Ondruch Pavel, Kucerik Jiri, Steinmetz Zacharias, Schaumann Gabriele E
Institute for Environmental Sciences, Workgroup of Environmental and Soil Chemistry, University of Koblenz-Landau , Fortstr. 7, 76829 Landau, Germany.
J Phys Chem A. 2017 Mar 30;121(12):2367-2376. doi: 10.1021/acs.jpca.6b10207. Epub 2017 Mar 16.
Water molecules in soil organic matter (SOM) can form clusters bridging neighboring molecular segments (water molecule bridges, WaMBs). WaMBs are hypothesized to enhance the physical entrapment of organic chemicals and to control the rigidity of the SOM supramolecular structure. However, the understanding of WaMBs dynamics in SOM is still limited. We investigated the relation between WaMBs stability and the physicochemical properties of their environment by treating a sapric histosol with various solvents and organic chemicals. On the basis of predictions from molecular modeling, we hypothesized that the stability of WaMBs, measured by differential scanning calorimetry, increases with the decreasing ability of a chemical to interact with water molecules of the WaMBs. The interaction ability between WaMBs and the chemicals was characterized by linear solvation energy relationships. The WaMBs stability in solvent-treated samples was found to decrease with increasing ability of a solvent to undergo H-donor/acceptor interactions. Spiking with an organic chemical stabilized (naphthalene) or destabilized (phenol) the WaMBs. The WaMBs stability and matrix rigidity were generally reduced strongly and quickly when hydrophilic chemicals entered the soil. The physicochemical aging following this destabilization is slow but leads to successive WaMBs stabilization and matrix stiffening.
土壤有机质（SOM）中的水分子可形成簇，桥接相邻的分子片段（水分子桥，WaMBs）。据推测，水分子桥可增强有机化学物质的物理截留，并控制土壤有机质超分子结构的刚性。然而，对土壤有机质中水分子桥动力学的理解仍然有限。我们通过用各种溶剂和有机化学品处理腐泥质有机土，研究了水分子桥稳定性与其环境理化性质之间的关系。基于分子模拟的预测，我们假设通过差示扫描量热法测量的水分子桥稳定性，会随着一种化学物质与水分子桥中水分子相互作用能力的降低而增加。水分子桥与化学物质之间的相互作用能力通过线性溶剂化能关系来表征。发现在溶剂处理的样品中，水分子桥稳定性会随着溶剂进行氢供体/受体相互作用能力的增加而降低。添加有机化学品会使水分子桥稳定（萘）或不稳定（苯酚）。当亲水性化学物质进入土壤时，水分子桥稳定性和基质刚性通常会迅速大幅降低。这种失稳后的物理化学老化过程缓慢，但会导致水分子桥相继稳定和基质硬化。
