Transport molecular devices

Fatty Acid Transporters. Figure 2 Quencher-based real-time fatty acid uptake assay with a fluorescently labeled FFA analogue (C1-Bodipy-C12). Predominantly protein-mediated fatty acid uptake by 3T3-L1 adipocytes (diamonds) was compared with diffusion-driven uptake by fibroblasts (squares) using the QBT Fatty Acid Uptake reagent (Molecular Devices Corp., CA, USA), which contains C1-Bodipy-C12 as substrate in conjunction with a cell impermeable quencher. Uptake kinetics was recorded using a Gemini fluorescence plate reader. Error bars indicate the standard deviations from 12 independent wells. RFU relative fluorescence units. 

Fig. 1 Sketches of break junction-type test beds for molecular transport. On the far left is a tunneling electron microscopy (TEM) image of the actual metallic structure in (mechanical) break junctions from the nanoelectronics group at University of Basel. The sketches in the middle (Reprinted by permission from Macmillan Publishers Ltd Nature Nanotechnology 4, 230-234 (2009), copyright 2009) and right (reproduced from Molecular Devices, A.M. Moore, D.L. Allara, and P.S. Weiss, in NNIN Nanotechnology Open Textbook (2007) with permission from the authors) show possible geometries for molecules between two gold electrodes, and (on the upper right) a molecule that has only one end attached across the junction...

As attested to by the breadth of topics in this volume, the subject of electron transport in molecular devices is a broad and active area. Within this general area, one often finds common fundamental problems relating to the nature of the entity producing the observed electronic response. Some of these issues include ... 

Structure of the molecular device [84-87, 129] with the well-established Green function formalism, to compute the transport characteristics. In such a way, it would be possible to distinguish self-consistently in the calculations different mechanisms, and their relative importance in experimental settings. 

Electron Transport in Two- and Three-terminal Molecular Devices... 

M. DiVentra, S.T. Pantelides, N.D. Lang, First-Principles Calculation of Transport Properties of a Molecular Device, Phys. Rev. Lett. 84 (2000) 979. 

There are a considerable number of reactions in which the products contain two electrons, more than the starting compounds, and the consecutive two-step one-electron electron transfer process proves to be energetically unfavorable. In such cases, it is presumed that the two-electron process occurs in one elementary two-electron step. An example of a two-electron process is the hydride transfer, when two electrons are transported together with a proton. BH4, hydroquinones and reduced nicotinamides are typical hydrid donors. A specific feature of quinones is the capacity to accept and then to reversibly release electrons one by one or two electrons as a hydride. Therefore, quinones can serve as a molecular device, which can switch consecutive one-electron process to single two-electron process. 

As macrocyclic chemistry has developed, the variety and scope of the applications of these molecules have continued to multiply. This concluding section is an attempt to provide an overview of only three of the applications of synthetic macrocycles. A particularly insightful treatment can be found in the Nobel Lecture of Jean-Marie Lehn, which describes the concept of supramolecular chemistry from simple recognition, to cation and anion receptors, multiple recognition, catalysis, transport, and molecular devices. 

Figure 11.2 The formation of excitons [9]. (Reprinted with permission from Y. Shirota and H. Kageyama, Charge carrier transporting molecular materials and their applications in devices, Chemical Reviews, 107, 953-1010, 2007. 2007 American Chemical Society.)...

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