<html xmlns:v="urn:schemas-microsoft-com:vml" xmlns:o="urn:schemas-microsoft-com:office:office" xmlns:w="urn:schemas-microsoft-com:office:word" xmlns:m="http://schemas.microsoft.com/office/2004/12/omml" xmlns="http://www.w3.org/TR/REC-html40"><head><meta http-equiv=Content-Type content="text/html; charset=us-ascii"><meta name=Generator content="Microsoft Word 14 (filtered medium)"><style><!--
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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Courier New"'>Dear RASMB,<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Courier New"'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Courier New"'>My recollection is that concentrations in excess of 1.0 mg/ml should be avoided due to the possibility of non-ideal interactions that would complicate the analysis of SV and SE measurements. However in two recent cases (in one case a mAb was being studied, and in another a globular viral capsid protein), we exceeded this value by a factor of five and failed to observe any evidence of non-ideal behavior. In both cases, it was possible to fit both SV and SE data without assuming any non-ideal interactions when the experiment was performed in PBS or HEPES.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Courier New"'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Courier New"'>I would be curious to hear if it is the experience of the community that non-ideality is commonly to be expected at concentrations >1.0mg/ml or whether the concentration cutoff for non-ideality is less of an actual cutoff being more a function of the particular properties of the molecule being studied.<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Courier New"'><o:p> </o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Courier New"'>Best regards<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Courier New"'>John Sumida<o:p></o:p></span></p><p class=MsoNormal><span style='font-size:12.0pt;font-family:"Courier New"'>University of Washington<o:p></o:p></span></p></div></body></html>