Abstract
Cyclic dipeptides show interesting biological activities such as antitumor, antiviral and so on. In biological systems, the bioavailability of drugs is determined by several parameters such as pKa values. In this study, we used DFT and thermodynamics cycle to determine pKa value of side chain of lysine in linear and cyclic dipeptides. All considered dipeptides were optimized using B3LYP and RMSD tool was used to compare the optimized structures. The calculated pKa values were compared with the available experimental data. Our results show that pKa of side chain of lysine increases for cyclic dipeptides compared to the linear ones. To justify the reason of increasing of pKa of cyclic dipeptides, we used NBO and AIM analyses. The analyses showed that a hydrogen bond in cyclic lysine dipeptides is responsible for increasing of pKa.
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