Adriana Memoli

Egg and soya phospholipids — Sonication and dialysis: A study on liposome characterization

Abstract Liposome-Triton X-100 interactions were studied by turbidity measurements and two detergent concentrations, corresponding to the maximum (i.e., detergent-saturated vesicles; R sat ) and minimum (i.e., completely disruped liposomes; R sat ) turbidity values, were identified. The tested liposomes (SUV) were prepared with phospholipids of different origin (egg and soya) and according to different methods (sonication and dialysis). The data obtained, together with size measurements carried out by electron microscopy, were related to the stability of the vesicles.

Comparison of microbial sensors based on amperometric and potentiometric electrodes

Abstract Microbial sensors based on oxygenn and carbon dioxide electrodes coupled with immobilized Saccharomyces are compared for measurements of glucose and other carbohydrates. With the oxygen sensor, the yeast works under aerobic conditions but anaerobically with the carbon dioxide sensor. The two metabolisms of the same strain make little difference to the lifetimes (> 15 days), selectivities and response rates (5–10 min) of the sensors. The effects of pH are very different owing to the pH sensitivity of the carbon dioxide sensor. The viable concentration ranges overlap; the oxygen-based sensor is more useful for low concentrations of glucose (0.01–1 mmol l −1 ) while the carbon dioxide-based sensor is better suited for 1–10 mmol l −1 . With the oxygen-based sensor, the response time is governed by the rate of metabolism; with the carbon dioxide-based sensor, the response time of the potentiometric carbon dioxide electrode is the rate determining step.

Solubility, spectroscopic properties and photostability of Rhein/cyclodextrin inclusion complex

The host-guest interaction between Rhein (Rh)--an anthraquinonic drug characterized by low water solubility and recently considered for its potential antidiabetic and antitumoral activities other than for the well-established anti-inflammatory properties--with cyclodextrins (CDs) was investigated using phase-solubility diagrams. The typical A(L) phase-solubility profiles suggest the formation of the 1:1 inclusion complexes between Rh and the two CDs investigated, namely beta-cyclodextrin and 2-hydroxypropyl-beta-cyclodextrin and the resulting constant values of complex formation, K(c), were estimated. Due to the higher K(c) value, complex of Rhein with 2-hydroxypropyl-beta-cyclodextrin was chosen for further investigation. Characterization in solution of 2-hydroxypropyl-beta-cyclodextrin/Rhein complex was achieved both by fluorescence and visible spectroscopic techniques. These results confirm the formation of inclusion complexes in solution and the 1:1 stoichiometry of the binary system. With respect to Rhein aqueous solution behavior, the inclusion complex appears to be able: (i) to enhance Rhein solubility; (ii) to control its neutral/anionic equilibrium; (iii) to affect both its electronic absorption and fluorescence spectra. Finally, the photostability of Rhein in the presence of cyclodextrins was evaluated.

Microbial sensor for alcohol

Abstract Candida vini was immobilized by physical suction on the pores of a filter of acetylcellulose; the filter was placed on the surface of an oxygen electrode and the bioprobe assembled proved to be useful as an alcohol biosensor. The linear range was 2·10 -5 –2·10 -4 mol l -1 , and the analytical features such as response time, lifetime, and selectivity were tested. Real samples were analyzed with the bioprobe with good accuracy and reproducibility.

Surfactant-induced leakage from liposomes: a comparison among different lecithin vesicles

The interactions, at sublytic concentration, of Triton X-100 and sodium cholate with sonicated and extruded liposomes of egg and soya lecithins were considered to analyze the integrity and/or the barrier efficiency of liposomal membranes. Results are discussed in terms of surfactant partition between the aqueous and the lipid phases and of the release of a fluorescent hydrophilic probe. Phospholipid nature and liposome size influence detergent partition, whereas the content release is mainly affected by the surfactant mole fraction in the bilayer, and by the liposome size.

Effects of surfactants on the spectral behaviour of calcein (II) : a method of evaluation

The spectral behavior of calcein, a water-soluble self quenching fluorescent marker often used in biomedical analysis, can be considerably affected by the presence of surfactants. With this study we intend to obtain further information on the photophysical properties of calcein, in the presence of surfactants and in the concentration range commonly used to investigate the release of such marker from vesicle dispersions. The experiments were carried out both in water and in a physiological buffer (HEPES, pH 7.5), in the presence of Triton X-100, sodium dodecyl sulphate and centyltrimethylammonium bromide, both below and above their critical micelle concentration (c.m.c.). The obtained results confirm that calcein fluorescence can be affected by the presence of surfactants. Thus, environmental conditions must always be carefully checked for the actual quantitative evaluation of this dye. Furthermore, this study sheds some light on the nature and mechanism of calcein quenching.

Surfactant as modulating agent of enzyme‐loaded liposome activity

Large phosphatydilcholine unilamellar vesicles appear to be suitable controlled and protective delivery systems of beta-galactosidase. Kinetic measurements carried out on intact loaded liposomes show that most of the enzyme is entrapped inside the liposomes and its activity is latent. Nevertheless, intact liposomes also show significant activity, which can be controlled by addition of detergent. At sublytic detergent concentrations, liposome enzymatic activity reaches values two or three times greater than those of intact liposomes. This increase seems to be due to membrane structure modification that also enhances the substrate permeability across the bilayer. (c) 1997 John Wiley & Sons, Inc. Biotechnol Bioeng 55: 261-266, 1997.

Kinetics of surfactant-induced release from liposomes: a time-dependent permeability model

Abstract The article examines membrane permeabilization and the consequent content release of lipid vesicles due to the addition of surfactant. Experimental results show that content release involves a complex kinetics where almost instantaneous release is followed by prolonged slow leakage. The model proposed therefore regards bilayer permeability as varying with the time elapsed from the moment of surfactant addition. A delta function followed by an exponentially decaying profile is assumed for these permeability curves. The effects of surfactant concentration and type (Triton X-100, Tween 20 and Tween 60) can be compared by comparing the fitting parameters of the permeability curves.

Glutathione stabilizes ascorbic acid in aqueous solution

This report shows that glutathione affects ascorbic acid degradation in aqueous solution resulting in a significant stabilization of the vitamin. For the GSH concentrations used in this work the effect was higher on diluted ascorbic acid solutions. It is also shown that for a fixed ascorbic acid concentration, as glutathione concentration increases the degradation reaction shifts from first to zero order.

Apparent Solubility and Dissolution Profile at Non-Sink Conditions as Quality Improvement Tools

Stefania Petralito1,*, Iacopo Zanardi2,*, Adriana Memoli1, M. Cristina Annesini3, Vincenzo Millucci4 and Valter Travagli2 1Dipartimento di Chimica e Tecnologie del Farmaco, Sapienza Universita di Roma, 2Dipartimento Farmaco Chimico Tecnologico, Universita degli Studi di Siena, 3Dipartimento di Ingegneria Chimica Materiali Ambiente, Sapienza Universita di Roma, 4Dipartimento di Fisica, Universita degli Studi di Siena, Italy