Handling Air Sensitive Samples ACSPRF Crystallography Boot Camp Thursday, August 4, 2004

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Handling Air Sensitive SamplesACS-PRF
Crystallography Boot CampThursday, August 4,
2004

• Paul G. Williard
• Brown University

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Structure determination methodologies

• Solid state
• X-ray crystallography
• results are not subject to interpretation
• have to grow crystals
• reactions happen in solution

• Gas phase
• Computational chemistry
• not synthetically challenging
• wide range of structures,
• transition states
• practical size limitations
• has to be supported by experimental evidence
• reactions happen in solution

• Solution state
• NMR spectroscopy
• reactions happen in solution
• direct structural information
• results are subject to interpretation
• nuclei involved limit available techniques
• Colligative properties
• direct determination of average aggregation
  numbers
• no structural information
• experimentally challenging

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Crystal Structures from my lab of aldol reaction
intermediates
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X-ray diffraction at subambient temp

• Cool a stable sample - when? - after
  crystallization - during crystallization
• Maintain a constant subambient temp to select,
  transfer and mount a crystal and during data
  collection
• Is the sample temperature sensitive?
• Is the sample oxygen and/or moisture senstive?

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Four circle diffractometer w/LT device
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Modern 3-circle diffractometer
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Q How to grow a crystal at subambient
temperature?

• A Grow it just like you would grow it at RT
  except put it in a refrigerator or a freezer!!!

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NO DRYBOXES

• WHY You cant manipulate crystals while wearing
  LARGE rubber gloves!

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What glassware do I use to grow temp moisture
sensitive crystals?
A round bottom centrifuge tube. (Sometimes user
adapted with an attached side arm and a stopcock,
i.e. a Schlenk tube)
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Isolation of air and temp. sensitive
organometallic crystals

• Quickly spin the mass of crystals down
• Remove excess mother liquor with a syringe
• Wash with fresh cold solvent - if you feel lucky
  (RECOMMENDED BUT NOT ABSOLUTELY NECESSARY)
• Remove traces of was solvent in vacuo - if youre
  on a roll
• TAKE an NMR spectrum to find out what youve
  isolated

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How do I get the crystal from here to there?
Seems like an long way to travel - and sometimes
it is!!
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First of all where is over there?

• Over there means firmly mounted on a
  diffractometer smack dab in the middle of a dry,
  cold stream of nitrogen gas preferably at exactly
  the temperature at which the crystal was grown

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What that thing (s)hes holding so delicately in
the gloved hand?

• Its a cryovial with a cryoloop mounted on a pin
  and it looks like this!!!!

BUT the crystal can also sit on the lip of a
(0.5 mm) QUARTZ capillary that has been broken
off
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But you, still didnt tell me how to get the
crystal from inside the centrifuge tube onto the
cryoloop or the tip of the quartz capillary!!!

• Let me recount numerous methods to do this
  starting with the sophisticated and ending with
  the practical

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An extremely sophisticated crystal examining and
mounting system
from Dietmar Stalke, Chem. Soc. Rev. 1998, 27,
171.
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Stalke Apparatus consists of
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Nozzle and crystal examining
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Schematic diagram
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Intermediate stage crystal transfer tools for
those with disposable
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The least sophisticated BUT practical
device/method for transferring crystals
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Magnetic Pins loops

• Left - copper cryo pin - can place a piece of a
  quartz capillary inside the copper pin and secure
  it with silly puddy/clay
• Right - simple loop - can simply coat loop with
  grease/oil whatever and place a crystal on it

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How sensitive can your compounds be to use this
method?
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• Even compounds containing t-butyl lithium can be
  handled this way!
• Williard, P. Sun, C. Mixed Aggregates
  containing n-Bu, sec-Bu, and t-Bu lithium and a
  chiral Li Amide derived from Valinol, J. Am.
  Chem. Soc., 1997, 119, 11693-11694.

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Commercial Capillary Tubes from Hampton Research
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Turbulance leads to ice build-up
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Picture of the Cold Stream Nozzle
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Design of the Cold Stream Nozzle
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How to mount crystal in capillary tube
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Hampton Research Brochure

• http//www.hamptonresearch.com/hrptoducts/smallmol
  cat.html
• Useful technical hints about crystallization
• Tools and supplies for crystallization,
  manipulation and mounting.

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Bibliography

• Walker, L.J. Moreno, P.O. Hope,H.
  Cryocrystallography effect of cooling medium on
  sample cooling rate, J. Appl. Crystalography,
  1998, 31(6), 954-956.
• Parkin, S. Hope, H. Macromolecular
  cryocrystallography cooling, mounting,storage
  and transportation of crystals, J. Appl.
  Crystallography, 1998, 31(6), 945-953.
• Stalke, D. Cryo crystal structure determination
  and application to intermediates, Chem. Soc.
  Rev., 1998, 27(3), 171-178.
• Bellamy, H.D. Phizackerley, R.P. Soltis, S.M.
  Hope, H. An open flow cryogenic cooler for
  single-crystal diffraction experiments, J. Appl.
  Crystallography, 1994, 27(6), 967-970.
• Hope, H. Cryocrystallography of biological
  macromolecules a generally applicable method,
  Acta Cryst, B Structural Sci., 1988, B44(1),
  22-26.

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Conclusions

• Handling air sensitive samples can be as simple
  or sophisticated as you wish
• For handling air sensitive materials I find it
  best often best to - KIS-AS-P (i.e. Keep It as
  Simple-AS-Possible)
• AND do it rapidly!!!!

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Acknowledgements

• Gene Carpenter
• My present former students
• Chuck Campana
• Arnie Rheingold
• NIH NSF ICI Americas
• ACS-PRF

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