<html><head></head><body style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">I would like to add that one should always run any sample at a series of concentrations - not only to test for self-association but also for non-ideality. Small peptides can often have a very high charge-to-mass ratio and will exhibit significant non-ideality even at 150 mM ionic strength. This is true in some cases for larger proteins as well. Always a good idea to either rule it out ... or in.<div><br></div><div>Also if you have no suitable chromophore, you can use interference optics if you have an XL-I. But be very careful with the dialysis so that you are assured of getting a good optical match between sample and buffer.</div><div><br></div><div>And as pointed out already, run at the highest speed possible.</div><div><br></div><div>You will have to use whole boundary fitting methods since you will not see a well defined boundary. Resolution will not be optimum (because of diffusion) , and you will definitely need to globally fit over a range of concentrations, both to demonstrate concentration dependence (or lack thereof) and to extract any other parameters (like equilibrium constants and non-ideality) if there is concentration dependence.<br><div>
<span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Arial; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Arial; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><span class="Apple-style-span" style="border-collapse: separate; color: rgb(0, 0, 0); font-family: Arial; font-style: normal; font-variant: normal; font-weight: normal; letter-spacing: normal; line-height: normal; orphans: 2; text-align: -webkit-auto; text-indent: 0px; text-transform: none; white-space: normal; widows: 2; word-spacing: 0px; -webkit-border-horizontal-spacing: 0px; -webkit-border-vertical-spacing: 0px; -webkit-text-decorations-in-effect: none; -webkit-text-size-adjust: auto; -webkit-text-stroke-width: 0px; font-size: medium; "><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">_________________________</div><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; ">Walter Stafford<br><a href="mailto:wstafford3@walterstafford.com">wstafford3@walterstafford.com</a></div><div style="word-wrap: break-word; -webkit-nbsp-mode: space; -webkit-line-break: after-white-space; "><br></div></span></div></span></span><br class="Apple-interchange-newline">
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<br><div><div>On Jul 9, 2013, at 05:51, Fasolini, Marina [Nervianoms] wrote:</div><br class="Apple-interchange-newline"><blockquote type="cite">
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<div><font size="2" face="Arial"><span class="207421909-09072013">Dear
All</span></font></div>
<div><font size="2" face="Arial"><span class="207421909-09072013">I need to follow the
aggregation of some peptides of about 4 KDa . I would like to estimate the
dimension of these aggregates. </span></font></div>
<div><font size="2" face="Arial"><span class="207421909-09072013">Since my experience
is mostly in protein sedimentation, I was wondering if you have some tips for
me. Which wavelength do you use for absorbance optic? Which is the best
concentration to run?</span></font></div>
<div><font size="2" face="Arial"><span class="207421909-09072013">At which speed do
you suggest me to run the experiment?</span></font></div>
<div><font size="2" face="Arial"><span class="207421909-09072013">Any help will be
appreciated.</span></font></div>
<div><font size="2" face="Arial"><span class="207421909-09072013">Thanks in
advance</span></font></div>
<div><font size="2" face="Arial"><span class="207421909-09072013">Marina</span></font></div>
<div><font size="2" face="Arial"><span class="207421909-09072013"></span></font> </div>
<div><font size="2" face="Arial"><span class="207421909-09072013"></span></font> </div>
<div> </div>
<div align="left">MARINA FASOLINI<br>Structural Chemistry<br><br>Nerviano Medical
Sciences <a href="http://www.nervianoms.com/">http://www.nervianoms.com</a><br>Viale Pasteur
10<br>20014 Nerviano - Milano<br><a href="mailto:marina.fasolini@nervianoms.com">marina.fasolini@nervianoms.com</a> <br>Tel.
+390331581462<br>Fax. +390331581360<br></div>
<div> </div></div>
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