Intrachain segregation

Starodubtsev, S.G. and Yoshikawa, K. (1996) Intrachain segregation in single giant DNA molecules induced by poly(2-vinylpyrrolidone). J. Phys. Chem., 100, 19702-19705. 

Fig. 3.2. Different scenarios in the folding transition of long polymers. (Top) Gradual shrink, that is, continuous transition, (middle) all-or-none discontinuous transition in the level of single chains, and (bottom) multiple-step transition through intrachain segregations. Note that due to the coexistence region characteristic to the finite-size system, all the cases look similar to the continuous transition in the macroscopic measurement...

Figure 23.1 (Upper) Fluorescence microscopic images of T4 dcDNA molecules (A) in lOmM MgCl2 and lOmM HEPES buffer solution (pH 7.1) (B) and (C) in the buffer solution with closed phospholipid liposomes outside and inside the liposomes, respectively. (Lower) Quasi three-dimensional pictures of the distribution of fluorescent intensity for the corresponding upper photographs. The bar is 10 pm. Careful inspection of the time-successive images, as in (B ) and (C ), reveals that the shrunken state corresponds to intrachain segregated state [10,11].

The somewhat smaller dimensions of DNA coils in highly concentrated surfactant solution, compared to those in a surfactant-free solution, can be explained with a consideration of two effects. First, by careful observation of unfolded DNAs in the coexistence region, namely at [NaBr] = 0.35 M, the individual DNA macromolecules in the intra-chain segregated state, as is exemplified in Fig. 5, are found. Due to the presence of the coiled unfolded part, these DNA molecules apparently reflect an unfolded state with a relatively slow Brownian motion, similar to the DNAs in the entirely unfolded coiled state. Thus, the smaller L value may be attributed to the existence of the intrachain-segregated DNAs in the solution. Second, the smaller DNA dimensions may be produced by the interaction between the long DNA chains and the rod-like micelles. At the threshold NaBr concentration, the shape transition of micelles from spherical (about 5-6 nm in diameter [49]) to rod-like (persistent length of about 44 nm at 35 °C in 0.5 M NaBr [49]) takes place. As the persistent length of the rod-like micelles is of the same... 

Dense polymer systems, such as melts, glasses, and crosslinked networks or rubber are extremely complex materials. Besides the local chemical interactions and density correlations which are common to all disordered hquids and solids, the chain conformations also play an important role. Their influence is twofold. First the intrachain entropy dominates over the positional entropy of the center of mass of the chains. This leads to the well known effect that a weak effective repulsion between different types of chains is sufficient to drive phase segregation. The static and dynamic properties of mixtures of two types of chains is an important and challenging problem, which is reviewed by Binder in Chapter 7 of this volume. Here we consider dense melts of ehains of the same chemical composition. In this case the entropy is at its maximum when the chains have a random walk structure. Since the average end-to-end distance Nfor a random... 

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