Retinal irradiation

Pulse radiolysis is used also for preparation of excited states of dienes and polyenes. This is done by irradiation of the diene/polyene in toluene solution. The radiolysis of toluene yield high concentration of molecules in the triplet excited state of the solute. Wilbrandt and coworkers61 pulse-radiolysed 1 mM solution of al I -lrans-1,3,5-heptatriene in toluene solution and observed the absorption spectra of the triplet state of the heptatriene with a maximum at 315 nm. The same group62 produced and measured the absorption spectra of several isomeric retinals in their lowest excited triplet state by pulse irradiation of their dilute solution in Ar-saturated benzene containing 10 2 M naphthalene. Nakabayashi and coworkers63 prepared the lowest triplet states of 1,3-cyclohexadiene,... 

Fig. 2.162. Absorption spectra of Amphiopl expressed in HEK293s cells (a) and the HPLC patterns of retinal oximes (b). Absorption spectra and the HPLC patterns were measured before (a, curve 1, and b, top trace) and after irradiation at 520 nm for 2 min (a, curve 2, and b, middle trace). The HPLC pattern of retinal oximes extracted from a mixture of irradiated and non-irradiated bovine rhodopsin in equal amounts is indicated as a reference (b, bottom trace). The absorption maxima of the original pigment and its phoroproduct are shown in panel (a). Reprinted with permission from M. Koyanagi et al. [334].

Cryptochromes and inner retinal non-visual irradiance detection... 

Foster Simplistically, in entrainment the rods and cones provide transitional information at the sharp junction between a LD cycle, and the inner retinal opsins provide irradiance information. What was striking about that rodless-coneless mouse under dim LD cycles is that it was phase advanced and the onsets were bouncing all over the place. Something about the precision of entrainment is lost with the rods and cones under relatively low light conditions. 

It now appears that nearly, if not all, chordates are tetrachromatic in retinal capability and it would be very strange if this capability was not used to process chrominance as well as luminance information. It is also clear that the human retina is tetrachromatic and that the human processes all of the available information (in spite of a blockage of irradiation at wavelengths shorter than 400 nm by the lens). 

Data is also shown for bovine rhodopsin, 63, for comparison. The hydroretinals 66-68 presumably assume 9-cis or 11 -cis like conformations when bound to opsin. Retinals 67 and 68 form non-bleachable pigments, i.e., no change in their A, occurs upon exposure to room light irradiation by UV light leads to decomposition products instead of separation of the chromophore from opsin. a In MeOH. In case of split chromophores the absorption maxima of the enal moieties are given. b Protonated Schiff base with n-butylamine in MeOH. ... 

Fig. 4. NME- spectra of all Irans retinal and the mixture obtained bv irradiation.

In the NMR spectrum of the irradiated retinal, the C-1, C-5, and C-9 methyl peaks remained unchanged and we do not observe a splitting in the spectrum of the mixture. But on the other hand, we notice, besides the C-13 methyl peak at 7.70 t, a peak at 7.88 t with a doublet shape (J = 1 Hz.). The integrated spectrum shows that the peaks altogether correspond to three protons. The peak at 7.88 r corresponds to the C-13-methyl of the 13-ct s isomer of the retinal. An upheld shift of 0.18 ppm when we change from the trans to the cis derivative is in perfect agreement with many examples of this kind. 

Earlier in this section we mentioned that 1 and 2 were essentially non-interconvertible, and this is generally true for alkenes. However, it is worth keeping in mind that isomerization can occur in certain cases, and this is usually brought about by irradiation with light of a particular wavelength. An example is isomerization of cis- and /raws-retinal, which is considered briefly in the Problems section. 

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