In the recent past the antioxidant properties of vitamin C,
vitamin E, and their derivatives have been
extensively studied, particularly for their peculiar activity as
radical scavengers. Furthermore, the
association of vitamin C with vitamin E shows an interesting synergic
effect in preventing the oxidation
of unsaturated fatty compounds such as linoleic acid, with vitamin C
acting as a protective shield for
vitamin E in solution against oxidizing agents. Vitamin C
derivatives, such as its alkanoyl-6-O-ascorbic
acid esters, act even better than ascorbic acid itself, because they
possess the amphiphilic structure that
allows the molecule to enter the hydrophobic region of a micelle or of
a liposome. In order to deepen the
understanding of the vitamin C/vitamin E mixed system and of the role
played by ascorbic acid in restoring
tocopherols, the miscibility properties of ascorbic acid derivatives
and of tocopherols need to be studied
in all states of aggregation (Langmuir monolayers, micellar
dispersions, vesicles). In this paper we report
a detailed study of the properties and behavior of monomolecular films
of stearoyl-6-O-ascorbic acid (ascorbyl
stearate), and α-(±)-tocopherol at different temperatures and pH,
and of their mixtures at 20 °C at the
gas/water interface. Our results show that ascorbyl stearate
produces monolayers with both liquid-expanded
and liquid-condensed phases, while α-tocopherol films are in the
liquid-expanded phase only. The two
pure components are completely miscible at the gas/water interface in
all ratios, and indicate the presence
of repulsive interactions between the hydrocarbon chains of the
surfactants.
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.
Silver−poly(acrylate) clusters have been synthesized in water by reduction of AgNO3 in the presence of poly(acrylates) of different molecular weights through two different methods, NaBH4 reduction and UV exposure. The structure of the clusters and the effect of the synthesis parameters on the size and polydispersity of the particles were evaluated by means of small-angle X-ray scattering (SAXS) and confirmed by UV−visible absorption and transmission electron microscopy (TEM). The results clearly show that the reduction method and the polymer chain length play key roles in the achievement of few-nanometer-sized nanoparticles. The effect of the pH was also investigated. The nanoparticle dispersions were then used to functionalize cotton, wool, and polyester samples in order to obtain antimicrobial textiles for biomedical applications. The antimicrobial activity of the as-treated samples has been tested against Staphylococcus aureus, Staphylococcus epidermidis, Pseudomonas aeruginosa, and Candida albicans.
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