Effect of the external donors on the polymerization of 4-methyl-1-pentene with high activity MgCl2/TiCl4 catalytic system

In order to find out correlations between the structure of an external donor and the obtained polymer, the effects of different external donors on the activity and stereospecificity of the MgCl₂/TiCl₄ catalytic system in the bulk polymerization of 4-methyl-1-pentene (4MP) were carefully studied. Different silane compounds of the structure R_nSi(OR')_4-n (where: n = 1–3, R = alkyl/phenyl, R = alkyl) and Al(i-Bu)₃ (TIBA) were used as external donors and cocatalyst, respectively. The effect of the donor/TIBA mole ratio on the activity and stereospecificity of the catalytic system was studied. Some major effects were observed for the three different external donors, namely, Me₃Si(OMe), Me₂Si(OMe)₂, and Me₃Si(OBu)₃, in the 4MP polymerization process. It was observed that the effect of the external silane donor on the polymerization strongly depends upon the size of the alkoxy and hydrocarbon (alkyl/phenyl) groups which are attached to the silicon atom. A selective deactivation of the non-stereospecific centers, as well as a transformation of the non-stereospecific into isospecific centers, is assumed to occur. On the basis of the obtained results and literature data available for the propene polymerization, the concept of structural conformity between the ligand-surrounded active center and the monomer molecule was carried forward.     

Contractile units in stress fibers of fetal human astroglia in tissue culture

The interaction between myosin and F-actin requires the enzyme, myosin light chain kinase (MLCK), as well as Ca2⁺-calmodulin and the calmodulin binding protein, caldesmon, which also binds to F-actin. Using immunofluorescence staining, we have demonstrated that in human fetal astroglia as in mouse astroglia (Abd-El-Basset et al., 1991) the stress fibers contain these contractile elements: F-actin, myosin, tropomyosin and caldesmon. F-actin extends continuously along the stress fibers, whereas myosin, tropomyosin and caldesmon are localized discontinuously in a periodic pattern. In addition, we have demonstrated that fetal human astroglia have the enzyme MLCK and calmodulin. The association of the contractile elements listed above together with calmodulin and MLCK constitutes what may be termed ‘contractile units’, suggesting that the stress fibers in astroglia may be contractile. Contractile stress fibers would enable astroglia to exert tension on the matrix surrounding them, thus facilitating rapid changes in cell shape.     

Comparison of hepatitis C viral loads in patients with or without coinfection with different genotypes

Hepatitis C virus genotyping was assessed for 257 chronic hepatitis C patients with viral loads above 1,000 IU/ml. Twelve patients were coinfected with more than one genotype. Their median viral loads did not differ significantly from those observed for monoinfected patients, which in turn did not vary significantly among different genotypes.     

Spinal neurons that express NK-1 receptors modulate descending controls that project through the dorsolateral funiculus

Selective ablation of spinal neurons possessing substance P receptors (NK-1 receptors) using the selective cytotoxin conjugate substance P-saporin (SP-SAP) decreases hyperalgesia and central sensitization. The mechanisms by which NK-1 expressing neurons modulate the excitability of other dorsal horn neurons are unclear. Because the majority of NK-1 expressing spinal neurons project rostrally, it is possible that they are part of a spinal-supraspinal circuitry that contributes to descending modulation of excitability of spinal nociceptive neurons. We therefore determined whether ablation of spinal neurons that possess the NK-1 receptor altered descending systems that travel via the dorsolateral funiculus (DLF). Spontaneous activity and responses of dorsal horn neurons evoked by mechanical (von Frey monofilaments) and heat (35-51 degrees C) stimuli were determined before and after transection of the DLF and were compared in rats pretreated with intrathecal application of vehicle or SP-SAP. In vehicle-treated rats, transection of the DLF caused a 233% increase in mean spontaneous activity of neurons and enhanced their responses to mechanical and heat stimuli, whereas these increases in excitation were blocked in rats pretreated with SP-SAP. Importantly, SP-SAP alone had no effect on spontaneous or evoked activity in the absence of DLF transection. These results demonstrate that spinal neurons expressing the NK-1 receptor appear to play a pivotal role in regulating descending systems that modulate activity of nociceptive dorsal horn neurons.     

Structural study of compounds modelling elementary polymer units, 6. X-ray structural and quantum-chemical investigation of the cis- and trans-isomeric models of the polynaphthoylenebenzimidazole elementary units

The X-ray structural investigation of the naphthoylenebis-(benzimidazole) ( 1 ) cis- and trans-isomers as models for the cis and trans elementary units of the corresponding poly(naphthoylene-benzimidazoles) (PNBI) was carried out. The correctness of the previous identification of the isomers was confirmed, and exact geometrical parameters of the PNBI elementary units (required, in particular, for the calculation of the Kuhn segment of PNBI) were determined. Quantum-chemical semi-empirical calculations of the ground and excited electronic states of the isomers were carried out. Both experimental and theoretical data confirm a larger stability of the planar π-conjugated structure of the trans-isomer in comparison with the cis-isomer in the ground as well as in the excited electronic state. Crystals of the cis- and trans-isomers obtained from trifluoroacetic acid solutions are the solvates of bis(trifluoroacetates) of diprotonated 1 with an extremely high content of the solvating trifluoroacetic acid. This peculiarity is favourable for modelling the main characteristics of the interaction between PNBI and protonic polar solvent molecules, viz. preferred types of H-bonding and a possibility of interaction of the electronic lone pairs of the solvent molecules with the π-electronic systems of the elementary units of PNBI by charge transfer complexes.     

HLA-DR2 frequency increase in severe aplastic anemia patients is mainly attributed to the prevalence of DR15 subtype

The association between severe aplastic anemia (AA) and DR2 antigen seems to be well established. However, since discrimination between two DR2-associated splits, namely DR15 and DR16, rarely was performed, it remains unclear whether one or both of these subvariants are responsible for AA susceptibility. In this study, we have analyzed the HLA-DR allelic distribution in a group of 37 AA patients of slavic origin from North-Western Russia. The experimental design included PCR-based amplification of DRB-specific sequences, followed by reverse dot-blot hybridization of the biotinylated PCR-product with the set of sequence-specific oligonucleotide probes. HLA-DRB alleles were identified by non-radioactive enzymatic reaction, then standard serological specificities of HLA-DR antigen were estimated according to the WHO nomenclature. Whereas DR15 subtype occurred more often in the patients (23.0% vs. 13.3%, p< 0.05), DR16 split did not show the same tendency. The results, show the overall predominance of HLA-DR2 specificity (DR15+DR16) did not reach statistical significance (24.4% vs.17.5%, p<0.2). Thus, we conclude that repeatedly reported DR2 frequency increase in AA patients is mainly attributed to the prevalence of DR15 subtype.