Preferential solvation and bimolecular quenching reactions of boronic acid dye at very low quencher concentrations studied by fluorescence spectrum in toluene and butanol binary mixtures

168-177Inferable from the significance of solvent mixtures in practical chemistry, toluene (TL) and butanol (BL) mixtures are used to studyfluorescence behavior of boronic acid dye 2-methoxy-5-fluoro-phenyl boronic acid (2MEFPBA). At the inception, preferential solvation is examined in TL-BL, to understand specific and nonspecific interactions. Suppan’s dielectric enrichment model is further used to understand the nonideality and dielectric enrichment in TL-BL mixtures for preferential solvation. Bimolecular quenching reaction studies of 2MEFPBA with aniline as quencher are made in mixtures of TL–BLto know the effect of viscosity and dielectric constant variation at room temperature.  The quenching process is studied in all solvent mixtures by steady state and transient state method. Quenching is characterized by S-V plots having upward curvature. Analysis of modified S-V equations which accounts both static and dynamic quenching allows calculating bimolecular quenching rate constant. The bimolecular quenching reactions are found to be significantly larger. Further finite sink approximation model is invoked so as to check whether reactions are diffusion limited. The extents of these rate parameters demonstrate that positive deviations in the Stern-Volmer (S-V) plot are because of the presence of apparent static and dynamic quenching process

Preferential solvation and bimolecular quenching reactions of boronic acid dye at very low quencher concentrations studied by fluorescence spectrum in toluene and butanol binary mixtures

Inferable from the significance of solvent mixtures in practical chemistry, toluene (TL) and butanol (BL) mixtures are used to studyfluorescence behavior of boronic acid dye 2-methoxy-5-fluoro-phenyl boronic acid (2MEFPBA). At the inception, preferential solvation is examined in TL-BL, to understand specific and nonspecific interactions. Suppan’s dielectric enrichment model is further used to understand the nonideality and dielectric enrichment in TL-BL mixtures for preferential solvation. Bimolecular quenching reaction studies of 2MEFPBA with aniline as quencher are made in mixtures of TL–BLto know the effect of viscosity and dielectric constant variation at room temperature. The quenching process is studied in all solvent mixtures by steady state and transient state method. Quenching is characterized by S-V plots having upward curvature. Analysis of modified S-V equations which accounts both static and dynamic quenching allows calculating bimolecular quenching rate constant. The bimolecular quenching reactions are found to be significantly larger. Further finite sink approximation model is invoked so as to check whether reactions are diffusion limited. The extents of these rate parameters demonstrate that positive deviations in the Stern-Volmer (S-V) plot are because of the presence of apparent static and dynamic quenching process

Effect of hydrogen bonding and solvent polarity on the fluorescence quenching and dipole moment of 2-methoxypyridin-3-yl-3-boronic acid

Two photophysical properties namely, fluorescence quenching and dipole moment (both ground state and excited state) of 2-methoxypyridin-3-yl-3-boronic acid (2MPBA) have been investigated in alcohol environment using steady state fluorescence technique at 300 K. In quenching studies, a rare but not unusual observation; negative Stern-Volmer (S-V) deviation has been noticed. It has been explained using the concept of solute’s conformational changes in the ground state due to inter-molecular and intra-molecular hydrogen bonding in alcohol environment. The spectroscopic data has been processed using Lehrer equation and thereby Stern-Volmer constant (KSV) has been evaluated. It has been found to be above 100 for most of the solvents used. The data related to dipole moment has been examined using different solvent polarity functions. Theoretical calculation of dipole moment in the ground state has been done using Gaussian software. The general solute–solvent interactions and hydrogen bond interactions have been found to be operative. An appreciable red shift of about 25 nm in the emission spectra has been identified with the rise in solvent polarity and decrease in molar mass of alcohols. It confirms the π→π* transition as well as the possibility of intra-molecular charge transfer (ICT) character in the emitting singlet state of 2MPBA

Solvent Effect on the Fluorescence Properties of Two Biologically Active Thiophene Carboxamido Molecules

The absorption and fluorescence spectra of two thiophene carboxamido molecules namely 2–( - trimethoxy phenyl) imino–3–N–ethylcarboxamido–4, 5, tetramethylene thiophene (X) and 2-( -N, N-dimethylaminophenyl) imino-3-(N- methylphenyl carboxamido)-4, 5, tetramethylene thiophene (Y) have been recorded at room temperature. The ground (mg) and excited (me) state dipole moments are estimated from Lippert, Bakhshiev, Kawski-Chamma-Viallet equations by using the variation of Stokes shift with microscopic solvent dielectric constant (e) and refractive index (n). The excited dipole moments were also estimated by using the variation of Stokes shift with microscopic empirical solvent polarity parameter and the values are compared. It was estimated that dipole moments of the excited state were higher than those of the ground state of both the molecules. Further, the change in dipole moment (Dm) were calculated both from solvatochromic shift method and on the basis of microscopic empirical solvent polarity parameter

Solvent Effect on Fluorescence Quenching of 7, 8 Benzo‑4‑azido Methyl Coumarin by Aniline

Fluorescence quenching of biologically active studies of 7, 8 benzo-4-azidomethyl coumarin (7BAMC) by aniline in four different organic solvents namely benzene, dioxane, tetrahydrofuran and acetonitrile has been carried out at room temperature with a view to understand the quenching mechanisms. The Stern–Volmer (S-V) plot has been found to be non-linear with a positive deviation for all the solvents studied. In order to interpret these results we have invoked the ground state complex formation and sphere of action static quenching models. Using these models various quenching rate parameters have been determined. The magnitudes of these parameters suggest that sphere of action static quenching model agrees well with the experimental results. Hence the positive deviation is attributed to the static and dynamic quenching. Further, with the use of Finite Sink approximation model, it was possible to check these bimolecular reactions as diffusion-limited and to estimate independently distance parameter R’ and mutual diffusion coefficient D. Finally an effort has been made to correlate the values of R’ and D with the values of the encounter distance R and the mutual coefficient D determined using the Edward’s empirical relation and Stokes – Einstein relation

Investigation of interaction between boronic acids and sugar: effect of structural change of sugars on binding affinity using steady state and time resolved fluorescence spectroscopy and molecular docking

Binding interactions of boronic acid derivatives viz. 2-Methylphenylboronic acid (B1) and 3-Methoxyphenylboronic acid (B2) with mono saccharides (arabinose, fructose and galactose) and disaccharides (sucrose, lactose and maltose) in aqueous condition at pH 7.4 by means of fluorescence spectroscopy is reported in the present investigation. Sugar sensing as well as continuous glucose monitoring (CGM) plays a significant role in diabetes regulation. Sugar sensors mediated through enzymes have their own drawbacks, which led to encouragement to search for designing new sensors through alternate approaches. Among many, fluorescence-based sensors are drawing more attention. Boronic acid-based fluorescence sensors have the capacity to bind reversibly with diols, which makes their demand high in applications. Addition of sugar reduces fluorescence intensities. Change in intensities is associated to cleavage of intermolecular hydrogen bonding which leads in reduced stability of boronate ester. Lineweaver-Burk and Benesi-Hildebrand equation is used for analysing data. Mono sugars are estimated to have higher binding constants. Mutarotation leads to structural changes in saccharides which play a key role in binding interactions. Sugars in furanose form are found to be highly favoured for binding. Molecular docking of B1 and B2 with proteins with PDB ID: 2IPL and 2IPM being periplasmic was done with the help of Schrodinger Maestro 11.2 version. GLIDE scores terms are used for expressing binding affinity.Scopu

Examining the spectroscopic features and quantum chemical computations of a Quinoline derivative: Experimental and theoretical insights into the photophysical characteristics

503-515The solvatochromic studies in a Quinoline derivative molecule namely Quinolin-8-ol (QO) have been carried out at ambient temperature using absorption and fluorescence spectroscopy. The QO molecule shows the bathochromic shift with increase in solvent polarity demonstrating π → π* transition. The solvatochromic data coupled with quantum mechanical calculations has been used to estimate change in dipole moment of the molecule after excitation. It has been found that excited state dipole moment is greater than the corresponding ground state dipole moment. Further, it is observed that excited and ground state dipole moments are parallel. The chemical reactivity and kinetic stability of QO molecule are investigated using Frontier molecular orbital (FMO) analysis. Natural bond orbital (NBO) analysis shows proton transfer within the selected donor-acceptor depicting large energy of stabilization for QO molecule. The calculated Fukui functions infer the local softness and local eletrophilicity index of QO molecule. The theoretically simulated UV-Vis absorption spectrum of QO molecule matches well with the experimental spectrum

Examining the spectroscopic features and quantum chemical computations of a Quinoline derivative: Experimental and theoretical insights into the photophysical characteristics

The solvatochromic studies in a Quinoline derivative molecule namely Quinolin-8-ol (QO) have been carried out at ambient temperature using absorption and fluorescence spectroscopy. The QO molecule shows the bathochromic shift with increase in solvent polarity demonstrating π → π* transition. The solvatochromic data coupled with quantum mechanical calculations has been used to estimate change in dipole moment of the molecule after excitation. It has been found that excited state dipole moment is greater than the corresponding ground state dipole moment. Further, it is observed that excited and ground state dipole moments are parallel. The chemical reactivity and kinetic stability of QO molecule are investigated using Frontier molecular orbital (FMO) analysis. Natural bond orbital (NBO) analysis shows proton transfer within the selected donor-acceptor depicting large energy of stabilization for QO molecule. The calculated Fukui functions infer the local softness and local eletrophilicity index of QO molecule. The theoretically simulated UV-Vis absorption spectrum of QO molecule matches well with the experimental spectrum