Kelli Sikorski  - Optical Properties of Humic Substances and CDOM: Effects of Borohydride Reduction

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      Publication Details (including relevant citation   information):

      Ma, J.; Del Vecchio, R.; Golanoski, K.S.; Boyle, E.S.; Blough,   N.V. Optical Properties of Humic Substances and CDOM: Effects of   Borohydride Reduction. Environ. Sci. Technol. 2010, 44,   5395–5402.

      Abstract:

      Treatment of Suwanee River humic (SRHA) and fulvic (SRFA) acids,   a commercial lignin (LAC), and a series of solid phase extracts   (C18) from the Middle Atlantic Bight (MAB extracts) with sodium   borohydride (NaBH4), a selective reductant of carbonyl-containing   compounds including quinones and aromatic ketones, produces a   preferential loss of visible absorption (g50% for SRFA) and   substantially enhanced, blue-shifted fluorescence emission (2- to   3-fold increase). Comparison of the results with those obtained   from a series of model quinones and hydroquinones demonstrates   that these spectral changes cannot be assigned directly to the   absorption and emission of visible light by   quinones/hydroquinones. Instead, these results are consistent   with a charge transfer model in which the visible absorption is   due primarily to charge transfer transitions arising among   hydroxy- (methoxy-)aromatic donors and carbonylcontaining   acceptors. Unlike most of the model hydroquinones, the changes in   optical properties of the natural samples following NaBH4   reduction were largely irreversible in the presence of air and   following addition of a Cu2+ catalyst, providing tentative   evidence that aromatic ketones (or other similar   carbonylcontaining structures) may play a more important role   than quinones in the optical properties of these materials.

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