ABSTRACT
Detoxification Using Nanotubes .................................................................................................................... 696 24.5 Nanotube Membranes for Bioseparations.................................................................................................................... 698
24.5.1 Antibody-Functionalized Nanotube Membranes for Selective Enantiomeric Separations............................ 698 24.5.2 Functionalized Nanotube Membranes with Hairpin-DNA Transporter with Single-Base
Mismatch Selectivity...................................................................................................................................... 699 24.5.3 Enantioseparations of Amino Acids Using Apoenzymes Immobilized in a Porous
Polymeric Membrane ..................................................................................................................................... 702 24.6 Conical Nanotubes: Mimicking Artificial Ion Channel ............................................................................................... 704 24.7 Conclusions .................................................................................................................................................................. 706 Acknowledgment ..................................................................................................................................................................... 707 References ................................................................................................................................................................................ 707
The ability to regulate transport across cellular boundaries is essential to the cell’s existence as an open system [1]. There is a steady traffic of ions, molecules, polymers, and other species across the plasma membrane. Consider the chemical exchanges between a human muscle cell and the extracellular fluid that surrounds it. For example, sugars, amino acids, and other nutrients enter the cell, and waste products of metabolism leave the cell. The cell takes in oxygen for cellular respiration and expels carbon dioxide. It also regulates its concentrations of inorganic ions, such as Naþ, Kþ, Ca2þ, and Cl, by shuttling them one way or the other across the plasma membrane. Mother Nature has created natural channels that are highly selective, that is, they allow certain molecules and ions to pass more easily than others (or they reject them). For example, there are highly specialized potassium protein channels that allow potassium cations to pass through with high selectivity than other ions. Other examples include water, Naþ, Ca2þ, Cl, glucose protein channels, nuclear pore, and complexes. The highly selective transportation of molecules and ions is controlled by molecular recognition between transporting species and protein channels present in the cell membranes.
