3312 zyxwvutsrqponm Macromolecules 1988,21, zyxwvu 3312-3320 Cowie, J. M. G.; Bywater, S.; Worsfold, D. J. Polymer 1967,8, zyxwvutsr 105. Noda, I.; Mizutani, K.; Kato, T.; Fujimoto, T.; Nagasawa, M. Macromolecules 1970, 3, 787. McCormick, H. W. zyxwvutsrqpo J. Polym. Sci. 1959, 41, 327. Altares, T.; Wyman, D. P.; Allen, V. R. J. Polym. Sci., Part A 1964, 2, 4533. Bianchi, U.; Dalpiaz, M.; Patrone, E. Makromol. Chem. 1964, 80, 112. Fox, T. G.; Kinsinger, J. B.; Mason, H. F.; Schuele, E. M. Polymer 1962, 3, 71. George, A.; Wilson, W. W.; Mays, J. W.; Lindner, J. S., to be submitted for publication. Muthukumar, M.; Freed, K. F. Macromolecules 1977,10,899. One could question the validity of using average values in Tables I11 and IV. It is our opinion, however, that considering the possible experimental errors the initial use of average values is a reasonable first approximation. Large standard deviations would therefore imply either experimental errors or trends in the data. Simionescu, C. I.; Simionescu, B. C.; Neamtu, I.; Ioan, zyxwvuts S. Polymer 1987,28,165. Simionescu, B. C.; Ioan, S.; Simionescu, C. I. J. Polym. Sci., Polym. Phys. Ed. 1987, 25, 829. (63) Appelt, B.; Meyerhoff, G. Macromolecules 1980, 13, 657. (64) Mays, J. W.; Hadjichristidis, N.; Fetters, L. J. Macromolecules 1985,18, 2231. (65) Schmidt, M.; Burchard, W. Macromolecules 1981, 14, 210. (66) Freed, K. F. Renormalization Group Theory zyx of Macromole- cules; Wiley: New York, 1987, Chapter 10. (67) Rey, A.; Freire, J.; Garcia de la Torre, J. Macromolecules 1987, 20, 342. (68) Wang, S. Q.; Douglas, J. F.; Freed, K. F. Macromolecules 1985, 18, 2469. (69) Wang, S. Q.; Douglas, J. F.; Freed, K. F. zyx J. Chem. Phys. 1985, 85, 3674. (70) As a reviewer pointed out, Ferry and co-workers at Wisconsin have also detected deviations from the least-draining limit (via viscoelastic measurements) for PS, PaMS, and other flexible polymers at high molecular weights in good solvents. See for example: Osaki, K.; Schrag, J. L.; Ferry, J. D. Macromolecules 1972, 5, 144. (71) Zimm, B. H. Macromolecules 1980, 13, 592. (72) Huber, K.; Burchard, W.; Akcasu, A. Z. Macromolecules 1985, 18, 2743. (73) LeGuillou, J. C.; Zinn-Justin, J. Phys. Rev. Lett. 1977,39, 95. (74) Adam, M.; Delsanti, M. Macromolecules 1977, 10, 1229. Solution Properties of Exocellular Microbial Polysaccharides. 3. Light Scattering from Gellan and from the Exocellular Polysaccharide of Rhizobium trifolii (Strain TA-1) in the Ordered State M. Dentini,t T. Coviello,t W. Burchard,*,$ and V. Crescenzit Dipartimento di Chimica, Universitd di Roma, “La Sapienza”, 00185 Rome, Italy, and Institut fur Makromolekulare Chemie, Universitat Freiburg, 7800 Freiburg, FRG. Received December 10, 1987; Revised Manuscript Received April 15, 1988 ABSTRACT: Exocellular microbial polysaccharides (EPS) from Rhizobium trifolii strain TA-1 (TA-1-EPS) and from Pseudomonas elodea (Gellan) have been studied in dilute aqueous salt solutions by static and dynamic light scattering (LS) under conditions where the two polysaccharides are in the ordered (helical) state. The two polymers show pronounced chain rigidity. Their LS behavior has been evaluated from static and dynamic Zimm plots, i.e., Kc/R8 versus q2 and D,,,(q) = r/q2 versus q2, and from Holtzer plots, i.e., qRB/(Kc) versus q = (4~/h) sin 8/2. From the two types of Zimm plots the common molecular parameters, Le., molecular weight M,, radius of gyration R, = (S2),1/2, and translational diffusion coefficient Dz, were obtained. The Holtzer plots exhibit a clear asymptotic rod behavior. The value of the asymptotic plateau at large q gives the linear mass density (=mass per unit length) ML = M/L. Comparison of the experimentally observed data to those calculated for a single-stranded helix allowed determination of the number of laterally associated strands which were found to be n = 3.02 & 0.07 and n = 1.85 * 0.02 for TA-1-EPS and Gellan, respectively. The Kuhn segment lengths could be estimated from the ratio of the heights of the maximum and asymptotic plateau in the Holtzer plot and were found to be lk = 152 nm for TA-1-EPS and lk = 322 nm for Gellan. These large values lie in the same range zyxwvuts as the Kuhn segment lengths for other microbial polysaccharides. The observed angular dependence was checked with the predictions by Koyama for stiff chains and by Benoit et al. for flexible chains with large excluded volume. A good agreement was found with Koyama’s prediction whereas application of the relationship for chains with large excluded-volume effect produces strong deviations. The large chain stiffness is confirmed by the value of the p-parameter R,/Rh, where Rh is the hydrodynamically effective radius. Introduction In recent years a number of exocellular microbial poly- saccharides (ESP) have aroused keen interest because of their unique solution and gelling properties.’ In many instances, these properties have already opened avenues to the industrial utilization of such biopolymers; while new species continue to appear as additional, interesting can- didates for both basic and applied re~earches.~ A feature which seems to be in common to all EPSs so far studied is that in very dilute aqueous solution more or less disordered chains (probably, but not necessarily, single * Author to whom correspondence should be addressed. t Universitl di Roma. * Universitat Freiburg. chains) would prevail. However, upon increasing polymer concentration and with added salt the EPS chains almost invariably undergo conformational disorder-order tran- sitions. Because of the often highly cooperative character, this transition can be easily monitored by common phys- ical-chemical techniques, e.g., chiroptical, calometric, and viscometric technique^.^,^ None of these experimental approaches can give, how- ever, an unambigious answer to the central question of the final ordered conformation for the chains in each case (e.g., single helix or multiple-stranded helix). Kinetic mea- surements can be of valuable help in elucidating this im- portant point6l7 In the context, radiation scattering (i.e., small-angle X-ray, small-angle neutron, and laser light scattering) appears quite naturally the most appropriate 0024-9297/88/2221-3312$01.50/0 zyxwvutsrqponmlkjihgfedcbaZYXWVUTSRQPONMLKJIHGFEDCBA 0 1988 American Chemical Society