The pH of the skin follows a sharp gradient across the stratum corneum (SC), which is suspected to play an important role in controlling the enzymatic activities involved in cellular metabolism and renewal. This gradient is maintained by several systems, such as sweat and sebum secretion and degradation as well as cellular metabolism. At the surface of the skin, what is measured is in fact an apparent skin pH due to extracted material from the SC diffusing into water applied at the surface. pH values recorded at the surface of a semi hydrophobic milieu such as the SC should be interpreted with great caution because it is obvious that hydrogen ions are not in a pure solution at the surface of the skin. For a correct measurement of skin surface pH, it is recommended to follow all practical operating conditions. Care must be taken in identifying the skin site, healthy controls (age, gender, skin type), the time of day of the measurement and the environmental conditions. Also, subjects should receive precise instructions before the test, mainly in terms of hygiene procedure or use of topical products. The interpretation of data should not overlook the fact that even small differences in pH may reflect significant modifications at the molecular level. Although it is usually agreed that the pH of the skin surface may influence the cutaneous microflora, much remains to be learnt about the role of the acid mantle of the skin with regard to defensins and other protective mechanisms.

Escherichia coli nucleoid-associated H-NS protein interacts with the Hha protein, a member of a new family of global modulators that also includes the YmoA protein from Yersinia enterocolitica. This interaction has been found to be involved in the regulation of the expression of the toxin alpha-hemolysin. In this study, we further characterize the interaction between H-NS and Hha. We show that the presence of DNA in preparations of copurified His-Hha and H-NS is not directly implicated in the interaction between the proteins. The precise molecular mass of the H-NS protein retained by Hha, obtained by mass spectrometry analysis, does not show any posttranslational modification other than removal of the N-terminal Met residue. We constructed an H-NS-His recombinant protein and found that, as expected, it interacts with Hha. We used a Ni(2+)-nitrilotriacetic acid agarose method for affinity chromatography copurification of proteins to identify the H-NS protein of Y. enterocolitica. We constructed a six-His-YmoA recombinant protein derived from YmoA, the homologue of Hha in Y. enterocolitica, and found that it interacts with Y. enterocolitica H-NS. We also cloned and sequenced the hns gene of this microorganism. In the course of these experiments we found that His-YmoA can also retain H-NS from E. coli. We also found that the hns gene of Y. enterocolitica can complement an hns mutation of E. coli. Finally, we describe for the first time systematic characterization of missense mutant alleles of hha and truncated Hha' proteins, and we report a striking and previously unnoticed similarity of the Hha family of proteins to the oligomerization domain of the H-NS proteins.

The mechanisms governing the subsolubilizing and solubilizing interaction of sodium dodecyl sulphate (SDS)/Triton X-100 mixtures and phosphatidylcholine liposomes were investigated. Permeability alterations were detected as a change in 5(6)-carboxy-fluorescein (CF) released from the interior of vesicles and bilayer solubilization as a decrease in the static light-scattered by liposome suspensions. Three parameters were described as the effective surfactant/lipid molar ratios (Re) at which the surfactant system a) resulted in 50% of CF release (Re50%CF); b) saturated the liposomes (ReSAT;c) led to a complete solubilization of these structures (ReSOL). From these parameters the corresponding surfactant partition coefficientsK50%CF,KSAT andKSOL were determined. The free surfactant concentrationsSW were lower than the mixed surfactant CMCs at subsolubilizing level, whereas they remained similar to these values during saturation and solubilization of bilayers in all cases. Although theRe increased as the mole fraction of the SDS rose (XSDS), theK parameters showed a maximum atXSDS values of about 0.6, 0.4 and 0.2 forK50%CF,KSAT andKSOL respectively. Thus, the higher the surfactant contribution in surfactant/lipid system, the lower theXSDS at which a maximum bilayer/water partitioning of mixed surfactant systems added took place and, consequently, the lower the influence of the SDS in this maximum bilayer/water partitioning.

The mechanisms governing the solubilizing interactions between zwitterionic/anionic mixed surfactant systems at different molar fractions of the zwitterionic surfactant (Xzwitter) and unilamellar liposomes were investigated. Solubilization was detected as a decrease in static lightscattering of liposome suspensions. Three parameters were regarded as corresponding to the effective surfactant/lipid molar ratios (Re) at which the surfactant system a) saturated the liposomesResat; b) resulted in 50% solubilization of liposomesRe50%, and c) led to a complete solubilization of these structuresResol. These parameters corresponded to theRe at which light scattering stars to decrease, reaches 50% of the original value and shows no further decrease. From these parameters the surfactant partition coefficients for these three steps (Ksat,K50% andKsol) were also determined. The mixed systems were formed byN-tetradecyl-N, N-dimethylbetaine (C14-Bet) and sodium dodecyl sulphate (SDS) in PIPES buffer at pH 7.20. Liposomes were formed by egg phosphatidylcholine and phosphatidic acid (9:1 molar ratio). When the range ofXzwitter was about 0.4–0.6Re andK parameters showed a maximum, whereas the critical micelle concentration (CMC) of these systems exhibited a minimum. Given that the ability of the surfactant systems to solubilize liposomes is inversely related toResol, this capacity appeared to be directly correlated with the CMC of the systems. The progressive rise ofK during the process indicates that an increasing surfactant partition equilibrium governs the interaction process from the saturation until the solubilization of vesicles, the free surfactant concentration remaining almost constant with similar values to the CMC for each mixed system studied.

The partition coefficients have been determined for a series of anionic alkyl sulfate surfactants (alkyl chain lengths C-10, C-12, and C-14) partitioning between the aqueous phase and the lipid bilayer of neutral or electronegatively charged liposomes. The release of the fluorescent agent 6-carboxyfluorescein induced by the surfactants was studied before these surfactants perturbed the bilayer architecture. Unilamellar liposomes formed by egg phosphatidyl choline plus or minus phosphatidic acid were used. From there results obtained we assume that there was a strong correlation between the partition coefficients and the ability of the different surfactants to modify the permeability of liposomes. Likewise, the results suggest that the hydrophobic interactions are the main forces involved in the alteration of the permeability of lipid bilayers although the electrostatic forces play a significant role in the modification of this parameter.

SynopsisMulticomponent gel formulations capable of assimilating, simultaneously, several active ingredients of potential application in the cosmetic field were studied.The possibility of formation of a transparent gel was determined using a method which consisted in the optimization of several lipophilic basic compositions, composed of oil, a mixture of surfactants, a sunscreen agent, several vitamins and antioxidants situated in the base of a regular tetrahedron that symbolized the considered system. To this, a polar phase made of water, a cosolvent and urea in appropriate proportions and situated in the fourth vertex, was progressively added.It may be concluded, that the use of phase diagrams on cosmetic systems, constitutes a useful way to select the components and their mutual ratios, allowing an adaptation to the specific requested conditions of formulation.

SynopsisTransparent formulations of a liposoluble sunscreen in an aqueous medium were studied, taking into account the different chemicals of a selected system situated in the vertices of a regular tetrahedron: sunscreen agent, co‐solvent, (surfactants ± mineral oil) mixture (in the tetrahedron base) and water as the fourth component. Several compositions were selected at optimized component ratios after which water was added progressively. Clear gel and liquid compositions were obtained yielding a sunscreen agent that it suitable for conventional use. The physico‐chemical properties of some compositions were assessed in terms of water/sunscreen agent content.

Synopsis Reduction of keratin cystine by thioglycolic acid incorporated in microemulsions of the water/sodium dodecilsulphate/n-pentanol/n-dodecane system has been determined. The results obtained have been interpreted in relation to the properties of the reaction media. Microemulsions with constant oil-to-surface active mixture weight ratios (R(o/s)) and different concentrations of water were chosen as reaction media. At low water concentrations a steep increase in reactivity with the increase of water was observed at all values of R(o/s). However it was more pronounced the higher the oil content. A relation between maximum cysteine formation and percolative behaviour of the microemulsion was found at high R(o/s) values.

Reduction of keratin cystine with thioglycolic acid using as reaction media microemulsions of the water/dodecylsulfate/n-pentanol/n-dodecane system has been investigated. Micrcmulsions with constant oil-to-surface active mixture weight ratios, RO/S,and different water contents were chosen. Cystine reactivity was found to depend on microstructure of the reaction medium as well as on partition of chemical agent among the different microemulsion domains.

Synopsis The study of ternary systems leads to the understanding of the physico-chemical aspect and allows the contribution of the different components to a cosmetic formulation to be developed. The present investigation was centred in the zone of transparent get belonging to a previously studied ternary system containing a broad variety of different structural compositions. The possibility of including an active sunscreen as well as the ability to increase the water content of the gel was studied. The microscopical study of the compositions with polarized light allowed us to assign the corresponding different structures. A correlation between these structures and their physico-chemical properties, with special emphasis to rheology, has been established.

A study is reported of the adsorption mechanism of two ionic surfactants (sodium dodecyl sulphate and hexadecyl trimethyl ammonium bromide)on wool in relation to the temperature or time of treatment, either in aqueous or in aqueous-ethanolic media. From the results obtained, the effects of these ionic surfactants on acid and alkaline treatments of wool were evaluated by the alkali-solubility test, determination of the cystine content of the fibres, and analysis of the new amino acids formed during the treatment of wool fibres with methylamine or dimethylamine.

Synopsis The physico-chemical and biological properties of an amphoteric/anionic system and its behaviour against a proteinic support have been thoroughly investigated. A considerable inhibition of adsorption of SLS (sodium lauryl sulphate) on human callus caused by the presence of definite amounts of AABet (alkyl-amido-betaines) in the treatment bath is observed. These physico-chemical results are in agreement with those obtained by some in vivo biological tests. A mechanism of the process via the formation of mixed micelles is postulated emphasizing the stability of such systems as a function of pH, the influence of the chain length of the amphoteric surfactant and the molar relative ratio SLS/AABet. Consequently, our work offers the possibility of a wide applicability of the synergic mixtures of both types of surfactants to inhibit considerably skin irritation of cosmetic finished products.