ULTRAVIOLET SPECTRA OF MATRIX-ISOLATED CYTOSINE AND SOME OF ITS DERIVATIVES, AND THE EFFECT OF FURTHER ULTRAVIOLET IRRADIATION

$^{1}$ M. Szczenniak, K. Szczepaniak, J. S. Kwiatkowaki, N. KuBulat, and W. B. Person, J. Am. Chem. Soc., 110. 8319, (1988); see also M. J. Nowak, L. Lapinski, J. Fulara, Spectrochim. Acta, to be published. We are grateful for support from NIH Research Grant No. 32988.Author Institution: Department of Chemistry, University of FloridaWe report here the UV spectra measured for cytocine isolated in an Argon matrix, together with similar studies for 1-methylcytosine and several cytosines halogenated at the 5- position. It is shown that the UV spectrum of this isolated cytosine can be interpreted as the sum of the spectra of 1-methylcytomine and of 5-fluorocytosine. Since the latter is a model for the hydroxy tautomer of cytosine, and the former is a model for the oxo tautomex of cytosine, this observation provides further confirmation of the conclusion1 that both tautomeric forms exist in equilibrium in this hydrophobic environment. Previous studies of the infrared spectra of cytosine isolated in an argon matrix1 have shown that UV photolysis of the isolated cytosine results in the selective photodecomposition of the oxo form of the molecule, leaving higher concentration of the hydroxy tautomer in the matrix after the irradiation. We believe that the key to understanding this selective photo-decomposition is provided by the comparison of the transmittance of the CsI filter through which the matrix was irradiated with the absorption from each of the two model compounds 1. methylcytoaine (as a model for the oxo tautomer), and 5-fluorocytosine (as a model for the hydroxy tautomer

FAR INFRARED INTENSITY STUDIES ON CHARGE TRANSFER COMPLEXES OF IODINE AND IODINE MONOCHLORIDE

Financial support from Public Health Service Research Grant No. GM-10168 from the Division of General Medicine, PHS, is gratefully acknowledged. $^{1}$ W. B. Person, R. E. Humphrey, W. A. Deskin and A. I. Popov, J. Am. Chem, Soc. 80, 2049 (1958). $^{2}$ W. B. Person, R. E. Humphrey and A. I. Popov, J. Am Chem. Soc. 81, 273 (1959). $^{3}$ W. B. Person, R. E. Erickson and R. E. Buckles, J. Am. Chem. Soc. 82, 29 (1960). $^{4}$ H. B. Friedrich and W. B. Person, J. Chem. Phys. 44, 2161 (1966).Author Institution: Department of Chemistry, University of IowaThe infrared intensities of the $\nu(I-CI), \nu(I-I)$ and $\nu (D-A)$ vibrational bands found in charge-transfer complexes of n and $\pi$ electron donors with $I_{2}$ and ICl have been measured in benzene and n-heptane solutions. A Beckman IR-11 spectrometer was used together with a cell constructed of high density polyethylene. Pathlength calibrations have been carried out using bands of known intensity in pure liquid $CHCl_{2} CCl_{4}$ and benzene, and it has been shown that the pathlength variation when using such a cell is sufficiently small to give good Beers Law plots and intensity values with a random error of less than $\pm 12$. The results extend the $earlier^{1-2}$ higher frequency intensity studies on complexes with $Br_{2}, ICl$ and ICN. Quantitative confirmation that the intensity of the $\nu(N-I)$ vibration is significantly lower than that of the $\nu (I-Cl)$ vibration in the pyridine-ICl complex has been obtained, indicating a smaller vibronic $effect^{4}$ in the former vibration

ABSOLUTE INFRARED INTENSITIES OF THE FUNDAMENTAL VIBRATIONS OF POLYCRYSTALLINE FILMS OF HALOGEN DERIVATIVES OF METHANE.

$^{1}$ H. Yamada and W. B. Person, J. Chem. Phys., 40, 309 (1964). $^{2}$ J. L. Hollenberg and D. A. Dows, J. Chem. Phys., 37, 1300 (1962). $^{3}$A. Kimoto and H. Yamada, Bull. of the Chem. Soc. Japan. 40, 243 (1967). $^{4}$Gas phase intensities: J. Herranz, R. de la Cierva, and J. Morcillo, Anales real. soc. espan, fis. y quim. (Madrid) 55(A), 59 (1959).Author Institution: Department of Chemistry, University of FloridaThe absolute in frared absorption intensities of the fundamental bands of some halogen derivatives of methane have been measured in the solid state at liquid nitrogen temperatures, using standard $techniques.^{1-3}$ Comparison of the results with the intensities obtained for these bands in the gas phase reveals that the changes are relatively small, especially for derivatives which do not contain H atoms. Primarily, results for chloroform $(CC/_{3}H)^{3}$ and trichlorofluoro methane $(CC/_{3}F)^{4}$ will be presented. Here the C-H stretch in $CC/_{3}H$ increases in intensity from gas to solid by a factor of $30,^{3}$ while the corresponding C-F stretching vibration in $CC/_{2}F$ changes only by a factor of 1.4. Other bands for both molecules show smaller changes (about a factor of 2). Financial support from the Army Research Office (Durham) and from Public Health Service Research Grant No. GM 14648 is gratefully acknowledge