Laura Fratoni

Specific ion effects on the growth rates of Staphylococcus aureus and Pseudomonas aeruginosa

Motivated by recent advances in the physical and chemical basis of the Hofmeister effect, we measured the rate cell growth of S. aureus--a halophilic pathogenic bacterium--and of P. aeruginosa, an opportunistic pathogen, in the presence of different aqueous salt solutions at different concentrations (0.2, 0.6 and 0.9 M). Microorganism growth rates depend strongly on the kind of anion in the growth medium. In the case of S. aureus, chloride provides a favorable growth medium, while both kosmotropes (water structure makers) and chaotropes (water structure breakers) reduce the microorganism growth. In the case of P. aeruginosa, all ions affect adversely the bacterial survival. In both cases, the trends parallel the specific ion, or Hofmeister, sequences observed in a wide range of physico-chemical systems. The correspondence with specific ion effect obtained in other studies, on the activities of a DNA restriction enzyme, of horseradish peroxidase, and of Lipase A (Aspergillus niger) is particularly striking. This work provides compelling evidence for Hofmeister effects, physical chemistry in action, in these organisms.

Modification of a Cellulosic Fabric with β-Cyclodextrin for Textile Finishing Applications

Grafting of cyclodextrin (CD) molecules on suitablefabrics provides hosting cavitiesthat can include a large variety of chemicals forspecific textile finishing. In this studywe permanently grafted β-CD onto the surfaceof a cellulosic fabric, namelyTencel® according todifferent procedures. After the treatment, benzoicacid, vanillin, iodine, N,N-diethyl-m-toluamide,and dimethyl-phthalate wereloaded, by either spraying their solutionson the CD-grafted fabric, or by grafting thepreviously prepared inclusion compound onTencel®. The untreated andtreated fabrics were evaluated through scanningelectron microscopy, differential scanningcalorimetry, UV-vis spectra, X-ray diffractometry,water absorbency, breaking load loss,aroma and antimicrobial finishing tests. Our resultsindicate that the included compoundsare efficiently hosted in the CD cavities, and thefabrics surface properties are notsignificantly modified by the chemical treatments.

Drugs solubilization in ascorbyl–decanoate micellar solutions

Abstract Alkanoyl-6- O -ascorbic acid esters are obtained upon esterification of ascorbic acids primary hydroxyl groups with fatty acids. Being more hydrophobic than vitamin C, they dissolve in lipophilic media, and behave as surfactants in water, where they produce micellar aggregates or spreading monolayers, depending on the side chain length. These amphiphiles keep the same antioxidant activity of vitamin C, and can be used for solubilization and protection of hydrophobic species from oxidative degradation. In this paper we report a study on the micellar aggregates formed by decanoyl-6- O -ascorbic acid in water, through surface tension, conductivity, and solubility experiments, and on its coagels produced at low temperatures, by means of differential scanning calorimetry and scanning electron microscopy. Solubilization of some hydrophobic molecules (phenacetin, danthron, and griseofulvin) in ascorbyl–decanoate (ASC10) micelles confirms that the supramolecular assemblies significantly enhance the solubility of these drugs in the liquid phase.

Water of hydration in coagelsPresented at the 17th Conference of the European Colloid & Interface Science Society, Firenze, Italy, September 21?26, 2003.

Vitamin C-based alkanoyl-6-O-ascorbic acid esters, ASCn, are a class of surfactants, interesting both on account of their phase behaviour, and of the properties of the supramolecular assemblies they form. When dispersed in water at room, or lower, temperatures above ca. 5% w/w concentration, they form coagels. At higher temperatures, the microstructure changes to micellar solutions for surfactants of low hydrocarbon chain length n. The longer chained systems form gel phases. The transition enthalpy change is dominated by rearrangements in hydrophobic chain packing. On the other hand the Krafft point seems instead to be dictated mainly by interactions between the polar headgroups and the solvent. The coagel phase is usually thought of as formed of surfactant lamellae separated by thin interlayers of strongly bound, essentially “frozen”, water molecules. In this work, DSC measurements were performed to explore the interactions between water and the surfactant molecules. Two kinds of water were detected: interlayer hydration water and bulk water. The number of hydration water molecules per polar headgroup was inferred from the experimental results. Further insights into the coagel structure were gained from X-ray diffraction and optical microscopy. The effects of glycerin (GLY), propylene glycol (PG), and poly(ethylene glycol) (PEG), as co-solvents were investigated by conductivity and DSC experiments. Glycerin seems to stabilize the coagel, probably through the formation of hydrogen bonds that compete for the polar headgroups with the strongly bound water molecules. By contrast, PG and PEG decrease the compactness of the lamellar structure. This is most likely because these compounds can penetrate into the lipid portion of the lamellae, and reduce the hydrophobic interactions that hold the compact assemblies together.