Surface active agents interaction with

The mechanisms by which this interaction occurs may be divided into two distinct groups (S4) first, the hydrodynamic behavior of a multiphase system can be changed by the addition of surface-active agents, and, as a result, the rate of mass transfer is altered secondly, surface contaminants can interfere directly with the transport of matter across a phase boundary by some mechanism of molecular blocking. 

Surface active agents, more commonly known as surfactants, are the groups of chemical compounds that in the most common form constitute an ionic or polar portion (hydrophilic head) and a hydrocarbon portion (hydrophobic tail). The ionic or polar portion interacts strongly with the water via dipole-dipole or ion-dipole interactions and... 

In drug studies, of main interest is the application of colloidal systems, which show specific and unspecific interaction with mainly lipophilic substances. An obvious application is the study of highly lipophilic and poorly absorbable drugs that are administered orally or transdermally (2). Such interactions with surface-active agents may either cause a diminution of the... 

The Hamiltonian of a single isolated nanoparticle consists of the magnetic anisotropy (which creates preferential directions of the magnetic moment orientation) and the Zeeman energy (which is the interaction energy between the magnetic moment and an external field). In the ensembles, the nanoparticles are supposed to be well separated by a nonconductive medium [i.e., a ferrofluid in which the particles are coated with a surfactant (surface-active agent)]. The... 

It is therefore apparent why the physical chemistry of surfaces and the structure and activity of surface-active agents are also of interest to the medicinal chemist. Antimicrobial detergents and many disinfectants exert their activity by interacting with biological surfaces and are important examples of surface-active drug effects. 

To rate the wetting tendency of surfactants for hydrophobic surfaces. A graphitic powder, for example, with its low heat of wetting in water, yields much higher heat effects if immersed in solutions of surface active agents. Heats of dilution and of demicellization can be taken into account, if desired, to arrive directly at energies of interaction. 

There are differences in isotherm shape, and for DTAB the behavior is not amenable to a simple explanation. Of particular interest are plots of the amount adsorbed against the mean ionic activity of the surface active agent (including the counterion of the added electrolyte). In the case of DTAB all the data, including others at various salt concentrations up to 0.5M, lie on one line which, after an initial steep rise, is linear to the c.m.c. This indicates that for other than the initial strong adsorption at low concentrations (possibly because of specific interactions with the surface) the adsorption follows the law of mass action. For SDS a similar result is obtained except that positive deviations from the straight line occur below a — 4 X 10 3M for the cases (salt concentration < O.lAf) when there is a point of inflection in the isotherm. These deviations may reflect specific interactions of the DS" with the surface when the ions are adsorbed in parallel orientation. 

Surface-active agents, or surfactants, all share interesting physicochemical characteristics at surfaces and interfaces. Surfactants (detergents and dispersants) are long chain hydrocarbons with polar headgroups which are called dipoles. Surfactants are molecules which consist of two well defined parts one which is oil-soluble hydrophobic and another which is water-soluble hydrophilic. The hydrophobic part is non-polar and usually consists of aliphatic or aromatic hydrocarbons. The hydrophilic part is polar and interacts strongly with water. 

Surfactants—Surface-active agents, which means that they have the property of interacting with surfaces. 

Most of the drugs form micelles at concentrations that they do not attain in vivo. It is therefore their surface activity, rather than their self-association tendency which is more important biologically. Surface-active drugs will tend to bind hydrophobically to proteins and other macromolecules and to associate with other amphipathic substances such as bile salts, phospholipids, and receptors. As with other surface-active agents, surface-active drugs may interact directly with biological membranes. The possible biological implications of surface activity is discussed by Attwood and Florence " in relation to the phenothiazine tranquillisers and local anesthetics. 

Surfactants produce micelles. Their amphophilic nature classifies them as detergents, surface-active agents that are composed of a hydrophilic group and a hydrophobic hydrocarbon chain. In addition to what is known as the critical micelle concentration (CMC), individual surfactant molecules (monomers) interact with each other to form aggregates or micelles, establishing a state of equilibrium between a constant monomer concentration and a rapidly increasing micelle concentration. 

Some ingredients of eye medications may increase the permeability of the cornea. Surface-active agents are knovm to interact with membranes to increase the permeability benzalkonium chloride has surfactant properties and may well have some effect on comeal permeability, although its primary purpose is as a bacteriostat and bactericide. Chlorhexidine acetate and cetrimide, both of which are surface-active, are also used. 

Ions of precipitate particles are adsorbed or attached at the surface of bubbles rising through a liquid, and are thereby separated. A substance which is not surface-active itself can be made so through union with, or adherence to, a surface-active agent (surfactant). Froth flotation involves separation (pre-concentration) by frothing. If an insoluble product is formed in interaction between the ion to be separated and a surfactant, the process is called ion flotation. If the ion is first precipitated and the precipitate is then floated with or without the addition of a surfactant, the process is called precipitate flotation. Flotation is accomplished in a special cylindrical vessel provided with a sintered glass disk at the bottom to break the gas (nitrogen, air) stream into small bubbles [92]. 

Lipid/DNA particles represent a nonliposomal but lipid-based delivery system for gene transfer. Monomeric or micellar lipids are allowed to interact with DNA in the presence of detergent or some other surface-active agent that is then removed by dialysis. As the surface-active agent diffuses out, solid, condensed particles of lipid and DNA form (17). These can be prepared such that they are smaller and more homogeneous than liposome/DNA complexes yet transfect cells equally well (F. Wong, unpublished observations). 

Tn nature proteins interact with ions, lipids, and other proteins as part of the broad spectrum of necessary biological processes including membrane functionality and antigen-antibody effects. Protein functionality can be altered greatly by the interaction of proteins with surface-active agents, and the subject of protein-surfactant interaction is important in relation to food, cosmetic, and biomedical areas. 

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