Light driven shuttle

Scheme 6.5.7. Light-driven shuttling of a rotaxane with internal hydrogen bonding.

SCHEME 19 A LIGHT-DRIVEN MOLECULAR SHUTTLE WITH WHICH MOLECULAR MOTIONS CAN BE INDUCED BY... 

In this rotaxane, a-CD exists at the trans-azobenzene part but it moves to the methylene part when the trans-azobenzene unit is converted into cts-azoben-zene. This light-driven locational change was regarded as a molecular shuttle system. 

As illustrated in Figure 5.23, Willner et al. [49] have developed a light-driven molecular shuttle. This device consists of a ferrocene-functionalized /3-cyclodextrin... 

Figure 18. Intramolecular mechanism for the light-driven switching of the ring R between the two stations Ai and A2. The dashed lines indicate processes that compete with those needed to perfom shuttling [47].

Willner and coworkers described an exciting light-driven molecular shuttle organized on the eledrode surface [72]. The assembly consists of a ferrocene-... 

Murakami, H, A Kawabuchi, K Kotoo, M Kunitake and N Nakashima (1997). A light-driven molecular shuttle based on a rotaxane. Journal of American Chemical Society, 119(32), 7605-7606. 

The earliest light-driven CD-based molecular shuttle consisted of an azobenzene moiety in the axis and a-CD (Fig. 4). NMR spectroscopy supported the formation of a rotaxane complex where a-CD stays at the central trans-azobenzene site. Trans-cis conversion with 360 nm light caused a shift of a-CD to the methylene spacer, due to the exclusion of the cts-azobenzene moiety from the CD cavity. Back photoreaction and repositioning of the macrocycle on the trarzs-azobenzene unit was obtained with irradiation at 430 nm. 

Fig. 4 Schematic structure of the first light driven molecular shuttle reproduced with permission from ref. 35. Copyright 1997 American Chemical Society.

Nakashima et al. reported the first light-driven molecular shuttle based on a rotaxane (Figure 55) comprising an a-CD linked mechanically with an axle containing an azobenzene unit located at the center, two paraquat units at each side of the azobenzene unit, and 2,4-dinitrophenyl stoppers. The location of a-CD could be changed between the azobenzene and ethylene moieties by lights of different wavelengths or by the heat both in water and in DMSO. 

Hydrogen ions are often needed in biochemical reactions carried out by enzymes. Several such enzymes use water wires to shuttle the ions from the solvent through the protein and into the active site where the reaction takes place. This happens, for example, in cytochrome and peroxidase enzymes, and in bacterio-rhodopsin, a light-driven proton pump used by some Archaea to transport protons across a membrane during the conversion of light energy into chemical energy. 

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