This is the summary to my posting on the above subject.
My original question: Is there a difference in solubility in regular and
deuterated solvents (e.g. between CHCl3 and CDCl3, etc.)? Was there ever a
study on this? I'm thinking of small and moderately-sized molecules (not
proteins).
The replies:
~~~~~~~~
I would not be surprised if there were, in LC-NMR there is a significant
difference in the chromatographic properties of deuterated vs
non-deuterated solvents.
~~~~~~~~
Though just at the moment I can't recall particulars, there are certainly
solubility differences between H2O and D2O, attributable to the different
length and strength of the OH vs. OD bond, and the related difference in
hydrogen bonding. I would expect differences in nonpolar solvents, OTOH,
to be negligible.
~~~~~~~~~
Of course the solubilities are slightly different. But even in the case of
water, you can forget these differenes from our viewpoint. Far below of 1%.
~~~~~~~~
interesting and practical question. I don't know, but will pass on the
two related pieces of information I do have. It is well-known in LC-NMR
that elution times will vary between D2O and H2O. For solvent gradients
the difference is usually slight. I had one case of an isocratic
separation carefully optimized in H2O where the analyte simply didn't come
off at similar D2O concentrations until I washed the column. Spraul's
chapter of Albert's book attributes this primarily to differences between
pH and pD.
~~~~~~~~~
>From my protein folding days we had examples of the denaturation
temperatures of proteins being markedly different - up to 6 C - between
the two. The explanation was that the vibrational zero-point energy of an
H-bond was different than a D-bond because of the two-fold mass
difference. This effects both the water-water, water-protein, and
protein-protein H-bonds, so the effects were not predictable.
~~~~~~~~~
My off the cuff response is that in principle you should not see a
difference without taking rather careful measurements. However, in
practice some of the deuterated solvents, because of the way they are
manufactured, can be rather acidic (CDCL3, CD3CN), depending on the
supplier. This can affect solubility.
Interesting question - I would expect no effect or subtle effect,
since the only chemical property that is affected (as far as I know :-))
going from hydrogen to deuterium is kinetics. I don't think kinetics
affects solubility (other than perhaps speed of dissolution.
I could be wrong. :-)
However, this raises more specific questions (which might be useful to
find the answer)
Are hydrogen bonding forces different in deuterated compounds than
protonated? (if so, should affect solubility)
Does water dissociation affect solubility and is the constant different
for water and D2O?
~~~~~~~~~
The only times I've found a difference is when the regular solvent
contains another compound as a stabilizer. For example, regular CHCl3
often has a small amount of ethanol (I think) which can aid solubility.
You can always add a tiny amount of CD3OD to your CDCl3 if necessary.
~~~~~~~~~
I do not know a publication on isotope effects on the solubility, however
we investigated Dynamic isotope effects (M.Holz et al. J.Chem. Phys. 104,
669-679 (1996) and 114, 3174 -3181, (2001) and found by the way at least
in water differences of the solubility. D2O can be regarded as 8°C colder
H2O! I would suppose that in liquids with high dynamic isotope effects as
water, also larger differencies in the solubility can occur, than in
liquids with small effects.
~~~~~~~~~
We observed that starch has difficulties to gelatinize in D2O contrary to
H2O at 60-70°C
~~~~~~~~~
Based on the daily practice in our NMR lab., basically there is not any
difference in solubility between regular and deuterated solvents.
Nevertheless, sometimes a given regular solvent seams to be
more dissolving than the deuterated one, but the difference might be due
to the presence of impurities in the regular solvent that might
contribute to the process of dissolving.
--
Edward T. Chainani
Chemistry Department &
National Chemistry Instrumentation Center (NCIC)
Ateneo de Manila University
Loyola Heights, Quezon City
Philippines
phone: (632) 426-6001 loc. 5628
FAX: (632) 426-1323
e-mail: etch_at_chem.admu.edu.ph
Received on Tue Jun 15 2004 - 13:08:51 MST