title: TD-DFT investigation of the magnetic circular dichroism spectra of some purine and pyrimidine bases of nucleic acids.
abstract: 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.
authors: †Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping, Sweden.
authors: Tobias
authors: T
authors: Fahleson
authors: †Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping, Sweden.
authors: Joanna
authors: J
authors: Kauczor
authors: †Department of Physics, Chemistry and Biology, Linköping University, SE-581 83 Linköping, Sweden.
authors: Patrick
authors: P
authors: Norman
authors: ‡Istituto di Chimica dei Composti Organometallici (ICCOM-CNR), Area della Ricerca del CNR, Via Moruzzi 1, I-56124 Pisa, Italy.
authors: Fabrizio
authors: F
authors: Santoro
authors: §Istituto di Biostrutture e Bioimmagini-CNR, Via Mezzocannone 6, I-80134 Napoli, Italy.
authors: Roberto
authors: R
authors: Improta
authors: ∥Dipartimento di Scienze Chimiche e Farmaceutiche, Università degli Studi di Trieste, Via L. Giorgieri 1, I-34127 Trieste, Italy.|⊥Aarhus Institute of Advanced Studies, Aarhus University, DK-8000 Aarhus C, Denmark.
authors: Sonia
authors: S
authors: Coriani
mesh_terms: D002942:Circular Dichroism; D003198:Computer Simulation; D003596:Cytosine / Q000737:chemistry*; D005740:Gases / Q000737:chemistry; D008956:Models, Chemical; D012997:Solvents / Q000737:chemistry; D013941:Thymine / Q000737:chemistry*; D014498:Uracil / Q000737:chemistry*; D014867:Water / Q000737:chemistry
chemical_list: D005740:Gases; D012997:Solvents; D014867:Water; D014498:Uracil; D003596:Cytosine; D013941:Thymine