Journal
CANADIAN JOURNAL OF CHEMISTRY-REVUE CANADIENNE DE CHIMIE
Volume 85, Issue 10, Pages 651-659Publisher
NATL RESEARCH COUNCIL CANADA-N R C RESEARCH PRESS
DOI: 10.1139/V07-024
Keywords
gold; X-ray absorption spectroscopy (XAS); cyanobacteria; transmission electron microscopy (TEM); precipitation; biosynthesis
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The mechanisms of gold precipitation by the interaction of cyanobacteria (Plectonema boryanum UTEX 485) and gold(III) chloride aqueous solutions (7.6 mmol/L final gold) have been studied at 25, 60, and 80 degrees C, using both laboratory and real-time synchrotron radiation absorption spectroscopy experiments. Addition of aqueous gold(III) chloride to the cyanobacterial culture initially promoted the precipitation of amorphous gold(l) sulfide at the cell walls and finally caused the formation of octahedral (I H) platelets (<1 to 6 mu m) of gold metal near cell surfaces and in solutions. X-ray absorption spectroscopy results confirmed that the reduction mechanism of gold(III) chloride to elemental gold by cyanobacteria involves the formation of an intermediate Au(I) species, gold(l) sulfide, with sulfur originating from cyanobacterial proteins, presumably cysteine or methionine. Although the bioreduction of gold(III) chloride to gold(l) sulfide was relatively rapid at all temperatures, the reaction rate increased with the increase in temperature. At the completion of the experiments, elemental gold was the major species present at all temperatures.
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