Pearl string model

FIGURE 8.5 Pearl string model A, solvent molecule 0 monomeric unit. 

A pearl necklace model in which the polypeptide chain forms the string of the necklace and the surfactant molecules form micelle-like clusters along the polypeptide chain, which passes through the micellar clusters in a a-helical conformation. In contrast to the rod-like particle model, this model assumes that the polypeptide chain is flexible. 

Kirkwood-Riseman Theory (1948) This theory is based on a model in which the chain consists of a sequence of monomer units. When a polymer molecule is placed in a fluid of surrounding medium (solvent molecules), the flow is perturbed by the resistance offered by each polymer unit. This model is known as the pearl string (or pearl necklace) model, where each monomer unit is a bead (see Figure 8.5). The emphasis of the Kirkwood-Riseman theory is on the hydrodynamic resistance of the indivdual beads. When the individual resistance is summed, we obtain the resistance of the whole molecule. 

You will recall the two-pearl string of molecules that 1 used as a simple model of a protein in Reaction 17 (1 reproduce it here as 5). There you saw that the... 

The focus of this chapter is on an intermediate class of models, a picture of which is shown in Fig. 1. The polymer molecule is a string of beads that interact via simple site-site interaction potentials. The simplest model is the freely jointed hard-sphere chain model where each molecule consists of a pearl necklace of tangent hard spheres of diameter a. There are no additional bending or torsional potentials. The next level of complexity is when a stiffness is introduced that is a function of the bond angle. In the semiflexible chain model, each molecule consists of a string of hard spheres with an additional bending potential, EB = kBTe( 1 + cos 0), where kB is Boltzmann s constant, T is... 

Figure 2. This figure shows how alkane would be converted to a Hamiltonian used in this model (a — b), and then how this periodic Hamiltonian could be further reduced (b c) to result in the "string of pearls" H below it. The new energies and couplings in this chain have the effects of the side groups renorrml-...

When C > C, the coils start to interpenetrate into each other. Daoud et al. proposed a blob model to describe such states of polymer chains (Daoud et al. 1975). As demonstrated in Fig. 4.8, they treated the single chain as a string of liquid droplets referred as blobs, which is similar to a pearl-necklace. The blob size is... 

Soutar et al. [125] measured the time-resolved anisotropy, r(f), for dilute solutions of PNIPAM, randomly labeled by ca. 5 mol.% acenaphthylene in water, methanol, and in the whole region of their mixtures at temperatures covering the LCST dependence (see Fig. 7) on the composition of the solvent mixture. They found that the anisotropy decays are double exponential in all cases. They used the string of pearls model for the system in pure water and in water-methanol mixtures, where they ascribed the short time to the rotation of probes in the highly solvated parts of the PNIPAM chain and the long time to the rotation of probes in coiled dehydrated parts. Because they also observed the double-exponential... 

---