x-dependence of the quark distribution functions in the χCQM<Subscript>config</Subscript>

Chiral constituent quark model with configuration mixing (χCQM_config) is known to provide a satisfactory explanation of the “proton spin problem” and related issues. In order to enlarge the scope of χCQM_config, we have attempted to phenomenologically incorporate x-dependence in the quark distribution functions. In particular, apart from calculating valence and sea quark distributions q_val(x) and q̄(x), we have carried out a detailed analysis to estimate the sea quark asymmetries d̄(x)-ū(x), d̄(x)/ū(x) and as well as spin independent structure functions F₂ ^p(x)-F₂ ⁿ(x) and F₂ ⁿ(x)/F₂ ^p(x) as functions of x. We are able to achieve a satisfactory fit for all the above mentioned quantities simultaneously. The inclusion of effects due to configuration mixing have also been examined in the case F₂ ^p(x)-F₂ ⁿ(x) and F₂ ⁿ(x)/F₂ ^p(x) where the valence quark distributions dominate and it is found that it leads to considerable improvement in the results. Further, the valence quark structure has also be tested by extrapolating the predictions of our model in the limit x→1 where data is not available.     

Construction of Polyheterocyclic Compounds by Lewis Acid Mediated Intramolecular [3+2] Cycloaddition Reaction

An efficient domino approach has been developed for the synthesis of polyheterocyclic derivatives constituting pyrrole moiety. Lewis acid catalyzed reaction of 2-substituted-2-hydroxy-indane-1,3-diones and 1,4-benzoxazinone derivatives resulted in the formation of polyheterocyclic compounds under metal-free and mild conditions in good to excellent yield. The reaction is highly regioselective for C−C and C−N bond construction proceeded via intramolecular [3+2] cycloaddition reaction. The protocol is highly efficient, obviates column chromatography and the products are obtained by simple filtration followed by washing with solvent.     

Synthesis and thermal behaviour of polyamide 6/bentonite/ammonium polyphosphate composites

In order to achieve acceptable levels of flame retardancy of polymers, phosphorus-based flame retardant (FR) additives at about 20-30% w/w are required which is too high for conventional synthetic fibres. To know whether more finely sized particles of conventional FRs with or without nanoclay are more effective at the same concentration, composites of PA6 with bentonite and ammonium polyphosphate (APP) have been prepared by melt processing in a twin-screw extruder. XRD peaks and TEM images of PA6/Org-bentonite composite show partially ordered intercalation and ordered exfoliation. Thermal analysis in He shows that thermal stability of PA6 nanocomposite has increased by 18 °C compared with pure PA6 during degradation after 425 °C but it has decreased by 100 °C on inclusion of APP in PA6/nanoclay composites. The char yield is increased by 20% in PA6/bentonite/APP composites. No effect on thermal stability or char yield is observed by reducing the particle size of APP.     

Synthesis and in vitro cytotoxic activity of a natural peptide of plant origin

Present work reports the first total synthesis of a phenylalanine and glycine-rich cyclopolypeptide podacycline B by coupling of tripeptide Boc-L-phe-gly-L-phe-OH and tetrapeptide L-ala-gly-L-thr-L-ile-OMe followed by cyclization of linear heptapeptide segment. The chemical structure of the compound was elucidated by FTIR, ¹H NMR, ¹³C NMR, FAB MS spectral data and elemental analyses. The newly synthesized peptide was subjected to biological screening and found to possess high cytotoxicity against Dalton’s lymphoma ascites (DLA) and Ehrlich’s ascites carcinoma (EAC) cell lines with IC₅₀ values of 13.2 and 15.5 μM, in addition to moderate anthelmintic activity against earthworms M. konkanensis, P. corethruses and Eudrilus sp. at a dose of 2 mg ml^?1.     

Rietveld refinement and impedance spectroscopy of calcium titanate

Single phase perovskite CaTiO₃ has been synthesized by conventional solid state reaction technique. The ceramic was characterized by XRD at room temperature and its Rietveld refinement inferred orthorhombic crystal structure with the space group Pbnm. The field dependence of dielectric relaxation and conductivity was measured over a wide frequency range from room temperature to 673 K. Analysis of Nyquist plots of CaTiO₃ revealed the contribution of many electrically active regions corresponding to bulk mechanism, distribution of grain boundaries and electrode processes. The dc conductivity depicted a semiconductor to metal type transition. Frequency dependence of dielectric constant (ε′) and tangent loss (tan δ) show a dispersive behavior at low frequencies and is explained on basis of Maxwell-Wagner model and Koop's theory. Both conductivity and electric modulus formalisms have been employed to study the relaxation dynamics of charge carriers. The variation of ac conductivity with frequency at different temperatures obeys the universal Jonscher's power law (σ_ac α ω^s). The values of exponent ‘s’ lie in the range 0.13 ≤ s ≤ 0.33, which in light of CBH model suggest a large polaron hopping type of conduction mechanism.