Synthesis and characterization of water-soluble silver(I) complexes with L-histidine (H2his) and (S)-(-)-2-pyrrolidone-5-carboxylic acid (H2pyrrld) showing a wide spectrum of effective antibacterial and antifungal activities.: Crystal structures of chiral helical polymers [Ag(Hhis)]n and {[Ag(Hpyrrld)]2}n in the solid state

Two water-soluble, silver(I) complexes showing a wide spectrum of effective antibacterial and antifungal activities, i.e., {[Ag(Hhis)].0.2EtOH}(2) (1; H(2)his =L-histidine) and [Ag(Hpyrrld)](2) (3; H(2)pyrrld = (S)-(-)-2-pyrrolidone-5-carboxylic acid) were prepared. In aqueous solution 1 and 3 were present as dimers, whereas in the solid state they were polymers. Crystallization of 1 by slow evaporation and/or vapor diffusion gave water-insoluble crystals of [Ag(Hhis)](n) (2) showing modest antimicrobial activities. The complex 1 in the solid state is a polymer formed by intermolecular hydrogen-bonding interactions between dimeric [Ag(Hhis)](2) cores, while 2 is a different polymer without a core complex. X-ray crystallography revealed that 2 was a left-handed helical polymer consisting of a bent, 2-coordinate silver(I) atom bonding to the N-amino atom of one Hhis(-) ligand and the N-pi atom of a different Hhis- ligand. Of particular note is the fact that O-carboxyl atoms do not participate in the coordination. X-ray crystallography also revealed that 3 was a left-handed helical polymer formed by self-assembly of dimeric [Ag-(Hpyrrld)](2) cores with an intramolecular metal(I)-metal(I) interaction (Ag-Ag distance, 2.9022(7) Angstrom). The FTIR and the solid-state C-13 and N-15 NMR spectra showed that the dimeric core of 1 was formed through Ag-N bonds, while that of 3 was formed through Ag-O bonds. The molecular ions of 1 and 3 were detected by the positive-ion electrospray ionization (ESI) mass spectrometry. For 1-3, characterization by elemental analysis, TG/DTA, PT-IR, and variable-temperature solid-state C-13 NMR and room-temperature N-15 NMR measurements was performed, and for 1 and 3, that by solution molecular weight measurements and solution (Ag-109,H-1, and C-13) NMR spectroscopies was also carried out. The antibacterial and antifungal activities of 1 and 3 were remarkable and comparable to those of the previous silver(I)-N-heterocycle complexes.