Side-chain association

In a similar way, we can study the mixed linear association of R A2) molecules and R B2 ones. The sequence distribution along an associated chain can be alternative, sequential, or statistically random, depending upon the strength of association constants. All these associated chains, or rings, are block copolymers if the primary molecules are polymers, so that they undergo microphase separation transition as well as macroscopic phase separation. This problem of competing micro- and macrophase separation in associating polymers is one of the important unsolved problems to be studied. 

As in the general theoretical scheme, we start with the free energy of the mixture 

4 Association of end-functional low-molecular weight molecules R Bj) to the side of a long polymer chain R Ay. Comb-like block copolymers are formed. 

The free energy change to form a (1, m)-mer from the primary molecules in the reference 

Imposing the chemical equilibrium conditions (5.19), we find the distribution function of the clusters in the form 

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For the sake of clarity, the resonances belonging to the individual groups have been isolated from the data and presented in tables III and IV. Table III shows the resonances associated with the side chain (carbons 16-19). Examination of the data reveals that each side chain presents a unique set of resonances (Table III). For example, resonances at 6 166.5, 136.8, 126.5 and 18.3 uniquely describe the side chain associated with elegin (XII), repdiolide (XIV) and epoxyrepdiolide (VII), i.e., a side chain ester with a double bond between C-17 and C-18. Likewise for each of the other three side chains one can completely describe them on the basis of their 33c-NMR spectra alone. 

Figure 12. Four state model of the hydration-mediated counterion—side chain association—dissociation equilibrium, of Mauritz. (Reprinted with permission from ref 107. Copyright 1982 American Chemical Society.)...

From the results on Pro-Leu-Gly-NH2 we can conclude that the force fields are highly reliable in their ability to reproduce observed frequencies of this type II /8-turn structure. In addition, we see again that j3-turn frequencies depend strongly on the specific dihedral angles and side chains associated with the turn. 

When phosphatidylcholine is suspended in water, the molecules associate by the hydrophobic effect, with the charged portion facing the solvent and the fatty acid side chains associating with each other. Instead of making a micelle, however, as palmitate does, these molecules associate into a bilayer, which eventually forms a spherical vesicle (termed a liposome) with a defined inside and outside. Liposomes are clearly similar to cell membranes, although they differ in some respects. 

S.3.2.4 The Disposition of Charged Side Chains Associated with the Crevasse Connecting the P - and a -Heme Groups for deoxyHb... 

The striking feature of the functional side chains associated with the redox sites... 

This chapter presents some important nongelling binary associating mixtures. Throughout this chapter, we assume the pairwise association of reactive groups, the strength of which can be expressed in terms of the three association constants for A-A, B-B, and A-B association. We apply the general theory presented in Chapter 5 to specific systems, such as dimerization, hnear association, side-chain association, hydration, etc. The main results are summarized in the form of phase diagrams. 

Fig. 6.5 Phase diagrams of side-chain association. The binodal (solid line), the spinodals (borderline of the gray areas), microphase separation transition Une (broken line), critical solution points (white circles), and Lifshitz points (black circles) are shown. The homogeneous mixture region, microphase region, and the macroscopicaUy unstable region are indicated by H, M, and U, respectively. Parameters are fixed at wa = 1000, f = 200, = 10, A.q = 1.0, and tjfi = 1.0. The...

Scope of this chapter. . 310 3.1.2 Side-chain associated ... 

Shirakawa polyacetylene, 3 Side-chain associated chromism, 331 a-conjugated polysilanes, 686... 

Next, identify the side chain (R group) associated with each residue. The side chains associated with Phe, Trp and Val are highlighted. 

Amino acids are the building blocks of proteins. In aqueous solutions, in the pH range 3-8, they are present in the amphiionic form NH3CH(A)COO , where X is a group referred to as the amino acid side chain. Association with lanthanides is expected to take place at the ionized carboxyl group. However, due to the proximity of the positively charged amino group it is likely that complex formation will be weaker than that with simple carboxylates. This effect... 

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