Related Experiment Video
Updated: Aug 7, 2026
08:00
DNA Nanotubes as a Versatile Tool to Study Semiflexible Polymers
Published on: October 25, 2017
Living helices in fluctuating polymer chains: Cooperative nucleation and dynamics
1Solid State and Structural Chemistry Unit Indian Institute of Science, Bengaluru 560012, India.
The Journal of Chemical Physics
|August 5, 2026
Summary
Transient helical segments in polymers, termed "living helices," emerge from cooperative interactions and fluctuations. A new theory explains their formation, size, and stability in flexible polymers and peptides.
Area of Science:
- Polymer Physics
- Statistical Mechanics
- Biophysics
Background:
- Transient helical segments in polymer chains are poorly understood.
- Their origin and stability in fluctuating systems remain unclear.
Purpose of the Study:
- To develop a statistical-mechanical theory for the emergence of transient helical segments ("living helices") in polymers.
- To elucidate the mechanisms governing the formation, size, and stability of these dynamic structures.
Main Methods:
- Developed a minimal coarse-grained statistical-mechanical theory.
- Utilized a three-state model with cooperative interactions.
- Formulated dynamics as a stochastic process and employed a mean first-passage framework.
Main Results:
- Helix formation proceeds via a multistep nucleation mechanism involving a pre-nucleus and cooperative stabilization.
- Marginally stable helices emerge from a balance between cooperative gains and nonlinear penalties (stiffness, strain, solvent fluctuations).
- Analytical expressions for formation times and lifetimes were derived, predicting nanosecond to sub-microsecond timescales.
Conclusions:
- Transient helices are finite, mobile, and fluctuating excitations in polymer systems.
- Cooperativity and fluctuations are key determinants of transient secondary structure formation and stability.
- The theory provides a unified physical picture for "living helices" in polymers and peptides.
Related Concept Videos
01:17Radical Chain-Growth Polymerization: Chain Branching
The skeletal structure of polymers synthesized via radical polymerization is always branched. For example, the polymerization of ethylene by radical polymerization results in a low-density grade of polyethylene with a heavily branched skeletal structure. Here, the radical site abstracts hydrogen from the growing chain, and the radical site shifts from the end (a primary carbon center) to anywhere within the growing chain (a secondary carbon center). Consequently, the part of the chain from the...
01:09Radical Chain-Growth Polymerization: Mechanism
The radical chain-growth polymerization mechanism consists of three steps: initiation, propagation, and termination of polymerization. The polymerization initiates when a free radical generated from the radical initiator adds to the unsaturated bond in the monomer. The unpaired electron of the free radical and one π electron in the unsaturated bond creates a σ bond between the free radical and the monomer. As a result, the other π electron in the unsaturated bond converts this species into the...
01:04Anionic Chain-Growth Polymerization: Mechanism
The mechanism for anionic chain-growth polymerization involves initiation, propagation, and termination steps. In the initiation step, a nucleophilic anion, such as butyl lithium, initiates the polymerization process by attacking the π bond of the vinylic monomer. As a result, a carbanion, stabilized by the electron‐withdrawing group, is generated. The resulting carbanion acts as a Michael donor in the propagation step and attacks the second vinylic monomer, which acts as a Michael acceptor.
01:20Anionic Chain-Growth Polymerization: Overview
The polymerization process that involves carbanion as an intermediate is called anionic polymerization. It is also a type of addition or chain-growth polymerization. Anionic polymerization gets initiated by a strong nucleophile such as an organolithium or a Grignard reagent. The most commonly used initiator for anionic polymerization is butyl lithium. Monomers involved in anionic polymerization must possess a vinyl group bonded to one or two electron-withdrawing groups. For instance,...
01:10Radical Chain-Growth Polymerization: Overview
Chain-growth or addition polymerization is successive addition reactions of monomers with a polymer chain. In radical chain-growth polymerization, the reaction proceeds via a free-radical intermediate. The free radical is formed from radical initiators, which spontaneously generate free radicals by homolytic fission. Organic peroxides (such as dibenzoyl peroxide, as shown in Figure 1) or azo compounds are popular radical initiators. A low concentration ratio of radical initiator to monomer is...
00:57Cationic Chain-Growth Polymerization: Mechanism
The cationic polymerization mechanism consists of three steps: initiation, propagation, and termination. In the initiation step of the polymerization process, the π bond of a monomer gets protonated by the Lewis acid catalyst, which is formed from boron trifluoride and water. The protonation of the π bond generates a carbocation stabilized by the electron‐donating group. In the propagation step, the π bond of the second monomer acts as a nucleophile and attacks the generated carbocation,...