Putting in my 2p worth (please forgive in advance if I'm out of date
here).
I think it's a pain that assigning ambiguously eg HB* on a single
resonance in a residue type assigned spin system doesn't behave in the
same way as it does in a sequence specifically assigned spin system i.e.
create an additional resonance and assign both HB2|HB3. I can appreciate
that for a non-residue type assigned spin system there are potential
problems with doing this - though even there I think that in the vast
majority of situations the same behaviour is going to be the most useful
one and unlikely to cause real world problems. I applaud the thinking that
users should really know what they imply by making a particular assignment
(do I know that both betas are actually here?), but in practice I find the
current behaviour a bit painful (where I've decided they are both here I'd
like the shortcut to save me the extra mouse clicks involved in creating
and assigning the additional resonance).
Similarly, the former shorthand (hba, hbb, etc) take up less
screen space than the HB2|HB3 type and are clear enough for me. There are
plenty of cases where initially ambiguous prochiral assignments are later
resolved and so will end up needing to be a & b and for the ones that
don't it doesn't really matter too much what we call them at the
assignment stage until we do have stereospecific info on them (if ever).
Also the distinction between prochirals and fully ambiguous single
resonances (e.g. methyl groups) is a bit spurious. Apart from practical
convenience, it seems to me that the argument is that the positions of a
methyl group are always equivalent because of motional averaging (is this
always true, even in low temp solids? What about e.g. -CHD2 type labelling
patterns?) - the same is surely essentially true for many prochirals that
exhibit degenerate chemical shifts.
Anyway, rant over.
Brian
Dr. Brian O. Smith ---------------------- B Smith at bio gla ac uk
Division of Biochemistry & Molecular Biology,
Institute Biomedical & Life Sciences,
Joseph Black Building, University of Glasgow, Glasgow G12 8QQ, UK.
Tel: 0141 330 5167/6459/3089 Fax: 0141 330 4600
