Mohan Gopalakrishnan

Inhibitory effect of apocarotenoids on the activity of tyrosinase : Multi-spectroscopic and docking studies

In this present study, the inhibitory mechanism of three selected apocarotenoids (bixin, norbixin and crocin) on the diphenolase activity of tyrosinase has been investigated. The preliminary screening results indicated that apocarotenoids inhibited tyrosinase activity in a dose-dependent manner. Kinetic analysis revealed that apocarotenoids reversibly inhibited tyrosinase activity. Analysis of fluorescence spectra showed that apocarotenoids quenched the intrinsic fluorescence intensity of the tyrosinase. Further, molecular docking results implied that apocarotenoids were allosterically bound to tyrosinase through hydrophobic interactions. The results of the in vitro studies suggested that higher concentrations of bixin and norbixin inhibited tyrosinase activity in B16F0 melanoma cells. Our results suggested that apocarotenoids could form the basis for the design of novel tyrosinase inhibitors.

Functionality study of santalin as tyrosinase inhibitor: A potential depigmentation agent

Excessive melanin production leads to hyperpigmentation disorders which results in distressing aesthetic values. Though there are some synthetic depigmentation agents available it has been reported to possess cytotoxic and mutagenic effects. Hence there is a need for the development of safe and non toxic natural tyrosinase inhibitors. Here we report the role of santalin, the chief constituent of Pterocarpus santalinus in inhibition of tyrosinase and melanin synthesis. Santalin inhibited tyrosinase activity dose dependently. Inhibitory kinetic studies revealed mixed type of inhibition with reversible mechanism. Santalin was found to interact with the fluorophore amino acid residue of tyrosinase. Analysis of circular dichroism spectra showed the binding of santalin to tyrosinase which induced the loss of secondary helical structure. Molecular docking result suggested that santalin interact with the catalytic core of tyrosinase through strong hydrogen and hydrophobic bonding. The results of in vitro studies showed santalin inhibited melanogenesis through down regulation of MITF, tyrosinase, TRP-1 and TRP-2 without any cytotoxic effects towards B16F0 melanoma cells. Therefore, our results suggested that santalin possesses anti-tyrosinase activity, which could be utilized as a safe depigmentation agent in the cosmetic field for the treatment of hyperpigmentation disorder.

Inhibitory effect of brazilein on tyrosinase and melanin synthesis: Kinetics and in silico approach.

In our present study, the inhibitory effect of brazilein from Caesalpinia sappan on tyrosinase activity was investigated through multi-spectroscopic and molecular docking techniques. The result has shown that brazilein reversibly inhibited tyrosinase in a mixed type manner. The interaction of brazilein with the amino acid residues of tyrosinase has been validated through fluorescence quenching studies. Copper interaction studies suggested that brazilein could bind with copper ions of the enzyme. Circular dichroism analysis confirmed that brazilein induced secondary structural changes in tyrosinase. Docking studies further authenticate that brazilein forms hydrophobic and hydrogen bonding with the active site residues of tyrosinase. Moreover, in vitro studies confirmed that the inhibitory mechanism of cellular tyrosinase and melanin synthesis by brazilein in B16F0 melanoma cells. These results suggested that brazilein act as a potential tyrosinase inhibitor and it would contribute as a of novel tyrosinase inhibitor in food, cosmetic and pharmaceutical industry.

A mixed Ni(II) ionic complex containing V-shaped water trimer: Synthesis, spectral, structural and thermal properties of {[Ni(2,2′-bpy)3][Ni(2-cpida)(2,2′ -bpy)]} (ClO4).3H2O

AbstractA mixed Ni(II) ionic complex of {[Ni(2,2′-bpy)3][Ni(2-cpida)(2,2′-bpy)]}(ClO4).3H2O (1) (2-H3cpida = N-(2-carboxyphenyl)iminodiacetic acid, 2,2′-bpy = 2,2′-bipyridyl) has been synthesized and characterized by infrared, ultraviolet and fluorescence spectroscopy, elemental and thermogravimetric analysis. The molecular structure of compound 1, as determined by single-crystal X-ray diffraction studies, showed all the three carboxylate groups are in monodendate mode. Compound 1 consists of a discrete mononuclear [Ni(2,2′-bpy)3]2+ cation, a [Ni(2-cpida)(2,2′-bpy)]− anion, a ClO4−

Sorption sites of microalgae possess metal binding ability towards Cr(VI) from tannery effluents—a kinetic and characterization study

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Eight membered cyclic-borasiloxanes: synthesis, structural, photophysical, steric strain and DFT calculations

anion and three lattice water molecules. The H-bonding interaction between three lattice water molecule forms a V-shaped trimer (H2O)3 which gives rise to a 1-D polymeric structure in the solid state. Graphical AbstractA mixed ionic complex of Ni(II) contains V-shaped water trimer (H2O)3 through inter molecular hydrogen bonding interactions.

New sterically hindered tin(IV) siloxane precursors to tinsilicate materials: synthesis, spectral, structural and photocatalytic studies

AbstractProminent microalgal species, namely Anabaena, Oscillatoria, Phormidium, and Spirogyra, were isolated from estuaries polluted with tannery effluents and studied to determine their Cr(VI) bio-sorption potential. The bio-sorption potential was determined by studying the effect of growth, biomass, reduction of Cr(VI) levels, and Cr(VI) absorption by the microalgal species. The respective values for Anabaena, Oscillatora, Phormidium, and Spirogyra compared with the control were as follows: growth in BG 11 medium containing tannery effluent was 53.99, 60.03, 55.76, and 55.85%; the biomass was 60.65, 77.61, 67.16, and 76.01%; the Cr(VI) reduction potential was 70.96, 80.64, 76.12, and 74.83%; and the bio-sorption potential was 75.48, 80.64, 79.35, and 77.41%. The removal of heavy metals by microalgal biomass involves bio-reduction and bio-sorption. Fourier-transform infrared spectroscopy and nuclear magnetic resonance results revealed the presence of microalgal sorption sites. All four species showed ma...

Synthesis and spectroscopic characterization of tris(tert-butoxy)siloxy titanium and hafnium complexes: Molecular precursor to [M/Si/O (M = Ti, Hf)] materials

Eight-membered cyclic borasiloxanes, Ph2Si[OBArO]2SiPh2 [Ar = 4-EtC6H4 (1), 4-tBuC6H4 (2), 2-PhC6H4 (3), 4-PhC6H4 (4) and β-C10H7 (Nap) (5); Ph = phenyl], were synthesized via the reaction of diphenylsilanediol with aryl boronic acid through a condensation reaction. The compounds were characterized using elemental analysis, FT-IR and NMR (1H, 13C, 29Si and 11B). The compounds 1, 3 and 5 were further confirmed using single crystal X-ray diffraction studies. This showed the eight-membered ring (B2O4Si2) configuration and that organic substituents occupied the axial and equatorial positions. Furthermore, non-covalent C–H⋯π and π⋯π interactions were observed in the crystal packing pattern. These borasiloxanes exhibited strong solid state fluorescence. The thermal behavior of the compounds 1–5 has been investigated using thermogravimetric analysis (TGA), which shows that the borasiloxanes 1 and 2 are thermally stable up to 220 °C and 180 °C respectively, whereas 3 and 4 are stable up to ∼120 °C and 5 is stable up to 230 °C. The band gap was calculated using the diffuse reflectance spectroscopic method. Compound 5 exhibits a low band gap (3.28 eV) which indicates that the naphthyl group shows more π-bonding delocalization within the molecule (strong intra-molecular charge transfer). The band gap decreases in the order of the compounds, 1 > 2 > 3 > 4 > 5. The theoretically computed band gap values were in good agreement with the experimentally observed trend. HOMO–LUMO analysis, TD-DFT, and the electrophilicity index, dipole moment and hyperpolarizability were computed using the B3LYP/6-31+G** method. The steric strain energies of the borasiloxanes and their degree of puckering conformation (O–Si–O, O–B–O and B–O–Si) were also analysed using DFT. This confirms that compound 3 has more strain, which is due to having a phenyl group in a sterically hindered ortho-position.

Synthesis, crystal structure, DNA binding and molecular docking studies on new copper(II) salicylate (Cu(DTBSA)2(2,2'-bpy))(dmf)

A series of sterically hindered tin(IV) siloxanes were synthesized by the reaction between tris(tert-butoxy)silanol/tri-phenylsilanol and organotin chlorides {[(tBu)2Sn(OSi(OtBu)3)2] (1), [(tBu)2Sn(OSi(OtBu)3)Cl] (2), [(n-Bu)2Sn(OSi(OtBu)3)2] (3), [(n-Bu)2Sn(OSi(OtBu)3)Cl] (4), [(Me)2Sn(OSi(OtBu)3)2] (5), [(Me)2Sn(OSi(OtBu)3)Cl] (6), [(tBu)2Sn(OSiPh3)2] (7), [(tBu)2Sn(OSiPh3)Cl] (8) whereas tBu = tertiary butyl; n-Bu = butyl; Me = methyl}. All the compounds were characterized by analytical and spectroscopic (FT-IR and 1H, 13C, 29Si, 119Sn NMR) methods. Compounds 1 and 7 were structurally characterized by single-crystal X-ray crystallography. The coordination geometry of tin (SnO2C2) is slightly distorted from tetrahedral due to sterically crowded ligands around the tin atom. In order to convert tinsilicate materials, compounds 1 and 3 were selected for thermolysis to give identical SnO2·2SiO2 materials at low temperature (∼350 °C). The degradation was investigated by thermal analysis (TGA/DTA), both compounds having butyl groups which facile eliminate to butene gas via a β-hydride elimination process (∼250 °C). The molecular route to oxide materials at low temperature described here represents an alternative to the sol–gel technique. The tinsilicate material was examined by several techniques including infrared, powder X-ray diffraction analysis (PXRD), scanning electron microscopy (SEM) and energy dispersive X-ray (EDX). The optical band gap of the material has been studied by UV-vis-NIR spectroscopy and the result is a low band gap value (Eg = 2.549 eV) due to the silicon oxide mixed with tin oxide. The prepared material acts as photocatalyst for the degradation of methylene blue (MB).

Monomeric mixed cadmium-2,2'-dipyridylamine complex derived from ferrocenecarboxylic acid: Structural, electrochemical and biological studies.

GRAPHICAL ABSTRACT ABSTRACT The reaction of one equivalent of metallocene dichloride Cp2MCl2 (M = Ti, Hf) with two molar equivalents of sodium salt of tri(tert-butoxy)siloxane, (tBuO)3SiONa, in toluene yields Cp2Ti[OSi(OtBu)3]2 (1) and Cp2Hf[OSi(OtBu)3]2 (2). These compounds were characterized by analytical and spectroscopic techniques (C/H/N analysis, FT-IR, NMR, EI-MS, and thermal analysis). An independent thermolysis of 1 and 2 at low temperature resulted in the formation of the corresponding metal silicates MO2·2 SiO2 [M = Ti (3) and Hf (4)] as evidenced by infrared spectroscopy, powder X-ray diffraction analysis (PXRD), and scanning electron microscopy (SEM). These thermally stable amorphous metal silicate materials (3 and 4), albeit exhibiting moderate surface areas, are found to be microporous by N2 adsorption studies. UV-vis-NIR spectroscopy shows low energy band gap Eg = 2.63 eV for 3 and 2.99 eV for 4 due to the silicon oxide mixed with the corresponding transition metal oxides. The photocatalytic activity of titanium silicate material (3) has been explored in terms of degradation of methylene blue.