Solvent effects on the spectroscopic properties of Damascone derivatives: A sequential Monte Carlo/Quantum Mechanics study

Molecular dynamic simulations, GIAO‐NMR and TD‐DFT spectroscopy analyze for zwitterionic isoleucine (ILE)N, 1 ≤ N ≤ 6, in water solution

“…This difference is observed by the fact that the CHARMM36 model addresses a standardized repeating mechanics for amino acids as N grows and therefore does not consider interactions that can reshape the electronic distribution. In this sense, it is important to highlight that polarized charge models in solution tend to better describe spectroscopic properties as can be seen in several previous works 29,31,43,44,53 , especially for NMR spectroscopy which is strongly related to the electronic distribution of the structure 25,26 , as observed for neutral and charged polymers. Despite these modifications, the CHARMM36 description for the dipole moment is very similar to that observed in DFT calculations (treating the solvent as point charges).…”

“…In this work, we have developed a theoretical study using molecular dynamics to generate (ILE) N , N = 1 to 6, molecular configurations in water and density functional theory to determine NMR spectroscopic results and absorption spectrum of these structures. The charge point model for the solvent has been used and shows to be a good approximation to include the solvent effects on the quantum calculations performed 29–31,44 . The use of molecular dynamics allows the study to have a richer analysis, also contributing to estimate the conformational effects of (ILE) N structures on spectroscopic results.…”

“…In these configurations, the molecule of interest was centered in the simulation box and all water molecules were treated as point charges using the atomic charges of the water TIP3P 40 model. Point charge treatment for solvent have shown efficiency in describing solvent effects in solvated systems as can be seen previous works 29,30,42–44 . Thus, for each ILE molecules, 100 quantum calculations were performed to obtain spectroscopic properties.…”

“…The charge point model for the solvent has been used and shows to be a good approximation to include the solvent effects on the quantum calculations performed. [29][30][31]44 The use of molecular dynamics allows the study to have a richer analysis, also contributing to estimate the conformational effects of (ILE) N structures on spectroscopic results. Our theoretical NMR results show good comparison with experimental results for oxygen atoms showing differences of only 2 ppm.…”

“…For the choice of this basis set functions and methodology, we have considered the number of the quantum mechanics calculations that should be performed during the work and, especially, the possibility of comparing the smallest structure (ILE) 1 results with the largest structure (ILE) 6 . 29,31,43,44,53 , especially for NMR spectroscopy which is strongly related to the electronic distribution of the structure 25,26 , as observed for neutral and charged polymers. Despite these modifications, the CHARMM36 description for the dipole moment is very similar to that observed in DFT calculations (treating the solvent as point charges).…”