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We present the results of our theoretical conformational analysis of hyaluronic acid (HA) and sodium hyaluronate. Empirical potential energy functions for steric, electrostatic, hydrogen bonding, torsional, and solvation energies were used to evaluate the conformational energy with the CAMSEQ Software System. A trisaccharide model of the HA polymer was employed. Three chemical states were studied: HA-, charged HA in the absence of a counter-ion, neutral pH, and very low ionic strength; HAH, uncharged, protonated HA, low pH; HA-• Na +, charged HA with sodium ion present, neutral pH, and high ionic strength. Two sets of conformational energy data were collected. The first was generated by a series of sequential and random scans followed by gradient-search minimizations at each of the local minima. This was intended to give a general picture of the energy surface of each form of HA. The second data set consisted of 10,000 randomly generated conformations for each form. This was sufficient to account for the minima found in the first data set. The second set of energies was employed to estimate the partition function and corresponding chain dimensions for comparison with available hydrodynamic data. In addition, we compare and contrast our structural findings with the published crystal structures ofHA. KEY WORDS Hyaluronic Acid I Conformational Analysis I Glycosaminoglycans I * Sloan Research Fellow, to whom reprint requests should be sent. Early viscosity studies on HA isolated from vitreous humor, umbilical cord, and synovial fluid by Blix and Snellman 4 showed a molecular weight of 200,000 to 500,000 and particle lengths of 4800A to 10,000A. Several other molecular

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82838-29-7; (+)-a-methoxy-a-(trifluoromethyl)phenylacetic acid, 20445-31-2; (+)-a-methoxy-a-(trifluoromethyl)phenylacetyl chloride, 20445-33-4; (-) --methoxy-a-(trifluoromethyl)phenylacetic acid, 17257-71-5; (-)-a-methoxy-a-(trifluoromethyl)phenylacetyl chloride, 39637-99-5.