Gold Adducts Research Articles

Synthesis, Characterization, and Comparative Theoretical Investigation of Dinitrogen-Bridged Group 6-Gold Heterobimetallic Complexes.

We have prepared and characterized a series of unprecedented group 6–group 11, N2-bridged, heterobimetallic [ML4(η1-N2)(μ-η1:η1-N2)Au(NHC)]+ complexes (M = Mo, W, L2 = diphosphine) by treatment of trans-[ML4(N2)2] with a cationic gold(I) complex [Au(NHC)]+. The adducts are very labile in solution and in the solid, especially in the case of molybdenum, and decomposition pathways are likely initiated by electron transfers from the zerovalent group 6 atom to gold. Spectroscopic and structural parameters point to the fact that the gold adducts are very similar to Lewis pairs formed out of strong main-group Lewis acids (LA) and low-valent, end-on dinitrogen complexes, with a bent M–N–N–Au motif. To verify how far the analogy goes, we computed the electronic structures of [W(depe)2(η1-N2)(μ-η1:η1-N2)AuNHC]+ (10W+) and [W(depe)2(η1-N2)(μ-η1:η1-N2)B(C6F5)3] (11W). A careful analysis of the frontier orbitals of both compounds shows that a filled orbital resulting from the combination of the π* orbital of the bridging N2 with a d orbital of the group 6 metal overlaps in 10W+ with an empty sd hybrid orbital at gold, whereas in 11W with an sp3 hybrid orbital at boron. The bent N–N–LA arrangement maximizes these interactions, providing a similar level of N2 “push–pull” activation in the two compounds. In the gold case, the HOMO–2 orbital is further delocalized to the empty carbenic p orbital, and an NBO analysis suggests an important electrostatic component in the μ-N2–[Au(NHC)]+ bond.

Structural Characterization of a Gold/Serum Albumin Complex.

The medicinal gold(III) dithiocarbamato complex AuL12 forms a stable adduct with bovine serum albumin. The crystal structure reveals that a single gold(I) center is bound to Cys34, with the dithiocarbamato ligand being released. To the best of our knowledge, this is the first structure for a gold adduct of serum albumin.

Human Serum Albumin-Delivered [Au(PEt3)]+ Is a Potent Inhibitor of T Cell Proliferation.

Using a modular library format in conjunction with cell viability (MTS) and flow cytometry assays, 90 cationic complexes [AuPL] n+ (P = phosphine ligand; L = thiourea derivative or chloride) were studied for their antiproliferative activity in CD8+ T lymphocyte cells. The activity of the compounds correlates with the steric bulk of the phosphine ligands. Thiourea serves as a leaving group that is readily replaced by cysteine thiol (NMR, ESI-MS). Taking advantage of selective thiourea ligand exchange, the fragments [Au(PEt3)]+ and [Au(JohnPhos)]+ (JohnPhos = 1,1'-biphenyl-2-yl)di-tert-butylphosphine) in compounds 1 and 2 were transferred to recombinant human serum albumin (rHSA). PEt3 promoted efficient modification of Cys34 in HSA (HSA-1), whereas use of bulky JohnPhos as a carrier ligand led to serum protein nonspecifically modified with multiple gold adducts (HSA-2) (Ellman's test, ESI-TOF MS). HSA-1, but not HSA-2, strongly inhibits T cell proliferation at nanomolar doses. The potential role of HSA as a delivery vehicle in gold-based autoimmune disease treatment is discussed.

Monomeric Copper(I), Silver(I), and Gold(I) Alkyne Complexes and the Coinage Metal Family Group Trends

A series of thermally stable, easily isolable, monomeric, and isoleptic coinage metal alkyne complexes have been reported. Treatment of [N{(C(3)F(7))C(Dipp)N}(2)]Li (the lithium salt of the 1,3,5-triazapentadiene [N{(C(3)F(7))C(Dipp)N}(2)]H) with AuCl, CF(3)SO(3)Ag or CF(3)SO(3)Cu in the presence of 3-hexyne led to the corresponding coinage metal alkyne complex [N{(C(3)F(7))C(Dipp)N}(2)]M(EtC[triple bond]CEt) in good yield (M = Au, Ag, Cu; Dipp = 2,6-diisopropylphenyl). X-ray crystal structures of the three coinage metal alkynes are remarkably similar, and show the presence of trigonal-planar metal sites with eta(2)-bonded 3-hexyne. The M-C and M-N bond distances vary in the order Cu < Au < Ag. The bending of the C-C[triple bond]C bond angle is largest for the gold, followed by Cu and Ag adducts. The gold adduct also shows the largest decrease in C[triple bond]C stretching frequency in Raman, while the Ag adduct shows the smallest change compared to that of the uncoordinated alkyne. DFT calculations on [N{(CF(3))C(Ph)N}(2)]M(EtC[triple bond]CEt) and the related ClM(EtC[triple bond]CEt) predict that the M-alkyne bond energy varies in the order Ag < Cu < Au. The gold adducts are also predicted to have the longest C[triple bond]C, largest deviation of C-C[triple bond]C bond angle from linearity, and smallest C[triple bond]C stretching frequency, followed by the Cu and Ag adducts. In these triazapentadienyl coinage metal adducts, the sigma-donation from alkyne --> M dominates over the M --> alkyne pi-back-donation.

Cation-Assisted Laser Desorption/Ionization for Matrix-Free Surface Mass Spectrometry of Alkanethiolate Self-Assembled Monolayers on Gold Substrates and Nanoparticles

We propose a new scheme of matrix-free laser desorption/ionization with cation assistance for surface mass spectrometry of self-assembled monolayers (SAMs) of alkanethiolates on gold substrates and gold nanoparticles (NPs). In a proof-of-concept experiment, a simple treatment using an aqueous salt solution such as NaI(aq) was shown to lead to a significant laser desorption/ionization, producing the characteristic (disulfide) ions of alkanethiolate molecules from the monolayers. Further efforts to understand the mechanism were also given, including laser power and salt concentration dependence studies. In the power dependence study, the characteristic ions were found to be produced at low laser power where no gold substrate species was seen. At high laser power, the generation of gold species, Au(+)-Au5(+), resulted in a saturation behavior in the characteristic mass peak for alkanethiolate molecules. In addition, characteristic ions with gold adducts were not observed at any laser power. With increasing salt concentration, the characteristic mass peak was gradually increased. The results suggest that the adduct formation of a cation with alkanethiolates in the monolayers provide a facile pathway to supply a charge to UV laser-desorbed secondary neutrals for mass spectrometric detection. This cation-assisted laser desorption/ionization (CALDI) mass spectrometry was further examined with the SAMs and mixed SAMs with various terminals such as -OH, -OCH3, -NH2, -ethylene (-CH=CH2), and -acetylene (-C[triple bond]CH). The CALDI method was also successfully applied to surface mass spectrometry of monolayer-protected gold NPs (approximately 16 nm diameter) with OH- and COOH-terminated SAMs. The unique advantages of the matrix-free CALDI method may extend our capability in investigations of interfacial chemistry at SAMs as well as mass spectrometric applications using biochips and nanoparticles.

Thermally Stable Gold(I) β-Diketiminate Complexes

The synthesis and X-ray structures of gold(I) adducts supported by beta-diketiminates have been reported. {[HC{(H)C(2,4,6-Br(3)C(6)H(2))N}(2)]Au}(2) and {[HC{(H)C(Dipp)N}(2)]Au}(2) [Dipp = 2,6-(i-Pr)(2)C(6)H(3)] are easily isolable solids and feature 12-membered macrocyclic ring structures. beta-Diketiminate ligands adopt a W-shaped conformation. Gold atoms are bonded to the nitrogen atoms in a linear fashion. (1)H NMR signals corresponding to the protons at the beta-diketiminate ligand beta-C position of the gold adducts appear at a notably high downfield region.

Prompt in situ emission of gold adducts from single impacts of large gold clusters on organics solids

We report the first observation of single impacts of 136 keV Au n 4+ (100 ≤ n ≤ 400) on organic solids, generating prolific emission of Au and Au 2 - containing fragments and molecular ions. We show that the individual impacting cluster is both the source of energy stimulating the emission, and the donor of atoms for adducts synthesis. The emission of Au and Au 2 was observed when n ≥ 100. The most abundant species is Au(CN) 2 −. The adduct yields behave as follows when the projectile size varies from n = 100 to 400: (a) they increase with n; (b) the dependence with n for the formation of Au(CN) 2 − differs from those for more complex species suggesting different pathways of synthesis; (c) the combined yields of the Au or the Au 2 - adducts are the same for different targets. There is evidence that the projectiles were implanted virtually intact in the organic targets, thus, the adduct synthesis involves a small number of Au atoms ablated from the projectile, which implies extensive ionization of the detached atoms. The abundance of three-body assemblies, e.g. Au(CN) 2 −, Au(CN) (M–H) −, suggests that the adduct formation occurs likely in a dense phase.

The First Imido Complex of Osmium(VI), [CpOs(NH)(CH2SiMe3)2][SO3CF3

Protonation of Os(η5-C5H5)(N)(CH2SiMe3)2 with either HBF4 or CF3SO3H at low temperature produces a thermally unstable imido complex, [Os(η5-C5H5)(NH)(CH2SiMe3)2][X] (X = BF4, SO3CF3). The imido com...

Direct observation of covalent adducts with Cys34 of human serum albumin using mass spectrometry

The interactions of the unpaired thiol residue (Cys34) of human serum albumin (HSA) with low-molecular-weight thiols and an Au(I)-based antiarthritic drug have been examined using electrospray ionization mass spectrometry. Early measurements of the amount of HSA containing Cys34 as the free thiol suggested that up to 30% of circulating HSA bound cysteine as a mixed disulfide. It has also been suggested that reaction of HSA with cysteine, occurs only on handling and storage of plasma. In our experiments, there were three components of HSA in freshly collected plasma from normal volunteers, HSA, HSA + cysteine, and HSA + glucose in the ratio ∼50:25:25. We addressed this controversy by using iodoacetamide to block the free thiol of HSA in fresh plasma, preventing its reaction with plasma cysteine. When iodoacetamide was injected into a vacutaner tube as blood was collected, the HSA was modified by iodoacetamide, with 20–30% present as the mixed disulfide with cysteine (HSA + cys). These data provide strong evidence that 20–30% of HSA in normal plasma contains one bound cysteine. Reaction of HSA with [Au(S 2O 3) 2] 3− resulted in formation of the adducts HSA + Au(S 2O 3) and HSA + Au. Reaction of HSA with iodoacetamide prior to treatment with [Au(S 2O 3) 2] 3− blocked the formation of gold adducts.

Synthesis and structural characterization of [NEt 4][Fe 3(μ 3-O)(μ 3-AuPPh 3)(μ-CO) 3(CO) 6], the new [Au 6(μ 3-S) 2(PPh 3) 6][Fe 3(μ 3-S)(μ-AuPPh 3)(CO) 9] 2 and [Au 6(μ 3-S) 2(PPh 3) 6][Fe 5(μ 3-S) 2(CO) 14] ionic solids containing assemblages of cluster-cations and cluster-anions

The new [Fe 3(μ 3-O)(μ 3-AuPPh 3)(μ-CO) 3(CO) 6] − and [Fe 3(μ 3-S)(μ-AuPPh 3)(CO) 9] − monoanionic congeners have been obtained by reacting the [Fe 3(μ 3-E)(CO) 9] 2− (E=O, S) dianions with one equivalent of Au(PPh 3)Cl. The gold adduct of the oxygen derivative has been crystallized as tetraethylammonium and trimethylbenzylammonium salt either from THF and n-hexane or acetone and isopropyl alcohol, and structurally characterized in its tetraethylammonium salt (monoclinic, C2 /c (No. 15), a=15.859(2), b=12.859(2), c=40.217(8) Å, β=96.41(1)° Z=8). The [Fe 3(μ 3-S)(μ-AuPPh 3)(CO) 9] − gold adduct, in contrast, partially reverts to the parent dianion upon crystallization under the above experimental conditions, and could be precipitated only as the [Au 6(μ 3-S) 2(PPh 3) 6][Fe 3(μ 3-S)(μ-AuPPh 3)(CO) 9] 2 salt (triclinic, P 1 ̄ (No. 2), a=18.998(8), b=19.933(8), c=22.94(1) Å, α=99.91(4), β=98.91(4), γ=107.42(3)°, Z=2), by addition of an equivalent of the [Au 3(μ 3-S)(PPh 3) 3] + sulfonium cation to the reaction mixture. The [Fe 5(μ 3-S) 2(CO) 14] 2− dianion does not form a gold adduct even in the presence of the sulfonium cation and only the corresponding [Au 6(μ 3-S) 2(PPh 3) 6][Fe 5(μ 3-S) 2(CO) 14] salt could be obtained. The [Fe 3(μ 3-O)(μ 3-AuPPh 3)(μ-CO) 3(CO) 6] − and [Fe 3(μ 3-S)(μ-AuPPh 3)(CO) 9] − gold adducts are not isostructural and the possible factors leading to their structural diversities are discussed. The [Au 6(μ 3-S) 2(PPh 3) 6][Fe 3(μ 3-S)(μ-AuPPh 3)(CO) 9] 2 and [Au 6(μ 3-S) 2(PPh 3) 6][Fe 5(μ 3-S) 2(CO) 14] salts represent further examples of ionic solids assembled from cluster-cations and cluster-anions.

X-ray crystal structure and phosphorus-31 NMR solution studies of [Ir2(dimen)4(PPH3)Au(PPh3)] (PF6)3 (dimen = 1,8-diisocyano-p-menthane). Observation of particle site preference in the formation of "outside" silver and gold adducts

The reaction of [M(PPh 3 ) 2 ](PF 6 ) (M=Ag, Au) with [Ir 2 (dimen) 4 ](PF 6 ) 2 leads to the formation of heteronuclear complexes of the general formula [Ir 2 (dimen) 4 (PPh 3 )M(PPh 3 )] (PF 6 ) 3

Synthesis and characterization of gold adducts of [M(tppme)(P3)][M = Co, Rh, or Ir; tppme = 1,1,1-tris(diphenylphosphinomethyl)ethane]. X-Ray crystal structures of [Au{M(tppme)(P3)}2]PF6(M = Co, Rh, or Ir)

Treatment of a dichloromethane solution of [M(tppme)(P3)][M = Co, Rh, or Ir; tppme = 1,1,1-tris(diphenylphosphinomethyl)ethane] with the complexes [AuCl(PR3)](R = Me or Ph) and [Au2Cl2{Ph2P(CH2)nPPh2}](n= 1 or 2) in the presence of TlPF6 invariably affords the compounds [Au{M(tppme)(P3)}2] PF6·solvent (M = Co, Rh, or Ir). X-Ray crystallographic analyses of the three isomorphous compounds showed that the gold atom is bound to two pairs of phosphorus atoms belonging to the P3 units of two [M(tppme)(P3)] fragments; the gold atom has a co-ordination geometry intermediate between tetrahedral and square planar. The unexpected elimination of the phosphane ligand from the gold fragments and the lengthening of the P–P bonds in which insertion of gold occurs are indicative of significant interaction between the gold atom and the MP3 clusters.

Fragmentation and rearrangement processes in the mass spectra of perhalogenoaromatic compounds. Part X. Pentafluorophenyl dimethyl derivatives of group V

A comprehensive low-resolution study of the mass spectra of the compounds C6F5M(CH3)2, where M = N, P, As, is described, fragmentation pathways being assigned with the aid of normal metastable ions and mass analyzed ion kinetic energy spectra (mikes). A comparison of these spectra has re-affirmed the absence of halogen transfer processes for atoms such as N which are incapable of providing the necessary vacant orbitals apparently prerequisite in the mechanisms. The influence of increased coordination to phosphorus and effects on halogen transfer processes are discussed with respect to the mass spectra of the compounds C6F5PX(CH3)2, X = O, S, Se and the gold adducts C6F5P(CH3)2•AuX, X = Cl, Br, I.