BIOPHYSICAL THEORY AND MODELING |
Osmotic pressure of aqueous chondroitin sulfate solution:
A molecular modeling investigation
Mark Bathe 1, Gregory C. Rutledge 1, Alan J. Grodzinsky 1 and Bruce Tidor 1*
1 MIT
* To whom correspondence should be addressed. E-mail: tidor{at}mit.edu.
Submitted on June 2, 2005
Revised on July 13, 2005
Accepted on 14 July 2005
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Abstract |
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The osmotic pressure of chondroitin sulfate (CS) solution in contact with an aqueous 1:1 salt reservoir of fixed ionic strength is studied using a recently developed coarse-grained molecular model (Bathe et al., 2005) (1). The effects of sulfation type (4- versus 6- sulfation), sulfation pattern (statistical distribution of sulfate groups along a chain), ionic strength, CS intrinsic stiffness, and steric interactions on CS osmotic pressure are investigated. At physiological ionic strength (0.15 M NaCl), sulfation type and pattern, as measured by a standard statistical description of copolymerization, are found to have a negligible influence on CS osmotic pressure, which depends principally on the mean volumetric fixed charge density. The intrinsic backbone stiffness characteristic of polysaccharides such as CS, however, is demonstrated to contribute significantly to its osmotic pressure behavior, which is similar to that of a solution of charged rods for the 20-disaccharide chains considered. Steric excluded volume is found to play a negligible role in determining CS osmotic pressure at physiological ionic strength due to the dominance of repulsive intermolecular electrostatic interactions that maintain chains maximally spaced in that regime, whereas at high ionic strength steric interactions become dominant due to electrostatic screening. Osmotic pressure predictions are compared to experimental data of Ehrlich et al., (1998) (2) and to well established theoretical models including Donnanm theory and the Poisson-Boltzmann cylindrical cell model.
Key Words:
aggrecan, cartilage, coarse-graining, glycosaminoglycan, osmotic pressure, polysaccharide
