Observation of Signal Enhancement via PHIP in a symmetric molecule. Experiments and a preliminary model

M. B. FRANZONI; L. BULJUBASICH; H. W. SPIESS; K. MÜNNEMANN

Conferencia; Euromar 2011; 2011

Two parahydrogen protons inserted in a molecule with symmetric structure occupy magnetically equivalent positions and, consequently, should remain in a singlet state, an NMR silent state. Surprisingly, this is not always the case and hyperpolarized signals from symmetric molecules can be observed1. Particularly, we have observed significant NMR signal enhancement during the parahydrogenation of acetylene dicarboxylic acid dimethylester, even though it is a symmetrical molecule and the same remains true for its product after a hydrogenation reaction. In this work we present new experiments where the behavior of this symmetric molecule in presence of different magnetic fields and for different evolution periods is studied. In this way, we were able to monitor the spin system evolving as a weak or as a strongly coupled one. By means of these experiments we obtained some important hints to model in a simple way the dominant relaxation mechanisms in the molecule2,3  in order to explain the unexpected observations