A Quantitative Structure-Property Relationship Study of the Adsorption of Amino Acids on Kaolinite Surfaces

1. Introduction

Clay minerals can process several reactions such as catalytic reaction and adsorption due to its physical and chemical characteristics (Borisover & Davis, 2015; McCabe & Adams, 2013; Shahidi, Roy, & Azzouz, 2015). Kaolinite is a kind of layered aluminosilicate, consisting of a SiO₄ tetrahedral sheet and an AlO₆ octahedral sheet. Many studies about the role of kaolinite on adsorption of organic compounds have been made (Michalková, Tunega, & Nagy, 2002; Michalkova Scott, Dawley, Orlando, Hill, & Leszczynski, 2012; Song, Wang, Qian, Zhang, & Zhang, 2013; Song, Zhong, Wang, Li, & Qian, 2014; Wang, Qian, Song, Zhang, & Dong, 2013). Song et al. (2014) used density functional theory (DFT) to investigate the interaction of amide molecules with kaolinite. They suggested that hydrogen bonds are formed between amide and hydroxyl groups of the Al-O surface or the basal oxygen atoms of the Si-O surface in kaolinite (Song et al., 2014). Wang et al. (2013) investigated the adsorption of 2,4-dinitrtoluene on kaolinite using the DFT method. Results showed that the adsorption of 2,4-DNT molecule is preferentially adsorbed on the Al-O surface of kaolinite because hydrogen bonds formed between. (Wang et al., 2013).

Amino acids widely spread in the soil environment owing to the decomposition of plant and animal residues (Dippold & Kuzyakov, 2013). The interaction between amino acid and clay mineral has been attracted enormous attention on the role of the metabolism of organic compounds and the synthesis of peptides in prebiotic periods (Aquino, Tunega, Gerzabek, & Lischka, 2004; Le Son, Suwannachot, Bujdak, & Rode, 1998). It is obvious that general mineral surface plays an important role on the origin of molecules of life (Hazen & Sverjensky, 2010). Therefore, investigating the adsorption of amino acids on clay mineral is the first job to study the origin of life.

In recent years, a great number of study probes the interaction between amino acids and clay minerals (Greenland, Laby, & Quirk, 1965; Lambert, Stievano, Lopes, Gharsallah, & Piao, 2009). Irrera et al. (2009) used the DFT theory to investigate the adsorption of glycine on ZnO (Irrera, Costa, & Marcus, 2009). They found that the carboxylic groups of glycine formed Zn-OCO-ZnO between two Zn atoms. Guo et al. (2011) also used DFT methods to study the adsorption of aspartic acid on rutile (Guo et al., 2011). When Asp approached the rutile surfaces (R(110)), both the amino and carboxyl groups formed a bidentate coordination to two surface. Ti atoms, the strongest adsorption occurred due to their adsorption energy analysis. The formation of hydrogen bonds between the H atoms of Asp and bridging-O atoms on the surface also contributed to the adsorption. However, for a series of amino acids, the properties related to the adsorption mechanism on kaolinite surface has not been investigated by theoretical calculations

Chang et al. (2014) has used four types of quantum-chemical reactivity descriptors, including electronic chemical potential, condensed local softness, atomic partial charge and the inverse of apolar surface, building a quantitative structure-property relationship (QSPR) and illustrated the four basic interactions (electron flow, polarization, electrostatic interaction and hydrophilic interaction) between volatile organic compounds (VOCs) and organoclay (Chang et al., 2014). For these reasons, the current study aims to investigate the adsorption energies of different types of amino acids interacting with kaolinite in the gas phase, and set up the QSPR models using molecular descriptors to study the adsorption mechanisms of a series of amino acids on kaolinite surfaces.