A facial microwave-assisted synthesis, spectroscopic characterization and preliminary complexation studies of calix[4]pyrroles containing the hydroxamic-acid moiety

The synthesis, spectroscopic characterization and preliminary complexation properties of functionalized calix[4]pyrroles are described. To date, two generalized preparative approaches have been pursued (i) modifying the basic pyrrole-plus-ketone synthesis of calix[4]pyrrole by using microwave irradiation protocol, (ii) the basic meso-tetra(methyl) meso-tetra(p-nitrophenyl) calix[4]pyrrole skeleton was functionalized to give hydroxamic acids, especially in the meso-position of the macrocycles. The structures of novel calix[4]pyrrole hydroxamic acid derivatives were confirmed on the basis of various physico-chemical techniques such as elemental analysis, FT-IR, ¹H NMR and FAB-Mass. The results of preliminary studies on the extraction of vanadium (V) with the host calix[4]pyrrole hydroxamic acids were elucidated by significant examination of UV–Vis spectroscopy and ICP-AES. Single crystal structure of basic meso-tetra(methyl) meso-tetra (p-nitro phenyl) calix[4]pyrrole moiety has also been reported.     

Coagulation of nanoparticles in reverse micellar systems: a Monte Carlo model

The process of formation of nanoparticles obtained by mixing two micellized, aqueous solutions has been simulated using the Monte Carlo technique. The model includes the phenomena of finite nucleation, growth via intermicellar exchange, and coagulation of nanoparticles after their formation. Using the model, an exploratory study has been conducted to analyze whether the coagulation of nanoparticles is the reason for the formation of nanoparticles whose sizes are comparable to the size of the reverse micelles. The model explains the possible mechanism of coagulation of semiconductor nanoparticles formed within reverse micelles and its effect on the evolution of their size with time. The model is predictive in nature, and the simulation results compare well with those observed experimentally.     

Enforcing solution phase nanoscopic aggregation in a palindromic tripeptide

C-terminal dimerization of a tripeptide palindrome afforded fibrillation in solution through an assembly probably driven by hydrogen bonding and hydrophobic contributions; such an approach provides an expeditious entry into fabrication of fibrillating peptides from non-fibrillating peptide sequences.     

Relationship between torsional frequency and potential barrier height forAB n type molecular system

A relationship between the torsional frequency (v ₁₀) and the potential barrier (V _n) has been determined forAB _n type molecular system havingn-fold symmetry axis. It is found thatv ₁₀ varies prominently asV _n ^1/2 ,V _n andV _n ² in certain ranges. TheV _n value computed fromv ₁₀ andI* _r has been compared with that obtained from other experimental data for someAB _n units in different molecular-crystalline systems. Although there is in general a good agreement, in some cases the values differ significantly, perhaps due to the erroneous assignment of torsional mode and/or the large errors in theV _n value obtained from other experimental data.     

Fluorescence and absorption spectra of Rose-Bengal dye in the presence of surfactants

The fluorescence and absorption spectra of Rose Bengal dye in aqueous solution have been studied in the presence of various nonionic, anionic and cationic surfactants. With cationic and nonionic surfactants, shifts occur in the absorption and emission peaks of the dye solution, with a large enhancement in the absorption and fluorescence intensity at the shifted λ_max. No appreciable change in the absorption and fluorescence spectra of the dye has been observed on the addition of anionic surfactants.All the changes observed in the absorption and fluorescence spectra of the dye solution with surfactants may be attributed, to binding of the surfactant with dye molecules and the disaggregation of the dye multimer forms into the monomeric form.     

Dependence of pion-nucleus total cross-section on the nuclear density and pion-nucleon off-shell amplitude

Total cross-section forπ ⁺, using the high energy approximation, have been calculated for¹²C and³²S at various energies around the (3, 3) resonance in the free pion-nucleon system. It is observed that the shift in energy of the position of the maximum in the pion-nucleus cross-section with respect to that in the free pion-nucleon system depends sensitively on the shape of the nuclear density. Using the realistic density it is further found that the shift due to the off-shell behaviour of the pion-nucleon scattering amplitude is very small. This observation is different from that reported in the literature by other authors.     

Effect of X-irradiation on PVAc thermoelectrets

TSD studies of PVAc thermoelectrets reveal that the magnitudes of β and α′-peaks increase whereas that of α-peak decreases with the time of X-irradiation. The total residual charge as well as the charge corresponding to the α-peak are found to decrease linearly with the time of X-irradiation.     

Quantitative Auger electron spectroscopy analysis of binary alloys with separate matrix correction factors for bulk and surface

A new method which takes into account the separate matrix correction factors for bulk and surface has been tried out for quantitative Auger electron spectroscopy analysis of binary alloys. The calculations use an iteration scheme. It has been applied to the Fe-Cr alloys studied at this Centre and the Auger electron spectroscopy data for the other alloy systems available in literature. The results are now more compatible with the expectation that the surface composition is different from the bulk.