Spin relaxation of stable 2,2,6,6-tetramethyl-4-oxypiperidine-1-oxyl radical on interaction in solutions with the porphyrin complexes with VO(II), Fe(III) Ni(II), Cu(II) and haemoglobin

The present paper on the basis of the experimental findings analyses the possibility of using the method of a paramagnetic probe (p.p.) for investigating the active metalloporphyrin centres of proteins and enzymes. The p.p. method is based on the phenomenon of relaxation of the spin-probe when it collides in solution with paramagnetic particles. This phenomenon is found from the widening of the components of the EPR spectrum of the spin-probe in the presence of paramagnetic compounds. In the work the authors studied the dependence of the experimentally observed parameters of relaxation on the nature of the metal-complex and the number and the nature of substituents in the porphyrin ring of the complexes. Iron-porphyrin complexes with mono-, di-, tri and tetracarbethoxyl groups in the porphyrin ring have been synthesized and characterized for the first time. Study of the interaction of the p.p. with haemoglobin suggests that in solution the active metalloporphyrin centres of haemoglobin are located in the protein globule. On the basis of the experimental findings outlined it is proposed that the method of the paramagnetic probe be used to investigate the active centres of protein and enzymes containing paramagnetic metal atoms.