basis set for neutral ten-vertex gold clusters. The values obtained for several structural parameters for known and novel optimized Au₁₀ systems are discussed.     

Neuropeptide co-localisation in the lepidopteran frontal ganglion studied by electron-microscopic gold-labelling immunocytochemistry

An immunogold-labelling electron-microscopic study of the frontal ganglion of two noctuids, Lacanobia oleracea and Helicoverpa armigera, has been carried out with antisera directed against three neuropeptides; allatostatins of the Y/FXFGL-NH₂ type, Manduca sexta allatostatin (Mas-AS) and M. sexta allatotropin. The ganglion of both noctuids has two pairs of large peptidergic neurones with many clusters of electron-dense granules, one pair being situated anteriorly and the other posteriorly. By means of a double-labelling (flip-flop) technique, with different sizes of gold particles, all possible paired combinations of the three different types of peptide have been visualised within granules of the anterior neurones, leading to the conclusion that the three peptides are co-packaged and co-stored in these cells. Within the posterior neurones of L. oleracea, gold labelling of granules is only linked to the Y/FXFGL-NH₂ allatostatin antisera and, in contrast to the anterior cells of this species in which double gold labelling results in a sparse accumulation of gold particles for any one peptide type, single labelling gives a more intense, uniform pattern of gold particles. In contrast to L. oleracea, the gold-labelling pattern seen in the posterior neurones of H. armigera reflects the co-localisation of allatostatins of the Y/FXFGL-NH₂ type with Mas-AS in this species. Allatotropin is absent in the posterior neurones of both species.Grant funding was from the Wellcome Trust: grant no. 068105 (A.T.)     

Intermolecular interactions between gold clusters and selected amino acids cysteine and glycine: a DFT study

The intermolecular interactions between Au_n (n = 3–4) clusters and selected amino acids cysteine and glycine have been investigated by means of density functional theory (DFT). Present calculations show that the complexes possessing Au-NH₂ anchoring bond are found to be energetically favored. The results of NBO and frontier molecular orbitals analysis indicate that for the complex with anchoring bonds, lone pair electrons of sulfur, oxygen, and nitrogen atoms are transferred to the antibonding orbitals of gold, while for the complex with the nonconventional hydrogen bonds (Au···H–O), the lone pair electrons of gold are transferred to the antibonding orbitals of O-H bonds during the interaction. Furthermore, the interaction energy calculations show that the complexes with Au-NH₂ anchoring bond have relatively high intermolecular interaction energy, which is consistent with previous computational studies.     

Theoretical study of the electronic properties of fluorographene

First-principles calculations were performed for fluorine-decorated graphene (fluorographene). Three different hexagonal clusters were used—circular (C₂₄H₁₂), triangular (C₂₃H₁₀) and rectangular (C₂₄H₁₂)—and the fluorine atoms were randomly distributed in the mesh. Graphene is structurally stable in the three geometries, but fluorographene stability is only attained for the circular and triangular clusters. Gaps of the circular graphene and the corresponding fluorographene are 2.94 and 1.13 eV, respectively; in the triangular case, the values are zero and 0.47 eV. Both the circular and triangular structures show a transition from ionic to covalent character.     

Investigating the mechanism of the selective hydrogenation reaction of cinnamaldehyde catalyzed by Pt<Subscript>n</Subscript> clusters

Cinnamaldehyde (CAL) belongs to the group of aromatic α,β-unsaturated aldehydes; the selective hydrogenation of CAL plays an important role in the fine chemical and pharmaceutical industries. Using Pt_n clusters as catalytic models, we studied the selective hydrogenation reaction mechanism for CAL catalyzed by Pt_n (n?=?6, 10, 14, 18) clusters by means of B3LYP in density functional theory at the 6-31+?G(d) level (the LanL2DZ extra basis set was used for the Pt atom). The rationality of the transition state was proved by vibration frequency analysis and intrinsic reaction coordinate computation. Moreover, atoms in molecules theory and nature bond orbital theory were applied to discuss the interaction among orbitals and the bonding characteristics. The results indicate that three kinds of products, namely 3-phenylpropyl aldehyde, 3-phenyl allyl alcohol and cinnamyl alcohol, are produced in the selective hydrogenation reaction catalyzed by Pt_n clusters; each pathway possesses two reaction channels. Pt_n clusters are more likely to catalyze the activation and hydrogenation of the C?=?O bond in CAL molecules, eventually producing cinnamic alcohol, which proves that Pt_n clusters have a strong reaction selectivity to catalyze CAL. The reaction selectivity of the catalyzer cluster is closely related to the size of the Pt_n cluster, with Pt₁₄ clusters having the greatest reaction selectivity.

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Graphical Abstract The reaction mechanism for the selective hydrogenation reaction ofcinnamaldehyde catalyzed by Pt_n clusters was studied by densityfunctional theory. The reactionselectivity of cluster catalyzer was concluded to be closely related to the size of Pt_n clusters, with Pt₁₄ clusters having the greatest reaction selectivity

     

M2X (M= Li,Na; X= F,Cl): the smallest superalkali clusters with significant NLO responses and electride characteristics

Hypervalent M₂X (M = Li, Na; X = F, Cl) clusters are prototype species possessing lower ionisation potentials than Li, therefore classified as superalkalis. This study reveals some interesting properties of these small clusters using ab initio MP2/aug-cc-pVTZ and QCISD/aug-cc-pVTZ methods. These clusters are shown as an ionic species, composed of positively charged cage of alkali metals (M₂⁺) and halogen anion (X^?). Therefore, the stability of M₂X is governed by both ionic and covalent interactions. We show that the excess valence electron of (M₂⁺) is pushed out by anionic X^?, which allows M₂X clusters to possess ‘electride’ characteristics. It is also due to this excess electron that M₂X clusters exhibit significant non-linear optical (NLO) properties. The dipole moment, mean polarisability and hyperpolarisability suggest their significant NLO responses, which are explained on the basis of electronic transitions in crucial excited states using TD-B3LYP/aug-cc-pVTZ method. The first static hyperpolarisabilities of Li₂F and Na₂F take the values of order of 10⁴ a.u. due to their lower transition energies. This study should provide new insights into the design of novel materials with significant NLO responses useful for electro-optical applications.     

A report describing the effect of di-2-pyridyl ligand architecture on the coordination properties with gold(III)

In an effort to develop novel gold-based chemotherapies, gold(III) coordination complexes possessing a series of di-2-pyridyl ligands were targeted as synthetic products. It was found that di-2-pyridyl ligands linked by different groups exhibited varying coordination to gold(III). Di-2-pyridyl sulfide (DPS) exhibited bidentate binding to gold(III), and formed a complex ion with a gold tetrachloride counter ion {[(DPS)AuCl₂]AuCl₄; compound 3}; di-2-pyridyl ether (DPO) formed a neutral monodentate coordination complex with gold(III) {[(DPO)(AuCl₃)]; compound 4}; and attempts to make a gold(III) complex with di-2-pyridyl ketone (DPK) were unsuccessful, as a complex ion possessing the protonated ligand and a gold tetrachloride anion was isolated {[HDPK][AuCl₄]; compound 5}. Compounds 3-5 were structurally characterized using X-ray crystallography, which confirmed the different coordination environments around the gold(III) metal centers.     

A novel large heteropolytungstate constructed from two types of lacunary Keggin anions: K7Na13[(PW11O39)2(PW9O34)2(W2O3)2] · 25H2O

A novel crown-shaped heteropolytungstate is formed by covalently linking two [PW₁₁O₃₉]⁷⁻ and two [PW₉O₃₄]⁹⁻ fragments with four WO₆ octahedra, which represents not only the largest tungstophosphate constructed from two types of building blocks without considering the 4f lanthanide or other 3d transition metal ion linkers but also the highest degree of aggregation known in the large clusters incorporating monovacant lacunary anions.     

Synthesis and size regulation of gold nanoparticles by controlled thermolysis of ammonium gold(I) thiolate in the absence or presence of amines

Controlled thermolysis of gold(I) complex with no use of solvent was investigated as a novel synthetic method of gold nanoparticles. A series of precursors, ammonium gold(I) thiolate [RN(CH₃)₃][Au(SC₁₂H₂₅)₂] (R = C₈H₁₇, C₁₂H₂₅, and C₁₄H₂₉) and [(C₁₈H₃₇)₂N(CH₃)₂][Au(SC₁₂H₂₅)₂], have been prepared and the thermolysis of those precursors was conducted at 180 °C for 5 h under an N₂ atmosphere, providing spherical gold nanoparticles stabilized by alkyl groups derived from the precursor, gold(I) complex. In spite of thermolysis process, the average diameter of gold nanoparticles deriving from [C₁₂H₂₅N(CH₃)₃][Au(SC₁₂H₂₅)₂] was 22 nm, but the size distribution ranges from 11 to 76 nm. For the purpose of the size regulation of the gold nanoparticles, equimolar primary, secondary, or tertiary alkylamines are added as stabilizer and mild reductant to the controlled thermolysis of gold(I) complex at lower temperature of 165 °C for 5 h. The gold nanoparticles obtained by the controlled thermolysis in the presence of stearylamine are well regulated and almost monodispersed nanoparticles with average diameter of 7.5 nm. Such size regulation resulted from the inhibition of the growth of gold nuclei by transforming reaction from ammonium and thiolate moieties to neutral tertiary amine, thiol and sulfide, which function as stabilizer for gold nanoparticles.     

Biophysical characterization of gold nanoparticles-loaded liposomes

Gold nanoparticles were prepared and loaded into the bilayer of dipalmitoylphosphatidylcholine (DPPC) liposomes, named as gold-loaded liposomes. Biophysical characterization of gold-loaded liposomes was studied by transmission electron microscopy (TEM) and Fourier transform infrared (FTIR) spectroscopy as well as turbidity and rheological measurements. FTIR measurements showed that gold nanoparticles made significant changes in the frequency of the CH₂ stretching bands, revealing that gold nanoparticles increased the number of gauche conformers and create a conformational change within the acyl chains of phospholipids. The transmission electron micrographs (TEM) revealed that gold nanoparticles were loaded in the liposomal bilayer. The zeta potential of DPPC liposomes had a more negative value after incorporating of Au NPs into liposomal membranes. Turbidity studies revealed that the loading of gold nanoparticles into DPPC liposomes results in shifting the temperature of the main phase transition to a lower value. The membrane fluidity of DPPC bilayer was increased by loading the gold nanoparticles as shown from rheological measurements. Knowledge gained in this study may open the door to pursuing liposomes as a viable strategy for Au NPs delivery in many diagnostic and therapeutic applications.     

Vesicle-associated proteins and P2X receptor clusters at single sympathetic varicosities in mouse vas deferens

1. Antibodies against vesicle-associated proteins of the SNARE complex (syntaxin (AbS), SNAP 25 (AbS25), synaptobrevin (VAMP; AbV) and the α1B subunit of calcium channels (Abα_1B) were located with respect to sympathetic varicosities (labelled with the ubiquitous vesicle proteoglycan antibody AbSV2) and to clusters of P2X receptor subunits (labelled with antibodies AbP2X₁ to AbP2X₆). In addition, these receptor clusters were located with respect to Schwann cells labelled with antibodies to S100 (AbS100). 2. The spatial relation between proteins of the SNARE complex and calcium channels was determined. AbS25 patches ranged from 250–500 nm in size and were often colocalised with smaller AbS patches (250–350 nm). Abα_1B patches (300–700 nm diameter) were always coincidental with AbS patches. AbV patches (400–1000 nm in diameter) also coincided with AbS patches. 3. The spatial relation between different P2X subunit clusters and varicosities labelled with AbSV2 was ascertained. Large (500–700 nm diameter) AbP2X₁ receptor clusters were found colocalised with many (91%) AbSV2 labelled varicosities, although small diameter (250–350 nm) AbP2X₁ clusters occurred at random over the muscle. Small AbP2X₂ clusters were found uniquely in the vicinity of AbSV2 labelled varicosities, but were not entirely coincidental with these. Small AbP2X₃ receptor clusters were found in close association with AbSV2 labelled nerves. Small diameter AbP2X₄ clusters (250–350 nm) were found throughout the muscle with some of these coincidental with AbSV2 labelling. Small diameter AbP2X₅ (250–350 nm) cluster labelling was found in juxtaposition to strings of AbSV2 labelled varicosities but were not coincidental with these. Small (250–350 nm) diameter AbP2X₆ clusters were also found in close juxtaposition to AbSV2 labelled nerves. 4. The spatial relation between different P2X subtype clusters and Schwann cells labelled with AbS100 was examined. Both AbP2X₁ and AbP2X₃ receptor clusters were found in close apposition with AbS100, with clusters of the former sometimes coincidental with patches of the latter. On the other hand AbP2X₂ was found in association with AbS100 at low levels while AbP2X₄ labelling was generally not coincidental with AbS100. AbP2X₅ and AbP2X₆ labelling was often colocalised with AbS100 labelling. 5. The spatial relation between proteins of the SNARE complex and P2X₁ receptors was determined. Large AbP2X₁ clusters were often found apposed by AbS, AbV and Abα_1B labelled patches. 6. Destruction of the sympathetic varicosities with 6-hydroxydopamine led to the virtual disappearance of AbP2X₂ labelling, but to a large increase in the number of small AbP2X₁ receptor clusters and a reduction in the number of large AbP2X₁ clusters. AbS100 Schwann cell labelling was largely unaffected. 7. These observations are interpreted as showing that most terminal sympathetic varicosities possess active zones about 250–700 nm diameter, delineated by syntaxin, SNAP 25 and N-type calcium channels and that synaptic vesicles are concentrated at these sites as indicated by the localisation of VAMP. Most of these terminal varicosities possess active zones that are precisely apposed to large clusters of P2X₁ receptors. However small clusters of P2X₂ to P2X₆ receptors can be found that are near the strings of varicosities but not usually coincidental with them except P2X₃. The functional significance of this arrangement of vesicle-associated proteins and P2X receptors for the generation of synaptic potentials at the autonomic neuromuscular junction is discussed.     

Differences between the structure of the anti-arthritic gold drug “myocrisin” in the solid state and in solution: a kinetic study of dissolution

Detailed analyses of changes in the ultraviolet-visible absorption spectra of the anti-aithritic gold drug disodium gold(I) thiomalate·0 3 glycerol·2H₂O with time, suggest that the solid may contain about 23% of a species with λ_max of 337 and 370 nm. This disappears in a two-step process soon after dissolution in water. The reaction was monitored at a variety of temperatures (20–47°C), pH's (6–11), and ionic strengths (0.05–0.61 M). The first step is complete in ca. 3 min. The second step is independent of Au(tm) concentration with k_o' = 8.5 × 10^?2min^?1 and activation parameters of ΔH^± = 82.1^≠ 4.1 kJmol^?1 and ΔS^≠ = 13.65 KJ^?1 mol^?1. The logarithm of the rate of this step increases linearly with the square root of the ionic strength. The reaction is readily reversed at high ionic strengths and is interpreted as a cooperative structural transition of polymeric gold(I) thiomalate, possibly involving Au(I)-Au(I) bonding. The relationship of these observations to reactions of other 1:1 Au(I) thiolate complexes and their method of preparation is discussed.