Aggregation of certain medicinal amines in aqueous solutions of their salts

Solubilization sites and acid-base forms of dibucaine-hydrochloride in neutral and charged micellar solutions

Steady-state and time-resolved emission spectroscopic techniques have been employed to characterize the drug species of dibucaine and to identify its location in micellar Triton X-100 (neutral), hexadecyltrimethyl ammonium bromide (cationic) and lithium dodecyl sulfate (anionic) solutions at 77 K. Under physiological conditions, the dibucaine is shown to exist in the free base form (D) while solubilized in the hydrocarbon core of neutral micelles. In cationic micellar solution, dibucaine exists as the monocation species (DH+) where the anesthetic is solubilized in the extramicellar aqueous solution and D is solubilized in the hydrophobic region with close proximity to the micellar interface. In the anionic micelles, interfacial solubilization is most consistent with a site in which the tertiary amino group of the monocation dibucaine (DH+) is anchored at the micellar interface with its quinoline analog penetrating the hydrophobic region. The distinct properties observed for the drug species (i.e. D and DH+) and their solubilization sites in micelles are consistent with a balance between hydrophobic forces, surface polarity and the interfacial electrostatic potential present in the micellar solubilization sites. These observations could lend insight into the molecular basis of pharmacological action, in particular the mechanism of local anesthetic drug transport across membranes.

Photophysical studies of local anesthetics, tetracaine and procaine: drug aggregations

The effects of solvent and concentration on the photophysical properties of tertiary amine local anesthetics, tetracaine and procaine were studied experimentally using low temperature (77 K) emission spectroscopy and confirmed theoretically using a HAM/3 method. For tetracaine free base in methylcyclohexane, a broad fluorescence band observed at approximately 375 nm for concentrations greater than 1 x 10(-3) M is assigned to the molecular self-associated species. The disappearance of this band in ethanol (i.e. a model hydrophobic environment) indicates a greater tendency of neutral tetracaine towards molecular hetero-association. In an aqueous solution of procaine.HCl, a broad emission band centered at approximately 400 nm is detected even at a concentration as low as 1 x 10(-4) M and is attributed to the charged aggregates of procaine.HCl. Two general observations for procaine, tetracaine and dibucaine are noted: (1) the monocation and free base local anesthetics in ethanol solutions give identical photophysical properties, suggesting that the monocation drug species in ethanol is H+ dissociative, and (2) the lowest singlet excited state of neutral local anesthetics is calculated to have a charge-transfer character originating from a non-bonding electron in the N of tertiary amine group to the pi orbital of aromatic ring. The possible pharmacological implications of the deprotonation, the drug aggregations and the charge-transfer excitations of local anesthetics on the molecular basis of anesthesia are discussed.

Self-association of local anaesthetic drugs in aqueous solution

The aggregation characteristics of a series of local anaesthetic drugs in water and electrolyte solution have been examined using total intensity light scattering, photon correlation spectroscopy and vapour pressure osmometry. The association of cinchocaine hydrochloride was micellar. An appreciable increase in the effective diffusion coefficient as solutions of cinchocaine were diluted close to the critical micelle concentration was observed and has been discussed. The association of amethocaine hydrochloride could be described using a co-operative stepwise association model. No association could be detected in water or 0.1 mol dm-3 electrolyte for butacaine hemisulphate and the hydrochlorides of procaine, proparacaine, mepivacaine, lignocaine, bupivacaine and prilocaine at drug concentrations of less than 0.2 mol dm-3.

Formation of micelles and membrane action of the local anesthetic tetracaine hydrochloride

The formation of micelles of the local anesthetic tetracaine hydrochloride in aqueous phosphate buffer solution of pH 6.5 and ionic strength (I) 0.10 was examined at 22 degrees C by surface tension and using the fluorescent indicators perylene (peri-dinaphthalene) and 8-anilino-1-naphthalene sulfonic acid, sodium salt (ANS). The critical micelle concentration was located at 0.069, 0.071 and 0.063 M by measurements of surface tension, perylene solubilization and enhancement of ANS fluorescence, respectively. In contrast to other cationic surfactants, the anesthetic monomer did not show evidence of forming a fluorescent molecular complex with ANS under the experimental conditions of this study. The formation of micelles by tetracaine-HCl showed a pronounced effect on lipid membranes by inducing an abrupt decrease in the scattered light of egg lecithin liposomes at an anesthetic concentration roughly similar to its critical micelle concentration. This optical behaviour is characteristic of liposome damage and can be interpreted to mean that the lipids become solubilized into tetracaine-HCl micelles. The ability of this local anesthetic to form micelles can be taken as a manifestation of the same hydrophobic forces that lead to partitioning of the drug into membranes.

Sodium chloride equivalents, cryoscopic properties, and hemolytic effects of certain medicinals in aqueous solution. III: Supplemental values

A supplemental table of sodium chloride equivalents and freezing-point depressions at various concentrations for 44 different substances in aqueous solution is presented. Also given in the table is the isosmotic concentration of each material that can form such a solution. The degree of hemolysis of human erythrocytes was determined in 24 different isosmotic solutions, and the data are presented in a table to supplement the previously pub lished values. Eleven isosmotic solutions prevented hemolysis, and 13 others failed to prevent hemolysis.

Aggregation of antihistamines in aqueous solution: micellar properties of some diphenylmethane derivatives

The micellar properties of the antihistamine drugs, diphenhydramine hydrochloride, bromodiphenhydramine hydrochloride, chlorcyclizine hydrochloride and diphenylpyraline hydrochloride, have been studied in aqueous solution. The zeta potentials of the micelles were calculated from their electrophoretic mobilities as determined by a dye-tracer technique. Estimates of the degree of ionization of the micelles using a combination of conductivity and electrophoresis data were in reasonable agreement with values previously determined by light scattering. The extent of micellar hydration has been calculated from viscosity data. The hydrophobic and electrical contributions to the free energy of micellization have been calculated and related to the chemical structure.