Syntheses, crystal structures and antimicrobial activities of polymeric silver(i) complexes with three amino-acids [aspartic acid (H2asp), glycine (Hgly) and asparagine (Hasn)]Note: For ease of reference during discussion of their anions, H2asp, Hgly and Hasn have been used as the abbreviations for the neutral amino-acids, rather than the conventional Asp, Gly and Asn, respectively.

As model compounds for silver(I)–protein interactions, silver(I) complexes with three amino-acid ligands, i.e. aspartic acid (H2asp), glycine (Hgly) and asparagine (Hasn), were prepared, characterized by elemental analysis, FTIR, TG/DTA, solution (1H and 13C) and solid-state (13C and 15N) NMR, and X-ray crystallography. Such complexes showed a wide spectrum of effective antimicrobial activities against Gram-negative (E. coli, P. aeruginosa) and -positive (B. subtilis and S. aureus) bacteria, yeasts (C. albicans and S. cerevisiae) and more than 11 tested molds. The crystal structures of four silver(I) complexes, {[Ag2(D-Hasp)(L-Hasp)]·1.5H2O}n1, {[Ag(gly)]2·H2O}n2, [Ag(L-asn)]n3 and [Ag(D-asn)]n4, were determined. The bonding modes of the silver(I) center were different for each complex, and different to those of the two recently reported silver(I) histidinates with only Ag–N bonds, i.e. water-soluble powder [{[Ag(Hhis)]·0.2EtOH}2]n6 and water-insoluble crystals [Ag(Hhis)]n7. Silver(I) complexes formed by amino-acids with N and O donor atoms and without an S atom can be classified into four types (I–IV) based on the bonding modes of the silver(I) center. Complex 1 belongs to type I which contains only Ag–O bonds, complex 2 belongs to type II, in which the two-coordinate O–Ag–O and N–Ag–N bonding units are alternately repeated, complexes 3 and 4 belong to type III, in which the two-coordinate N–Ag–O bonding units are repeated, and complexes that contain only Ag–N bonds, as recently found in the two silver(I) histidinates 6 and 7, belong to type IV.