Adsorption onto material surfaces

BaUet, T.L.B., Brechet, Y., Bruckert, F., Weidenhaupt, M. Protein conformational changes induced by adsorption onto material surfaces an important issue for biomedical applications of material science. BuU. Pol. Acad. Sci. 58, 303-315 (2010)... 

Preservative availability may be appreciably reduced by interaction with packaging materials. Examples include the permeation of phenolic preservatives into the rubber wads and teats of multi-dose injection or eye-drop containers and by their interaction with flexible nylon tubes for creams. Quaternary ammonium preservative levels in formulations have been significantly reduced by adsorption onto the surfaces of plastic and glass containers. Volatile preservatives such as chloroform are so readily lost by the routine opening and closing of containers that their usefulness is somewhat restricted to preservation of medicines in sealed, impervious containers during storage, with quite short use lives once opened. 

Another important type of physical chemical interaction that may alter absorption is that of drug binding or adsorption onto the surface of another material. As with complexation and micellarization, adsorption will reduce the effective concentration gradient between gut fluids and the bloodstream, which is the driving force for passive absorption. While adsorption frequently reduces the rate of absorption, the interaction is often readily reversible and will not affect the extent of absorption. A major exception is adsorption onto charcoal, which in many cases appears to be irreversible, at least during the time of residence within the GIT. As a result, charcoal often reduces the extent of drug absorption. Indeed, this fact... 

Scavenging The removal of dissolved materials (such as trace metals) from seawater by adsorption onto the surfaces of sinking particles. 

Few comprehensive classification schemes for CCP exist. The American Society for Testing and Materials (ASTM 1994) classifies two catgories of fly ash (Class F and Class C) based upon chemical and physical properties of the fly ash (the total amount of Si + A1 + Fe, sulphate, loss on ignition). This classification system was developed for the use of fly ash as an admixture in concrete. More recently, new classification schemes have been developed that place emphasis on textural descriptions, the form of carbon (or char ), and the surface properties of fly ash (Hower Mastalerz 2001). These new classification schemes for fly ash may be the result of growing concern over mercury emissions from coal-fired boilers. Studies have shown that mercury adsorption onto the surface of fly ash particles is a function of both the total carbon content and the gas temperature at the point of fly ash collection (Hower et al. 2000). 

In starting a residue analysis in foods, the choice of proper vials for sample preparation is very important. Available vials are made of either glass or polymeric materials such as polyethylene, polypropylene, or polytetrafluoroethylene. The choice of the proper material depends strongly on the physicochemical properties of the analyte. For a number of compounds that have the tendency to irreversible adsorption onto glass surfaces, the polymer-based vials are obviously the best choice. However, the surface of the polymer-based vials may contain phthalates or plasticizers that can dissolve in certain solvents and may interfere with the identification of analytes. When using dichloromethane, for example, phthalates may be the reason for the appearance of a series of unexpected peaks in the mass spectra of the samples. Plasticizers, on the other hand, fluoresce and may interfere with the detection of fluorescence analytes. Thus, for handling of troublesome analytes, use of vials made of polytetrafluoroethylene is recommended. This material does not contain any plasticizers or organic acids, can withstand temperatures up to 500 K, and lacks active sites that could adsorb polar compounds on its surface. 

Analytes may accumulate in the sorption phase either by adsorption onto the surface of solid sorbent materials or by absorption in absorbent liquids or polymers that behave like subcooled liquids.The advantage of solid adsorbents is the potential to select materials with a high affinity and selectivity for target analytes. However, the sorption capacity of adsorbents is usually limited, and the description of adsorption/desorption kinetics of analytes to adsorbents is complex. Typically, the adsorbent materials used in passive samplers are similar to those used in solid-phase extraction techniques. 

Studies on pellicle composition are hampered by the fact that only limited amounts (minute quantities) of pellicle material can be collected and recovered from human teeth in vivo for analytical investigations. It has been calculated that the pellicle layer formed per labial surface of a tooth over 2 h in vivo only contains approximately 1 xg of protein [39], Therefore, much work has been performed using in vitro models to mimic the formation of the salivary pellicle. Glandular salivary secretions or whole saliva supernatants are used to form a pellicle-like protein layer adsorbed on hydroxyapatite or tooth enamel. Although considerable insight into the selectivity and affinity characteristics of salivary proteins during adsorption onto these surfaces has been obtained from... 

Blood plasma is a concentrated protein solution, and the adsorption behavior onto material surfaces may be estimated from the amount and the type of adsorption for major plasma proteins in dilute solution, where the adsorption theory for a monomolecular layer is applied. 

The relative extent of protein adsorption onto polymer surfaces is influenced by the surface tensions of the substrate material, of the suspending liquid and of the proteins themselves. For one and the same substrate material the extent of protein adsorption depends on the relative hydrophobic ty of the proteins. For the situation where YlV > YPV more hydrophobic proteins will adsorb to the largest extent. 

Polar, Uncharged Surfaces. Polar, uncharged surfaces include many of the synthetic polymeric materials such as polyesters, polyamides, and polyacrylates, as well as many natural materials such as cotton and silk. As a result of their surface makeup, the mechanism and extent of adsorption onto such materials is of great potential technological importance, particularly in terms of dyeing processes, waterproofing, and detergency. The mechanism of adsorption onto these surfaces can be much more complex than that of the nonpolar case discussed above, since such factors as orientation will be determined by a balance of several forces. 

Takami Y. Yamane S. Makinouchi K. Otsuka G. Glueck J. Benkowski R. et al. Protein adsorption onto ceramic surfaces. Journal of Biomedical Materials Research 1998 40(l) 24-30. 

For an adsorption process the enthalpy change is invariably an exotherm, and is a function of the acidic and basic characters of the adsorbate and the adsorbent surface. With modern calorimetric techniqnes this enthalpy change is relatively easily measured. Furthermore, for adsorptions onto materials with low specific surface areas it can be more accurately measured than the qnantities of adsorbate. However, as will be described in more detail, FMC in conjnnction with frontal analysis nsing HPLC detectors offers the ability to measure both the enthalpic changes and the qnantities of adsorbate. 

In another study, QCM-D provides insight into how a protein interacts with a hydrogel film, e.g., monolayer or multilayer adsorption onto the surface versus penetration into the material. Alf et al. (2011a) show how bovine serum albumin penetrates an expanded thermo-responsive copolymer but forms an adsorbed monolayer when the material is collapsed above the phase transition temperature (Figure 6.11). 

There are three modes by which clays and other materials can exert non-covalent adsorptive power on various molecules, from the liquid or gaseous state. These are 1) physical, non-ionic adsorption onto the surfaces of finely divided materials, such as clay particles with large surface areas that are comprised in a small volume, 2) ion exchange, by electrostatic interaction and exchange, and 3) zeolitic action, by inclusion of small molecules in cavities or pores, and partial or complete exclusion of larger molecules by such small cavities. 

The adsorption of surfactants onto a clean nonpolar surface must occur with the hydrophilic group oriented outward into the aqueous phase. Adsorption, therefore, will always result in an increase in the hydrophilic character of the surface. Such action is responsible for the generally increased dispersibility of materials such as carbon black in aqueous surfactant systems, and the stability of aqueous latex polymers in paints. The action of surfactant adsorption onto colloidal surfaces can be useful to destabilize as well as stabilize systems. It may be useful, for example, to break an aqueous dispersion, to isolate the dispersed material, or to facilitate the process of separating dispersed solids in the sewage treatment process, although polymers and polyvalent cation salts are most commonly employed in such... 

In this chapter, the preparation of Ag colloids in aqueous surfactant solutions and their stability were investigated. Depending on the nature of the materials prepared, two types of adsorption onto the surface of particles may be considered. If the surface of particles is hydrophobic, the hydrophobic part of the surfactant will adsorb onto the surface of particles and form a monomolecular film in an aqueous solution. If the surface of particles is hydrophilic, the hydrophilic part will adsorb onto the surface of particles and a bilayer surfactant film will form at the surface of particles in the aqueous solution because the hydrophobic part of the surfactant cannot be oriented toward the aqueous solution. 

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