Dimerization, wavelength dependence

Freeman, S. E., et al., Wavelength dependence of pyrimidine dimer formation in DNA of human skin irradiated in situ with ultraviolet light, Proc. Natl. Acad. Sci. U S A 86,... 

Matsunaga, T. Hieda, K. Nikaido, O. Wavelength dependent formation of th5mine dimers and (6-4) photoproducts in DNA by monochromatic ultraviolet light ranging from 150 to 365 nm. Photochem. Photobiol. 1991, 54 (3), 403-410. 

The quantum yield for formation of dimers in solutions of TpT (16a, R = H) is about 0.01, wavelength dependent, and the yield for dissociation of the dimers is about 0.5, wavelength independent. At... 

The cross sections for formation of the two dimers are similar, but not identical, with those for the formation of two of the dimers from UpU, and the wavelength dependencies are similar. Hydrate formation occurs more rapidly in d-UpU than in UpU. The marked quantitative and qualitative differences in the photochemistry of these two closely similar dinucleotides, along with the additional difference in results observed with poly U, to be discussed below, make it clear that the factors influencing the course of the photolysis of polynucleotides are not well known. It must be pointed out that the structures of the various... 

Fig. 19. Wavelength dependence of the cross sections for formation of the hydrate, d-UpU, and the two dimers in the photolysis of d-UpU (Helleiner, Pearson, and Johns73).

Yamada H, Hieda K (1992) Wavelength dependence (150-290 nm) of the formation of the cyclobutane dimer and the (6-4) photoproduct of thymine. Photochem Photobiol 55 541-548 Yan M, Becker D, Summerfield S, Renke P, Sevilla MD (1992) Relative abundance and reactivity of primary ion radicals in y-irradiated DNA at low temperatures. 2. Single- vs double-stranded DNA. J Phys Chem 96 1983-1989... 

Photodissociation of the dimer [2-2] to the pyridinyl radical (2 ) occurs readily in thin films at low temperatures or in acetonitrile solutions. Although excitation spectra could not be obtained from these experiments a new technique was used 1) the wavelength dependence of radical formation from dimer generated electro-chemically in small amounts, 2) the measurement of the radical produced by a rapid jump to a potential at which reoxidation of the radical takes place. Since the photodissociation spectra of dimers may well determine their practical use, a convenient procedure is useful. 

Using 1,1 -linked uracils, intramolecular dimerization is wavelength dependent and also reversible, as shown in Scheme 27, (88CJC1027). Such a photoreversible reaction provides a rare example of a C=C to C=N [2 -I- 2]-photocycloaddition (76TL449) (Scheme 27). 

A.G.J. Buma, A.H. Engelen, W.W.C. Gieskes (1997). Wavelength dependent induction of thymine dimers and growth rate reduction in the marine diatom Cyclotella sp. exposed to ultraviolet radiation. Mar. Ecol. Progr. Ser., 153,91-97. 

Equilibrium between monomer and aggregates with different absorption characteristics is hkely to result in wavelength-dependent chemistry. For example, 1,3-cyclohexadiene upon irradiation with 254-nm light gives 1,3,5-hexatriene as the only product but irradiation at 313 nm produces dimers (Scheme 10)." Upon irradiation at 254 nm, mainly the monomer is expected, while at 313 nm the dimer is excited with the two yielding different products. 

Irradiation of ethyleneimine (341,342) with light of short wavelength ia the gas phase has been carried out direcdy and with sensitization (343—349). Photolysis products found were hydrogen, nitrogen, ethylene, ammonium, saturated hydrocarbons (methane, ethane, propane, / -butane), and the dimer of the ethyleneimino radical. The nature and the amount of the reaction products is highly dependent on the conditions used. For example, the photoproducts identified ia a fast flow photoreactor iacluded hydrocyanic acid and acetonitrile (345), ia addition to those found ia a steady state system. The reaction of hydrogen radicals with ethyleneimine results ia the formation of hydrocyanic acid ia addition to methane (350). Important processes ia the photolysis of ethyleneimine are nitrene extmsion and homolysis of the N—H bond, as suggested and simulated by ab initio SCF calculations (351). The occurrence of ethyleneimine as an iatermediate ia the photolytic formation of hydrocyanic acid from acetylene and ammonia ia the atmosphere of the planet Jupiter has been postulated (352), but is disputed (353). 

---