Investigating the Structural Basis of the Optical and Photochemical Properties of Chromophoric Dissolve Organic Matter

在过去的20年里，发色溶解有机物（CDOM）对淡水和海水沃茨的光场和地球化学的重要性已经得到了很好的确立;然而，其光学和光化学性质的结构基础仍然不清楚，特别是对于海洋沃茨。来自马里兰州大学的科学家将通过对在横穿赤道大西洋的巡航中收集的样本（固相C-18提取物和原始沃茨（如果可能））应用一套全面的光学、质谱、化学和光化学测量来解决这个问题。 本研究的结果将与从大西洋中部湾的淡水、河口和沿海沃茨获得的结果进行比较。将获得吸收和荧光发射的完整光谱依赖性，并与木质素酚含量、超高分辨率质谱、通过凝胶渗透色谱法测定的相对平均尺寸和溶解的有机碳含量进行比较。 两个指标的光化学反应性，过氧化氢的光生产和光敏氧化的酚类，将进一步研究如何反应性的影响，从新鲜的，沿海和近海沃茨收集的CDOM的结构差异。用硼氢化钠（醛、酮和醌的选择性还原剂）处理后，光谱、超高分辨率质谱和光化学反应性的变化将用于测试电荷转移相互作用的存在及其对光学性质的可能贡献，以及潜在地建立CDOM来源的明确标记。 就更广泛的影响而言，这项研究将为发色溶解有机物的光学和光化学性质的结构基础提供新的见解，并限制这种材料的来源。 作为该项目的一部分，将支助和培训两名研究生。 预计马里兰州大学的本科生和克莱蒙费朗国立化学学院化学工程学院的法国本科生也将参加这项研究，但不承担项目费用。

The importance of chromophoric dissolved organic matter (CDOM) to the aquatic light field and the biogeochemistry of both fresh and marine waters has been well established over the last 20 years; however, the structural basis of its optical and photochemical properties remain unclear, particularly for marine waters. Scientists from the University of Maryland will address this issue by a applying a comprehensive suite of optical, mass spectral, chemical, and photochemical measurements to samples (solid phase C-18 extracts and the original waters when possible) collected on a cruise transecting the equatorial Atlantic. Results from this study will be compared with those obtained from fresh, estuarine, and coastal waters of the Middle Atlantic Bight. The complete spectral dependencies of absorption and fluorescence emission will be acquired and compared with the lignin phenol content, the ultra-high resolution mass spectra, relative average size as determined by gel permeation chromatography, and dissolved organic carbon content. Two indices of photochemical reactivity, the photo-production of hydrogen peroxide and the photo-sensitized oxidation of selected phenols, will be further employed to examine how reactivity is affected by structural differences in CDOM collected from fresh, coastal and offshore waters. Changes in the optical spectra, ultra-high resolution mass spectra and photochemical reactivity following treatment with sodium borohydride, a selective reductant of aldehydes, ketones and quinones, will be used to test for the presence of charge-transfer interactions and their possible contribution to the optical properties, as well as to potentially establish unequivocal markers of CDOM source. In terms of broader impacts, this research would provide new insights on the structural basis for the optical and photochemical properties of chromophoric dissolved organic matter, as well as place constraints on the sources of this material. Two graduate students would be supported and trained as part of this project. It is anticipated that University of Maryland undergraduate students and French undergraduate students from the Engineering School of Chemistry of the Ecole Nationale Superieure de Chimie de Clermont Ferrand also would participate in the study but at no cost to the project.