Kelch Sabrina E, Barrios-Cerda Benjamin, Park Yeonsoo, Ferrage Eric, Aristilde Ludmilla
Department of Biological and Environmental Engineering, College of Agriculture and Life Sciences, Cornell University, Ithaca, NY 14853, USA.
Department of Civil and Environmental Engineering, McCormick School of Engineering and Applied Science, Northwestern University, Evanston, IL 60208, USA.
PNAS Nexus. 2025 Aug 9;4(8):pgaf259. doi: 10.1093/pnasnexus/pgaf259. eCollection 2025 Aug.
Clay minerals are well documented to facilitate the retention of water and organic matter in terrestrial soils, Martian regolith, and meteorites. Yet, the mechanisms underlying water trapping within these mineral-organic matter associations are poorly understood. Here, we investigate these mechanisms with montmorillonite, a smectite clay, populated with carbohydrates of different structures. By capturing relative proportion of bound versus freely exchangeable waters by mass spectrometry during thermogravimetric analysis, we observe up to a 2.3-fold increase in bound waters in samples with adsorbed carbohydrates. Temperature-dependent carbon loss from adsorbed C-labeled carbohydrate determines increase in carbohydrate trapping at low moisture. We determine that the amount of trapped organic carbon is correlated positively with the population of bound waters. Molecular dynamics simulations of a carbohydrate-populated clay nanopore identify different interfacial waters, involving direct single or multiple hydrogen bonds on the clay surface without or with simultaneous hydrogen bonding with adsorbed carbohydrates. Quantum mechanics-based computations highlight up to 5-fold greater binding energy for bound waters associated with adsorbed carbohydrates on the clay surface, compared to bound waters in the absence of carbohydrates. Thus, our experimental and theoretical results collectively reveal that interfacial waters bridging hydrated organic matter to the clay surface facilitate water trapping within mineral-organic associations.
黏土矿物在促进陆地土壤、火星风化层和陨石中水分和有机物的保留方面已有充分记录。然而，这些矿物 - 有机物结合体中截留水分的潜在机制却鲜为人知。在此，我们用蒙脱石（一种蒙脱石黏土）与不同结构的碳水化合物结合来研究这些机制。通过在热重分析过程中用质谱法捕获结合水与自由交换水的相对比例，我们观察到吸附了碳水化合物的样品中结合水增加了2.3倍。吸附的C标记碳水化合物随温度的碳损失决定了在低湿度下碳水化合物截留量的增加。我们确定截留的有机碳量与结合水的含量呈正相关。对充满碳水化合物的黏土纳米孔进行分子动力学模拟，识别出不同的界面水，包括在黏土表面直接形成单个或多个氢键，且不与或同时与吸附的碳水化合物形成氢键。基于量子力学的计算表明，与没有碳水化合物时的结合水相比，黏土表面吸附碳水化合物的结合水的结合能高出5倍。因此，我们的实验和理论结果共同表明，将水合有机物与黏土表面连接起来的界面水促进了矿物 - 有机物结合体中的水分截留。
