Long-Lived 1H Singlet Spin States Originating from Para-Hydrogen in Cs-Symmetric Molecules Stored for Minutes in High Magnetic Fields

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

JOURNAL OF THE AMERICAN CHEMICAL SOCIETY

AMER CHEMICAL SOC

Lugar: Washington; Año: 2012 vol. 134 p. 10393 - 10396

0002-7863

Nuclear  magnetic  resonance  (NMR)  is a very powerful tool in physics, chemistry, and life sciences, although limited by low sensitivity. This problem can be overcome  by  hyperpolarization  techniques  dramatically enhancing  the  NMR  signal.  However, this approach  is restricted to relatively short time scales depending on the nuclear  spin-lattice  relaxation  time  T1 in  the  range  of seconds. This makes long-lived singlet states very useful as a  way  to  extend  the  hyperpolarization  lifetimes.  Para-hydrogen  induced  polarization  (PHIP)  is  particularly suitable,  because  para-H2 possesses  singlet  symmetry. Most PHIP  experiments, however,  are  performed on asymmetric  molecules,  and  the  initial  singlet  state  is directly  converted  to  a  NMR  observable  triplet  state decaying with T1 , in the order of seconds. We demonstrate that  in  symmetric  molecules,  a  long-lived  singlet  state created by PHIP can be stored for several minutes on protons  in  high  magnetic fi elds.  Subsequently,  it  is converted into observable high nonthermal magnetization by controlled singlet − triplet conversion via level anticrossing.