Isidro S. Monzó

Spectroscopic study of intermolecular complexes between FAD and some β-carboline derivatives

Abstract The formation of molecular complexes between flavine adenine dinucleotide (FAD) and some β-carboline derivatives [antidepressant drugs that have a pronounced inhibition of monoamine oxidase (MAO)] has been studied by using electronic absorption and fluorescence spectroscopic methods. Thermodynamic parameters have been determined from the values of association constants for the molecular complexes at various temperatures. The influence of substituents in the β-carboline molecule on the stability of the complexes formed was also investigated.

Spectroscopic study of molecular associations between riboflavin and some β-carboline derivatives

The formation of molecular complexes between riboflavin (RFN) and some β-carboline derivatives (antidepressant drugs that have a pronounced inhibition of monoamine oxidase) has been studied by using electronic absorption and fluorescence spectroscopic methods in aqueous solution. The formation constants for the molecular complexes were determined from data of absorption, using the Foster–Hammick–Wardley method. The quenching phenomenon observed in RFN fluorescence is related to the concentration of the β-carboline derivatives, allowing the calculation of the quenching constants for RFN–β-carboline complexes. Thermodynamic parameters have been determined from the values of associations constants for the molecular complexes at various temperatures. The influence of substituents in the β-carboline molecule on the stability of the complexes formed was also investigated.

Elucidation of Carbohydrate Molecular Interaction Mechanism of Recombinant and Native ArtinM

The quartz crystal microbalance (QCM) technique has been applied for monitoring the biorecognition of ArtinM lectins at low horseradish peroxidase glycoprotein (HRP) concentrations, using a simple kinetic model based on Langmuir isotherm in previous work.18 The latter approach was consistent with the data at dilute conditions but it fails to explain the small differences existing in the jArtinM and rArtinM due to ligand binding concentration limit. Here we extend this analysis to differentiate sugar-binding event of recombinant (rArtinM) and native (jArtinM) ArtinM lectins beyond dilute conditions. Equivalently, functionalized quartz crystal microbalance with dissipation monitoring (QCM-D) was used as real-time label-free technique but structural-dependent kinetic features of the interaction were detailed by using combined analysis of mass and dissipation factor variation. The stated kinetic model not only was able to predict the diluted conditions but also allowed to differentiate ArtinM avidities. For instance, it was found that rArtinM avidity is higher than jArtinM avidity whereas their conformational flexibility is lower. Additionally, it was possible to monitor the hydration shell of the binding complex with ArtinM lectins under dynamic conditions. Such information is key in understanding and differentiating protein binding avidity, biological functionality, and kinetics.

Apparent dipole moments and molar volumes of β-carbolines and carbazole in dioxane solution

The apparent molecular polarization at infinite dilution, P2∞, molecular refraction, RD, dipole moment, µ2, and partial molar volume, V2°, of carbazole and some β-carboline derivatives have been determined from dielectric permittivity, specific volume, and refractive index measurements in 1,4-dioxane solutions at 25 °C. Evidence of hydrogen-bonding interaction with solvent has been found from i.r. spectroscopy and the apparent molar volumes. A relation has been found between literature pKa values of β-carboline derivatives studied in the ground state and their corresponding dipole moments in solution.

Modeling of the role of conformational dynamics in kinetics of the antigen-antibody interaction in heterogeneous phase.

A novel approach that may potentially be used to study biomolecular interactions including the simultaneous determination of structural and kinetic binding parameters is described in this Article for the first time. It allows a rigid distinction between the possible reaction mechanisms of biomolecular recognition, induced fit and conformational selection. The relative importance of the two pathways is determined not by comparing rate constants but the structural aspects of the interaction instead. So the exact location of antigen molecules with respect to the capture antibody is depicted experimentally, avoiding the use of X-ray crystallography. The proposed pattern is applied to study the anti-BSA Immunoglobulin G (IgG)-free Bovine Serum Albumin (BSA) interaction, in which IgG is anchored on a silicon chip sensing surface in an oriented manner. The exact location of the receptor with respect to the ligand was monitored during the binding process, thus drawing the full reaction scheme. IgG forms an asymmetric (FabBSA)2 complex with BSA molecules, even though it has two identical fragment antigen binding arms. This is thought to be due to steric hindrance caused by the binding of the first BSA molecule. Furthermore, the proposed model allows one to characterize reaction intermediates without the need of isolating them. These intermediates not characterized in situ so far are the keystone to understand how antibodies are able to identify antigens.

Kinetics and mechanism between chloranil and s-butylamine in cyclohexane solution

The interaction of chloranil (CA) with s-butylamine (A), in cyclohexane solution has been studied by measuring visible and ultraviolet absorption spectra at various temperatures in the range 279–308 K. Kinetic and thermodynamic parameters have been derived and a mechanism has been proposed for this reaction. The results indicate the existence of a charge-transfer complex in the presence of an excess of s-butylamine, which decomposes to give a final product (D: the disubstituted product of CA). The reaction path has been found to be autocatalysed by the presence of the amine.

Modelling the Hydrogen-Bonding Interactions in a Copolymer/Biodegradable Homopolymer Blend through Excess Functions

A recent theoretical approach based on the coupling of both the Flory-Huggins (FH) and the Association Equilibria thermodynamic (AET) theories was modified and adapted to study the miscibility properties of a multicomponent system formed by two polymers (a proton-donor and a proton-acceptor) and a proton-acceptor solvent, named copolymer(A)/solvent(B)/polymer(C). Compatibility between polymers was mainly attained by hydrogenbonding between the hydroxyl group on the phenol unit of the poly(styrene-co-vinyl phenol) (PSVPh) and the carbonyl group of the biodegradable and environmentally friendly poly(3-hydroxybutyrate) (PHB). However, the self-association of PSVPh and specific interactions between the PSVPh and the H-acceptor group (an ether oxygen atom) of the epichlorohydrin (ECH) solvent were also established in a lower extension, which competed with the polymer-polymer association. All the binary specific interactions and their dependence with the system composition as well as with the copolymer content were evaluated and quantified by means of two excess functions of the Gibbs free energy, ΔgAB and ΔgAC. Experimental results from fluorescence spectroscopy were consistent with the theoretical simulations derived with the model, which could also be applied and extended to predict the miscibility in solution of any polymer blend with specific interactions.

Spectroscopic study of molecular associations between flavins FAD and RFN and some indole derivatives

Abstract The formation of complexes between two flavins [flavine adenine dinucleotide (FAD) and riboflavin (RFN)] and some indole derivatives has been studied in aqueous solution. The molecular associations have been examined by means of electronic absorption spectra, since in each, a new charge-transfer like band has been located, and also by observing the variation of the fluorescence emission of FAD or RFN on the solutions. The formation constants for the molecular complexes were determined from data of absorption using the Foster—Hammick—Wardley method. The quenching fluorescence phenomena observed for the FAD and RFN were related to the concentration of the indole derivatives and the corresponding quenching constants have been determined. Thermodynamic parameters have been derived from the values of association constants for the molecular complexes at several temperatures. Clear evidence is found for the influence on the stability of these complexes of the different substituent groups in the indole derivatives and the molecular structure of both flavins.

Kinetics and Mechanism of the Reactions between Chloranil and n-Butylamine in Cyclohexane Solution

Interaction between chloranil (CA) and n-butylamine (A) at several temperatures has been studied by u.v.–visible spectroscopy. Kinetic and thermodynamic parameters, as well as a mechanism, have been proposed for this reaction. The results indicate the initial formation of charge-transfer complexes between CA and A, in the presence of an excess of amine, which decomposes to give a final product (D)(disubstituted product of CA). The reaction path is autocatalysed by the presence of amine.

Determination of the complexes between dimethylphenols and pyridine by a dielectric constant method in non-polar solvents

The apparent equilibrium constants for the association of pyridine with dimethylphenols in benzene and in cyclohexane at 25 °C have been measured by the method of dielectric constant variation, in order to check and extend the results obtained by spectroscopic methods. Solvent effects were detected. Excess of dipole moments have been derived and related with pKa values from the literature. The influence of the relative positions of the methyl substituents on complex formation are discussed qualitatively.