Andrés F. Olea

Solubilization of phenols in surfactant/polyelectrolyte systems

The properties of the microheterogeneous systems formed by mixtures of cetyltrimethylammonium bromide (CTAB) and an alternating copolymer of maleic acid and styrene, MAS, and their anionic monoesters, MAS-n with n=2, 4, 6, 8, were investigated. The fluorescence of pyrene was used to sense the polarity of the polymer/CTAB aggregates. Measurements of the ratio III/I in pyrene fluorescence spectra indicate that the polymer/CTAB aggregates are more hydrophobic than normal micelles. A series of p-alkyl substituted phenols were employed to probe the solubilization ability of these aggregates. The distribution constant K(S) of phenol, p-methylphenol, p-ethylphenol, and p-propylphenol between water and MAS-n/CTAB aggregates and the corresponding free energy of transfer Deltamicro(0)(t) have been determined using the pseudo-phase model. The results show that the distribution is mainly determined by the phenol structure, and a linear free energy relationship has been found between Deltamicro(0)(t) and the structure of phenols. On the other hand, an increase in the number of methylene groups in the side alkyl chain has no effect on Deltamicro(0)(t). The results are discussed and compared with those obtained for ionic micelles.

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

Copolymerization of Maleic Anhydride with Styrene and α‐Olefins. Molecular and Thermal Characterization

Copolymers of styrene‐maleic anhydride, SMA, and maleic anhydride‐α‐olefins (1‐hexene, 1‐octene, 1‐decene, 1‐dodecene, 1‐tetradecene and 1‐hexadecene) have been synthesized by free radical polymerization, using azobisisobutironitrile and benzoyl peroxide as initiators. Copolymers were characterized by gel permeation chromatography, viscosity measurements, FT‐IR, differential scanning calorimetry (DSC) and thermal gravimetry analysis (TGA). The copolymers of maleic anhydride‐α‐olefins exhibit a monomodal molecular weight distribution. During the TGA analysis, decomposition of maleic anhydride and α‐olefins was observed by FT‐IR. Carboxylic acids and gaseous CO2 were identified as decomposition products of the copolymers close to 200°C. The SMA copolymer was esterified with 2‐propanol, sec‐butanol and tert‐butanol at 65°C using 4‐dimethylaminopyridine catalyst and tetrahydrofurane solvent. The rate of reaction and limiting ester yields are lower than those obtained in the esterification with primary alcohols.

Solvent effects on the photophysical properties of 9,10-dicyanoanthracene

The quantum yields of fluorescence, ΦF and of triplet state production, ΦT of 9,10-dicyanoanthracene and the fluorescence lifetimes have been measured in fourteen different solvents. It has been shown that ΦF + ΦT is less than one in all the solvents except bromobenzene. Delayed fluorescence of 9,10-dicyanoanthracene arising following triplet–triplet annihilation is observed in all solvents. It consists of excimer as well as monomer emission, the relative intensities of which were shown to be different from the ratio for prompt fluorescence and to vary with solvent polarity. The rate constants for fluorescence quenching by the three heavy-atom-containing quenchers, iodopropane, iodobenzene and dimethyliodobenzene, kIPS, kIBS and kDMIBS, respectively have been measured and in all solvents it was found that kIPS<kIBS<kDMIBS. Reasons for this are discussed in terms of the charge transfer interactions of the first excited singlet state of 9,10-dicyanoanthracene with the quenchers and with the different solvents.

Effect of Polymer Micelles on Antifungal Activity of Geranylorcinol Compounds against Botrytis cinerea.

Herein, we explore the potential use of two micelle-forming block copolymers, i.e., Pluronic F-127 and poly(ethylene oxide)-b-poly(caprolactone), for application of fungicide agents. The polymer effect on the in vitro fungicide activity of a series of geranyl orcinol derivatives against Botrytis cinerea has been assessed. The results show that, for all test compounds, the incorporation into micelles, formed by Pluronic F-127, produces a great enhancement of the inhibitory effect on the growth of B. cinerea. For some compounds, at the lowest tested concentration (50 ppm), the percentage of inhibition increases significantly (from 0-10 to 80-90%) when the application is made using a polymer solution instead of an ethanol/water mixture. The synthesis and structural determination of a series of eight geranylphenols/diacetates, which were used as fungicide agents, are also discussed. These results suggest that polymer micelles are promising systems for application of crop-protecting agents.

Synergism in mixtures of cationic surfactant and anionic copolymers.

Surface tension measurements have been made in aqueous solutions of anionic hemiesters of an alternating copolymer of maleic acid and styrene, MAS-n with n=0-12, in the presence of dodecyltrimethylammonium bromide, DTAB. A synergistic aspect of surface tension reduction efficiency was observed for all systems studied. The pseudo-phase separation approach and regular solution approximation have been applied, and the interaction parameter, beta, and the mole fraction of DTAB in the adsorbed layer (on a surfactant/repetitive unit basis), X, were obtained. Negative values of beta, ranging from -3 to -11, were calculated. On the other hand, the molar fraction of DTAB varies from 0.52 to 0.26. These results are discussed in terms of hydrophobic effects on the distribution of the aggregates between the interface and the bulk of the solution. The conditions predicted by the model to obtain synergism in the tension reduction efficiency are completely satisfied in all cases.

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.

MONOESTERIFICATION OF STYRENE-MALEIC ANHYDRIDE COPOLYMERS WITH ALIPHATIC ALCOHOLS

Se han sintetizado copolimeros de anhidrido maleico-estireno en solucion acetona-tolueno a 60°C iniciado por azo-bisisobutironitrilo. Los copolimeros se han caracterizado por cromatografia de permeacion de geles y calorimetria diferencial de barrido. Se llevo a cabo la monoesterificacion de los copolimeros de anhidrido maleico-estireno con metano, etanol, n-propil, n-butil, n-hexil, n-octil alcohol y n-decil alcohol en tetrahidrofurano a 65°C, catalizada por 4-dimetilaminopiridina. El grado de esterificacion de los copolimeros se determino mediante FT-IR y fluctuo entre 68-85%. Un aumento de la velocidad de reaccion fue observada con el aumento de la cadena del alcohol. Las temperaturas de transicion vitrea de los copolimeros monoesterificados fueron tambien determinados y fluctuaron entre 242°C y 136°C para los copolimeros con metanol y n-decanol respectivamente

Thermodynamic and Kinetic Study of the Interaction between Alkylpyridinium Ions and Pyrene Derivatives in Aqueous Solution

Abstract— The kinetics of fluorescence quenching of pyrene and three of its derivatives by a series of n ‐alkylpyridinium ions has been studied. The quenching process is diffusion controlled for all the systems studied, independent of the charge in the aromatic molecule and the size of the alkyl chain in the pyridinium ions. Pyrensulfonate, PS, and pyranine form ground‐state complexes with these quenchers. The association constants were determined by using a kinetic scheme where both dynamic and static quenching were included. A linear relationship between the free energy change and number of carbon atoms was found for PS, and a methylene contribution equal to ‐1.1 kJ/mol was determined from the slope. A similar correlation was established for pyranine, but a slope change was observed when the alkyl chain has more than 10 carbon atoms. From the initial slope, an incremental free energy of ‐0.35 kJ/mol was obtained. The ground‐state complex formation is determined mainly by an electrostatic interaction, but there is a hydrophobic effect on the value of the measured association constants.

PHOTOINTERACTION OF BENZOPHENONE TRIPLET WITH LYSOZYME

Abstract