ERP spektroskopija suprahiperfinog međudjelovanja bakarnog paramagnetskog centra u kristalima citozin monohidrata

The planar complex of Cu(II) with two cytosine bases was formed by gamma irradiation of the cytosine monohydrate crystal, containing copper impurities. The paramagnetic complex was probably formed by trapping the radiation-induced migrating holes by Cu(I), that is originally present in the crystal lattice. The structure of the complex was analyzed from the superhyperfine pattern of its EPR spectra. The experimentally evaluated tensor elements of the three 14N couplings and the observation of an additional proton coupling unequivocally confirm the structure. The ab initio B3LYP density functional method calculations are in good agreement with the experiments. Both experiments and the calculations demonstrate large spin delocalization in the cytosine ring plane.Gama ozračivanjem kristala citozin monohidrata, koji je sadržavao bakarne nečistoće, pripremali smo planarni kompleks Cu(II) s dvije citozinske baze. Paramagnetski se kompleks vjerojatno stvarao vezanjem zračenjem proizvedenih šupljina i Cu(I) koji je prvotno bio u kristalnoj rešetci. Proučavali smo strukturu kompleksa analizirajući suprahiperfinu strukturu njegovog EPR spektra. Eksperimentalno određeni elementi tenzora triju vezanja 14N i opažanje dodatnog protonskog vezanja pouzdano potvrđuju strukturu. Ab initio B3LYP računi metodom funkcionala gustoće u dobrom su slaganju s mjerenjima. Eksperimenti i računi pokazuju jaku delokalizaciju spina u ravnini citozinskog prstena

A new cytosine-copper paramagnetic complex spectroscopic study

Two different copper complexes with cytosine molecules are formed in the process of crystal growth from the aqueous solution with traces of copper. One of them is diamagnetic, turning into paramagnetic upon ionizing irradiation (complex I). The other, the subject of the present study, is paramagnetic (complex II) as prepared. For complex II, EPR spectra demonstrate that the copper ion is coordinated with one nitrogen atom and three oxygen atoms. On the basis of the detailed EPR spectroscopic analysis and quantum-chemical calculations (in the DFT approach) the model of the complex has been proposed. Both experimental data and the theoretical results support the model with the copper atom, located between the two cytosine ribbons, ligated to a nitrogen and an oxygen atom from two opposing cytosine molecules and two oxygen atoms from water molecules. For complex II the Raman spectra demonstrated concerted restructuring of the hydrogen bonding in the cytosine crystal matrix upon insertion of copper ions