Chromophoric Dissolved Organic Matter Photochemistry and Photophysics: Testing the Charge Transfer Model

OCE-0648414有色溶解有机物(CDOM)广泛存在于水生环境中，通过其对水生光场的影响及其光化学反应发挥着核心作用。马里兰大学帕克分校的两位研究人员提出，CDOM的光学吸收和发射性质部分是由于可溶木质素前体部分氧化形成的羟基-芳香族给体和奎宁受体之间的分子内电荷转移相互作用(即电荷转移模型)。科学家们认为，电荷转移模型可以在很大程度上解释这种材料产生的各种光化学反应，并计划使用一系列光化学和光物理测量来验证这一假设，其中包括：1)H_2O_2量子产率与O2浓度及其相关的波长相关性；2)选定的(苯酚)给体的氧化速率与O2浓度和给体浓度的相关性，以及相关的波长相关性；3)1O2产量与O2浓度的相关性；以及4)发射量子产率和寿命的波长相关性。全套测量将在一个标准(苏瓦尼河黄腐酸)和三个特征良好的水生腐殖质(HS)上进行，这些物质是在先前的野外工作中从贫营养、陆架和河口水域收集的。0.2M过滤的全水样品的H_2O_2产率与O2浓度的光谱相关性将与HS样品的光谱关系进行比较，以量化HS样品的性质在多大程度上反映了获取它们的原始水域的性质。还将进行进一步的测试，检查潜在的关键参数，如pH值、盐度和金属离子含量的影响。至于更广泛的影响，作为该项目的一部分，将支持和培训一名博士后和一名研究生。预计本科生也将参与这项研究，并学习最先进的光化学和光物理方法。

OCE-0648414Chromophoric dissolved organic matter (CDOM) is found ubiquitously in aquatic environments where its plays a central role, both through its impact on the aquatic light field and its photochemical reactions. Two researchers from the University of Maryland-College Park have proposed that optical absorption and emission properties of CDOM arise in part from intramolecular charge transfer interactions between hydroxy-aromatic donors and quinoid acceptors formed by the partial oxidation of soluble lignin precursors (i.e., charge transfer model). The scientists propose that the charge transfer model can largely explain the diverse suite of photochemical reactions attributed to this material and plan to test the hypothesis using a series of photochemical and photophysical measurements including the following: 1) the dependence of H2O2 quantum yields on O2 concentration and its associated wavelength dependence; 2) the dependence of the oxidation rates of selected (phenol) donors on both O2 concentration and donor concentration, as well as the associated wavelength dependencies; 3) the dependence of 1O2 yields on O2 concentrations; and 4) the wavelength dependence of emission quantum yields and lifetimes. The complete suite of measurements will be performed on one standard (Suwanee River fulvic acid) and three well-characterized aquatic humic substances (HS) collected on prior field work from oligotrophic, shelf and estuarine waters. The spectral dependence of the H2O2 yields on O2 concentration for 0.2 M-filtered, whole water samples will be compared to that of the HS samples to quantify the extent to which the properties of the HS samples reflect those of the original waters from which they were obtained. Further tests examining the impact of potentially key parameters such as pH, salinity, and metal ion content will also be conducted.As regards broader impacts, one post doc and one graduate student will be supported and trained as part of this project. It is anticipated that undergraduate students will also participate in this study and learn about state of the art photochemical and photophysical methods.