DFT Study of the Adsorption of Aspartic Acid on Pure, N-Doped, and Ca-Doped Rutile (110) Surfaces

Understanding the interaction mechanism between titanium oxide surfaces and proteins/peptides/amino acids is crucial to the success of Ti implants. Aspartic acid (abbreviated as Asp or D) is one of the most abundant amino acid in nature. In this study, Dmol(3), a quantum mechanics first-principles density functional theory code, was employed to investigate the interaction of Asp with pure, nitrogen-doped, and calcium-doped rutile (R(110)) surfaces. The effect of water on the interaction was also studied. The adsorption energy analysis demonstrated that the strongest adsorption happened when both the amino and carboxyl groups of Asp approached the R(110) surfaces and formed a bidentate coordination to two surface Ti atoms. Hydrogen bonds from the H atoms of Asp and bridging-O atoms on the surface also contributed to the adsorption. Water hindered the Asp adsorption. N-doping and Ca-doping were not beneficial to Asp adsorption. The results imply that we may realize selective protein/peptide/amino acid adsorption on materials and determine the adsorption of specific biomolecules by an elaborately designed ion doping process. Our results could have potential impact on the design of effective material surface treatments for biomedical applications.