Abstract
Introduction: Understanding the binding mechanism between gold and is a fundamental step for numerous applications in biosensors and targeted drug delivery. This study aims to clarify the adsorption behaviors of CYS and GSH on the gold surface using a small gold Au8 cluster as a model reactant.
 Methods: Here, we examine in details the molecular interaction between Au8 cluster with (CYS) and (GSH) by means of density functional theory (DFT). The PBE functional is employed in combination with the basis set for non-metal atoms and the basis set for gold. Harmonic frequencies are also computed to confirm optimized geometries as local minima or transition states on the potential energy surfaces.
 Results: The calculated results show that these molecules prefer to anchor on the gold cluster via the sulfur atom with the adsorption energies of 20.3 and 30.8 / for CYS and GSH, respectively, in gas phase. In water, such values are considerably reduced, namely 19.0 / for CYS and 26.4 / for GSH. If a visible light with a frequency of v = 6x1014 Hz (500 nm) is applied, the time for the recovery of CYS and GSH from the most stable complexes will be about 1.24 and 6.03x107 seconds at 298 K in gas phase.
 Conclusion: The Au8 cluster could be a promising material for designing sensor in CYS and GSH selective detection.
Highlights
Understanding the binding mechanism between gold nanoparticles and biomolecules is a fundamental step for numerous applications in biosensors and targeted drug delivery
Harmonic vibrational frequencies were computed to verify that optimized geometries are true local minima and to estimate the zero-point vibrational energy (ZPE) corrections
The structures, energetic properties and effects of water solution on the interaction of cysteine and glutathione molecules with the Au8 cluster was thoroughly examined by means of density functional theory (DFT) calculations
Summary
Understanding the binding mechanism between gold nanoparticles and biomolecules is a fundamental step for numerous applications in biosensors and targeted drug delivery. Results: The calculated results show that these molecules prefer to anchor on the gold cluster via the sulfur atom with the adsorption energies of 20.3 and 30.8 kcal/mol for CYS and GSH, respectively, in gas phase. In water, such values are considerably reduced, namely. According to Xie et al 12, the interaction between gold cluster Aun (n = 3, 4) with cysteine and glycine is stabilized mainly due to Au-NH2 bond via the transfer of charge from the amine group to the Au atom. Other striking finding is that gold clusters prefer to anchor on the terminal amide group 13–15
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