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Molecular Transport in Membranes
Published in Allen J. Bard, Michael V. Mirkin, Scanning Electrochemical Microscopy, 2022
This chapter is focused on scanning electrochemical microscopy (SECM) studies of molecular transport in biological membranes [1–3] and new membrane materials [4] over the last decade. During this period, remarkable progress was made to investigate membrane transport by SECM with unprecedentedly high resolutions and chemical selectivity. Specifically, the spatial resolution of SECM reached ∼30 nm to image or detect molecular transport at single membrane nanostructures such as single nanopores and single vesicles. Moreover, extremely high mass-transport conditions were achieved by employing nanoscale SECM to monitor otherwise unmeasurably fast molecular transport through ultrathin porous membranes. Furthermore, SECM tips were not only miniaturized to the nanometer scale but also rendered highly selective to quantitatively detect a target molecule while multiple species are co-transported through the membrane, thereby resolving complicated transport mechanisms. These advanced capabilities of SECM are exemplified in this chapter by studies of neuronal exocytosis, artificial and biological nanopore membranes, bacterial membranes, and cancer cells. A greater understanding of these membrane transport processes is relevant broadly to various research areas, including neuroscience, materials science, biomedicine, and microbiology.
Membrane Systems
Published in Agis F. Kydonieus, Controlled Release Technologies: Methods, Theory, and Applications, 2019
The factors governing the behavior of membrane systems used for barrier, permselective, or controlled release applications are similar in that the physicochemical composition and structure of the polymeric membrane system govern the solution and transport properties. Extensive investigations in the science and technology of membrane transport are serving as both a theoretical and practical basis for the utilization of membrane systems, especially in the area of controlled delivery. The principles, which shall be interpreted here primarily in the context of the development of drug-delivery systems, are equally applicable for other systems and other purposes, as the succeeding chapter on pesticide and consumer products applications will illustrate. Examples of other delivery technologies such as microencapsulation, which are discussed in detail in Volume II, will be mentioned briefly when it is clear that these make use of the same rate-moderating mechanisms as are involved in macroscopic membrane systems.
Bioenergy Principles and Applications
Published in Eduardo Rincón-Mejía, Alejandro de las Heras, Sustainable Energy Technologies, 2017
Marina Islas-Espinoza, Alejandro de las Heras
All living cells have membranes. Ions cannot penetrate, except through open pores and ion channels. Ions penetrate the membrane mostly through ion channels. Their opening and closing drives the transmission of electric signals (Cooper and Hausman, 2015). Ion pumps are responsible for maintaining internal ion concentrations and introducing a substance inside a membrane against its concentration gradient. Sometimes this requires membrane transport proteins, which can follow the concentration gradient (facilitated diffusion) or go against this gradient (active transport carried out by proteins (metabolic pumps) that use an extra source of energy). Ion pumps in particular use ATP.
Structure and diversity of bacterial communities in the water column of three reservoirs in Yun-Gui Plateau, China
Published in Inland Waters, 2023
The gene functions in these reservoirs suggested that the bacterial community is involved in various biogeochemical processes, including carbohydrate, energy, and lipid metabolisms. The dominant abundance of the ‘environmental information processing’ category may indicate the presence of different types of compounds in the water, such as organic nutrients, heavy metals, or other pollutants. Some of these compounds would be uptaken by cells, which requires membrane transport (belongs to environmental information processing). Membrane transport proteins play an essential role in efficient metabolism and the translocation of solutes, such as nutrients, ions, drugs, and endogenous bioactive substances (Piepenbreier et al. 2017). Moreover, metabolism dominance proved the numerous activities bacteria involved in various pathways concerning metabolism. These results highlighted the gene diversity of bacteria and the multi-facet roles played by bacteria in such plateau reservoirs. To some extent, the increasing nutrient contents could increase the bacterial diversity, which implies the eutrophic status of these reservoirs.