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</o:shapelayout></xml><![endif]--></head><body lang=EN-US link=blue vlink=purple><div class=WordSection1><p class=MsoNormal>Dear RASMB,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>We’ve been measuring the density and refractive index increments of proteins and nanoparticles and we notice that in general density of both materials scale with concentration. That is as one decreases the concentration so also the RI and density of the solution decreases, I believe this to be generally correct and in agreement with previous observations by Stouthart et. al. and more recently by Huang et. al. (Spectrochimica Acta, Part A, vol 75 2010 pp 1031-1335)<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>However it is curious to me that this does not appear to hold up at concentrations close to and below 0.1mgs/ml where there appears to be inverse relationship between density and concentration, (we’ve observed same also for RI and concentration); for CdSe qdot this effect seems to be quite large. Naturally it is possible that our initial worry was that our instrumentation was out of calibration but after calibrating the DMA5000 with degassed milliQ water and air, and successfully measuring vbar and dn/dc for BSA at 0.73 and 0.186 respectively I am beginning to wonder if this effect is artifactual.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Wondering if anyone may have any comments on this observation and if so if it would be possible to be pointed at any relevant references on the matter?<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Thank you all for your attention and any help, advice or comments you may have.<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>Best regards,<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal>John Sumida<o:p></o:p></p><p class=MsoNormal>Analytical Biopharmacy Core<o:p></o:p></p><p class=MsoNormal>Dept. of Medicinal Chemistry<o:p></o:p></p><p class=MsoNormal>University of Washington<o:p></o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p><p class=MsoNormal><o:p> </o:p></p></div></body></html>