parahydrogen Induced Polarization by Homogeneous Catalysis

LISANDRO BULJUBASICH; MARÍA BELÉN FRANZONI; KERSTIN MÜNNEMANN

Topics in Current Chemistry - HYPERPOLARIZATION METHODS IN NMR SPECTROSCOPY

Springer Berlin Heidelberg

Lugar: Heidelberg; Año: 2013; p. 1 - 42

 The alignment of the nuclear spins in parahydrogen can be transferred to other molecules by a homogeneously catalyzed hydrogenation reaction resulting in dramatically enhanced NMR signals. In this chapter we introduce the involved theoretical concepts by two different approaches: the well known, intuitive population approach and the more complex but more complete density operator formalism. Furthermore, we present two interesting applications of PHIP employing homogeneous catalysis. The first demonstrates the feasibility of using PHIP hyperpolarized molecules as contrast agents in 1H MRI. The contrast arises from the J-coupling induced rephasing of the NMR signal of molecules hyperpolarized via PHIP. It allows for the discrimination of a small amount of hyperpolarized molecules from a large background signal and may open up unprecedented opportunities to use the standard MRI nucleus 1H for, e.g., metabolic imaging in the future. The second application shows  the possibility of continuously producing  hyperpolarization via  PHIP by employing hollow fiber membranes. The continuous generation of hyperpolarization can overcome the problem of fast relaxation times inherent in all hyperpolarization techniques employed in liquid-state NMR. It allows, for instance, the recording of a reliable 2D spectrum much faster than performing the same experiment with thermally  polarized  protons. The  membrane  technique  can  be  straightforwardly extended to produce a continuous flow of a hyperpolarized liquid for MRI enabling important applications in natural sciences and medicine.