Catalytic cyclopropanation of olefins using copper(I) diphosphinoamines

Catalytic cyclopropanation reactions of olefins with ethyl diazoacetate were carried out using copper(I) diphosphinoamine (PPh₂)₂N(R) (R = ⁱPr, H, Ph and –CH₂–C₆H₄–CHCH₂) complexes at 40 °C in chloroform. High yields of the cyclopropanes were obtained in all cases. The rate of the reaction was influenced by the nuclearity of the complex and the binding mode of the ligand which was either bridging or chelating. Comparison of isostructural complexes shows that the rate follows the order R = ⁱPr > H > Ph, where R is the substituent on the N. However, cyclopropane formation versus dimerization of the carbene, and trans to cis ratios of cyclopropane was similar in all cases. The nearly identical selectivity for different products formed was indicative of a common catalytic intermediate. A labile “copper–olefin” complex which does not involve the phosphine or the counterion is the most likely candidate. The differences in the reaction rates for different complexes are attributed to differences in the concentration of the catalytically active species which are in equilibrium with the catalytically inactive copper–phosphinoamine complex. To test the hypothesis a diphosphinoamine polymer complexed to copper(I) was used as a heterogeneous catalyst. Leaching of copper(I) and deactivation of the catalyst confirmed the proposed mechanism.     

Structural investigations on Quinone Methides for understanding their properties in confined media

Encapsulation of 4−[(4′-hydroxy−3′,5′-dimethylphenyl)(aryl)-methylene]−2,6−dimethyl-cyclohexa−2,5−dienones (when aryl=4−hydroxyphenyl 1, 4−methoxyphenyl 2, 2,3,4-trimethoxy phenyl 3) by β-cyclodextrin is studied. The compound 2 is selectively encapsulated by β-cyclodextrin. The result is rationalised by analysing the structural parameters from the crystal structure of 1–3. The visible spectra of the compounds 2 and 3 at pH 9.0 show red shifts on the absorption maxima upon addition of cetyltrimethylammonium bromide (CTAB). For example, addition of a solution of CTAB to aqueous ethanolic solution of 2 at pH 9 causes shift of the absorption at 578–593 nm (Δλ_max=15 nm). The advantage of this observation is taken to use 2 and 3 to determine the critical micelle concentration of CTAB in basic medium.Graphical Abstract Structural investigations on quinone methides for understanding their properties in confined media Rupam J. Sarma, Andrei S. Batsanov, Ritu Kataky, Jubaraj B. Baruah      

Measuring microelastic properties of stratum corneum

We explore the compression moduli of a thin biological tissue through probe microscopy. The elastic modulus (E') of isolated stratum corneum is measured at varying depths through the use of an atomic force microscope (AFM) as well as a nano-indentor (Hysitron Triboscope). In addition, a nano-DMA is used to measure visco-elastic properties. Measurements on dry and hydrated stratum corneum show an order of magnitude difference in E' and the measured tandelta (E'/E') is seen to increase from approximately 0.1 to 0.25. In addition, extensive validation of the experiments is conducted with different indentation probes at different force ranges to reveal the effects of indentor geometry and indentation depth on the measured elastic modulus. The sensitivity of the measurements is tested with applying known treatments to stratum corneum and exploring their effects on biomechanical parameters.     

Visible-light-mediated Gomberg-Bachmann reaction: An efficient photocatalytic approach to 2-aminobiphenyls

An efficient, metal-free and highly selective protocol for the synthesis of 2-aminobiphenyls via visible-light-mediated arylation of anilines using aryl diazonium salts (Gomberg-Bachmann reaction) has been reported. The reaction is an example of photoredox catalysed direct C(sp²)–H arylation of anilines using eosin Y as an organophotoredox catalyst. The presented visible-light-mediated environmentally sustainable approach has the potential to earn a decent position among the classical and contemporary methods for the synthesis of aminobiaryls.     

Anomalously large contributions of vacancies and dislocations to Hall coefficient and thermoelectric power of copper films

Effect of vacancies and dislocations on Hall coefficient (R_H) and thermoelectric power (TEP) of copper films has been deduced from annealing behaviour of various transport properties. The large contributions of these defects may be attributed to variations in the density of hole-like states and/or the energy dependence of conductivity (at the Fermi surface), caused by changes in the extent and/or degree of curvature of the necks at Fermi surface.     

Visible light triggered regioselective ring expansion of N-tosylaziridines: An efficient approach to 2-nitroazetidines

Visible light induced ring expansion of N-tosylaziridines with 1-bromo-1-nitroalkanes to afford 2-nitroazetdines in moderate to excellent yields with high regio- and diastereoselectivity is reported. The salient features of the protocol include the first synthesis of 2-nitroazetidines, operational simplicity, utilization of clean, inexpensive and sustainable resources like visible light and atmospheric oxygen under photoredox catalysis at room temperature in one-pot procedure.     

Photocatalytic synthesis of tetra-substituted furans promoted by carbon dioxide

We report a simple protocol for the transition metal-free, visible-light-driven conversion of 1,3-diketones to tetra-substituted furan skeleton compounds in carbon dioxide (CO₂) atmosphere under mild conditions. It was found that CO₂ could be incorporated at the diketone enolic OH position, which was key to enabling the cleavage of a C–O bond during the rearrangement of a cyclopropane intermediate. This method allows for the same-pot construction of two isomers of the high-value tetra-substituted furan scaffold. The synthetic scope and preliminary mechanistic investigations are presented.

A CO₂-promoted transition metal-free photocatalytic synthesis of tetra-substituted furan derivatives from 1,3-diketones as the only starting material.     

A Convenient Synthesis of Aryl‐Substituted N‐Carbamoyl/N‐Thiocarbamoyl Narcotine and Related Compounds

The reaction of nornarcotine and 5‐bromonornarcotine, synthesized from noscapine, with suitable aromatic isocyanates or isothiocyanates provides a general method for the synthesis of aryl‐substituted N‐carbamoyl or N‐thiocarbamoylnarcotine and related compounds. Similarly, 15a has been prepared via the reduction of the lactone ring moiety of noscapine. Also, an improved procedure, which utilizes narcotine N‐oxide⋅HCl for generation of nornarcotine, is described.     

MnO2 Nanowires as an Electrode Material for Gel Polymer Electrolyte-Based Zn-Air Battery

Zn-air batteries (ZABs) have drawn an attention due to their high energy density, less complicated chemistry, and relatively low cost. Electrocatalyst plays a significant role in the oxygen reduction reaction (ORR) and oxygen evolution reaction (OER) that occurs during the operation. Various valance states of manganese make MnO₂ as an attractive electrocatalyst. In the present work, MnO₂ nanowires with diameter of 80–90 nm are synthesized via hydrothermal route and tested for electrocatalytic performance in a comparative study of ZABs fabricated using liquid and gel polymer electrolytes (GPEs). The open circuit voltage (OCV) of device lies in the range of 1.35–1.4 V. GPEs based devices show higher stability and exhibited 45 cycles (20 min per cycle) having discharge plateau above 1.06 V at a discharge current density of 1.59 mA cm⁻² while liquid electrolyte-based devices show 20 cycles (4 min per cycle at discharge current rate of 3 mA cm⁻²).     

Impact of Multimeric Ferrocene-containing Cyclodecapeptide Scaffold on Host-Guest Interactions at a β-Cyclodextrin Covered Surface

Among non-covalent bonds, the host-guest interaction is an attractive way to attach biomolecules to solid surfaces since the binding strength can be tuned by the nature of host and guest partners or through the valency of the interaction. For that purpose, we synthesized cyclodecapeptide scaffolds exhibiting in a spatially controlled manner two independent domains enabling the multimeric presentation of guest molecules on one face and the other face enabling the potential grafting of a biomolecule of interest. In this work, we were interested in the β-cyclodextrin/ferrocene inclusion complex formed on β-CD monolayers functionalized surfaces. By using surface sensitive techniques such as quartz crystal microbalance and surface plasmon resonance, we quantified the influence of the guest valency on the stability of the inclusion complexes. The results show a drastic enhancement of the affinity with the gradual increase of guest valency. Considering that the sequential binding events are equal and independent, we applied the multivalent model developed by the Huskens group to extract intrinsic binding constants and an effective concentration of host.