Biological membranes, surface viscosity

Amido alcohol functional groups increase the surface hydrophilicity and thereby reduce interactions with biological membranes or proteins. The amino alcohols chosen (HNR1R2, where Rj and R2 each have at least one hydroxyl group) must provide the best compromise between hydrophilic coverage and viscosity while retaining high solubility. 

The pharmacokinetics of PVP is well understood as a result of this agent s experimental use to determine the properties of pores in biological membranes. PVP molecules can readily penetrate hydrophilic pores in membranes if they are small enough, and they are also taken up by pinocytotic vesicles. Apparently, PVP is not detectably bound to membrane surfaces and hence does not provide long-lasting viscosity enhancement beyond the normal residence time in the tears. 

An important feature of the mosaic or subunit model of the molecular organization of lipid and lipid-protein films and membranes (4, 5,12) is the cohesion between subunits and between molecules within each subunit (2, 13). The latter can be measured as microviscosity by polarization of fluorescence (14) of the surface film the former is measured as surface viscosity by various techniques (15,16). The relevance of this parameter to the exploration of biological surfaces cannot be overemphasized. Surface viscosity, in fact, has also been invoked as a force stabilizing pulmonary alveoli (6, 7,13, 16). 

Both simple and complex species (e.g., water, lipids, proteins, lipoproteins, antibodies, enzymes, viruses, and small and large electrolyte ions) may be adsorbed on or transported across the interfaces of biological membranes, membrane subunits, and particles. These translocations are associated with membrane or particle formation, fusion, exchange, and lysis. The processes may be relevant to the movement, exchange, and clearance of extracellular material at the alveolar lining layer of the lung (7). Within this framework, the role of surface and hypophase viscosity has not been investigated. 

The influence of adsorbed proteins on interfacial viscosity is relevant to the fluidity of biological membranes. An unusual effect is observed when lipid molecules are incorporated into protein monolayers, first reported by Schulman and Rideal As the mixed film is compressed, T] increases normally but then goes through a maximum, thereafter decreasing sharply with further increase of 11(6). Evidently, above a certain surface density, lipid molecules disrupt interactions between protein chains. The... 

The role of surface viscosity and elasticity on the motion of a solid particle trapped in a thin film, at an interface, or at a membrane of a spherical vesicle has been recently investigated in Refs. [856,857]. The theoretical results [856,857] have been applied to process the experimental data for the drag coefficient of polystyrene latex particles moving throughout the membrane of a giant lipid vesicle [858-864]. Thus, the interfacial viscosity of membranes has been determined. The motion of particles with different shapes trapped in thin liquid films and at Langmuir monolayers is studied intensively both theoretically and experimentally because of biological and medical applications [865-887]. 

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