Chromophore structures

Structure of GFP and its chromophore. To study the chro-mophore of GFP, a sample of GFP was denatured by heating it at 90°C. It was digested with papain, and then a peptide containing the fluorophore was isolated and purified from the digested mixture. The structural study of the peptide has indicated that the chromophore of GFP is an imidazolone derivative shown below (Shimomura, 1979). This chromophore structure was confirmed later by Cody etal. (1993) in a hexapeptide isolated from GFP. It is intriguing that the structure of the GFP chromophore is a part of the structure of coelenterazine. 

Fig. 9.11 Structures of the model compounds KM-1 and KM-2, and a possible structure of PM-1 drawn on the assumption that PMs contain the same chromophore structure as in KM-2.

Tretyakova YA, Pakhomov AA, Martynov VI (2007) Chromophore structure of the kindling fluorescent protein asFP595 from Ammonia sulcata. J Am Chem Soc 129 7748-7749... 

Quinoid-type chromophoric structures, reactions of, 21 36-37 Quinoline (QI), 12 723, 725-726 soluble dyes, 7 373t Quinoline-4-carboxylic acids, 21 190 Quinoline derivatives, 21 196-214 Quinoline-derived drugs, 21 197-198t Quinoline dyes, 21 196 Quinoline, formation of, 21 109. See also Quinolines... 

The broad emission and low-fluorescence quantum yield of PPS suggested a distribution of trapping sites in the Si skeleton, which were also considered responsible for the lower-than-expected conductivity. The far-IR spectrum of PPS suggested the existence of cyclohexasilane rings connected by linear chains.361,362 Subsequent investigations by Irie et al. on the electronic absorption spectra of radical ions of poly(alkylsilyne)s were taken to indicate the presence of various cyclic silicon species, in corroboration of this conclusion.363 The large Stokes shift and broadness of the fluorescence emission indicate a range of fluorophore structures, different from the chromophore structures. This is... 

Scheme 1. Principle of cyanine dye synthesis leading to trimethine (n = l), pentamethine (n = 2) and heptamethine (n = 3) chromophores. Structures comprising indolic subunits are usually named indocarbocyanine, indodicarbocyanine and indotricarbocyanine, respectively. Formic acid, malonic aldehyde, glutaconic aldehyde are used in their protected dianUide or orthoester form. They can be applied as substituted derivatives to introduce residues into the polymethine unit. The indolic substructure might bear further residues or annelated aromatic rings...

Because 1,2-diphenylcyclo-l-butene (DPCB) has a rigid planar structure with the c-St-chromophore structurally constrained by the cyclobutene ring, and because it is stable for geometrical isomerizations, TPCB" is expected to have the same rigid planar structure. Pulse radiolysis of DPCB in DCE produces DPCB, which shows bands at... 

Figure 83 The electronic energies of a CuCl chromophore structural pathway461,489,1108...

Photomorphogenesis, 231 Phycocyanobilin, 237 Phytochrome, 230 molecular weight of, 232 native undegraded, 232 P(r (far-red absorbing form), 236 bilatrene chromophore structure of, 236 photophysical properties of, 236 Pfr — Pr transformation, 234 Pr — Pfr transformation of, 234 chemical nature of individual reaction steps of, 263... 

The lignin model compounds selected for this study possess two functional groups, a phenolic hydroxyl group, and an aliphatic hydroxyl group located on the side chain para to the phenolic hydroxyl group. Experiments were performed to determine the effect of blocking each of these two sites relative to the formation of chromophoric structures. 

Phenolic Hydroxyl Group. An ethanolic solution of 3,4,5-tri-methoxybenzyl alcohol (4-0-methylsyringyl alcohol) and sodium hydroxide was prepared, and ultraviolet spectra of the solution were recorded immediately and 3 days after preparation. These spectra were compared with the spectrum of the model compound in neutral ethanol. The three spectra were identical with the absorption curve possessing a broad maximum in the 270-280 m/x region. Further visual observation of the alkaline solution for 2 weeks revealed no color formation. This suggests that phenoxide ion formation may be a necessary initial step in reactions leading to the development of chromophoric structures from lignin model compounds. 

At present the only colored product that has been identified in the reaction of syringyl alcohol with aqueous alkali is 2,6-dimethoxyquinone. No evidence exists that dimeric chromophoric structures such as a dipheno-quinone or a stilbenequinone, which have been found to be products in the oxidative reactions of phenols in other studies (/, J, I5y 23), are also products of this reaction. However, with the identification of 2,6-dimethoxyquinone and the two colorless products, bis-4-hydroxy-3,5-dimethoxyphenylmethane and syringaldehyde, one of the logical pathways for the reaction is suggested and discussed. 

TABLE 16.3. Chromophores Structures of Organic Molecules and Their Respective Electronic Transitions... 

In a series of experiments with a spruce chemimechanical pulp, it was established that, regardless of the initial irradiation time, a second irradiation period of five minutes with UV-containing radiation after 24 hours storage was sufficient to eliminate the photochromic brightness increase, as shown in Figure 4. If the chromophoric structures are present in the pulp from beginning in their uncoloured or potential chromophore form or whether they are formed by reactions during the initial irradiation is not known and may in fact also depend on the prehistory or the type of pulp. 

Photocycling of Chromophoric Structures during Irradiation of High-Yield Pulps... 

---