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Spin simulation and iteration: the best way to analyze complex NMR signals
With ever increasing magnetic fields, the probability for higher order signals
is smaller than ever. However, spin systems such as e.g. AA'BB' are higher order
by definition, irrespective of field strength due to the magnetic inequivalence
of the spins (1). Furthermore, NMR multiplets can be very complicated and
difficult to analyze even if they are first order because many coupling
constants can contribute to the signal. A proton coupled to 4 non-equivalent H1s
should result in a 2 x 2 x 2 x 2 = 16 line multiplet. Rarely are 16 lines easily
visible, instead, due to overlap of some lines, complicated multiplets with
sometimes unexpected intensities arise. In such cases there are two
possibilities: (a) describe it as a multiplet without knowing the underlying
coupling constants or (b) fire up a spin simulation program and find out
what couplings are responsible for the complex multiplet.
Spin simulation/iteration has been implemented on all our data stations in the
form of a program called SpinWorks. A PDF document has been created and
can be found here
to assist in the usage of this program. SpinWorks is accessible through the
button Spin Simulation on the EZ NMR P+P panel but it can also be
downloaded for free from the University of Manitoba (http://www.umanitoba.ca/chemistry/nmr/spinworks/)
and installed on a Windows computer. It is a windows-based program!
The version implemented on our Linux machines is 2.5.5 but the U of Manitoba
site has newer versions available. It is typically prudent to not go with the
cutting edge latest version...
(1)
More often than not, these systems are first-order like but, strictly speaking,
they are not.
u500: second
attempt at finding the "ideal" probe
Much was said and written about the first, long attempt to install a
C13-optimized cryo probe on the u500. After much effort and time, we
returned to the old RT-probe.
This is about to change. In the first week of March, the installation of a
so-called dual cold probe will take place. While not as sensitive for C13
as the Xsens, at 1300:1 it is still ca. 5 times better than the current probe
while retaining the convenience of ProTune. Note that also the 2000:1
H1 sensitivity will be higher than any of our spectrometers, except the
v700 (in comparison, i600 is 1200:1).
In case you wonder about the reasons for the increase in sensitivity, here is a
short description
of what leads to this massive improvement.
u500 will be unavailable for about one or two weeks before returning,
hopefully, in great shape for C13 direct detection and H1.
Change from VNMRJ 2.1B to 2.3A
The new u500 cryoprobe cannot be operated with our current software
(VNMRJ 2.1B), therefore the spectrometer will be changed over to 2.3A. This
software level is already implemented on i600 and v700. It is
expected that after the completion of the u500 cryo probe installation,
all other spectrometers and data stations will be switched to 2.3A. There are
not many significant changes, other than data manipulation. A
PDF How-To document
is available with step-by-step instructions on how to do this.
Changes to the
i600
The i600 spectrometer has been upgraded and expanded to full
solid state capabilities. It is currently used as before the upgrade,
pending the solution of a few outstanding issues with Varian and until
decisions are made in the Department regarding the use of the
instrument.
Personnel changes in the NMR
lab
Lai Kong, who joined the NMR lab in the Department over 35 years ago,
retires at the end of March 2010. Lai worked part-time since 2006. Lai
is currently at the Olympics in Vancouver as a volunteer but will return
briefly at the end of March. Please join her NMR colleagues in thanking
her for a very long time of service for the betterment of NMR in this
Department and wishing her the very best for her retirement.
The list of upcoming changes is not
finished. The NMR supervisor, i.e. also the editor of NMR News, will
leave at the end of May 2010. How the Department exactly proceeds in
these difficult financial times re. NMR staff is unclear at the moment.
What is pretty obvious is that with these retirements and the loss of
Glen Bigam in 2009, the NMR facility has lost manpower while the number
of instruments and instrument complexity has actually gone up. Until
everything is sorted out, the best approach is to use some patience when
it comes to NMR issues.
26 years in the Department has been a very interesting part of my life.
I would like to thank everybody who expressed interest in the NMR
facility, and especially those who contributed with more than
encouraging words to the improvements and modernization in the NMR
facility. In case that this should turn out to be the last NMR News, I
wish everybody all the best!
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