Regarding the significance of protein tyrosine and tryptophan nitration in the onset and progress of various chronic disorders, this study addressed ZnO nanoparticles (NPs) interaction with tyrosine and tryptophan and their nitrated counterparts. (ZnO)12 cage-like cluster was selected to model ZnO NPs, where the density functional theory was employed to determine the binding energy, active site and electronic structure of the bioconjugated systems. The results indicated the tendency of pristine amino acids to interact with (ZnO)12 through their aromatic ring; while the nitro group is the preferred site of nitrated amino acids. Comparison of electronic structure of (ZnO)12-Tyr/Trp with Tyr/Trp clearly explain the fluorescence quenching of tryptophan and tyrosine upon interaction with ZnO NPs. Emergence of new states above the Fermi level of (ZnO)12-nTyr/nTrp can result in unique response of ZnO nanoparticles to nitrated amino acids introducing small clusters of ZnO as promising candidates for detection of nitrosative stress-induced post-translation modifications leading to early diagnosis of different chronic disorders.

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