Date: Wed, 22 Jan 1997 09:38:34 -0600
Message-Id: <v01530509af0ce2975692@[128.252.197.88]>
To: abrfhyp@cco.caltech.edu
From: rskubish@pharmdec.wustl.edu (Richard Skubish)
Subject: Recrystallization
>From: "Medvedkin, Viatcheslav" <VIATCHESLAV.MEDVEDKIN@nrc.ca>
>Old-To: "abrf@aecom.yu.edu" <abrf@aecom.yu.edu>
>Subject: RE: Recrystallization
>Date: Fri, 27 Sep 96 19:36:00 EDT
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>To: Recipients of ABRF List <abrf@aecom.yu.edu>
>Sender: Association of Biomolecular Resource Facilities
><abrf-request@aecom.yu.edu>
>Precedence: bulk
>
> It is impossible to write in details how to crystallize organic
>compounds. It is one of many experiences that differentiates good organic
>chemists from bad ones.
>
> Good luck with your first crystallization. Not all of them will be
>successful... But it is good, because otherwise people wouldn't invent
>chromatography!
>
>Viacheslav Medvedkin Ph.D.
>(Peptide and protein chemistry)
>slava@biotech.lan.nrc.ca
>
>Below is suggested protocol for crystallization.
>
>Although many people think recrystallization ia a simple process - it is
>not true. First, you should know what solvent or pair of solvent to use. You
>can find it from the literature. Use round-bottom flask - if you took too
>much solvent - you can evaporate part on the rotor evaporator. When a pair of
>solvents are given (EtOAc-hexan, EtOH-di-isopropyl ether, etc) the first
>solvent is given to increase solubility and the second - to decrease it.
>Preferably they both should have close boiling points. Add some amount of the
>first solvent at room temperature to the solid in the flask so that it does
>not dissolve completely. Heat it on the water bath until the solvent almost
>boil (be aware of vapors!!! - heat burns, inflamability and toxicity should
>be considered). As a rule, Fmoc-amino acids can be heated up to 60-70 degrees
>and even higher without serious danger of decomposition or losses of optical
>purity. Try to dissolve ALL solid. If not dissolved- add more solvent. Do not
>afraid to take large flasks - usually amount of the solvent can be half of
>the volume. When everything is dissolved, it is a must to close the flask
>with inert cork (glass, polyethylene is OK, but not rubber). By this you will
>protect yourself from unnesessary solvent evaporation and create stable
>conditions for crystallization. Let your solute to cool slowly to room
>temperature. If not precipitated - try to initiate crystallization with
>spatula(organic chemists will show you how to do it). If still not
>crystallized - heat up to 40-50C and add drop-by drop the second solvent,
>(that decreases solubility). The slight milky shades will quickly disappear
>until you add ENOUGH, which means - all solute became opalescent. Avoid oily
>drops formation. Heat solute 5- 10 degrees higher until it became clear
>again, close with cork and wait. Leave for couple hours at room temperature
>and then put into refrigerator (2-4 C is enough).
>Filter your
>beautiful crystals, wash them with second solvent, dry and weigh. The yields
>of recrystallization are not very high, but if you obtain less than 60% of
>initial weight you better try to evaporate the rest of the solvent and try
>to obtain more crystals from it. For loading of 2 g. expect to obtain about
>1.5 g. The longer you wait in crystallization - the better crystals you can
>obtain. In fact, you can wait for a very long time and sometimes your
>internal voice will prompt you - OK, now I KNOW what Crystallization is.
>
>
>
>
>
Richard Skubish
rskubish@pharmdec.wustl.edu
314-362-0283
Washington University Medical School
Box 8103 - PNACL
660 S. Euclid
St. Louis, MO 63110