Pore-forming capability

In the larger peptide antibiotic compounds comprising the class of lantibiotics, the shape of the molecule is determined by several cyclic peptides, including two annulated peptide rings, present within one molecule, giving the lantibiotic a unique way to interact with the target molecule lipid II and subsequent pore-forming capabilities in phospholipid membranes [2]. 

Like some other membrane active proteins and peptides [95-97], Cry toxins bind to the cell siuface in a water soluble form, followed by an irreversible conformational change converting into a form capable of inserting into the membrane [35]. The Cry toxin structures revealed that putative membrane-spaiming amphipathic helices located in domain I might be involved in pore formation [30,31]. Since the amphipathic helices predicted to span the membrane are buried in the helical bundle in domain I, a conformational change was predicted to expose a relatively non-polar/hydrophobic hairpin composed of helices a4 and a5 to initiate membrane insertion [30,31]. 

This material was able to act as a solid Bronslcd base catalyst and accelerated the Knoevenagel condensation of ethyl cyanoacetate with benzaldehyde better than basic forms of mesoporous sieves and zeolite catalysts. It was found that this carboxylate-functionafized LLC material exhibited enhanced basicity due to the ordered nanostructure, and that the LLC pores were capable of substrate molecular size exclusion [114],... 

Silica gel n. A form of colloidal sihca consisting of grains having many fine pores and capable of adsorbing, and firmly... 

Silica Gel n A form of colloidal silica consisting of grains having many fine pores and capable of adsorbing, and firmly retaining at room temperature, substantial quantities of water and some other compounds. It is used to dry gas streams and organic liquids to very low moisture levels. It can be reactivated by heating to temperatures above 100°C. Compare Molecular Sieve. 

In addition to the intrinsic properties of the polymer, the film-forming capabilities are important. When selecting a membrane material, two main properties are targeted, namely, stability and formability. Stability refiects on the durability of the membrane and its ability to perform under harsh operation conditions. This includes flexibility, which is important for membrane installation and handling. Formability is related to the fihn-forming capabilities of the material with control over porosity, pore size, and pore size distribution. Material hydrophobicity is also an important factor depending on the intended application. Selection of membrane fabrication technique depends on the choice of the polymer and the desired structure of the membrane. The most commonly used techniques for the preparation of... 

Many of the toxins obtained from coelenterates and echinoderms, because of their hemolytic or cytotoxic actions, are assumed to have a general disruptive action on cell membranes. However, since many of these toxins are capable of forming pores or channels in the plasma membrane of cells, their cytolytic actions may be a result of this highly selective action. On the other hand, the saponins from starfish and sea cucumbers have a direct lytic action as a result of their detergent action on the integrity of cells. 

The filter-cake formed in this process, however, is highly dispersible to the produced fluid and thus is effectively removed by placing the well on production. No acid treatment or other removal techniques are required. The primary bridging agent in this fluid is a sized calcium carbonate with particle sizes capable of initiating bridging in pore diameters in excess of 100 p. 

A mixture of lignosulfonates, alkali-treated brown coal, and minor amounts of organic silicon compounds (e.g., ethyl silicone) reduces the permeability of cements [1019]. The additives may interact with the crystallization centers of the cement slurry and form a gel system in its pores and capillaries, thus reducing the permeability of the cement and increasing its isolating capability. Furthermore, it is claimed that the additive retards the setting rate of cement up to 200° C and increases the resistance to corrosive media. 

The rate at which selected liquids penetrate into tablets can be used to study their pore structure. A knowledge of the rate of liquid penetration should also provide information on the disintegration/dissolution behavior of a tablet on administration. Such investigations are capable of forming a valuable link between physico-mechanical characteristics and in vivo performance. 

The blocking of the pores of the filter medium by particles is a complex phenomenon, partly because of the complicated nature of the surface structure of the usual types of filter media, and partly because the lines of movement of the particles are not well defined. At the start of filtration, the manner in which the cake forms will lie between two extremes — the penetration of the pores by particles and the shielding of the entry to the pores by the particles forming bridges. Heertjes(11) considered a number of idealised cases in which suspensions of specified pore size distributions were filtered on a cloth with a regular pore distribution. First, it was assumed that an individual particle was capable on its own of blocking a single pore, then, as filtration proceeded, successive pores would be blocked, so that the apparent value of the specific resistance of the filter cake would depend on the amount of solids deposited. 

---