Tailoring, chromophores

Positive identification of receptors in preparations of subcellular fractions is feasible only on conditions that the receptor protein has been labeled before the disruption of the membrane. The labeling techniques commonly employed for the identification of receptor proteins are inadequate, however, since the latter constitute only a minor component of the total cell proteins. In principle, affinity labeling provides the high specificity needed for this purpose. By this method, the reagent interacts reversibly and specifically with the active site of the receptor and then forms a stable covalent bond with amino acid residues located at or near the active site. The attached moiety can be detected by virtue of a tailored chromophore that is radioactive, fluorescent, or spin label. In this connection it is of interest that affinity labeling of the norepinephrine a-receptor was reported as early as 1945. ... 

This review article attempts to summarize and discuss recent developments in the studies of photoinduced electron transfer in functionalized polyelectrolyte systems. The rates of photoinduced forward and thermal back electron transfers are dramatically changed when photoactive chromophores are incorporated into polyelectrolytes by covalent bonding. The origins of such changes are discussed in terms of the interfacial electrostatic potential on the molecular surface of the polyelectrolyte as well as the microphase structure formed by amphiphilic polyelectrolytes. The promise of tailored amphiphilic polyelectrolytes for designing efficient photoinduced charge separation systems is afso discussed. 

Conceptually and synthetically more straightforward molecules can be prepared through incorporation of chromophores onto simple phosphine moieties. The phosphorus fragment can be used either to influence or to organise the n-con-jugated systems. This section will focus only on derivatives tailored in order to exhibit specific properties related to applications in NLO,opto-electronics or as sensors. 

An important challenge in the design of novel conjugated polymers is the synthesis of materials with tailor-made solid-state electronic properties. This section outlines the synthesis of the most significant classes of poly(para-phenylenevinylene)s (PPVs), poly(para-phenylene)s (PPPs), and related structures. Furthermore, this review demonstrates that the chromophoric and electronic properties of conjugated rr-systems are sensitive to their molecular and supra-molecular architecture. 

There are no clear advantages in terms of functional performance between the two classes of dyes, except that phthalocyanines are generally more light stable but tend to be more expensive to synthesize and modify. Phthalocyanine dyes are not suitable for DVD-R media, since the main chromophore cannot readily be modified to produce a sufficiently large hypsochromic shift. Other dyes potentially suitable for DVD-R include metal azo complexes, quinophthalones, and diphenyl-methanes. The cyanine dyes are particularly useful as they can be readily modified to tailor the optical absorbance requirements for all current optical disk recording applications.199... 

With the aim of preparing photoinduced electron transfer devices or simply to be used as fluorescent reporter groups, the synthesis and utility of pyrene-L-alanine have been reported on several occasions. Regarding the development of charge-transfer devices, it was shown that intramolecular electron transfer occurred in 310- and a-helical peptidic systems, such as 182 and 185, between a pyrene and a dimethylaminophenyl chromophore (Scheme 51).[95 101] The rates depend on the relative orientation of the chromophoric side chains and on the framework conformation. Therefore, the preparation of tailor-made charge-transfer devices with tunable properties can be envisaged. 

In free retinal, illumination will produce a mixture of several single- and doublebond isomeric configurations. Protein-bound retinal is more restricted in its motional possibilities in the rhodopsins the binding pocket is tailored to fit only a few specific retinal configurations. Indeed, the light-initiated reaction cycles of the bacterial rhodopsins are based exclusively on dlX-trans to 13-cw isomerization of their retinal chromophores. When under some conditions other isomers are produced upon illumination, such as 9 cis, they accumulate in limited quantities [90-92]. 

LBK films are highly ordered and densely packed supramolecular assemblies. The packing of the chromophores in LBK films influences their photo-reaction. Therefore, LBK films have to be tailored by the choice of the amphiphilic molecules and the transfer conditions to provide a matrix for the chromophores that has sufficient flexibility and free volume for the photoreaction to occur. On the other hand, the LBK film s structure can be tailored in such a way that the photoreaction of the chromophore enhances the structure or the properties of the entire film. In this way, photoactive films can be designed to show a much more sophisticated photoresponse than that of a chromophore in an inert matrix. 

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