Shifts intermediate

I and II. At very low temperatures a transient form photorhodopsin with a wavelength maximum at 580 nm may precede bathorhodopsin.461b,501-502a Furthermore, nanosecond photolysis of rhodopsin has revealed a blue-shifted intermediate that follows bathorhodopsin within 40 ns and decays into lumirhodopsin.500,503,504 The overall result is the light-induced isomerization of the bound 11-czs-retinal to all-fraus-retinal (Eq. 23-38) and free opsin. Tire free opsin can then combine with a new molecule of 11-czs-retinal to complete the photochemical cycle. 

Dehydronorcamphor (1, norborn-5-en-2-one) was first reported to undergo, via a 1,3-shift intermediate product (i.e. bicyclo[3.2.0]hept-2-en-7-one, 2), quantitative photolytic fragmentation into ketene and cyclopentadiene in a variety of solvents at temperatures from — 70 to 25°C with a quantum yield of 0.25. -... 

The reaction of LiAlH4 with SnCU in diethyl ether at low temperature can be followed in the Mossbauer spectrum [93]. The initial SnCU-etherate complex has a chemical isomer shift intermediate between the final product SnH4 and an intermediate compound assumed to be Sn(AlH4)4. At — 100°C the reaction is slow, but at —80°C the Sn(AlH4)4 is gradually formed, and this decomposes slowly to SnH4 at —40°C. /3-tin is the end-product at —35°C. 

In two earlier seetions, we introduced the speetra of some other commonly encountered types of systems. The NMR speetra of both styrene oxide (Fig. 5.10) and vinyl acetate (Fig. 5.17) contain examples of AMX systems, where M, being in the middle of the alphabet, indicates a chemical shift intermediate between A and X. That is, aU three ehemical shifts (A, M, and X) are separated widely. trans-Cmnarmc acid (Fig. 5.16) is an example of an AX system. 

V (Fig. lOf) produces a shift intermediate between tho.se due to -C-OH in hydroquinone and to -C=0 in benzoquinone. It has been si gesled 125.38) that such an intermediate shift corresponds to an intermediate functionality involving a bridged structure, discussed below. Typical shifts between the C 1.V peak from the oxidized sample and the graphitic C l.v peak are 1.5 cV for -OH functionality, 2.0 eV for the bridged structure, 3.2 eV for a C=0-typc functionality, and around 4.2 eV for carboxyl (COOH/CO5) or ester (COOR)-type functionalities. Features due to 7t — 7t transitions occur at shifts of around 6.1 eV. 

Gensch T, Strassburger JM, Gartner W and Braslavsky SE (1998) Volume and enthalpy changes upon photoexci tation of bovine rhodopsin derived from optoacoustic studies by using an equilibrium between bathorho dopsin and blue-shifted intermediate. Israel Journal of Chemistry 38 231 236. 

Craven, C.J., Derix, N.M., Hendriks, J., Boelens, R., Hellingwerf, K.J., and Kaptein, R., Probing the nature of the blue-shifted intermediate of photoactive yellow protein in solation by NMR Hydro-gen-deuterium exchange data and pH studies. Biochemistry, 39, 47, 14392-14399, 2000. 

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