Structure and emission properties of mixed-ligand Cu(I) complexes containing phosphinesulfide ligands

Mixed-ligand Cu(I) complexes containing phosphinesulfide ligands were synthesized, and the structure and emission properties were studied for the Cu(I) complexes. X-ray crystallographic study showed that a chelating phosphinesulfide and diimine are coordinated to Cu(I) center. Coordination geometry around Cu(I) center of each complex is described as a distorted tetrahedron. Some of the complexes show photoluminescence in the solid state.     

Electrospray mass spectrometry study of tiopronin monolayer-protected gold nanoclusters

Electrospray ionization time-of-flight mass spectrometry (ESI-TOF MS) and gel permeation chromatography (GPC) were used to study the synthesis of a series of tiopronin monolayer-protected gold nanoclusters (MPCs) and to monitor their postsynthesis peptide ligand place-exchange reactions. All mass spectra identified the presence of cyclic gold(I)-thiolates with a strong preference for tetrameric species. During the synthesis of pre-monolayer-protected nanoclusters (pre-MPCs), esterified gold(I)-thiolate tetramers were initially observed in minor abundance (with respect to disulfide bridged tiopronin species) before dramatically increasing in abundance and precipitating from solution. After conversion of pre-MPCs to MPCs, ESI-TOF mass spectra demonstrated an overall predominance of tetrameric species with conversion from ester-terminated end groups to carboxyl-terminated end groups. Further modifications were performed through postsynthesis ligand place-exchange reactions to validate the existence of the tetramers. This work suggests that monolayer protection is accomplished by cyclized gold(I)-thiolate tetramers on the gold core surface, and/or that gold(I)-thiolates are a basic building block within the nanoparticles.     

Neutral gold(I) metallosupramolecular compounds: synthesis and characterization, photophysical properties, and density functional theory studies

The reaction of the tris-indole InTREN ligand (L) with different gold phosphine fragments allows the construction of new gold(I) complexes with different geometries depending on the chosen phosphine. A metallodendrimeric structure is obtained when the gold atom is linked to a triphenylphosphine ligand, and neutral gold(I) metallocryptands are constructed when a triphosphine is used. Characterization of the compounds was accomplished by 31P{1H} and 1H NMR, IR, absorption, and fluorescence spectroscopies, electrospray ionization mass spectrometry (ESI-MS(+)), and elemental analysis, and their geometry was optimized using density functional theory (B3LYP). Time-dependent density functional theory (TD-DFT) calculations have been used to assign the lowest energy absorption bands to LMCT N(p, tertiary amine)-->Au transitions. Photophysical characterization of the complexes shows strong luminescence in the solid state. The formation of heterobimetallic species has been detected in solution in the presence of equimolar quantities of metal cations, and their structures have been identified by a combination of spectroscopic methods and mass spectrometry.     

Gold(I) and gold(III) corroles

Corrole complexes with gold(I) and gold(III) were synthesized and their structural, photophysical, and electrochemical properties investigated. This work includes the X-ray crystallography characterization of gold(I) and gold(III) complexes, both chelated by a corrole with fully brominated β-pyrrole carbon atoms. The mononuclear and chiral gold(I) corrole appears to be the first of its kind within the porphyrinoid family, while the most unique property of the gold(III) corrole is that it displays phosphorescence at ambient temperatures.     

Tetranuclear copper(I) clusters: impact of bridging carboxylate ligands on solid state structure and photoluminescence

The X-ray crystallographic characterization and solid state photoluminescence (PL) study of three new tetranuclear copper(I) clusters, [Cu4(O2CR)4], R = (3-F)C6H4 (1), (2,3,4-F)3C6H2 (2), and CF3/C6F5 (3), revealed a dependence of PL on the structural type.     

Reversible oxidative addition and reductive elimination of fluorinated disulfides at gold(I) thiolate complexes: a new ligand exchange mechanism

Reaction of HAuCl4 x 3 H2O with excess HSAr (Ar = C6F5 or C6F4H) in ethanol, followed by addition of [Et4N]Cl, produced [Et4N][Au(SAr)4] (Ar = C6F5 (1a) or C6F4H (1b)) as red crystalline solids in high yield. These complexes are rare examples of homoleptic gold(III) thiolate complexes. The crystal structures 1 show square planar geometry at the gold center with elongated Au-S bonds. Both complexes undergo reversible reductive elimination/oxidative addition processes in solution via thermal and photochemical pathways. Equilibrium constant and photostationary state measurements indicate that the relative importance of the two pathways depends on the nature of the aromatic groups. The metal-containing reductive elimination products, [Et4N][Au(SAr)2] (Ar = C6F5 (2a) or C6F4H (2b)), were confirmed by both independent synthesis and crystallographic characterization. Cross-reactions between either 1 or 2 and various disulfides led to ligand exchange via an addition-elimination process, a previously unknown reaction pathway for ligand exchange at gold(I) centers.     

Aurophilicity in gold(I) thiosemicarbazone clusters

The reaction of the phosphine thiosemicarbazone ligands HLPH and HLPMe with Au(I) ions yields the gold complexes [Au(3)(HLPH)(2)Cl(2)]Cl·2MeOH (1·2MeOH) and [Au(2)(HLPMe)Cl(2)] (2). The structures determined by X Ray diffraction, [Au(3)(HLPH)(2)Cl(2)]Cl·4MeOH (1·4MeOH) and [Au(2)(HLPMe)Cl(2)](2) (2), are the first examples of gold(I) thiosemicarbazone clusters showing aurophilicity. The structure of the trinuclear cation 1 contains the Au(1) atom located in an inversion centre, being connected to another gold(I) atom, Au(2), through a phosphino thiosemicarbazone molecule which acts as a S,P-bridging ligand. Additionally, every gold(I) atom in the trinuclear cation 1 assembles into trinuclear linear cluster units by means of close gold-gold interactions, being connected through the crystal cell in a 2D zigzag mode. The crystal structure of [Au(2)(HLPMe)Cl(2)](2) (2) contains one discrete molecule [(AuCl)(2)(HLPMe)] in the asymmetric unit, which is further assembled into tetranuclear [(AuCl)(2)(HLPMe)](2) units by means of close gold-gold interactions. Both clusters are highly luminescent in solution.     

Synthesis, characterization, and luminescent properties of dinuclear gold(I) xanthate complexes: X-ray structure of [Au2(nBu-xanthate)2

The synthesis and characterization of gold(I) complexes of butyl xanthate [Au(2)((n)()Bu-xanthate)(2)], 1, and ethyl xanthate [Au(2)(Et-xanthate)(2)], 2, are described. These complexes are readily prepared from the reaction between Au(THT)Cl (THT = tetrahydrothiophene) and the corresponding xanthate ligands as the potassium salts. The two xanthate complexes are characterized by (1)H NMR, IR, mass spectrometry, elemental analysis, and UV-vis techniques. Thermal gravimetric analysis (TGA) and differential thermal analysis (DTA) show that the gold xanthate complexes decompose to yield mainly gold metal at approximately 200 degrees C, confirmed by X-ray powder diffraction. Excitation of the complexes at 450 nm in the solid state at 77 K produces a strong red emission at ca. 690 nm with a broad asymmetric profile tailing to 850 nm. The dinuclear gold(I) xanthate complex, [Au(2)(nBu-xanthate)(2)], 1, is the first structurally characterized binary Au(I) xanthate. The Au...Au distance in the eight-membered ring is 2.8494(15) A while the shortest intermolecular Au...Au interaction between independent units is 3.64 A. The angle between the planes containing the molecules in the unit cell is approximately 69.56 degrees. The light green plates of [Au(mu-S(2)COBu(n))](2) crystallize in the orthorhombic space group P2(1)2(1)2 with a = 37.254(14) A, b = 7.287(3) A, c = 6.054(2) A, alpha = beta = gamma = 90 degrees, Z = 4, and V = 1643.4(11) A(3).     

Oligothiophene phosphoramidites for oligonucleotide labelling

We report the synthesis and characterization of two oligonucleotides (a tetramer and a 19-mer) labelled with a fluorescent oligothiophene and obtained by means of the phosphoramidite of the fluorophore. The conjugate compounds were synthesized in solid phase and characterized by means of mass spectrometry, multinuclear NMR, UV-vis and photoluminescence spectroscopies. The results show that this approach is suitable as a general route for the preparation of oligonucleotides labelled with oligothiophene-based fluorophores.     

金(Ⅰ)化合物中的亲金相互作用

In the 1980s, interaction between gold atoms in gold (Ⅰ) species was discovered, which is afterwards named "aurophilicity". Based on in-depth researches conducted on these compounds, chemists are able to explain the reason for formation, the interacting mechanism and the theoretical foundation of them. This article reviews on the discovery of "aurophilicity", its historical development with typical examples, and its fresh applications in branches of physics and chemistry.     

How far can we go with structural mass spectrometry of protein complexes?

Physical interactions between proteins and the formation of stable complexes form the basis of most biological functions. Therefore, a critical step toward understanding the integrated workings of the cell is to determine the structure of protein complexes, and reveal how their structural organization dictates function. Studying the three-dimensional organization of protein assemblies, however, represents a major challenge for structural biologists, due to the large size of the complexes, their heterogeneous composition, their flexibility, and their asymmetric structure. In the last decade, mass spectrometry has proven to be a valuable tool for analyzing such noncovalent complexes. Here, I illustrate the breadth of structural information that can be obtained from this approach, and the steps taken to elucidate the stoichiometry, topology, packing, dynamics, and shape of protein complexes. In addition, I illustrate the challenges that lie ahead, and the future directions toward which the field might be heading.     

Synthesis and solution- and solid-state characterization of gold(I) rings with short Au...Au interactions. Spontaneous resolution of a gold(I) complex

We report the synthesis and solution- and solid-state characterization of gold(I) rings with short 1,9-transannular Au...Au interactions. The 9- and 16-membered gold(I) rings were prepared by reacting 9,9-dimethyl-4,5-bis(diphenylphosphino)-xanthene and (Me2S)AuCl in the presence of AgNO3 in the molar ratio of 1:0.5:1 and 1:1:1, respectively. X-ray crystallographic measurements in conjunction with solution X-ray diffraction and NMR methods have been used to determine the structure of gold(I) rings, and we also gained insight into the dynamics. The nine-membered gold(I) ring is chiral, and the crystal contains only one of the two enantiomers, either right- or left-handed. To the best of our knowledge this represents the first example of crystallization-induced spontaneous resolution of a binuclear gold(I) cycle. The 16-membered ring with 1,9-transannular Au...Au interaction is in a figure-eight conformation.     

Bipyridyl/carbazolate silver(I) and gold(I) N-heterocyclic carbene complexes: A systematic study of geometric constraints and electronic properties

A series of silver(I) and gold(I) carbene complexes of the type [M(L)(2,2′-bipyridine)][PF₆] (L = 1-benzyl-3-(2-pyridylmethyl)benzimidazolylidene; M = Ag ( 1 ); M = Au ( 3 )) and [M(L)(carbazole)] (M = Ag ( 2 ); M = Au ( 4 )) were synthesized and analyzed using a range of spectroscopic and crystallographic techniques. Inspection of the solid-state structures of 1 , 2 and 4 revealed a number of intermolecular noncovalent interactions. In the solid-state structure adopted by 1 , π–π and Ag–Ag interactions directed the complexes to orient in a head-to-tail fashion. The photophysical properties were found to be influenced by the ancillary ligands in solution as well as in the solid-state. Calculations were performed to support the aforementioned structural and optoelectronic assignments.     

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.     

Probing hemoglobin structure by means of traveling-wave ion mobility mass spectrometry

Hemoglobin (Hb) is a tetrameric noncovalent complex consisting of two α- and two β-globin chains each associated with a heme group. Its exact assembly pathway is a matter of debate. Disorders of hemoglobin are the most common inherited disorders and subsequently the molecule has been extensively studied. This work attempts to further elucidate the structural properties of the hemoglobin tetramer and its components. Gas-phase conformations of hemoglobin tetramers and their constituents were investigated by means of traveling-wave ion mobility mass spectrometry. Sickle (HbS) and normal (HbA) hemoglobin molecules were analyzed to determine whether conformational differences in their quaternary structure could be observed. Rotationally averaged collision cross sections were estimated for tetramer, dimer, apo-, and holo-monomers with reference to a protein standard with known cross sections. Estimates of cross section obtained for the tetramers were compared to values calculated from X-ray crystallographic structures. HbS was consistently estimated to have a larger cross section than that of HbA, comparable with values obtained from X-ray crystallographic structures. Nontetrameric species observed included apo- and holo- forms of α- and β-monomers and heterodimers; α- and β-monomers in both apo- and holo- forms were found to have similar cross sections, suggesting they maintain a similar fold in the gas phase in both the presence and the absence of heme. Heme-deficient dimer, observed in the spectrum when analyzing commercially prepared Hb, was not observed when analyzing fresh blood. This implies that holo-α-apo-β is not an essential intermediate within the Hb assembly pathway, as previously proposed.     

Heterophase ligand exchange and metal transfer between monolayer protected clusters

This paper describes reactions in which ligands are exchanged and metals are transferred between monolayer-protected metal clusters (MPCs) that are in different phases (heterophase exchange) or are in the same phase. For example, contact of toluene solutions of alkanethiolate-coated gold MPCs with aqueous solutions of tiopronin-coated gold MPCs yields toluene-phase MPCs that have some tiopronin ligands and aqueous-phase MPCs that have some alkanethiolate ligands. In a second example, heterophase transfer reactions occur between toluene solutions of alkanethiolate-coated gold MPCs and aqueous solutions of tiopronin-coated silver MPCs, in which tiopronin ligands are transferred to the former and gold metal to the latter phase. These ligand and metal exchange reactions are inhibited when conducted under N(2). The results implicate participation of an oxidized form of Au (such as a Au(I) thiolate, Au(I)-SR) as both a ligand and metal carrier in the exchange reactions. Au(I)-SR is demonstrated to be an exchange catalyst.     

MALDI coupled to modified traveling wave ion mobility mass spectrometry for fast enantiomeric determination

In this work, the use of MALDI traveling wave ion mobility spectrometry‐mass spectrometry (MALDI‐TWIMS‐MS) for stereoselective structural analysis of direct cleavage and identification of 2‐substituted piperidines obtained through solid‐phase asymmetric synthesis by using heterogeneous 8‐phenylmenthyl‐based chiral auxiliary resins. A strategy for gas‐phase chiral and structural characterization of small molecular weight molecules by using MALDI‐IMS‐MS technique is discussed. Because both MALDI and IMS do not directly offer chiral resolution, an easy methodology by adding a chiral phase is described to carry out in situ online ion/molecule complexation with different chiral analytes inside the mass spectrometer. Piperidine enantiomers were resolved, and separation obtained shows dependence of surface areas. To corroborate this assumption and elucidate the separation mechanism to accomplish an analytical technique by which fast determination of the chirality of molecules may be determined for a wide range organic compound applications, it was performed DFT calculations to determine the cross‐sectional areas of proton‐bound dimer complexes. Drift times are affected by cross‐sectional areas, correlating bigger times with bigger molecular volumes during the ion mobility experiments of proton‐bound dimer complexes.     

Gold liquid crystals displaying luminescence in the mesophase and short F...F interactions in the solid state

Rodlike gold(I) complexes, [Au(C6F4OCmH2m+1)(C(triple bond)NC6H4C6H4OCnH2n+1)] (m=2, n=4, 10; m=6, n=10; m=10, n=6, 10), display interesting features. They are liquid crystals and show photoluminescence in the mesophase, as well as in the solid state and in solution. The single-crystal, X-ray diffraction structure of [Au(C6F4OC2H5)(C(triple bond)NC6H4C6H4OC4H9)] confirms its rodlike structure, with a linear coordination around the gold atom, and reveals the absence of any Au...Au interactions (such interactions are often present in luminescent gold complexes). Well-defined, intermolecular Fortho...Fmeta interactions, with remarkably short intermolecular FF distances (2.66 A), are observed; these interactions seem to be responsible for the crystal packing, which consists of an antiparallel arrangement of molecules. Experiments under different conditions support the explanation that the photoluminescence has an intramolecular origin.     

Gold(I)-coordination triggered multistep and multiple photochromic reactions in multi-dithienylethene (DTE) systems

The preparation, characterization, and photochromic properties of a mononuclear gold(I) complex (1oo) with two identical DTE-acetylides and a dinuclear gold(I) complex (2ooo) with both DTE-acetylide and DTE-diphosphine are described. Both gold(I) complexes exhibit multistep and multiple photocyclization/cycloreversion reactions. Particularly, four-state and four-color photochromic switch is successfully achieved for the dinuclear gold(I) complex upon irradiation with appropriate wavelengths of light. In contrast, fully ring-closed form is unattained through multiple photocyclization for the two corresponding model organic compounds coupling with the same DTE units as gold(I) complexes but without gold(I)-participation. It is demonstrated that coordination of gold(I) ion to DTE-acetylides exerts indeed a crucial role in achieving stepwise and selective photocyclization and cycloreversion reactions for both gold(I) complexes, in which the coordinated gold(I) atom acts as an effective "barrier" to prohibit intramolecular energy transfer between multi-DTE moieties.     

An Integrated Mass Spectrometry Based Approach to Probe the Structure of the Full‐Length Wild‐Type Tetrameric p53 Tumor Suppressor

We present an integrated approach for investigating the topology of proteins through native mass spectrometry (MS) and cross‐linking/MS, which we applied to the full‐length wild‐type p53 tetramer. For the first time, the two techniques were combined in one workflow to obtain not only structural insight in the p53 tetramer, but also information on the cross‐linking efficiency and the impact of cross‐linker modification on the conformation of an intrinsically disordered protein (IDP). P53 cross‐linking was monitored by native MS and as such, our strategy serves as a quality control for different cross‐linking reagents. Our approach can be applied to the structural investigation of various protein systems, including IDPs and large protein assemblies, which are challenging to study by the conventional methods used for protein structure characterization.