Raúl G. Barraza

HYDROPHOBICALLY MODIFIED POLYELECTROLYTES AS POTENTIAL DRUGS RESERVOIRS OF N-ALKYL-NITROIMIDAZOLES

The solubilization of three commercial drugs (ornindazole, metronidazole and tinidazole) and model compounds (N-alkyl-2-methyl-4-nitroimidazoles) on aggregates formed by anionic polyelectrolytes, carrying alkyl side chains of different length, have been investigated in aqueous solution at pH 3.0, 7.0 and 11.0. Potassium salts of poly(maleic acid-co-1-olefins), PA-nK2 with n ranging from 8 to 18, were used as micelle-forming polymers. The partition of these drugs between water and the hydrophobic microdomains provided by PA-nK2 was studied by the pseudo-phase model to determinate the distribution coefficient KS, and the standard free energy of transfer Δμot. The results indicate that solubility of alkyl-nitroimidazoles on these polymer micelles depends moderately on the length of the alkyl chain, and therefore is mainly determined by the heterocyclic group. On the other hand, the solubilization of 1-hexyl-2-methyl-4-nitroimidazole increase with decreasing length of the side alkyl chain; i.e. KS follows the order PA-8K2 > PA-10K2 > PA-12K2 > PA-14K2 > PA-16K2 >PA-18K2

Adsorption of hydrophobically modified polyelectrolytes at the n-octane/water interface

The interfacial activity of polyelectrolytes carrying alkyl side chains of different length has been studied. Potassium salts of poly(maleic acid-co-1-olefins), PA-n K2 with n=12 , 14, 16, 18, were synthesized, and the interfacial tension at the aqueous solution/n -octane interface was measured as a function of the length of the alkyl side chain. The results show that the interfacial tension lowering, the limiting excess concentration Gamma (m), and the efficiency of adsorption pC (20) depend on the number of methylene groups in the alkyl side chain. According to Rosen the last two parameters define two different contributions to the standard free energy of adsorption: one arises from the distribution of the polymer between the bulk of the solution and the interface Delta G (dist )(0), and another comes from the configuration adopted at the interface Delta G (int )(0). These free energies were plotted as a function of the number of carbon atoms in the alkyl side chain and a linear relation was found for both of them. From these plots contributions of 0.83 and -0.58 per methylene group were determined for Delta G (0)(dist ) and Delta G (0)(int ), respectively. The positive value for the incremental free energy of distribution is attributed to the formation of a polymer micelle which is stabilized by longer alkyl side chains. On the other hand, the negative value for Delta G (0)(int ) indicates that at the interface the polymer adopts a configuration where the hydrocarbon tail is interacting with the octane molecules.

ELECTRICAL CONDUCTIVITY OF HYDROPHOBICALLY MODIFIED POLYELECTROLYTES IN METHANOL/WATER SOLUTION

Measurements of the electrical equivalent conductivity of potassium salts of poly(maleic acid-co-1-olefins), PA-nK2 with n = 12, 18 has been carried out in methanol-water mixtures in the whole range of composition. The relative interaction parameter f*, was determined as a function of the mole fraction of methanol. The values of f* do not follow the same tendency of the limiting equivalent conductivity. This unusual behavior was rationalized in terms of a methanol-induced conformational transition that takes the polymer chain from a compact to an expanded structure. As a consequence of this transition the average charge distance in the polyion increases with increasing mole fraction of methanol. This brings about a decrease of the linear charge density parameter, and therefore an increase of the fraction of polymer charges dissociated from their counterions. The existence of the conformational transition of the PA-nK2 copolymers was confirmed through fluorescence probing experiments

Behavior of low-solubility detergents

Abstract The solubility behavior in water of different salts of cetyltrimethyl ammonium (CTA + ), such as iodide (CTAI), thiocyanate (CTASCN), and perchlorate (CTAClO 4 ), is reported. The order of solubilities is CTASCN > CTAI > CTAClO 4 . Ion-pair association was established by using the Kraus-Bray conductimetric method. Results indicate that CTAI is 50% and CTASCN is about 30% associated in water solutions. CTAClO 4 has solubility too low to measure by the conductimetric method. In the presence of CTAB and CTAOTOS micelles, the conductivity of these systems is constant as a function of detergent concentration above the micellar concentration, indicating that the dissolved monomers are incorporated into the micellar phase. This produces an increase in the micellar size and in the degree of dissociation. Finally, micellar features of the series (CTAF, CTACl, CTAB, and CTAI) can be related to the radii of the hydrated counterions.

Thermodynamics of the isopropanol/n-hexane and isopropanol/n-heptane systems. Part III. Gas/liquid equilibrium

Vapour pressure measurements are carried out at different temperatures; the activity coefficients are calculated and compared with those devived from IR and NMR data (parts I and II).ZusammenfassungEs wurden Dampfdruckmessungen bei verschiedenen Temperaturen ausgeführt. Die daraus bestimmten Aktivitätskoeffizienten wurden mit den aus IR- und NMR-Daten berechneten (siehe Mitt. I und II) verglichen.

Preferential Adsorption Phenomena in Polyelectrolytes in Methanol/Water Solution: Effect of the Counterion

The preferential adsorption behaviour of nitrate and chloride salts of poly(N,N-dimethyl-N-(2-hydroxypropyl)ammonium) in solutions of methanol/ water mixtures is analysed. At low methanol content both polyions show an adsorption of methanol which is 2·5 times larger for chloride polyion than that for nitrate salt. In the former case, the amount of methanol adsorption is enough to produce an important change in the average distances between charges. This change induces an anomalous behaviour of the conductimetric interaction parameter with solvent composition. This effect is not observed in the case of nitrate polyion and the trend of the conductimetric interaction parameter correlates well with the nature of the medium. This effect is attributed to the low methanol adsorption in this case.

DETERMINATION OF THE COUNTERION-POLYION PARAMETER FOR MALEIC ACID-OLEFIN COPOLYMERS.: EFFECTOF THE ALKYL SIDE CHAIN LENGTH

Se estudia la interaccion entre el poliion y sus contraiones para una serie de sales de potasio derivadas de poli( acido maleico-co-vinil-n-alquilo), PA-nK2, con n= 8,10,12,14 y 16 atomos de carbono en la cadena lateral. Se determina el parametro de interaccion poliion-contraion, a partir de mediciones de conductividad electrica. Se encuentra que este parametro es funcion de la longitud de la cadena lateral, atribuyendo esta variacion a un cambio en la distancia promedio entre cargas

INTERACTION BETWEEN ANIONIC POLYELECTROLYTES AND CTAB MICELLES: A POTENTIOMETRIC STUDY

The interaction between a series of anionic copolymers having variable hydrophobic character with cationic micelles of cetyltrimethylammonium bromide (CTAB) has been studied by measuring the free bromide ion concentration. The results are discussed in terms of the effect of polymer concentration on the ionization degree (a) of the CTAB micelles. The value of a increases with increasing polymer concentration. The magnitude of this effect depends on the hydrophobicity of the polymer chain, which is determined by the length of the alkyl side chain