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[EMAIL PROTECTED] wrote on 12/04/2006 02:08:48 PM: > *** For details on how to be removed from this list visit the *** > *** CCP4 home page http://www.ccp4.ac.uk *** > > > Hi > > Just a quick question.. for doign hanging drop, is there anyway that we > can decrease the pH of the drops on a (somewhat) controlled way, say over > a period of couple of weeks? Thanks > > > Andrew > Hi Andrew - Acetic acid is volatile, so you could use an acidic well solution with an acetate buffer to accomplish this. You don't need to have the well very acidic - even pH 5 - 6 will leave enough free acetic acid to diffuse into the drop and lower its pH. The kinetics of this are a lot faster than weeks, though - some tests I did in grad school suggest that it's on the order of minutes to days depending on the pH of the drop and the well. You could also use carbonic acid (CO2). In a higher pH range, you could have ammonium ion in the drop, and allow the ammonia to diffuse *out*. I'm not sure if chloride ions (HCl) can actually diffuse across the air gap at neutral-ish pH - the concentration of HCl in solution will be so low. At pH below 6, I'll bet this works as well given enough time. If the pH change has to happen over weeks, you'll probably need a series of well solutions, and transfer the drop between wells every couple of days. - Matt -- Matthew Franklin , Ph.D. Senior Scientist, ImClone Systems 180 Varick Street, 6th floor New York, NY 10014 phone:(917)606-4116 fax:(212)645-2054 Confidentiality Note: This e-mail, and any attachment to it, contains privileged and confidential information intended only for the use of the individual(s) or entity named on the e-mail. If the reader of this e-mail is not the intended recipient, or the employee or agent responsible for delivering it to the intended recipient, you are hereby notified that reading it is strictly prohibited. If you have received this e-mail in error, please immediately return it to the sender and delete it from your system. Thank you.
