  At the magnetic fields of common NMR instruments, electron Zeeman frequencies
are too high for efficient electron-nuclear dipolar cross-relaxation to occur
in solution. The rate of that process fades with the electron Zeeman frequency
as omega^{-2} - in the absence of isotropic hyperfine couplings, liquid state
dynamic nuclear polarisation (DNP) in high-field magnets is therefore
impractical. However, contact coupling and dipolar cross-relaxation are not the
only mechanisms that can move electron magnetisation to nuclei in liquids:
multiple cross-correlated (CC) relaxation processes also exist, involving
various combinations of interaction tensor anisotropies. The rates of some of
those processes have more favourable high-field behaviour than dipolar
cross-relaxation, but due to the difficulty of their numerical - and
particularly analytical - treatment, they remain largely uncharted. In this
communication, we report analytical evaluation of every rotationally driven
relaxation process in liquid state for 1e1n and 2e1n spin systems, as well as
numerical optimisations of the steady-state DNP with respect to spin
Hamiltonian parameters. A previously unreported cross-correlation DNP (CCDNP)
mechanism was identified for the 2e1n system, involving multiple relaxation
interference effects and inter-electron exchange coupling. Using simulations,
we found realistic spin Hamiltonian parameters that yield stronger nuclear
polarisation at high magnetic fields than dipolar cross-relaxation.
