Fahleson, T., Kauczor, J., Norman, P., Santoro, F., Improta, R., Coriani, S., Fahleson, T., Kauczor, J., Norman, P., Santoro, F., Improta, R., and Coriani, S.
We present a computational study of the magnetic circular dichroism (MCD) spectra in the 200-300 nm wavelength region of purine and its derivative hypoxanthine, as well as of the pyrimidine bases of nucleic acids uracil, thymine, and cytosine, using the B3LYP and CAM-B3LYP functionals. Solvent effects are investigated within the polarizable continuum model and by inclusion of explicit water molecules. In general, the computed spectra are found to be in good agreement with the experimental ones, apart from some overall blue shifts. Both the pseudo-A term shape of the MCD spectra of the purines and the B term shape of the spectra of pyrimidine bases are reproduced. Our calculations also correctly reproduce the reversed phase of the MCD bands in purine compared to that of its derivatives present in nucleic acids. Solvent effects are sizable and system specific, but they do not in general alter the qualitative shape of the spectra. The bands are dominated by the bright π → π∗ transitions, and our calculations in solution nicely reproduce their energy differences, improving the estimates obtained in the gas phase. Shoulders are predicted for purine and uracil due to n → π∗ excitations, but they are too weak to be observed in the experiment. © 2015 American Chemical Society., References: Mason, W.R., (2007) A Practical Guide to Magnetic Circular Dichroism Spectroscopy, , Wiley: New York; Voelter, W., Records, R., Bunnenberg, E., Djerassi, C., Magnetic Circular Dichroism Studies. VI. Investigation of Some Purines, Pyrimidines, and Nucleosides (1968) J. Am. Chem. Soc., 90, p. 6163; Djerassi, C., Bunnenberg, E., Elder, D.L., Organic Chemical Applications of Magnetic Circular Dichroism (1971) Pure Appl. Chem., 25, pp. 57-90; Coriani, S., Jørgensen, P., Ruud, K., Rizzo, A., Olsen, J., Ab Initio Determinations of Magnetic Circular Dichroism (1999) Chem. Phys. Lett., 300, pp. 61-68; Coriani, S., Hättig, C., Jørgensen, P., Helgaker, T., Gauge-Origin Independent Magneto-Optical Activity within Coupled Cluster Response Theory (2000) J. Chem. Phys., 113, pp. 3561-3572; Kjærgaard, T., Jansik, B., Jørgensen, P., Coriani, S., Michl, J., Gauge-Origin-Independent Coupled Cluster Singles and Doubles Calculation of Magnetic Circular Dichroism of Azabenzenes and Phosphabenzene using London Orbitals (2007) J. Phys. Chem. A, 111, pp. 11278-11286; Seth, M., Ziegler, T., Banerjee, A., Autschbach, J., Van Gisbergen, S.J.A., Baerends, E.J., Calculation of the A Term of Magnetic Circular Dichroism Based on Time Dependent-Density Functional Theory I. Formulation and Implementation (2004) J. Chem. Phys., 120, pp. 10942-10954; Seth, M., Ziegler, T., Autschbach, J., Ab Initio Calculation of the C/D Ratio of Magnetic Circular Dichroism (2005) J. Chem. Phys., 122, p. 094112; Seth, M., Ziegler, T., Calculation of the B term of Magnetic Circular Dichroism. A Time-Dependent Density Functional Approach (2007) J. Chem. Theory Comput., 3, pp. 434-447; Seth, M., Ziegler, T., Calculation of Magnetic Circular Dichroism Spectra with Time-Dependent Density Functional Theory (2010) Adv. Inorg. Chem., 62, pp. 41-109; Solheim, H., Frediani, L., Ruud, K., Coriani, S., An IEF-PCM Study of Solvent Effects on the Faraday B Term of MCD (2008) Theor. Chem. Acc., 119, pp. 231-244; Solhe