TOCSY, HOHAHA, and gs-TOCSY

TOCSY TOtal Correlation SpectroscopY
HOHAHA HOmonuclear HArtmann- HAhn
gs-TOCSY gradient selected - TOtal Correlation SpectroscopY

Introduction:
In contrast to the COSY experiment , a fundamentally different method for the transfer of coupling information is utilized in the TOCSY experiment. The TOCSY (also called HOHAHA for HOmonuclear Hartmann- HAhn) experiment correlates protons that are in same spin system (i.e. along a peptide chain) but in reality protons are never more than 2 or 3 bonds apart from another proton. Mixing is achieved while a spin-lock field is applied, and ideally the effect of chemical shift is completely removed. This means, that basically all energy levels are equivalent or "degenerate", which leads to strongly coupled systems. The spin-lock pulses are termed "isotropic mixing" or Hartmann-Hahn mixing. Isotropic mixing leads to spectra with mixed phases (phase modulation), whereas Hartmann-Hahn mixing pure phases are obtained. The multiplets, even when generated over different mixing times, give rise to combinations of different mirror-symmetric multiplet patterns. Ideally cross peaks are formed between all nuclei in a spin system.

References:

TOCSY or HOHAHA:

  • L. Braunschweiler, R.R. Ernst, J. Magn. Reson. 1983, 53, 521-528.
  • A. Bax, D.G. Davis, J. Magn. Reson. 1985, 65, 355-360.
  • G.E. Martin, A.S. Zektzer, Two-Dimensional NMR Methods for Establishing Molecular Connectivity, VCH, Weinheim, 1998, 303-316.

    • gs-TOCSY:

  • R.E. Hurd, J. Magn. Reson. 1990, 87, 422-428.
  • A. Bax, D.G. Davis, J. Magn. Reson. 1985, 65, 355-360.
  • K.E. Kövér, D. Uhrín, V.J. Hubry, J. Magn. Reson. 1998, 130, 162-168.
    		•