Armando Codoñer

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

Abstract The spectrophotometric and thermodynamic properties of molecular complexes of riboflavin (RFN) with some dihydro β-carboline derivatives have been investigated by using electronic absorption and fluorescence spectroscopic methods in aqueous solution. The molecular associations have been examined by means of eletronic 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 RFN on the solutions. The formation constants for the molecular complexes were determined from absorption data, using the Forster—Hammick—Wardley method. The quenching phenomenon observed in RFN fluorescence is related to the concentration of the dihydro β-carboline derivatives, allowing the calculation of the quenching constants for RFN—β-carboline complexes. Thermodynamic parameters have been determined from the values of association constants for the molecular complexes at various temperatures. The influence of substituents in the dihydro β-carboline molecule on the stability of the complexes formed was also investigated.

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.

Binding of a fluorescent dansylcadaverine-substance P analogue to negatively charged phospholipid membranes.

We have investigated the binding of a new dansylcadaverine derivative of substance P (DNC-SP) with negatively charged small unilamellar vesicles composed of a mixture of phosphatidylcholine (PC) and either phosphatidylglycerol (PG) or phosphatidylserine (PS) using fluorescence spectroscopic techniques. The changes in fluorescence properties were used to obtain association isotherms at variable membrane negative charges and at different ionic strengths. The experimental association isotherms were analyzed using two binding approaches: (i) the Langmuir adsorption isotherm and the partition equilibrium model, that neglect the activity coefficients; and (ii) the partition equilibrium model combined with the Gouy-Chapman formalism that considers electrostatic effects. A consistent quantitative analysis of each DNC-SP binding curve at different lipid composition was achieved by means of the Gouy-Chapman approach using a peptide effective interfacial charge (v) value of (0.95 +/- 0.02), which is lower than the physical charge of the peptide. For PC/PG membranes, the partition equilibrium constant were 7.8 x 10(3) M(-1) (9/1, mol/mol) and 6.9 x 10(3) M(-1) (7/3, mol/mol), whereas for PC/PS membranes an average value of 6.8 x 10(3) M(-1) was estimated. These partition equilibrium constants were similar to those obtained for the interaction of DNC-SP with neutral PC membranes (4.9 x 10(3) M(-1)), as theoretically expected. We demonstrate that the v parameter is a determinant factor to obtain a unique value of the binding constant independently of the surface charge density of the vesicles. Also, the potential of fluorescent dansylated SP analogue in studies involving interactions with cell membranes is discussed.

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.

Comparative evaluation of the swelling and degrees of cross-linking in three organic gel packings for SEC through some geometric parameters

The size exclusion chromatographic (SEC) behavior of five solvent/polymer systems in three organic column packings based on polystyrene/divinylbenzene (PS/DVB) copolymer, TSK-Gel H(HR), mu-styragel and TSK-Gel H(XL), has been compared. All the packings offer similar characteristics (pore size, particle size and efficiency) but some differences have been found when eluting the same systems. The different elution behavior observed in both polymeric gels has been analyzed in terms of their swelling and cross-linking degrees and of the fractal parameters. From the Universal Calibration plots, values of the chromatographic partition coefficient, K(p), have been obtained and using some equations previously reported, values of the volume fraction of the network in the swollen state have been determined for the three sets of columns. Overall, for a given hydrodynamic volume and solvent-polymeric solute system the fraction of cross-linked polymer in the stationary phase was ordered according to: TSK-Gel H(XL)>mu-styragel>TSK-Gel H(HR). This means an enhanced swelling degree for TSK-Gel H(HR). In general, fractal calculations support the thermodynamic predictions since both the fractal dimension and the pore size can be ordered as TSK-Gel H(HR)>mu-styragel>TSK-Gel H(XL) (in 10 of the 15 situations studied). The exceptions can be explained in terms of strong preferential solvation.

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.

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.

Spectroscopic study of molecular associations between FMN and β-carbolines

Abstract The spectrophotometric and thermodynamic properties of molecular complexes of flavin mononucleotide (FMN) (riboflavin 5′-phosphate) with some β-carboline derivatives have been investigated in aqueous solution. The molecular associations have been examined by means of electronic absorption spectra, since in each a new charge-transfer band has been located, and also the variation of the fluorescence emission of FMN on the solutions has been observed. The formation constants for the molecular complexes were determined from absorption data using the Foster—Hammick—Wardley method. The quenching phenomenon observed in FMN fluorescence is related to the concentration of the β-carboline derivatives, allowing the calculation of the quenching constants for FMN-β-carboline complexes. 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 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.

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.