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首页> 外文期刊>Journal of Agricultural and Food Chemistry >Complementary Multianalytical Approach To Study the Distinctive Structural Features of the Main Humic Fractions in Solution: Gray Humic Acid, Brown Humic Acid, and Fulvic Acid
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Complementary Multianalytical Approach To Study the Distinctive Structural Features of the Main Humic Fractions in Solution: Gray Humic Acid, Brown Humic Acid, and Fulvic Acid

机译：互补多重分析方法，用于研究溶液中主要腐殖质组分（灰色腐殖酸，棕色腐殖酸和黄腐酸）的独特结构特征

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Previous studies have indicated that the main fractions of humic substances (HS), gray humic acid (GHA), brown humic acid (BHA), and fulvic acid (FA), present different molecular patterns in water solution that are probably associated with specific structural features. However, the techniques used in these previous studies did not permit clarification of the principal qualitative characteristics of these structures. To study more in depth this subject several GHA, BHA, and FA have been analyzed through the complementary use of UV-visible and FTIR spectroscopy, ~(13)C NMR, thermogravimetry, and pyrolysis GC-MS. The results indicate that the studied humic fractions have different and distinctive structural features. Thus, large and nonpolar structural units (paraffins, olefins, terpenes) and aliphatic structures seem to accumulate in the gray fraction, whereas the smallest and more polar (furfural, phenols) and simpler structural units (sugar- and amino acid-related structures) are present in the fulvic one. BHA has a higher content in polycyclic aromatic moieties, S-containing compounds and aromatic structures, thus suggesting the presence of more condensed aromatic rings/Likewise, differences in both the presence of polar groups and the apparent molecular size explain the pattern of solubility as a function of pH and ionic strength (I) that defines each HS fraction. These results also indicate that the structural differences among the HS fractions are not only quantitative (the presence of the same type of structures differing in size and the concentration of functional groups) but also qualitative, because each fraction presented different and distinctive structural domains. These structural domains explain the molecular patterns associated with each HS fraction. Thus, the presence of smaller and more O-functionalized structural units including aromatic domains in FA explain their tendency to form molecular aggregates (hydrogen bridges, metal bridges, and hydrophobic interactions) in solution. This fact could also explain the presence of molecular aggregates in BHA, although to a lesser extent than in FA. Finally, the dominant aliphatic and less functionalized character of GHA may justify its lower tendency to form aggregates in solution at neutral and alkaline pH. Likewise, the results also indicate that the different structural domains associated with these fractions may be the consequence of diverse biosynthetic pathways involving different precursors.
机译：先前的研究表明，腐殖质（HS），灰色腐殖酸（GHA），棕色腐殖酸（BHA）和富里酸（FA）的主要部分在水溶液中呈现出不同的分子模式，这可能与特定的结构有关特征。但是，这些以前的研究中使用的技术不能澄清这些结构的主要定性特征。为了更深入地研究该主题，通过互补使用紫外可见光谱和FTIR光谱，〜（13）C NMR，热重分析和热解GC-MS对几种GHA，BHA和FA进行了分析。结果表明，所研究的腐殖质组分具有不同而独特的结构特征。因此，大的和非极性的结构单元（石蜡，烯烃，萜烯）和脂肪族结构似乎在灰色部分中积累，而最小且极性更大的（糠醛，酚）和更简单的结构单元（与糖和氨基酸相关的结构）存在于fulvic中。 BHA在多环芳族部分，含S的化合物和芳族结构中含量较高，因此表明存在更稠合的芳环/类似地，极性基团的存在和表观分子大小的差异解释了溶解度的变化。定义每个HS分数的pH和离子强度（I）的函数。这些结果还表明，HS馏分之间的结构差异不仅是定量的（存在相同类型的结构，其大小和官能团的浓度不同），而且是定性的，因为每个馏分都呈现出不同且独特的结构域。这些结构域解释了与每个HS片段相关的分子模式。因此，FA中包含芳族结构域的较小且更多的O-官能化结构单元的存在解释了它们在溶液中形成分子聚集体（氢桥，金属桥和疏水相互作用）的趋势。这个事实也可以解释BHA中分子聚集体的存在，尽管程度要比FA中小。最后，GHA的主要脂肪族和功能化程度较低的特征可证明其在中性和碱性pH值下在溶液中形成聚集体的倾向较低。同样，结果还表明与这些级分相关的不同结构域可能是涉及不同前体的多种生物合成途径的结果。

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