Phospholipid adsorption

Keywords silica nanoparticle, sulfur-containing amino acid, human serum albumin, phospholipids, adsorption mechanism, quantum chemistry... 

If the redox mediator is a hydrophobic species, the ET at the monolayer or bilayer modified electrodes may not occur by tnnneling, but rather by diffusion through the pinholes with ET at the free sites of the electrode. This was confirmed by SECM studies of ET reactions of ferrocenemethanol at tetradecanethiol SAMs on the gold surface and at the bilayer formed by phospholipid adsorption on the first tetradecanethiol layer (106). 

In summary, it is clear that ITIES provide a unique support to study phospholipid adsorption and the interaction of the phosphatidyl moiety with aqueous cation. It has been observed many times that a compact monolayer can hinder the transfer of some cations such TEA+, but does seem to be an effective barrier to the transfer of anions. Finally, charge-transfer studies combined to electrocapillary data have clearly shown that phosphatidylcholine acts as a strong ionophore for alkali metal cations and peptides. 

Ishihara K, Shibata N, Tanaka S, Iwasaki Y, Kurosaki T, and Nakabayashi N. Improved blood compatibility of segmented polyurethane by polymeric additives having phospholipids polar group. U. Dispersion state of polymeric additive and protein adsorption on the surface. J Biomed Mater Res, 1996, 32(3), 401 18. 

Adsorption chromatography using small particle silica or alumina has also been employed in the separation of biologically meaningful substances. Phospholipids, for example, have been separated on silica (38). One of the big problems for such substances is detection, since many of the compounds are not U.V. active. Generally, the refractive index detector is employed for isocratic operation, and the moving wire detector for gradient operation. Formation of U.V.-active derivatives is also possible (39). 

The popular applications of the adsorption potential measurements are those dealing with the surface potential changes at the water/air and water/hydrocarbon interface when a monolayer film is formed by an adsorbed substance. " " " Phospholipid monolayers, for instance, formed at such interfaces have been extensively used to study the surface properties of the monolayers. These are expected to represent, to some extent, the surface properties of bilayers and biological as well as various artificial membranes. An interest in a number of applications of ordered thin organic films (e.g., Langmuir and Blodgett layers) dominated research on the insoluble monolayer during the past decade. 

Kakiuchi et al. [75] used the capacitance measurements to study the adsorption of dilauroylphosphatidylcholine at the ideally polarized water-nitrobenzene interface, as an alternative approach to the surface tension measurements for the same system [51]. In the potential range, where the aqueous phase had a negative potential with respect to the nitrobenzene phase, the interfacial capacity was found to decrease with the increasing phospholipid concentration in the organic solvent phase (Fig. 11). The saturated mono-layer in the liquid-expanded state was formed at the phospholipid concentration exceeding 20 /amol dm, with an area of 0.73 nm occupied by a single molecule. The adsorption was described by the Frumkin isotherm. 

Dynamic surface tension has also been measured by quasielastic light scattering (QELS) from interfacial capillary waves [30]. It was shown that QELS gives the same result for the surface tension as the traditional Wilhelmy plate method down to the molecular area of 70 A. QELS has recently utilized in the study of adsorption dynamics of phospholipids on water-1,2-DCE, water-nitrobenzene and water-tetrachloromethane interfaces [31]. This technique is still in its infancy in liquid-liquid systems and its true power is to be shown in the near future. 

Eisenberg, M. Gresalfi, T. Riccio, T. McLaughlin, S., Adsorption of monovalent cations to bilayer membranes containing negative phospholipids, Biochemistry 18, 5213-5223... 

Ishihara K, Nomura H, Mihara T et al (1998) Why do phospholipid polymers reduce protein adsorption J Biomed Mater Res 39 323-330... 

Mono-, di- and triacylglycerols may all be measured by determination of the amount of glycerol released by hydrolysis. The lipid is first extracted into chloroform-methanol (2 1) and saponification is performed under conditions that will not affect any phosphate ester bonds, otherwise glycerol originating from phosphoglycerides would also be measured. Heating at 70°C for 30 min with alcoholic potassium hydroxide (0.5 mol l-1) has been shown to be satisfactory. However, the phospholipids may be removed prior to saponification either by extraction or by adsorption on activated silicic acid. 

Through van der Waals and hydrophobic interactions, CNTs were functionalised and made water soluble by the strong adsorption of phospholipids (PLs) grafted onto amino-terminated polyethylene glycol (PEG). The group of Dai bound nucleic acids (DNA and RNA) and proteins to CNTs for specific detection of antibodies (Chen et al., 2003 Kam et al., 2005a, b Liu et al., 2007b). 

Adsorption and kinetics of electroreduction of safranine T in self-assembled phospholipid monolayer deposited on mercury have also been studied [157]. 

Seki and Tirrell [436] studied the pH-dependent complexation of poly(acrylic acid) derivatives with phospholipid vesicle membranes. These authors found that polyfacrylic acid), poly(methacrylic arid) and poly(ethacrylic acid) modify the properties of a phospholipid vesicle membrane. At or below a critical pH the polymers complex with the membrane, resulting in broadening of the melting transition. The value of the critical pH depends on the chemical structure and tacticity of the polymer and increases with polymer hydro-phobicity from approximately 4.6 for poly(acrylic acid) to approximately 8 for poly(ethacrylic acid). Subsequent photophysical and calorimetric experiments [437] and kinetic studies [398] support the hypothesis that these transitions are caused by pH dependent adsorption of hydrophobic polymeric carboxylic acids... 

Hydrogels are used in the refining of edible oils to adsorb phospholipids, trace metals, and soaps (103). The adsorption capacity depends on the ease of hydration of the adsorbates, so best performance demands careful control of moisture content in the system (104). Silica hydrogel in combination with alumina has been found to be useful for purifying used cooking oils in order to extend their life and enhance the quality of the fried food (105). 

Organized adsorption layer of phospholipids (Biomembrane-Iike surface)... 

The photoreduction of AuC14 in the presence of dimyristoyl-L-alpha-phosphati-dyl-DL-glycerol, which is a negatively charged phospholipid, gives rise to Au NPs coated through electrostatic adsorption of a biomolecule, leading to a nanosized model of a biomembrane [148]. 

The influence of adsorption of polyelectrolytes on bimolecular phospholipid leaflets was studied. All polyelectrolytes studied were adsorbed on the surface of the film, as demonstrated by greatly increased drainage times. Only some of the polyelectrolytes investigated are able to decrease the d.c. resistance, notably a protein derived from ox erythrocyte ghosts and a Na-K polyphosphate. The combination of these latter substances proved particularly effective. It is concluded that the decrease of d.c. resistance is caused by adsorption and penetration of the polyelectrolytes into the membrane, resulting in the formation of pores or water channels, and not by the possibility of transport of charged macromolecules through the membrane. 

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