Kuantum mekanığı metodları kullanarak, bazı pirimidin türevlerinin dna nükleo bazlarıyla tepkimelerinin incelenmesi

Quantum mechanical calculations employing DFT/B3LYP method and (3-21G, 6-31G, 6-31G++dp and aug-cc-pVDZ) basis sets are conducted to investigate the properties of the pyrimidine and its derivatives with the DNA (Adenine, Guanine, Cytosine and Thymine). The bond lengths, bond angles, total energy, dipole moment and HOMO-LUNO were calculated and the results were very good comparing to the experimental data, and generally the biggest basis sets (6-31G++dp and aug-cc-pVDZ) were the most accurate. The pyrimidines have very important biological properties as chemotherapeutic agents, in addition to pyrimidines, cisplatin has a wide use as an anticancer agent. Hence, in this work novel complexes of platinum (II) with some DNA nucleobases (Adenine and Cytosine) were designed and optimized using DFT/B3LYP method and (3-21G, 6-31G, 6-31G++dp, and 6-311G) basis sets for (Carbon, Chlorine, Nitrogen, Oxygen and Hydrogen) atoms, for platinum atom two basis sets have been used, Stuttgart/Dresden (SDD) basis set is used for outer shell electrons, and Los Alamos National Laboratory 2 (LANL2) basis set (effective core potentials) is used for the core electrons. The calculations of frequency showed positive result for all complexes (no imaginary frequency) so all complexes are expected to be stable. Also, the bond lengths and bond angles of the complexes were compared to the experimental data of cisplatin and they have a good agreement. Moreover, the dihedral values showed a good square planar geometry for Adenine complexes and some distortion in Cytosine complex. In the HOMO orbitals, electrons are localized mainly in the (Cl) leaving group of the complex, meanwhile in the LUMO orbitals, electrons are localized mainly over the ligand molecular part for all three complexes. Finally, the reaction pathway of synthesizing one of these three complexes has been studied and it is predicted to be non-spontaneous process with two steps, for the first step ∆G1=4.79 Kcal/Mol, and for second step ∆G2=11.94 Kcal/Mol. KEYWORDS: DFT, Cisplatin, DNA, Adenine, Guanine, Cytosine, Thymine, Pyrimidine, Quantum mechanical methods, Platinum (II) complexes.