Syntheses, Structures,
and Antimicrobial Activities
of Remarkably Light-Stable and Water-Soluble Silver Complexes with
Amino Acid Derivatives, Silver(I) <i>N</i>-Acetylmethioninates
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Abstract
Reaction of l- and dl-<i>N</i>-acetylmethionine
(Hacmet) and Ag<sub>2</sub>O in water at ambient temperature afforded
the remarkably light-stable silver complexes {[Ag(l-acmet)]}<sub><i>n</i></sub> (<b>1</b>) and {[Ag<sub>2</sub>(d-acmet)(l-acmet)]}<sub><i>n</i></sub> (<b>2</b>), respectively. The color of the solids and aqueous solutions
of <b>1</b> and <b>2</b> did not change for more than
1 month under air without any shields. The light stability of these
two silver(I) complexes is much higher than that of silver(I) methioninate
{[Ag<sub>2</sub>(d-met)(l-met)]}<sub><i>n</i></sub> (<b>3</b>) (Hmet = methionine), silver(I) <i>S</i>-methyl-l-cysteinate {[Ag(l-mecys)]}<sub><i>n</i></sub> (<b>4</b>), and silver(I) l-cysteinate
{[Ag(l-Hcys)]}<sub><i>n</i></sub> (<b>5</b>). X-ray crystallography of <b>1</b> obtained by vapor diffusion
revealed that ladder-like coordination polymers with two O- and two
S-donor atoms were formed. The acetyl group of acmet<sup>–</sup> prevents chelate formation of the ligand to the metal center, which
is frequently observed in amino acid metal complexes, but allows for
formation of hydrogen bonds between the ligands in the crystals of <b>1</b>. These two silver(I) <i>N</i>-acetylmethioninates
showed a wide spectrum of effective antimicrobial activities against
Gram-negative bacteria (<i>Escherichia coli</i> and <i>Pseudomonas aeruginosa</i>) and yeasts (<i>Candida albicans</i> and <i>Saccharomyces cerevisiae</i>), the effectiveness
of which was comparable to that of water-soluble Ag–O bonding
complexes
