title: Mechanism of photolytic decomposition of N-halamine antimicrobial siloxane coatings.
abstract: Generally, antimicrobial N-halamine siloxane coatings can be rehalogenated repetitively upon loss of their biocidal efficacies, a marked advantage over coatings containing other antimicrobial materials. However, the N-halamine materials tend to slowly decompose upon exposure to ultraviolet irradiation as in direct sunlight. In this work the mechanism of photolytic decomposition for the N-halamine siloxanes has been studied using spectroscopic and theoretical methods. It was found that the N-chlorinated coatings slowly decomposed upon UVA irradiation, whereas the unhalogenated coatings did not. Model compound evidence in this work suggests that upon UVA irradiation, the N-Cl bond dissociates homolytically, followed by a Cl radical migration to the alkyl side chain connected to the siloxane tethering group. An alpha and/or beta scission then occurs causing partial loss of the biocidal moiety from the surface of the coated material, thus precluding complete rechlorination. NMR, FTIR, GCMS, and computations at the DFT (U)B3LYP/6-311++G(2d,p) level of theory have been employed in reaching this conclusion.
authors.affiliation: Department of Polymer and Fiber Engineering, Auburn University, Auburn, Alabama 36849, USA.
authors.forename: Hasan B
authors.initials: HB
authors.lastname: Kocer
authors.forename: Akin
authors.initials: A
authors.lastname: Akdag
authors.forename: S D
authors.initials: SD
authors.lastname: Worley
authors.forename: Orlando
authors.initials: O
authors.lastname: Acevedo
authors.forename: R M
authors.initials: RM
authors.lastname: Broughton
authors.forename: Yonnie
authors.initials: Y
authors.lastname: Wu
mesh_terms: D000890:Anti-Infective Agents / Q000737:chemistry*; D002482:Cellulose / Q000737:chemistry; D002712:Chlorides / Q000737:chemistry; D020099:Coated Materials, Biocompatible / Q000737:chemistry*; D019277:Entropy; D006860:Hydrogen Bonding; D010777:Photochemistry; D012833:Siloxanes / Q000737:chemistry*; D014466:Ultraviolet Rays
chemical_list: D000890:Anti-Infective Agents; D002712:Chlorides; D020099:Coated Materials, Biocompatible; D012833:Siloxanes; D002482:Cellulose