Re: CNBr cleavage

Richard Laursen (laursen@bu.edu)
Wed, 3 Mar 1999 18:10:10 -0500 (EST)

You should open bottles and do all weighings in a well ventilated hood.
CNBr is rather volatile and is a powerful lacrymator (tear gas). It would
be a good idea to wear sugical rubber gloves to keep it off your skin.
Since it is difficult to weigh small quantities (as it evaporates quickly),
weigh out a larger amount (a few hundred mg) and make a stock solution, for
example in 70% formic acid. You may end up throwing away 95% of the stock
solution, but it is easier than trying to weigh out just what you need.
Weigh out some CNBr and then add the appropriate amount of 90% or 100%
formic acid. When the solid is dissolved, add the appropriate amount of
water. CNBr dissolves more easily in pure formic acid. The solution of
CNBr should be made up just before use. Don't try to store it for long
periods.

We usually use a concentration of 50 mg/mL of CNBr in 70% formic acid for
cleavages. Just add some of the stock solution to your lyophilized protein
and keep it in the dark for 16-24 hours.

CNBr is toxic and is especially irritating to the eyes, but you don't have
to be afraid of it if you use care. Also CNBr should be white, waxey
crystals. If it is a yellow powder, it has decomposed and should be
discarded.

Richard Laursen
--------------------------

>I am thinking about using CNBr for chemical cleavage of some samples. I
>never used it before but I know it is very harmful. I would like to know
>the safety conditions to work with this reagent in routine.
>
>thanks in advance,
>
>Jaime Paba M.
>University of Brasilia

Richard A. Laursen
Department of Chemistry
Boston University
590 Commonwealth Ave.
Boston, MA 02215
Tel (617) 353-2491; FAX (617) 353-6466
email: <laursen@bu.edu>