Fabrication of a GUMBOS-based acid-base indicator: smart probe for sensing acids and bases in any solvent.

This report outlines the synthesis of an ionic liquid-based pH-responsive indicator to sense acids or bases in non-polar as well as polar solvents. Herein, we have assembled a new ionic liquid (IL) comprised of a group of uniform materials based on organic salts (GUMBOS) by attaching a quaternary phosphonium ionic liquid with a very common acid-base indicator, methyl orange, via simple ion-exchange reaction. This integrated IL-based indicator is highly soluble in less polar solvents and exhibits good sensitivity toward the presence of acids/bases in those media.

A ZnS quantum dot-based super selective fluorescent chemosensor for soluble ppb-level total arsenic [As(iii) + As(v)] in aqueous media: direct assay utilizing aggregation-enhanced emission (AEE) for analytical application.

This study brings out a novel, superselective detection employing thiosalicylic acid-capped ZnS-based quantum dots that display photoluminescence "turn-on" characteristics only in the presence of arsenic in the aquatic medium for the first time. It shows a splendid limit of detection of soluble arsenic down to a few ppb level, much below than the MCL reported value, without being interfered by any other ions.

Effect of casein on pure lecithin liposome: Mixed biomacromolecular system for providing superior stabilization to hydrophobic molecules.

Formulation of new liposoma-based systems can always be in the spotlight for their unique utilization as carriers. Some changes in the composition of lipids may give rise to new mixed liposomes exhibiting modified size and physico-chemical characteristics. Consequently, these display different encapsulating properties toward various molecules.

Simultaneous Binding of Folic Acid and Methotrexate to Human Serum Albumin: Insights into the Structural Changes of Protein and the Location and Competitive Displacement of Drugs.

Protein structure can be flexible to adopt multiple conformations to house small molecules. In this paper, we have attempted to experimentally figure out how the structure of a transport protein steer the drug-drug competition (DDC) by maintaining the equilibrium distribution of the bound and unbound fractions of drugs. This understanding is an important facet in biophysical and medicinal chemistry to ascertain the effectiveness of drugs.

Counterpointing Scenarios on the Fate of Different Prototropic Forms of Norfloxacin Housed in the Pocket of Lysozyme: The Nonelectrostatic Interactions in the Protein Interior Are in the Controlling Role on the Prototropic Equilibria of the Guest.

Herein, we report a comprehensive study on the interaction of three protomeric forms of the antibacterial drug norfloxacin (nfx) with the enzymatic protein human lysozyme (lyz). Norfloxacin, having the option for two-stage acid-base equilibria, converts from cationic (nfx) to zwitterionic (nfx) form, followed by an anionic (nfx) species, with increasing pH. Among these protomeric forms, lysozyme binds nfx most robustly, whereas nfx has a weak association and nfx does not show any interaction.

Optical Spectroscopic and Morphological Characterizations of Curcuminized Silk Biomaterials: A Perspective from Drug Stabilization.

Silk protein fibroins have gained remarkable attention in recent years as a potential drug carrier in the developing medicinal field of research. In this work, the stability of anticancer agent curcumin in the presence of two different silk protein fibroins from nonmulberry (Am) and mulberry (Bm) has been examined, and the possible mechanism of stabilization in a physiologically relevant medium has also been explored. In solution phase, upon treatment with curcumin, the predominated β-sheet structure of Am is marginally altered, whereas in the case of Bm, a substantial structural changeover has been observed (from coil to β-sheet) to accommodate the hydrophobic drug.

Investigations on the Effect of Fatty Acid Additives on Casein Micelles: Role of Ethylenic Unsaturation on the Interaction and Structural Diversity.

Casein, one of the major constituent of milk protein, is considered to be a good candidate for oral drug delivery system. Also, milk transports various essential fatty acid to blood through dietary supplements. In this study, we have explored the alteration in the structural characteristic in terms of the modulations in the microenvironment of the protein in the presence of different types of fatty acids.

Proton Transfer Pathways of 2,2'-Bipyridine-3,3'-diol in pH Responsive Fatty Acid Self-Assemblies: Multiwavelength Fluorescence Lifetime Imaging in a Single Vesicle.

Fatty acids are known to form different supramolecular aggregates in aqueous solutions depending on the pH of the medium. The dynamics of the transformation of oleate micelles into oleic acid/oleate vesicles has been investigated using a pH-sensitive intramolecular proton transfer fluorophore, 2,2'-bipyridine-3,3'-diol [BP(OH)]. Different prototropic forms of BP(OH) exist in different pH values of the system, and thus, the ground state and the excited state dynamics of BP(OH) have been modulated in these confined media.

Modulation and Salt-Induced Reverse Modulation of the Excited-State Proton-Transfer Process of Lysozymized Pyranine: The Contrasting Scenario of the Ground-State Acid-Base Equilibrium of the Photoacid.

Here we report on the excited-state behavior in terms of the excited-state proton-transfer (ESPT) reaction as well as the ground-state acid-base property of pyranine [8-hydroxypyrene-1,3,6-trisulfonate (HPTS)] in the presence of an enzymatic protein, human lysozyme (LYZ). HPTS forms a 1:1 ground-state complex with LYZ having the binding constant KBH = (1.4 ± 0.

Exploration of electrostatic interaction in the hydrophobic pocket of lysozyme: Importance of ligand-induced perturbation of the secondary structure on the mode of binding of exogenous ligand and possible consequences.

Exogenous ligand binding can be adequate to alter the secondary structure of biomolecules besides other external stimuli. In such cases, structural alterations can complicate on the nature of interaction with the exogenous molecules. In order to accommodate the exogenous ligand, the biomolecule has to unfold resulting in a considerable change to its properties.

Distilbene derivative as a new environment-sensitive bifunctional ligand for the possible induction of serum protein aggregation: a spectroscopic investigation and potential consequences.

The photophysical properties of a new distilbene fluorophore, DPDB, belonging to the conjugated polyene family is found to be well modulated with the variation of the microenvironment. Compared to the ground state, the excited-state photophysical properties of the fluorophore have been altered to larger extents with the variation of polarity and the hydrogen-bonding nature of solvents. The change in the fluorescence intensity of DPDB shows a nice correlation with the aggregation behavior of different surfactants which have been utilized for the determination of the CMC of surfactants.

Synthesis of a new class of furo[3,2-c]coumarins and its anticancer activity.

A series of furo[3,2-c]coumarin derivatives 1a-d were synthesized and evaluated for their antiproliferative activity against MCF-7 breast and HCT-15 colon cancer cell lines using Sulfo-rhodamine B (SRB) assay. Compounds 1b and 1d showed higher antiproliferative activity than 1a and 1c. UV-Vis spectroscopy was used for DNA and BSA-binding affinity of the compounds 1b and 1d and gave overall affinity constants of K1b-DNA=8.

Detailed scenario of the acid-base behavior of prototropic molecules in the subdomain-IIA pocket of serum albumin: results and prospects in drug delivery.

The protein pocket performs magically in controlling, inhibiting, or optimizing various biochemical processes. The elegant 3D disposition of different side chains in the cavity is a key point in accommodating specific ligands. Anion receptors in the subdomain-IIA pocket of serum albumin (SA) prefer to home anionic ligands.

Detailed scrutiny of the anion receptor pocket in subdomain IIA of serum proteins toward individual response to specific ligands: HSA-pocket resembles flexible biological slide-wrench unlike BSA.

Present study reveals that the subdomain IIA cavity of two homologous serum albumins (HSA, BSA) has inherent mutual structural and functional deviations which render noticeable difference in behavior toward specific ligands. The major drug binding site (subdomain IIA) of HSA is found to be largely hydrophobic while that of BSA is partially exposed to water. Larger shift in REE spectra and greater change in solvent reorganization energy of coumarin 343 (C343)-anion in HSA clearly reveals that binding pocket is relatively large and water molecules penetrate deeper into it unlike BSA.

Exploration of pH-dependent behavior of the anion receptor pocket of subdomain IIA of HSA: determination of effective pocket charge using the Debye-Hückel limiting law.

Protein-ligand electrostatic interaction can be looked upon as ion receptor-ligand interaction, and the binding cavity of protein can be either an anion or cation receptor depending on the charge of the guest. Here we focus on the exploration of pH-modulated binding of a number of anionic ligands, specific to the subdomain IIA cavity of HSA, such as carmoisine, tartrazine, cochineal red, and warfarin. The logarithm of the binding constant is found to vary linearly with the square-root of ionic strength, indicating applicability of the Debye-Hückel limiting law to protein-ligand electrostatic binding equilibrium, and concludes that the subdomain IIA cavity is an anion receptor.

Effect of encapsulation in the anion receptor pocket of sub-domain IIA of human serum albumin on the modulation of pKa of warfarin and structurally similar acidic guests: a possible implication on biological activity.

Supramolecular and bio-supramolecular host assisted pKa shift of biologically relevant acidic guests, warfarin and coumarin 343, has been monitored using both steady-state and time resolved fluorescence spectroscopy. The anion receptors present in sub-domain IIA of human serum albumin (HSA) stabilize the anionic form of the guest and thereby shift pKa towards acidic range. On the other hand, the preferential binding of the neutral form of guests in the non-polar hydrophobic cavity of β-cyclodextrin results in up-shifted pKa.

pH-insensitive electrostatic interaction of carmoisine with two serum proteins: a possible caution on its uses in food and pharmaceutical industry.

Here we have investigated the binding of carmoisine, a water-soluble azo food colorant, with serum proteins (HSA and BSA) by fluorescence and UV-VIS spectroscopy, circular dichroism and molecular docking studies. Results indicate that fluorescence quenching of protein has been due to site-specific binding of the dye with biomacromolecules. Site marker competitive binding and molecular docking explorations show that interaction occurs in the sub-domain ІІA of HSA and the sub-domains ІІA and ІB in the case of BSA.

Modulation of accessibility of subdomain IB in the pH-dependent interaction of bovine serum albumin with Cochineal Red A: a combined view from spectroscopy and docking simulations.

Our recent report on the binding of Cochineal Red A, a food dye, with HSA and BSA at pH 7.4 has revealed that electrostatic forces is the principal cause of interaction. In that study issues relating to complications arising out of modulation of dye binding affinity of BSA with pH had not been explored.

Spectroscopic investigation of the effect of salt on binding of tartrazine with two homologous serum albumins: quantification by use of the Debye-Hückel limiting law and observation of enthalpy-entropy compensation.

Formation of ion pair between charged molecule and protein can lead to interesting biochemical phenomena. We report the evolution of thermodynamics of the binding of tartrazine, a negatively charged azo colorant, and serum albumins with salt. The dye binds predominantly electrostatically in low buffer strengths; however, on increasing salt concentration, affinity decreases considerably.

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.

Accumulation and interaction of hypericin in low-density lipoprotein--a photophysical study.

The accumulation and interaction of hypericin with the biologically important macromolecule, low-density lipoprotein (LDL), is investigated using various steady-state and time-resolved fluorescence measurements. It is concluded that multiple hypericins can penetrate considerably deeply into the LDL molecule. Up to approximately 20 nonaggregated hypericin molecules can enter LDL; but upon increasing the hypericin concentration, the fluorescence lifetime of hypericin decreases drastically, suggesting most likely the self-quenching of aggregated hypericin.

Solvation dynamics in protein environments: comparison of fluorescence upconversion measurements of coumarin 153 in monomeric hemeproteins with molecular dynamics simulations.

The complexes of the fluorescence probe coumarin 153 with apomyoglobin and apoleghemoglobin are used as model systems to study solvation dynamics in proteins. Time-resolved Stokes shift experiments are compared with molecular dynamics simulations, and very good agreement is obtained. The solvation of the coumarin probe is very rapid with approximately 60% occurring within 300 fs and is attributed to interactions with water (or possibly to the protein itself).

Assessing the roles of the constituents of ionic liquids in dynamic solvation: Comparison of an ionic liquid in micellar and bulk form.

Dynamic solvation of the dye, coumarin 153, is compared in an ionic liquid that forms micelles in water against the bulk solvent. This provides the unprecedented opportunity of investigating the behavior of the ionic liquid in two globally different configurations. It is proposed that the imidazolium moiety is in both cases responsible for the majority of the solvation, which manifests itself in the first 100 ps.

Characterization of the interactions of fluorescent probes with proteins: coumarin 153 and 1,8-ANS in complex with holo- and apomyoglobin.

In order to provide a thorough characterization of a system with which to study the dielectric response of a protein, a well-defined system complex of a fluorescent probe and protein is required. We have argued that such a system is provided by coumarin 153 and apomyoglobin (Photochem. Photobiol.

Dynamic solvation in imidazolium-based ionic liquids on short time scales.

Steady-state and time-resolved Stokes shift data for the probe coumarin 153 in two imidazoles, six imidazolium-based ionic liquids, and several other solvents are presented. These results are consistent with our original suggestion (J. Phys.