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ABSTRACT:Intrinsic viscosities [11] for sodium hyaluronate in aqueous sodium chloride at 25°C were determined for 12 samples ranging in weight-average molecular weight Mw from 3.8 x 10 3 to 3.5 x 10 5 at NaCl concentrations C, between 0.005 and 2.5 M. They were analyzed on the basis of the Yamakawa-Fujii-Yoshizaki theory for [11] ofan unperturbed wormlike chain combined with the Yamakawa-Stockmayer-Shimada theory for excluded-volume effects to estimate the total persistence length q and the excluded-volume strength B as functions of C,. At any C, studied, excluded-volume effects on [11] became appreciable when Mw exceeded 1 x 10 4~2 x 10 4 . The C, dependence of q yielded 4.0 nm for q0 (the intrinsic persistence length) of the polysaccharide chain at infinite ionic strength. It was found that the values of q-q0 (i.e., the electrostatic contribution to q) at C,<0.02M were roughly 70% larger than predicted by the Le Bret theory and the Odijk-Skolnick-Fixman theory. On the other hand, the estimated B values agreed fairly well with Fixman and Skolnick's theory for the excluded-volume interaction between a pair of charged rodlike segments unless C, was lower than 0.05 M, KEY WORDS Polyelectrolyte / Hyaluronic Acid / Wormlike Chain / Chain Stiffness / Electrostatic Persistence Length/ Excluded-Volume Effect/The current polyelectrolyte theory 1 -4 predicts that the persistence length q of a charged linear polymer in aqueous salt increases with lowering salt concentration c., provided the polyelectrolyte is modeled by the Kratky-Porod wormlike chain. 5 This prediction for the electrostatic stiffening effect seems to be substantiated experimentally for intrinsically stiff polymers undergoing no appreciable intramolecular excluded-volume effect. Notably for double-stranded DNA, 6 almost quantitative agreement was obtained between theoretical and experimental values for the electrostatic persistence length q.1 (the electrostatic contribution to q).On the other hand, our understanding of q. 1 for polyelectrolytes with intrinsically weak stiffness is far from satisfactory. The primary difficulty in the experimental determination of q. 1 or q for those polymers is that the effects of chain stiffness and volume exclusion on measured properties can hardly be separated without resort to a relevant excluded-volume theory. Some previous workers 7 -9 deliberately or undeliberately ignored the latter effect in their estimation of q and discussed apparent values so estimated for q or q. 1 • Others 10 -12 took account of volume effects, but they invoked the Fixman-Skolnick theory 13 for the electrostatic binary cluster integral and early theories 14 · 15 for the radius expansion factor a. based on the random flight model.Here, °' • is defined as the ratio of the perturbed to unperturbed radius of gyration. It is probably fair to say that no established way of estimating the chain stiffness is as yet known for intrinsically flexible or weakly stiff polyelectrolytes unless the ionic strength is high enough. We note that although scatt...

ABSTRACT:Five sodium salt samples ofhyaluronic acid ranging in weight-average molecular weight Mw from 1.9 x 10 5 to 1.5 x 10 6 have been studied by light scattering and viscometry in aqueous sodium chloride at 25°C. The intrinsic viscosity ([11]) data obtained at 10 different NaCl concentrations C, covering a range from 0.005 to 2.5 M are analyzed along with previous data for lower Mw on the basis of the Yamakawa-Fujii-Yoshizaki theory for unperturbed wormlike chains combined with the quasi-two-parameter (QTP) theory for excluded-volume effects. Fairly satisfactory agreement is observed between theory and experiment at C, higher than 0.01 M over the range of molecular weight from 3.8 x 10 3 to 1.5 x 10 6 , though the degree of agreement tends to lower with decreasing C,. When the wormlike chain parameters and the excluded-volume strength estimated from [11] are used, the QTP theory with the known expression for (S 2 ) (the mean-square radius of gyration) of the unperturbed wormlike chain is found to describe almost quantitatively the measured (S 2 ) for Na hyaluronate at C, = 0.02, 0.1, and 0.5 M. Thus, it is concluded that this theory for nonionic chains is applicable, in a fairly good approximation, to (S 2 ) and [11] of the charged polysaccharide in aqueous NaCl unless C, is lower than 0.02M.KEY WORDS Hyaluronic Acid/ Polysaccharide / Polyelectrolyte / Excluded-Volume Effect/ Wormlike Chain/ According to recent experimental studies, 1 • 2 the quasitwo-parameter (QTP) theory 3 based on the wormlike 4 or helical wormlike 3 chain allows an almost quantitative, consistent description of excluded-volume effects on the mean-square radius of gyration (S 2 ) and the intrinsic viscosity [17] for nonionic, linear polymers, both flexible and stiff. In contrast to this situation, our understanding of those effects in ionic chains still remains in a quite unsatisfactory stage.In our previous work, Hayashi et al. 5 • 6 examined, as a first step toward solving the electrostatic excludedvolume problem, the applicability of the QTP theory to [17] of sodium hyaluronate, a charged linear polysaccharide with intrinsically weak stiffness, in aqueous sodium chloride with the aid of the Yamakawa-Fujiiy oshizaki theory 7 • 8 for unperturbed wormlike cylinders. The general agreement between theory and experiment was not bad over the entire range of weight-average molecular weight Mw (3.8xl0 3 4 x 10 4 where excluded-volume effects were significant. Nonetheless, the discrepancies between the theoretical and experimental [17] were too subtle to draw a definite conclusion on the applicability of the QTP scheme to Na hyaluronate. Thus it seemed necessary to extend the work to a higher molecular weight region where volume effects are more pronounced.In the present study, viscosity data were obtained for five hyaluronate samples...