Abstract
Due to their vast range of promising biomedical and electronic applications, there is a growing interest in bioinorganic lamellar nanomaterials. MXenes are one such class of materials, which stand out by virtue of their demonstrated biocompatibility, pharmacological applicability, energy storage performance, and feasibility as single-molecule sensors. Here, we report on first-principles predictions, based on density functional theory, of the binding energies and ground-state configurations of six selected amino acids (AAs) adsorbed on O-terminated two-dimensional titanium carbide, Ti2CO2. We find that most AAs (aspartic acid, cysteine, glycine, and phenylalanine) prefer to adsorb via their nitrogen atom, which forms a weak bond with a surface Ti atom, with bond lengths of around 2.35 Å. In contrast, histidine and serine tend to adsorb parallel to the MXene surface, with their α carbon about 3 Å away from it. In both adsorption configurations, the adsorption energies are on the order of the tenths of an electronvolt. In addition, we find a positive, nearly linear correlation between the binding energy of each studied AA and its van der Waals volume, which suggests an adsorption dominated by van der Waals forces. This relationship allowed us to predict the adsorption energies for all of the proteinogenic AAs on the same Ti2CO2 MXene. Our analysis additionally shows that in the parallel adsorption mode there is a negligible transfer of charge density from the AA to the surface but noticeable in the N-bonded adsorption mode. In the latter, the isosurfaces of charge density differences show accumulation of shared electrons in the region between N and Ti, confirming the predicted N-Ti bond. The moderate adsorption energy values calculated, as well as the preservation of the integrity of both the AAs and the surface upon adsorption, reinforce the capability of Ti2CO2 as a promising reusable biosensor for amino acids.
Highlights
The isolation of graphene in 2004 triggered the beginning of an era of extensive study of dozens of families of two-dimensional (2D) materials.[1]
Using first-principles calculations based in the density functional theory (DFT) framework, we have predicted the adsorption behavior of amino acids on the MXene Ti2CO2
At T = 0 K, we found that most of the studied molecules prefer to adsorb via their amine N atom, chemically bound to a surface Ti atom, the latter being pulled towards the amino acids (AAs), sitting at a Ti-N distance of about 2.35 Å
Summary
The isolation of graphene in 2004 triggered the beginning of an era of extensive study of dozens of families of two-dimensional (2D) materials.[1] In 2011, a new class of 2D materials, comprising transition-metal nitrides, carbides, or carbonitrides, was reported for the first time.[2] Since these materials are obtained from MAX phases, with details on their synthesis and properties given in a recent review,[3] they were named MXenes. Ti2CO2 has been shown to be suitable for detecting amino acids (namely arginine) via adsorption,[22] and its interaction with lysozyme has been experimentally studied.[23] DNA molecules have been shown to be able to cross Ti2CO2 nanopores, and DNA transport studies through MXene membranes suggest the potential of this class of 2D materials for DNA translocation and single-molecule sensing applications.[24] the fact that Ti2CO2 contains the most biocompatible transition metal, makes it readily versatile for biomedical applications.[25]
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