57Fe Mössbauer investigations in the series Fe4−2xRuxSix(1.0≦x≦1.7)

⁵⁷Fe Mössbauer and magnetization studies on a new series Fe_4–2xRu_xSi_x (1.0x1.7) are reported. The system is seen to transform from a collinear ferromagnet for x1.2 to a cluster spin glass for x>=1.54 In the intermediate region the magnetic behaviour of the system, as probed by the Mössbauer effect, is dominated by the presence of clusters and their dynamics. The alloys have large ordering temperatures ( 750 K) throughout the series except for x>1.54 where they drop sharply. The moment values, in contrast, fall sharply from 4.8_B at x=1 to 0.5_B at x=1.6C. The average value of the HF at⁵⁷Fe measured at 15 K does not change significantly throughout the series.     

Variable electronegativity SCF-MO calculations on the electronic structure and spectra of some substituted benzenes I. Monosubstitutions

π-electron SCF-MO theory in its variable electronegativity formalism has been applied to some monosubstituted benzenes. Calculated charge densities and bond orders for the ground and the first excited electronic states are correlated with chemical reactivity and the changes in molecular geometry on electronic excitation. The calculated results for spectra are compared with those obtained using the PPP method and also with the available experimental data.     

Interaction between photons, “trapped electron” and vibronic excitation

The role of “trapped electron,” photon, and vibronic state coupling has been worked out in relation to an aspect of cancer, namely, to the activity of an anticancer drug. The main emphasis for such study comes from the fact that in cancerous systems the participation of usual electronic states of the molecule may not be sufficient. Because of disorder in the cancer tumour, additional states, viz. trapped electron states, could be formed in the manner of localised states in solids. The drug activity of mitomycin C obtained in this way agrees with the experimental values. An additional feature of the study is that it shows that it will be effective mainly in the initial phases of cancer.     

Chemical modification of silica surface by immobilization of functional groups for extractive concentration of metal ions

Increased utilization of mechanically stable synthetic matrices particularly silica gel as a solid support and its surface modification either by impregnation of organic ligands directly or covalent grafting through spacer unit for extractive concentration of trace elements are highlighted in the present article. Experimental evidences for existence of surface silanol and its chemical nature have explored the idea of silica surface modification. Recent methods of development in functionalized silica synthesis by attachment of various ligands or organic reagents to the silica surface and techniques of characterization of the modified surface have been reported. Analytical applications of various modified silica surfaces, in particular, adsorption of trace elements taking separation and preconcentration into account from complex synthetic mixture as well as natural water is presented.     

Sulfated nanozirconia: an investigation on acid-base properties and n-butane isomerization activity

Hydrated zirconia was synthesized by an organo-inorganic route employing surfactant and was sulfated using aqueous ammonium persulfate, followed by drying at 110 degrees C. The sample thus obtained was calcined at 600 degrees C to obtain sulfated zirconia and was characterized by several physicochemical methods. Crystallite sizes of sulfated zirconia were calculated from X-ray line broadening using the Debye-Scherer equation and were found to be in the range of 25 nm. When pretreated in air, the catalyst was found to exhibit butane isomerization activity at a temperature as low as 35 degrees C under atmospheric pressure. It showed conversion as high as 37% at 100 degrees C under normal pressure when pretreated in air, whereas nitrogen-pretreated catalyst showed zero activity under similar conditions. NH(3) and CO(2) temperature-programmed desorption studies on air- and helium-pretreated samples indicated that the catalyst surface changes appreciably during air pretreatment. Results on butane isomerization in conjunction with TPD studies suggest that zirconium-oxy sites play an important role in butane activation during the reaction.     

Recoil128I atoms in iodine pentoxide under /n, γ/ process

An attempt js made to study the behaviour of recoil¹²⁸I atoms in neutron irradiated I₂O₅ at ambient temperature. The initial retention is found to be 44±2%. However, a substantial increase /57±2%/ in the value is observed upon heating the sample at 473 K for 1 h prior to irradiation. A kinetic study of post-recoil thermal annealing of neutron irradiated material is also presented. Effect of pre-heat treatment results in a decrease of rate constants and saturation retention values at respective temperatures while the E_act for the overall process remains almost unaltered.     

Hot atom chemistry in oxyanion targets,part II1: Recoil behaviour of56Mn in permanganates

Fractional precipitation techniques have been utilized to separate the lower valent and parent forms of⁵⁶Mn in permanganate targets and an attempt is made to study a few aspects of chemical stabilization of recoil⁵⁶Mn in permanganates. Ammonium permanganate, recoil behaviour of which has not been studied previously, is chosen as one of the targets along with the potassium permanganate for initial retention and also for isothermal annealing.⁵⁶Mn initial retentions of about 12% and about 4% are obtained for potassium and ammonium permanganate, respectively, by activation from a Ra–Be neutron source. A usual trend for KMnO₄ and the reduction of recoil fragments by ammonium ions in NH₄MnO₄ are seen through the isothermal annealing study.     

Total synchronous fluorescence scan spectra of petroleum products

Extending the two-dimensional synchronous fluorescence scan to a three-dimensional total synchronous fluorescence scan (TSFS) spectral measurement gives the total synchronous fluorescence characteristics of a multifluorophoric sample at various possible wavelength intervals (Deltalambda), which could help to characterize multifluorophoric systems better. TSFS spectra of petroleum products such as diesel, kerosene, petrol, engine oil etc., available in the Indian market, are reported. Fluorescence in these samples is due to the presence of polycyclic aromatic hydrocarbons (PAHs) of various ring sizes. The TSFS contour plot profiles of the neat samples measured at right-angle geometry is a result of various energy-degrading photophysical processes such as inner filter effect, light attenuation, resonance energy transfer, collisional quenching etc. TSFS plots make it easy to obtain the optimized Deltalambda of an unknown sample of analytical interest. TSFS and the excitation-emission matrix (EEM) techniques are similar, but the contour profiles generated are different. The response of the TSFS contour profiles to dilution is different from that in the EEM contour profiles. Thus, TSFS can provide an alternative way of presenting the fluorescence response of concentrated multifluorophoric samples.     

One-Pot Convenient and High Yielding Synthesis of Dithiocarbamates

Summary. A convenient and high yielding method for the synthesis of diverse dithiocarbamates having various substituents including alkyl, aryl, heteroaryl, and alkylaryl at the thiol chain or at the amine chain or at both thiol and amine chains were developed by the one-pot reaction of mercaptans, amines, and bis(benzotriazolyl)methanethione in presence of amidine base under mild reaction conditions.