"inverse" experiments on non-inverse probe and gradient on routine service 300

Kirk Marat (kirk_marat@umanitoba.ca)
Mon, 19 Apr 1999 13:20:08 -0400

A so-called inverse probe has the inner coil tuned to proton and
the outer coil tuned to the X-nucleus, typically 13C or 15N. This
gives optimum proton sensitivity and optimum decoupler B2 homogeneity
as seen by the inner observe coil. This last characteristic is important
because of the large number of decoupler 180 degree pulses in these
"inverse" experiments. A so-called Bruker C/H dual probe, on the other
hand, has the inner coil tuned to carbon (optimum sensitivity) and a
slightly
larger outer coil for proton.

My first question is, has anyone ever tried to use a C/H dual probe for
inverse experiments
such as HSQC, HMBC or HMQC? And what sort of performance did they get. The
use of
composite pulses for the decoupler 180s may be of some use. The reason I
am curious, is that we are currently in the process of replacing our AM300
console with
one that is inverse capable, and we would like to know if we can do some
routine inverse experiments with our C/H dual probe and at least temporarily
avoid
the expense of a dedicated inverse probe.

My next question concerns gradients. I have no doubt of the utility of
gradients on
higher field instruments, especially for proteins, etc. in H2O. How about
for a
routine service 300 MHz instrument? Is a single axis gradient set-up for
coherence
selection worth the expense? Can you really get quick HMQCs etc.? It seems
to me
that at lower fields, you need a number of scans for signal to noise reasons
anyway, so that
cutting down the phase cycle with gradients doesn't get you much. What have
others found?

Cheers,
-Kirk

Kirk Marat, Ph.D. NMR Facility Manager
Dept. of Chemistry and Prairie Regional NMR Centre
University of Manitoba
Winnipeg, Manitoba, R3T 2N2, CANADA
ph. (204) 474-6259 FAX (204) 474-7608
kirk_marat@umanitoba.ca