On the origin of the optical properties of humic substances
On the origin of the optical properties of humic substances
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DOI：
10.1021/es049912h
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发表时间：
2004-07-15
影响因子：
11.4
通讯作者：
Blough, NV
中科院分区：
文献类型：
--
作者：
Del Vecchio, R;Blough, NV
利用吸收光谱、荧光光谱和激光光漂白实验研究了腐殖物质光学性质的成因。发光量子产率和最大发射波长的Suwannee河腐殖酸（SRHA）和富里酸（SRFA）在一系列广泛的激发波长在紫外和可见光。在紫外线和可见光的一系列波长的激光照射，进一步采用选择性地破坏在特定波长吸收的发色团，使用吸收光谱法跟踪随照射时间的吸收损失。结果提供了明确的证据，这些材料的吸收和发射光谱不能仅仅从一个简单的线性叠加的光谱的许多独立的发色团。相反，HS的长波长吸收尾（>350 nm）似乎是由耦合态的连续体引起的。我们认为，这种行为是由于木质素前体部分氧化形成的羟基芳族供体和醌型受体之间的分子内电荷转移相互作用。我们进一步提出，这些供体-受体相互作用可能是一种常见的现象，发生在所有天然的羟基或多羟基芳香族聚合物，形成适当的受体部分氧化后。此类物质的实例包括木质素、多酚、单宁和黑色素。
Absorption and fluorescence spectroscopy and laser photobleaching experiments were employed to probe the origins of the optical properties of humic substances (HS). Luminescence quantum yields and the wavelengths of maximum emission were acquired for Suwannee River humic acid (SRHA) and fulvic acid (SRFA) at an extensive series of excitation wavelengths across the ultraviolet and visible. Laser irradiation at a series wavelength across the ultraviolet and visible was further employed to destroy selectively chromophores absorbing at specific wavelengths, using absorption spectroscopy to follow the absorption losses with irradiation time. The results provide unequivocal evidence that the absorption and emission spectra of these materials cannot result solely from a simple linear superposition of the spectra of numerous independent chromophores. Instead, the long wavelength absorption tail of HS (>350 nm) appears to arise from a continuum of coupled states. We propose that this behavior results from intramolecular charge-transfer interactions between hydroxy-aromatic donors and quinoid acceptors formed by the partial oxidation of lignin precursors. We further propose that these donor-acceptor interactions may be a common phenomenon, occurring within all natural hydroxy- or polyhydroxy-aromatic polymers that form appropriate acceptors upon partial oxidation. Examples of such species include lignin, polyphenols, tannins, and melanins.