Boron is an essential plant micronutrient responsible for several important functions. Boron availability in soils may be influenced by binding with soil organic matter (SOM), particularly with aromatic diol and polyphenol groups on SOM. The mechanism by which aromatic diols bind boron, however, remains unclear. The objective of this work is to further investigate interaction between boric acid and varying concentrations of an aromatic, polyphenolic SOM analogue (tannic acid at 5, 10 and 20 g L⁻¹) from pH = 5–9. UV/Visible spectroscopy showed boric acid enhanced tannic acid deprotonation at pH = 7.0 and 9.0, resulting in singly deprotonated tannic acid subunits. Attenuated total reflectance-Fourier transform infrared spectroscopy (ATR-FTIR) showed boric acid/tannic acid binding for all concentrations at pH = 7 and 9, whereas binding at pH = 5.0 was observed only at 20 g L⁻¹ tannic acid. Uncomplexed boron species were not evident at pH = 9.0, but were detectable at pH = 7.0 at lower tannic acid concentrations and prevalent at pH = 5.0, qualitatively indicating binding affinity increases from pH = 5.0 to 9.0. ATR-FTIR results indicated tetrahedral coordination of boron upon complexation to tannic acid with a monodentate mechanism. These results collectively highlight a transition of solution planar boric acid to a tetrahedral, monodentate coordination with a single phenol group in tannic acid polyphenols. This contrasts with previous spectroscopic studies, which indicated bidentate tetrahedral or monodentate trigonal planar orientations prevail at aromatic diol sites. This work presents a previously unobserved boric acid coordination mechanism to an SOM analogue and, therefore, may better inform prediction and modeling of boron behavior in soils.

硼是一种重要的植物微量营养素，具有多种重要功能。土壤中硼的有效性可能受到与土壤有机质（SOM）的结合的影响，特别是与SOM上的芳香族二醇和多酚基团的结合。但是，尚不清楚芳族二醇与硼结合的机理。这项工作的目的是进一步研究硼酸与各种浓度的芳香族多酚SOM类似物（5、10和20 g L ^-1的鞣酸）之间的相互作用。），pH值为5–9。紫外/可见光谱法显示，硼酸在pH = 7.0和9.0时增强了单宁酸的去质子化作用，从而导致单去质子化的单宁酸亚基。衰减的全反射傅里叶红外光谱（ATR-FTIR）显示，硼酸/鞣酸在pH = 7和9的所有浓度下均具有结合力，而在pH = 5.0时仅在20 g L ^-1时才观察到结合力单宁酸。未络合的硼物质在pH = 9.0时不明显，但在较低的鞣酸浓度下在pH = 7.0时可检测到，并在pH = 5.0时普遍存在，定性表明结合亲和力从pH = 5.0增加到9.0。ATR-FTIR结果表明，以单齿机理与硼酸络合后，硼的四面体配位作用。这些结果共同突出了单宁酸多酚中平面硼酸溶液向单面配位的四面体单齿配位的过渡。这与以前的光谱研究相反，后者表明二齿四面体或单齿三角平面取向普遍存在于芳族二醇位点。这项工作为SOM类似物提出了以前未曾观察到的硼酸配位机制，因此，