Chromophores, artificial

A second approach with respect to anisotropic flavin (photo-)chemistry has been described by Trissl 18°) and Frehland and Trissl61). These authors anchored flavins in artificial lipid bilayers by means of C18-hydrocarbon chains at various positions of the chromophore. From fluorescence polarization analysis and model calculations they conclude, that the rotational relaxation time of the chromophore within the membrane is small compared to the fluorescence lifetime (about 2 ns74)). They further obtain the surprising result that the chromophore is localized within the water/lipid interface, with a tilt angle of about 30° (long axis of the chromophore against the normal of the membrane), irrespective of the position where the hydrocarbon chain is bound to the flavin nucleus. They estimate an upper limit of the microviscosity of the membrane of 1 Poise. 

Figure 12.12 Building blocks of an artificial photosynthesis system for hydrogen production using a chromophore (C), an electron acceptor (A) and a sacrificial donor(D)...

The water-soluble compound 2-amino[l,8]naphthyridine is a novel DNA-binding photosensitizer, which may be employed for the one-electron oxidation of DNA. It is also reported to be an excellent chromophore for the design of artificial electron-accepting nucleobases <1999TL6029>. 

The above studies provide evidence for the donor-to-donor energy migration within the assemblies of the chromophores built from a variety of systems, but they all share a common matrix for assembly. Such systems may be of interest in the construction of artificial light-harvesting antennas [67,72],... 

Aprotic solvents mimic the hydrophobic protein interior. However, a functional artificial receptor for flavin binding under physiological conditions must be able to interact with the guest even in competitive solvents. As found by spectroscopic measurements with phenothiazene-labeled cyclene, the coordinative bond between flavin and Lewis-acidic macrocyclic zinc in methanol was strong enough for this function. Stiochiometry of the complex was proved by Job s plot analysis. Redox properties of the assemblies in methanol were studied by cyclic voltammetry which showed that the binding motif allowed interception of the ECE reduction mechanism and stabilisation of a flavosemiquinone radical anion in a polar solvent. As a consequence, the flavin chromophore switched from a two-electron-one-step process to a two-step-one-electron-each by coordination. 

A cumulative success of artificial ion-channel functions by simple molecules may disclose a wide gate for the design of ion channels and possible applications to ionics devices. Incorporation of these channels into bilayer lipid membrane systems may trigger the developments towards ionics devices. The conventional BLM system, however, is not very stable, one major drawback for the practical applications, and some stabilization methods, such as impregnating the material in micro-porous polycarbonate or polyester filters, are required.127 132-137 On the other hand, the conventional LB technique prohibits rapid photochemical reactions of incorporated chromophores and many efforts to overcome the problems have been made.138-141... 

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