Micelle-mediated synthesis of quinoxaline, 1,4-benzoxazine and 1,4-benzothiazine scaffolds from styrenes.

A range of heterocycles based on quinoxalines, 1,4-benzoxazines and 1,4-benzothiazines have been accessed from styrenes by reacting them with benzene-1,2-diamine, 2-aminophenol and 2-aminothiophenol respectively in micellar medium. This reaction occurring in a less explored cetylpyridinium bromide (CPB) micellar medium operates in the presence of NBS through a tandem hydrobromination-oxidation cascade, converting styrenes to phenacyl bromides. Its subsequent nucleophilic addition with aromatic 1,2-dinucleophiles and further transformations led to the formation of heterocyclic constructs. The locus of the reaction site was confirmed through NMR studies and the types of interactions between the CPB and solubilizates were established by DFT calculations.

Insights into the binding mechanism of ascorbic acid and violaxanthin with violaxanthin de-epoxidase (VDE) and chlorophycean violaxanthin de-epoxidase (CVDE) enzymes.

Photosynthetic organisms have evolved to work under low and high lights in photoprotection, acting as a scavenger of reactive oxygen species. The light-dependent xanthophyll cycle involved in this process is performed by a key enzyme (present in the thylakoid lumen), Violaxanthin De-Epoxidase (VDE), in the presence of violaxanthin (Vio) and ascorbic acid substrates. Phylogenetically, VDE is found to be connected with an ancestral enzyme Chlorophycean Violaxanthin De-Epoxidase (CVDE), present in the green algae on the stromal side of the thylakoid membrane. However, the structure and functions of CVDE were not known. In search of functional similarities involving this cycle, the structure, binding conformation, stability, and interaction mechanism of CVDE are explored with the two substrates compared to VDE. The structure of CVDE was determined by homology modeling and validated. In silico docking (of first-principles optimized substrates) revealed it has a larger catalytic domain than VDE. A thorough analysis of the binding affinity and stability of four enzyme-substrate complexes is performed by computing free energies and their decomposition, the root-mean-square deviation (RMSD) and fluctuation (RMSF), the radius of gyration, salt bridge, and hydrogen bonding interactions in molecular dynamics. Based on these, violaxanthin interacts with CVDE to a similar extent as that of VDE. Hence, its role is expected to be the same for both enzymes. On the contrary, ascorbic acid has a weaker interaction with CVDE than VDE. Given these interactions drive epoxidation or de-epoxidation in the xanthophyll cycle, it immediately discerns that either ascorbic acid does not participate in de-epoxidation or a different cofactor is necessary as CVDE has a weaker interaction with ascorbic acid than VDE.

Anion Sensing by Novel Triarylboranes Containing Boraanthracene: DFT Functional Assessment, Selective Interactions, and Mechanism Demonstration.

Analytical methods often involve expensive instrumentation and tedious sample pretreatment for an analyte detection. Being toxic and detrimental to human health, sensing of cyanide (CN-), fluoride (F-), chloride (Cl-), bromide (Br-), nitrate (NO3 -), acetate (CH3COO-), and bisulfate (HSO4 -) is performed by a boron-based molecular receptor, N,N,N,3,5-pentamethyl-4-{2-thia-9-boratricyclo[8.4.0.03,8]tetradeca-1(10),3(8),4,6,11,13-hexaen-9-yl}anili-nium (1), and the three newly designed receptors from it. Thermodynamics, electronic structure, and photophysical properties are computed by employing density functional theory (DFT) and time-dependent density functional theory (TD-DFT) to explore selective sensing of these anions and its mechanism. Free-energy changes (ΔG) and binding energies (ΔE) suggest that among these anions, only binding of CN- and F- is thermodynamically feasible with a very strong binding affinity with the receptors. Boron atoms containing positive natural charges act as the electrophilic centers to bind the anions involving a 2p-2p orbital overlap resulting in charge transfer. In the receptor-analyte complexes with CN- and F-, fluorescence is quenched due to the intramolecular charge transfer transitions (π-π* transitions in the case of the receptors lead to fluorescence), internal conversion, and associated configurational changes. Among the six tested functionals, CAM-B3LYP/6-31G(d) is found to be the most accurate one. The designed receptors are better fluorescent probes for F- and CN-, demonstrating their importance for the practical utility.

Exploring Bikaverin as Metal Ion Biosensor: A Computational Approach.

A computational exploration of fungi produced pigment bikaverin as a biosensor towards bioavailable metal ions is presented. Systematic studies of the optimized ground and excited state geometries were attempted for exploring metal ion binding pocket, comparative binding propensity and optical properties of the bikaverin and its adducts with studied metal ions. The screening of thirteen (13) bioavailable metal ions, revealed a range of binding strength towards bikaverin receptor with Ca2+, Mg2+ and Al3+as the strongest binders. Besides, upon binding to bikaverin receptor an enhancement in its fluorescence intensity was observed in the order Ca2+> Al3+> Mg2+. The computationally predicted selectivity of bikaverin receptor towards Ca2+was experimentally corroborated through the preliminary fluorescence studies. The bikaverin probe showed an enhancement of fluorescence emission in presence of Ca2+ ions in buffered aqueous medium.