sodium-acetate--anhydrous and sodium-sulfate

The energetics of lysozyme adsorption on aminopropyl-grafted MCF silica (MCF-NH2) are compared to the trends observed during lysozyme adsorption on native MCF silica using flow microcalorimetry (FMC). Surface modification on MCF silica affects adsorption energetics significantly. All thermograms consist of two initial exothermic peaks and one later endothermic peak, but the heat signal trends of MCF-NH2 are opposite from those observed for adsorption onto native MCF silica in salt solutions of sodium acetate and sodium sulfate. At low ionic strength (0.01 M), LYS adsorption onto MCF-NH2 was accompanied by a large exotherm followed by a desorption endotherm. With increasing ionic strength (0.1 and 3.01 M), the magnitude of the thermal signal decreased and the total process became less exothermic. Also a higher protein loading of 14 μmol g(-1) was obtained at low ionic strength in batch adsorption isotherm measurements. Taken together, the FMC thermograms and batch adsorption isotherms reveal that MCF-NH2 has the nature of an ion exchange adsorbent, even though lysozyme and the aminopropyl ligands have like net charges at the adsorption pH. Reduced electrostatic interaction, reduced Debye length, and increased adsorption-site competition attenuate exothermicity at higher ionic strengths. Thermograms from flow microcalorimetry (FMC) give rich insight into the mechanisms of protein adsorption. A two-step adsorption mechanism is proposed in which negatively charged surface amino acid side chains on the lysozyme surface make an initial attachment to surface aminopropyl ligands by electrostatic interaction (low ionic strength) or van der Waals interaction (high ionic strength). Secondary attachments take place between protruding amino acid side chains and silanol groups on the silica surface. The reduced secondary adsorption heat is attributed to the inhibitory effect of the enhanced steric barrier of aminopropyl group on MCF silica.

Topics: Adsorption; Amines; Animals; Calorimetry, Differential Scanning; Chickens; Hydrophobic and Hydrophilic Interactions; Models, Chemical; Muramidase; Osmolar Concentration; Proteins; Silicon Dioxide; Sodium Acetate; Sulfates; Thermodynamics; Thermogravimetry

This study examines a new method for the remote loading of doxorubicin into liposomes. It was shown that doxorubicin can be loaded to a level of up to 98% into large unilamellar vesicles composed of egg phosphatidylcholine/cholesterol (7/3 mol/mol) with a transmembrane phosphate gradient. The different encapsulation efficiencies which were achieved with ammonium salts (citrate 100%, phosphate 98%, sulfate 95%, acetate 77%) were significantly higher as compared to the loading via sodium salts (citrate 54%, phosphate 52%, sulfate 44%, acetate 16%). Various factors, including pH-value, buffer capacity, solubility of doxorubicin in different salt solutions and base counter-flow, which likely has an influence on drug accumulation in the intraliposomal interior are taken into account. In contrast to other methods, the newly developed remote loading method exhibits a pH-dependent drug release property which may be effective in tumor tissues. At physiological pH-value doxorubicin is retained in the liposomes, whereas drug release is achieved by lowering the pH to 5.5 (approximately 25% release at 25 degrees C or 30% at 37 degrees C within two h). The DXR release of liposomes which were loaded via a sulfate gradient showed a maximum of 3% at pH 5.5.

Topics: Acetates; Ammonium Sulfate; Cholesterol; Citrates; Citric Acid; Doxorubicin; Hydrogen-Ion Concentration; Liposomes; Microscopy, Electron, Transmission; Phosphates; Phosphatidylcholines; Quaternary Ammonium Compounds; Sodium; Sodium Acetate; Sodium Citrate; Sulfates

The adsorption behavior of 6-thioguanine (6TG) on a hanging mercury drop electrode has been studied with ac and cyclic voltammetry in 0.1 M Na2SO4 and 0.01 M sodium acetate solutions at pH 4.3. Several condensed phases of chemically adsorbed 6TG as well as one phase of physically adsorbed 6TG have been characterized. Under total coverage conditions, the films of chemiadsorbed molecules inhibit rather efficiently the electrode reaction of mercury oxide formation.

Topics: Adsorption; Electrochemistry; Electrodes; Mercury; Sodium Acetate; Sulfates; Surface Properties; Thioguanine