Synthesis and crystal structure of tetrameric silver(I) 3,5-di-tert-butyl-pyrazolate

A tetrameric [Ag(μ-3,5-^tBu₂pz)]₄ · CH₂Cl₂ (1 · CH₂Cl₂) has been prepared and structurally characterized. The four Ag-atoms are in an approximate rhombic arrangement with pyrazolato bridges alternating on either side of the Ag₄-plane. A ¹H NMR study shows partial decomposition of 1 to the mononuclear [Ag(3,5-^tBu₂pzH)₂]⁺ in solution.     

Preparation of silver nanoparticles from silver(I) nano-coordination polymer

Nanorods of two-dimensional organometallic coordination polymer, [Ag(μ₄-DPOAc)]_n (1) [DPOAc⁻ = diphenylacetate], has been synthesized by the reaction of potassium diphenylacetate (DPOAcK) and AgNO₃ by sonochemical process. Reaction conditions, such as the concentration of the initial reagents played important roles in the size and growth process of the final product. Silver nanoparticles were synthesized from nanorods of compound 1. These nano-coordination polymer and nanoparticles were characterized by X-ray powder diffraction (XRD) and scanning electron microscopy (SEM). Thermal stability of nano and crystal samples of compound 1 were studied and compared with each other.     

Macrocyclic dinuclear gold(I) and silver(I) NHCs complexes

The ligands bis-(imidazolium) hexafluorophosphate (Himy = -C₃N₂H₃-, imidazolium; R = 1-naphthylmethylene, 1a; 9-anthracenylmethylene, 1b) with an oxoether chain were easily prepared by the reaction of substituted imidazole with the diglycol diiodide, followed by exchange of anions with . 1a and 1b reacted with Ag₂O in DMSO or CH₃CN to yield [2 + 2] dinuclear Ag(I) NHCs macrocyclic complexes 2a and 2b, which showed much different conformation in solid corresponding to the R- substituent. Carbene transmetalation reactions of 2a-b with Au(SMe₂)Cl give dinuclear Au(I) analogs 3a and 3b. The new NHCs complexes were characterized by elemental analyses, ¹H NMR, ¹³C NMR and the structures of 2a-b and 3a were confirmed by X-ray diffraction determination.     

Theoretical insights into the nature of intermolecular interactions in cytosine dimer

In this study we discuss stacking interactions in cytosine dimer in conformations appearing in B-DNA crystals. The variational–perturbational scheme was applied for decomposition of the intermolecular interaction energy at the MP2 level of theory. The significant influence of the mutual orientation of cytosine monomers was observed not only on the total intermolecular interaction energy but also on its components: Different components of intermolecular interaction energy depend in different manner on parameters describing mutual orientation of cytosine monomers.     

Syntheses and characterizations of six hydrogen-bonded silver(I) complexes from assembly of silver(I) nitrate and aminobenzoic acid

Six hydrogen-bonded silver(I) complexes, Ag(4-abaH)₂(NO₃) (1), [Ag(4-abaH)₂(NO₃)]_n (2), {[Ag(4-aba)(4-abaH)] · H₂O}_n (3), {[Ag(4,4^′-bipy)(H₂O)](4-aba)_0.5(NO₃)_0.5 · (H₂O)_0.5}_n (4), [Ag[(3-abaH_0.5)₂] (5), and {[Ag(3-aba)] · H₂O}_n (6) (4-abaH=4-aminobenzoic acid, 3-abaH=3-aminobenzoic acid), have been synthesized and characterized by single-crystal X-ray diffraction analyses. In 1, 4-abaH serves as a monodentate ligand coordinating to Ag(I) through its nitrogen atom, while uncoordinated carboxylic group links (4-abaH)-Ag-(4-abaH) into a one-dimensional metallic carboxylic synthon. 2 may be regarded as an extension of 1 into a two-dimensional carboxylic synthon through NO₃ ⁻ bridging two adjacent Ag(I) centers. In 3, 4-abaH in a monodentate mode and 4-aba in a μ-N,O bridging mode link three-coordinated Ag(I) to form a one-dimensional swallow-like chain, which is further extended into a two-dimensional layer structure through inter-chain hydrogen bonding interactions. The alternating Ag(I) and 4,4^′-bipy in 4 give rise to a slightly distorted linear chain, which is further extended into a two-dimensional layer through the completely overlapping and off-set stacking interactions. The hydrogen bonds involving in weakly coordinated aqueous molecules and 4-aba further extend it into a three-dimensional framework. In 5, the inter-molecular hydrogen bonding and π-π stacking interactions extend Ag[(3-abaH_0.5)₂] into a two-dimensional supramolecular architecture. In 6, 3-aba in a μ₃-N,O,O^′ coordination mode links three three-coordinated Ag(I) into a two-dimensional network. Uncoordinated aqueous molecules and the adjacent 3-aba oxygen atoms form intermolecular hydrogen bonds.     

Crystal and molecular structure of bis(tricyclohexylphosphine)silver(I)nitrate and bis(tricyclohexylphosphine)silver(I)perchlorate; correlation of the structures with the silver-phosphorus coupling constants

Two (1:2) silver monophosphine complexes have been studied by X-ray diffraction methods and in solution by P NMR spectroscopy. Both are monomeric and tricoordinated in the solid state but one of them, the perchlorate compound, is probably associated as a dimer species in solution from the lower ¹J(¹⁰⁷Ag³¹P) value when compared to the nitrate analogue. Previous structural correlations found in other silver-phosphine complexes have been confirmed for these new compounds. Thus, larger PAgP bond angles are associated with shorter AgP bond distances, longer Aganion bond distances and lower Lewis basicity of the anions. Selected structural data are: PAgP bond angle of 139.04(9)°, AgP bond lengths of 2.440(3) and 2.445(3) Å for the nitrate complex and 147.34(3)°, 2.429(1) Å and 2.432(1) Å, for the perchlorate one. J(¹⁰⁷Ag³¹P) is 457 Hz and 447 Hz, respectively. The complexes are triclinic, Z = 2, with the parameters: a = 9.258(2), b = 9.828(2), c = 23.385(5) Å, α = 94.73(2)°, β = 96.35(2)°, γ = 116.42(1)° (nitrate) and a = 9.505(2), b = 9.790(2), c = 23.667(6) Å, α= 99.03(2) β = 95.44(2) γ = 115.97(1)° (perchlorate).     

Mono- and bimetallic gold(I) and silver(I) pentafluoropropionates and related compounds

A series of eight new carboxylate complexes of the general type (L)_nMOC(O)R (L=PMe₃; n=1; M=Ag, Au; R=C₂F₅. L=PPh₃; n=1-3; M=Ag; R=C₂F₅, t-Bu) have been prepared in high yields. Crystal and molecular structures have been determined for three representative examples. The crystal structure of (Ph₃P)AgOC(O)C₂F₅ contains dimers in which the silver atoms are bridged by the carboxylate oxygen atoms. This bridging resembles the structural motif found in silver carboxylates without ligand support. Usage of the smaller phosphine PMe₃ leads to the formation of a polymeric chain structure in (Me₃P)AgOC(O)C₂F₅ with bridging carboxylate anions and short Ag-Ag contacts holding the monomers together. The reaction of (4-Me₂N-C₆H₄)Ph₂ PAuCl with two equivalents of C₂F₅CO₂Ag leads to the formation of a mixed metal product containing both gold and silver. The crystal structure analysis of this compound revealed a tetranuclear complex containing a central dimeric silver pentafluoropropionate unit which is chelated by the (triarylphosphine)gold(I) pentafluoropropionate molecules via Ag-Au metallophilic contacts and Ag-O donor/acceptor interactions.     

Observation of specific intermolecular interactions in the X-ray crystal structure of Cu(I) (1,1,1,3,5,5,5-hepta-fluoropentane-2,4-dionato) (vinyltrimethylsilane)

The determination of the X-ray crystal structure of Cu^(I) (1,1,1,3,5,5,5-heptafluoro-pentane-2,4-dionato) (vinyltrimethylsilane) or Cu(pfac)(VTMS), a close analogue to Cu(hfac)(VTMS), which is the most widely used precursor for copper CVD, gives us an unique insight about the molecular structure of such compounds. In particular, two short F…H distances between CF₃ groups of a molecule and the alkenyl hydrogen atoms of the neighboring molecule reveal intermolecular interactions specifically related to the structure of the VTMS ligand.     

1,2,4-triazolo[4,3-a]pyrimidines: a new kind of ligands. Structure of the silver(I) dimer with the 7-oxo derivative

This paper describes the silver dinuclear complex [Ag₂L₂(NO₃)₂] · 2H₂O, where L represents the bridging ligand 7,8-dihydro-7-oxo-1,2,4-triazolo[4,3-a]pyrimidine, this being the first example of a coordination compound of a 1,2,4-triazolo[4,3-a]pyrimidine derivative. As a difference with the most studied 1,2,4-triazolo[1,5-a]pyrimidine derivatives, the coordination takes place through the contiguous nitrogen atoms of the triazole ring, closing a six member Ag₂N₄ core with a higher intermetallic distance, 3.4791(3) Å. Linear coordination of silver is not possible in this geometry, so flat trigonal coordination involving also the nitrate counteranion is found instead.     

Secondary ion mass spectrometry of nonvolatile isocyanide complexes of silver(I) and copper(I)

A series of silver and copper coordination complexes has been studied using secondary ion mass spectrometry (SIMS). Results are presented for the monomeric silver(I) complexes [Ag(CNR)₄]X, where R = cyclohexyl for X  ClO₄⁻, and R = methyl or t-butyl for X  PF₆⁻. Likewise, Cu(I) complexes [Cu(CNR)₄]PF₆, where R =methyl, t-butyl, or cyclohexyl, were examined. The presence of AgL₂⁺ (L represents the intact RNC ligand) and the absence of AgL₃⁺ and AgL₄⁺ species attests to the gas phase stability of two-coordinate silver(I). Similar results to these were obtained for the Cu(I) complexes, with the exception of [Cu(CNCH₃)₄]PF₆ whose spectrum contains CuL₄⁺, CuL₃⁺, CuL₂⁺, CuL⁺, and Cu⁺ ions. The latter result reflects the enhanced stability of the tetrahedral Cu(I) geometry compared to Ag(I) in the gas phase. Cross labeling experiments and isotopic labeling studies have provided insights into fragmentation mechanisms. Ligand exchange occurs when mixtures are examined. These exchange reactions provide evidence for extensive molecular mixing which can accompany SIMS even under low primary ion dose conditions. Cluster ion formation as well as the observation of α-cleavage of the NC bonds of RNC ligands have been observed and these results are discussed. Granulated graphite and ammonium chloride were employed to study matrix effects. Granulated graphite enhanced NC cleavage for the silver complexes but had little effect on the relative abundance of silver cluster ions. On the other hand, copper cluster ions were more sensitive to matrix effects.     

The structure of silver(I) iodide and bromide,and the silver(I) solvate in tetrahydrothiophene solution: An X-ray scattering and raman spectroscopic study

Structures of silver(I) iodide and bromide, and the solvated silver(I) ion are determined in tetrahydrothiophene solution with Large Angle X-ray Scattering (LAXS) technique. In a silver(I) perchlorate tetrahydrothiophene solution, silver(I) is solvated by four tetrahydrothiophene molecules in a regular tetrahedron. The main peak in the radial distribution function corresponds to four AgS distances at 2.526(7) Å. An SS distance at 2.65(2) Å in the solvent bulk is also included in the main peak. This shows that an internal structure exists in the tetrahydrothiophene bulk. Silver(I) iodide and bromide are tetrameric complexes with a stella quadrangula configuration, in saturated solution. The distances in the [AgI(SC₄H₈)]₄ complex are AgI 2.799(4); AgAg, 3.072(6) and II, 4.638(19) Å and in the [AgBr(SC₄H₈)]₄ complex they are AgBr, 2.592(3); AgAg, 2.866(5) and BrBr, 4.25(4) Å. The AgI bond distances in the [AgI(SC₄H₈)]₄ complex is shorter in solution than in the solid solvate. This is because bulk tetrahydrothiophene is a markedly weaker donor than free tetrahydrothiophene due to the sulfursulfur interactions in the bulk, shown to be around 2.65 Å. Raman spectroscopic studies on silver(I) and copper(I) iodide and silver(I) chloride tetrahydrothiophene solutions show that the polymetric structures predominate in concentrated solution and that they disintegrate upon dilution.     

Antimicrobial properties of highly fluorinated silver(I) tris(pyrazolyl)borates

Highly fluorinated tris(pyrazolyl)borate ligand [HB(3,5-(CF3)2Pz)3]- has been used in the isolation of air- and light-stable silver complex, [HB(3,5-(CF3)2Pz)3]Ag(OSMe2). It is a monomeric tetrahedral silver complex with an O-bonded dimethylsulfoxide ligand. The silver adduct [HB(3,5-(CF3)2Pz)3]Ag(OSMe2) and the related [HB(3,5-(CF3)2Pz)3] Ag(THF) (where OSMe2 = dimethyl sulfoxide; THF = tetrahydrofuran) show good antibacterial activity, and their antimicrobial efficacy against Staphylococcus aureus is greater than those of AgNO3 and silver sulfadiazine.     

Copper(I)-organophosphine complexes of bis(3,5-dimethylpyrazol-1-yl)dithioacetate ligand

Copper(I) complexes have been synthesized from the reaction of CuCl, monodentate tertiary phosphines PR₃ (PR₃ = P(C₆H₅)₃; P(C₆H₅)₂(4-C₆H₄COOH); P(C₆H₅)₂(2-C₆H₄COOH); PTA, 1,3,5-triaza-7-phosphaadamantane; P(CH₂OH)₃, tris(hydroxymethyl)phosphine) and lithium bis(3,5-dimethylpyrazolyl)dithioacetate, Li[LCS₂]. Mono-nuclear complexes of the type [LCS₂]Cu[PR₃] have been obtained and characterized by elemental analyses, FT-IR, ESI-MS and multinuclear (¹H, ¹³C and ³¹P) NMR spectral data; in these complexes the ligand behaves as a κ³-N,N,S scorpionate system. One exception to this stoichiometry was observed in the complex [LCS₂]Cu[P(CH₂OH)₃]₂, where two phosphine co-ligands are coordinated to the copper(I) centre. The solid-state X-ray crystal structure of [LCS₂]Cu[P(C₆H₅)₃] has been determined. The [LCS₂]Cu[P(C₆H₅)₃] complex has a pseudo tetrahedral copper site where the bis(3,5-dimethylpyrazolyl)dithioacetate ligand acts as a κ³-N,N,S donor.     

Interaction of amino acids with silver(I) ions.

The reactivity of silver(I) ions towards twenty amino acids has been studied in aqueous unbuffered solutions using an ion-selective electrode as a highly sensitive monitor. Contrary to general belief, silver ions are not completely specific for cysteine, but also react with lysine, arginine, methionine and, to a minor extent, cystine. Nevertheless the interaction with all of these species except cysteine is too weak to affect significantly the determination of thiol in proteins by the customary argentometric titration method. The possible origin of errors arising in such titrations is discussed.     

Formation of a type I collagen RNA dimer by intermolecular base-pairing of a conserved sequence around the translation initiation site.

A symmetrical sequence around the translation initiation site of several collagen genes is highly conserved. Deletions in this sequence increase translational efficiency of an alpha 2(I) collagen - CAT chimeric gene after DNA transfection of NIH 3T3 fibroblasts (Schmidt, Rossi and de Crombrugghe, submitted). The secondary structure, predicted by the sequence of this segment, was shown to exist in solution in 200 mM NaCl at 37 degrees C. Cell-free translation of the corresponding RNA using a reticulocyte lysate is inhibited 2 to 4-fold by preincubation with a 0.5 M NaCl extract of an NIH 3T3 ribosomal eluate. Cell-free translation of two mutant RNAs, with partial deletions of the conserved sequence, is not inhibited by such preincubation. This inhibition is not due to degradation of the RNA and requires a protein component of the ribosomal eluate, which, however, is not required after the preincubation step. Preincubation of the RNA with the ribosomal eluate from NIH 3T3 fibroblasts causes the reversible formation of an intermolecular dimer in which the conserved symmetrical sequences hybridize to each other. This results in an increase in the degree of secondary structure of the conserved segment around the translation initiation site. We speculate that translational efficiency could be modulated by influencing the equilibrium between monomer and dimer.     

Proton-NMR study of the interaction of trans-dichloro-diamine-platinum(II) with poly(I) and poly(I).poly(C)

The fixation of trans-(NH₃)₂Cl₂ Pt(II) to poly(I)·poly(C) at low r_b (< 0.05) leads to the formation of two complexed species. The major species (ca. 82% of bound platinum) involves coordination of platinum to a single hypoxanthine base, while the other species involves coordination of two hypoxanthine bases, which are either far apart on the same strand or on separate poly(I) strands, to the platinum. These same two species are found after reaction with poly(I), as are two other species throughout the entire r_b range studied (r_b = 0–0.30). The latter two species are assigned to trans-Pt bound to two bases on a poly(I) strand with (a) one or (b) two free bases between the two bound bases. These two species, (a) and (b), account for ca. 35% of the bound platinum, although the 1:1 species remains dominant (ca. 55%). These two additional species are observed at high r_b (>0.075) after reaction with poly(I)·poly(C) but as very minor species. They are formed by reaction with melted poly(I) loops. Also at high r_b, we have observed a shifted cytidine H⁵ resonance arising from interaction of trans-Pt with a melted loop of poly(C). Most probably, this arises from an intramolecular poly(I) to poly(C) crosslink. Results from the reaction of trans-Pt with poly(C) are presented for comparison.     

The interaction between subunits in the tubulin dimer.

Limited proteolysis and chemical cross-linking techniques have been used to study the interaction between alpha- and beta-tubulin subunits. Trypsin digestion of tubulin dimer resulted in the cleavage of the alpha-subunit into two fragments, whereas chymotrypsin cleaved the beta-subunit into two distinct fragments. All of these fragments have been mapped on the tubulin subunits by further proteolysis with formic acid. Cross-linking of trypsin- and chymotrypsin-cleaved subunits has been performed with two different cross-linker agents of different cross-linking distance. The addition of formaldehyde resulted in the cross-linking of the alpha-tubulin N-terminal fragment with beta-tubulin C-terminal domain. The same result was obtained when methyl 4-mercaptobutyrimidate was used.     

Peculiar features of the aggregation effect of silver(I) ion on hemoglobin

Silver(I) ion has been shown to produce aggregation effect on bovine oxyhemoglobin (HbO(2)) in Tris buffer even when taken in amounts corresponding to only two or less silver ions per one HbO(2) tetramer. The extent of produced effect is comparable to those previously observed for Hg(II), Cd, Zn, and Ni in spite of significantly different electronic configurations of the ions in question. Aggregation effect of the silver is ascribed to an interaction of the reactive thiol group sulfur-bound silver atom with the carboxylate residues surrounding the reactive thiol group-bearing cysteine beta93 group of hemoglobin. Mercury ligands, in particular, Tris molecules and OH(-) anions markedly suppress the protein coagulation, thereby supporting the proposed protein aggregation mechanism.     

T178 deletion impairs intermolecular interaction of the peptide Nramp1(164–191)

Natural resistance associated macrophage protein 1 (Nramp1), an integral membrane protein with 12 predicted transmembrane domains (TMs), is a divalent cation transporter associated with infectious and autoimmune diseases. A naturally occurring mutation G169D within TM4 of Nramp1 leads to the loss of function, suggesting potential importance of TM4 for the biological function of the protein. In this study, we determine the three‐dimensional structure and topology of a synthetic peptide, del(T178), corresponding to Nramp1(164‐191) (basically consisting of the putative TM4 of Nramp1) with Thr178 deletion in TFE and SDS micelles using NMR and CD spectroscopic techniques, and compare the results with those of the wildtype peptide. Similarly to the wildtype peptide, the del(T178) peptide still forms an amphiphilic‐like α‐helical structure in both membrane mimics and is embedded in SDS micelles. Differently, whereas the wild‐type peptide forms a helix bundle with the hydrophilic side facing the interior of the bundle, the del(T178) peptide exists as a monomer in the membrane mimics and the hydrophilic side of the helix is located near the interface of SDS micelles. Moreover, a strongly cooperative protonation occurs between intramolecular Asp residues for the del(T178) peptide in SDS micelles, while the cooperative proton binding between intermolecular Asp residues was observed for the wildtype peptide. The difference in the results of the two peptides suggests that the deletion of Thr178 impairs intermolecular interaction of the peptide. Copyright © 2009 European Peptide Society and John Wiley & Sons, Ltd.