Reaction variables, chain structure

Oligosaccharides are intermediate DP hydrolysates of polysaccharides or are synthesized by enzymes. They are empirically differentiated from polysaccharides by a chain length of 2-20 monomers (Munk, 1989) Ikan (1991) limits the differentiation to ten monomers. These species are important moieties in polysaccharide structural elucidation by gas chromatography and mass spectroscopy, because their long segments are identical to those of the original primary chain. By manipulating the reaction variables, the DP can be tailored to functional specifications. 

Polymerization and crosslinking reactions used for the synthesis of elastomers are reviewed. Step and chain polymerizations are characterized in terms of the reaction variables which must be controlled to obtain an elastomer. Radical and ionic chain polymerizations are discussed as well as the structural variations possible through copolymerization and stereoregularity... 

In 1988, Walde and coworkers studied the kinetic and structural properties of another serine protease, namely trypsin, in two reverse micellar systems, AOT/ isooctane and CTAB/chloroform/isooctane, employing three different model substrates, an amide and two esters [71], The main aim of this work was to compare the behavior of trypsin in reverse micelles with that of a-chymotrypsin. In the case of trypsin, superactivity was not observed and in general no obvious similarities between the two enzymes were recorded. Some years later, reverse micelles formulated with biocompatible surfactants such as lecithin of variable chain lengths in isooctane/alcohol were studied in relation to their capacity to solubilize a-chymotrypsin and trypsin [72]. The hydrolytic behavior of the same serine proteases, namely a-chymotrypsin and trypsin, in both AOT and CTAB microemulsions was studied and related to the polarity of the reaction medium as expressed by the logP value and measured by the hydrophilic probe 1-methyl-8-oxyquinolinium betaine [39], In this study a remarkable superactivity of trypsin in reverse micelles formed with the cationic surfactant CTAB was reported. 

An interesting aspect of the PP chain structure is the existence of distinct configurational isomers resulting from the presence of a pseudo asymmetric carbon atom. The actual polymer stereogularity or tacticity, as it is termed, is quite variable, being dependent on the nature of the catalyst, the presence or absence of additives, and other parameters such as temperature or reaction medium. Since the polymer morphology and hence physical properties are crucially dependent on the tacticity of the PP, the measurement of these properties is of considerable importance both in commercial production and fundamental investigations. 

Another differential reaction is copolymerization. An equi-molar mixture of styrene and methyl methacrylate gives copolymers of different composition depending on the initiator. The radical chains started by benzoyl peroxide are 51 % polystyrene, the cationic chains from stannic chloride or boron trifluoride etherate are 100% polystyrene, and the anionic chains from sodium or potassium are more than 99 % polymethyl methacrylate.444 The radicals attack either monomer indiscriminately, the carbanions prefer methyl methacrylate and the carbonium ions prefer styrene. As can be seen from the data of Table XIV, the reactivity of a radical varies considerably with its structure, and it is worth considering whether this variability would be enough to make a radical derived from sodium or potassium give 99 % polymethyl methacrylate.446 If so, the alkali metal intitiated polymerization would not need to be a carbanionic chain reaction. However, the polymer initiated by triphenylmethyl sodium is also about 99% polymethyl methacrylate, whereas tert-butyl peroxide and >-chlorobenzoyl peroxide give 49 to 51 % styrene in the initial polymer.445... 

Fig.8 The solid-state structures of the compounds [N(CH2CH2)3N]-H-[OOC(CH2) COOH] (n=l-7) obtained hy co-grinding the dicarhoxyhc acid of variable carbon atom chain length with the base [N(CH2CH2)3N]. Single crystals of the adducts can be grown from solution and used to fuUy characterize the reaction products...

Among the classic methods for the extension of the aldose chain by one carbon atom from the reducing end [9J, the Kiliani-Fischer cyanohydrin synthesis [10] is a milestone in carbohydrate chemistry. However after 110 years from discovery and numerous applications [11], including the preparation of carbon and hydrogen isotopically labeled compounds for mechanistic and structural studies [12], there are still several drawbacks that make the method impractical. These are the low and variable degree of selectivity and the harsh reaction conditions that are required to reveal the aldose from either the aldonic acid or directly from the cyanohydrin. Synthetic applications that have appeared in recent times confirmed these limitations. For instance, a quite low selectivity was registered [13] in the addition of the cyanide ion to the D-ga/acfo-hexodialdo-l,5-pyranose derivative 1... 

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