RESUMEN
The interaction between composite dipalmitoylphosphatidylcholine (DPPC)/dioctadecyldimethylammonium bromide (DODAB) bilayer vesicles in the gel state and silica is investigated over the 0-20% DODAB range from determination of adsorption curves, silica sedimentation, particle sizing and zeta-potentials. At 1 mg/mL silica, 0% DODAB, pH 6.3, over the 0-150 mM NaCl range of ionic strengths, high affinity adsorption curves were barely affected by ionic strength and all of them exhibited limiting adsorption values above the level expected for single bilayer deposition. At 1 mg/mL silica, 2% DODAB, pH 6.3 and 1 mM NaCl, high affinity adsorption curves fortuitously presented limiting adsorption indicative of one bilayer deposition on each silica particle. At %DODAB<2% or %DODAB>2%, limiting adsorption was above and below the level expected for bilayer deposition, respectively. Increasing %DODAB in the vesicle composition negatively modulated the limiting adsorption on silica despite the increasing surface charge on vesicles and electrostatic attraction between vesicles and particles. The results point out the difficulty of closed vesicle disruption (required for bilayer deposition from vesicles) when the bilayer is tightly packed in the rigid gel state and might be of interest for analytical applications of immobilized vesicles on silica.
Asunto(s)
1,2-Dipalmitoilfosfatidilcolina/química , Membrana Dobles de Lípidos/química , Compuestos de Amonio Cuaternario/química , Dióxido de Silicio/química , Adsorción , Geles/química , Concentración de Iones de Hidrógeno , Tamaño de la Partícula , Cloruro de Sodio/químicaRESUMEN
Biomimetic particles supporting lipid bilayers are becoming increasingly important to isolate and reconstitute protein function. Cholera toxin (CT) from Vibrio cholerae, an 87-kDa AB5 hexameric protein, and its receptor, the monosialoganglioside GM1, a cell membrane glycolipid, self-assembled on phosphatidylcholine (PC) bilayer-covered silica particles at 1 CT/5 GM1 molar ratio in perfect agreement with literature. This receptor-ligand recognition represented a proof-of-concept that receptors in general can be isolated and their function reconstituted using biomimetic particles, i.e., bilayer-covered silica. After incubation of colloidal silica with small unilamellar PC vesicles in saline solution, pH 7.4, PC adsorption isotherms on silica from inorganic phosphorus analysis showed a high PC affinity for silica with maximal PC adsorption at bilayer deposition. At 0.3 mM PC, fluorescence of pyrene-labeled GM(1) showed that GM(1) incorporation in biomimetic particles increased as a function of particles concentration. At 1 mg/mL silica, receptor incorporation increased to a maximum of 40% at 0.2-0.3 mM PC and then decreased as a function of PC concentration. At 5 microM GM(1), 0.3 mM PC, and 1 mg/mL silica, CT binding increased as a function of CT concentration with a plateau at 2 mg bound CT/m2 silica, which corresponded to the 5 GM(1)/1 CT molar proportion and showed successful reconstitution of receptor-ligand interaction.
Asunto(s)
Toxina del Cólera/química , Gangliósido G(M1)/química , Membrana Dobles de Lípidos/química , Fosfolípidos/química , Receptores de Superficie Celular/fisiología , Adsorción , Animales , Biomimética/métodos , Bovinos , Fenómenos Químicos , Química Física , Calor , Control de Infecciones , Liposomas/química , Lípidos de la Membrana , Tamaño de la Partícula , Fosfatidilcolinas/química , Pirenos/química , Receptores de Superficie Celular/aislamiento & purificación , Dióxido de Silicio/química , Vibrio cholerae/enzimologíaRESUMEN
The effect of ionic strength and pH on phosphatidylcholine (PC) adsorption from vesicles on silica nanoparticles was investigated over a range of NaCl concentrations (0.1-150 mM) at pH 6.3 and 7.4 from determination of adsorption isotherms, colloid stability, particle sizing, and zeta-potentials. At and above 10 mM ionic strength, pH 6.3, high-affinity adsorption isotherms with limiting adsorption indicative of one-bilayer deposition on each silica particle were obtained. At 10 mM ionic strength, adsorption isotherms indicated lower affinity between PC and silica at pH 7.4 than at pH 6.3, suggesting a role of hydrogen bonding between silanol on silica and phosphate on PC in promoting bilayer deposition at low pH. Under conditions where high affinity and bilayer deposition were achieved, silica sedimentation documented from photographs was absent, suggesting particle stabilization induced by bilayer coverage. However, at physiological (150 mM NaCl) or close to physiological ionic strength (140 mM NaCl), the large colloid stability similarly achieved at pH 6.3 or 7.4 suggested the major role of van der Waals attraction between the PC bilayer vesicle and silica particle in determining bilayer deposition. The effect of increasing ionic strength was increasing van der Waals attraction, which caused PC vesicle disruption with bilayer deposition and bilayer-induced silica stabilization.
Asunto(s)
Biomimética , Coloides/química , Membrana Dobles de Lípidos/química , Fosfolípidos/química , Dióxido de Silicio/química , Adsorción , Relación Dosis-Respuesta a Droga , Concentración de Iones de Hidrógeno , Iones , Ligandos , Lípidos/química , Lípidos de la Membrana/química , Fosfatidilcolinas/química , Cloruro de Sodio/química , Propiedades de SuperficieRESUMEN
The present high-power electrical stimulator can generate monopolar or bipolar pulses for stimulation of excitable tissues and cells in physiological experiments...