Chlorine photolysis and subsequent OH radical production during UV treatment of chlorinated water

The photodegradation of chlorine-based disinfectants NH(2)Cl, HOCl, and OCl(-) under UV irradiation from low- (LP) and medium-pressure (MP) Hg lamps was studied. The quantum yields of aqueous chlorine and chloramine under 254nm (LP UV) irradiation were greater than 1.2molEs(-1) for free chlorine in the pH range of 4-10 and 0.4molEs(-1) for monochloramine at pH 9. Quantum yields for MP (200-350nm) ranged from 1.2 to 1.7molEs(-1) at neutral and basic pH to 3.7molEs(-1) at pH 4 for free chlorine, and 0.8molEs(-1) for monochloramine. Degradation of free chlorine was enhanced under acidic water conditions, but water quality negatively impacted the MP Hg lamp degradation of free chlorine, compared to the LP UV source. The production of hydroxyl radical via chlorine photolysis was assessed along with the rate of reaction between ()OH and HOCl using radical scavengers (parachlorobenzoic acid and nitrobenzene) in chlorinated solutions at pH 4. The quantum yield of OH radical production from HOCl at 254nm was found to be 1.4molEs(-1), while the reaction of HOCl with OH radical was measured as 8.5x10(4)M(-1)s(-1). NH(2)Cl was relatively stable in all irradiated solutions, with <0.3mgL(-1) increase in nitrate following a UV dose of 1000mJcm(-2). For water treatment plants, no significant changes in chlorine concentration would be expected under typical pH levels and UV doses; however, the formation of ()OH could have implications for chlorinated byproducts or decay of unwanted chemical contaminants.     

Synthesis and catalysis

Research projects of the Department of Chemistry, University of Basel are reviewed ranging from the synthesis of complex natural products to the development of metalorganic catalysts and organocatalysts.     

Rheological evaluation of the isothermal cure characteristics of medical grade silicone elastomers

Silicone elastomer systems have been shown to offer potential for the fabrication of medical devices and sustained release drug delivery devices comprising low molecular weight drugs and protein therapeutics. For drug delivery systems in particular, there is often no clear rationale for selection of the silicone elastomer grade, particularly in respect of optimizing the manufacturing conditions to ensure thermal stability of the active agent and short cycle times. In this study, the cure characteristics of a range of addition‐cure and condensation‐cure, low‐consistency, implant‐grade silicone elastomers, either as supplied or loaded with the model protein bovine serum albumin (BSA) and the model hydrophilic excipient glycine, were investigated using oscillatory rheology with a view to better understanding the isothermal cure characteristics. The results demonstrate the influence of elastomer type, cure temperature, protein loading, and glycine loading on isothermal cure properties. By measuring the cure time required to achieve tan delta values representative of early and late‐stage cure conditions, a ratio t₁/t₂ was defined that allowed the cure characteristics of the various systems to be compared. Sustained in vitro release of BSA from glycine‐loaded silicone elastomer covered rod devices was also demonstrated over 14 days. © 2010 Wiley Periodicals, Inc. J Appl Polym Sci, 2010