M. T. Garcia

Permeability changes of phospholipid vesicles caused by surfactants

The partition coefficient at equilibrium of different surfactants between the aqueous phase and the lipid bilayer of small unilamellar vesicle (SUV) liposome has been determined. The release of the fluorescent agent 5-(6) carboxyfluorescein from the interior of liposomes, induced by a nonionic surfactant octylphenol ethoxylated with 10 units of ethylene oxide (Triton X-100), by two anionic surfactants — sodium dodecyl sulphate and sodium dodecyl ether sulphate — and by an amphoteric surfactant dodecyl betaine was studied at sub-solubilizing concentrations. The following increasing order of the partition coefficients obtained for each surfactant can be observed: Triton X-100 > sodium dodecyl ether sulphate > sodium dodecyl sulphate > dodecyl betaine. There was a strong positive association between coefficient of partition and the ability of the different surfactants to modify the permeability of liposomes. The importance of the presence of ethylene oxide units in the molecular structure of the surfactant in relation to alter the partition coefficient in front of SUV liposomes is indicated.

Monomer-micelle equilibrium in the diffusion of surfactants in binary systems through collagen films

Three different binary systems (two anionic/nonionic and one anionic/amphoteric) were selected to study the behavior of these mixtures in their diffusion through a collagen film and the formation of micelle aggregates in such systems. The inhibition observed in the surfactant diffusion of anionic/nonionic and anionic/amphoteric binary mixtures through a collagen film, in comparison with that of single surfactants, has been related to the behavior of these binary systems in the micellization process. The surfactant flux in these systems is mainly determined by the monomeric species. The modification of the equilibrium monomers-micelle aggregates shown by these surfactant binary systems could be also associated with the reduction of the irritancy power for such binary systems.

Structure-Activity Relationships for Sorption of Alkyl Trimethyl Ammonium Compounds on Activated Sludge

Abstract Association of quaternary ammonium based surfactants with activated sludge from wastewater treatment plants has been studied. Adsorption isotherms on activated sludge particles and surface properties of a series of alkyl trimethyl ammonium compounds have been investigated. The effect of alkyl chain length and the water hardness in those physical-chemical properties have been evaluated. Adsorption on sludge increased with increasing the alkyl chain length in the cationic surfactant molecule. Linear relationships between critical micelle concentration (-log CMC) and efficiency of adsorption at the liquid/gas interface (pC20), and the number of carbon atoms in the alkyl chain length were found for the alkyl trimethyl ammonium compounds. Water hardness decreased the CMC values of the tested alkyl trimethyl ammonium homologues and the extent of their sorption to activated sludge. Langmuir and Freundlich adsorption isotherms described satisfactorily the equilibrium adsorption of the cationic surfactants on activated sludge.

Effect of homolog distribution on the toxicity of alcohol ethoxylates

Previous work established a high correlation between the potential environmental toxicity of oxyethylenated nonionic surfactants and the average degree of ethoxylation. For this reason, it was considered of interest to determine whether a narrow- or broad-range homolog distribution of polydisperse commercial alcohol ethoxylates would influence toxicity. Ethoxylated fatty alcohols, both linear and branched, were synthesized with sodium hydroxide or an unconventional calcium-based catalyst. Toxicity tests were run onDaphnia magna and luminescent marine bacteria. Toxicity of ethoxylated alcohols as a function of type of ethoxylate homolog distribution (narrow or broad) and average degree of polyaddition is analogous for both test species. However, narrow-range ethoxylates show lower toxicity values than conventional ethoxylates. Differences in toxicity values between broad- and narrow-range ethoxylates depend on the degree of ethoxylation.

Permeability changes in the phospholipid bilayer caused by nonionic surfactants

Abstract The liposome-nonionic surfactant interaction is investigated through the disrupting effect promoted by these surfactant molecules on unilamellar liposome vesicles (mean vesicle size 100 nm) prepared by reverse-phase evaporation. This interaction leads, at the outset, to modifications in the permeability of vesicles which are monitored by changes in the release of the fluorescent dye 5 (6)-carboxyfluorescein (CF) trapped inside the phospholipid bilayers. The nonionic surfactant tested was octylphenol polyethoxylated with, on average, between 8.5 and 20.0 ethylene oxide units, in the subsolubilizing range of surfactant concentrations. The coefficient of the equilibrium partition of each surfactant between the aqueous phase and the lipid bilayer is investigated. The surfactant that shows the highest value from the partition coefficients obtained is the octylphenol with 9.5 ethylene oxide units. There seems to exist a positive correlation between the partition coefficient of the surfactant and its ability to modify the permeability of liposomes. The importance of the hydrophilic-lipophilic balance (HLB) of each surfactant tested on the modification of partition coefficients versus the liposomes is noted.

The alteration of permeability of small unilamellar liposomes by amphoteric alkylbetaine surfactants

Abstract The partition coefficients have been determined for a series of amphoteric alkyl betaine surfactants (alkyl chain lengths C-10, C-12, and C-14), partitioning between the aqueous phase and the lipid bilayer of small unilamellar vesicle liposomes (SUV) made from egg phosphatidylcholine and phosphatidic acid (9:1 molar ratio). The release of the fluorescent agent 5-(6)carboxyfluorescein, induced by the surfactants, was studied at sub-solubilizing concentrations. The following order of the partition coefficients was obtained for the surfactants: tetradecylbetaine > dodecylbetaine > decylbetaine. There was a strong correlation between the partition coefficient and the ability of the different surfactants to modify the permeability of liposomes.

Pphotobacterium phosphoreum test data of non‐ionic surfactants

A series of chemical compounds belonging to the non‐ionic polyethoxylated surfactants family were selected: fatty alcohols, alkyl phenols and fatty amines. Their toxicity was determined against a biological test system: luminiscent marine bacteria, Photobacterium phosphoreum. Toxicity of chemicals was monitored by the decrease in intensity of the ligth emitted by bacteria as a consequence of their contact with surfactants. From the results obtained through the above mentioned biological toxicity test, a direct relationship between the hydrophobic chain length and the toxicity for a series of linear alcohols has been established. Also, for a series of ethoxylated alcohols, alkyl phenols and fatty amines, the toxicity of homologous is very dependent of the ethoxylation grade, e.g. the greater the HLB value of the homologous, the smallest its toxicity.

The environmental impact of chromium salts: Ecotoxicity and inhibition of surfactant biodegradation

A comparative study of the potential toxicity and environmental impact of CrIII (CrCI3.6H2O) and CrVI (K2Cr2O7) salts was carried out. This evaluation was carried out on three biological substrates: a microcrustaceum (Daphnia magna), a luminiscent marine bacterium (Photobacterium phosphoreum) and a mixed bacterial population responsible of aerobic biodegradation processes. In the two first bioassays, direct toxic effects were measured while in the third, potential toxicity was determined through its inhibition effect on the biodegradation process of an anionic surfactant, sodium dodecyl sulphate. The results obtained show that the toxicity depends on the biological substrate used. Usually, CrIII salts are thought to have lower toxicity than CrVI salts. This study, however, has shown that, towards bacterial populations, CrIII salt is more toxic than the coresponding to CrVI salt. This may be due to pH changes induced by CrIII in aqueous solutions.

Comparative Study of Conventional and Compact Detergents

Experimental work has been carried out on conventional and compact detergent formulations. Comparative study has focused not only on the package size but also on the type of builder contained in the finished product. The detergency as a function of dosage and some parameters concerning the environmental impact of each category of formulation also have been evaluated. Soiled (with carbon black/olive oil) cotton and polyester/cotton fabrics have been used to determine the detergency (% soil removal). Considering the overall results obtained, it can be stated that compact tripolyphosphate-built detergents impose the lowest chemical load upon the environment for the same detergency performance.

Effect of various parameters on sodium dodecyl sulfate (SDS) flux through a collagen membrane

The influence of various experimental parameters on the flux of sodium dodecyl sulfate (SDS) through a collagen membrane has been studied. The variables evaluated were donor concentration, time, temperature, pH and ionic strength. Data on the influence of both surfactant concentration and time on surfactant diffusion through the collagen film allow one to postulate a diffusion process mainly of the monomeric type. This diffusion mechanism based on surfactant monomers has been corroborated by studying the effect of ionic strength. Thisin vitro technique could be a useful tool to predict the effect of diverse experimental parameters on the percutaneous absorption of surfactants.