Single chains collapse

What can we find out about globulisation How does it proceed How do polymer networks coUapse How does coil-globule transition develops in biopolymers, such as DNA and proteins It turns out that the scenarios are about as diverse as in the case of water and vapor — or more diverse. We will discuss later some other cases, but here we would like to concentrate on one particular possibility for a single chain collapse which we like because we think it is beautiful. 

We throw a bridge from the single chain collapse transition to the phase transition occurring in a polymer solutioa We observe the theta temperature of the system... 

Fig. 4.9 Dynamic Monte Carlo simulation results of single-chain collapse transition, (a) The curves of mean square radius of gyration /(N—l) vs. B/kT for varying chain lengths N as labeled. (0.032, 0.26) is the theta point, (b) Radial distributions of local-average concentrations < q > of chain units in 512-mer at various temperatures (Hu 1998) (Reprinted with permission)...

Chu, B., Ying, Q., Grosberg, A. Y., Two-stage Kinetics of Single-chain Collapse. Polystyrene in Cyclohexane, Macrowo/ecufei, 1995,28, 180-189. 

When polymer solutions encounter situations for which the thermodynamic quality of the solvent becomes poor, individual chains undergo a coil-to-globule collapse, the globules associate immediately, and macroscopic phase separation seems unavoidable. However, it has been reported that a number of polymers in water or in organic solvents form equilibrium globules, i.e. single-chain globules that remain in solution without immediate association and precipitation. 

Whereas the minimum of the free energy of a single chain is obtained for a complete collapse of all beads into one point, the minimum of the free energy of the assembly of chain molecules corresponds to the... 

Ichiba, Y. and Yoshikawa, K. (1998) Single chain observation on collapse transition in giant DNA induced by negatively-charged polymer. Biochem. Biophys. Res. Commun., 242, 441 145. 

As we will see in Sect. 3.4, such a relatively trivial modification of the standard HP model can lead to some nontrivial consequences when studying the collapse for the single-chain amphiphilic polymers and their aggregation in solution. 

Here, we describe and compare the results of simulations for two multichain systems corresponding to alternating and protein-like HA copolymers [212], The multichain systems consisting of 127-unit copolymers were simulated for the range of the effective interaction parameter / (which is similar to the Flory-Huggins parameter) under solvent conditions when single chains can form strongly collapsed conformations. 

In this review, hydrophilically and hydrophobically modified poly(N-iso-propylacrylamide) (PNIPAM) copolymers are mainly used to illustrate how amphiphilic copolymer chains can fold from an extended random coil to a collapsed globule in extremely dilute solutions and associate to form a stable mesoglobular phase which exists between single-chain globules and macroscopic precipitation. The copolymers used can be prepared by free-radical reaction. 

Fig. 3 Dissolving kinetics (in terms of average hydrodynamic radius Rh) of collapsed single-chain PNIPAM globules, where t is the standing time after the solution temperature was quenched from 33.02 to 30.02 °C and the dashed line represents a stable average value of Rh of individual PNIPAM random coils at 30.02 °C. The weight-average molar mass (Mw) of the PNIPAM sample used is 1.08 x 107g/mol with a polydispersity index (Mw/Mn) less than 1.1 [32]...

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