Syntheses, crystal structures and antimicrobial activities of polymeric silver(I) complexes with three amino-acids [aspartic acid (H2asp), glycine (Hgly) and asparagine (Hasn)]

As model compounds for silver(I)-protein interactions, silver(I) complexes with three amino-acid ligands, i.e. aspartic acid (H(2)asp), glycine (Hgly) and asparagine (Hasn), were prepared, characterized by elemental analysis, FTIR, TG/DTA, solution (H-1 and C-13) and solid-state (C-13 and N-15) 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, {[Ag-2(-Hasp)(L-Hasp)].1.5H(2)O}(n) 1, {[Ag(gly)](2).H2O}(n) 2, [Ag(L-asn)](n) 3 and [Ag(D-asn)](n) 4, 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)](n) 6 and water-insoluble crystals [Ag(Hhis)](n) 7. 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.