13C-NMR Signal Enhancement by using Parahydrogen Induced Polarization and Appropriate Pulse Sequences.

M. ROTH; R. H. ACOSTA; J. BARGON; H.W. SPIESS; A. KOCH; K. MÜNNEMANN

Angra dos Reis, Brasil

Congreso; 12th Nuclear Magnetic Resonance Users Meeting & 3rd Iberoamerican NMR Meeting.; 2009

Parahydrogen induced polarization (PHIP) has turned out to be a versatile technique to obtain hyperpolarized molecules exhibiting strong NMR signals via a chemical approach. PHIP makes use of breaking the initially high symmetry of parahydrogen during homogeneously catalyzed hydrogenations of unsaturated substrates and, therefore, of the creation of nonequivalent protons in the products. Consequently, the population of the energy levels of their spin states deviates from the Boltzmann distribution characteristic for systems in thermal equilibrium. This leads to absorption and emission signals in the NMR spectra if recorded in situ and a theoretical signal increase of up to 105, which is in practice limited by relaxation processes in the product. Transfer of polarization to hetero-nuclei can be implemented randomly in weak magnetic fields or selectively via special pulse sequences. Optimization of polarization transfer to e.g. 13C is crucial for applications like metabolic imaging where the highest possible 13C polarization is required to obtain high SNR images