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Biomedical subjects

J Estelrich

Publications and source records attributed to J Estelrich.

At least 19 recordsLinked to original sources
PubMed2003

Influence of the temperature in the adsorption of sodium dodecyl sulfate on phosphatidylcholine liposomes.

The influence of the temperature on the adsorption of monomeric and micellar solutions of the anionic surfactant sodium dodecyl sulfate (SDS) on phosphatidylcholine (PC) liposomes was investigated using the fluorescent probe 2-(p-toluidinyl)-naphthalene-6-sodium sulfonate (TNS). The number of adsorbed molecules was quantified by measuring changes in the electrostatic potential (Psi(o)) of the liposomes/probe during an incubation with SDS at varying temperatures. At low surfactant concentrations (from 0.05 to 0.25 mM), the increase in temperature reduced the number of surfactant molecules incorporated per vesicle regardless of the incubation time, whereas at high surfactant concentrations (from 0.50 to 1.0 mM) the incubation time has an opposite effect on this process. Thus, after 10s, the surfactant adsorption decreased with temperature, yet it increased progressively with time. The adsorption was linear with temperature below critical micellar concentration (CMC) of SDS and this linear tendency did not change above CMC. This suggests an adsorption of SDS monomers regardless of the surfactant concentration.

Adsorption↗
PubMed2001

Location of Pinacyanol in Micellar Solutions of N-Alkyl Trimethylammonium Bromide Surfactants.

The interaction of pinacyanol (PIN), a cationic dye formed by monomer and dimer species, with three cationic surfactants (DTAB, TTAB, and HTAB) has been studied spectroscopically and by acid-base equilibrium in the micellar concentration range. In the presence of surfactants, the absorption maximum of the two main peaks undergoes bathochromic shifts. The spectral shifts suggest a hydrophobic environment of the chromophore. The presence of micelles favors the monomer species; i.e., it reduces the extent of dimerization. The pK(a) of PIN in micellar medium is similar to the value in pure water. When acid-base equilibrium was considered, the changes in the interfacial pK(a) allowed to us to determine the constant dielectric for the interfacial region (epsilon=69). This led to the conclusion that the dye must be solubilized between the solution and the hydrocarbon chain core, i.e., in the aqueous micellar interface. This location can be explained by a cation-pi interaction between the uncharged ring system of the dye and the cationic headgroups of the surfactants. Copyright 2001 Academic Press.

Journal Article↗
PubMed2001

Interaction of alpha-amylase with n-alkylammonium bromides.

The interaction of alpha-amylase with n-alkylammonium bromides above and below their critical micellar concentrations (cmc) has been studied in buffer at pH 7 and 10 by UV spectrophotometry, photon correlation spectroscopy and Doppler microelectrophoresis. This interaction produces a complex that is dependent on pH of the medium. This complex appears at surfactant concentrations below the cmc, which means that individual surfactant molecules can bind tightly to native alpha-amylase. The complex maintains its aggregation state when the concentration of surfactants with a hydrocarbon chain of 16 carbons increases, but not for surfactants of 12 and 14 carbons. Measurements of zeta-potential indicate the influence of electrostatic and hydrophobic forces. When the size of the aggregate is maximal, proteins are at their point of zero charge. In such conditions, Van der Waals forces and contacts between the alkyl chain and the hydrophobic core of the protein favour the formation of a larger aggregate.

Bromides↗
PubMed2001

Use of a fluorescence spectroscopy technique to study the adsorption of sodium dodecylsulfonate on liposomes.

The fluorescent probe 2-(p-toluidinyl)-naphthalene-6-sodium sulfonate was used to study the surface adsorption of sublytic concentrations of the anionic surfactant sodium dodecylsulfonate (C(12)-SO(3)) on phosphatidylcholine bilayers. The number of adsorbed molecules was quantified by determination of the electrostatic potential (psi(0)) of the bilayers. The abrupt decrease in the fluorescence intensity already detected 10 s after the surfactant addition and the slight fluorescence variations with time indicated that the surfactant adsorption was very fast and almost complete. For a given number of monomers adsorbed, a linear dependence between the lipid and C(12)-SO(3) concentrations was obtained, indicating a similar adsorption mechanism regardless of the surfactant concentration. Hence, a monomeric adsorption is assumed even in systems with a C(12)-SO(3) concentration above its critical micellar concentration (CMC). In addition, this linear correlation allowed us to determine the surfactant/lipid molar ratios (Re) (inversely related to the C(12)-SO(3) ability to be adsorbed on liposomes) and the bilayer/aqueous phase coefficients (K). The fact that the lowest values for Re were always reached after 10 s of incubation corroborates the rapid kinetic of the process. The decrease in the C(12)-SO(3) partitioning (K) when the number of surfactant molecules exceeded 15000 was possibly due to the electrostatic repulsion between the free and the adsorbed monomers, which could hinder the incorporation of new monomers on the charged surface of liposomes.

Adsorption↗
PubMed2001

Use of a fluorescence spectroscopy technique to study the adsorption of sodium dodecylsulfonate on liposomes.

The fluorescent probe 2-(p-toluidinyl)-naphthalene-6-sodium sulfonate (TNS) was used to study the surface adsorption of sublytic concentrations of the anionic surfactant sodium dodecylsulfonate (C(12)-SO(3)) on phosphatidylcholine (PC) bilayers. The number of adsorbed molecules was quantified by determination of the electrostatic potential (psi(o)) of the bilayers. The abrupt decrease in the fluorescence intensity detected even 10 s after the surfactant addition and the slight fluorescence variations with time indicated that the surfactant adsorption was very fast and almost complete. For a given number of monomers adsorbed a linear dependence between the lipid and C12-SO3 concentrations was obtained, indicating similar adsorption mechanism regardless of the surfactant concentration. Hence, a monomeric adsorption is assumed even in systems with a C12-SO3 concentration above its CMC. In addition, this linear correlation allowed us to determine the surfactant/lipid molar ratios (Re) (inversely related to the C12-SO3 ability to be adsorbed on liposomes) and the bilayer/aqueous phase coefficients (K). The fact that the lowest values for Re were always reached after 10 s of incubation corroborates the rapid kinetics of the process. The decrease in the C12-SO3 partitioning (K) when the number of surfactant molecules exceeded 15000 was possibly due to the electrostatic repulsion between the free and the adsorbed monomers, which could hinder the incorporation of new monomers on the charged surface of liposomes.

Adsorption↗
PubMed2000

Influence of cholesterol on liposome fluidity by EPR. Relationship with percutaneous absorption.

The influence of liposome composition on bilayer fluidity and its effect on the percutaneous absorption into the skin were investigated. Liposomes formed with saturated or unsaturated phospholipids (H-PC or PC) with varying amounts of cholesterol were prepared and their penetration behaviour into the stratum corneum was followed up by means of the stripping method. The order and dynamics of the hydrophobic domain of the vesicles were studied using electron paramagnetic resonance (EPR) methodology. Phospholipid composition and the amount of cholesterol exert a considerable influence on the penetration behaviour of the probe encapsulated in the liposomes. This behaviour is closely related to the fluidity characteristics of these liposomes studied by EPR. Therefore, a penetration mechanism of the vesicles into the skin, based on the incorporation of lipids into the skin lipids and on fluidity behaviour, is suggested.

Administration, Cutaneous↗
PubMed2000

Electrophoretic properties of dodecyltrimethylammonium bromide micelles in KBr solution.

Charge in ionic micelles determines the trends of their stability and their practical applications. Charge can be calculated from zeta potential (zeta) measurements, which, in turn, can be obtained by Doppler microelectrophoresis. In this study, the electrophoretic properties of dodecyltrimethylammonium bromide (DTAB) in KBr aqueous solution (0-6 mM) were determined by Doppler microelectrophoresis. At very low surfactant concentrations (up to 6 mM), zeta potential was quite constant and due to the ionized monomers (DTA+). Above 6 mM, zeta potential increased to a maximum at surfactant concentrations still below the critical micellar concentration (CMC). This increase could be explained by a formation of nonmicellar aggregates of DTAB. Then, above the CMC, zeta potential underwent an abrupt reduction, which was dependent qualitatively and quantitatively on KBr concentration, and which could be due to an increase of the number of counterions adsorbed on the micelle surface. Calculation of effective micellar charge from zeta potential gave the surface charge density. Comparing this value with the theoretical, obtained from geometrical considerations, a fraction of 0.29 of charged micellar headgroups was obtained when DTAB was in aqueous solution, which is consistent with the value obtained by conductivity measurements.

Bromides↗
PubMed2000

Chemical degradation of liposomes by serum components detected by NMR.

Interaction between serum components and liposomes is an oxygen-dependent exothermic process. We studied the interaction of 100 nm extruded liposomes (bearing positive, negative or no charge) with foetal calf serum by 1H NMR and 13C NMR, in order to further our understanding of these reactions. Studies of aqueous or organic extracts obtained after 2 h, 1 day or 1 week, showed hydrolysis to be a degradation process concomitant with the interaction with serum. Oxidation was identified as additional to hydrolysis in the process of degradation. Oxidation produced aldehydes, acids and alcohols, although aldehydes and alcohols were prone to further decomposition and only appeared transiently. Alkenes and other oxidized compounds predominated in those products derived from oxidation. In stearylamine-containing liposomes some aldehydes and a nitroderivative were found as degradation products. Such metabolites are apolar and their presence might explain the intrinsic toxicity of this kind of liposome in cell cultures. The work described in the present study revealed the chemical degradation of liposomes in the serum used. In all cases the results obtained were compared with liposomes not incubated with serum.

Aldehydes↗
PubMed1998

Influence of Size on Electrokinetic Behavior of Phosphatidylserine and Phosphatidylethanolamine Lipid Vesicles.

The aim of this study was to examine the electrokinetic properties of liposomes containing either phosphatidylethanolamine (PE) or phosphatidylserine (PS). Zeta potential was determined by laser-Doppler microelectrophoresis. The presence of PE enhanced the slight negative charge on the phosphate group of phosphatidylcholine. A linear relation between zeta potential and PE concentration was found. Absolute values of zeta potential were higher in PS liposomes and showed an exponential dependence on the PS content. The electrophoretic mobility depended not only on the percentage of aminophospholipid but also on the size of vesicles. This behavior can be explained by the relaxation effect. From geometrical considerations, it was possible to calculate the theoretical surface charge densities. Comparing experimental with theoretical values, an underestimation of zeta potential was found by the electrokinetic classic theory in the experimental conditions used. Copyright 1998 Academic Press.

Journal Article↗
PubMed1997

Determination of polyethylene glycol activated with cyanuric chloride in liposomes.

A simple method was developed for the determination of polyethylene glycol (PEG) 5000 activated with cyanuric chloride attached or adsorbed to the liposome membrane. The procedure is based in the measurement of the absorbance at 234 nm of the triazine ring of cyanuric chloride after disrupting the liposomal structure with CHCl3/MeOH (1/8, v/v). In this medium, the molar absorptivity of the molecule is the highest, and lipid does not interfere with the measurement. This procedure results in a convenient, sensitive, and rapid method for the determination of this kind of activated polyethylene glycol in liposomes. The minimal concentration of PEG measured is 50 microM, and so the method is sufficiently sensitive to quantify PEG 5000 in the minimal amounts used for protecting the liposomes from the action of serum. Values calculated by this method have been compared with those obtained by 1H NMR, and a good correlation between them has been obtained.

Cross-Linking Reagents↗
PubMed1997

Serum-liposome interaction is an oxygen-dependent process.

Measurements of heat dissipation, oxygen concentration and average vesicle size were correlated to study the effect of serum components on different types of liposome. The results indicate that the interaction between serum components and liposomes is exothermic and oxygen dependent, and leads to disruption of vesicles. The dependence of this effect on serum concentration, vesicle surface charge and type of liposome was also evaluated. Serum components did not produce any effect on conventional liposomes in the absence of oxygen. Moreover, in hypoxic conditions the serum-liposome interaction was delayed. Both results suggest that this interaction is an oxygen-dependent event. Finally, we confirmed that sterically stabilised liposomes remain unalterated in the presence of serum.

Animals↗
PubMed1997

Physicochemical properties of enrofloxacin.

The physicochemical properties of enrofloxacin, a fluoroquinolone that inhibits the activity of bacterial DNA gyrase, are described. Its spectral, solubility and related physicochemical characteristics are discussed. The dissociation behaviour of enrofloxacin was examined by UV spectrophotometry at 25 degrees C in a series of buffers ranging from pH 1 to 10. The corresponding macro- and microscopic dissociation constants were calculated. The apparent n-octanol-water partition coefficients were measured from pH 2 to 10.

Anti-Infective Agents↗
PubMed1994

Design and applications of a new fluorimetric assay of thioguanine in liposomes.

This paper describes the systematic design of a modification that overcomes the difficulties encountered with the original fluorimetric method for thioguanine. It allows the determination of thioguanine alone, as well as in a lipid medium (specifically in liposomes). It consists of an earlier lipid extraction based on liquid-solid extraction cartridges; then the oxidation of thioguanine in the lipid-free solution is performed by adding hydrogen peroxide in pH 4.7 acetate buffer at 50 degrees C for 30 min. A central composite design was used to finally optimize the method. The assay is precise (RSD values were 1.8 and 2.1% for intra-day and between-day precision, respectively). The detection limit was 0.05 microM and the limit of quantitation 0.08 microM.

Hydrogen Peroxide↗
PubMed1989

Physicochemical properties of a human glycoprotein bearing blood group A activity.

A human erythrocyte glycoprotein was isolated and purified from blood of group A+1 by a procedure involving chloroform-methanol extraction and affinity chromatography on Helix pomatia lectin-Sepharose 6MB, and some of its physicochemical properties were determined. The resulting preparation was homogeneous as indicated by polyacrylamide gel electrophoresis. The glycoprotein contained nearly 60% carbohydrate and 40% protein. It was water-soluble and inhibited the agglutination of A-erythrocytes. Its molecular weight was 41,900 (amino acid analysis) or 55,200 (light scattering), whereas electrophoresis revealed two bands of 43,000 and 76,000 Da. The ORD spectrum was consistent with 30% alpha-helix, 20% beta-sheet, and 50% random coil. Intrinsic viscosity was 14.61 ml.g-1, partial specific volume was roughly 0.66, isoelectric and isoionic points were 6.90 and 6.95, respectively. The glycoprotein differs from glycophorin and appears to be one of the minor glycoproteins of the human erythrocyte membrane.

ABO Blood-Group System↗
PubMed1987

Measurement of a glycoprotein with blood group A activity by light scattering.

A light scattering method for quantifying glycoproteins is presented. Conditions of ethanol concentration, wavelength, time of reading, and sample and reagent volumes have been examined. The definitive assay involves addition of 9 vol absolute ethanol to 1 vol sample, mixing, and readings at 105 degrees angle at the interval between 10 and 13 min after placing the cell into the photometer. The obtained values are temperature-dependent. Thus, temperature control is essential. In this assay, a concentration range of 10-60 micrograms glycoprotein has been used. As described, the method is independent of the chemical composition of the different glycoproteins and is barely influenced by size and shape of glycoproteins.

ABO Blood-Group System↗
PubMedDate not supplied

Interaction of doxorubicin with lipid systems.

The action of doxorubicin, a cancer chemotherapeutic agent, on liposomes of dipalmitoylphosphatidylcholine obtained by extrusion, with or without cholesterol, and on monolayers of the same composition, was determined by photon correlation spectroscopy, penetration kinetics, and adsorption isotherms. Doxorubicin produced a wider vesicle distribution in both of liposomes, but liposomes containing cholesterol underwent an increase of mean diameter as well as polydispersity. In contrast, films containing cholesterol showed least interaction with the drug. Since both lipids are neutral, any interaction must be primarily hydrophobic.

1,2-Dipalmitoylphosphatidylcholine↗
PubMedDate not supplied

Bilayer distribution of phosphatidylserine and phosphatidylethanolamine in lipid vesicles.

The distribution of phosphatidylethanolamine (PE) and phosphatydilserine (PS) in liposomes was studied as a function of aminophospholipid concentration using fluorescamine as labeling reagent. The method is suitable for such determination since, in the assay conditions, fluorescamine does not penetrate the vesicles nor does it disrupt them. The liposomes were obtained by sonication, extrusion, or mechanical dispersion (MLV). For any kind of vesicle, the percentage of PS in the external monolayer is higher than that obtained for PE in the corresponding vesicles. In extruded PS liposomes, this aminophospholipid is located preferentially in the outer layer, while for PE liposomes the localization depends on the size of vesicle. Sonicated liposomes present an asymmetrical distribution of both aminophospholipids, and the external location of PS or PE always predominates. In contrast, in MLV, aminophospholipids are mainly found in the inner layers of the vesicles, except for liposomes formed by the lowest PS proportion. A remarkable feature of PS liposomes is the reduction of vesicle size, especially in MLV liposomes, in comparison with neutral liposomes.

Fluorescamine↗