Location of PRODAN in lipid layer of HDL particle: a Raman study.

FT Raman spectroscopy has been applied to determine the location of PRODAN within HDL and to investigate its influence on the structure of the particle. The complex spectra of HDL and HDL labeled with PRODAN were divided into three regions according to the wave numbers, and adherent spectra were compared separately. Additionally, recorded spectra of protein and lipid fractions of HDL were used as a support for the assignment of particular vibrations in intact particles. In high frequency region, the shift in vibrational frequencies of CH3 groups but almost negligible shift of CH2 groups suggests that PRODAN is situated at the water/lipid interface in the vicinity of the protein. The statement is supported by the observed influence of PRODAN on particular lipid vibrations of phospholipids head-groups. In the fingerprint region, the influence of PRODAN is observed as the slight change in beta-strand secondary structure of apolipoprotein and strongly reduced vibrations of the acyl chain in lipids. That additionally confirms that PRODAN mainly interacts with the lipid domain of the particle. In the low frequency region, the lack of change in Tyr Fermi resonance doublet and only slight differences in the pattern of CS and SS stretching vibrations in labeled HDL confirms that PRODAN has no influence on structure of apolipoprotein embedded in lipid domain. The main conclusions drawn from the vibrational spectra of HDL with and without PRODAN clearly confirm that PRODAN induces negligible changes in HDL structure and hence is reliable fluorescent label for the structural analysis.

An EPR study of the transfer and trapping of holes produced by radiation in guanine(thioguanine) hydrochloride single crystals.

Single crystals of guanine hydrochloride monohydrate, guanine hydrochloride dihydrate and anhydrous guanine dihydrochloride, doped with thioguanine, were irradiated with X and gamma rays. In all three systems the dominant radicals were associated with thioguanine. In the former two systems the stabilized species is the thiyl radical, formed by initial loss of an electron at some of the guanines in the crystal lattice, followed by hole migration to thioguanine and subsequent deprotonation of the radical formed. In the anhydrous guanine(thioguanine) dihydrochloride, that process is followed by acquisition of a chlorine ion. In the guanine hydrochloride monohydrate and guanine hydrochloride dihydrate lattices, systems of interacting closely spaced stacked bases and strings of chloride ions might support the migration of electrons and/or holes. In anhydrous guanine dihydrochloride, neither the bases nor the Cl- ions alone are capable of providing the means for the long-range electron, energy and spin transfer. It is the interchangeable sequence of the charged bases and the Cl- ions that makes the supporting strings or networks. The ultimate chlorination of the thioguanine-centered electron-loss radicals depends mainly on the availability of the Cl- ions and the space for their accommodation in the vicinity of the sulfur atom.

Very slow autoxidation of low-density lipoprotein spares alpha-tocopherol.

Low-density lipoprotein (LDL) in solution, supplemented with EDTA, is spontaneously oxidized at physiological temperature. In closed systems, three distinct phases of oxidation are present. In the lag period no change of any of the usually measured 'markers' of oxidation have been detected. In the second phase oxygen is consumed and subsequently the level of lipid hydroperoxides is increased. In the third phase, after consumption of oxygen, hydroperoxides decrease in concentration and the apoprotein-associated free radicals are formed. In the entire process alpha-tocopherol is conserved. The participation and preservation of alpha-tocopherol in the process is interpreted in terms of the tocopherol-mediated peroxidation. In the latter two phases alpha-tocopherol oscillates between the oxidized and reduced states.

Nature of the chlorine-centred paramagnetic species in irradiated crystals of cytosine hydrochloride doped with thiocytosine.

It has been demonstrated that the paramagnetic species formed in crystals of cytosine hydrochloride doped with thiocytosine are most likely the radicals formed by association of thiocytosine and chlorine. The unpaired electron is positively identified on the Cl atom and on at least one of the pyrimidine atoms, and the data are consistent with the formation of the 'three-electron' S-Cl sigma sigma * bonds. The spin density derived from the measured 35Cl and 14N coupling tensors compare reasonably well with the MO calculations for the 'in-plane' conformations of three hypothetical radicals formed by initial ionization of either thiocytosine or Cl- followed by their reaction. Two distinct and related centres, A and B, probably represent two different conformations of chemically the same radical in the crystal lattice of cytosine-HCL.

Mild autoxidation of low density lipoproteins.

The autoxidation of low density lipoproteins was investigated in a closed system, with limited amount of oxygen. The concentrations of several components were monitored: oxygen, aldehydic oxidation products and alpha-tocopherol. The concentration of lipid radicals generated in the processes of lipid peroxidation was monitored by the EPR spin trapping method. It was observed that the consumption of oxygen starts quickly after the onset of incubation at physiological temperature. After prolonged incubation, several types of trapped radicals were formed. At the same time, no consumption of alpha-tocopherol and no formation of aldehydic products of oxidation took place, indicating that the oxidation process is rather mild. The dynamics of oxidation processes were simulated by a mathematical model in which the oxidation is initiated by the degradation products of the pre-existing lipid peroxides. The best agreement between the theoretical predictions and experimental results was obtained with the rate constants which are several orders of magnitude smaller than the corresponding rate constants in "neat' lipids. The possible reasons for the behaviour observed are discussed.

Postirradiation long-range energy transfer in a single crystal of cytosine monohydrate: an EPR study.

Thiocytosine molecules incorporated in the cytosine monohydrate crystal lattice act as traps for both electrons and holes. The radiation-induced cytosine ion radicals, C(+) and C(-), release their charge upon heating. The excess electrons and holes migrate long distances in the crystal lattice. The migration of holes has been demonstrated by the postirradiation, thermally activated accumulation of thiocytosine cation radicals, T(+), and the migration of electrons by formation of the S-centered radicals of an anionic nature. It is estimated that the migration length of the holes is at least 30 interbase distances, and the migration length of the electrons is more than 100 interbase distances. The selective formation of the cationic and anionic trap radicals, depending on the trap concentration, is discussed in terms of differences between the migration of electrons and holes.