Unexpected regioselective debenzylation leading to modification of both rims of α-cyclodextrin

Diisobutylaluminum hydride-mediated debenzylation of perbenzylated α-cyclodextrin was investigated using modified conditions. It was found that the reaction proceeded much slower to allow a more controlled removal of benzyl groups. Prolonged reaction time led to the unprecedented observation that a cleavage of up to two benzyl groups can occur at the secondary rim in a highly regioselective manner.     

Study of quality control and metal distribution in urban airborne particulates

In this investigation, results of 33 elements in airborne samples collected continuously over nine urban locations are discussed. Inductively coupled plasma-atomic emission spectrometry technique was used for determining concentration of metals. Quality control was established prior to analysis of real air samples. The guidelines followed are based on USEPA Compendium Method IO-3.4. Uncertainty in analysis was also established. Based on the concentration of metals in airborne particulates, we attempted to study the metal distribution characteristics in ambient air at various urban locations. Metals such as Al, Ca, Fe were comparatively at higher concentrations than the other elements under study at most of the locations. The city vehicles operate on lead-free fuels; however, concentration of lead in urban dust was observed in the concentration range of 0.33–6.24 μg/m³. Soil samples were also collected from sites close to the air sampling locations. Soil samples were also analysed for metal content. Enrichment factor was determined for elements measured at nine urban locations. The data supports interpretation of results in terms of contribution of metals in airborne particulates from anthropogenic and noncrustal origin.     

Hypervalent iodine(V) mediated mild and convenient synthesis of substituted 2-amino-1,3,4-oxadiazoles

A simple protocol for the synthesis of 2-amino-1,3,4-oxadiazoles starting from the corresponding acylhydrazides by cyclodesulfurization of intermediate acylthiosemicarbazides mediated by o-iodoxybenzoic acid in good yields has been described. The protocol is mild with wide substrate scope, and thus a range of 2-amino-1,3,4-oxadiazoles have been prepared.     

Synthesis and characterization of metal substituted AlxCr1−x(acetylacetonate)3 single-source precursors for their application to MOCVD of thin films

A detailed study, involving the synthesis of a single-source precursor containing two metal ions sharing the same crystallographic site, has been undertaken to elucidate the use of such a single-source precursor in a CVD process for growing thin films of oxides comprising these two metals, ensuring a uniform composition and distribution of metal ions. The substituted complexes Cr_1−xAl_x(acac)₃, where acac = acetylacetonate, have been prepared by a co-synthesis method, and characterized using UV–Vis spectroscopy, TGA/DTA measurements, and single crystal X-ray diffraction at low temperature. All the studied compositions crystallize in the monoclinic space group P2₁/c with Z = 4 in the unit cell. It was observed that the ratio (Al:Cr) of the site occupancy for the metal ions, obtained from single crystal refinement, is in agreement with the results obtained from complexometric titrations. All the solid state structures have the metal in an octahedral environment forming six-membered chelate rings. M–O acac bond lengths and disorder in the terminal carbon have been studied in detail for these substituted metal–organic complexes. One composition among these was chosen to evaluate their suitability as a single-source precursor in a LPMOCVD process (low-pressure metal–organic chemical vapour deposition) for the deposition of a substituted binary metal oxide thin film. The resulting thin films were characterized by X-ray diffraction, scanning electron microscopy, and infrared spectroscopy.     

Photo Catalytic Degradation of Azo Dyes over Mn2+ Doped TiO2 Catalyst under UV/Solar Light:An Insight to the Route of Electron Transfer in the Mixed Phase of Anatase and Rutile

Mn²⁺ ion was doped into the TiO₂ matrix and its photocatalytic activity was evaluated for the degradation of a mono azo dye methyl orange (MO) and a di‐azo dye brilliant yellow (BY) under UV/solar light. X‐ray diffraction results revealed the phase transformation from anatase to rutile due to the inclusion of Mn²⁺ ion into the TiO₂ matrix. All the doped catalysts showed a red shift in the band gap to the visible region. The degradation reaction of the dyes was found to be dependent on its structure. It was found that mono azo dye degrades faster than di azo dye under UV/solar light. The rate constant under identical conditions calculated for the degradation of MO is 2.4 times (under UV light) and 4.5 times (under solar light) higher compared to BY. Among the photocatalysts studied, Mn²⁺(0.06 at.%)‐TiO₂ showed higher activity under both UV and solar light illumination. The synergestic effect in the bicrystalline framework of anatase and rutile effectively suppresses the charge carrier recombination and enhances the photocatalytic activity. The degradation reaction was followed by UV‐visible spectroscopy and the photoproducts formed were analyzed by GC‐MS techniques.     

An empirical study of ICASE learning curves and probability bounds for software development effort

In this paper, we investigate the existence of learning curves in software development. Under the assumption of independent and identical distribution (iid) of programmer’s experience and identical effort-experience learning curve relationship for different programmers, we illustrate the existence of an exponentially decreasing learning curve relationship between a programmer’s effort and his/her ICASE tool experience, and show that the effort-experience relationship is inelastic when a programmer’s ICASE tool experience is low. We analyze the impact of our assumptions on actual software development effort, and propose a tight probability upper bound and a central-limit theorem based probability estimator for estimating the approximate probability that the software development effort will be less than or equal to a certain number. Examples to illustrate the use of the probability estimator are also provided.     

A lead (II) selective PVC membrane potentiometric sensor based on a tetraazamacrocyclic ligand

A polymeric membrane based Pb(II) selective potentiometric sensor was developed by using 1,3,7,9-tetraaza-2,8-dithia-4,10-dimethyl-6,12-diphenylcyclododeca-4,6,10,12-tetraene (TDDDCT) as an electroactive material along with anion excluder sodium tetraphenylborate (NaTPB) and plasticizer dioctylphthalate (DOP). The best performance in terms of slope, concentration range and response time was exhibited by the membrane having TDDDCT:PVC:DOP:NaTPB in the ratio 3:32:62:3 (w/w%). Potentiometric results show that the developed sensor works well in the concentration range 5.0 × 10^?7–1.0 × 10^?1 M with a near Nernstian slope of 29.5 (±0.5) mV decade^?1. The detection limit is down to 2.5 × 10^?7 M. The working pH range of this sensor is 2.8–7.0 and it works well in partially nonaqueous medium up to 25 % (v/v) methanol and ethanol. It exhibits a fast response time of 10 s. Selectivity coefficient values of various interfering ions were determined by the fixed interference method (FIM). The sensor reveals good selectivity for Pb(II) ions over other metal ions investigated. The developed sensor is used in the determination of lead in ‘Eveready battery waste’ and as an indicator electrode in the potentiometric titration of Pb(II) against EDTA.     

Highly Efficient Proline Ester‐based Nickel Catalysts for Michael Addition of Thiophenols to α,β‐Enones

Two N₃O₂ pentadentate ligands, BMPP and BPPP, were prepared for synthesizing highly efficient nickel catalysts, [Ni(BMPP)(CH₃CN)](ClO₄)₂ ( 1 ) and [Ni(BPPP)(CH₃CN)](BPh₄)(ClO₄) ( 2 ), for thia‐Michael addition of thiophenols to α,β‐enones. X‐ray structures of 1 and 2 revealed that a labile CH₃CN molecule was bound to the nickel center of the catalysts. ESI‐MS spectroscopy indicated that thiolate replaced the bound CH₃CN molecule and coordinated to the nickel center during the catalytic cycle.     

Thermal studies on different classes of clinical dental composites

Various classes of dental composites have evolved over the years for various clinical applications, differing mainly in the relative proportions of their individual components (BisGMA, TEGDMA, UDMA, fillers, etc.). Four classes of composites have been investigated here via DSC and TG (after curing with blue light from a halogen light-curing unit): a ‘microhybrid’, a ‘nanocomposite’, a ‘flowable’ and a ‘fluoride-releasing’ variety. The aims were to compare various thermal properties amongst the four classes and also to compare the quality of polymerization of halogen light cure. We concluded that the DSC scans of all the polymers showed no exotherms, signifying the absence of any residual reactivity. However, the scans showed onset of endothermic regions before glass transition temperature (GTT), which may signify structural rearrangements within the polymers. The overall enthalpy ranged from ?1.4 to ?50 J g^?1, with significant differences between the ‘fluoride-releasing’ variety and the rest. The ‘fluoride-releasing’ variety showed the largest endotherm, signifying greater mass loss than the rest. The GTT (129 °C) did not differ significantly amongst the composite types. These same parameters, on a second DSC run of the same samples, followed a pattern similar to the first run, albeit to a lesser degree in magnitude. Hence, no benefit was gained by heating after the initial ‘light’ cure. The initial and total mass losses were higher for ‘fluoride-releasing’ (19 and 46%) and ‘flowable’ (12 and 38%) types compared to ‘microhybrid’ (3 and 24%) and ‘nanocomposite’ (4 and 20%). In a clinical scenario, the ‘fluoride-releasing’ composite may adequately photopolymerize, given its use in thin layers. The microhybrid and nanocomposites might also polymerize well in thinner layers without the need for a secondary heat treatment. The ‘flowable’ variety on the other hand, is not recommended to be subjected to a secondary heat treatment, due to its inferior thermal stability.