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# John Butler (experimenter)   Gerard Wong (PI) <jbutler1@uiuc.edu>
# requesting 4 days, at minimum=4 days
# beamline 33BM, Investigation of inter-ion correlations in condensed polyelectrolyte systems
# instrument 33BM-B XAFS
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# top:/home/www/beamtime-requests/req00573.txt
# UNICAT Member Beam Time Request  #573
# created Wed Apr 14 16:38:15 CDT 2004
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beamline:
	33BM

collaboration:
	Yes

contact:
	jbutler1@uiuc.edu

days:
	4

description:
	In this continuing program of research, we will use EXAFS techniques to investigate the spatial arrangement of counterions in like-charged polyelectrolyte bundles. While it is well known that many biological polyelectrolytes condense in the presence of oppositely charged multivalent ions, the mechanism of attraction is still not well understood. By studying the inter-ion correlations of the counterions that participate in bundling at molecular length scales, we will gain a better understanding of the role the counterions play in electrostatic condensation events. We will investigate the behavior of divalent Sr ions on F-actin, and trivalent cobalt hexamine ions on DNA, by looking at the inter-ion distances as a function of global ion concentration, and counterion valence. 

The inter-ion distances on DNA can be estimated by Co-Co distances, and those on F-actin by Sr-Sr distances. Both Co and Sr have core-shell levels that are accessible using EXAFS at beamline 33BM.  Data from our preliminary experiment in 4/2004 indicate that we need to remove water from the actin–Sr complexes, which consist of a solvent-permeated meshwork of dense actin-Sr bundles, in order to separate the signal from the solvent and the condensate. We have devised a number of methods for systematically removing solvent from the complex, in order to maximize the signal from the actin-Sr bundles.

equipment_required:
	Typical EXAFS experimental equipment.

experiment:
	Investigation of inter-ion correlations in condensed polyelectrolyte systems

foreign_nationals:
	Abhijit Mishra

hazards:
	Most samples will be brought to the APS in hermetically sealed quartz capillaries.  However, solutions of strontium, cobalt hexamine, F-Actin, and DNA will be brought to the APS in case we need to prepare new samples.  Otherwise, we do not anticipate any hazards associated with the experiment.

instrument:
	33BM-B XAFS

instrument_other:
	

minimumdays:
	4

name:
	John Butler (experimenter)   Gerard Wong (PI)

nonmembers:
	None

unacceptable_dates:
	May 26th - June 12th

z34ID_details:
	


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