FIZIKA A 14 (2005) 1 , 9-18

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EPR SPECTROSCOPY OF SUPERHYPERFINE INTERACTION IN THE COPPER PARAMAGNETIC CENTER IN THE CRYSTAL OF CYTOSINE MONOHYDRATE

DUBRAVKA KRILOVa, ANDRICA LEKIĆ b, ERIM BEŠIĆ c, VJERAN GOMZIc
and JANKO N. HERAKc

aMedical School, University of Zagreb, Šalata 3b, 10001 Zagreb, Croatia
bMedical School, University of Rijeka, B. Branchetta 20, 51000 Rijeka, Croatia
cFaculty of Pharmacy and Biochemistry, University of Zagreb, A. Kovačića 1, 10001 Zagreb, Croatia

Dedicated to the memory of Professor Vladimir Šips

Received 28 January 2005;   revised manuscript received    11 April 2005
Accepted 18 April 2005      Online 21 October 2005

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.

PACS numbers: 76.30.-v
UDC 538.955

Keywords: copper complex, cytosine, EPR spectroscopy, superhyperfine interaction

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