Site specific interaction between ZnO nanoparticles and tryptophan: A first principles quantum mechanical study

First principles density functional theory calculations are performed on tryptophan-ZnO nanoparticles complex in order to study site specific interactions between tryptophan and ZnO. The calculated results find the salt bridge structure involving the -COOH group and ZnO cluster to be energetically more favorable than other interacting sites, such as indole and amine groups in tryptophan. The interaction between tryptophan and ZnO appears to be mediated by both ionic and hydrogen bonds. The calculated molecular orbital energy levels and charge distributions suggest non-radiative energy transfer from an excited state of tryptophan to states associated with ZnO, which may lead to a reduction in the emission intensity assigned to the π-π* transition of the indole functional group of tryptophan. © 2011 the Owner Societies

Tryptophan-Gold Nanoparticle Interaction: A First-Principles Quantum Mechanical Study

The nature of interaction between tryptophan (Trp) and gold (Au) nanoparticles is studied using first-principles density functional theory calculations and described in terms of equilibrium configurations, interaction energies, density of states, molecular orbitals, and charge density. The calculated results find the binding involving both carboxyl and indole functional groups with mixed salt–bridge and charge–solvation structure to be energetically preferred and is attributed to the stronger-than-expected π interactions facilitated by the indole group in Trp. In the Trp–Au conjugates, modification of the molecular orbitals associated with Trp occurs because states associated with Au and the hybrid orbitals have mixed metal–molecule character. We find that the nonradiative energy transfer from excited states of Trp to hybrid states of Trp–Au may reduce intrinsic fluorescence intensity of Trp in the conjugated system

First-principles study of nanoparticle-biomolecular interactions: Anchoring of a (ZnO) \u3c inf\u3e 12 cluster on nucleobases

We report the results of theoretical calculations on interaction of the nucleotide bases of deoxyribonucleic acid (DNA) and ribonucleic acid (RNA) with a (ZnO)12 cluster, carried out within density-functional theory framework. In all cases, (ZnO)12 prefers to bind with a ring nitrogen atom having a lone electron pair relative to the other possible binding sites of the bases. The degree of hybridization between Zn-d and N-p orbitals determines the relative interaction strength at the N-site of individual nucleobases with (ZnO)12 in contrast to the cases of interaction of metallic clusters and carbon nanostructures with nucleobases where either electrostatic or van der Waals interactions dominates the bonding characteristics of the conjugate complexes. The predicted site-preference of (ZnO)12 toward the nucleobases appears to be similar to that of the metal clusters, which indicates that the metal clusters retain their site-preference even in their oxidized state. © 2011 American Chemical Society