Oligo isomerization

The first monomer mi is converted into m2 by some simple reaction, such as di-, oligo-, isomerization, etc. (in this case ethylene is converted into a-butene) at the active center Mi (for instance, Ni(II)). Copolymerization of mi and m2 proceeds at an active center M2. The microcell containing both active sites is the size of about half the average distance between two neighboring centers in the bifunctional catalyst. In turn, the distance between Mi and M2 can be specified at the stage of catalyst preparation [117]. Sometimes such an approach is called tandem catalysis [118]. 

The mechanism for hydrosilylation in Figs. 6 and 7 clearly has much in common with suggestions regarding homogeneous transition metal catalysis for other processes involving olefins, such as hydrogenation, isomerization, the oxo reaction, and oligo- and polymerization. 

Watanabe J, Ishihara K (2005) Cell engineering biointerface focusing on cytocompatibility using phospholipid polymer with an isomeric oligo(lactic acid) segment. Biomacromolecules 6 1797-1802... 

The sequence analysis, tacticity, primary and secondary structure, influences of (a) cis-trans isomerization, (b) neighboring residue effects, and (c) type and concentration of solvent on chemical shifts for a number of synthetic polypeptides have been reported by Kricheldorf and coworkers. The investigated polypeptides (excluding homopolyglycine which is usually considered as a polyamide) include various poly-, oligo-, and copolypeptides (10, 13, 18-19, 20-23), and particularly polymers based on glycyl-glycine units, (15, 16, 21, 24) D- and L-amino acids (17, 25-28), and L-lysine and iso-L-lysine (29). 

The interaction of many hydrocarbons (both aliphatic and aromatic) with zeolites has been investigated. HY zeolite catalyses the conversion of cyclopropane at room temperature to isobutane. The proposed mechanism involves a non-classical protonated cyclopropane ion intermediate. At 200 cyclopropane isomerizes to propene and also forms aromatic species. Adsorption and transformation of but-ene has been widely studied. It is useful to draw a distinction between hydroxylated and dehydroxylated samples. On hydroxylated samples but-ene isomerizes and also oligo-The -OH groups vibrating at 3640 cm" were found to be... 

The first amide-based oligo[2]catenanes were successfully prepared, via route 2 in Scheme 17.3, by Geerts etol. in 1995 (see Scheme 17.4) [62]. Here, the first stage of the synthesis involved the creation of a dibromide-functionalized [2]catenane, via Hunter s two-step strategy, such that two isomers - IN-OUT 6a and OUT-OUT 6b -were obtained in 5% and 9% yields, respectively. However, due to the inter-molecular hydrogen bonding, the isomeric catenanes were conformationally frozen and could not be interconverted, even at relatively high temperature [60-63]. A... 

Of the two pinene monomers (Fig. Ij, k), which can be isomerized into each other (cf. Scheme 3), the a-isomer exhibits an endocychc double bond and is thus the less reactive (and also less frequently used) in polymerization reactions. However, the polymerization of a-pinene was reported as early as 1937, using AICI3 as catalyst in hydrocarbon (i.e., benzene, toluene, xylene, or hexane) solution at <15°C, yielding 75%. Polymerization in the presence of aromatics, with AICI3 as Friedel-Crafts catalyst, takes place without the interaction of aromatic and terpene. However, structures and MWs of the polymers formed were not given [80]. A later comparative study shows that the polymerization of a-pinene produces 35% or less solid polymer with MWs of 0.6-0.7 kg/mol, depending on the catalyst used (p-pinene yield up to 96%, MW = 0.8-3.1 kg/mol). The molecular structure of the oligo(a-pinene) was, however, not provided [66]. 

The discovery of antiviral activity of oligo(nucleoside methane-phosphonate)s (44) and oligo(nucleotide phosphorothioate)s (45-47), so far chemically prepared by the nonstereocontrolled methods, attracted the attention of several research establishments to the search for stereospecific synthesis of those classes of oligonucleotide analogs. Since their routine synthesis via phosphoramidite or any other approach leads to the mixture of m diastereoisomers, the question may be asked whether desired antiviral activity is owing to all m components of diastereo-isomeric mixture or to the fraction possessing the proper sense of chirality at each modified phosphate. Moreover, since the seminal works of... 

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