Liquid spherical shells are a non-equilibrium steady state

Abstract

Liquid-liquid phase separation is the process in which two immiscible liquids demix. This spontaneous phenomenon yields spherical droplets that eventually coarsen to one large, stable droplet governed by the principle of minimal free energy. In chemically fueled phase separation, the formation of phase-separating molecules is coupled to a fuel-driven, non-equilibrium reaction cycle. Chemically fueled phase separation yields dissipative structures sustained by a continuous fuel conversion. Such dissipative structures are ubiquitous in biology but poorly understood as they are governed by non-equilibrium thermodynamics. Here, we bridge the gap between passive, close-to-equilibrium, and active, dissipative structures with chemically fueled phase separation. We observe that spherical, active droplets can transition into a new morphology, i.e., a liquid, spherical shell of droplet material. A spherical shell would be highly unstable at equilibrium. Only by continuously converting chemical energy, this dissipative structure can be sustained. We demonstrate the transition mechanism, which is related to the activation of a product outside of the droplet, and the deactivation within the droplets leading to gradients of droplet material. We characterize how far out of equilibrium the spherical shell state is and the chemical power necessary to sustain it. Our work suggests new avenues for assembling complex stable morphologies, which might already be exploited to form membraneless organelles by cells.

Spatiotemporal visualization of DNA replication by click chemistry reveals bubbling of viral DNA in virion formation

“…Virus particle formation may thus start at the interface of two distinct nuclear domains, the VRC and the 52K condensate. By analogy with chemically-fuelled phase separated droplets ( 95 ), VRC can be considered a nonequilibrium condensate, akin to nucleoli, PML bodies or transcriptional condensates ( 13, 96 ), but unlike the quasi-equilibrated 52K condensate. The interface between these compartments may give rise to structures with emerging properties, such as the bubbles containing nascent virus particles.…”

Opto-controlled C9orf72 poly-PR forms anisotropic condensates causative of TDP-43 pathology in the nucleus

“…Upon (r)RNA depletion, these condensates undergo fusion into a larger (>500 nm) hollow-centre structure (Fig.S5A). Anisotropic condensate is a non-equilibrium state that may require ATP to be established and maintained (Bergmann et al , 2023), and in our system, this state is fuelled by the light-induced Cry2olig oligomerisation. Nuclear poly-PR condensates not overlapping with nucleolar markers form in transgenic mice (Zhang et al ., 2019), and it would be interesting to establish whether they adopt a hollow-centre structure at any point during their biogenesis.…”

Constitutional adaptation to pKa modulation by remote ester hydrolysis

“…Several reports show how peptide-based supramolecular systems are able to assemble/disassemble in response to ester/ anhydride hydrolysis, as a result of solubility differences between the generated carboxylate groups and the parent units. [38][39][40][41] However, the change in the reactivity of vicinal functionalities in response to such ester hydrolysis (e.g., potential decrease in the nucleophilicity of surrounding groups by supramolecular cross-talks, see biological example in Fig. 1A) has been quite overlooked, as well as its implementation in dynamic covalent libraries.…”