PubMed · 7231395
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1981. Membrane spectroscopy.. https://pubmed.ncbi.nlm.nih.gov/7231395/
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A mathematical description is presented of osmotic flows across both ideally semipermeable membranes and membranes permeable not only for the solvent but also for the solute. The principles of thermodynamics of irreversible processes used for the description are given and illustrated on the example of electroosmosis. Modern ideas about the physical basis of osmotic pressure on porous membranes are discussed and an experiment is described that models the processes of osmosis on a macroscopic level.
From seashells to DNA, chirality is expressed at every level of biological structures. In self-assembled structures it may emerge cooperatively from chirality at the molecular scale. Amphiphilic molecules, for example, can form a variety of aggregates and mesophases that express the chirality of their constituent molecules at a supramolecular scale of micrometres. Quantitative prediction of the large-scale chirality based on that at the molecular scale remains a largely unsolved problem. Furthermore, experimental control over the expression of chirality at the supramolecular level is difficult to achieve: mixing of different enantiomers usually results in phase separation. Here we present an experimental and theoretical description of a system in which chirality can be varied continuously and controllably ('tuned') in micrometre-scale structures. We observe the formation of twisted ribbons consisting of bilayers of gemini surfactants (two surfactant molecules covalently linked at their charged head groups). We find that the degree of twist and the pitch of the ribbons can be tuned by the introduction of opposite-handed chiral counterions in various proportions. This degree of control might be of practical value; for example, in the use of the helical structures as templates for helical crystallization of macromolecules.
A large variety of membrane-modifying agents have been used for the enhancement of DNA(lipo)polycation complex based gene transfer. The magnitude of improvement depends on the nature of the membrane-modifying agent and the (poly)cationic carrier. Within the lipid-free polymer-based systems (polyfection), ligand-polylysine mediated gene transfer can be improved up to more than 1000-fold by pH-specific endosomolytic peptides, glycerol, bacterial proteins or adenovirus particles. Ligand-polyethylenimine or dendrimer-based systems with per se higher efficiency are only slightly (about ten-fold) enhanced by endosomolytic agents. Membrane-active agents show only minor effects when applied to cationic lipid-based gene transfer (lipofection) with DNA complexes formed under optimized conditions using an three- to four-fold excess of positive charges. Less positively charged lipofection complexes can be strongly improved by the addition of membrane-active peptides.