A TD-DFT Study for the Excited State Calculations of Microhydration of N-Acetyl-Phenylalaninylamide (NAPA)

Investigating the impact of microhydration on excited-states and electronic excitation properties biomolecules has remained one important yet challenging aspects science because complexity developing models. However, with advent computational chemistry methods such as TD-DFT, many useful insights about energy excited-state nature can be explored. Accordingly, in our study, we have incorporated TD-DFT/wB97XD/cc-pVTZ method to study excited state N-acetyl phenylalanine amide (NAPA-A(H2O) n) (n = 1 4) clusters from ground tenth lowest gaseous singlet state. We found that C=O bond length gradually increases both N-terminal C-terminal after sequential addition water molecules intermolecular H-bonding this becomes weaker H2O molecules. The UV absorption maxima NAPA-A (H2O)n - consisted two peaks are S5←S0 (1st absorption) S6←S0 (2nd excitations. first were blue-shifted increase oscillator strength. This means strong H-bonds reduce charge transfer make more rigid. On other hand, second red-shifted decrease In ECD spectra, negative bands indicate presence an L-configuration micro hydrated clusters. Finally, calculated fluorescence confirm all (H2O) n 0 revert fluorescent by emitting around 5.490 eV light.