Entropy and Random Walk Trails Water Confinement and Non-Thermal Equilibrium in Photon-Induced Nanocavities

Molecules near surfaces are regularly trapped in small cavitations. Molecular confinement, especially water confinement, shows intriguing and unexpected behavior including surface entropy adjustment; nevertheless, observations of entropic variation during molecular confinement are scarce. An experimental assessment of the correlation between surface strain and entropy during molecular confinement in tiny crevices is difficult because strain variances fall in the nanometer scale. In this work, entropic variations during water confinement in 2D nano/micro cavitations were observed. Experimental results and random walk simulations of water molecules inside different size nanocavitations show that the mean escaping time of molecular water from nanocavities largely deviates from the mean collision time of water molecules near surfaces, crafted by 157 nm vacuum ultraviolet laser light on polyacrylamide matrixes. The mean escape time distribution of a few molecules indicates a non-thermal equilibrium state inside the cavity. The time differentiation inside and outside nanocavities reveals an additional state of ordered arrangements between nanocavities and molecular water ensembles of fixed molecular length near the surface. The configured number of microstates correctly counts for the experimental surface entropy deviation during molecular water confinement. The methodology has the potential to identify confined water molecules in nanocavities with life science importance.

An Envelope Protein of a Prokaryotic Organelle Function towards Conserving Catalytic Activity of the Native Enzyme at Higher Temperatures

A classic example of an all-protein natural nano-bioreactor, the bacterial microcompartments are a special kind of prokaryotic organelles that confine enzymes within a small volume enveloped by an outer layer of shell proteins. This arrangement provides conditional metabolic aid to the bacteria. The outer shell allows selective diffusion of small molecules and sequesters toxic metabolites. In this work we use 1,2-propanediol utilization microcompartment as a model to study the effect of molecular confinement on the stability and catalytic activity of native enzymes in microcompartment. We observe a 50% decrease in the activity of free enzyme PduCDE at 45°C, while PduMCP retains its optimum activity till 50°C followed by more than 40% reduced activity at 55°C. PduBB’, the major component of the outer shell contributes to the increased catalytic activity of PduCDE. PduBB’ also prevents the unfolding and aggregation of PduCDE under thermal stress. Using a combination of experimental and theoretical studies we probe the interactions of the shell proteins PduBB’, N-terminal truncated PduB and single mutant PduB’M38L with PduCDE. We observe that all the three variants of PduB* shell proteins interact with the enzyme in vitro, but only PduBB’ influences its activity and stability, underscoring the significance of the unique combination of PduB and PduB’ in PduMCP assembly.

Direct Molecular Confinement in Layered Double Hydroxides: From Fundamentals to Advanced Photo-luminescent Hybrid Materials

Two-dimensional organic-inorganic hybrid materials based on layered double hydroxides (LDHs) have drawn significant attention during the last decade. The development of such materials is usually based on the intercalation of...