Luminescence of Dinucleotides at 77°K

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Abstract
The ultraviolet rays-induced excited states and energy transfer in dinucleotides at 77°K have been studied by luminescence measurements. From the investigation of concentration dependence, the anomalous fluorescence of several stacked dinucleotides can be regarded as the intramolecular excimer fluorescence. In addition, the dinucleotides CpA(cytidylyl(3'–5')adenosine), UpA(uridylyl(3'–5')adenosine), ApG(adenylyl(3'–5')guanosine), and GpA(guanylyl(3'–5')adenosine) show the normal fluorescence of A(adenosine) in CpA and UpA or G(guanosine) in ApG and GpA as well as the excimer fluorescence. However, the fluorescence of GpC(guanylyl(3'–5')cytidine) and CpG(cytidylyl(3'–5')guanosine) is the sum of independent fluorescence of G and C(cytidine). On the other hand, the phosphorescence of dinucleotides containing A and C, U(uridine), or G is always characteristic of A while that of GpC and CpG is identical to G. In all the dinucleotides containing A, the energy transfer takes place via the excimer state from C, U, or G to the triplet state of A. In the case of CpA, UpA, ApG, and GpA, a part of energy is converted to the normal fluorescence of A in CpA and UpA or G in ApG and GpA. Therefore, it is assumed that in above four dinucleotides the excimer fluorescence process can compete with normal fluorescence one. In the case of GpC and CpG, the intramolecular triplet-triplet transfer occurs from C to G.

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