%0 Journal Article %T A Computational Study of Microhydrated N-Acetyl-Phenylalaninylamide (NAPA): Kinetics and Thermodynamics %A Mohammad Alauddin %A Mohammad Masud Parvez %A Mohammad Abdul Matin %J Computational Molecular Bioscience %P 63-74 %@ 2165-3453 %D 2023 %I Scientific Research Publishing %R 10.4236/cmb.2023.134005 %X The formations of [NAPA-A(H2O)n (n = 1, 2, 3, 4)] complexes have been studied employing DFT/wB97XD/cc-pVTZ computational level to understand the kinetics and thermodynamics for the hydration reactions of N-acetyl-phenylalaninylamide (NAPA). Thermodynamic parameters such as reaction energy (E), enthalpy (H), Gibb¡¯s free energy (G), specific heat capacity (Cv), entropy (S), and change of these parameters (¦¤Er, ¦¤Hr, ¦¤Gr, ¦¤Cr, and ¦¤Sr) were studied using the explicit solvent model. The predicted values of H, G, C, and S increase with the sequential addition of water in NAPA-A due to the increase in the total number of vibrational modes. On the other hand, the value of ¦¤Er, ¦¤Hr, and ¦¤Gr increases (more negative to less negative) gradually for n = 1, 2, 3, and 4 that indicates an increase of hydration in NAPA-A makes exothermic to endothermic reactions. The barrier heights for the transition states (TS) of [NAPA-A(H2O)n (n = 1, 2, 3, 4)] complexes are predicted to lie at 4.41, 4.05, 3.72 and 2.26 kcal/mol respectively below the reactants. According to the calculations, the formations of [NAPA-A(H2O)1] and [NAPA-A(H2O)2] complexes are barrierless reactions because both water molecules are strongly bonded via two hydrogen bonds in the backbone of NAPA-A. On the contrary, the reactions of [NAPA-A(H2O)3] and [NAPA-A(H2O)4] complexation are endothermic and the barrier heights are predicted to stay at 6.30 and 10.54 kcal/mol respectively above the reactants. The free energy of activation (¦¤‡G0) for the reaction of [NAPA-A(H2O)1], [NAPA-A(H2O)2], [NAPA-A(H2O)3], and [NAPA-A(H2O)4] complexation are 4.43, 4.28, 3.83 and 5.11 kcal/mol respectively which are very low. As well as the rates of reactions are 3.490 ¡Á 109 s-1, 4.514 ¡Á 109 s-1, 9.688 ¡Á 109 s-1, and 1.108 ¡Á 109 s-1 respectively which are very fast and spontaneous. %K Microhydration %K DFT %K Transition States %K Kinetics %K Thermodynamics %U http://www.scirp.org/journal/PaperInformation.aspx?PaperID=129773