A. N. Shchegolikhin

Ozone-induced oxidative modification of plasma fibrin-stabilizing factor.

The plasma fibrin-stabilizing factor (pFXIII) function is to maintain a hemostasis by the fibrin clot stabilization. The conversion of pFXIII to the active form of the enzyme (FXIIIа) is a multistage process. Ozone-induced oxidation of pFXIII has been investigated at different stages of its enzyme activation. The biochemical results point to a decrease of an enzymatic activity of FXIIIа depending largely on the stage of the pFXIII conversion into FXIIIа at which oxidation was carried out. UV-, FTIR- and Raman spectroscopy demonstrated that chemical transformation of cyclic, NH, SH and S-S groups mainly determines the oxidation of amino acid residues of pFXIII polypeptide chains. Conversion of pFXIII to FXIIIa proved to increase protein sensitivity to oxidation in the order: pFXIII<pFXIII activated by thrombin<pFXIII in the presence of calcium ions<FXIIIa. The dynamic light scattering data indicate that the three-dimensional structure of pFXIII becomes loosened due to oxidative modification. ESR spectroscopy data also point to conformational changes of the fibrin-stabilizing factor under oxidation. Taking into account these new findings it seems reasonable to assume that the inhibitory/carrier FXIII-B subunits can serve as scavengers of ROS. Hypothetically, this mechanism could help to protect the key amino acid residues of the FXIII-A subunits responsible for the enzymatic function of FXIIIa.

The effect of multi-walled carbon nanotubes addition on the thermo-oxidative decomposition and flammability of PP/MWCNT nanocomposites

Studies of thermo-oxidative and fire-resistant properties of the polypropylene/multi-walled carbon nanotube composites (PP/MWCNT) prepared by melt intercalation are discussed. The effective kinetic parameters of the PP/MWCNT thermo-oxidative decomposition were computed according to the model-based kinetic analysis. The thermo-oxidative decomposition behavior of PP/MWCNT and stabilizing effect caused by addition of MWCNT has been investigated by means of TGA and EPR spectroscopy. Comparative analysis of the flammability characteristics for PP-clay/MWCNT nanocomposites was provided in order to emphasize the specific behavior of the nanocomposites.

Oxidized modification of fragments D and E from fibrinogen induced by ozone

Ozone-induced free-radical oxidation of fragments D and E from fibrinogen has been studied. The methods of elastic and dynamic light scattering in combination with electrophoresis of unreduced samples have shown the acceleration of enzymatic covalent crosslinking of molecules of oxidation-modified fragment D under the action of factor XIIIa. UV and IR spectroscopy shows that free-radical oxidation of amino acid residues of polypeptide chains catalyzed by ozone affects the cyclic and amino groups, giving rise to generation of mainly oxygen-containing products. Comparison of the IR spectra obtained for the oxidation-modified D and E fragments revealed more significant transformation of functional groups for the D fragment. EPR spectroscopy showed that the rotational correlation time of spin labels bound to the ozonized proteins decreased in comparison with the non-ozonized proteins. The rotation correlation time of the radicals covalently bound to the ozonized D and E fragments suggests that D fragment of fibrinogen is more sensitive to free-radical oxidation followed by local structural changes. Possible causes of different degrees of oxidation for fragments D and E are discussed.

Microwave plasma in liquid n-heptane: A study of plasma-chemical reaction products

It has been found that a microwave discharge in liquid n-heptane leads to the formation of a solid phase in the form of carbonaceous nanoparticles. The composition and size of the particles have been determined by means of scanning electron microscopy with energy dispersive analysis and Raman spectroscopy. Using electronic absorption and luminescence spectroscopy, it has been shown that the discharge treatment results in the formation of polycyclic aromatic hydrocarbons in liquid n-heptane.

Polyethylene-layered silicate nanocomposites: Synthesis, structure, and properties

This work studies the structure and main properties of nanocomposites based on polyethylene (PE) and modified montmorillonite (MMT) and prepared by intercalation polymerization. This method provides virtually complete exfoliation of precursor MMT particles into nanometer-thick single layers dispersed in the nascent PE matrix, as proven by small-angle X-ray scattering, very cold neutron (VCN) scattering, and transmission electron microscopy. In low-MMT nanocomposites, a number of important performance parameters are strongly improved compared to those of unfilled PE; they have higher barrier properties, a considerably increased dynamic mechanical modulus over a wide temperature range, improved heat resistance and thermooxidative stability, and a unique ability for oxidative carbonization during high-temperature pyrolysis and burning. As a result, we can classify these polymer nanocomposites with low-combustibility materials.

Covalent structure of single-stranded fibrin oligomers cross-linked by FXIIIa

FXIIIa-mediated isopeptide γ-γ bonds are produced between γ polypeptide chains of adjacent monomeric fibrin. Despite the use of the different methodological approaches there are apparently conflicting ideas regarding the orientation of γ-γ bonds. To identify the orientation of these bonds a novel approach has been applied. It was based on self-assembly of soluble cross-linked fibrin protofibrils ongoing in the urea solution of moderate concentrations followed by dissociation of protofibrils in the conditions of increasing urea concentration. The oligomers were composed of monomeric desA fibrin molecules created by cleavage of the fibrinopeptides A from fibrinogen molecules with thrombin-like enzyme, reptilase. The results of elastic and dynamic light scattering coupled with analytical ultracentrifugation indicated an emergence of the double-stranded rod-like fibrin protofibrils. For the first time, the protofibrils are proved to exhibit an ability to dissociate under increasing urea concentration to yield single-stranded structures. Since no accumulation of α polymers has been found the covalent structure of soluble single-stranded fibrin oligomers is entirely brought about by γ-γ bonds. The results of this study provide an extra evidence to support the model of the longitudinal γ-γ bonds that form between the γ chains end-to-end within the same strand of a protofibril.

Ozone-induced oxidative modification of fibrinogen molecules

Ozone-induced oxidation of fibrinogen has been investigated. The conversion of oxidized fibrinogen to fibrin catalyzed either by thrombin or by a reptilase-like enzyme, ancistron, in both cases is accompanied by production of gels characterized by a higher weight/length ratio of fibrils in comparison with the native fibrin gels. IR spectra of the D and E fragments isolated from unoxidized and oxidized fibrinogen suggest a noticeable transformation of functional groups by oxidation. A decrease in content of N-H groups in the peptide backbone and in the number of C-H bonds in aromatic structures, as well as a decrease in the intensity of the C-H valence vibrations in aliphatic fragments CH2 and CH3 were found. The appearance in the differential spectra of the D fragments of rather intense peaks in the interval of 1200–800 cm−1 clearly indicates the interaction of ozone with amino acid residues of methionine, tryptophan, histidine, and phenylalanine. Comparison of the differential spectra for the D and E fragments suggests that fibrinogen fragment D is more sensitive to the oxidant action than fragment E. Using EPR spectroscopy, differences are found in the spectra of spin labels bound with degradation products of oxidized and unoxidized fibrinogen, the D and E fragments, caused by structural and dynamical modifications of the protein molecules in the areas of localization of the spin labels. The relationship between the molecular mechanism of oxidation of fibrinogen and its three-dimensional structure is discussed.

The study of the interaction between chitosan and 2,2-bis(hydroxymethyl)propionic acid during solid-phase synthesis

New polymer salts and N-acetylated chitosan derivatives are prepared in an extruder by the method of solid-phase synthesis via the interaction of chitosan and 2,2-bis(hydroxymethyl)propionic acid. The effect of the initial component ratio and temperature on the yield and structure of the target products is studied. Joint deformation of solid components at room temperature is found to cause the quantitative formation of salt bonds between carboxylic groups of the acid and amino groups of chitosan. At elevated temperatures of synthesis, the corresponding acetylated derivatives with a degree of substitution of amino groups varying from 0.16 to 0.43 are prepared. The relaxation and phase transitions in the polymer salts and acetylated chitosan derivatives and their sorptional activity are studied. The films prepared from aqueous solutions of the new salt modification of chitosan are characterized by a homogeneous structure and improved mechanical characteristics relative to those of the films based on chitosan acetates. An additional thermal treatment of the products of the solid-phase synthesis leads to the formation of crosslinked and water-swollen materials that can be used for the development of novel polymeric chitosan-based membranes and sorbents.

Elementary supramolecular strings in solutions of chiral trifluoroacetylated amino alcohols

IR spectroscopy is applied to studying the effect of nonpolar and low-polar solvents on the molecular structure of solid-state quasi-one-dimensional strings formed through the chiral self-assembly from solutions of trifluoroacetylated homochiral amino alcohols (TFAAA). It is experimentally confirmed that in stable two-phase string/solvent gels and respective xerogels, solid-phase strings contain no solvent molecules as a structural element, experiencing, however, a weak disturbing influence of solvent molecules. It is shown that the process of spontaneous self-assembly of chiral strings in solutions is accompanied by the formation of a complex system of hydrogen bonds involving the C=O, N–H, and O–H functional groups of dissolved TFAAA molecules and by the displacement of solvent molecules to the periphery of the resulting quasi-one-dimensional strings. The results of the present work, together with data obtained by other experimental methods, indicate that TFAAA-based elementary strings have diameters of 1–2 nm, being crystalline, molecularly thin, quasi-one-dimensional objects. The amplitude of the thermally activated bending vibrations (transverse phonons) of elementary strings is sufficient to cause the entanglement of elementary strings, which leads to the formation of larger diameter supercoiled strings.

Nature of active intermediate particles formed during ozone-induced oxidation

139 Ozone as a representative of reactive oxygen spee cies (ROS) is one of the most toxic components of the atmosphere. A number of studies have shown that ozone is able to generate other ROS, including HO • , , H 2 O 2 , etc. [1, 2]. In some cases, these secondary ROS can be even more deleterious than the ozone molecules themselves. It is now generally recognized that proteins are among the main targets of ROS. Under the action of ROS, proteins undergo oxidative modifications, which disturb their structures and functions. Oxidationnmodified proteins accumulate in the course of aging, oxidative stress, and various diss eases [3]. It was shown that fibrinogen is 20 times more sensitive to oxidative modification than other major plasma proteins (albumin, immunoglobulins, transs ferrin, and ceruloplasmin) [4]. Therefore, fibrinogen, which accounts for approximately 4% of the total plasma proteins, is an easily vulnerable target for oxii dants. It was previously shown that a number of proteins (fibrinogen [5, 6], fibrinnstabilizing factor [7], bovine serum albumin [8], etc.) are involved in oxidative proo cesses under the influence of ozone. In studying the ozonization of fibrinogen, it was found that moderate oxidation leads to a decrease in the content of not only reactive groups (NH x , > SH, etc.), but also to a marked reduction in the content of СН 2 groups, whose reactivity compared to that of NH x and SHHgroups is smaller by 7 and 4 orders of magnitude, respectively [9]. This interesting feature of the reaction could not be attributed to the molecular reaction of ozone but, rather, was due to the action of an as yet unidentified secondary ROS and required further explanation. Since ozone in the liquid phase can form highly toxic secondary ROS, the discriminaa O 2 • − tion between the effects of the molecular oxidation and the free radical oxidation caused by the generation of free radicals under the influence of ozone during ozonation is one of the key problems in understanding the mechanism of oxidation of different biological tarr gets with ozone. In this study, we investigated this problem using fibrinogen as an example. The oxidation of fibrinogen under the action of ozone was performed as described previously [6]. The amount of ozone in the reactor varied from 5 × 10 –8 to 2 × 10 ⎯7 moles. The generation of hydroxyl radicals generated under the …