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A flexible molecule can adjust its shape to diffuse through a pore having a diameter smaller than its average dimension. The fluctuations of molecular dimensions as well as the rotations of the molecule inside the pores require special attention to the definition of the molecular size descriptors for diffusive transport in the pores. Within the framework of the previously proposed theory of the steric free energy barrier, we suggest an effective spherical model of a molecule of an arbitrary shape and define two size descriptors-the effective average radius of the molecule and its variance. The two geometric parameters effectively encode both the fluctuations of the molecule and its rotation in the pore. Once determined for a molecule, they can be used to estimate the steric free energy in a pore of arbitrary radius. The results can be applied to diffusive transport through biological nanopores as well as to size-exclusion molecular filtering. (c) 2025 Author(s). All article content, except where otherwise noted, is licensed under a Creative Commons Attribution (CC BY) license(https://creativecommons.org/licenses/by/4.0/).https://doi.org/10.1063/5.0284331

JTD

Efficient drug delivery across the blood–brain barrier (BBB) remains a significant obstacle in treating central nervous system (CNS) disorders. This review provides an in-depth analysis of the structural and molecular mechanisms underlying BBB integrity and its functional properties. We detail the role of key cellular and molecular components that regulate selective molecular transport across the barrier, alongside a description of the current therapeutic approaches for brain drug delivery, including those leveraging receptor-mediated transcytosis. Emphasis is placed on multivalency-based strategies that enhance the specificity of nanoparticle targeting and improve transport efficacy across the BBB. Additionally, we discuss the added value of integrating mathematical and computational models with experimental validation for accelerating BBB-targeted delivery systems optimisation.

JTD

Metabolism in biological systems involves the continuous formation and breakdown of chemical and structural components, driven by chemical energy. In specific, metabolic processes on cellular membranes result in in situ formation and degradation of the constituent phospholipid molecules, by consuming fuel, to dynamically regulate the properties. Synthetic analogs of such chemically fueled phospholipid vesicles have been challenging. Here we report a bio-inspired approach for the in situ formation of phospholipids, from water soluble precursors, and their fuel driven self-assembly into vesicles. We show that the kinetic competition between anabolic and catabolic-like reactions leads to the formation and enzymatic degradation of the double-tailed, vesicle-forming phospholipid. Spectroscopic and microscopic analysis demonstrate the formation of transient vesicles whose lifetime can be easily tuned from minutes to hours. Importantly, our design results in the formation of uniform sized (65 nm) vesicles simply by mixing the precursors, thus avoiding the traditional complex methods. Finally, our sub-100 nm vesicles are of the right size for application in drug delivery. We have demonstrated that the release kinetics of the incorporated cargo molecules can be dynamically regulated for potential applications in adaptive nanomedicine.

JTD Keywords: Droplets, Mode, Phospholipids, Supramolecular chemistry, Systems chemistry, Transient assembl, Vesicles