Photonic signals transduction

To summarize, absorption of a photon by a conjugated polymer creates an exciton that can then sample many potential binding sites within its lifetime. Emission from the excited state is observed only if there is no bound analyte encountered by the migrating exciton. If the analyte is encountered there is quenching of the emission, and it is this amplified dimunition in emission intensity that serves as an indication (signal transduction) that the analyte is present. 

Photonic activation of electrobiocatalytic functions of redox proteins and the electrochemical transduction of recorded photonic signals... 

The retinal pool of 11 -cis-retinal is clearly critical for photon detection and visual signal transduction. There are two key aspects regarding this that are important to consider the precursor(s) from which 11 -cis-retinal derived, and, bioconversion of isomerized trans-retinal back to 11-cis-retinal that can recombine with opsin to re-form rhodopsin. The latter aspect is obligatory for restoration of the dark state, regenerating a photosensitive receptor capable of undergoing another cycle of photon detection and signal transduction. Considered together, these events represent the retinoid cycle in the visual process (22). The entire process of re-isomerization and formation of a new rhodopsin molecule occurs in two different retinal tissues and involves several enzymatic steps that are described below (see Fig. 7.14). 

Recently Inoue and coworkers also reported ab initio study of shieldings for linear jr-conjugated systems. A photoreceptive protein such as rhodopsin (Rh) or bacte-riorhodopsin (bR) possesses a retinal isomer bound to a lysine residue via the protonated Schiff base linkage. Rh exists in the rod cell of the retina of vertebrate and possesses 11 -c/s-rcli iial (Figure 2), which is isomerized into the al l-Zraw.v form by the absorption of photons, finally leading to signal transduction. 

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