Additional Stabilizing Influences

Two additional stabilizing influences will be summarized next that of viscoelastic films and that of solid-particle films. In general, where electrical surface charge is an important determinant of stability, it is easier to formulate a very stable O/W emulsion than a W/O emulsion because the electric double layer thickness is much greater in water than in oil. (This is sometimes incorrectly stated in terms of greater charge being present on droplets in an O/W emulsion.) However, there are ways to effectively stabilize W/O emulsions. 

The introduction of an additional stabilizing influence on the a-alkoxy anion may serve two purposes. Firstly the anions are easier to prepare, generally by hydrogen-lithium exchange. Secondly the effective oxidation state of the a-carbon atom is increased. 

During the insertion mechanism, the metal is inserted into the carbon-oxygen bond. The insertion is promoted by a strong metal—oxygen interaction. It is thought that unreduced metal ions may play an important role in the insertion mechanism (electrophilic catalysis). The type of the catalyst, the method of preparation, and the additives can influence the concentration and stability of these ions. 

Surfactants are well-known protein denaturants. However, when sufficiently dilute, some surfactants (e.g. polysorbate) exert a stabilizing influence on some protein types. Proteins display a tendency to aggregate at interfaces (air—liquid or liquid—liquid), a process that often promotes their denaturation. Addition of surfactant reduces surface tension of aqueous solutions and often increases the solubility of proteins dissolved therein. This helps reduce the rate of protein... 

The published values for the activation energies and pre-exponential factors of transesterification and glycolysis vary significantly. Catalysts and stabilizers influence the overall reaction rate markedly, and investigations using different additives cannot be compared directly. Most investigations are affected by mass transport and without knowledge of the respective mass transport parameters, kinetic results cannot be transferred to other systems. 

How can the substituent influence the resonance shown in Figure 7-15 The answer is that if the substituent can create another resonance structure, the sigma complex is further stabilized. This additional stabilization leads to a preference for a certain attack. 

Systems in which one liquid phase is finely dispersed in another under the stabilizing influence of one or more additional components find applications in countless areas. As consumers, we encounter many of these every day. Floor waxes, shaving lotions, beverage concentrates,... 

For optimal performance of dual function isomerization catalysts based on zeolite Y or mordenite, extensive removal of sodium is necessary. The finished catalyst must be highly crystalline, and the finely dispersed metallic hydrogenation function should be well distributed throughout the catalyst particles. The proposed mechanism explains the stabilizing influence on conversion and the suppression of cracking reactions by addition of the metallic hydrogenation function to the active acidic catalyst base. 

Fluorination has a particularly profound effect on the additions of nucleophiles to per-fluorinated alkenes where the intermediate is anionic. Such processes are dramatically assisted by the strongly stabilizing influence of perfluoroalkyl groups substituted at the incipient anionic site.66 Similar to carbocations (see Section 1.4.), the effect of fluorination in such systems is often ambiguous when monofluorination is involved. a-Halogens generally stabilize anions in the order bromine > chlorine > fluorine, which is the exact opposite to the inductive electron-withdrawing order of the substituents. This effect reflects the importance of l7t-repulsion.67... 

In addition to the covalent peptide bonds formed between adjacent amino acids within a polypeptide chain, covalent disulfide bonds can be formed within the same polypeptide chain or between different polypeptide chains (fig. 3.11). Such disulfide linkages have an important stabilizing influence on the structures formed by many proteins (see chapter 4). 

Simple a-diimines are hydrolytically unstable, but can be stabilized as metal complexes by virtue of the formation of stable five-membered chelate rings.68 69 a-Diketones and glyoxal undergo metal template reactions with amines to yield complexes of multidentate ligands such as (34),70 (35)71 and (36).72>73 In the last case, the metal exerts its stabilizing influence on the a-diimine partner in an equilibrium process (Scheme 5). The same phenomenon occurs with amino alcohols74 75 in addition to amino thiols. The thiolate complexes (37) can be converted to macrocyclic complexes by alkylation in a kinetic template reaction (Scheme 5).76 77... 

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