Gold Chemistry Research Articles

Nanoparticles for the Treatment of Metastatic Non Small Cell Lung Cancer with 225Ac

Non small cell lung cancer (NSCLC) is the most common form of primary lung neoplasia with nearly 40% of patients having metastasis at the time of diagnosis, resulting in a 5year survival rate ranging from 13-36% in patients with nodal metastasis, and decreasing to as little as 2% for those with distant metastasis. Furthermore, pulmonary metastatic disease is the most common form of secondary lung tumors, being identified in 30-55% of all cancer patients. Targeted α-radiotherapy (TAT) agents have great potential for treating micro-metastatic disease, given their short, densely ionizing track length and high relative biologic effect (RBE). The use of in vivo alpha generators allows for multiple alpha decays from a single radioactive nucleus, but retaining the radioactive daughters at the target site throughout the decay process is a challenge. We present preclinical data describing a multilayered nanoparticle-antibody conjugate that can deliver multiple α radiations from the in vivo α-generator 225Ac at biologically relevant receptor sites while also containing the radioactive daughters at those sites. The layered nanoparticles (NP) consist of an 225Ac-doped (La0.5Gd0.5)PO4 core coated with four layers of GdPO4 and an outer layer of Au. These multi-shell particles combine the radiation resistance of crystalline lanthanide (Ln) phosphate to contain atoms of the therapeutic radionuclide and its radioactive daughters, the magnetic properties of gadolinium for facile separation during synthesis, and the chemistry of gold for attachment of targeting agents to the nanoparticle surface. In a proximity delivery model of cancer, 225Ac-NPs conjugated to mAb 201b resulted in a 73% decrease in the number of EMT6 colonies in the lung five days after treatment [1]. On biodistribution studies and SPECT/CT imaging, over 85% of the injected dose was delivered to the target tissue, and approximately 90% of the fourth daughter, 213Bi, was retained in the target 24 hours after injection. Competition assays demonstrated specific binding of the conjugated radiopharmaceutical to the target. Current studies are evaluating the application of these 225Ac nanoparticles to A549 NSCLC grown in a mouse orthotopic lung cancer model, while a spontaneous cancer model in canine patients is also being explored. [1]M.F. McLaughlin, J.D. Robertson, P.H. Pevsner, J.S. Wall, S. Mirzadeh, and J. Kennel, “LnPO4 Nanoparticles Doped with Ac-225 and Sequestered Daughters for Targeted Alpha Therapy,” Cancer Biotherapy and Radiopharmaceuticals 29(1), 34-41 (2014).

Unsaturated vicinal frustrated phosphane/borane Lewis pairs as ligands in gold(i) chemistry.

The P/B FLP 6, formed by the 1,1-hydroboration of dimesitylphosphino(trimethylsilyl)acetylene with HB(C6F5)2 forms the Au(i)X complexes 9a (X: Cl) and 10a (X: NTf2), respectively. Both show marked AuB interactions. The P/B FLP isomer 8, featuring the bulky SiMe3 substituent at the carbon adjacent to boron forms gold complexes 9b and 10b, both of which show weaker AuB interactions. Complex 10a was employed in the catalytic hydroamination of a series of alkynes with p-toluidine. Complexes 9 and 10 were characterized by X-ray diffraction.

Reproducible mesoporous silica-coated gold@silver nanoprobes for the bright colorimetric sensing of ascorbic acid

Herein, a colorimetric approach for the detection of ascorbic acid (AA) was developed by controlling the surface chemistry of silica-coated gold nanorod@silver nanoparticles (AuNR@Ag@mSiO2).

Coordination chemistry of gold with N-phosphine oxide-substituted imidazolylidenes (POxIms)

Diverse gold complexes are found to be accessible with the title ligands, which exhibit peculiar structural features and promising catalytic performances.

In My Element: How did I land in a gold mine?

The In My Element series celebrates the personal accounts from Chemistry – A European Journal Editorial Board members for the 2019 International Year of the Periodic Table. In this contribution, Pekka Pyykkö gives his story on gold. In late 1975 Jean-Paul Desclaux and I had developed a fully relativistic (or non-relativistic) quantum chemical approach for hydride molecules, MHn. It converged well at short M−H bond lengths so we needed a molecule in which that was indeed the case. It turned out that AuH was one, so we tried it and it worked. There was a sizable relativistic contraction of the Au−H bond length. Moreover, relativistic effects explained most of the differences from AgH to AuH. We had the audacity to say that “the chemical difference between silver and gold may mainly be a relativistic effect”1 (see Figure 1). Earlier band-structure studies on Au metal had indicated large relativistic effects2 but in a germ, there may have been a trace of originality in our coupling of chemical periodicity to relativity. That turned out to be a scientific gold mine. Because the shell structure of gold has a local maximum of valence-shell relativistic effects, which normally scale as Z2, that was a lucky start. The relativistic (R) and non-relativistic (NR) orbital energies of the diatomic AgH and AuH (a.u. is atomic units). Data from Ref. 1. Figure from Ref. 17. A decade later, when lecturing at the Technical University of Munich, I learned from Hubert Schmidbaur about a strange attraction between two or more closed-shell AuI cations.3 They had both crystallographic and NMR evidence for it. Both cations carried a positive charge and had no open-shell electrons to make covalent bonds with. Yet they enjoyed an “aurophilic attraction” comparable in strength with a good hydrogen bond. Our explanation for it was a dispersion-type van der Waals interaction.4 Although other mechanisms also may contribute, for example electrostatic multipole interactions or induction,5-7 this is at least a partial explanation. That dispersion-type interaction is also comparable for silver,8, 9 and thus not specific for gold. We are not aware of a known case in which a suggested 6s–6p–5d hybridization10 would be sufficient to yield an observable attraction. Moreover, certain main-group elements also show it. Not only is gold a laboratory of relativistic quantum chemistry. Also, quantum electrodynamic (QED) effects can be seen in the ionization potential and electron affinity of the Au atom by pushing the current theories to their limits.11 Predicting new species with Au was a third aspect. Two examples were the first noble-metal−noble-gas bond12 in AuXe+, observed in mass-spectroscopy, or the predicted nanocluster WAu12,13 also subsequently made.14 Among novel covalent bonds, take the newly prepared unbridged AuII−AuII bonds.15 Both homogeneous and heterogeneous catalysis involving gold have become vast fields. Partially inspired by this application, the studies of both naked and ligand-covered gold nanoclusters are being intensively studied.16 Thus, keeping an eye on the theoretical chemistry of gold is a very good idea.17-20 Position Professor Emeritus of Chemistry E-mail [email protected] Homepage www.chem.helsinki.fi/∼pyykko ORCID 0000-0003-1395-8712 Education University of Turku, Finland, M.Sc. 1964, Ph.D. 1967. Post-doc at Aarhus, Denmark 1968–69 Post-doc at Gothenburg, Sweden 1969–70 Awards A.I. Virtanen Prize 1997, E.J. Nyström Prize 1998 decorated by President of Finland (FVR R I, 1995) Humboldt Prize 2002, Palmes Académiques (France) 2009 Schrödinger medal 2012 Honorary Fellow of Chinese Chemical Society 2012 Research interests Quantum chemistry of heavy elements Recently: simple models for eutectics

Synthesis of unnatural α-amino esters using ethyl nitroacetate and condensation or cycloaddition reactions.

We report here on the use of ethyl nitroacetate as a glycine template to produce α-amino esters. This started with a study of its condensation with various arylacetals to give ethyl 3-aryl-2-nitroacrylates followed by a reduction (NaBH4 and then zinc/HCl) into α-amino esters. The scope of this method was explored as well as an alternative with arylacylals instead. We also focused on various [2 + 3] cycloadditions, one leading to a spiroacetal, which led to the undesired ethyl 5-(benzamidomethyl)isoxazole-3-carboxylate. The addition of ethyl nitroacetate on a 5-methylene-4,5-dihydrooxazole using cerium(IV) ammonium nitrate was also explored and the synthesis of other oxazole-bearing α-amino esters was achieved using gold(I) chemistry.

The light triggered dissolution of gold wires using potassium ferrocyanide solutions enables cumulative illumination sensing

Electronic systems with on-demand dissolution or destruction capabilities offer unusual opportunities in hardware-oriented security devices, advanced military spying and controlled biological treatment. Here, the dissolution chemistry of gold, generally known as inert metal, in potassium ferricyanide and potassium ferrocyanide solutions has been investigated upon light exposure. While a pure aqueous solution of potassium ferricyanide–K3[Fe(CN)6] does not dissolve gold, an aqueous solution of potassium ferrocyanide–K4[Fe(CN)6] irradiated with ambient light is able to completely dissolve a gold electrode within several minutes. Photo activation and dissolution kinetics were assessed at different initial pH values, light irradiation intensities and ferrocyanide concentrations. Addition of small amounts of the heavy metal thallium (260 ppb) also provides tunability of the dissolution kinetics. An investigation of the involved chemical and physical processes of photochemistry, cyanide diffusion and surface reaction results in an understanding of the rate limiting steps and yields an overall transformation of irradiated light energy to dissolved gold of 2.6%. A potential application of this novel gold dissolution method as a cumulative light sensor is demonstrated and discussed.

Mixed-valence Compounds: AuO2 and AuS.

Mixed-valence compounds are of great interest due to their interesting properties and wide applications. Recently, gold (Au) chemistry has experienced an unprecedented development. However, Au with mixed-valence states in Au-O compounds has not been reported thus far. Here, two hitherto unknown AuO2 and AuS compounds with mixed-valence character were identified with the aid of first-principles swarm structure searching calculations. AuO2 consists of quasi-square AuO4 moiety and AuO6 octahedron in which Au shows the mixed-valence states of III and V, the first example in Au-O binary compounds. AuS contains the linear AuS2 and quasi-square AuS4 units exhibiting AuI/III mixed-valence states. The analysis of electronic property demonstrates that AuO2 and AuS are narrow band gap semiconductors with strong hybridization between Au 5d and O 2p or S 3p. With the increase of pressure, Au-O and Au-S compounds show completely different thermodynamic stabilities, resulting from distinct shifting of pressure-induced atomic orbital energy levels of O and S atoms. Our work provides an opportunity for understanding mixed-valence character in Au-O and Au-S compounds.

Thermally Stable Gold(III) Alkene and Alkyne Complexes: Synthesis, Structures, and Assessment of the trans‐Influence on Gold–Ligand Bond Enthalpies

The reaction of [C^C)Au(OEt2 )2 ]+ with 1,5-cyclooctadiene or norbornadiene affords the corresponding olefin complexes [(C^C)Au(COD)]SbF6 and [(C^C)Au(NBD)]SbF6 , which are thermally stable in solution and the solid state (C^C=4,4'-di-tert-butylbiphenyl-2,2'-diyl). The crystal structures of these complexes have been determined. By contrast, dienones such as dibenzylideneacetone are O- rather than C=C-bonded. The reactions of (C^C)Au(OAcF )(L) (L=PMe3 or CNxyl) with B(C6 F5 )3 in the presence of bis(1-adamantyl)acetylene give the mixed-ligand alkyne complexes [(C^C)Au(AdC≡CAd)(L)]+ , the first complexes of their type in gold chemistry. In the presence of an excess of acetylene these compounds are thermally stable in solution and as solids. The bonding of n- and π-donor ligands to AuIII fragments and the effect of the trans influence exerted by N- and C-donors was explored with the aid of DFT calculations. Results show that the Au-L bond enthalpies trans to anionic C are 35-60 % of the enthalpies trans to N, with strong π-acceptors being particularly affected. In comparison with [Me2 Au]+ , the [(C^C)Au]+ fragment is more polar and in bond enthalpy terms resembles Me2 Pt.

Morphology and chemistry of placer gold in the Bagrote and Dainter streams, northern Pakistan: Implications for provenance and exploration

The Bagrote and Dainter valleys in Gilgit Baltistan Pakistan, belonging to the Kohistan island arc and southwestern domain of the Karakorum metamorphic complex, respectively, are a location of regional placer gold mining. However, no in situ hydrothermal gold deposits have been discovered in this region. Here, we report the textural, morphological, and geochemical characteristics of placer gold from the stream sediments of the Bagrote and Dainter valleys with a view to trace the provenance. The morphological features of the studied gold grains indicate proximal source mineralization. The gold grains display a microtexture typical of mechanical abrasion rather than chemical activity. Their chemical composition of most of the grains from each stream falls in a restricted range (minor alloying elements mainly Cu) with high fineness (1,000 Au/(Au + Ag)), suggesting derivation from a homogeneous source or limited number of mineralization types. The high Cu content of the gold grains from the Bagrote stream suggests that the gold here might be associated with previously undiscovered porphyry gold mineralization, whereas the Au–Ag–Hg alloys from the Dainter stream suggest a genetic linkage with undiscovered fault‐controlled auriferous veins of epithermal origin in the southwestern part of the Karakorum metamorphic complex. The chemical composition of both streams placer gold in triangular diagram in terms of Au–Ag–Cu shows all the gold grains from Dainter stream were derived from epithermal type of mineralization, and most of the plots of Bagrote stream fall on the domain of porphyry epithermal type of deposits which are also in consistent with a continental arc setting in the study area. The mechanically developed microtexture, homogeneous chemical composition in individual grains from core to rim, and absence of high fineness rims of the gold grains from both streams, suggest the absence of any supergene regrowth and direct transfer from the primary source through glacier to the fluvial system. The Gilgit Baltistan province, dominated by dry temperate climate and glacial environment having steep geomorphology, precluding any significant supergene processes such as silver leaching and addition of authigenic gold on detrital gold grains.

Comparison of arsenic methylation capacity and polymorphisms of arsenic methylation genes between bladder cancer and upper tract urothelial carcinoma

Arsenic exposure is an environmental risk factor for urothelial carcinoma (UC). The natural history of upper tract urothelial carcinoma (UTUC) differs from that of bladder cancer (BC). However, the risk factors of BC and UTUC are not exactly the same and should be discussed separately. The aims of this study were to evaluate 1) the association between arsenic methylation capacity and UTUC and/or BC, separately, and 2) the association between polymorphisms of the arsenic metabolism-related genes AS3MT, GSTOs, and PNP against BC and/or UTUC, separately. We conducted a hospital-based study and collected 216 BC and 212 UTUC cases, and 813 healthy controls, from September 2007 to October 2011. Urinary arsenic profiles were measured using high-performance liquid chromatography-hydride generator-atomic absorption spectrometry. The polymorphisms of AS3MT, GSTO, and PNP were identified using the Sequenom MassARRAY platform with iPLEX Gold chemistry. We found that inefficient arsenic methylation capacity was associated with BC in a significant dose-response relationship, but only found that high urinary total arsenic concentration was related to the risk of UTUC, also in a significant dose-response manner. Those with a total urinary arsenic level of > 30.28 μg/L compared to ≤ 9.78 μg/L, had a odds ratio (OR), and 95% confidence interval (CI) of UTUC, of 4.80 (2.22–10.39). The polymorphisms of AS3MT rs11191438, AS3MT rs10748835, and AS3MT rs1046778 were related to the risk of BC and UTUC, while the polymorphisms of AS3MT rs3740393, AS3MT rs11191453, and AS3MT rs11191454 were associated with arsenic methylation capacity. The AS3MT gene polymorphisms and arsenic methylation capacity appear to independently affect the risk of BC and UTUC.

Two-Dimensional AuMX2 (M = Al, Ga, In; X = S, Se) Monolayers Featuring Intracrystalline Aurophilic Interactions with Novel Electronic and Optical Properties.

Aurophilicity, known as aurophilic interaction, is a strong attractive van der Waals interaction between cationic gold(I) centers, whose strength is comparable to the hydrogen bond. Here, we show that aurophilicity can serve as an engineering approach to expand the structural dimensionality for nanomaterials design. Specifically, based on a global-structure search method and density functional theory calculations, we predict a series of stable two-dimensional (2D) AuMX2 (M = Al, Ga, In; X = S, Se) structures featuring intracrystalline aurophilic interactions. All the AuMX2 monolayers designed are semiconductors with moderate band gaps, excellent carrier mobilities, and good optical properties. The intriguing chemistry of aurophilicity coupled with novel electronic properties render AuMX2 monolayers a potentially new series of 2D materials that are of fundamental importance in gold chemistry and of technological importance for nanoelectronics.

Polymorphisms of Arsenic (+3 Oxidation State) Methyltransferase and Arsenic Methylation Capacity Affect the Risk of Bladder Cancer.

The mechanisms underlying how arsenic methylation capacity affects bladder cancer (BC) are still unclear. The objective of this study was to explore the effects of polymorphisms of arsenic (+3 oxidation state) methyltransferase (AS3MT) on BC risk. We conducted a hospital-based study and enrolled 216 BC and 648 healthy controls from 2007 to 2011. Urinary arsenic profiles were measured using high-performance liquid chromatography-hydride generation-atomic absorption spectrometry. The gene polymorphisms of AS3MT were identified using the Sequenom MassARRAY platform with iPLEX Gold chemistry. Inefficient arsenic methylation capacity (high monomethylarsonic acid percentage [MMA%] and low dimethylarsinic acid percentage [DMA%]) was associated with increased risk of BC in a dose-response relationship. AS3MT rs11191438 (C > G) G/G genotype, AS3MT rs10748835 (A > G) G/G genotype, and AS3MT rs1046778 (C > T) T/T genotype were found to be related to BC risk, where the odds ratio (OR) (95% CI) was 0.50 (0.31-0.82), 0.49 (0.30-0.79), and 0.54 (0.36-0.80), respectively. The combination of AS3MT haplotype 2 (AS3MT rs11191453, rs11191454, rs10748835, and rs1046778)'s high-risk haplotype (C-G-A-C, T-A-A-C, and T-G-G-T) was significantly associated with increased risk of BC. Among controls, only 3 of the 9 candidate genotypes evaluated, rs1119438 C/C, rs10748835 A/A and rs1046778 C/C, were associated with significantly higher MMA% compared with the other genotypes. No other genotypes or haplotypes were related to arsenic methylation capacity. High MMA%, low DMA% and AS3MT rs1046778 C/C + C/T genotype predicted a significantly higher risk of BC according to stepwise multiple logistic regression analyses. AS3MT gene polymorphisms and arsenic methylation capacity appeared to affect BC risk independently.

Evaluating Gold and Selenium Chemistry for Selective Transformations of Lignin Model Compounds

AbstractApplications of gold and selenium chemistry are reported as novel approaches to promote lignin depolymerization into more valuable chemicals via selective oxidation reactions (alcohol oxidations and Baeyer‐Villiger reactions). In this study, we proposed two different oxidative methodologies using Au/SiO2 and phenylseleninic acid resin (PAR) as stable and reusable catalysts to promote selective transformations of the β‐O‐4 linkage of lignin model compounds. After evaluating the catalytic systems under batch conditions, they were both applied in a packed‐bed reactor for continuous flow operations. By using Au/SiO2 as a catalyst under flow conditions, ketones were efficiently obtained (up to 86% conversion) from the oxidation of alcohols with a residence time (tR) of 30 min. In the case of Baeyer‐Villiger oxidations catalyzed by phenylseleninic acid resin, the corresponding esters were obtained in up to 91% conversion (tR=30 min). Both systems efficiently catalyzed the conversion of the lignin model compounds.magnified image

Biological and Geochemical Development of Placer Gold Deposits at Rich Hill, Arizona, USA

Placer gold from the Devils Nest deposits at Rich Hill, Arizona, USA, was studied using a range of micro-analytical and microbiological techniques to assess if differences in (paleo)-environmental conditions of three stratigraphically-adjacent placer units are recorded by the gold particles themselves. High-angle basin and range faulting at 5–17 Ma produced a shallow basin that preserved three placer units. The stratigraphically-oldest unit is thin gold-rich gravel within bedrock gravity traps, hosting elongated and flattened placer gold particles coated with manganese-, iron-, barium- (Mn-Fe-Ba) oxide crusts. These crusts host abundant nano-particulate and microcrystalline secondary gold, as well as thick biomats. Gold surfaces display unusual plumate-dendritic structures of putative secondary gold. A new micro-aerophilic Betaproteobacterium, identified as a strain of Comamonas testosteroni, was isolated from these biomats. Significantly, this ‘black’ placer gold is the radiogenically youngest of the gold from the three placer units. The middle unit has well-rounded gold nuggets with deep chemical weathering rims, which likely recorded chemical weathering during a wetter period in Arizona’s history. Biomats, nano-particulate gold and secondary gold growths were not observed here. The uppermost unit is a pulse placer deposited by debris flows during a recent drier period. Deep cracks and pits in the rough and angular gold from this unit host biomats and nano-particulate gold. During this late arid period, and continuing to the present, microbial communities established within the wet, oxygen-poor bedrock traps of the lowermost placer unit, which resulted in biological modification of placer gold chemistry, and production of Mn-Fe-Ba oxide biomats, which have coated and cemented both gold and sediments. Similarly, deep cracks and pits in gold from the uppermost unit provided a moist and sheltered micro-environment for additional gold-tolerant biological communities. In conclusion, placer gold from the Devils Nest deposits at Rich Hill, Arizona, USA, preserves a detailed record of physical, chemical and biological modifications.

Gold(I)-Catalyzed Glycosylation with Glycosyl o-Alkynylbenzoates as Donors.

Naturally occurring glycans and glycoconjugates have extremely diverse structures and biological functions. Syntheses of these molecules and their artificial mimics, which have attracted the interest of those developing new therapeutic agents, rely on glycosylation methodologies to construct the various glycosidic linkages. In this regard, a wide array of glycosylation methods have been developed, and they mainly involve the substitution of a leaving group on the anomeric carbon of a glycosyl donor with an acceptor (a nucleophile) under the action of a particular promoter (usually a stoichiometric electrophile). However, glycosylations involving inherently unstable or unreactive donors/acceptors are still problematic. In those systems, reactions involving nucleophilic, electrophilic, or acidic species present on the leaving group and the promoter could become competitive and detrimental to the glycosylation. To address this problem, we applied the recently developed chemistry of alkynophilic gold(I) catalysts to the development of new glycosylation reactions that would avoid the use of the conventional leaving groups and promoters. Gratifyingly, glycosyl o-alkynylbenzoates (namely, glycosyl o-hexynyl- and o-cyclopropylethynylbenzoates) turned out to be privileged donors under gold(I) catalysis with Ph3PAuNTf2 and Ph3PAuOTf. The merits of this new glycosylation protocol include the following: (1) the donors are easily prepared and are generally shelf-stable; (2) the promotion is catalytic; (3) the substrate scope is extremely wide; (4) relatively few side reactions are observed; (5) the glycosylation conditions are orthogonal to those of conventional methods; and (6) the method is operationally simple. Indeed, this method has been successfully applied in the synthesis of a wide variety of complex glycans and glycoconjugates, including complex glycosides of epoxides, nucleobases, flavonoids, lignans, steroids, triterpenes, and peptides. The direct glycosylation of some sensitive aglycones, such as dammarane C20-ol and sugar oximes, and the glycosylation-initiated polymerization of tetrahydrofuran were achieved for the first time. The gold(I) catalytic cycle of the present glycosylation protocol has been fully elucidated. In particular, key intermediates, such as the 1-glycosyloxyisochromenylium-4-gold(I) and isochromen-4-ylgold(I) complexes, have been unambiguously characterized. Exploiting the former glycosyloxypyrylium intermediate, SN2-type glycosylations were realized in specific cases, such as β-mannosylation/rhamnosylation. The protodeauration of the latter vinylgold(I) intermediate has been reported to be critically important for the gold(I) catalytic cycle. Thus, the addition of a strong acid as a cocatalyst can dramatically reduce the required loading of the gold(I) catalyst (down to 0.001 equiv). C-Glycosylation with silyl nucleophiles can proceed catalytically when moisture, which is sequestered by molecular sieves, can serve as the H+ donor for the required protodeauration step. Indeed, the unique mechanism explains the merits and broad applicability of the present glycosylation method and provides a foundation for future developments in glycosylation methodologies that mainly involve improving the diastereoselectivity and catalytic efficiency of glycosylations.

Isocyanide insertion into Au-H bonds: first gold iminoformyl complexes.

Isocyanides insert into gold(iii)-hydrogen bonds to give the first examples of gold iminoformyl complexes. The reaction is initiated by catalytic amounts of radicals; DFT calculations indicate that this is an equilibrium reaction driven forward by isocyanide in sufficient excess to trap the Au(ii) intermediate.

Bond dissociation energies of carbonyl gold complexes: a new descriptor of ligand effects in gold(i) complexes?

Ligand electronic effects in gold(i) chemistry have been evaluated by means of the experimental determination of M-CO bond dissociation energies for 16 [L-Au-CO]+ complexes, bearing L ligands widely used in gold catalysis. Energy-resolved analyses have been made using tandem mass spectrometry with collision-induced dissociation. Coupled with DFT calculations, this approach enables the quantification of ligand effects based on the LAu-CO bond strength. A further energy decomposition analysis gives access to detailed insights into this bond's characteristics. Whereas small differences are observed between phosphine- and phosphite-containing gold complexes, carbene ligands are shown to stabilize the gold-carbonyl bond much more efficiently.

Spin-Forbidden Reactions: Adiabatic Transition States Using Spin-Orbit Coupled Density Functional Theory.

A spin-forbidden chemical reaction involves a change in the total electronic spin state from reactants to products. The mechanistic study is challenging because such a reaction does not occur on a single diabatic potential energy surface (PES), but rather on two (or multiple) spin diabatic PESs. One possible approach is to calculate the so-called "minimum energy crossing point" (MECP) between the diabatic PESs, which however is not a stationary point. Inclusion of spin-orbit coupling between spin states (SOC approach) allows the reaction to occur on a single adiabatic PES, in which a transition state (TS SOC) as well as activation free energy can be calculated. This Concept article summarizes a previously published application in which, for the first time, the SOC effects, using spin-orbit ZORA Hamiltonian within density functional theory (DFT) framework, are included and account for the mechanism of a spin-forbidden reaction in gold chemistry. The merits of the MECP and TS SOC approaches and the accuracy of the results are compared, considering both our recent calculations on molecular oxygen addition to gold(I)-hydride complexes and new calculations for the prototype spin-forbidden N2 O and N2 Se dissociation reactions.

The Quest for Mononuclear Gold(II) and Its Potential Role in Photocatalysis and Drug Action.

The chemistry of gold strongly focuses on the ubiquitous oxidation states +I and +III. The intermediate oxidation state +II is generally avoided in mononuclear gold species. In recent years, gold(II) has been increasingly suggested as a key intermediate in artificial photosynthesis systems, with gold(III) moieties acting as electron acceptors, as well as in gold-catalyzed photoredox catalysis and radical chemistry. This Minireview provides a concise summary of confirmed and characterized mononuclear open-shell gold(II) complexes. Recent findings on structural motifs and reactivity patterns will be discussed. Exciting developments in the fields of photosynthesis, photocatalysis, and potential roles in medicinal chemistry will be outlined.