Triplet States in DOPA-Melanin and in Its Complexes with Kanamycin and Copper Cu(II) Ions

Abstract

The mono-and biradical forms of DOPA-melanin (DOPA-eumelanin) were studied by EPR spectroscopy in 100-300 K temperature range. The existence of triplet states in DOPA-melanin was proved. The analysis of EPR spectra has shown that in DOPA-melanin and its complexes with kanamycin and Cu 2+ ions, two kinds of paramagnetic centres exist. The first of them are in doublet ground state with spin S = 1/2 and they obey the Curie law. The paramagnetic centres of the second group are in thermally excited triplet state with spin S = 1 and in this case the Curie law is not fulfilled.

Influence of Microwave Power on EPR Signal of Melanin Radical and Copper(II) Ions in DOPA-Melanin Complexes

“…In lower temperature besides paramagnetic centers with spin S = 1/2, there exist biradical forms with spin S = 1 [8]. The EPR method provides information about concentration of paramagnetic centers, about interaction spinspin and spinlattice, about surrounding of unpaired electrons, and shows changes in shape of EPR line under inuence of drugs and metal ions (diaand paramagnetic) added to melanin.…”

Determination of the fraction of paramagnetic centers not-fulfilling the Curie law in coal macerals by the two-temperature EPR measurement method

“…This method was used during examination of spin excitations of bitumens [11] and in searching of triplet states in DOPA-melanin and its complexes with kanamycin and copper Cu(II) ions [12]. The mathematical formula describing the temperature dependence of EPR line intensity I d connected with the paramagnetic centers in doublet state (S = ½) is presented in the form of the Curie law [11]: (1) where I d -line intensity generated by paramagnetic centers in doublet state (S = ½), a -constant, N d -number of paramagnetic centers in doublet state (S = ½), k -Boltzmann constant [J/K] and T [K] -temperature of measurement.…”

“…The temperature behavior of the EPR line intensity connected with paramagnetic centers in triplet state (S = 1) is given by the formula derived by Bleaney & Bowers [13]: (2) where I t denotes the line intensity generated by paramagnetic centers in triplet state (S = 1), N s-t is a sum of the number of centers in singlet (S = 0) and triplet states (S = 1), and J [K] is the excitation energy singlet-triplet. Total intensity of EPR line taking into account the existence of paramagnetic centers in singlet and triplet states is presented in the form [12]: (3) where B and C [K] are constants equal to and aN d /2k, respectively [12]. Accordingly, relative contributions of paramagnetic centers in singlet (S = 0) and triplet (S = 1) states to whole amount of centers in doublet, singlet, and triplet states are given in the form [12]: (4) As mentioned earlier, it was shown [6][7][8][9] that in the total group of paramagnetic centers generating components lines in the form of Lorentzian L1 shape in EPR spectra of coal macerals, exinite, and vitrinite, there is a part of centers in excited triplet state (S = 1).…”

“…Total intensity of EPR line taking into account the existence of paramagnetic centers in singlet and triplet states is presented in the form [12]: (3) where B and C [K] are constants equal to and aN d /2k, respectively [12]. Accordingly, relative contributions of paramagnetic centers in singlet (S = 0) and triplet (S = 1) states to whole amount of centers in doublet, singlet, and triplet states are given in the form [12]: (4) As mentioned earlier, it was shown [6][7][8][9] that in the total group of paramagnetic centers generating components lines in the form of Lorentzian L1 shape in EPR spectra of coal macerals, exinite, and vitrinite, there is a part of centers in excited triplet state (S = 1). Accordingly, these centers do not fulfi l the Curie law represented by the formula I = C/T.…”

Application of EPR Spectroscopy for Examination of Free Radical Formation in Thermally Sterilized Betamethasone, Clobetasol, and Dexamethasone

“…The EPR method was used to examine the free radical formation in other sterilized drugs [10][11][12][13][14][15][16][17][18][19][20][21][22][23][24][25][26][27]. Both heating and gamma irradiation caused the free radicals formation in aminoglycoside antibiotics [13].…”