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

在过去的20年里，生色溶解有机物(CDOM)对水生光场以及淡水和海水的生物地球化学的重要性已经得到了很好的证实；然而，其光学和光化学特性的结构基础仍然不清楚，特别是对于海洋水域。马里兰大学的科学家将通过对在横跨赤道大西洋的邮轮上收集的样品(可能的话，包括C-18固相萃取物和原始水域)进行一套全面的光学、质谱学、化学和光化学测量来解决这个问题。这项研究的结果将与从中大西洋海湾的淡水、河口和沿海水域获得的结果进行比较。获得了吸收和荧光发射的完整光谱关系，并与木质素酚含量、超高分辨率质谱图、凝胶渗透色谱测定的相对平均尺寸和溶解有机碳含量进行了比较。光化学反应性的两个指标--过氧化氢的光产生和选定酚类的光敏化氧化--将进一步用来研究从淡水、沿海和近海水域收集的CDOM的结构差异如何影响反应性。用醛、酮和醌的选择性还原剂硼氢化钠处理后的光谱、超高分辨质谱和光化学反应的变化将被用来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。在更广泛的影响方面，这项研究将为生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，并对这种材料的来源施加限制。作为该项目的一部分，两名研究生将得到支持和培训。预计马里兰大学的本科生和费朗国立高等学院化学工程学院的法国本科生也将参与这项研究，但不会对该项目产生任何费用。

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.