Reverse Micelle Induced Flipping of Binding Site and Efficiency of Albumin Protein with an Ionic Styryl Dye

Three water-soluble acylhydrazone tetranuclear transition metal complexes: Crystal structures, DNA/BSA interactions and cytotoxicity studies

2-acetylpyridine-4-chloropyridine-2‑carbonyl hydrazone (C₁₃H₁₁ClN₄O, HL) and its three water-soluble tetranuclear complexes [Cu₄(NO₃)₂(L)₄]·(NO₃)₂ (1), [Co₄(NO₃)₂(H₂O)(C₂H₅OH)(L)₄]·(NO₃)₂ (2) and [Zn₄(NO₃)₂(H₂O)(C₂H₅OH)(L)₄]·(NO₃)₂ (3) were synthesized and characterized showing that 1-3 were all tetranuclear complexes. The interactions of HL, 1-3 with calf thymus DNA (CT-DNA) and bovine serum albumin (BSA) were explored using ultraviolet-visible (UV-Vis) titration, fluorescence spectroscopy, microcalorimetry and molecular docking techniques. The UV-Vis spectroscopy measurements showed that complexes 1-3 could strongly bind to CT-DNA by the intercalation mode, while HL interacted with CT-DNA through groove binding. From the fluorescence spectroscopy results, the interaction between HL, 1-3 and BSA was a static quenching procedure, in which complexes 1-3 had two binding sites near Trp residues of BSA while HL only had one. The microcalorimetric studies revealed that the interactions of HL and 1-3 to CT-DNA/BSA were all endothermic and the duration of each interaction was all less than 30 min. The in silico molecular docking illustrated intermolecular interactions of 1-3 binding with DNA/BSA included hydrogen bond, halogen bond, hydrophobic and electrostatic interactions. 3-(4,5-dimethylthiazol-2-yl)-2,5-diphenyltetrazolium bromide (MTT) assay indicated that complex 1 possessed better cytotoxicity against HeLa, A549, MCF7 and HCT-116 than cisplatin and could be used as an alternative anticancer drug.

Fluorescence turn-on and turn-off sensing of pesticides by carbon dot-based sensor

Green chemistry C-Dot-based ‘turn-on’ and ‘turn-off’ fluorescence sensor for pesticides [imidacloprid (LOD ∼ 0.013 μM) and tetradifon (LOD ∼ 0.04 μM)] in aqueous solution.

Fluorescence Resonance Energy Transfer, Small-Angle Neutron Scattering, and Dynamic Light Scattering Study on Interactions of Gemini Surfactants Having Different Spacer Groups with Protein at Various Regions of Binding Isotherms

The binding interactions of three gemini surfactants having different spacer groups (12-4-12, 12-8-12, and 12-4(OH)-12) with a high concentration (150 μM) of bovine serum albumin (BSA) at various regions of binding isotherms have been studied by means of steady-state fluorescence and fluorescence anisotropy, time-correlated single-photon counting fluorescence of trans-2-[4-(dimethylamino)styryl]benzothiazole, small-angle neutron scattering (SANS), and dynamic light scattering (DLS) measurements. The fluorescence resonance energy transfer phenomenon between the twisted intramolecular charge transfer fluorescent molecule, trans-2-[4-(dimethylamino)styryl]benzothiazole as an acceptor, and tryptophan 213 (Trp-213) of BSA as a donor has been successfully used to probe the binding interactions of gemini surfactants with protein at all regions of binding isotherms. The increasing order of energy transfer efficiency at a higher concentration range of surfactants is 12-8-12 > 12-4-12 > 12-4(OH)-12. Stronger binding of micelles of gemini surfactant molecules having a comparatively more hydrophobic spacer group with the hydrophobic segments of the protein results in closer approach of trans-2-[4-(dimethylamino)styryl]benzothiazole molecules solubilized in micelles to Trp-213. The average excited-state lifetimes become shorter with a trend of increase in contribution from the fast component and decrease in contribution from the slow component to the decay with increasing concentration of a surfactant. The nonradiative rate constant of trans-2-[4-(dimethylamino)styryl]benzothiazole increases with increasing concentration of a surfactant because the average microenvironment around it in protein-surfactant aggregates is more polar as compared to that in native protein. SANS and DLS measurements were carried out for the study of the structural deformations in the protein, on enhancement of the concentration of the gemini surfactants. The necklace and bead model has been used for the analysis of SANS data for the protein-surfactant complexes. At a higher concentration range, 12-8-12 and 12-4-12 have a slightly smaller fractal dimension and a larger correlation length as compared to 12-4(OH)-12. DLS data show that the increasing order of hydrodynamic diameter for the complexes of protein with three gemini surfactants in their high concentration range is 12-4(OH)-12 < 12-4-12 < 12-8-12.

Domain-Specific Association of a Phenanthrene-Pyrene-Based Synthetic Fluorescent Probe with Bovine Serum Albumin: Spectroscopic and Molecular Docking Analysis

In this report, the interaction between a phenanthrene-pyrene-based fluorescent probe (PPI) and bovine serum albumin (BSA), a transport protein, has been explored by steady-state emission spectroscopy, fluorescence anisotropy, far-ultraviolet circular dichroism (CD), time-resolved spectral measurements, and molecular docking simulation study. The blue shift along with emission enhancement indicates the interaction between PPI and BSA. The binding of the probe causes quenching of BSA fluorescence through both static and dynamic quenching mechanisms, revealing a 1:1 interaction, as delineated from Benesi-Hildebrand plot, with a binding constant of ∼10⁵ M^-1, which is in excellent agreement with the binding constant extracted from fluorescence anisotropy measurements. The thermodynamic parameters, ΔH°, ΔS°, and ΔG°, as determined from van't Hoff relationship indicate the predominance of van der Waals/extensive hydrogen-bonding interactions for the binding phenomenon. The molecular docking and site-selective binding studies reveal the predominant binding of PPI in subdomain IIA of BSA. From the fluorescence resonance energy transfer study, the average distance between tryptophan 213 of the BSA donor and the PPI acceptor is found to be 3.04 nm. CD study demonstrates the reduction of α-helical content of BSA protein on binding with PPI, clearly indicating the change of conformation of BSA.

Time-Resolved Fluorescence of Water-Soluble Pyridinium Salt: Sensitive Detection of the Conformational Changes of Bovine Serum Albumin

In this paper, we report a pyridinium salt "turn-on" fluorescent probe, 4-[2-(4-Dimethylamino-phenyl)-vinyl]-1-methylpyridinium iodide (p-DASPMI), and applied its time-resolved fluorescence (TRF) to monitor the protein conformational changes. Both the fluorescence lifetime and quantum yield (QY) of p-DASPMI were increased about two orders of magnitude after binding to the protein bovine serum albumin (BSA). The free p-DASPMI in solution presents an ultrashort fluorescence lifetime (12.4 ps), thus it does not interfere the detection of bound p-DASPMI which has nanosecond fluorescence lifetime. Decay-associated spectra (DAS) show that p-DASPMI molecules bind to subdomains IIA and IIIA of BSA. The TRF decay profiles of p-DASPMI can be described by multi-exponential decay function ([Formula: see text]), and the obtained parameters, such as lifetimes ([Formula: see text]), fractional amplitudes ([Formula: see text]), and fractional intensities ([Formula: see text]), may be used to deduce the conformational changes of BSA. The pH and Cu²⁺ induced conformational changes of BSA were investigated through the TRF of p-DASPMI. The results show that the p-DASPMI is a candidate fluorescent probe in studying the conformational changes of proteins through TRF spectroscopy and microscopy in the visible range.

Switching of emission of a styryl dye in cucurbit[7]uril: a comprehensive experimental and theoretical study

Intriguing colour change and change in fluorescence band of 2-(4-(dimethylamino)styryl)-1-methylpyridinium iodide from nonpolar to polar protic solvent, and also from molecular container cucurbit[7]uril environment to polar protic solvent has been reported here. This interesting colour change of this dye with respect to the medium makes this dye useful as a sensor. Change in spectral characteristics of DASPMI along with change of colour from orange to yellow with increasing polarity of medium is interpreted as due to negative solvatochromatism. Complexations of probe-cucurbit[7]uril (1:1 and 2:1) cause structural change of the probe molecule due to hydrogen bond interaction of cationic part of the dye with CO group of cucurbit[7]uril and the colour change of the solution ensued. On addition of sodium chloride to the inclusion complex the dye is released from cucurbit[7]uril interior with colour of the solution reverted back. Theoretical results show that one carbon atom in the styryl part containing the positive charge gets too close to a carbon atom of cucurbit[7]uril to cause a phenomenal increase of dipole moment by 10X.

Optical spectroscopic exploration of binding of Cochineal Red A with two homologous serum albumins

Cochineal Red A is a negatively charged synthetic azo food colorant and a potential carcinogen. We present here the study of binding of Cochineal Red A with two homologous serum albumins, human (HSA) and bovine (BSA), in aqueous pH 7.4 buffer by optical spectroscopic techniques. Protein intrinsic fluorescence quenching by Cochineal Red A occurs through ground-state static interaction and its binding with BSA is stronger than with HSA. The magnitudes of thermodynamic parameters suggest that dye binding occurs principally via electrostatic complexation. Site-marker competitive binding shows that Cochineal Red A binds primarily to site I of serum albumins. Circular dichroic spectra indicate that dye binding results in some conformational modification of serum albumins. Increased ionic strength of the medium results in lowering of binding. This study provides an important insight into possible means of removal of dye toxicity.