A shape-driven reentrant jamming transition in confluent monolayers of synthetic cell-mimics.

Many critical biological processes, like wound healing, require densely packed cell monolayers/tissues to transition from a jammed solid-like to a fluid-like state. Although numerical studies anticipate changes in the cell shape alone can lead to unjamming, experimental support for this prediction is not definitive because, in living systems, fluidization due to density changes cannot be ruled out. Additionally, a cell's ability to modulate its motility only compounds difficulties since even in assemblies of rigid active particles, changing the nature of self-propulsion has non-trivial effects on the dynamics. Here, we design and assemble a monolayer of synthetic cell-mimics and examine their collective behaviour. By systematically increasing the persistence time of self-propulsion, we discovered a cell shape-driven, density-independent, re-entrant jamming transition. Notably, we observed cell shape and shape variability were mutually constrained in the confluent limit and followed the same universal scaling as that observed in confluent epithelia. Dynamical heterogeneities, however, did not conform to this scaling, with the fast cells showing suppressed shape variability, which our simulations revealed is due to a transient confinement effect of these cells by their slower neighbors. Our experiments unequivocally establish a morphodynamic link, demonstrating that geometric constraints alone can dictate epithelial jamming/unjamming.

Visible light-mediated synthesis of quinazolinones and benzothiadiazine-1,1-dioxides utilizing aliphatic alcohols.

The activation and utilization of challenging aliphatic alcohols like methanol and ethanol is a very appealing approach to synthesize valuable organic molecules. Utilization of methanol and ethanol as a coupling partner has emerged as a valuable alternative to synthesize industrially relevant N-heterocycles because they can be easily procured from renewable sources unlike other activated coupling partners which are expensive and also unstable. Herein, a mild and metal-free photocatalytic protocol to synthesize quinazolinones and more challenging benzothiadiazine-1,1-dioxides, which is unprecedented at room temperature, is demonstrated. This methodology showcased broad substrate scope and provided important N-heterocycles more efficiently than the transition metal-based high temperature protocols. An unexplored reactivity with allyl alcohol is observed following the developed protocol. A series of control experiments were carried out to understand the mechanism.

Formation of a Reactive [Mn(III)-O-Ce(IV)] Species and its Facile Equilibrium with Related Mn(IV)(OX) (X = Sc or H) Complexes.

Lewis acid-bound high valent Mn-oxo species are of great importance due to their relevance to photosystem II. Here, we report the synthesis of a unique [(BnTPEN)Mn(III)-O-Ce(IV)(NO3 )4 ]+ adduct (2) by the reaction of (BnTPEN)Mn(II) (1) with 4 eq. ceric ammonium nitrate. 2 has been characterized using UV/Vis, NMR, resonance Raman spectroscopy, as well as by mass spectrometry. Treatment of 2 with Sc(III)(OTf)3 results in the formation of (BnTPEN)Mn(IV)-O-Sc(III) (3), while HClO4 addition to 2 forms (BnTPEN)Mn(IV)-OH (4), reverting to 2 upon Ce(III)(NO3 )3 addition. 2 can also be prepared by the oxidation of 1 eq. Ce(III)(NO3 )3 with [(BnTPEN)Mn(IV)=O]2+ (5). In addition, the EPR spectroscopy revealed the elegant temperature-dependent equilibria between 2 and Mn(IV) species. The binding of redox-active Ce(IV) boosts electron transfer efficiency of 2 towards ferrocenes. Remarkably, the newly characterized Mn(III)-O-Ce(IV) species can carry out O-atom and H-atom transfer reactions.

Mn(II) Polypyridyl Complexes: Precursors to High Valent Mn(V)=O Species and Inhibitors of Cancer Cell Proliferation.

The reaction of [(L)MnII ]2+ (L = neutral polypyridine ligand framework) in the presence of mCPBA (mCPBA = m-Chloroperoxybenzoic acid) generates a putative MnV =O species at RT. The proposed MnV =O species is capable of performing the aromatic hydroxylation of Cl-benzoic acid derived from mCPBA to give [(L)MnIII (m-Cl-salicylate)]+ , which in the presence of excess mCPBA generates a metastable [(L)MnV (O)(m-Cl-salicylate)]+ , characterized by UV/Vis absorption, EPR, resonance Raman spectroscopy, and ESI-MS studies. The current study highlights the fact that [(L)MnIII (m-Cl-salicylate)]+ formation may not be a dead end for catalysis. Further, a plausible mechanism has been proposed for the formation of [(L)MnV (O)-m-Cl-salicylate)]+ from [(L)MnIII (m-Cl-salicylate)]+ . The characterized transient [(L)MnV (O)-m-Cl-salicylate)]+ reported in the current work exhibits high reactivity for oxygen atom transfer reactions, supported by the electrophilic character depicted from Hammett studies using a series of para-substituted thioanisoles. The unprecedented study starting from a non-heme neutral polypyridine ligand framework paves a path for mimicking the natural active site of photosystem II under ambient conditions. Finally, evaluating the intracellular effect of Mn(II) complexes revealed an enhanced intracellular ROS and mitochondrial dysfunction to prevent the proliferation of hepatocellular carcinoma and breast cancer cells.

Motile Topological Defects Hinder Dynamical Arrest in Dense Liquids of Active Ellipsoids.

Recent numerical studies have identified the persistence time of active motion as a critical parameter governing glassy dynamics in dense active matter. Here we studied dynamics in liquids of granular active ellipsoids with tunable persistence and velocity. We show that increasing the persistence time at moderate supercooling is equivalent to increasing the strength of attraction in equilibrium liquids and results in reentrant dynamics not just in the translational degrees of freedom, as anticipated, but also in the orientational ones. However, at high densities, motile topological defects, unique to active liquids of elongated particles, hindered dynamical arrest. Most remarkably, for the highest activity, we observed intermittent dynamics due to the jamming-unjamming of these defects for the first time.

Emergent stereoselective interactions and self-recognition in polar chiral active ellipsoids.

In many active matter systems, particle trajectories have a well-defined handedness or chirality. Whether such chiral activity can introduce stereoselective interactions between particles is not known. Here, we developed a strategy to tune the nature of chiral activity of three-dimensionally printed granular ellipsoids without altering their shape or size. In vertically agitated monolayers of these particles, we observed two types of dimers form depending on the chirality of the pairing monomers. Heterochiral dimers moved collectively as a single achiral active unit, while homochiral ones formed a translationally immobile spinner. In active racemic mixtures, the former was more abundant than the latter, indicating that interactions were stereoselective. Through dimer lifetime measurements, we further provide evidence for chiral self-recognition in mixtures of particles with different chiral activities. We lastly show that, at fixed particle number density, changing the net chirality of a dense active liquid fundamentally alters the nature of collective relaxation.