Nontraditional Use of the Biocide DBNPA in Coatings Manufacture

By Mary C. Chervenak, Gerald B. Konst, William R. Schwingel

The synthesis and molecular, structure of 2, 2-dibwmo-3-nitdlopwpion­amide (DBNPA) was reported by Hesse in 1896,¹ but its antimicrobial prop­erties were not discovered until nearly 50 years later. The DBNPA molecule was employed initially only as a seed fungicide, ² but was later used as a slimicide in pulp and paper and in cooling water applications.³ More re­cently, its use as an antimicrobial agent has expanded into enhanced oil re­covery and into aqueous metalworking fluids.⁴

DBNPA is a powerful biocide with two unique properties: it kills micro­organisms immediately upon addition and it degrades rapidly. Although DBNPA is compatible with many chemical classes, including oxidizing agents, it will react readily with nucleophilic agents and sulfur-containing re­ducing agents. The facile reaction of DBNPA with sulfur-containing nucle­ophiles common to microorganisms, such as glutathione or cysteine, is the basis of its mode of antimicrobial action.

DBNPA is therefore not a typical oxidizing or halogen-releasing biocide. Unlike other thiol-reactive biocides, its action is such that thiol-based amino acids, like cysteine, are oxidized be­yond the formation of disulfide species.⁵ This reaction irreversibly disrupts the function of cell-surface components, interrupting transport across cell membranes, and inhibiting key biological functions. DBNPA degrades rap­idly by both nucleophilic and hydrolytic pathways to relatively nontoxic products. ⁶ The rate of hydrolysis of DBNPA is strongly pH-dependent: at pH 6.0 and 25° C, the DBNPA molecule has a half-life of 155 hours (about 6.5 days), but at pH 8.0 and 25 ° C, its half-life is about two hours.

The ultimate degradation products of DBNPA are ammonia, carbon dioxide, and bromide ion. DBNPA, when formulated as a 20% solution in water and polyethylene glycol, is completely miscible with water and readily disperses upon intro­duction into a water-based system. The DBNPA molecule begins functioning as an antimicrobial agent immediately upon introduction into a system; the rate of this activity is not affected by pH and antimicrobial control is usually presented at the 82nd Annual Meeting of the Federation of Societies for Coatings Technology, October 27-29, 2004, in Chicago, IL.