Biomedical subjects

G N Valsami

Publications and source records attributed to G N Valsami.

8 recordsLinked to original sources

PubMed1999

Studies on the interaction of diflunisal ion with cyclodextrins using ion-selective electrode potentiometry.

The interaction of diflunisal ion (DF) with beta-cyclodextrin (betaCD), gamma-cyclodextrin (gammaCD), and hydroxypropyl-beta-cyclodextrin (HPbetaCD) was studied in phosphate buffer, pH 7.4, at 5-37 degrees C and various CD concentrations using a home-made diflunisal ion-selective electrode. Typical direct binding plots and Scatchard plots were obtained with HPbetaCD. The Scatchard model for one class of binding sites was used for the estimation of binding parameters for the DF/HPbetaCD interaction. The estimates for n (number of binding sites per CD molecule) were in all cases very close to unity, indicating 1:1 complexation. The association constant (K) estimates decrease with increasing temperature. Sigmoidal direct binding plots and concave-downwards Scatchard plots were obtained with various betaCD or gammaCD concentrations. The Hill model was used for the estimation of the binding parameters for the DF/betaCD and DF/gammaCD interactions. Both the Hill coefficients and the binding constants were markedly dependent on the CD concentration. These findings indicate the cooperative character of DF/betaCD and DF/gammaCD interactions. The free energy change, DeltaG, and the thermodynamic parameters, DeltaH and DeltaS, were estimated for each of the interactions studied using the Van't Hoff equation.

Algorithms↗

PubMed1994

General treatment of competitive binding as applied to the potentiometric ion probe technique: application to the interaction of nonsteroidal anti-inflammatory drugs with bovine serum albumin.

The binding of naproxen, ketoprofen, phenylbutazone, salicylic acid, azapropazone, and indobufen to bovine serum albumin was studied by applying the potentiometric ion probe technique. An ion-selective electrode for the ion probe 1-anilino-8-naphthalene-sulfonate was utilized for the purposes of this study. A modified site-oriented competitive binding model was used for the estimation of the drugs' binding parameters, considering different number of binding sites on the competing binding class(es) for the probe and the drug. Calculations were based exclusively on the concentration data of the free probe. The model's ability for accurate estimations of binding parameters was evaluated by simulation studies. The following values of binding parameters were found at 25 degrees C for the drugs under study; naproxen, n1 = 9.1, k1 = 9.4 x 10(5) M-1; ketoprofen, n1 = 8.8, k1 = 10.8 x 10(5) M-1; phenylbutazone, n1 = 3.2, k1 = 1.4 x 10(5) M-1; salicylic acid, n1 = 2.6, k1 = 1.8 x 10(5) M-1, n2 = 21.5, k2 = 1.0 x 10(4) M-1; azapropazone, n1 = 0.5, k1 = 7.8 x 10(5) M-1, n2 = 26.3, k2 = 1.9 x 10(4) M-1; indobufen, n1 = 5.8, k1 = 5.8 x 10(5) M-1, n2 = 19.9, k2 = 3.8 x 10(5) M-1, where ni the number of binding sites of the i class and ki the corresponding association constant.

Anilino Naphthalenesulfonates↗

PubMed1994

Automated flow-injection technique for use in dissolution studies of sustained-release formulations: application to iron(II) formulations.

The application of flow-injection analysis (FIA) to automated dissolution studies of sustained-release formulations is described. The long-term stability of the dissolution-FIA analyser was checked during unattended operation for 42 h. The construction of multiple calibration curves with the so-called electronic dilution FIA procedure was used to extend the linear range of the determination. The computer-controlled FIA system and the principles of associated software are described and applied to dissolution studies of sustained-release formulations of iron(II) using its sensitive reaction with the colour reagent, ferrozine. The extended linear range of the determination is 1-130 ppm iron(II) and the precision (RSD) better than 3% (n = 3).

Calibration↗

PubMed1992

Determination of association constants in cyclodextrin/drug complexation using the Scatchard plot: application to beta-cyclodextrin-anilinonaphthalenesulfonates.

The appropriate Scatchard equation was developed for a system involving the formation of 1:1 and 1:2 substrate:cyclodextrin complexes. Simulation of this system was performed under the most common experimental conditions encountered in this type of study. The use of the equation allows for nonlinear least-squares estimation of the association constants. The interaction of the model compounds 1-anilino-8-naphthalenesulfonate (1,8-ANS) and 2(p-toluidinyl)-6-naphthalenesulfonate (2,6-TNS) with beta-cyclodextrin (beta-CD) was used to evaluate the theoretical model. Binding experiments were performed using either potentiometric titration or fluorimetric detection. The experimental data for 1,8-ANS/beta-CD fit well to the 1:1 binding model, with an association constant of 87 +/- 1 M-1. The association constants of the 1:1 and 1:2 2,6-TNS/beta-CD complexes utilizing direct potentiometry were 3737 +/- 6 and 149 +/- 2 M-1. It is shown that fluorimetry can give biased estimates for the association constants of the complexation 2,6-TNS/beta-CD, since the assumption of an equivalent quantum yield of bound species is not valid.

Anilino Naphthalenesulfonates↗

PubMed1992

Complexation studies of cyclodextrins with tricyclic antidepressants using ion-selective electrodes.

The complexation of six tricyclic antidepressant drugs [amitriptylin (AMN), nortriptylin (NRN), imipramin (IMN), doxepin (DXN), protriptylin (PTN), and maprotilin (MPN)] with alpha- and beta-cyclodextrins (CDs) using ion-selective electrodes (ISEs) as drug ion sensors is described. Binding parameters were calculated by nonlinear fitting of the model described by the Scatchard equation, to the experimental data of a titration of a CD solution with the ion of interest. One binding site (the CD cavity) was found in all cases with both CDs. The calculated association constants at 25 degrees C using CD concentrations in the range of 0.0100-0.0010 M, varied from 4.81 x 10(3) M-1 (MPN) to 23.9 x 10(3) M-1 (AMN) in the case of beta-CD and from 50 M-1 (DXN) to 123 M-1 (MPN) in the case of alpha-CD. The precision for the estimation of the binding parameters was 0.1-5.0% (within-run RSD%) and 8-10% (between-run RSD%; n = 3). The complexation of the drugs with beta-CD was also examined as a function of temperature in the range of 5-37 degrees C; it was found to decrease by increasing temperature. Van't Hoff analysis gave good correlations (r greater than or equal to 0.989) for all drug ions studied. The estimates of the thermodynamic parameters indicate that the formation of inclusion complexes is enthalpy driven. A compensation plot based on the thermodynamic parameters delta H and delta S resulted in a linear relationship, which is indicative of a common type of force involved in the complexation of drugs to beta-CD.

Antidepressive Agents, Tricyclic↗

PubMed1991

Binding study of the fluorescence probe 1-anilino-8-naphthalensulfonate to human plasma and human and bovine serum albumin using potentiometric titration.

The binding of 1-anilino-8-naphthalenesulfonate (ANS) to bovine serum albumin (BSA), human serum albumin (HSA), and human plasma has been studied by potentiometric titration utilizing a laboratory constructed ion selective electrode (ISE) of ANS. Three classes of ANS binding sites were found on BSA, HSA, and plasma at 25 and 37 degrees C. Computer analysis of the data resulted in estimates for the association constants, number of binding sites (HSA, BSA), and binding capacity of each class. The association constants for the first class of binding sites at 25 degrees C were found to be 7.53 (+/- 0.59) x 10(5), 2.70 (+/- 0.20) x 10(5), and 2.64 (+/- 0.26) x 10(5) M-1 for BSA, HSA, and plasma, respectively. Lower values for the association constants of all binding classes were estimated at the higher temperature (37 degrees C). The binding capacity for ANS decreased in the order BSA, plasma, HSA.

Anilino Naphthalenesulfonates↗

PubMed1990

Binding studies of ions with cyclodextrins using ion-selective electrodes.

The use of ion-selective electrodes (ISEs) to study the binding of various organic ions to alpha- and beta-cyclodextrins (CDs) is described. The ISEs respond selectively, directly, and continuously to the activity of the free ion of interest in solution. Binding parameters (intrinsic binding constants and number of binding sites) are calculated with a computer program which performs a nonlinear fit of the Scatchard model to the experimental data (electrode potential versus total ion concentration) of a titration of a CD solution with the ion of interest. Electrodes selective to chloramine-T, naproxenate, p-nitrophenolate, and chlorpromazine ions were used as models. One binding site was found for all cases, with binding constants varying from 0.67 x 10(3) M-1 (naproxenate to beta CD) to 1.27 x 10(4) M-1 (chlorpromazine to beta CD) at 25 degrees C and a CD concentration of 0.010 M. Precision for the estimations of the binding parameters was 2.0-7.5% within run and 8-10% between run (n = 3). Nonspecific binding was observed for CAT: beta CD and CPM: beta CD interactions. The effects of pH, temperature, CD concentration, and ionic strength on the binding are also presented. The overall binding phenomenon is discussed in light of the estimates of the thermodynamic parameters in relation to the size of the guest molecule, the possible mechanism(s) involved, and the forces participating in the interaction of ions with CDs.

Cyclodextrins↗

PubMed1989

Construction of a naproxen ion-selective electrode and its application to pharmaceutical analysis.

A naproxenate-selective electrode with a liquid membrane consisting of a tetraheptylammonium-naproxenate ion pair dissolved in p-nitrocumene is described. The electrode exhibits a rapid and near-Nernstian response to naproxenate activity from 10(-1) to 10(-4) M at pH 9.0 (borate buffer). No serious interference from common ions and tablet excipients was found and the electrode was used for the direct assay of naproxen tablets by means of the calibration graph technique and of suppositories using the standard additions technique. A dissolution study of naproxen tablets was also carried out and the results compared favourably with those given by the USP XXI methods.

Electrodes↗