Theoretical Study On Intramolecular Proton Transfer For2-substituted Benzoxazole Compounds With Alkali(earth) Metal Ions

Proton transfer as one of the basic reaction of chemical and biochemical systems,exist in a variety of chemical and biochemical processes. The alkaline and alkalineearth metal cations, e.g., Li⁺, Na⁺, K⁺, Be²⁺, Mg²⁺, Ca²⁺, as the importantmicroelement, play a very important role in living matters. For example, the synthesis,replication, and cleavage of DNA or RNA are somewhat affected by these cations. Inthis dissertation, the interaction between the metal ions and2-substituted benzoxazolecompounds, and the effect of the metal ions on intramolecular proton transfer havebeen studied by using quantum chemical computation. The main results are asfollows:1、The coupling characteristics of2-（3′-hydroxy-2′-pyridyl）benzoxazole （HPyBO）with alkaline （earth） metal ions and its intramolecular proton transfer were studied atthe B3LYP/6-311++G（d,p） level. The results show that alkaline （earth） metal ions canform monodentate or bidentate complexes with HPyBO. In addition, the metal ionscause the intramolecular hydrogen bond lengths of HPyBO change. The effects aredifferent with coupling orientation of the metal ions. The energy decompositionanalysis show that there are some different for binding energies between alkalinemetal complex and alkaline earth metal complex. The total binding energies mainlycome from the ΔEelstatfor alkaline metal ion complexes and from the ΔEoifor alkalineearth metal ion complexes. The relative energies and the barrier heights reveal that theproton transfer is more difficult for bidentate complex which is relatively stable and iseasier for monodentate complex which is relatively unstable.2、The36kinds of initial structure of cation-π complexes of alkaline （earth）metal ions and HPyBO were optimized at B3LYP/6-311++G（d,p） level and18stablecation-π complexes were obtained. The results show that alkaline metal ions are easierto characterized a cation-π complexes than alkaline earth metal ions. The results ofbinding energies show that the interaction between alkaline earth metal ions andHPyBO are very strong, even reached the strength of normal chemical bond. Therelative energies of the complexes reveal that the presence of alkali （earth） metal ionscan change the energy barrier of intramolecular proton transfer process in HPyBO,and can even cause the advantage configuration inversion. 3、 The coupling characteristics of2-（3′-mercapto-2′-pyridyl）benzoxazole（SPyBO） with alkaline （earth） metal ions and its intramolecular proton transfer werestudied at the B3LYP/6-311++G（d,p） level. The results show that the alkali （earth）metal ions mainly couple with S2, N5, O6and N8of SPyBO characterizedmonodentate or bidentate complexes. The relative energies and the barrier heightsreveal that the presence of the metal ions hindered the intramolecular proton transferprocess of SPyBO, make the enolic form S1more stable.4、 The density functional theory method have been used to study cation-πinteraction between2-（3′-mercapto-2′-pyridyl）benzoxazole （SPyBO） and alkaline（earth） metal ions. Results show that the cation-π interactions between SPyBO andalkaline （earth） metal ions are very strong, even reached the strength of normalchemical bond. The properties at the BCPs （Bond Critical Points） of intramolecularhydrogen bond in the complexes using the atoms in molecules theory （AIM）. Theresults show that there is a relationship between intramolecular hydrogen bond andintramolecular proton transfer, that is more stronger the intramolecular hydrogen bondis, more easily the intramolecular proton transfer. The studies of intramolecularproton transfer mechanism reveal that the presence of alkali （earth） metal ions canpromote or hinder the intramolecular proton transfer process in SPyBO, and can evencause the advantage configuration inversion.