Abstract
Various concentrations of molybdate were added to the protein containing and deproteinated exopolymers of a marine bacterium, Deleya marina. The interaction was investigated by X-ray photoelectron spectroscopy (XPS) and electron spin resonance (ESR). Molybdate reduction was observed exclusively in the deaerated protein containing exopolymer, resulting in the formation of a Mo5+ species. This species appeared to be susceptible to reoxidation in the presence of soluble oxygen. Thus, only hexavalent molybdenum was seen in the aerated suspension. The "reducing agents" could be the residual proteins which remained in the exopolymer without subsequent deproteination. The influence of this reduction on the corrosion resistance of Mo-bearing stainless steels was simulated with an austenitic stainless steel, AISI 304, whose surface was treated with molybdate prior to the exposure to the exopolymer. In addition to the formation of the Mo5+ species, a small amount of MoO2 was detected. The hydration of the passive film of the steel was increased, although no evidence indicated that the exopolymer attachment compromised the corrosion resistance of the steel in deaerated 0.1 M HCl. This work suggests that MoO42- reduction may be a bonding mechanism for the biofilm to attach to the Mo-bearing stainless steels.
