Laser Light Scattering. - Basic ideas – what is it? - The experiment – how do you do it? - Some examples systems – why do it?. Coherent beam. Extra path length. screen. +. +. =. =. Double Slit Experiment. Scatterers in solution (Brownian motion). Scattered light.
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- Basic ideas – what is it?
- The experiment – how do you do it?
- Some examples systems – why do it?
Extra path length
Scatterers in solution (Brownian motion)
Laser at fo
Narrow line incident laser
0 is way off scale
Df ~ 1 part in 1010 - 1015
How can we analyze the fluctuations in intensity?
Data = g(t) = <I(t) I(t + t)>t = intensity autocorrelation function
For small t
For larger t
where R is the radius of the equivalent sphere and h is the viscosity of the solvent
Problems: Dust and
best with monodisperse samples
where = Watson-Crick-Franklin double stranded DNA
pBR322 = small (3 million molecular weight) plasmid DNA
Laser light scattering measurements ofD vs q give a length L = 440 nm and a diameter d = 10 nm
DNA-drug interactions: intercalating agent PtTS produces a 26o unwinding of DNA/molecule of drug bound
Since D ~ 1/size, as more PtTS is added and DNA is “relaxed,” we expect a minimum in D
As drug is added DNA first unwinds to open circle and then overwinds with opposite handedness. At minimum in D the DNA is unwound.
This told us that there are 34 superhelical turns in native pBR
pBR is a major player in cloning – very important to characterize well
Conformational change with pH results in a 5% change in D – seen by LLS and modeled as a swinging hinge
Study monomer size/shape, polymerization kinetics, gel/network structures formed, interactions with other actin-binding proteins
Epithelial cell under fluorescent microscope
Actin = red, microtubules = green, nucleus = blue
what factors cause or promote aggregation?
what is the structure of the aggregates?
how can proteins be protected from aggregating?
Focus on the onset of gelation –
what are the mechanisms causing gelation?how can we control them?what leads to the irreversibility of gelation?
Thanks to NSF, Union College for $$