Molecular Gates

For cells to carry out their functions, glucose and other nutrients must be brought in, and urea and other waste products must be expelled. This would be an impossible task if cell membranes were composed only of phospholipids. Farge protein molecules act as molecular gates through the membranes (see Chapter 13 for the structures of proteins). These proteins are embedded in the bilayers but protrude into the surrounding water and/or into the cell interiors, as Figure 12-19 indicates. 

Norregaard, L. and Gether, U. (2001) The monoamine neurotransmitter transporters structure, conformational changes and molecular gating. Curr. Opin. DrugDiscov. Dev. 4,591-601. 

Kosbash It could be that there is a RNA oscillation of some other gene—a kinase or secretory model, for example, which is required for PDF terminal accumulation and release. We have no idea what the molecular gate is for PDF terminal accumulation. 

Kuo, T.C., Cannon, D.M., Jr., Shannon, M.A., Bohn, P.W., Sweedler, J.V., Hybrid three-dimensional nanofluidic/microfluidic devices using molecular gates, Sensors Actuators A 2003, 102, 223-233. 

Figure 19.12 Control of the pore aperture by interaction of molecular gates with guests of different size and shape.

The device yield of TFTs with molecular gate dielectrics would be expected to be low, because of defects in the thin self-assembled monolayer arising from the imperfect surface of the evaporated aluminum bottom electrode. Results obtained on... 

Various recent papers have discussed possible applications of dendrimers [3, 4, 11, 14, 20, 23]. From the point of view of electron transfer, the interest in highly branched structures such as dendrimers is related not so much to their size, but rather to the presence of different components. In fact, an ordered array of different components can generate valuable properties, such as the presence of cavities with different size, surfaces with specific functions, gradients for photoinduced energy and electron transfer, and sites for multielectron transfer catalysis. At this point it is perhaps worth summarizing the practical applications of dendrimers encountered in this chapter. Dendrimers have already been used (i) in catalytic processes [122, 149, 172] (ii) in the functionalization of electrodes [48, 63, 172-175] which can also work as sensors [44, 48, 63] (iii) in the fabrication of nanoparticles [170-172] and (iv) in other devices such as LEDs [140-148] and molecular gates [173, 174], Moreover, as many different exciting applications will certainly be added to this list in the future, it is easy to foresee a remarkable expansion in dendrimer related research. 

Liu, Y., Shah, K., Yang, F., Witucki, L., and Shokat, K.M. (1998) A molecular gate which controls unnatural ATP analogue recognition by the tyrosine kinase v-Src. Bioorg. Med. Chem. 6, 1219-26. 

MVCs are important effectors ofTRPS. The MVC binding site is located in the /3-subunit separate from the catalytic site. Sodium ions strongly favor the accumulation of the external aldimine species by stabilizing a partially open conformation of the enzyme, whereas cesium ions stabilize the a-aminoacrylate and the closed state. " MVCs bound to the /3-subunit also proved to alter the conformation of the side chains of the residues acting as molecular gate. ... 

Halik, M., Klauk, H., Zschieschang, U., Schmid, G., Dehm, C., Schutz, M., Maisch, S., Effenberger, R, Brunnbauer, M. and Stellacci, F., Low-voltage organic transistors with an amorphous molecular gate dielectric. Nature, 431, 963-966, 2004. 

Hahk, M., Klauk, H., and Zschieschang, U., Low-voltage organic transistors with an amorphous molecular gate dielectric. Nature 431, 963-966, 2004. 

Manipulation of the permeability of the SAM to selected redox molecules can be achieved through the inclusion of molecular gates [28-38] or changes in the charge density of the SAM via an ionizable moiety [39-43]. These manipulations are directed toward the fabrication of selective chemical sensors. 

Fig. 11 Schematic illustration of a molecular gate consisting of PAMAM dendrimers and n-alkanethiols immobilized on a Au surface. Adapted from Ref 102.

Engelhard Corporation, Molecular Gate Technology for Nitrogen Rejection, brochure... 

Beedholm-Ebsen, R., Van De Wetering, K., Hardlei, T., Nexo, E., Borst, P, Moestrup, S. K. 2010. Identification of multidrug resistance protein 1 (MRPl/ABCCl) as a molecular gate for cellular export of cobalamin. Blood, 115, 1632-9. 

A unique application of spiropyrans is in molecular gating. Aznar et al. utilized spiropyrans to control nanoarchitecture through the creation of a gating system consisting of mesoporous MCM-41 incorporated with spiropyran moieties (which functioned as a 3D support) and 1.5 poly(amidoamine) dendrimers, which served as nanomechanical stoppers [32]. UV light exposure resulted in the attraction of the... 

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