Specific anion effects on the optical rotation of glucose and serine.

Optical activity is directly related to molecular conformation through the anisotropic polarizabilities of molecules and the refractive index of materials. L-amino acids and D-sugars are characteristic essential bioactive molecules. Since molecular recognition and enzyme activity are related to the conformation of substrates, the relevance of optical activity to biological processes is evident. Specific ion, or Hofmeister, effects that occur with electrolytes at moderately high concentrations modify the behavior of interfaces, molecular forces between membranes, of bulk solutions, of enzymes, and even of DNA. Such effects are universal. Here we report a study on the change in optical rotation induced by some sodium salts for the enantiomers of serine and glucose in water solution. The optical rotation is shown to depend on the kind of anion and on the salt concentration. To obtain further insights into the mechanism behind the phenomenon, Fourier transform infrared (FTIR) spectral studies of serine and glucose solutions in electrolytes were also carried out. The results suggest that it is the differences in interactions of anions at specific chemical sites of the solutes that are responsible for the effects. These forces depend strongly on anion polarizability in water. Such specific ion preferential interactions can affect conformation and internal field, and result in significant changes in optical rotation.

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.

Coagels from alkanoyl-6-O-ascorbic acid derivatives as drug carriers: structure and rheology.

6-O-Ascorbic acid alkanoates (ASCn, where n is the number of carbon atoms in the alkyl chain) behave as surfactants and form stable supramolecular assemblies in water, depending on chemical structure, concentration and temperature. In concentrated water dispersions, ASCn form liquid crystalline structures ('coagels'), below the critical micellar temperature (CMT), with a typical Krafft phenomenon. Such semisolid systems incorporate and stabilize drugs like anthralin, which is insoluble and unstable in aqueous media. The rheological behavior of coagels obtained from aqueous ASC8, ASC10, ASC11, ASC12, ASC14 and ASC16 was evaluated and related to the coagel structure. For ASC8, ASC12, ASC14 and ASC16 complex rheology was observed and spur values were determined. This behavior is indicative of a high three-dimensional structure. The spur value represents a sharp point of structural breakdown at low shear rate. At this point the semisolids acquire pseudoplastic flow with a very low viscosity. Instead, ASC10 and ASC11 coagels showed pseudoplastic flow and--in the case of ASC11--thixotropy was observed. The ASCn coagel rheological behavior and their capability to load pharmacologically active compounds point to a potentially valuable capacity for such systems as drug carriers.

Water absorbency by wool fibers: Hofmeister effect.

Wool is a complex material, composed of cuticle and epicuticle cells, surrounded by a cell membrane complex. Wool fibers absorb moisture from air, and, once immersed in water, they take up considerable amounts of liquid. The water absorbency parameter can be determined from weight gain, according to a standard method, and used to quantify this phenomenon. In this paper we report a study on the water absorbency (or retention) of untreated wool fibers in the presence of aqueous 1 M salt solutions at 29 degrees C and a relative humidity of either 33% or 56%. The effect of anions was determined by selecting a wide range of different sodium salts, while the effect of cations was checked through some chlorides and nitrates. Our results show a significant specific ion and ion pair "Hofmeister" effects, that change the amount of water absorbed by the fibers. To understand this phenomenon, the water absorbency parameter (A(w)) is compared to different physicochemical parameters such as the lyotropic number, free energy of hydration of ions, molar surface tension increment, polarizability, refractive index increment, and molar refractivity. The data indicate that this Hofmeister phenomenon is controlled by dispersion forces that depend on the polarizability of ionic species, their adsorption frequencies, the solvent, and the substrate. These dispersion forces dominate the behavior in concentrated solutions. They are in accord with new developing theories of solutions and molecular interactions in colloidal systems that account for Hofmeister effects.

Solubilization of hydrophobic drugs in octanoyl-6-O-ascorbic acid micellar dispersions.

Alkanoyl-6-O-ascorbic acid esters are easily obtained from vitamin C, and produce self-assembled aggregates in water solutions, with an inner hydrophobic pool surrounded by an external hydrophilic shell. Compared to ascorbic acid, their solubility in oils and fats is greatly enhanced, while the peculiar antioxidant activity is retained in the polar head groups of such surfactants. In virtue of their amphiphilic nature, ascorbic acid-based supramolecular systems can dissolve relevant amounts of hydrophobic, poorly water soluble chemicals such as drugs, vitamins, and so on, and at the same time they provide a suitable shield against oxidative deterioration of valuable materials. In this article we report our study on the self-assembling properties of octanoyl-6-O-ascorbic acid in water, and on the solubilization of some lipophilic molecules in its dispersions.