Chromophores photoisomerization

Amphiphilic cationic azobenzene derivatives (scheme Fig. 14) have been used as the guest species for intercalation into the layered silicates magadiite and montmorillonite (182-185). The azobenzene chromophore photoisomerized effectively in the interlayer space of silicates, despite the fact that the azobenzene... 

Gonzalez-Luque, R., Garavelli, M.> Bernard , R, Mer-chdn, M., Robb, M. A., Olivucci, M. (2000). Computational evidence in favor of a two-state, two-mode model of the retinal chromophore photoisomerization. Proceedings of the National Academy of Sciences of the United States of America, 97(17), 9379-9384. 

Case Studies of Isolated Chromophores Photoisomerization in a Rhodopsin Chromophore Model... 

The first study in which a full CASSCE treatment was used for the non-adiabatic dynamics of a polyatomic system was a study on a model of the retinal chromophore [86]. The cis-trans photoisomerization of retinal is the primary event in vision, but despite much study the mechanism for this process is still unclear. The minimal model for retinal is l-cis-CjH NHj, which had been studied in an earlier quantum chemisti7 study [230]. There, it had been established that a conical intersection exists between the Si and So states with the cis-trans defining torsion angle at approximately a = 80° (cis is at 0°). Two... 

P -Bonding is obviously also the initiating step in the complex photoisomerization sequence of the stereoisomeric 1,5-dien-3-ones (162) and (163) in ethanol. After low conversions of the starting dienones, an isomer containing an analogous chromophoric system [(164) and (165), respectively] was found to build up temporarily in each case. On longer photolysis times, both compound pairs (162)/(164) and (163)/(165), are consumed, and the mixtures of the four diastereomers (166)-(169) were isolated from both runs. According to separate irradiation experiments with each of these products, (166) and (167) on one hand, and (168) and (169) on the other, are... 

Voliani V, Bizzarri R, Nifosi R, Abbruzzetti S, Grandi E, Viappiani C, Beltram F (2008) Cis-trans photoisomerization of fluorescent-protein chromophores. J Phys Chem B 112 10714-10722... 

Yang JS, Huang GJ, Liu YH, Peng SM (2008) Photoisomerization of the green fluorescence protein chromophore and the meta- and para-amino analogues. Chem Commun 1344-1346... 

Nifosi R, Tozzini V (2006) Cis-trans photoisomerization of the chromophore in the green fluorescent protein variant E(2)GFP a molecular dynamics study. Chem Phys 323 358-368... 

The CP MAS NMR spectroscopy has been also extensively used for studies of proteins containing retinylidene chromophore like proteorhodopsin or bacteriorhodopsin. Bacteriorhodopsin is a protein component of purple membrane of Halobacterium salinarium.71 7 This protein contains 248 amino acids residues, forming a 7-helix bundle and a retinal chromophore covalently bound to Lys-216 via a Schiff base linkage. It is a light-driven proton pump that translocates protons from the inside to the outside of the cell. After photoisomerization of retinal, the reaction cycle is described by several intermediate states (J, K, L, M, N, O). Between L and M intermediate states, a proton transfer takes place from the protonated Schiff base to the anionic Asp85 at the central part of the protein. In the M and/or N intermediate states, the global conformational changes of the protein backbone take place. 

Organic compounds which show reversible color change by a photochemical reaction are potentially applicable to optical switching and/or memory materials. Azobenzenes and its derivatives are one of the most suitable candidates of photochemical switching molecular devices because of their well characterized photochromic behavior attributed to trans-cis photoisomerization reaction. Many works on photochromism of azobenzenes in monolayers LB films, and bilayer membranes, have been reported. Photochemical isomerization reaction of the azobenzene chromophore is well known to trigger phase transitions of liquid crystals [29-31]. Recently we have found the isothermal phase transition from the state VI to the state I of the cast film of CgAzoCioN+ Br induced by photoirradiation [32]. 

The evidence to-date shows that vertebrate photoreception is mediated by a closely related group of proteins termed opsins. These are G protein-coupled receptors characterized by their ability to bind a vitamin A based chromophore ( -cis-retinal) via a Schiff base linkage using a lysine residue in the 7th transmembrane a helix (Fig. 1). The primary events of image detection by the rods and cones occurs with the absorption of a photon of light by ll-r/r-retinal and its photoisomerization to the AUtrans state (Bums Baylor 2001, Menon et al 2001). Although photoreception is best understood in retinal rods and cones, photoreception is not confined to these structures. In non-mammalian... 

In such a way we were able to conclude that the illumination of suspensions of photoreceptor outer segments by 450 nm light at 77°K, which was known to result in the rhodopsin— prelumirhodopsin transition (corresponding to 11-cis-retinal— transretinal photoisomerization of chromophore), leads also to the appearance of some reduction centers and to the conformational change of membrane. 

It is necessary to differentiate between reactions where the two identical moieties undergoing photocyclodimerization, i.e. the chromophores, are part of the same molecule (such reactions are formally photoisomerizations with coincident ring formation) on the one hand and intermolecular photocyclodimerizations on the other. The former reactions, which will be treated first, can occur in molecules where the two (identical) moieties are linked together by a simple chain (to afford polycyclic systems), or by a ring system (to afford cage compounds). 

The photoisomerization of A.A -dibenzylstyrylacetamidc (1) to the tricyclic lactam 2 in methanol in 95% yield represents the first example of an intramolecular cycloaddition of a styrene chromophore to an arene.0... 

The Photoactive Yellow Protein (PYP) is thought to be the photoreceptor responsible for the negative phototaxis of the bacterium Halorhodospira halophila [1]. Its chromophore, the deprotonated 4-hydroxycinnamic (or p-coumaric) acid, is covalently linked to the side chain of the Cys69 residue by a thioester bond. Trans-cis photoisomerization of the chromophore was proved to occur during the early steps of the PYP photocycle. Nevertheless, the reaction pathway leading to the cis isomer is still discussed (for a review, see ref. [2]). Time-resolved spectroscopy showed that it involves subpicosecond and picosecond components [3-7], some of which could correspond to a flipping motion of the chromophore carbonyl group [8,9]. 

We have presented the first published results of a QM/MM wavepacket dynamics study of a photochemical reaction. The photoisomerization mechanism for the GFP chromophore that we observe has the signatures of HT motion, even in the complete absence of an environment. The HT mechanism is aborted in both the gas phase and solution, but the... 

Retinol A. can be enzymically formed from retinoic acid. B. is transported from the intestine to the liver in chylomicrons. C. is the light-absorbing portion of rhodopsin. D. is phosphorylated and dephosphorylated during the visual cycle. E. mediates most of the actions of the retinoids. Correct answer = B. Retinyf esters are incorporated into chylomicrons. Retinoic acid cannot be reduced to retinol. Retinal, the aldehyde form of retinol, is the chromophore for rhodopsin. Retinal is photoisomerized during the visual cycle. Retinoic acid, not retinol, is the most important retinoid. 

Studies by Nishiyama and Fujihara [149] utilizing azobenzene derivative (27) as isomerizable chromophores have demonstrated the importance of reaction cavity free volume in L-B films. The L-B films of amphiphilic derivative 4-octyl-4 -(3-carboxytrimethyleneoxy)-azobenzene (27) upon irradiation was found to be stable, no geometric isomerization of the azobennzene moiety occurred. This compound forms L-B films with water soluble polyallylamine 28 at an air-water interface. Reversible cis-trans photoisomerization occurs in the film containing 28. The reversible photoisomerization reaction in polyion complexed films is thought to occur because of the increased area per molecule provided in the film. The cross sections of molecule 27 in the pure film and in film containing 28 were estimated to be 0.28 and 0.39 nm2. Such an increased area per molecule... 

So far, various kinds of polymers which change their conformation reversibly by photoirradiation have been reported [1-6]. The polymers contain pendant or backbone photoisomerizable chromophores, and the molecular property changes, such as geometrical structure or dipole moment changes, control the conformation. The polymers change their conformation in proportion to the number of photoisomerized chromophores. Thus, when the polymers contain more photoisomerizable chromophores and absorb more photons, the conformation changes more. Physical and chemical properties associated with the conformation changes also vary with the number of absorbed photons. 

These conclusions are still consistent with the finding that significant conformational differences between Pr and Pfr do in fact exist ([65,147] for reviews see [8c, 148]). They can be rationalized—albeit not with conclusive rigour—by a conformational adaptation of the apoprotein part located around the bilatriene-binding pocket, following the Z E photoisomerization of the chromophore. This local change then should suffice to determine through bilatriene chromophore-protein interactions the spectroscopic characteristics of the chromophore as well as stability and reactivity of the two photochromic forms of phytochrome. 

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