<html><DIV><FONT size=2 face=Verdana>Greetings David:</FONT></DIV>
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<DIV><FONT size=2>Acetate is commonly used. The acid and base forms for all buffers can have different absorbances, so expect some pH dependence. Also, if you are doing temperature melts, keep in mind that the enthalpy of protonization results in a pKa change that can cause the pH to drift with temperature. Acetate and phosphate are better, Tris and Tricine poor. Of course, keep in mind that there can be specific interactions between some samples and buffers, so some combinations will not work. At a low enough pHs (2?) self buffering kicks in, so the need for a buffer isn't as severe as at pH 7. At the other extreme, pH >10 will etch silica, so keep these experiments brief.</FONT></DIV>
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<DIV><FONT size=2>Keep in mind that that salts added for ionic strength can absorb too. If possible, keep these low, or substitute (when possible) non-absorbing salts for NaCl.</FONT></DIV>
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<DIV><FONT size=2>You can use the CD's dynode voltage to estimate the buffer absorbance. Most UV-Vis spectrometers don't go below 250 nm, so a CD spectrum of a new buffer is frequently the best test to see if it is going to work.</FONT></DIV>
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<DIV><FONT size=2>When possible, boost the sample concentration, use a shorter path length, and the CD signal will be the same but the buffer absorbance will be reduced. 1 mm may be the standard for CD, but it is not a requirement.</FONT></DIV>
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<DIV><FONT size=2>Glen</FONT></DIV>
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<P>Glen Ramsay, Ph.D. <BR>Chief Scientist <BR>glen@avivbiomedical.com <BR>Aviv Biomedical, Inc. <BR>750 Vassar Ave. <BR>Lakewood, New Jersey 08701 <BR>USA <BR>(732) 370-1300 <BR>(732) 370-1303 FAX <BR><A href="http://www.avivbiomedical.com/" mce_href="http://www.avivbiomedical.com/">http://www.avivbiomedical.com/</A></P>
<P>Sent from from out of office.</P>
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<BLOCKQUOTE style="BORDER-LEFT: #0000ff 2px solid; PADDING-LEFT: 5px; MARGIN-LEFT: 5px; MARGIN-RIGHT: 0px"><FONT size=2 face=Tahoma>-----Original Message-----<BR><B>From:</B> David Scott [mailto:David.Scott@nottingham.ac.uk]<BR><B>Sent:</B> Thursday, February 9, 2012 08:00 AM<BR><B>To:</B> rasmb@rasmb.bbri.org<BR><B>Subject:</B> [RASMB] Buffers for CD<BR><BR></FONT><?XML:NAMESPACE PREFIX = O /><O:SMARTTAGTYPE name="country-region" namespaceuri="urn:schemas-microsoft-com:office:smarttags"><O:SMARTTAGTYPE name="PlaceType" namespaceuri="urn:schemas-microsoft-com:office:smarttags"><O:SMARTTAGTYPE name="PlaceName" namespaceuri="urn:schemas-microsoft-com:office:smarttags"><O:SMARTTAGTYPE name="place" namespaceuri="urn:schemas-microsoft-com:office:smarttags">
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<P class=MsoNormal><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt">Hello All in RASMB-land,</SPAN></FONT></P><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt"><O:P> </O:P></SPAN></FONT>
<P class=MsoNormal><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt">I have a question on buffers for CD. I am performing CD experiments at different pH?s. Obviously for pH 7, a nice optically clear phosphate buffer means I can see down to 185 nm on a Jasco 815 spectrometer. However, I am having problems getting buffers that are equally optically clear at pH 5.5 and pH 3.0. Any suggestions? Advice and comments on suitable sources of chemicals to make the buffer that don?t have contaminating components in are also welcome.</SPAN></FONT></P><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt"><O:P> </O:P></SPAN></FONT>
<P class=MsoNormal><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt">Best wishes</SPAN></FONT></P><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt"><O:P> </O:P></SPAN></FONT>
<P class=MsoNormal><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt">Dave</SPAN></FONT></P><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt"><O:P> </O:P></SPAN></FONT>
<P><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt">>>>>>>>>>>>>>>>>>>>>>>>>>></SPAN></FONT> <BR><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt">Dr. David J. Scott</SPAN></FONT> <BR><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt">Associate Professor and Reader in Physical Biochemistry</SPAN></FONT> <BR><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt">National Centre for Macromolecular Hydrodynamics</SPAN></FONT> <BR><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt">School of <?XML:NAMESPACE PREFIX = ST1 /><ST1:PLACENAME w:st="on">Biosciences</ST1:PLACENAME></SPAN></FONT> <BR><ST1:PLACETYPE w:st="on"><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt">University</SPAN></FONT></ST1:PLACETYPE><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt"> of <ST1:PLACE w:st="on">Nottingham</ST1:PLACE></SPAN></FONT> <BR><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt">Sutton Bonington Campus</SPAN></FONT> <BR><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt">Leicestershire. LE12 5RD.</SPAN></FONT> <BR><ST1:COUNTRY-REGION w:st="on"><ST1:PLACE w:st="on"><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt">United Kingdom</SPAN></FONT></ST1:PLACE></ST1:COUNTRY-REGION><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt">.</SPAN></FONT> <BR><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt">Phone: +44 (0) 115 951 6221</SPAN></FONT> <BR><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt">Fax: +44 (0) 115 951 6142</SPAN></FONT> <BR><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt">Email: dj.scott@nottingham.ac.uk</SPAN></FONT> <BR><FONT size=2 face=Georgia><SPAN style="FONT-FAMILY: Georgia; FONT-SIZE: 10pt">Web: www.nottingham.ac.uk/ncmh</SPAN></FONT> </P><FONT size=3 face="Times New Roman"><SPAN style="FONT-SIZE: 12pt"><O:P> </O:P></SPAN></FONT></DIV><BR>
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