[keetner]

Hey guys,

I'm wondering just how much will particle size affect absorbance? A lot of work I've done with spectrophotometry has usually involved protein concentration only, so I'm a little confused if size would.

The reason why I'm wondering about this is because, specifically, I did this experiment where I was observing nanodisc formation of lipids upon the addition of apolipoprotein. The lipid samples were separated, not mixed, and they were phosphatidylcholine and phosphatidylglycerol. PC and PG differ in structure, so I assume one lipid will be able to pack together more tightly than the other (whether in a lipid membrane or in a nanodisc). Subsequently, I would assume the one that can't pack as tightly would result in more nanodiscs floating around. But could potentially increase absorbance readings? And just as an analogy: it's like if you have small and large apples, you can fit the small apples into one crate, while the large apples will need 3 crates. That kind of thing.

So with more conglomerated lipids, does this change absorbance?

I'm also a bit confused about the packing ability of PC and PG. I would've assumed PG would pack more tightly since it's phosphate head is smaller, but at the same time, it's charge is -1, which might not be so great. However, in the experiment we did add NaCl, so I'm assuming Na+ ions were there to stabilize it, but I'm wondering if that effect is as great compared to a lipid with a positive charge already? And since we added Na+ to PC, would that screw up the stability of the protein considering you're making it slightly more positive than it already is??

Any in put would be greatly appreciated -- thanks!

[Babcock_Hall]

Sometimes spectrophotometers are used to measure turbidity, as opposed to absorbance.  Do the nanodisks make the solution cloudy in appearance at all?

[keetner]

Ah, I see! Yes, they did from what I noticed at least.