differences between hydrogen bonding

I am trying (using Gaussian 94) to estimate the differences between hydrogen bonding between A-T and 2-amino purine-T. I also have other base analogues with which I want to do the same. Would you please indicate me some references or some advices about the approach for such kind of studies?
  Thanks a lot in advance,
Vlad Cojocaru Max Planck Institut for Biophysical Chemistry Deparment: 060 Am Fassberg 11, 37077 Goettingen, Germany tel: ++49-551-201.1389 e-mail: Vlad.Cojocaru[ AT ]mpi-bpc.mpg.de