Maria Szögyi

Charge transfer chromatography used to study the interaction between synthetic phospholipids and nonylphenyl-nonylglycolate

The interaction between 8 synthetic phospholipids and the nonionic tenzide nonylphenyl-nonylglycolate was studied by charge transfer chromatography. The method has been improved by carrying out the determination at different organic phase concentrations of eluent and by extrapolating the interactive strength back to pure water. It was suggested that two types of interaction of commensurable strength may exist between the tenzide and the phospholipids; hydrophil-hydrophil interactions between the polar head groups of phospholipids and the hydrophilic ethylene-oxide chain of tenzide; hydrophob-hydrophob interactions between the fatty acid chains of phospholipids and the alkyl chain of tenzide. This last effect strongly depends on the length of the fatty acid chain, but it is independent of the presence of double bonds in the lipophilic region of phospholipid.

Interaction of some non-ionic tensides with dioleoyl phosphatidyl choline, studied by charge-transfer chromatography

Abstract The interaction of the membrane phospholipid, dioleoyl phosphatidyl choline (DOPC), with 23 non-ionic tensides belonging to four homologous series was studied by charge-transfer reversed-phase thin-layer chromatography. The dependence of the lipophilicity of DOPC on the tenside concentration of the eluent was considered to be linearity related to the stability of the complex. The polyethoxylated nonylphenyl and tributylphenyl derivatives showed similar behaviour patterns. They formed complexes with DOPC, but the strength of complexation depended neither on the type of hydrophobic moiety nor on the number of ethylene oxide groups per molecule. However, for polyethoxylated oleyl alcohol derivatives, the stability of the complex depended considerably on the number of ethylene oxide groups, thus suggesting a different form of interaction. The length of the alkyl chain in the hydrophobic part of the tensides also influenced the strength of complex formation.

Determination of the lipophilicity of some peptides: Effect of surface pH of silica

The lipophilicities of 22 peptides were determined by reversed-phase thin-layer chromatography using methanol as organic modifier in the concentration range 0-90 vol.-% on silica supports with surface pH values of 2.0,4.5,6.0,7.5 and 9.0. Only one of the 22 peptides (Trp-Ala-Ile) followed the general rule, i.e., its RM value decreased linearly with increasing proportion of organic modifier over the whole concentration range. Most peptides exhibited typical silanophilic retention behaviour, the RM value decreasing with increasing organic phase concentration in the lower concentration range and then increasing with further increase in the proportion of organic modifier. In some instances the lipophilicity increased linearly with increasing proportion of methanol. The silanophilic effect depended not only on the structure of the peptide, but also on the surface pH of the silica support. The retention behaviour of peptides can be well described by a polynomial function, the linear and quadratic forms of methanol concentration and surface pH being the independent variables. Principal component analysis showed that the presence of a ring structure in the peptides has the greatest impact on their retention behaviour, the overall polarity (basic, neutral or acidic) being of secondary importance. The number of amino acids in the peptide has a negligible effect on the chromatographic behaviour.

Reversed-phased thin-layer chromatography used to study the simultaneous effect of pH and ion strength on the lipophilicity of chlorphexidine

The effect of ion strength and pH value of the eluent on the determination of the lipophilicity of chlorhexidine was studied by reversed-phase thin-layer chromatography. The method has been improved by using various buffers: aqueous solutions of formic, acetic and propionic acids and their sodium salts in different ratios and in various concentrations. Stepwise regression analysis separated the effect of pH value, ion strength and acid type on the lipophilicity of chlorhexidine and proved that the ion strength exerted a higher impact than the pH value did. The effect of alkyl chain length of the acids was of secondary importance.

Differential scanning calorimetry to study the possible ternary complex formation between chlorhexidine, phosphatidylcholine and some nonionic tenzides

The effect of chlorhexidine and its molecular complexes with some nonionic tenzides (Tween and Myrj series) on the phase transfer parameters of dipalmitoylphosphatidylcholine has been studied by differential scanning calorimetry. The application of principal component analysis facilitated the evaluation of the experimental data matrix. It was found that both the lipophilicity of the tenzide and the strength of interaction between chlorhexidine and nonionic tenzide had a considerable impact on some of the phase transition parameters of dipalmitoylphosphatidylcholine. These findings indicate the possible existence of ternary complexes. This ternary complex formation may cause a decrease of chlorhexidine activity in the presence of nonionic tenzides.

Physicochemical interaction of some benzodiazepine derivatives with amino acids and phospholipids

Abstract The interaction of 18 benzodiazepine (BDZs) derivatives with amino acids and with the membrane phospholipid di-palmitoylphosphatidylcholine (DPPC) was studied using charge-transfer reversed-phase chromatography and differential scanning calorimetry, respectively. A weak hydrophobic interaction was observed between the BDZs and Trp. Midazolam and medazepam were strongly bound to dicarboxylic amino acids, the strength of interaction being higher in ionic environment. BDZs modified the phase transition parameters of DPPC, indicating direct interaction. The enthalpy of the main transition of DPPC showed a nonlinear dependence on the specific hydrophobic surface area of BDZs, thus demonstrating the hydrophobic nature of the interaction.

Interaction of monoamine oxidase inhibitory drugs with some phospholipids

The effect of 17 monoamine oxidase inhibitory drugs (propargylamine derivatives) on the phase transition parameters of some synthetic phospholipids has been studied by differential scanning calorimetry. The drugs modified the thermal behaviour of phospholipids proving the existence of phospholipid-drug interactions. Phosphatidylethanolamine, phosphatidylcholine and phosphatidic acid equally interact with the monoamine oxidase inhibitory drugs. Significant correlations were found between the change of the phase transition parameters of phospholipids and the hydrophilic and hydrophobic molecular parameters of drugs. Calculations suggest that both hydrophilic (between the head group of phospholipids and the polar propargylamine group of drugs) and hydrophobic (between the apolar fatty acid chains of phospholipids and the lipophilic substructures of drugs) forces are involved in the phospholipid-drug interaction. Chloro substitution in the hydrophobic moiety of drugs enhances considerably the strength of interaction.

Hydrophilic interactions between charged amino acids and the effect of ions on the strength of interaction

The interaction between oppositely charged amino acids was studied by charge-transfer reversed- phase thin-layer chromatography. The dependence of the lipophilicity of Arg, Lys and Orn on the concentration of G lu , Asp, Gln and Asn in the eluent was considered to be related to the strength of interaction. The interaction of dibasic amino acids with Glu and Asp was stronger than with Gln and Asn. Mono- (Li+, Na+, K+, Rb+ and Cs+) and divalent (Mg2+ and Ca2+) cation s decreased the strength of interaction suggesting the electrostatic character of the interaction. Their inhibitory effect mainly depended on their concentration and to a lesser extent on the ion charge and hydrated ion radii. Stepwise regression analysis proved that the strength of interaction depends on the polarity parameters of amino acids and is independent of their chemical structure.