当前位置: X-MOL 学术ACS Earth Space Chem. › 论文详情
Our official English website, www.x-mol.net, welcomes your feedback! (Note: you will need to create a separate account there.)
Density Functional Theory Predictions of Noncovalent Hydrogen Isotope Effects during Octane Sorption to a Kaolinite Surface
ACS Earth and Space Chemistry ( IF 3.4 ) Pub Date : 2020-09-02 , DOI: 10.1021/acsearthspacechem.0c00148
Allison C. Fox 1 , Jason D. Boettger 2 , James D. Kubicki 2 , Katherine H. Freeman 1
Affiliation  

Interactions with mineral surfaces are crucial to the short- and long-term survival of organic compounds in the natural environment. The weak interactions that drive sorption of organic phases to mineral surfaces have the potential to impart H isotope effects that could complicate the interpretation of 2H/1H signatures in modern and ancient organic materials. The influence of hydrophobic interactions on H isotope signatures of n-octane during sorption to a kaolinite surface was studied using diffuse reflectance infrared Fourier transform spectroscopy (DRIFTS). These experimental results were compared to both harmonic and anharmonic vibrational frequencies calculated with density functional theory (DFT) to determine the role of anharmonicity in predicting isotope effects during noncovalent interactions of the molecule and mineral surface. The experimental results showed a relatively minor (<2‰) 2H-depletion of the sorbed octane, indicating that hydrophobic interactions do not impart significant isotope effects during sorption. Comparisons of the experimental and computational results highlighted the importance of anharmonic contributions to the direction of noncovalent isotope effects. Calculations that incorporated anharmonicity predicted a 3.5‰ depletion of sorbed octane, whereas purely harmonic calculations predicted a 0.9‰ enrichment. Differences in C–1H and C–2H bond lengths influence the molecular polarizability, surface area, and molar volume. The longer C–1H bonds are more hydrophobic and interact with the kaolinite surface more strongly, leading to a slight 2H depletion in sorbed octane. Harmonic approximations cannot account for differences in bond length and are insufficient for predicting noncovalent isotope effects caused by hydrophobic intermolecular interactions.

中文翻译:

密度泛函理论预测辛烷对高岭石表面吸附过程中非共价氢同位素效应

与矿物表面的相互作用对于有机化合物在自然环境中的短期和长期生存至关重要。促使有机相吸附到矿物表面的弱相互作用可能会赋予氢同位素效应,这可能会使现代和古代有机材料中2 H / 1 H特征的解释变得复杂。疏水相互作用对n-的H同位素特征的影响使用漫反射红外傅里叶变换光谱(DRIFTS)研究了吸附到高岭石表面上的辛烷值。将这些实验结果与使用密度泛函理论(DFT)计算的谐波和非谐振动频率进行比较,以确定非谐性在预测分子与矿物表面非共价相互作用过程中同位素效应中的作用。实验结果显示相对较小(<2‰)2吸附的辛烷的H耗竭,表明疏水作用在吸附过程中不会产生明显的同位素效应。实验和计算结果的比较突出了非谐贡献对非共价同位素效应方向的重要性。结合了非谐性的计算预测吸附的辛烷值将减少3.5‰,而纯谐波计算预测的吸附度将达到0.9‰。C- 1 H和C- 2 H键长的差异会影响分子极化率,表面积和摩尔体积。较长的C– 1 H键更具疏水性,并且与高岭石表面的相互作用更强,导致轻微的2吸附的辛烷中的氢耗竭。谐波近似不能解释键长的差异,并且不足以预测由疏水性分子间相互作用引起的非共价同位素效应。
更新日期:2020-10-16
down
wechat
bug