The rotational, strengths of the two longer wavelength transitions B 2U ' B lU ' of four mononucleosides (adenosine~ guanosine, uridine and cytidine) as a function of the glycosidic rotational angles have been investigated theoretically.The transition in each base is characterized by transition monopoles; the sugar is treated as a sum of bond pol arizabilities.The interaction among these polarizabilities is also considered.Rotational strengths were calculated using three different sets of transition monopoles and many combinations of bond polarizabilities.t'le conclude that adenosine, uridine and cytidine may have primarily one conformation, but that in guanosine the base is not definitely fixed with respect to the ribose.Calculation on different anomeric nucleosides of adenosine and uridine shows that the configuration at the anomeric carbon eCl I) determines the sign of the optical rotation.The configuration at C2 1 influences the glycosidic angular dependence of rotational strength more profoundly than that at C3 1 and C5 1 • These results are in good agreement with experiments.The signs and magnitude ?f the c~lculated rotational strengths are in good agreement with experiment for the anti conformation of all the isomers of adenosine.As the conformation of the nucleosides in B-form ..-2-DNA is quite different from the anti form~ we calculate that the rotationals trengths of 'the nucl eos i des in the po lynucl eottde are very different from those in solution, ';; ....
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Teng et al. (1971) studied this question.