Synthesis and Antimicrobial Activity of Silver Citrate Complexes

Stojan Djokić

doi:10.1155/2008/436458

Abstract

Formation of silver citrate/citric acid complexed solutions was investigated. Although, silver citrate is minimally soluble in water, it can successfully be dissolved in citric acid solutions. The maximum concentration of Ag(I) in solution is estimated at 23 to 25 g/L if the concentration of citric acid is at least 4 mol/L or higher. The dissolution of silver citrate in citric acid solutions was attributed to the formation of silver citrate complexes of a general formula [Ag3(C6H5O7)n+1]3n−. The silver citrate/citric acid solutions, containing more than about 13 g/L Ag+ ion, have exhibited a decrease in Ag(I) concentration in solution over time, due to crystallization. The crystallization product was attributed to the formation of [Ag3C6H5O7]x·nH2O. Importantly, the diluted silver citrate/citric acid complexed solutions have exhibited very strong bacteriostatic and bactericidal activities.

Highlights

It is well established that only silver in its ionic or complexed forms is antimicrobially active, while the elemental silver, even in the so-called “nanocrystalline” state is not [1]
Analytical methods employed in the present work have included volumetric determination of total silver in the solution or in the silver citrate precipitate, X-ray diffraction (XRD), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM)
Simple bacteriostatic tests [13] against Pseudomonas aeruginosa were used in order to demonstrate antimicrobial activity of silver citrate complexed solutions synthesized in the present work

Summary

Introduction

It is well established that only silver in its ionic or complexed forms is antimicrobially active, while the elemental silver, even in the so-called “nanocrystalline” state is not [1]. Various forms of silver and its compounds have been investigated in the past few decades due to the antimicrobial activity of silver ions, and there is an increased interest in the potential use of silver(I) as a therapeutic agent for different antimicrobial applications. The silver complexes, for example, silver chelates have been described as more effective therapeutic agents than free silver ions [4]. A few amino acids with N- and O-donor ligands, which show a very wide spectrum of effective antimicrobial activities against bacteria and yeast, were used to obtain watersoluble silver complexes [5]. O-donor ligands, such as αhydroxycarboxylic acids (mandelic, glycolic, malic, tartaric, etc.) form complexes with Ag(I)

Methods

Results

Conclusion