Chiranjit Patra

Binding affinities of Schiff base Fe(II) complex with BSA and calf-thymus DNA: Spectroscopic investigations and molecular docking analysis.

The binding interaction of a synthesized Schiff base Fe(II) complex with biological macromolecules viz., bovine serum albumin (BSA) and calf thymus(ct)-DNA have been investigated using different spectroscopic techniques coupled with viscosity measurements at physiological pH and 298K. Regular amendments in emission intensities of BSA upon the action of the complex indicate significant interaction between them, and the binding interaction have been characterized by Stern Volmer plots and thermodynamic binding parameters. On the basis of this quenching technique one binding site with binding constant (Kb=(7.6±0.21)×10(5)) between complex and protein have been obtained at 298K. Time-resolved fluorescence studies have also been encountered to understand the mechanism of quenching induced by the complex. Binding affinities of the complex to the fluorophores of BSA namely tryptophan (Trp) and tyrosine (Tyr) have been judged by synchronous fluorescence studies. Secondary structural changes of BSA rooted by the complex has been revealed by CD spectra. On the other hand, hypochromicity of absorption spectra of the complex with the addition of ct-DNA and the gradual reduction in emission intensities of ethidium bromide bound ct-DNA in presence of the complex indicate noticeable interaction between ct-DNA and the complex with the binding constant (4.2±0.11)×10(6)M(-1). Life-time measurements have been studied to determine the relative amplitude of binding of the complex to ct-DNA base pairs. Mode of binding interaction of the complex with ct-DNA has been deciphered by viscosity measurements. CD spectra have also been used to understand the changes in ct-DNA structure upon binding with the metal complex. Density functional theory (DFT) and molecular docking analysis have been employed in highlighting the interactive phenomenon and binding location of the complex with the macromolecules.

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.

Coumarinyl thioether Schiff base as a turn-on fluorescent Zn(II) sensor and the complex as chemosensor for the selective recognition of ATP, along with its application in whole cell imaging

The coumarinyl thioether Schiff base, H2L, demonstrates turn-on fluorescence sensing towards Zn2+ ion with a limit of detection (LOD) of 0.068 μM. Different physicochemical techniques (mass, 1H NMR, Jobs) support the formation of a 1 : 1 metal-to-ligand complex, [ZnL]. The fluorogenic complex [ZnL] recognizes ATP in the presence of all other common anions, inorganic phosphates and biologically important phosphates (nucleosides, nucleotides). The proposed sensor has efficiently been used for ATP sensing with a LOD of 6.7 μM, which is the lowest in literature. Exogenous zinc ions in SCC084 (human oral carcinoma) cells have been checked through fluorescence cell imaging process by adding H2L in the medium.

Imine-functionalized thioether Zn(II) turn-on fluorescent sensor and its selective sequential logic operations with H2PO4−, DFT computation and live cell imaging

The diformyl thioether Schiff base (H2L) exhibits fluorescent sensing behaviour towards Zn2+ with a limit of detection (LOD) of 0.050 μM, which is far below the WHO guideline (76 μM) in drinking water. The formation of a 1 : 1 metal-to-ligand complex, [ZnL], has been ascertained by X-ray crystallography, Jobs plot and mass spectra. The fluorogenic complex, [ZnL] (either in situ or a solution of the isolated complex) has shown selective ON–OFF emission toward H2PO4−. A two-input, one-output sequential INHIBIT logic circuit has been constructed from H2L, Zn2+ and H2PO4−. The practical applicability of H2L has been examined by the identification of Zn2+ and H2PO4− in the intracellular fluid of African monkey Vero cells.

Characterization of domain-specific interaction of synthesized dye with serum proteins by spectroscopic and docking approaches along with determination of in vitro cytotoxicity and antiviral activity

The interaction between a synthesized dye with proteins, bovine, and human serum albumin (BSA, HSA, respectively) under physiological conditions has been characterized in detail, by means of steady-state and time-resolved fluorescence, UV–vis absorption, and circular dichroism (CD) techniques. An extensive time-resolved fluorescence spectroscopic characterization of the quenching process has been undertaken in conjugation with temperature-dependent fluorescence quenching studies to divulge the actual quenching mechanism. From the thermodynamic observations, it is clear that the binding process is a spontaneous molecular interaction, in which van der Waals and hydrogen bonding interactions play the major roles. The UV–vis absorption and CD results confirm that the dye can induce conformational and micro-environmental changes of both the proteins. In addition, the dye binding provokes the functionality of the native proteins in terms of esterase-like activity. The average binding distance (r) between proteins and dye has been calculated using FRET. Cytotoxicity and antiviral effects of the dye have been found using Vero cell and HSV-1F virus by performing MTT assay. The AutoDock-based docking simulation reveals the probable binding location of dye within the sub-domain IIA of HSA and IB of BSA.

Highly selective and sensitive recognition of Zn(II) by a novel coumarinyl scaffold following spectrofluorometric technique and its application in living cells

A probe of 8,8′-((1Z,1′Z)-(((propane-1,3-diylbis(oxy))bis(2,1-phenylene))bis(azanylylidene))bis(methanylylidene))bis(7-hydroxy-4-methyl-2H-chromen-2-one) (H2L) was able to recognize Zn2+via its turn-on emission at 510 nm in a MeCN–water (9 : 1, v/v) solution in the presence of a large number of biologically important cations with a very low limit of detection (LOD), namely 11 nM, which meant it was about 3500 times more sensitive than the WHO recommended permissible standard for zinc in drinking water (3 ppm). The probe, H2L, showed solvent polarity sensitive absorption and emission properties and the λmax showed negative solvatochromism. The composition of the complex, [ZnL], was established by a Jobs plot, HR-MS data, and single-crystal X-ray diffraction measurements. The selectivity and sensitivity of the probe, H2L, was successfully applied to the detection of intracellular Zn2+ in human hepato-cellular-carcinoma (HepG2) cells. H2L is also applicable for the analysis of Zn2+ ions in tap water.

The structure and photophysics of di-iodo-zinc(II) complexes of long alkyl chain substituted imidazolyl motif of arylazoimidazoles and the DFT computation.

Distorted tetrahedral structure of [Zn(Haai-C10H21)2I2] (Haai-C10H21, 1-decayl-2-(arylazo)imidazole) has been supported by single crystal X-ray diffraction study. The structures of other complexes, [Zn(Raai-CnH2n+1)2I2] (n=10, 12, 14, 16, 18, 20, 22) have been determined by spectroscopic data (FT-IR, UV-vis, (1)H NMR). The complexes show light induced photoisomerisation, E-to-Z (trans-to-cis) of coordinated, Raai-CnH2n+1. The Z-to-E (cis-to-trans) isomerisation is also carried out by thermal activation route. The quantum yields of the E→Z progression (ϕE→Z) of the complexes are less than that of free ligand, which could be due to increase in molar mass and molar volume of the complexes than that of free ligands. The activation energy (Ea) of Z→E isomerisation of the complexes is is less than that of free ligands. This observation is also consistent with femtosecond transient absorption results which suggests that the E(trans)→Z(cis) isomerization occurs through the motion of pendant NNAr of the molecule. The temporal profiles of free ligand shows three decay processes corresponds to 0.24ps (S2 state) and subsequent decay, 0.85ps of the S1 state and finally 5ps to the hot ground state at 500nm. The complexes also show three decay periods approximately at 0.25ps, 1.3ps and 13ps. The spectral property and photochromic efficiency have been explained by DFT computation of optimized geometry of the complexes.