1 H NMR exploiting the para-hydrogen singlet state nature: hyperpolarization, contrast properties for imaging and long-lived states in Cs-symmetric molecules.

MARÍA BELÉN FRANZONI

Conferencia; GDch FGMR 34th Annual Discussion Meeting; 2012

The hydrogenation with parahydrogen (pH 2 ) is a promising technique to boost the low sensitivity in NMR experiments[1]. The Parahydrogen Induced Polarization (PHIP) technique involves a catalytic reaction in which hydrogen molecules enriched in the parastate are added to an unsaturated precursor. If the intrinsic symmetry of the pH 2 is broken in the product molecule, the resulting NMR spectrum intensities are strongly enhanced. In this talk, two methods which take advantage of the nature of the initial singlet state are introduced. Once the symmetry of the pH 2  state is broken, for example in high fields, the initial state and consequent evolution differs from the Boltzmann initial state. This difference promotes the use of PHIP technique as contrast agent for MRI, even in experiments where the observation of hyperpolarized signal is limited by the enormous amount of protons in the background [2]. In the second approach the relative short time scales that, depending on the spin-lattice relaxation time (T 1 ), restrict the NMR experiments are overcome. The singlet-state, which is immune to the dominant T 1  relaxation mechanisms in liquids, is preserved in a Cs-symmetrical molecule. This enables the storage of a hyperpolarized long-lived state for minutes in high fields and subsequent conversion into observable by controlled singlet-triplet transition via level anticrossing[3].  [1] Bowers, C. R. & Weitekamp, D. P. Phys. Rev. Lett.57, 2645–2648 (1986). [2] Dechent, J. F., Buljubasich, L., Schreiber, L. M., Spiess, H. W. &Münnemann, K. Phys. Chem. Chem. Phys. 14, 2346–2352(2012) [3] Franzoni, M. B., Buljubasich, L., Spiess, H. W. & Münnemann, K.  J. Am. Chem. Soc. (2012).doi:10.1021/ja304285s