Abstract
The recently theoretically described nuclear spin-induced circular dichroism (NSCD) is a promising method for the optical detection of nuclear magnetization. NSCD involves both optical excitations of the molecule and hyperfine interactions and, thus, it offers a means to realize a spectroscopy with spatially localized, high-resolution information. To survey the factors relating the molecular and electronic structure to the NSCD signal, we theoretically investigate NSCD of twenty structures of the four most common nucleic acid bases (adenine, guanine, thymine, cytosine). The NSCD signal correlates with the spatial distribution of the excited states and couplings between them, reflecting changes in molecular structure and conformation. This constitutes a marked difference to the nuclear magnetic resonance (NMR) chemical shift, which only reflects the local molecular structure in the ground electronic state. The calculated NSCD spectra are rationalized by means of changes in the electronic density and by a sum-over-states approach, which allows to identify the contributions of the individual excited states. Two separate contributions to NSCD are identified and their physical origins and relative magnitudes are discussed. The results underline NSCD spectroscopy as a plausible tool with a power for the identification of not only different molecules, but their specific structures as well.
Highlights
As resolving polarized inequivalent nuclear sites within one molecule
It may be speculated that nuclear spin-induced circular dichroism (NSCD) will be the method of choice over nuclear spin-induced optical rotation (NSOR) in spectroscopic investigations of molecules by the analogy of NSCD with natural and magnetic circular dichroism, which are much more popular methods than the corresponding birefringent effects of optical rotation and Faraday rotation
We begin with the discussion of the NSCD spectra of the pair cyt2/cyt[3] shown in Fig. 2 together with the difference densities corresponding to the changes of the electron cloud upon excitation from the electronic ground state to each excited state in question
Summary
As resolving polarized inequivalent nuclear sites within one molecule. The differences in rotation between molecules have already been experimentally verified[5], while high-resolution nuclear site specificity still awaits experimental confirmation. It may be speculated that NSCD will be the method of choice over NSOR in spectroscopic investigations of molecules by the analogy of NSCD with natural and magnetic circular dichroism, which are much more popular methods than the corresponding birefringent effects of optical rotation and Faraday rotation. Both the magnitude of the NSCD effect, its likely information-richer nature and the ability to single out a particular molecular species in the mixture - as it is, unlike NSOR, intimately dependent on the specific excited state in question - underlie this anticipation. This situation is observable in the case of Bd-term dominated spectra
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