Spin Probe Determination of Molecular Orientation Distribution and Rotational Mobility in Liquid Crystals: Model-Free Approach.

A model-free approach for simulation of EPR spectra of nitroxide spin probes in liquid-crystalline materials was suggested and used to obtain parameters of molecular orientation and rotational mobility. The developed method is based on experimental recording and numerical simulation of the angular dependence of EPR spectra, which is shown to be much more informative in comparison with a single EPR spectrum. Quantitative spectral simulations considering both local orientational ordering and distribution of local directors in the sample were used for discrimination of models of rotational mobility and orientational alignment. The method was applied for detailed quantitative characterization of axial, orthorhombic, and low-symmetry non-orthorhombic molecular orientation distributions. It is shown that the ordinarily used model of rotational diffusion in a mean-field potential is suitable for the description of molecular mobility and orientational ordering only for relatively low sample temperatures and low-mobility probe molecules with large sizes. In cases of high molecular mobility, the more realistic jump mechanism of molecular moves can be approximately described as quasi-librations. For ordered liquid crystals it was found that mostly the order parameters up to rank 12-14 are essential and easily determined. When well-aligned materials are described, the order parameters up to 18th rank or even higher become meaningful. Both molecular and sample biaxiality is analyzed and quantitatively characterized. The local molecular ordering and sample orientational alignment are quantitatively characterized separately.

Formation of gapless triplets in the bond-doped spin-gap antiferromagnet (C4H12N2)(Cu2Cl6).

We report results of an electron spin resonance (ESR) study of a spin-gap antiferromagnet (C(4)H(12)N(2))(Cu(2(Cl(6)) (nicknamed PHCC) with chlorine ions partially substituted by bromine. We found that up to 10% of nominal doping the contribution of the random defects to the absorption spectra remains at about 0.1% per copper ion, which is almost the same as in the pure system. Instead, a particular kind of ESR absorption corresponding to gapless S = 1 triplets is observed at low temperatures in samples with high nominal bromine content x ≥ 5%. Increase of bromine concentration also leads to the systematic broadening of ESR absorption line, indicating reduction of the quasi-particles lifetime.

Molecular orientational order of nitroxide radicals in liquid crystalline media.

The orientational distribution of a set of stable nitroxide radicals in aligned liquid crystals 5CB (nematic) and 8CB (smectic A) was studied in detail by numerical simulation of EPR spectra. The order parameters up to the 10th rank were measured. The directions of the principal orientation axes of the radicals were determined. It was shown that the ordering of the probe molecules is controlled by their interaction with the matrix molecules more than the inherent geometry of the probes themselves. The rigid fused phenanthrene-based (A5) and 2-azaphenalene (A4) nitroxides as well as the rigid core elongated C11 and 5α-cholestane (CLS) nitroxides were found to be most sensitive to the orientation of the liquid crystal matrixes.

Order parameters , , and of aligned nematic liquid-crystalline polymer as determined by numerical simulation of electron paramagnetic resonance spectra.

High rank order parameters may comprise substantial information about molecular orientational distribution of liquid-crystalline materials. There are few experimental procedures targeted at the determination of high rank order parameters. We suggest a procedure for the determination of order parameters of a spin probe by numerical simulation of electron paramagnetic resonance (EPR) spectra. The procedure is based on revealing the molecular orientation axis of a spin probe. Order parameters , , and of the spin probe in aligned liquid-crystalline polymer have been measured by the suggested procedure. It was shown that the procedure gives more reliable and complete characteristics of molecular order than does polarized UV-visible spectroscopy.

Effect of melatonin on burn-induced gastric mucosal injury in rats.

We studied the effect of melatonin treatment on gastric mucosal damage induced by experimental burns and its possible relation to changes in gastric lipid peroxidation status. Melatonin was intraperitoneally applied immediately after third-degree burns over 30% of total body skin surface area of rats. Malondialdehyde (MDA), uric acid (UA) and sulphydril (SH) levels were determined in gastric mucosa and blood plasma and used as biomarkers of the oxidative stress. The results showed that the skin burn caused oxidative stress evidenced by accumulation of MDA and UA as well as the depletion of SHs in gastric mucosa. Plasma MDA concentrations were elevated, while plasma SH concentrations were decreased after burns. Melatonin (10 mg per kg body weight) protected gastric mucosa from oxidative damage by suppressing lipid peroxidation and activating the antioxidant defence. It may be hypothesised that melatonin restores the redox balance in the gastric mucosa and protects it from burn-induced oxidative injury. Melatonin has no significant influence on the concentrations of plasma MDA and antioxidants after burn; therefore, it should largely be considered as a limiting factor for tissue-damage.

Polyphenols and antioxidant capacity of Bulgarian medicinal plants.

Extracts of 21 plants used in Bulgarian phytotherapy for the treatment of respiratory, gastrointestinal and other inflammatory disorders were screened in vitro for antioxidant activity and phenolic compounds content. Plant extracts were prepared as herbal teas following the ethnic use. The water-phase TEAC (Trolox equivalent antioxidant capacity) of the teas were compared to that of the famous tea-like beverages mate, rooibos and honeybush, and to that of green and black tea, well known for their high antioxidant potential. The content of total phenolics in the teas was determined spectrometrically according to the Folin-Ciocalteu procedure and calculated as quercetin equivalents (QE). Seven Bulgarian medicinal plants were with high phenolics content and antioxidant properties: Pulmonaria officinalis L. (Boraginaceae) (TEAC 2.02+/-0.14 mM/QE 673.39+/-9.92 microM), Hypericum perforatum L. (Hypericaceae) (TEAC 3.75+/-0.14 mM/QE 881.93+/-6.68 microM), Agrimonia eupatoria L. (Rosaceae) (TEAC 3.76+/-0.5mM/QE 702.29+/-6.82 microM), Origanum vulgare L. (Lamiaceae) (TEAC 5.87+/-0.2mM/QE 1653.61+/-11.52 microM), Melissa officinalis L. (Lamiaceae) (TEAC 4.06+/-0.31 mM/QE 1370.09+/-41.38 microM), Rubus sp. diversa (Rosaceae) (TEAC 4.23+/-0,12 mM/QE 608.95+/-5.95 microM), Cotinus coggygria Scop. (Anacardiaceae) (TEAC 7.05+/-0.19 mM/QE 923.33+/-14.19 microM). Therefore, Bulgarian herbs can be considered to be a rich source of water-soluble antioxidants and/or phenolic compounds as compared to studied foreign plants.

Combined application of alpha-tocopherol and FC-43 perfluorocarbon emulsion suppresses early postburn lipid peroxidation and improves deformability of erythrocytes.

The effect of FC-43 perfluorocarbon emulsion and alpha-tocopherol on lipid peroxidative damage and deformability of erythrocytes was evaluated in rats (full skin thickness burns over 15-20% of total body surface) at third hour after burns. The animals were divided into five groups: (1) non-burnt non-treated (controls); (2) burnt non-treated; (3) burnt but treated with alpha-tocopherol ("Serva", Germany, 20 mg/kg b.m. i.p.) (4) burnt treated with FC-43 emulsion ("Green Cross Corp.," Japan, 5 ml/kg, i.v.); (5) burnt treated with combination of alpha-tocopherol (20 mg/kg) and FC-43 perfluorocarbon emulsion (5 ml/kg). In the burnt non-treated group the concentration of alpha-tocopherol decreased by 38% (p < 0.05), the levels of malonyl dialdehyde (MDA) and fluorescent damaged products raised by 32% (p < 0.001) and by 52% (p < 0.001) of the controls, respectively, whereas the deformability of red blood cells diminished by 34% (p < 0.001). Both the accumulation of MDA and fluorescent lipid peroxidation products and the decrease in deformability of affected cells were suppressed significantly by alpha-tocopherol treatment which also prevented the decrease in erythrocyte alpha-tocopherol content. FC-43 emulsion lowered the level of MDA but did not restrain the reduction in erythrocyte deformability significantly. The combined application of alpha-tocopherol and FC-43 emulsion immediately after thermal skin injury decreases peroxidative membrane damage and improved erythrocyte deformability more significantly than alpha-tocopherol at the third hour after thermal skin injury.

alpha-Tocopherol and reduced glutathione deficiency and decreased deformability of erythrocytes after thermal skin injury.

Burns are followed by oxidative changes in red blood cells, probably as a result of ischemia/reperfusion which takes place in the microvasculature of the injured tissues. This leads to a marked decrease in the erythrocyte deformability, one of the most prominent factors for haemorheological disorders in the early post-burn period. We found that at the 24 th hour after burn skin injury of rats, the decrease in erythrocyte deformability was accompanied by an increase of fluorescent product levels in red blood cells. The erythrocyte systems for antioxidative protection fail to control the oxidative burst after burning. This was due to the decreased concentration of vitamin E (a-tocopherol) and reduced glutathione (GSH) and the increased oxidized glutathione (GSSG) in red blood cells. Both alpha-tocopherol and GSH-deficiency potentiate the susceptibility of red blood cells to oxidative membrane injury, and decrease the deformability of thermally affected erythrocytes. Treatment with alpha-tocopherol (20 ml/kg b.m., immediately after thermal skin injury) prevented the vitamin E reduction and peroxidative membrane damage of erythrocytes and improved their deformability. These results provided strong evidence that the decreased erythrocyte deformability is partly related with alpha-tocopherol deficiency and oxidative membrane damage of red blood cells in the early post burn period.

An apparatus for measuring the optical density of human ocular media to blue light.

The paper describes an apparatus constructed by the authors and aimed at evaluating the optical density of human ocular media by a non-invasive psychophysical method described previously (Sample et al. 1988). The device has two light sources within the wavelength bands of 437 +/- 6 nm and 557 +/- 6 nm, respectively. They are a square-wave alternated at 1 Hz. The radiance of each can be controlled by the subject and adjusted at visibility threshold or at subjective equiluminance. Upon scotopic vision, the ratio between the two thresholds (or ratio of radiances at equiluminance) is a function of the ocular optical density at the short wavelength. The psychophysical procedures of adjustment of the 437 nm source at the absolute threshold and at equality with the 557 nm source had been tested with volunteers aged between 24 and 67 years. The dependence of blue-light sensitivities on age, obtained with the two procedures, suggests, in agreement with the literature, two main sources of sensitivity decline with age: senile myosis and ocular-media density increase at the short wavelength end of the visible spectrum.

Suppressive effect of FC-43 perfluorocarbon emulsion on enhanced oxidative haemolysis in the early postburn phase.

The effect of FC-43 perfluorocarbon emulsion on resistance of red blood cells to oxidative haemolysis and lipid peroxidation was evaluated in rats (full skin thickness burns over 15-20 per cent of total body surface area). The content of erythrocyte malonyl dialdehyde (MDA), alpha-tocopherol, glutathione (reduced and oxidized forms) and oxidative haemolysis were measured at 24 h after burn injury. Four groups were employed: (1) non-burned non-treated, (2) non-burned but treated with FC-43 perfluorocarbon emulsion (5 ml/kg bodymass i.v.), (3) burned non-treated, (4) burned but treated with FC-43 emulsion (5 ml/kg bodymass i.v.). The non-burned groups showed no significant differences in oxidative haemolysis, MDA levels or alpha-tocopherol and glutathione content. In the burned non-treated group the oxidative haemolysis elevated by 190 per cent (P < 0.001), MDA content increased by 43 per cent (P < 0.05), whereas the concentration of alpha-tocopherol and reduced glutathione (GSH) decreased significantly by 36 per cent and 18 per cent, respectively. The results showed reduction in the postburn MDA content by 30 per cent (P < 0.02) and oxidative haemolysis by 44 per cent (P < 0.001) after treatment with FC-43 emulsion. FC-43 emulsion did not change significantly the levels of alpha-tocopherol and GSH in erythrocytes after thermal injury. It is concluded that FC-43 perfluorocarbon emulsion administration suppresses early postburn lipid peroxidation and increases the resistance of red blood cells to oxidative haemolysis.

Lipofuscin product accumulation, insufficient antioxidant defence in erythrocytes and plasma and enhanced susceptibility to oxidative haemolysis after thermal trauma.

The mechanism of increased susceptibility of red blood cells to oxidative haemolysis in the early post-burn period remains unclear. In this study it was revealed that the accumulation of lipofuscin products in red blood cells was accompanied by the elevation of oxidative haemolysis on the 24th hour after thermal trauma of rats (full thickness skin, on 20% of TBSA). Enhanced thiobarbituric acid reactive substrates (TBARS) and lowered levels of antioxidants such as alpha-tocopherol, ceruloplasmin and albumin were found in plasma. The activity of superoxide dismutase (SOD) and the concentration of alpha-tocopherol and reduced glutathione (GSH) in erythrocytes were also diminished. The results from this study suggest that plasma and intracellular antioxidant deficiency can potentiate oxidative membrane damage. There was a positive correlation (r = 0.72) between increased levels of lipofuscin products and oxidative haemolysis of red blood cells. The enhanced susceptibility of erythrocytes to oxidative haemolysis may be considered as an indirect but sensitive indicator of the impaired antioxidant defence of these blood cells following thermal skin injury. The decreased resistance of red blood cell to oxidative haemolysis under the conditions of reduced antioxidant defence of erythrocytes and blood plasma suggests that adequate antioxidant therapy could prevent all these complications after thermal skin injury.

Increased antioxidant capacity, suppression of free radical damage and erythrocyte aggrerability after combined application of alpha-tocopherol and FC-43 perfluorocarbon emulsion in early postburn period in rats.

Certain rheological disorders such as enhanced aggregation and reduced deformability of erythrocytes are closely associated with microcirculatory disturbances, decreased tissue oxygen supply and represent a major problem in severely burnt patients [1-4]. Vitamin E (alpha-tocopherol) and vitamin A (retinol) exert an important plasma antioxidant properties against free radical-induced damage [11,12]. They possess chain-breaking properties and act as synergists [13]. Plasma antioxidant capacity may be decreased in severely burnt patients as a result of the enhanced consumption and inadequate restoration of antioxidants in the conditions of activated peroxidative process [14]. Treatment with alpha-tocopherol suppresses lipid peroxidation in blood and therefore improves erythrocyte rheology [15]. Perfluorocarbon emulsions improve microcirculation and rheological blood properties [16-18] and preserve the structure and function of endothelial cells [19]. The very small particle size, low viscosity and high oxygen carrying capacity ensure their penetration into the microvasculature even under conditions of ischemia and acidosis [20, 21]. Perfluorocarbons have been reported to inhibit leukocyte activation and superoxide radical production [22]. The aim of the present study was to examine the antioxidant capacity, free radical mediated damage and erythrocyte aggregation in plasma of rats with thermal skin injury in the early postburn period and to evaluate the effect of treatment with alpha-tocopherol and FC-43 perfluorocarbon emulsion alone and in combination. We might conclude that thermal skin injury in rats reduces the antioxidant capacity, enhances free radical mediated damage and erythrocyte aggregation on the third hour after injury. The combined application of alpha-tocopherol and FC-43 perfluorocarbon emulsion immediately after thermal skin injury in rats increases plasma antioxidant capacity, decreases free radical mediated damage of erythrocytes and suppresses their aggregation on the third hour after the injury.

Reduced erythrocyte deformability related to activated lipid peroxidation during the early postburn period.

The role of lipid peroxidation in reduced red cell deformability has been examined after thermal injury of rats (full skin thickness over 15-20 per cent of total body surface). An increased concentration of erythrocyte malonyldialdehyde (MDA) and blood thiobarbituric acid (TBA) reactive product levels during the first 3 days after thermal trauma was established. There was a remarkable decrease in red cell superoxide dismutase (SOD) activity after burns and an increase in glucose-6-phosphate dehydrogenase (G-6-PD) on day 3 postburn. The deformability of erythrocytes was diminished significantly during the first 3 days after burns. There was a significant negative correlation between the deformability and the amount of MDA accumulated in erythrocytes (r = -0.92). Both the accumulation of MDA and the reduction of SOD activity in erythrocytes were suppressed by alpha-tocopherol treatment, which also prevented the decrease in erythrocyte deformability. These results suggest that the activation of the peroxidative process is a possible mechanism for the decreased deformability of erythrocytes during the early stage after thermal injury.

Lipid peroxidation and vitamin E in red blood cells and plasma in hemodialysis patients under rhEPO treatment.

Lipid peroxidation, measured by malonyldialdehyde (MDA) and vitamin E in red blood cells (RBC) and plasma, was investigated in 25 hemodialysis (HD) patients before and after 6 months rhEPO therapy. RBC-MDA was significantly elevated, but plasma MDA was in the reference range. After recombinant human erythropoietin (rhEPO) treatment, the MDA level was significantly decreased in both compartments. Marked vitamin E deficiency was established in RBC as well as in plasma. rhEPO therapy restored vitamin E levels in both compartments. Our data suggest a possible positive rhEPO-antioxidant effect in HD patients.

Erythrocyte rheology and lipid peroxidation in burns.

Alterations in the erythrocyte rheology and the contents of activated free radical oxidation products (conjugated dienes, products of thiobarbituric acid and Schiff bases) in the acute phase of experimental thermic injury of the skin were studied. Erythrocyte flexibility reduction and erythrocyte aggregation increase correlated with elevated amounts of free radical oxidation products. Alpha-tocopherol avoided the accumulation of free radical oxidation products and improved both antioxidant defence and erythrocyte rheology. Thus we suppose that free radical oxidation products probably participate in the pathogenesis of erythrocyte rheology disturbances after thermic trauma.

Dependence between the free-radical peroxidation, the activity of the superoxide dismutase glucose-6-phosphate dehydrogenase and erythrocytes haemolysis after thermal trauma and alpha-tocopherol treatment.

Experimental thermal trauma of IIIa-IIIb degree was induced on an area of 15-20% in male Wistar rats weighing 200-250 g. The changes in the content of the products of free-radical oxidation (FRO) - conjugated dienes and thiobarbituric acid (TBA) products in the blood, haemodialysis, the activity of superoxide dismutase (SOD) and of G-6-PHD-ase in the erythrocytes during the acute period after thermal trauma (24, 48 and 72 hours) were traced. The experimental data have shown that the percentage of haemolysed erythrocytes increases with the potentiation of FRO after burning. Intraperitoneal administration of alpha-tocopherol in a dose of 20 mg/kg body mass is followed by a reduction of the FRO products and by a rise in the antioxidative protection and resistance of the erythrocytes. The role of FRO in the pathogenesis of the damage of the erythrocytic membrane after thermal trauma and the protective effect of alpha-tocopherol are discussed.