Influence of the cavity size of cyclodextrins on the photochromism of azoimidazoles

1-Alkyl-2-(arylazo)imidazole (RaaiR^/) exists in trans configuration about the –NN- bond. Upon optical excitation in UV region the trans-configuration isomerises to cis-RaaiR^/. The photochromism is very susceptible to internal substituents and external environment like solvent polarity, viscosity and presence of innocent foreign species. In this work, the trans-to-cis photoisomerisation of RaaiR^/has been studied in DMF solution of cyclodextrin (α/β/γ-CD). The rate of trans-to-cis isomerisation is decreased in presence of CD compared to native form of RaaiR^/. The quantum yield of the photoisomerisation is decreased by 35–55% in inclusion phase, [email protected]^/, than free photochrome and follows the rate sequence: free state > γ-cyclodextrin > β-cyclodextrin > α-cyclodextrin. The cis-to-trans isomerisation proceeds slowly in visible light irradiation while it is appreciably fast with increasing temperature. The activation energy (E_a) of cis → trans thermal isomerisation is also diminished compared to free state of photochrome. The absorption spectral studies have been used in case of Pai-C₁₈H₃₇ with β-CD and inclusion constant is K_b ?= ?0. 121 M^?1. The ¹H NMR spectral measurement also suggests interaction of aryl protons with cavity protons of β-CD. DFT computation is also attempted to examine the inclusion of RaaiR^/with CD and the negative values of binding energy show that the process of inclusion is spontaneous and complexes formed are stable.     

Synthetic studies on trans-clerodane diterpenoids and congeners : stereocontrolled total synthesis of (±)-4-methylene-9α-(3-oxobutyl)-5β, 8β,9β-trimethyl-trans-decalin and related intermediates

A stereocontrolled total synthesis of the title compound, a marine natural product as well as a degradation product of sigmosceptrellins and palauolide, has been accomplished by a simple route broadly applicable to certain trans-clerodanes and congeners. In addition, the synthesis of two key degradation products of ilimaquinone, which can serve as trans-clerodane precursors, and 4,4-ethylene-dioxy-9α-(2-hydroxyethyl)-5β, 8β,9β-trimethyl-trans-decalin, an intermediate employed earlier in a total synthesis of (±)-annonene, are described.     

Crystallization-Induced Emission Enhancement of Nanoclusters and One-Step Conversion of “Nanoclusters to Nanoparticles” as the Basis for Intracellular Logic Operations

Herein, we report the construction of intracellular logic operations using luminescent histidine stabilized gold nanoclusters (His Au NCs). The luminescence intensity of His Au NCs was found to be significantly enhanced following interaction with zinc ions, owing to “Crystallization induced emission enhancement”. Further, the luminescence intensity of His Au NCs was found to be effectively quenched in presence of sulphide ions, owing to transformation of emissive His Au NCs to non-emissive gold nanoparticles. Thus, the collective and individual effects of zinc ions and sulphide ions causing significant variation in the luminescence intensity of His Au NCs, were used as input parameters for construction of intracellular logic operations such as Tri state buffer, “on-off” switch and INHIBIT gate within mammalian cells.     

Simultaneous parallel and antiparallel self-assembly in a triazole/amide macrocycle conformationally homologous to D-,L-α-amino acid based cyclic peptides: NMR and molecular modeling study

A 1,4-linked triazole/amide based peptidomimetic macrocycle, synthesized from a triazole amide oligomer of cis-furanoid sugar triazole amino acids, possesses a conformation resembling the D-,L-α-amino acid based cyclic peptides despite having uniform backbone chirality. It undergoes a unique mode of self-assembly through an antiparallel backbone to backbone intermolecular H-bonding involving amide NH and triazole N2/N3 as well as parallel stacking via amide NH and carbonyl oxygen H-bonding, leading to the formation of a tubular nanostructure.     

Addition of halide to π-bond directly from aqueous NaX solution: a general strategy for installation of two different functional groups

Activation of π-bond with organic Lewis acid and cationic surfactant mediated direct transfer of halides to alkyne and alkene are demonstrated to afford α,α-dihaloketones and other valuable synthons with outstanding selectivities.     

Exploring naphthyl derivatives as SARS-CoV papain-like protease (PLpro) inhibitors and its implications in COVID-19 drug discovery

Molecular Diversity - Novel coronavirus disease 2019 (COVID-19) emerges as a serious threat to public health globally. The rapid spreading of COVID-19, caused by severe acute respiratory syndrome...     

Utility of a Ferrocene Unit in a Cyclometallated Cp*Ir(III) Catalyst during Water Oxidation: Exploring Bimetallic Cooperativity

Ferrocene functionalized 2-phenylpyridine iridium(III) pentamethylcyclopentadienyl complex is synthesized and probed for oxygen evolution from water. The excellent activity of this system has been rationalized by proposing a Fe(III)/Ir(IV) transient intermediate where bimetallic redox synergism between the Fe and Ir centres possibly provide an alternative pathway rather than a conventional Ir(V) based cycle.