Abstract
We study active topological glass under spherical confinement, allowing us to exceed the chain lengths simulated previously and determine the critical exponents of the arrested conformations. We find a previously unresolved “tank-treading” dynamic mode of active segments along the ring contour. This mode can enhance active–passive phase separation in the state of active topological glass when both diffusional and conformational relaxation of the rings are significantly suppressed. Within the observational time, we see no systematic trends in the positioning of the separated active domains within the confining sphere. The arrested state exhibits coherent stochastic rotations. We discuss possible connections of the conformational and dynamic features of the system to chromosomes enclosed in the nucleus of a living cell.
Highlights
Active topological glass (ATG) is a state of matter composed of polymers with fixed, circular, unknotted topology that vitrifies upon turning a block of monomers active and fluidizes reversibly.[1]
As we have shown here, this tanktreading diffusion can alter the underlying microphase separation but does not seem to affect the overall stability of the ATG
Despite the fact that a number of threading detection methods already exist,[31−33] none so far is tuned to detect all the latter aspects. Such a tool would help to clarify the conjectured existence of topological glass in equilibrium, where it should arise in the limit of long rings, as suggested by simulations[3−5] and analytical works.[34,35]
Summary
Active topological glass (ATG) is a state of matter composed of polymers with fixed, circular, unknotted topology that vitrifies upon turning a block of monomers active and fluidizes reversibly.[1]. The equilibrium melt of rings exhibits conformational properties consistent with the large-scale, populationaveraged properties of chromatin fiber in the interphase nuclei of higher eukaryotes.[8−10] In detail, the territorial segregation of distinct chains, the critical exponents ν = 1/3 and γ ≃ 1.1 governing the scaling of the gyration radius R(s) ∼ sν and the probability of end-contacts P(s) ∼ s−γ of a segment of length s, respectively, coincide for the two systems and characterize the so-called fractal (crumpled) globule conformations.[11] to partly active rings, chromatin is out of equilibrium on smaller scales as well. We observe tank-treading of active segments along the ring contour in the glass that acts to enhance active−passive phase separation when both the chain’s diffusion and the conformational rearrangements are suppressed
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