Conformation and Solution Properties

Porter and co-workers (111) have considered the factors that contribute to the equilibrium conformation of the heterocyclic (or C-) ring of flavan-3-ols and shown that it may be described by the equilibrium  

Low temperature H NMR studies (111) showed that the E A ratio for catechin (14) and epicatechin (11) were 62 38 and 86 14 respectively. Acetylation of the 3-hydroxy group stabilised the A-conformation of catechin and changed the ratio to 48 52. 

Substitution at C-4 by a hydroxy or aryl substituent strongly favors the E-conformation (i.e. as in catechin-4 or epicatechin-4 units) due to minimization of 1,3-diaxial interactions and thep ewrfo-allylic or A(l, 3)-strain effect (111). It was also concluded that the favored E-conformers of catechin-4 and epicatechin-4 units would adopt C(2)-sofa and half-chair conformation, respectively as minimum energy species. 

Mattice and co-workers (144) investigated this problem using rotational isomeric state theory. The characteristic ratios and components of the persistence 

Current evidence also supports the view that proanthocyanidin homopolymers do not possess such regiospecificity of interflavanoid bonds, and maintain a similar ratio of 4- 8/4- 6 units to that observed in naturally occurring trimers, approximately 3 to 4 1. Moreover, a proportion of chains will be branched (Sect. 7.7.2.1). 

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Conformations and Solution Properties of Star-Branched Polyelectrolytes... 

We start with a brief review of the theory for conformational and solution properties of neutral (uncharged) star-branched polymers. 

We have presented an overview of theories that describe the conformations and solution properties of star-branched PEs. Whereas the principal qualitative results can be obtained on the basis of a simplified box-like cell model, systematic... 

In this chapter, we have focused on a discussion of the efferts of progressively increasing topological and chemical complexity of maaomolecules on their conformations and solution properties. 

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