Substrates with Strongly Charged Sites

Adsorption in this manner may also account for the increased reactivity of wool cystine disulfide bonds to attack by alkali in the presence of cationic surfactants and their decreased reactivity in the presence of anionics (Meichelbeck, 1971). The adsorption of cationic surfactants onto the wool surface, which is negatively charged in an alkaline medium, can impart a positive charge to the surface, thus increasing its attraction for hydroxide and sulfite ions, with consequent increase in its rate of reaction with these ions. In analogous fashion the acid hydrolysis of peptide bonds in the wool is increased by the presence of anionic surfactants (which 

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S6) and since the apolar product is not negatively charged, we felt that our catalyst with strong binding sites would be effective with this substrate. The hydrolysis was followed to 75% of completion, and a rate enhancement of 230-fold over the imidazole catalysed rate was found at pH 8.2 (Fig. 7). Constant activity after repeated treatments with excesses of substrate showed that the catalyst was regenerated. 

In general, enzymes are proteins and cany charges the perfect assumption for enzyme reactions would be multiple active sites for binding substrates with a strong affinity to hold on to substrate. In an enzyme mechanism, the second substrate molecule can bind to the enzyme as well, which is based on the free sites available in the dimensional structure of the enzyme. Sometimes large amounts of substrate cause the enzyme-catalysed reaction to diminish such a phenomenon is known as inhibition. It is good to concentrate on reaction mechanisms and define how the enzyme reaction may proceed in the presence of two different substrates. The reaction mechanisms with rate constants are defined as ... 

Practical applications of surfactants usually involve some manner of surfactant adsorption on a solid surface. This adsorption is always associated with a decrease in free-surface energy, the magnitude of which must be determined indirectly. The force with which the adsorbate is held on the adsorbent may be roughly classified as physical, ionic, or chemical. Physical adsorption is a weak attraction caused primarily by van der Waals forces. Ionic adsorption occurs between charged sites on the substrate and oppositely charged surfactant ions, and is usually a strong attractive force. The term chemisorption is applied when the adsorbate is joined to the adsorbent by covalent bonds or forces of comparable strength. 

However, if the orientation of the adsorbate is parallel to the interface, as may occur when the surfactant has two ionic groups of charge opposite to that of the substrate at opposite ends of the surfactant molecule, or when the hydrophobic chain interacts strongly with the surface (e.g., electron-rich aromatic nuclei in the adsorbate and positively charged sites on the adsorbent (Snyder, 1968)), then effectiveness of adsorption may decrease with increase in chain length, because this may increase the cross-sectional area of the molecule on the surface, and thus saturation of the surface will be accomplished by a smaller number of molecules (Kolbel, 1959). 

The intermolecular electrostatic interactions are found in bimolecular reactions of a charged reactant approaching a molecule with strong dipolar bonds or even charges (e.g., in enzyme-catalyzed reactions, where they are used not only to properly position a substrate in the active site of an enzyme but also to lower the activation energy barrier for the subsequent chemical transformation of a substrate). 

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