Appropriate Buffers for Studying the Bioinorganic Chemistry of Silver(I)

Silver(I) is being largely studied for its antimicrobial properties. In parallel to that growing interest, some researchers are investigating the effect of this ion on eukaryotes and the mechanism of silver resistance of certain bacteria. For these studies, and more generally in biology, it is necessary to work in buffer systems that are most suitable, i.e., that interact least with silver cations. Selected buffers such as 4-(2-hydroxyethyl)-1-piperazineethane sulfonic acid (HEPES) were therefore investigated for their use in the presence of silver nitrate. Potentiometric titrations allowed to determine stability constants for the formation of (Ag(Buffer)) complexes. The obtained values were adapted to extract the apparent binding constants at physiological pH. The percentage of metal ions bound to the buffer was calculated at this pH for given concentrations of buffer and silver to realize at which extent silver was interacting with the buffer. We found that in the micromolar range, HEPES buffer is sufficiently coordinating to silver to have a non-negligible effect on the thermodynamic parameters determined for an analyte. Morpholinic buffers were more suitable as they turned out to be weaker complexing agents. We thus recommend the use of MOPS for studies of physiological pH.

A series of silver(I) pyridone-sulfonates with 1-D "butterfly" chain, 2-D lamellar network and 3-D pillared layered frameworks: syntheses, structures and characterizations

A series of silver(I) pyridone-sulfonates, namely [Ag5(HL1)3(NO3)2(H2O)]n (1) [Ag2(HL1)2]n.2nH2O (2), [Ag2(HL1)(NO3)]n (3), and [Ag3(HL2)2(NO3)(H2O)]n (4) (HL1 = 4(1H)-pyridone-3-sulfonate monoanion, HL2 = 2(1H)-pyridone-5-sulfonate monoanion), have been synthesized and characterized by elemental analyses, IR, TG, PL and X-ray analyses. Complex 1, which exhibits a novel continuous silver polyhedral framework containing four kinds of coordination spheres, has been recently reported. Complex 2 presents the first one-dimensional (1-D) "butterfly" array composed of SO3-bridged columns of Ag(I) ions and symmetric pendant organic groups in silver(I) sulfonates, while complex 3 possesses a two-dimensional (2-D) layer structure in which the inorganic network substructure consists of helical chains of edge-sharing Ag1 distorted octahedra linked through dimers of edge-sharing Ag2 distorted anti-trigonal prisms by sharing two corners and two edges. Replacing H2L1 by H2L2 leads to the formation of complex 4, a three-dimensional (3-D) pillared layered framework, which is also extended by the rare mu4 nitrate anion. In complexes 1-4, all the inorganic parts can be considered as being built up from versatile polyhedra of silver(I) centers by sharing corners, edges or faces. The sulfonic group shows some novel coordination modes, which is first reported here. Solid-state fluorescence quenching and thermal stability are discussed for all of these complexes.

Structural Study of Silver(I) Sulfonate Complexes with Pyrazine Derivatives

In this Article, 11 silver complexes, namely, [Ag(L1)(2-Pyr)(H2O)] (1), Ag(L1)(2,3-Pyr) (2), [Ag2(L1)2(2Et,3Me-Pyr)2(H2O)] (3), [Ag(2,6-Pyr)](L1).1.5H2O (4), Ag(L1)(2,5-Pyr) (5), [Ag(H2O)2](L2).H2O (6), [Ag(L2)(2-Pyr)] (7), [Ag(L2)(2,3-Pyr)].1.5H2O (8), [Ag(L2)(2Et,3Me-Pyr)].2H2O (9), [Ag2(L2)(2,6-Pyr)(H2O)2](L2).H2O (10) and [Ag(L2)(2,5-Pyr)].H2O (11) (2-Pyr=2-methylpyrazine; 2,3-Pyr=2,3-dimethylpyrazine; 2Et,3Me-Pyr=2-ethyl-3-methylpyrazine; 2,6-Pyr=2,6-dimethylpyrazine; 2,5-Pyr=2,5-dimethylpyrazine; L1=p-aminobenzenesulfonate anion and L2=6-amino-1-naphthalenesulfonate anion), have been synthesized and characterized by elemental analyses, IR spectroscopy, and X-ray crystallography. In 1, 3, and 4, Ag(I) centers are linked by bridging pyrazine ligands to form one-dimensional chains, whereas compound 2 shows a double-chain structure through weak Ag-C interactions. The structure analyses show that both 5 and 11 form two-dimensional networks composed of 26-membered metallocycles. Unexpectedly, compounds 6 and 10 show discrete structures. In compound 7, silver(I) centers are bridged by sulfonate anions to form a polymeric helical structure, and the 2-Pyr molecule acts as a monodentate ligand. Compounds 8 and 9 show hinged chain structures containing 14-membered rings, and these chains interlace with each other to generate unique three-dimensional structures. These results indicate that the substituting groups and the substituting sites of pyrazine derivatives play an important role in the framework formation of silver complexes. Additionally, the luminescent properties of these compounds are also discussed.

Influence of Neutral Ligands on the Structures of Silver(I) Sulfonates

This article represents a systematical examination of the structures of silver(I) sulfonates incorporating neutral ligands. To survey the influence of the properties of neutral ligands on the structures of silver(I) sulfonates, three kinds of sulfonate anions (L1=1-naphthalenesulfonate, L2=p-toluenesulfonate, and L3=1, 3, 6, 8-pyrenetetrasulfonate) and three kinds of neutral ligands (pyrazine, Pyr, a divergent bidentate ligand; hexamethylenetetramine, hmt, a divergent tetradentate ligand; and beta-picoline, Pic, a monodentate ligand) were selected for study, and five novel silver(I) sulfonates containing neutral ligands have been synthesized: [Ag(L1)(Pyr)].H2O, Ag(L2)(Pyr), Ag4(L3)(Pyr)4(H2O)2, [Ag(L1)(hmt)].H2O, and Ag(L1)(Pic)2. The crystal structures have been determined by single-crystal X-ray diffraction, and these compounds show a variety of structures with different dimensionalities. Moreover, the luminescent properties of compounds and are also discussed.