Marine algal antagonists targeting 3CL protease and spike glycoprotein of SARS-CoV-2: a computational approach for anti-COVID-19 drug discovery.

The COVID-19 pandemic has severely destructed human life worldwide, with no suitable treatment until now. SARS-CoV-2 virus is unprecedented, resistance against number of therapeutics and spreading rapidly with high mortality, which warrants the need to discover new effective drugs to combat this situation. This current study is undertaken to explore the antiviral potential of marine algal compounds to inhibit the viral entry and its multiplication using computational analysis. Among the proven drug discovery targets of SARS-CoV-2, spike glycoprotein and 3-chymotrypsin-like protease are responsible for the virus attachment and viral genome replication in the host cell. In this study, the above-mentioned drug targets were docked with marine algal compounds (sulfated polysaccharides, polysaccharide derivatives and polyphenols) using molecular docking tools (AutoDockTools). The obtained results indicate that κ-carrageenan, laminarin, eckol, trifucol and ß-D-galactose are the top-ranking compounds showing better docking scores with SARS-CoV-2 targets, than the current experimental COVID-19 antiviral drugs like dexamethasone, remdesivir, favipiravir and MIV-150. Further, molecular dynamic simulation, ADMET and density functional theory calculations were evaluated to substantiate the findings. To the best of our knowledge, this is the first report on in silico analysis of aforesaid algal metabolites against SARS-CoV-2 targets. This study concludes that these metabolites can be curative for COVID-19 in the hour of need after further validations in in vitro and in vivo testings.Communicated by Ramaswamy H. Sarma.

Anthracene-based fluorescent probe: Synthesis, characterization, aggregation-induced emission, mechanochromism, and sensing of nitroaromatics in aqueous media.

The sensitive and selective detection of nitroexplosive molecules thorough a simple methodology has received a significant field of research affecting global security and public safety. In the present study, the synthesis of anthracene-based chalcone (S1) was conducted using a simple condensation method. S1 was found to exhibit unique properties, such as aggregation-induced emission in solution and mechanochromic behavior in solid state. A fluorescent aggregate was applied to sense electron-deficient picric acid (PA) and 2,4-dinitrophenol (2,4-DNP) in an aqueous solution. Notably, the developed test strip-based sensor (S1) could be used to effectively detect PA and 2,4-DNP, which were visualized by the naked eye. Photophysical analysis revealed the occurrence of an electron transfer from electron-rich S1 to the electron-deficient nitro compounds, which was confirmed using density functional theory and 1H-nuclear magnetic resonance studies. In addition, the observed results confirmed the simple synthesis of S1 as a promising material for the development of test strip-based sensor devices for the detection of toxic and explosive aromatic nitro molecules.

An aerobic oxidation of alcohols into carbonyl synthons using bipyridyl-cinchona based palladium catalyst.

We have reported an aerobic oxidation of primary and secondary alcohols to respective aldehydes and ketones using a bipyridyl-cinchona alkaloid based palladium catalytic system (PdAc-5) using oxygen at moderate pressure. The PdAc-5 catalyst was analysed using SEM, EDAX, and XPS analysis. The above catalytic system is used in experiments for different oxidation systems which include different solvents, additives, and bases which are cheap, robust, non-toxic, and commercially available on the industrial bench. The obtained products are quite appreciable in both yield and selectivity (70-85%). In addition, numerous important studies, such as comparisons with various commercial catalysts, solvent systems, mixture of solvents, and catalyst mole%, were conducted using PdAc-5. The synthetic strategy of oxidation of alcohol into carbonyl compounds was well established and all the products were analysed using 1H NMR, 13CNMR and GC-mass analyses.

Novel star-shaped D-π-D-π-D and (D-π)2-D-(π-D)2 anthracene-based hole transporting materials for perovskite solar cells.

Three types of novel star-shaped molecular architectures, D-π-D-π-D and (D-π)2-D-(π-D)2 anthracene (ANTTPA, AOME, AOHE) based hole transporting materials, are designed for hybrid perovskite solar cells using the Gaussian 09 computation program with the B3LYP/6-31g (d, p) basis set level. The HOMO energy level of the designed materials has a higher HOMO energy level compared to the perovskite HOMO energy level, which is more facile for hole transport from the hole transporting layer to the oxidized perovskite layer. Thereafter, anthracene-based derivatives were synthesized from Buchwald-Hartwig and Mizoroki-Heck cross coupling reactions. The behaviors of the transporting charges were determined by both UV-visible absorbance and emission spectroscopy through solvatochromism experiments. Furthermore, the electrochemical properties also proved that the synthesized compounds had an optimal HOMO energy level in the TiO2/perovskite/HTM interface. Our hole transport materials (HTMs) have a good film formation compared to the spiro-OMeTAD, which was confirmed from scanning electron microscopy images. The obtained theoretical and experimental data show the suitability of designing anthracene-based derivatives with the potential to be used as hole transporting materials in organic-inorganic hybrid perovskite solar cells.

A highly sensitive and selective Schiff-base probe as a colorimetric sensor for Co2+ and a fluorimetric sensor for F- and its utility in bio-imaging, molecular logic gate and real sample analysis.

In this work, we designed a novel Schiff-base probe from the condensation reaction of 3,5-diiodosalicylaldehyde with isoniazid. Treatment of the sensor molecule with different metal ions like K+, Ba2+, Ca2+, Mg2+, Fe2+, Mn2+, Co2+, Cu2+, Cd2+, Ni2+, Hg2+, Zn2+, Pb2+ and Al3+ in visual inspection and absorption measurements explained its colorimetric sensing ability. The sensor DISN displays a remarkable color variation from pale yellow to brownish-orange towards Co2+ ion. The absorption and emission spectra of DISN, upon treating with various anions including F-, Br-, Cl-, I-, HSO4-, NO3-, H2PO4-, and CN- were tested. The addition of the fluoride ion to the receptor caused not only the intense color variation from pale yellow to orange but also a significant fluorescence turn-on response. Job's plot method fixed the binding of Co2+ and F- to DISN separately, in 2:1 and 1:1 binding stoichiometry, respectively. The detection limit of 1.24 × 10-7 M and 0.108 × 10-6 M was attained for Co2+ and F-, respectively. The TD-DFT calculations further supported the photophysical properties involved in the free probe and its complexes. The YES and INHIBIT logic function was found to operate from modulation in the absorbance and fluorescence behavior of Co2+ and F- ions with DISN. Furthermore, DISN displays its practical applicability in filter-paper strips, live cell imaging, and real sample analyses.

Turn-on Fluorescence Chemosensor for Zn2+ Ion Using Salicylate Based Azo Derivatives and their Application in Cell-Bioimaging.

The synthesis and optical studies of salicylate based azo derivatives (DPSAD and IPSAD) are reported. The receptors act as a versatile fluorogenic chemosensor for Zn2+ causing a selective enhancement of fluorescence over other competing cations. The complex formed between receptors and Zn2+ are identified on the basis of absorption and fluorescence titration and further confirmed by ESI-MS. DFT/TD-DFT calculations support the observed optical changes happens only upon complexation with Zn2+ ion. Moreover, receptors are further applied to intracellular sensing and imaging studies. Graphical Abstract Salicylate based azo derivatives (DPSAD and IPSAD) as fluorogenic chemosensor for the detection of Zn2+ ion.

A new multifunctional benzimidazole tagged coumarin as ratiometric fluorophore for the detection of Cd2+/F- ions and imaging in live cells.

A novel multifunctional ratiometric fluorescent probe has been designed and synthesized for the selective recognition of Cd2+/F- ions. The probe (3)-((2)-(1H-benzoimidazole-2-yl)-phenylimino) methyl-4-chloro-methyl-2H-chromen-2-ene (BIMC) displays excellent ratiometric responses towards Cd2+/F- ions over the tested cations/anions. The lowest detection limits observed for Cd2+ and F- are 1.5 × 10-10 mol/l and 1.2 × 10-10 mol/l respectively. Job's plot and Electro spray Ionization mass spectral (ESI-MS) studies confirms 1:1 binding stoichiometry of BIMC with Cd2+/F- ions, which is further evidenced by 1H NMR titration studies. The reversibility studies of BIMC with Cd2+ have been investigated using ethylenediaminetetraacetic acid (EDTA). Upon binding to Cd2+/F- ions, the probe features strong ratiometric response in both UV-Visible and fluorescence spectra due to the inhibition of intramolecular charge transfer (ICT). Furthermore, the mechanism of ICT has been rationalized via solvatochromism and DFT calculations.

A highly enantioselective asymmetric Darzens reaction catalysed by proline based efficient organocatalysts for the synthesis of di- and tri-substituted epoxides.

A new class of easily available and readily tunable proline based chiral organocatalysts was found to efficiently catalyse an unprecedented highly enantioselective asymmetric Darzens reaction of α-chloroketones and substituted α-chloroketones with various aldehydes, which directly produces optically active di- and tri-substituted chiral epoxides with higher product yields (up to 97%) and excellent ee's (up to 99%) under mild reaction conditions.

One-pot synthesis of α,ß-epoxy ketones through domino reaction between alkenes and aldehydes catalyzed by proline based chiral organocatalysts.

Proline based metal free organocatalysts were developed by using a new approach for the synthesis of epoxide derivatives through a domino reaction. This domino reaction (oxidative coupling) allows a direct access to epoxides from various alkenes and aldehydes through C-H functionalization and C-C/C-O bond formation. The catalytic efficiencies of the newly synthesized organocatalysts were also determined by domino reaction in the presence of various functional groups containing aldehyde and alkene derivatives with very good yields (up to 95%) and ee's (up to 99%).

Highly selective colorimetric detection of cyanide anions in aqueous media by triphenylamine and phenanthro(9,10-d)imidazole based probes.

Two novel fluorescent probes based on triphenylamine (TPC) and phenanthro(9,10-d-imidazole) (PITP) have been synthesized and studied as cyanide selective indicators in aqueous media. Complete colour bleaching was observed due to the nucleophilic addition of cyanide to the 2-vinylmalononitrile of TPC, which results in the disruption of the extended conjugation and turns off the intramolecular charge transfer (ICT) process. Furthermore, a visible color change was observed with a large Stokes shift (108 nm) upon the addition of cyanide anions to PITP, due to the formation of hydrogen bonding between the CN- anion and -NH of PITP, which increased the electron density on the donor moiety and induced strong ICT.

Highly enantioselective asymmetric Henry reaction catalyzed by novel chiral phase transfer catalysts derived from cinchona alkaloids.

A new type of di-site chiral phase transfer catalyst has been designed and synthesized from cinchona alkaloids as a chiral precursor. The prepared catalysts are applied in the asymmetric Henry reaction to a wide range of aldehydes using mild concentrations of a base and solvent and under room-temperature conditions. Under the optimized reaction conditions, the highest chemical yields up to 99% along with an excellent enantiomeric excess (ee) up to 99% were obtained using the prepared cinchona alkaloid based chiral phase transfer catalysts.

Binaphthyl-based chiral bifunctional organocatalysts for water mediated asymmetric List-Lerner-Barbas aldol reactions.

Novel binaphthyl-based chiral bifunctional organocatalysts were designed, synthesized and successfully applied to the asymmetric List-Lerner-Barbas aldol reaction in the presence of water. These organocatalysts were found to be effective catalysts for the reactions of symmetrical, unsymmetrical and cyclic ketones with different aldehydes to give the corresponding aldol products with higher yields (up to 98%) and very good ee's up to 99%. The catalytic system leads to higher yields and selectivities than the previously reported well-known proline based organocatalysts. In addition to the effect of solvent, additives, catalyst concentration, temperature and the substrate scope of the reactions were also investigated.

Piezoflurochromism and Aggregation Induced Emission Properties of 9, 10-bis (trisalkoxystyryl) Anthracene Derivatives.

We report the synthesis of trisalkoxy substituted 9, 10-bis styrylanthracene derivatives (C8-ant and C12-ant) by Heck coupling with very good yield and their photophysical properties. Both C8-ant and C12-ant exhibit aggregation induced emission (AIE), mechnoflurochromism and thermochromism. Trisubstituted 9, 10-distyrylanthracene molecules having all the luminescent properties in a single molecule are first of its kind.

Synthesis, characterization and photophysical studies of self-assembled azo biphenyl urea derivatives.

We reported the synthesis of a new series of azobiphenyl based urea derivatives 7 and their stimulus-responsive supramolecular structures in the form of sheet like self-assembled formations. The self-assembled nanostructural formations of azo derivatives 7 are strongly dependent on the nature of the solvent present in the systems. Further, we found that the amide hydrogen played a crucial role in hydrogen bonding interactions to form a sheet like morphology upon stimulus responsive self-assembly. This was confirmed by transmission electron microscopy and atomic force microscopy.

Cinchona alkaloid-based chiral catalysts act as highly efficient multifunctional organocatalysts for the asymmetric conjugate addition of malonates to nitroolefins.

New pentaerythritol tetrabromide-based chiral quaternary ammonium salts acting as organocatalysts (7a and 7b) have been prepared and used as organocatalysts for enantioselective Michael addition reactions between various nitroolefins and Michael donors (malonates) under mild reaction conditions, such as lower concentration of base and catalyst and room temperature, with very good chemical yields (up to 97%) and ee's (up to 99%).

Aminobenzohydrazide based colorimetric and 'turn-on' fluorescence chemosensor for selective recognition of fluoride.

Chemosensors based on aminobenzohydrazide Schiff bases bearing pyrene/anthracene as fluorophores have been designed and synthesized for F(-) ion recognition. The addition of fluoride ions to the receptors causes a dramatically observable colour change from pale yellow to brown/red. (1)H NMR studies confirm that the F(-) ion facilitates its recognition by forming hydrogen bond with hydrogens of amide and amine groups. Moreover these sensors have also been successfully applied to detection of fluoride ion in commercial tooth paste solution.

Charge instability of symmetry broken dipolar states in quadrupolar and octupolar triphenylamine derivatives.

The quadrupolar and octupolar cyano triphenylamines shows symmetry broken dipolar charge transfer state, however, its stability can be controlled by the rotation of N-C bond of amino and phenylene moiety.

Exploring the heterogeneous interfaces in organic or ruthenium dye-sensitized liquid- and solid-state solar cells.

The interfacial properties were systematically investigated using an organic sensitizer (3-(5'-{4-[(4-tert-butyl-phenyl)-p-tolyl-amino]-phenyl}-[2,2']bithiophenyl-5-yl)-2-cyano-acrylic acid (D)) and inorganic sensitizer (bis(tetrabutylammonium) cis-bis(thiocyanato)bis(2,2'-bipyridine-4,4'-dicarboxylato) ruthenium(II) (N719)) in a liquid-state and a solid-state dye-sensitized solar cell (DSC). For liquid-DSCs, the faster charge recombination for the surface of D-sensitized TiO2 resulted in shorter diffusion length (LD) of ∼3.9 µm than that of N719 (∼7.5 µm), limiting the solar cell performance at thicker films used in liquid-DSCs. On the other hand, for solid-DSCs using thin TiO2 films (∼ 2 µm), D-sensitized device outperforms the N719-sensitized device in an identical fabrication condition, mainly due to less perfect wetting ability of solid hole conductor into the porous TiO2 network, inducing the dye monolayer act as an insulation layer, while liquid electrolyte is able to fully wet the surface of TiO2. Such insulation effect was attributed to the fact that the significant increase in recombination resistance (from 865 to 4,400 Ω/cm(2)) but shorter electron lifetime (from 10.8 to 0.8 ms) when compared to liquid-DSCs. Higher recombination resistance for solid-DSCs induced the electron transport-limited situation, showing poor performance of N719-sensitized device which has shorter electron transport time and similar LD (2.9 µm) with D-sensitized device (3.0 µm).