Structural environments of carboxyl groups in natural organic molecules from terrestrial systems. Part 1: Infrared spectroscopy
Structural environments of carboxyl groups in natural organic molecules from terrestrial systems. Part 1: Infrared spectroscopy
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DOI：
10.1016/j.gca.2007.03.038
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发表时间：
2007-07-15
影响因子：
5
通讯作者：
Myneni, Satish C. B.
中科院分区：
文献类型：
--
作者：
Hay, Michael B.;Myneni, Satish C. B.
羧基在环境中的天然有机分子化学中起着重要的作用，其行为依赖于大分子内的局部结构环境。我们研究了溶解NOM的结构环境中的羧基从松树贫瘠（新泽西，美国），和IHSS NOM分离物从土壤和河流沃茨使用衰减全反射傅里叶变换红外（ATR-FTIR）光谱。它是公认的羧酸根阴离子（COO-）的不对称伸缩振动的能量是敏感的羧基的结构环境。这些能量是从以前的小有机酸的各种各样的羧基结构环境的红外研究编译和比较的NOM样品的羧基光谱特征。我们发现，所有NOM样品的不对称伸缩峰发生在以1578 cm（-1）为中心的窄范围内，这表明所有NOM样品主要含有非常相似的羧基结构，与样品来源和所采用的分离技术无关。含有羟基的小脂肪酸（例如，D-乳酸盐、葡萄糖酸盐）、醚/酯（甲氧基乙酸酯、乙酰氧基乙酸酯）和羧酸酯α-碳上的（丙二酸酯）取代，以及水杨酸芳族酸（邻-OH）和呋喃羧酸盐（O-杂环），表现出与NOM范围的强烈重叠，不对称峰的宽度表明NOM中主要羧基构型之间的结构不均匀性，小了然而，在远离1578 cm-1处的峰的能量处，峰面积随pH值的变化可能表明一小部分其他芳香族羧基和脂肪族结构缺乏α-取代。这些信息对于理解NOM-金属和矿物-表面络合以及建立腐殖物质的适当结构和机理模型非常重要。(C)2007爱思唯尔有限公司保留所有权利。
Carboxyls play an important role in the chemistry of natural organic molecules (NOM) in the environment, and their behavior is dependent on local structural environment within the macromolecule. We studied the structural environments of carboxyl groups in dissolved NOM from the Pine Barrens (New Jersey, USA), and IHSS NOM isolates from soils and river waters using attenuated total reflection Fourier-transform infrared (ATR-FTIR) spectroscopy. It is well established that the energies of the asymmetric stretching vibrations of the carboxylate anion (COO-) are sensitive to the structural environment of the carboxyl group. These energies were compiled from previous infrared studies on small organic acids for a wide variety of carboxyl structural environments and compared with the carboxyl spectral features of the NOM samples. We found that the asymmetric stretching peaks for all NOM samples occur within a narrow range centered at 1578 cm(-1) suggesting that all NOM samples examined primarily contain very similar carboxyl structures, independent of sample source and isolation techniques employed. The small aliphatic acids containing hydroxyl (e.g., D-lactate, gluconate), ether/ester (methoxyacetate, acetoxyacetate), and carboxylate (malonate) substitutions on the alpha-carbon, and the aromatic acids salicylate (ortho-OH) and furancarboxylate (O-heterocycle), exhibit strong overlap with the NOM range, indicating that similar structures may be common in NOM. The width of the asymmetric peak suggests that the structural heterogeneity among the predominant carboxyl configurations in NOM is small. Changes in peak area with pH at energies distant from the peak at 1578 cm-1, however, may be indicative of a small fraction of other aromatic carboxyls and aliphatic structures lacking alpha-substitution. This information is important in understanding NOM-metal and mineral-surface complexation, and in building appropriate structural and mechanistic models of humic materials. (C) 2007 Elsevier Ltd. All rights reserved.