Stearic hindrance

Acid hydrolysis yields 16 of the 20 coded amino acids tryptophan is destroyed, cysteine recovery is unreliable, and asparagine and glutamine are converted to aspartic acid and glutamic acid, respectively. Furthermore, some side groups, such as the hydroxyl in serine, promote the breakdown of the residue, whereas aliphatic amino acids, protected by stearic hindrance, require longer hydrolysis time. This variation in yield can be overcome by hydrolyzing samples for 24, 48, and 72 h and extrapolating the results to zero time point. 

This category of the molecular interactions and its implication may be well understood, if one thinks of saturated-unsaturated mixed-acid TAG, such as SOS (Table 1, to be further discussed below). SOS has five polymorphs in which the DCL structure appears in the least stable polymorph of a, and TCL is revealed in the more stable forms of y, P, and two P forms (10). This means that structural stabilization prevails in the TCL structure compared with the D(X structure. Apparently, the modes of the methyl end stacking and glycerol conformation look simpler in the DCL structure than in the TCL structure, since two types of the methyl end stacking are formed, and thereby local molecular packing around the glycerol groups may be destabilized in the TCL structure. However, in the case of SOS, stearic hindrance... 

To move the active group away from the bead surface and reduce stearic hindrance. 

Woodall et al. suggested that the different reactivities of the carotenoids against free radicals can be partly attributed to the differences in electron distribution along the polyene chain of different chromophores that would alter the susceptibility of free radical addition to the conjugated double bond system. However, other factors must be also considered. Stearic hindrance, hydrogen abstraction from the allylic position to the polyene chain (C-4 of P-carotene and its derivatives, end of lycopene), would reduce radical scavenging activity. In addition, the stability of the polyene radical is important in determining the rate of the loss of carotenoids and hence it affects their antioxidant activity. 

In spite of MA versatility, it was commonly believed and taught until the early 1960s that this monomer would not homopolymerize. In fact, the reluctance of MA to polymerize was so well known that it was often used as an example to reinforce the concept that stearic hindrance, polar effects, etc., retard or prohibit the homopolymerizability of 1,2-disubstituted olefins. This long established thought was shattered in 1961 when it was reported that MA had been homopolymerized. " Subsequent studies confirmed the discovery and additional studies showed that MA can be polymerized with both y and UV radiation, in the presence of free-radical initiators, with various pyridine-type bases, electrochemically, and under shock waves. 

Long-chain alkali metal polyphosphates seldom, if ever, crystallize when salted out of aqueous solutions. Knotting and coiling is probably a factor in this behavior. The anions are too irregular to fit into a crystal lattice and POP linkages are not being broken and reformed as they are in a melt. As noted earlier, all polyphosphates we tested could be crystallized from aqueous solution as the acridinium salts. Here stearic hindrance, caused by the very large flat cations. 

In general, the conversion yield of epoxides into polyols is above 75% (Zlatanic et al., 2004). AU of these reactions lead to polyols with secondary hydroxyl groups. This leaves the remainder of the carbon-carbon chain dangling, allowing it to act as a plasticizer. Furthermore, reactions such as epoxidation and hydroxylation using an alcohol leave alkyl ether groups within (he polyol stracture, which increases stearic hindrance and may limit the yield of further reactions. 

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