مجله علوم جمهوری اسلامی ایران
سال:1383 | دوره:15 | شماره:4 |تعداد مقالات:19

Amphibians have a large variety of antimicrobial peptides that serve as natural innate barriers limiting microbial infection or, in some instances, act as an integral component in response to inflammation or microbial infection. A novel peptide with antibacterial effects and without hemolytic activity was purified from skin secretions of Rana ridibunda by multisteps cation-exchange FPLC, reversedphase HPLC and was called Ridibundin 1. Circular dichroism spectra revealed that this peptide strongly prefers to form an amphipathic ل-helical structure in the presence of 50% trifluoroethanol. Acting as wide-spectrum microbicides against a variety of bacteria, Ridibundin 1 also shows no hemolytic activity on erythrocyte. These properties reveal its unique characteristics and potential therapeutic application.

Various plant organ segments including segments from roots (root tip, and root collar), stems, leaves, and also seeds of several Hyoscyamus species (i.e. H. pusillus, H. arachnoideus, annual and biennial H. niger from two distinct geographical regions) were cultured on MS media with various growth regulator combinations, to assess the ability of flower production. Statistical assessments showed significant differences between various explants cultured on different media. That is, the subculture of the leaves obtained from H. pusills leaf culture on MS medium containing BAP (1.5 mg/L), on MS medium containing IAA (0.2 mg/L) and Kin (1.5 mg/L), led to the highest flower production. In addition, when cultured on MS medium containing 2,4-D (0.32 mg/L), the seeds of annual H. niger showed high flower production.

The inhibition of human erythrocyte glucose 6-phosphate dehydrogenase (G6PD) by Cd (II), Al (III) and Ni (II) was studied. The enzyme was partially purified having specific activity of 1.4 U/mg protein. Cadmium inhibited G6PD activity progressively up to 1.5 mM concentration where about 65% of the enzyme activity was lost. The inhibition was uncompetitive and noncompetitive with respect to glucose 6-phosphate and NADP+, respectively. Cd (II) also increased maximum emission spectrum of the intrinsic protein fluorescence. Sulfhydryl compounds such as glutathione (1.2 mM), â-mercaptoethanol (1.2 mM) or dithiothreitol (1.25 mM) protected the enzyme activity against Cd (II) inhibition and restored the native protein fluorescence. The data suggest that sulfhydryl groups are involved in Cd (II) inhibition. The inhibition patterns for Al (III) were mixed type and competitive when NADP+ and glucose 6-phosphate were the variable substrates, respectively. The enzyme inhibition by Al (III) was increased as the pH of the incubation mixture decreased indicating that mainly the ionized form of Al (III) abolishes the enzyme activity. The types of the enzyme inhibition by Ni (II) were competitive with respect to NADP+ and mixed type when glucose 6-phosphate varied. Ki values of 1.5 mM, 0.039 mM 0.05 mM for Cd (II), Al (III) and Ni (II) were calculated from the slope replots, respectively. The data suggest that direct interaction of these metal ions with human erythrocyte G6PD produces a reversible inhibition of the enzyme and that their toxicity, at least in part, may be due to the inhibition of this enzyme.

Conventional cytogenetic is the standard technique for detection of Philadelphia (Ph) chromosome in chronic myeloid leukemia (CML). Evaluation of abelson murine leukemia/breakpoint cluster region (abl/bcr) fusion using dualcolour fluorescence in situ hybridization (D-FISH) is an alternative approach allowing rapid and reliable detection of the disease. We employed the technique of interphase D-FISH to detect the abl/bcr fusion in 21 patients and the results were compared to those of conventional cytogenetic analysis. A significant agreement was observed between the results, indicating the accuracy of interphase D-FISH. The technique can overcome the disadvantage of conventional cytogenetic methods, which depends on cell culture and analysis of banded chromosomes, since the analysis is performed by signal counting on uncultured target cells. Furthermore D-FISH provides a more reliable method for evaluating the degree of clone remission to patients with CML after therapy compared to the conventional cytogenetic analysis.

Ti-MCM-41 was synthesized at pH 3, 7 and 11. The titanium content was determined by AAS and found to be 4%, 3.2% and 4.5%, respectively. In order to increase the titanium content in Ti-MCM-41, Ti(IV) ions were grafted onto Ti- MCM-41 using TiCl4 in toluene and Ti(OBu)4 in ethanol. The incorporation of Ti was determined to be 28% and 30%, respectively. The oxidation of olefins such as cyclopentene, cyclohexene, norbornene and trans-2-hexene-1-ol with TBHP in the presence of Ti-grafted Ti-MCM-41 were carried out in CHCl3. This system successfully catalized the oxidation of these olefins toward the corresponding epoxides with 60 to 90% reactivity and 95 to 100% selectivity.

Efficient and chemoselective protection of aldehydes to the corresponding dimethyl acetals have been carried out by mixture of trimethyl orthoformate and methanol in the presence of a catalytic amount of TMSCl or AlCl3 under microwave irradiation. Under these conditions, acetalization of ketones does not take place and they remain intact under reaction conditions. The results are compared with the reaction of an aldehyde with trimethyl orthoformate in the presence of a mild Lewis acid.

Organic stabilizers have been investigated as thermal stabilizers for rigid polyvinyl chloride (PVC) at 180°C in inert atmosphere by measuring the rate of dehydrochlorination and changes in intrinsic viscosity, UV absorption spectra, FT-IR spectra and levels of unsaturation in the degraded polymer samples have been used to assess the effects of the materials on the degraded polymer. Theirs stabilizing efficiencies are based on measuring the length of the induction period (TS), the period during which no detectable amounts of HCl gas could be observed, and also from the rate of the dehydrochlorination as measured by bromometry titration on the one hand, and the extent of discoloration of the degraded polymer samples on the other. The results revealed the greater stabilizing efficiencies of the investigated materials as shown by their longer induction periods (TS) and by the lower dehydrochlorination rate in relation to blank PVC. The stabilizer efficiency attributed to the replacement of the labile chlorine on the PVC chains by a relatively more thermally stable aromatic and aliphatic moiety. A radical mechanism for the stabilizing action of the investigated stabilizers is offered. A synergistic effect achieved when the material under investigation were blended in 1:1 weight ratio with either. The results reveal that mixing of the stabilizers improves the TS values, the rate of dehydrochlorination and the extent of discoloration.

It is shown that a commutative reduced ring R is a Baer ring if and only if it is a CS-ring; if and only if every dense subset of Spec (R) containing Max (R) is an extremally disconnected space; if and only if every non-zero ideal of R is essential in a principal ideal generated by an idempotent.

In this paper we examine the absorption and dispersion properties of a weak probe field via Electromagnetically Induced Transparency (EIT) in a four-level system. It is shown that under certain condition, using this model, the absorption cancellation is appeared and the medium becomes transparent to the weak probe field. It will be shown that the controlling of absorption and dispersion spectrum depends on some atomic parameters. The effects of quantum interference on the absorption and dispersion spectrum are also investigated.