Subphase pH Values Research Articles

Attachment of 80S ribosome to lipid monolayers at air/water interface: An electron microscopy study

The adsorption of 80S ribosome from rat liver to the surface of lipid monolayers at the air/water interface was examined by electron microscopy (EM) using a negative staining method. The results showed that, a large number of 80S ribosomes can be adsorbed to the lipid monolayers containing positively charged octadecylamine (SA), whereas the adsorption of ribosomes to the surface of neutral or negatively charged lipid monolayers was negligible. There existed a proper ratio of SA to complemented neutral lipids which facilitated the maximum binding of ribosomes. Increasing the subphase pH value will enhance the adsorption of ribosome, but when raising the subphase concentrations of K +, Mg 2+ and glycerol, the adsorption of ribosomes can be weakened, suggesting that the driving forces of the adsorption mainly come from the electrostatic interactions between the ribosome and the lipids. The important characteristics of such interactions between the 80S rat liver ribosomes and the lipid membranes, as revealed by this new technology, which may help in the further understanding of the protein biosynthesis is discussed.

Mechanisms underlying the desorption of long-chain lipolytic products by cyclodextrins: application to lipase kinetics in monolayer

The desorption rates of monolayers of insoluble lipolytic products, oleic acid (OA) and mono-olein (MO), spread at the air-water interface, were measured in the presence of β-cyclodextrin (β-CD) or α-cyclodextrin (α-CD) at various subphase pH values. The desorption rates of the CD-OA complex at pH 2 can be satisfactorily described by a kinetic Langmuir equation revealing the existence of an energy barrier in the complex formation of the CD-OA. The dramatic increase observed in the desorption rates of the CD-OA complex at alkaline pH is in agreement with the theoretical prediction that a diffusion process is likely to occur from the surface to the bulk phase. Our results are consistent with the formation of hydrogen bonds between the ionized OA molecule and the O(6)H groups in the CD cavity. In the presence of β-CD in the subphase, comparable rates of hydrolysis of medium and long-chain monomolecular films of various glycerides by human pancreatic lipase (HPL) and Humicola lanuginosa lipase (HL) were observed. Comparisons between the above rates of enzymatic hydrolysis and the desorption rates of the CD-lipolytic product complexes indicated that the monomolecular film hydrolysis is rate limiting and does not depend on the type of CD used.

Monolayers and multilayers of uranyl arachidate: in-plane structure of uranyl arachidate multilayers

The molecular in-plane structure of uranyl arachidate Langmuir-Blodgett (LB) films formed at different subphase pH values was analysed by means of X-ray grazing-incidence diffraction. For multilayers formed at low subphase pH a reorganisation of the arachidic acid film structure is confirmed. At appropriate subphase pH values, reorganisation of the film structure e.g. via the formation of three-dimensional crystallites, is prevented by the presence of the uranyl ions and by the subsequent introduction of conformational disorder ( gauche defects) in the alkyl chains. The observation of a macroscopic flow-induced in-plane texture in these uranyl arachidate LB films has profound implications for the design of ordered, supramolecular structures by the Langmuir-Blodgett technique.

Ellipsometric studies on uranyl arachidate Langmuir-Blodgett films

In the presence of counterions, the quality of fatty acid monolayers, prepared by the Langmuir-Blodgett (LB) technique is highly influenced by the subphase pH value. In this paper, we present ellipsometric studies on arachidic acid LB films, prepared at different subphase pH values, with uranyl (O U O) 2+ as the counterion. In order to obtain the refractive indices and thickness, independently, the films were prepared as steps with bilayer step size. Refractive index, real and imaginary part, monolayer thickness and surface roughness on a microscopic and macroscopic scale have been determined for three different pH values. The results show that films prepared at a pH value of 4.8 and 4.0 are of good optical quality, whereas those prepared at pH 2.5 are inhomogeneous.

Isomerization and Acid−Base Behavior in Polyion Complex Langmuir−Blodgett Films

The nature of an azobenzene moiety incorporated into a polyion complex Langmuir−Blodgett (LB) film over a range of subphase pH values was investigated by UV−visible spectroscopy. The azobenzene unit was substituted with both carboxyl, and hydroxyl groups and the charge per polymer segment was varied by altering the pH of the subphase. The trans isomer of the azobenzene is present in films transferred from a neutral pH subphase. At a higher pH where both the carboxyl and hydroxyl groups are ionized in aqueous solution, the complex LB film formed from this subphase exhibits the cis isomer of the singly charged polymer segment. By comparison with a water-soluble polyion−surfactant complex for which the cis isomer is not observed, it is concluded that the LB film has considerable rigidity which stabilizes the cis isomer. The severely limited photoisomerization of the trans isomer in the film is further indication of the restricted molecular motion within the polyion complex LB film.

Monomeric and polymeric molecular films from the diethylene glycol diamine pentacosadiynoic amide

A new positively charged polymerizable single chain surfactant was synthesized and analyzed. Monomolecular films made from this surfactant were investigated. Their physical characteristics were evaluated using standard film balance techniques and studied as a function of the subphase pH. The pK of these films was determined to be 6.8±0.5. At room temperature these films exhibit a pronounced fluid/solid coexistence with a transmission enthalpy of 35±3 kJ/mol for high subphase pH values