Chain Selection

Bisphosphites such as (7) combine excellent reactivity, straight-chain selectivity, and high resistance to the typical phosphite degradation reactions (29). Further, the corresponding 0x0 catalysts are excellent olefin isomerization catalysts so that high normal-to-branched isomer ratios are obtained even from internal olefins, enabling, in certain instances, the use of inexpensive mixed isomer olefin feedstocks. 

It is important to note, however, that beyond a = 1/2 by no means all of the material will be combined into infinite molecules. For example, in spite of the favorable probability of branching, a chain selected at random may be terminated at both ends by unreacted functional groups. Or it may possess a branch at only one end, and both of the succeeding two chains may lead to unreacted dead ends. These and other finite species will coexist with infinite networks as long as l/2[Pg.353]

Reaction features (exothermic, endothermic, reversible, irreversible, number of species, parallel, consecutive, chain, selectivity)... 

Collagen Chain Selection, Trimerization, and Triple Helix Formation 506... 

An alternative would be to establish the aryl side chain selectively by a rearrangement process ... 

Carboxypeptidase A"" (CPA, EC 3.4.17.1) is a proteolytic enzyme that cleaves C-terminal amino acid residues with hydrophobic side chains selectively. Several X-ray structures are available" The active site of CPA consists of a hydrophobic pocket (primary substrate recognition site) that is primarily responsible for the substrate specificity, a guanidinium moiety of Argl45 that forms hydrogen bonds to the carboxylate of the substrate, and Glu270, whose carboxylate plays a critical role, functioning either as a nucleophile to attack the scissUe carboxamide carbonyl carbon of the substrate or as a base to activate the zinc-bound water molecule, which in turn attacks the scissile peptide bond ". However, semiempirical calculations had shown that the direct attack of... 

The viewpoint parallels that of many other theories of condensed state behavior. The van der Waals theory develops an equation of state for dense gases from the assumption that each molecule moves in an average field provided by its neighbors and that the molecules contribute additively to the pressure. The Flory-Huggins thermodynamic theory of concentrated polymer solutions proceeds similarly. Chains select configurations on a lattice partially occupied by... 

To derive the condition for the gel point in random crosslinking of existing chains of arbitrary molecular weight distribution, let us consider a primary chain selected at random having P monomer units. If one unit of the selected chain happens to be crosslinked, the probability that this unit is a part of the selected chain is equal to the weight fraction wP of the P-mer. The expected number of additional crosslinked units in the P-mer is then q(P — 1). The mean expected number of additional crosslinked units in a chain is... 

The ligands tris(2-pyridylmethyl)amine (tpma), tris(3,5-dimethyl-l-pyrazolylmethyl)amine (metpyma) and tris(3,5-dimethyl-l-pyrazolylethyl)amine (metpyea) are examples of tetraden-tate tripod-shaped ligands containing three heterocyclic nitrogen donors connected to an apical tertiary nitrogn donor by.aliphatic chains. Selected nickel(II) complexes with these ligands are reported in Table 50. 

Exercise 5-2 Geraniol is a naturally occurring compound found in certain grasses and is used in perfumes to simulate the odor of roses. The IUPAC name for this compound is 3,7-dimethyl-frans-2,6-octadien-1-ol (where "-1-01 signifies that there is an OH group on the lowest-numbered carbon of the chain). Select the correct structure... 

Dendritic molecules, forming predominately hexagonal columnar and micellar cubic phases, have been introduced and intensively investigated by Percec et al. and this field has recently been reviewed [143], The mesophases of these dendrons can also be stabilized and modified by replacing alkyl chains by fluorinated chains selected examples will be discussed in the next sections. 

J. N. Levy, and M. Stukus, Side chain selectivity and kinetics of penidllin G amidase in acylating a cis-racemic / -lactam intermediate in the synthesis of Loracarbef, New J. Chem. 1994, 38, 425 434. 

The two substituents on the four-membered ring may be short carbon chains selective reduction of the aldehydes 255 with sodium borohydride produced the cyclic hemiketamine 256 <1995TL7771>. One chain may be longer. For instance, the aldehyde 257 was cyclized by a mixture of chromium(ll) chloride and nickel(n) chloride in THF to the racemic alcohol 258 <1998EJO 543>. 

Battling, C.M., Raetz, C.R. Crystal structure and acyl chain selectivity of Escherichia coli LpxD, the JV-acyltransferase of lipid a biosynthesis. Biochemistry 48 (2009) 8672-8683. 

Williams, A.H., Raetz, C.R. Structural basis for the acyl chain selectivity and mechanism of UDP-IV-acetylglucosamine acyltransferase. Proc Natl Acad Sci USA 104 (2007) 13543-13550. 

React with metal complex M (side-chain selective)... 

Under such chromatographic conditions it is possible to determine the heterogeneities of the polymer chain selectively and without any influence of the polymer chain length. LC-CC has been successfully used for the determination of the functionality type distribution of telechelics and macromonomers [104-109], for the analysis of block copolymers [111-114], macrocyclic polymers [115], and polymer blends [116-118]. 

Antibodies possessing glycosidase activity have been induced by immunization of mice with conjugates of the transition-state analogue 21 (Fig. 5.10A). A combinatorial phage-Fab library was then constructed by PCR amplification of the heavy and light chains. Selection with a BSA-conjugated suicide inhibitor 22 (Fig. 5.10B) was then... 

Unsaturated polyesters (UPs) crosslinked with styrene are often used as a matrix of fiber reinforced plastics. Several reports treated the degradation of the crosslinked UPs with high temperature treatment in water (1,2), acetic acid (5), alcohols including glycols (4,5), and amines (6), often in the presence of catalysts. In these literatures, recovery of polymeric materials from the crosslinked UPs was not a main objective. However, in case we can hydrolyze polyester chains selectively, linear polystyrene derivatives can be obtained as recycled materials. 

Schalkwijk CG, Marki F, and Van den Bosch H. (1990). Studies on the acyl-chain selectivity of cellular AosphotipasesA2. Biochim. Biophys. Acta. 1044,139-146. 

The jHTobaility that a tethered chain selected at random occupies at least n path steps... 

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