Dear Cheignon,

As you say, BrCN is a difficult substance to handle and has some quite curious physical chemistry (mp = 52°C and bp = 62°C). When in water then the BrCN becomes HCN and HOBr ... which is where the danger lies! A quick look on Wiki says that you will need a formic acid or HCl buffer for the reaction, these can also cause problems at the drying step.

With regards to drying, there are a many things to consider, first, the most suitable drying system and then how to safely handle the sample(s) and the evolved gasses and waste solvents.

To protect your sample then drying under vacuum is the most obvious solutions (vacuum means the boiling point is low, so the sample is cold). There are 4 systems to consider, a lyophilisation system, a rotary evaporator, a vacuum centrifuge, and a vacuum oven. I would not use a rotary evaporator for a protein becuase the rotation will cause mechanical damage to the protein. A vacuum oven is only good for semi-solids or solids, e.g. wet sand. All systems have a problem with materials of construction, in that the HCl or formic acid buffer and the HOBr that are evolved will corrode metal parts of the system and will damange an oil based vacuum pump. HCN will also attack many plastics used in vacuum systems. There are no really good solutions here except one, the fully acid resistant Genevac vacuum centrifuges, designed for strong acids, even the vacuum pumps are OK. The problem, they are intended for high use labs, and as you would expect are expensive. If you only have a small(er) volume of this sample and will only use this process onece, then a regular freeze dryer is probably the next not bad solution ... but you will have to clean the surfaces of the freeze dryer and the ice trap, and change the pump oil after use to preserve the system.

You will need to take great care with any system for the route of the gases that are not trapped, containing HCN and acid(s). The ice trap on any unit will not trap all of these, even with a super low temperature at -100°C the ice trap is not 100%. Ensure that the outfolw of gas from the trap is taken away from the system, and the lab users with a suitable pipe into the fume handling system. Unless your institution has a really good fume containment system I would think that they will not like these going up the regular fume hood, best to check with the supervisor. Neutralisign the gas may be required.

An alternative would be to use membrane systems to concentrate the protein. These are messy, do not yield 100% and you need a centrifuge, but you are working in solution the whole time. You will never become 100% dry, but may work for what you need. Problem is they are made 100% in plastics so check that they are compatible with your solvent(s) and reagents.

Kind regards,

Rob

Thank you for your fast answer Rob Darrington, it is very useful.

Regards,

Clémence

We use CnBr treatment regularly in protein cleavage. Cleavage mixture either in formic acid or HCl, carefully pour into lyophilization flask or 50 ml tube if you have speedvac. For 50 ml i will add only 15 to 20 ml of solution and freeze it in -70C for 6 h to overnight. Swtich on the lyophilizer and add 2N NaOH in the cold trap around 20 to 30 ml to neutralize acid and Cn and Br as sodium salt. Once it appropriate temperature reached in the trap, take the frozen tube and do the lyophilization.

Cleaning the trap add further 20 ml 2N NaOH and allow the temperature to attain room temperature to dissolve the CnBr in the trap along with acid. During this entire process keep the trap closed or if the trap removable, place it in fume hood allow the condensate to melt. Add 2 litre of water and discard according to university regulations. During this process please follow the necessary precautions for handling CnBr.