Free chromophore

The interaction integral J12 is then given by summing all Coulomb interactions of translationally equivalent transition dipoles. The excitation energy AE of the aggregated chromophores is approximately represented by that of the free chromophores AE and the interaction integral as AE = AE 22 J12 (3)... 

The free chromophore was extracted in acetone from dark adapted cells, dried and photooxidized in vitro by irradiation for a few hours with a dim light (below 10 W/m2). Finally the sample was purified by HPLC. No attempt was done to separate the five closely related forms of the molecule, that share the same n-electron system [9]. 

Fig. 1-left gives a general overview of the differential absorption spectra recorded for the free chromophore, oxyblepharismin, dissolved in DMSO for reference the steady-state absorption and (uncorrected) fluorescence spectra are also given below, in dotted lines. At all pump-probe delay times, the overall picture is a superposition of the structured bleaching and gain bands, as expected from the steady-state spectra, and broad transient absorption bands around 530 nm and 750 nm (weaker). These apparently homothetic spectra are very similar to... 

The blue-shift results from the chemical environment inside the pores of MCM-41, which is dominated by residual silanol and, especially, non reacted amino groups, and thus more basic compared to that in solution. The interaction of the dye molecules with the host is further confirmed by a broadening of the absorption bands of anchored dyes (e.g. rhodamine B sulfonylchloride, Figure 4) in comparison to the main bands of the free chromophores in solution. 

At low concentrations of the anchored rhodamine dye, the samples exhibit a strong fluorescence, which indicates the presence of individual, free chromophore moieties. To avoid... 

Extrinsic Cotton effects are due to the inherent dissymmetry of the enzyme-bound chromophore (an inherent effect) and/or to the interactions of the chromophore with the encompassing dissymmetric environment (interactive effects). The inherent effects are those which the free chromophore would exhibit if its conformation were identical with that of the enzyme-bound form. The interactive effects result from protein-ligand interactions or ligand-ligand interactions. The main problem in interpretation of die CD of enzyme-bound chromophores is distinguishing between the inherent and the interactive effects. 

With the exception of photodissociation to radical ions observed for retinol in polar solvents (144), cis-trans isomerization is the major photochemical transformation undergone by all forms of the free retinyl-polyene chromophore. [Unidentified photochemical damage has been reported to occur with very low quantum yields, e.g., 0.04 in the case of all-trans retinal (177).] We shall subsequently see that critical comparisons between the photochemical behavior of the biopigments and that of the opsin-free chromophore have led to the conclusion that the protein moiety plays a major role in governing the photochemical mechanism in rhodopsin (176). It is, therefore, natural that in parallel to spectroscopic and theoretical investigations, considerable attention has been devoted to the photoisomerization of model compounds, particularly to that of retinal isomers. 

Conclusions. The accumulated evidence discussed above led to a classification of mechanisms of cis-trans photoisomerization in the main derivatives of the free chromophore ... 

The ultraviolet spectra of many proteins exhibit small shifts of absorption maxima to shorter wavelengths and small decreases in extinction coefficient at these maxima when the native conformations are disrupted in aqueous solution (see Beaven and Holiday, 1952 Beaven, 1961 and the article by Wetlaufer in this volume). These effects are presumably due to the special environments in which chromophoric side chains, particularly those of tyrosine and tryptophan, find themselves within the native protein molecule as compared to the free chromophores in aqueous solutions. The special properties of these native environments have been attributed variously to hydrogen bonding, particularly of tyrosine residues (Scheraga and Laskowski, 1957), vicinal electrical effects, including ion-... 

At time t = 0, a dc field is applied it produces an electric field-induced Pockels effect (EFIPE), which is solely due to a third-order effect Eq) in the case of the copolymer because the molecules are not oriented by the dc field alone at room temperature, but which also contains a part due to the rotation, in a polar manner, of free chromophores in the guest-host system (induced The value of x is measured from the modulations of ATR... 

Cleavage from the Protein and Investigation of the Free Chromophore.H4... 

Polyphosphazenes are suitable materials to be used as carriers for nonlinear optical (NLO) chromophores. Second order NLO properties have been studied for the polymer (128) and blends of (129) with the free chromophore (130) or the cyclophosphazene (131). All systems have glass transition temperatures higher than 135°C and a wide transparency window. The system (129)-(130) appears to exhibit the highest second-harmonic generation (SHG) response. For possible applications the SHG capability has to be enhanced. ... 

During the fermentation, chromophore and protein are probably produced separately, and only part of the chromophore is attached to the largomycin F-II protein. The existence of free chromophore explains the appearance of biological activity in a fermentation broth before the appearance of largomycin F-II, and why total bioactivity does not necessarily correlate with total amount of F-II. 

The concept of photomodulation of peptide conformation was also applied to the photoinduction of a /Miairpin formed by 10 amino acids which mimic a 12-mer peptide inside which the original Pro-Gly sequence was replaced with a diarylazo moiety [132,133], The rate of light-induced cis — trans isomerization of the peptide was only 30% slower than that of the free chromophore, suggesting... 

Note that the latter chromophore shows an absorption band at higher energy [zmax = 260 ntn [97]] compared to the bpy chromophore. The absorption spectra of the Eu3 + and Tb3+ complexes of ligands 40 and 41 have maxima at 260 nm, as the free chromophore, with very high molar absorption coefficients [97]. 

It should be possible, in principle, to separate the two contributions to by control of the temperature. Extensive experiments with solutions of aromatic chromophores unbound to polymer chains have shown that at sufficiently low temperatures, excimer formation will be diffiision controlled. At sufficiently high temperatures, the Birks dynamic equilibrium regime will be reached, and the binding energy of the system will be the important parameter. This treatment of the photophysics appears to work quite well for the free chromophores in solution and even for the end-labeled chains... 

Occurrence S. is the prosthetic group of sulfite and nitrite reductases of numerous bacteria and plants. S. plays an important part in the global nitrogen and sulfur cycles. The reduced, metal-free chromophore [si-rohydrochlorin, C42H46N40,6, Mr 862.84, uv, , (oc-... 

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