Adsorption multipoint

Surface area Nitrogen adsorption multipoint Brunauer-Emmett-Teller method... 

Suface Area by Multipoint Hitrogen Adsorption, ASTM Method D3663-78,1978. 

There is a one-point modification of a chemisorption method, which is widely used for measurements of Ac. In this case, only one adsorption point of a chemisorption isotherm is measured, and is compared with only one point on a chemisorption isotherm on a reference material (usually, powder [black] or foil). The identity of the chemisorption properties of the active components in supported and pure form is postulated, but very often does not fulfill, making one-point modification an inaccurate procedure, which can hardly be used in scientific studies. For example, studies of supported Rh catalysts by 02 and CO chemosorption have shown that three different blacks of Rh yield three different results [88], The multipoint comparison of chemisorption isotherms shown that only one black had a chemisorption isotherm that had affinity to the isotherm on a supported metal. 

The microporous active carbon was studied by nitrogen adsorption at 77 K. According to obtained data the multipoint BET method gave 771 m2/g however, CM (f-method) method gave 123 m2/g. Explain the difference in the results of BET and comparative methods. 

Clearly, proteins with a high concentration of binding sites on their surfaces may adsorb in the proper orientation, resulting in a multipoint attachment and high adsorption-free energy, even without any conformational adjustment. Thus, hysteresis can be present in some systems even at very short contact times. Proteins with very stable tertiary or quaternary structures may not show significant time-dependence due to the low probability for conformational change. 

Based on the observation that the best ee is obtained with bifunctional chiral agents (ephedrine, pseudoephedrine, norephedrine, and valinol see Scheme 43), we tentatively conclude that a multipoint interaction between the reactant molecule, the chiral inductor, and the zeolite interior is necessary to induce preferential adsorption of tropolone alkyl ether from a single enantiotopic face. The dependence of chiral induction (% ee) on the nature of cations (Scheme 45) suggests a crucial role of the cation present in the supercages in the chiral induction process. This is further strengthened by the results observed with wet and dry zeolites. The presence of water decreases chiral selectivity (Scheme 45). Water molecules... 

ASTM D 4820-96. Carbon black - surface area by multipoint BET nitrogen adsorption. 

As the surface area exposed to the site of administration determines the speed with which a particle dissolves in accordance with the Noyes-Whitney equation, these determinations are important. In addition, in those instances where the particle size is difficult to measure, a gross estimation of the surface area is the second best parameter to characterize the drug. The most common methods of surface area measurement, including gas adsorption (nitrogen or krypton), based on what is most commonly described as the Braunauer, Emmet, and Teller (BET) method, is applied either as a multipoint or single-point determination. 

Its strong adsorption to the particle or droplet by multipoint attachment with several alkyl chains this ensures a lack of desorption and displacement of the... 

Surface areas are usually determined by gas adsorption (nitrogen or krypton) and although there are a number of theories describing this phenomenon, the most widely used method is the Brunauer, Emmet and Teller, or BET, method. Adsorption methods for surface area determination have been reviewed in detail by Sing (1992). Two methods are used the multipoint and single-point. 

The size of a molecule is an important feature because proteins form multiple contacts with the surface (e.g., 77 contact points in the case of the albumin molecule and 703 contact points in the case of the fibrinogen molecule adsorbed on silica [10]). Multipoint binding usually causes adsorption irreversibility having a dynamic nature in the absence of irreversible denaturation. The rates of desorption are, as a rule, much lower than those of adsorption, and in many cases it is virtually impossible to attain the equilibrium state desorbing the adsorbed protein [11]. In other words, the formation of one or several bonds with the surface increases the probability of adsorption of neighboring sites of the same molecule. On the other hand, the desorption of a protein molecule requires the simultaneous rupture of a large number of bonds and, for kinetic reasons, equilibrium is not attained [12-14], This corresponds to a considerable difference between the activation energies for the adsorption and desorption processes [15,16],... 

Samples were characterized by powder X-ray difiraction using an Enraf Nonius PSD120 diffractometer with a monochromatic CuK source operated at 40 keV and 30 mA. Surface areas of the catalysts were determined by multipoint nitrogen adsorption at -196 °C and data were treated in accordance... 

On the other hand, the ionic adsorption of K lipolytica lipase on MANAE-agarose showed activity retention, immobilization yield and immobilized activity of 61%, 97% and 17 U/g, respectively (Table 1). The use of ionic adsorption has been very successfully used for lipase immobilization [24], Although, the above results are better than the YLL lipase immobilized by adsorption in polypropylene support [25], they showed that these immobilization procedures did not lead to lipase hyperactivation phenomenon, as it was described for hpases of different sources [17, 18], Hyperactivation of the lipase when immobilized on very hydrophobic octadecyl-sepabeads derivative probably occurs because it occurred with the open structure of the lipase that is also much more active than the corresponding closed structure even when undergoing multipoint covalent immobilization. In our study, this phenomenon was not observed probably due to the absence of the lid in this Y. lipolytica lipase [26],... 

The YLL lipase immobilized onto octadecyl-sepabeads was the most stable one in all conditions, presenting half-life ten times higher than the soluble preparation at pH 7.0. Palomo et al. [8] demonstrated that the interfacial adsorption on a hydrophobic resin (octadecyl-sepabeads) was the best immobilization technique for B. thermocatenulatus lipase. This immobilized preparation, retaining 100% of the initial activity at high temperature, is even better than the covalent immobilization by multipoint interaction on glyoxyl support, where the lipase retained only 80% activity. 

This work shows that lipase from Y lipolytica does not undergo hyperactivation phenomenon that is largely observed for lipases from other sources when immobilized in hydrophobic supports [12, 13], However, immobilization by physical adsorption showed to be the key for the immobilization process and especially in very high hydrophobic supports that are by far, the best way to get an optimal compromise between activity and stability. Our results also showed that YLL lost activity when immobilized by multipoint covalent attachment. 

Specific area measurements are performed with a "Quantasorb Jr." apparatus by N2 adsorption in liquid nitrogen temperature (standard multipoint BET method). 

---