Sudipa Mondal

Structural characterization of new Schiff bases of sulfamethoxazole and sulfathiazole, their antibacterial activity and docking computation with DHPS protein structure

New Schiff bases (1, 2) of substituted salicylaldehydes and sulfamethoxazole (SMX)/sulfathiazole (STZ) are synthesized and characterized by elemental analysis and spectroscopic data. Single crystal X-ray structure of one of the compounds (E)-4-((3,5-dichloro-2-hydroxybenzylidene)amino)-N-(5-methylisoxazol-3-yl)benzenesulfonamide (1c) has been determined. Antimicrobial activities of the Schiff bases and parent sulfonamides (SMX, STZ) have been examined against several Gram-positive and Gram-negative bacteria and sulfonamide resistant pathogens; the lowest MIC is observed for (E)-4-((3,5-dichloro-2-hydroxybenzylidene)amino)-N-(thiazol-2-yl)benzene sulfonamide (2c) (8.0 μg mL(-1)) and (E)-4-((3,5-dichloro-2-hydroxybenzylidene)amino)-N-(5-methylisoxazol-3-yl)benzene sulfonamide (1c) (16.0 μg mL(-1)) against sulfonamide resistant pathogens. DFT optimized structures of the Schiff bases have been used to carry out molecular docking studies with DHPS (dihydropteroate synthase) protein structure (downloaded from Protein Data Bank) using Discovery Studio 3.5 to find the most preferred binding mode of the ligand inside the protein cavity. The theoretical data have been well correlated with the experimental results. Cell viability assay and ADMET studies predict that 1c and 2c have good drug like characters.

Fluorescence sensing and intracellular imaging of Al3+ ions by using naphthalene based sulfonamide chemosensor: structure, computation and biological studies

A naphthalene based sulfonamide Schiff base, (E)-4-(((2-hydroxynaphthalen-1-yl)methylene)amino)-N-(5-methylisoxazol-3-yl)benzenesulfonamide (HL) has been found to be a flourescence turn-on probe for selective detection of Al3+ in aqueous system. Structure of the probe has been established by FTIR, 1H NMR, mass spectra and X-ray single crystal study. The probe has shown 24 times flourescence enhancement in presence of Al3+. The limit of detection (LOD) obtained by 3σ method is 33.2 nM. The probable co-ordination environment of L-Al2+ complex has been supported by mass spectral data and DFT computational study. By TD-DFT calculation UV-Vis spectra of HL and L-Al2+ complex has been predicted and that has well correlated with experimental data. Cell imaging study reveals that the probe can be used for the intracellular detection of Al3+ in cultured Vero cell. Antimicrobial activity of HL has also been evaluated and probable mode of binding inside the DHPS cavity has been predicted by docking study. This sensor is unique with reference to two other predecessors because of its bio-compatibility of sulfonamide derivative and nonmutagenicity.

An efficient vanillinyl Schiff base as a turn on fluorescent probe for zinc(II) and cell imaging

6,6′-((1Z,1′Z)-(((Ethane-1,2-diylbis(oxy))bis(2,1-phenylene))bis(azanylylidene))bis(methanyl ylidene))bis(3-methoxyphenol), a vanillinyl Schiff base, shows unprecedented fluorescent zinc sensing properties and has been examined for zinc bioimaging. Zinc induced turn-on fluorescence enhancement is observed at 472 nm and steady state photophysical studies establish the metal promoted deprotonation and chelation enhancement of emission. Formation of the 1:1 metal-to-ligand complex has been ascertained by 1H NMR, mass spectral analysis and Jobs plot. Limit of detection (LOD) is the lowest, 0.018 μM in the family of fluorogenic Zn2+-sensors. Apart from this, theoretical interpretation of the experimental outcome has also been obtained by applying density functional theory (DFT) to the ligand and the complex. The practical applicability of the ligand has been examined in living cells (African Monkey Vero Cells). MTT assay proves the no toxicity of probe upto 300 μg ml−1.

The crystal structure of sulfamethoxazole, interaction with DNA, DFT calculation, and molecular docking studies.

Sulfamethoxazole (SMX) [4-amino-N-(5-methyl-1,2-oxazol-3-yl)benzenesulfonamide] is structurally established by single crystal X-ray diffraction measurement. The crystal packing shows H-bonded 2D polymer through N(7)-H(7A)-O(2), N(7)-H(7B)-O(3), N(1)-H(1)-N(2), C(5)-H(5)-O(3)-S(1) and N(7)-(H7A)-O(2)-S(1). Density Functional Theory (DFT) and Time Dependent-DFT (TD-DFT) computations of optimized structure of SMX determine the electronic structure and has explained the electronic spectral transitions. The interaction of SMX with CT-DNA has been studied by absorption spectroscopy and the binding constant (Kb) is 4.37×10(4)M(-1). The in silico test of SMX with DHPS from Escherichia coli and Streptococcus pneumoniae helps to understand drug metabolism and accounts the drug-molecule interactions. The molecular docking of SMX-DNA also helps to predict the interaction feature.

Triply phenoxo bridged Eu(III) and Sm(III) complexes with 2,6-diformyl-4-methylphenol-di(benzoylhydrazone): structure, spectra and biological study in human cell lines

Two dinuclear lanthanide(III) complexes, [M2(HL)3] (M = Sm(III) (1), Eu(III) (2); H3L, 2,6-diformyl-4-methylphenol-di(benzoylhydrazone)) were generated with good yield and characterised systematically. The single crystal X-ray structure determination of [Eu2(HL)3] (2) confirmed the tricapped trigonal prismatic geometry of the N3O6 coordination environment around europium. Indeed, Eu(1) and Eu(2) are bridged by phenolato-O belonging to the p-cresol ring, by deprotonated ‘enol’ groups from the benzoyl hydrazide part and by the imine-N centres. A temperature dependent magnetic study suggested that anti-ferromagnetic coupling occurs between the two Eu(III) ions and the magnetic moment was found to vary from 0.48 B.M. at 5 K to 3.03 B.M. at 300 K. Electron paramagnetic resonance spectroscopy confirmed that anti-ferromagnetic coupling occurs between the atoms of Eu(III) and Sm(III). Both the complexes show emission in the visible range. The ligand, H3L and the complexes exhibit anti-mycobacterial activity against M. tuberculosis H37Rv (ATCC 27294) and M. tuberculosis H37Ra (ATCC 25177) strains. The molecular docking of H3L with the enoyl acyl carrier protein reductase of M. tuberculosis H37Rv (PDB ID: 4U0K) was examined and the best docked pose of H3L was shown to have one hydrogen bond with Thr196 (2.03 A).

The structural characterization and biological activity of sulfamethoxazolyl-azo-p-cresol, its copper(II) complex and their theoretical studies

(E)-4-((2-Hydroxy-5-methylphenyl)diazenyl)-N-(5-methylisoxazole-3-yl)benzene sulfonamide (SMX-NN-C6H3(p-Me)-OH, 1) and its Cu(II) complex, [Cu(SMX-NN-C6H3(p-Me)-O)2]n (2), have been characterized by spectroscopic data and single crystal X-ray diffraction studies. The supramolecular 1D chain of 1 is constituted by inter- and intra-molecular hydrogen bonds and also by π⋯π interactions of aromatic rings. Complex 2 has a tetragonally distorted octahedral structure in which ligand 1 serves as an N,O chelator and forms a planar Cu(N,O)2 motif; two axial positions are occupied by the oxazolyl-N of neighbouring units and a 3D structure is formed. The biological activities of these compounds have been evaluated against Gram positive (B. subtilis; IC50: 105 μg ml−1 (1) and 105 μg ml−1 (2)) and Gram negative bacteria (E. coli; IC50: 66.36 μg ml−1 (1) and 62.2 μg ml−1 (2)) and the complexes exhibit better efficiency. Interactions of DNA with 1 and 2 have been examined and the binding constants are Kb(1), 5.920 × 104 M−1 and Kb(2), 4.445 × 104 M−1. The in silico test is used to predict the most favoured binding mode of 1 and 2 with the active site residues of DHPS (dihydropteroate synthetase) of E. coli and of DNA. The Cu(II) complex (2) binds more efficiently (CDOCKER energy, 2, −61.35 a.u.) in the DHPS cavity than ligand 1 (CDOCKER energy, 1, −43.90 a.u.). The electronic structures and spectral properties of 1 and 2 have been investigated by DFT and TD-DFT computation of optimized geometries of the compounds.

A Ni(II) dinuclear complex bridged by end-on azide-N and phenolate-O atoms: spectral interpretation, magnetism and biological study

A potential tetradentate monoanionic N2O2 chelator, HL, derived from the condensation of o-vanillin and N,N-dimethylethylenediammine, has been reacted with nickel perchlorate and sodium azide to yield the dinuclear Ni(II) complex [Ni(L)(μ1,1-N3)Ni(L)(OH2)2]·ClO4 (1), where L = Me2N(CH2)2NCH–C6H3(O−)(OCH3). The complex has been characterized by X-ray diffraction analysis and different spectroscopic techniques. The coordination geometry around the Ni(II) centres is a distorted octahedron, with the azide ligand and the phenolato oxygen atom bridging in μ1,1 and μ2 mode, respectively. The EPR spectra, recorded at liquid nitrogen temperature (77 K) and room temperature (298 K), show g factors of 2.080 and 2.085, in agreement with the structure determined by X-ray diffraction analysis. The VTM study confirms that there are ferromagnetic interactions between the bridging binuclear Ni(II) ions (S = 1). The evaluation of cytotoxic effects on different human cancer cell lines (A-549, MCF-7 and CaCo-2) suggests that both the ligand and complex 1 have potential anticancer properties. Furthermore, they also exhibit anti-mycobacterial activity against M. tuberculosis H37Rv (ATCC 27294) and M. tuberculosis H37Ra (ATCC 25177) strains. Molecular docking of HL with the enoyl acyl carrier protein reductase of M. tuberculosis H37Rv (PDB ID: 4U0K) has been examined, showing that HL forms two hydrogen bonds with Lys165 (1.94 and 2.53 A) in its best docked pose.

The spectroscopic characterization, photochromism of cadmium(II)-iodo complexes of 1-alkyl-2-(arylazo)imidazoles and DFT computation of representative complexes.

[Cd(Raai-C(n)H(2n+1))(μ-I)I]2 and [Cd(Raai-C(n)H(2n+1))2I2] are synthesized by the reaction of CdI2 with 1-alkyl-2-(arylazo)imidazole (Raai-C(n)H(2n+1), n=4, 6, 8) in MeOH in 1:1 and 1:2 M ratio of salt and ligands, respectively. The complexes have been characterized by spectral data (UV-Vis, IR, (1)H NMR, Mass). The coordinated Raai-C(n)H(2n+1) shows photochromism, E(trans)-to-Z(cis) isomerisation, upon UV light irradiation. The reverse process, Z-to-E, is very slow in visible light irradiation process while the reaction is sensitive to change of reaction temperature. The quantum yields (ϕE→Z) for E-to-Z and the activation energy (Ea) of Z-to-E isomerisation are calculated and found that the complexes show subordinate results compared to free ligand. DFT computations of two representative complexes were carried out to explain the spectral and photochromic phenomena.

An enolato-bridged dinuclear Cu(II) complex with a coumarin-assisted precursor: a spectral, magnetic and biological study

A new, phenoxo-bridged CuII dinuclear complex Cu2[(L)2(DMF)2] (1) has been obtained by employing the coumarin-assisted tridentate precursor, H2L, [benzoic acid(7-hydroxy-4-methyl-2-oxo-2H-chromen-8-ylmethylene)-hydrazide]. Complex 1 has been systematically characterized by FTIR, UV-Vis, fluorescence and EPR spectrometry. The single crystal X-ray diffraction analysis of 1 shows that the geometry around each copper ion is square pyramidal, comprising two enolato oxygen atoms belonging to different ligands (which assemble the dimer bridging the two metal centers), one imine-N and one phenolic-O atoms of the Schiff base and one oxygen atom from the DMF molecule. The temperature dependent magnetic interpretation agrees with the existence of weak ferromagnetic interactions between the bridging dinuclear Cu(II) ions. Both the ligand and complex 1 exhibit anti-mycobacterial activity and considerable efficacy towards M. tuberculosis H37Rv ATCC 27294 and M. tuberculosis H37Ra ATCC 25177 strains. The cytotoxicity study on human adenocarcinoma cell lines (MCF7) suggests that the ligand and complex 1 have potential anticancer properties. Molecular docking of H2L with the enoyl acyl carrier protein reductase of M. tuberculosis H37Rv (PDB ID: 4U0K) is examined and the best docked pose of H2L shows one hydrogen bond with Thr196 (1.99 A).