Rimola Albert, Sodupe Mariona, Tosoni Sergio, Civalleri Bartolomeo, Ugliengo Piero
Departament de Química, Universitat Autònoma de Barcelona, Bellaterra 08193, Spain.
Langmuir. 2006 Jul 18;22(15):6593-604. doi: 10.1021/la0610203.
The adsorption of a glycine molecule on a model silica surface terminated by an isolated hydroxyl group has been studied ab initio using a double-zeta polarized Gaussian basis set, the hybrid B3LYP functional, and a full periodic treatment of the silica surface/glycine system. The hydroxylated silica surface has been simulated using either a 2D slab or a single polymer strand cut out from the (001) surface of an all-silica edingtonite. A number of B3LYP-optimized structures have been found by docking glycine on the silica surface exploiting all possible hydrogen bond patterns. Whereas glycine is generally adsorbed in its neutral form, two structures show glycine adsorbed as a zwitterion, the surface playing the role of a "solid solvent" whereas intrastrand hydrogen bond cooperativity stabilizes the zwitterions. The adsorbed zwitterionic structures are no longer formed at a lower glycine coverage as simulated by enlarging the unit cell so as to break intrastrand hydrogen bonds, showing the importance of H-bond cooperativity in stabilizing the zwitterionic forms. Each structure has been characterized by computing its harmonic vibrational spectrum at the Gamma point, which also allowed us to calculate the free energy of adsorption. The experimental infrared features of chemical-vapor-deposited glycine on a silica surface are in agreement with those computed for glycine adsorbed in its neutral form and engaging three hydrogen bonds with the surface silanols, two of them involving the C=O bond and one originating from the glycine OH group. The NH(2) group plays only a minor role as a weak hydrogen bond donor.
使用双ζ极化高斯基组、混合B3LYP泛函以及对二氧化硅表面/甘氨酸体系进行全周期处理，从头算研究了甘氨酸分子在由孤立羟基终止的模型二氧化硅表面上的吸附。已使用二维平板或从全硅埃丁顿石（edingtonite）的（001）表面切出的单聚合物链来模拟羟基化的二氧化硅表面。通过利用所有可能的氢键模式将甘氨酸对接在二氧化硅表面上，发现了许多经B3LYP优化的结构。虽然甘氨酸通常以中性形式吸附，但有两种结构显示甘氨酸以两性离子形式吸附，表面起到“固体溶剂”的作用，而链内氢键协同作用稳定了两性离子。通过扩大晶胞以破坏链内氢键来模拟，在较低的甘氨酸覆盖度下不再形成吸附的两性离子结构，这表明氢键协同作用在稳定两性离子形式中的重要性。通过计算每个结构在Γ点的谐波振动光谱对其进行了表征，这也使我们能够计算吸附自由能。在二氧化硅表面上化学气相沉积的甘氨酸的实验红外特征与计算得到的以中性形式吸附并与表面硅醇形成三个氢键的甘氨酸的红外特征一致，其中两个氢键涉及C=O键，一个源自甘氨酸的OH基团。NH₂基团作为弱氢键供体仅起次要作用。
