A Mild and Efficient CH2‐Extrusion Reaction for the Enantiospecific Synthesis of Highly Configurationally Stable Tröger Bases

A novel CH₂‐extrusion reaction leading to the transformation of ethano‐Tröger bases into disubstituted methano derivatives is reported (yields up to 93 %). Under mild and metal‐free oxidative conditions, a loss of CH₂ and a ring contraction are provoked. Despite two bond cleavages at stereogenic nitrogen and carbon centers and a temporary rupture of the bicyclic structure, a very high enantiospecificity (es≥98 %) is observed for this unusual reaction.     

Determination of boron concentration in borosilicate glass,boron carbide and graphite samples by conventional wet-chemical and nuclear analytical methods

Boron is an important element in nuclear technology. A comparative study was carried out for the determination of boron in borosilicate glass, boron carbide and graphite samples by wet-chemical and nuclear analytical methods. Wet chemical methods namely titrimetry, Inductively Coupled Plasma Mass Spectrometry and ICP Optical Emission Spectrometry and nuclear analytical methods namely Particle Induced Gamma-Ray Emission and Nuclear Reaction Analysis were used. Boron concentrations were in trace (mg kg^?1) level in graphite and percentage level in borosilicate glass and boron carbide.     

Performance of digital gamma ray spectrometer for loss free counting and its application to NAA using short-lived radionuclides

A digital gamma-ray spectrometer with loss-free counting system was used for real time correction for dead time (DT) due to pulse processing in the electronics. This spectrometer was used for radioactive assay of samples having constant as well as varying DT conditions. The system was tested by measuring activity of short and medium lived nuclides namely ²⁸Al, ⁵²V and ¹²⁸I in the DT ranges of 80–2 %. Using this spectrometer and neutron activation analysis (NAA), concentrations of Al, V, Ti, Ca, Dy and Mn were determined in some samples and reference materials.     

Determination of aluminium contents in selected food samples by instrumental neutron activation analysis

Food and food products are the main sources of Aluminium entering the human body. In order to know aluminium contents in food and food products, selected 26 samples from local market were analyzed by instrumental neutron activation analysis (INAA) using reactor neutrons and high resolution gamma-ray spectrometry. INAA using 1,779 keV γ-ray of ²⁸Al (2.24 min) was used for aluminium concentrations in the range of 33–529 mg kg^?1. Two NIST standard reference materials (SRMs) and two IAEA reference materials (RMs) were analyzed by INAA for quantification of aluminium as a part of method validation.     

Utilization of pneumatic carrier facility of Dhruva reactor for trace element determination by neutron activation analysis

The pneumatic carrier facility (PCF) of Dhruva reactor is being extensively used for neutron activation analysis (NAA) studies pertaining to research work as well as routine sample analysis. It is useful for the determination of trace elements using short and medium half-lives radioisotopes produced in neutron activation with available higher neutron flux (~5 × 10¹³ cm^?1 s^?1). Solid samples placed in high density polypropylene capsule, are irradiated for 1 min duration and radioactive assay is carried out by high resolution gamma ray spectrometry. Design aspects of PCF and various applications to samples of diverse matrices using NAA are presented.     

Angular distributions and cross-sections of projectile-like fragments in the 19F + 159Tb reaction

The angular distribution of projectile-like fragments (PLFs) in the ¹⁹F + ¹⁵⁹Tb reaction have been measured at beam energy equal to 98MeV. Angular distributions of PLFs showed a systematic change with increasing mass transfer, starting from the peaking at grazing angle for heavier PLFs to very forward peaked angular distributions for lighter PLFs. Cross-sections of the different PLFs were obtained by integrating their centre-of-mass angular distributions. The PLF cross-sections have been compared with the incomplete fusion cross-sections obtained from the earlier measurement of the evaporation residue cross-section. Reduced cross-sections for lighter PLFs were observed to be higher compared to those observed in ¹⁹F + ⁶⁶Zn reaction at similar values of E _cm/V _b. Also, elastic scattering measurements were carried out to get information about the grazing angle and total reaction cross-section.     

Exhaustive analysis of frontal copolymerization of functionalized monovinyl and divinyl monomers

A series of copolymers of 2-hydroxyethyl methacrylate (HEMA)/glycidyl methacrylate (GMA) and ethylene dimethacrylate (EGDM) were synthesized by frontal polymerization (FP). This study was conducted to investigate the effect of crosslink density, type and concentration of initiator, the use of a complex initiator system, porogen, and diluent on the most relevant parameters of FP, such as sustainability of the front, temperature profile, front velocity, and yield. The products were also characterized for intruded pore volume, pore-size distribution, epoxy-functionality number, and surface morphology. Higher crosslink densities (CLDs) and initiator concentration produced higher front velocities, whereas no trend in front temperature was noted. A complex initiation system was effective in stabilizing and increasing the polymerization yield. Relative to suspension polymerization (SP), FP products synthesized without a solvent were microporous, whereas micro-to-macroporous products were obtained in the presence of a solvent (for HEMA-EGDM polymers). We also present, explain, and discuss the exotic patterns observed under a microscope. We observed two basic types of spatial patterns, namely, planar and nonplanar patterns. The type of planar pattern observed under scanning electron microscopy (SEM) has a spatial impulse that appears as a loop followed by regular periodic motion in the radial and axial directions. This behavior gives rise to a repeating pattern that is a few microns thick. Also, nonplanar patterns, namely, layered concentric rings and winding staircase patterns, were observed under SEM.     

A Shimizu Non‐Aldol Approach to the Formal Total Synthesis of Palmerolide A

A formal total synthesis of palmerolide A has been accomplished by assembling three fragments by means of successive Julia–Kocienski olefination, Yamaguchi esterification, and ring‐closing metathesis (RCM). Our initial efforts to combine the first two fragments through a Julia–Kocienski reaction between a secondary sulfone and a ketone were not successful; nevertheless, it was feasible between a primary sulfone and aldehyde. Yamaguchi esterification with the third fragment then set the stage for a RCM reaction. Initial failure of the RCM with a PMB‐ether adjacent to the olefins and the difficulty in cleaving the PMB‐ether prompted us to change the choice of protecting groups, which then paved the way to the macrocyclic core of palmerolide A.     

Copper-free click biofunctionalization of silicon nitride surfaces via strain-promoted alkyne-azide cycloaddition reactions

Cu-free "click" chemistry is explored on silicon nitride (Si(3)N(4)) surfaces as an effective way for oriented immobilization of biomolecules. An ω-unsaturated ester was grafted onto Si(3)N(4) using UV irradiation. Hydrolysis followed by carbodiimide-mediated activation yielded surface-bound active succinimidyl and pentafluorophenyl ester groups. These reactive surfaces were employed for the attachment of bicyclononyne with an amine spacer, which subsequently enabled room temperature strain-promoted azide-alkyne cycloaddition (SPAAC). This stepwise approach was characterized by means of static water contact angle, X-ray photoelectron spectroscopy, and fluorescence microscopy. The surface-bound SPAAC reaction was studied with both a fluorine-tagged azide and an azide-linked lactose, yielding hydrophobic and bioactive surfaces for which the presence of trace amounts of Cu ions would have been problematic. Additionally, patterning of the Si(3)N(4) surface using this metal-free click reaction with a fluorescent azide is shown. These results demonstrate the ability of the SPAAC as a generic tool for anchoring complex molecules onto a surface under extremely mild, namely ambient and metal-free, conditions in a clean and relatively fast manner.     

Investigation of Nanoscopic Free Volume and Interfacial Interaction in an Epoxy Resin/Modified Clay Nanocomposite Using Positron Annihilation Spectroscopy

Epoxy/clay nanocomposites are synthesized using clay modified with the organic modifier N,N‐dimethyl benzyl hydrogenated tallow quaternary ammonium salt (Cloisite 10A). The purpose is to investigate the influence of the clay concentration on the nanostructure, mainly on the free‐volume properties and the interfacial interactions, of the epoxy/clay nanocomposite. Nanocomposites having 1, 3, 5 and 7.5 wt. % clay concentrations are prepared using the solvent‐casting method. The dispersion of clay silicate layers and the morphologies of the fractured surfaces in the nanocomposites are studied using X‐ray diffraction (XRD) and scanning electron microscopy (SEM), respectively. The observed XRD patterns reveal an exfoliated clay structure in the nanocomposite with the lowest clay concentration (≤1 wt. %). The ortho‐positronium lifetime (τ₃), a measure of the free‐volume size, as well as the fractional free volume (f_v) are seen to decrease in the nanocomposites as compared to pristine epoxy. The intensity of free positron annihilation (I₂), an index of the epoxy–clay interaction, decreases with the addition of clay (1 wt. %) but increases linearly at higher clay concentrations. Positron age‐momentum correlation measurements are also carried out to elucidate the positron/positronium states in pristine epoxy and in the nanocomposites. The results suggest that in the case of the nanocomposite with the studied lowest clay concentration (1 wt. %), free positrons are primarily localized in the epoxy–clay interfaces, whereas at higher clay concentrations, annihilation takes place from the intercalated clay layers.