An ONIOM-XS MD simulation has been performed to characterize the CH₃NH₃⁺-water hydrogen bonds (HBs) in aqueous solution. The sphere which includes the CH₃NH₃⁺ ion and its surrounding waters was treated by the HF/DZP method, while the rest was described by classical pair potentials. The ONIOM-XS MD results clearly reveal a flexible CH₃NH₃⁺ solvation, showing various numbers of water molecules, ranging from 3 to 8 and from 12 to 19, cooperatively involved in the primary region of the -NH₃⁺ and -CH₃ species, respectively. The –NH₃⁺ group participates in about 3.6 HBs with its nearest-neighbor waters, and the HBs between the –NH₃⁺ hydrogens and their nearest-neighbor waters are relatively weaker than the HBs of bulk water. It is evident that the “hydrophobic effect” of the –CH₃ species results in slightly more attractive water-water HB interactions in this region. Such phenomenon corresponds to a clear “structure-breaking” ability of CH₃NH₃⁺ in aqueous solution.

中文翻译：

---

电解质水溶液中甲基铵离子（CH ₃ NH ₃ ⁺）的特性：ONIOM-XS MD模拟研究

已经进行了ONIOM-XS MD模拟，以表征水溶液中的CH ₃ NH ₃ ^+-水氢键（HBs）。通过HF / DZP方法处理了包含CH ₃ NH ₃ ⁺离子及其周围水域的球体，而其余​​部分则通过经典对势进行了描述。ONIOM-XS MD结果清楚地揭示了一种灵活的CH ₃ NH ₃ ⁺溶剂化作用，表明在-NH ₃ ⁺和-CH的主要区域中协同参与了3至8个和12至19个不同数量的水分子分别为₃种。–NH ₃ ⁺该组成员与其近邻水域共参与约3.6 HBs，–NH ₃ ⁺氢与其近邻水域之间的HBs相对弱于散水的HBs。显然，–CH ₃物种的“疏水作用”导致该区域水-水HB相互作用更具吸引力。这种现象对应于水溶液中CH ₃ NH ₃ ⁺的明显的“破坏结构”能力。