T H E CELLULOSE MOLECULE’ PHYSICAL-CHEMICAL STUDIES THE SVEDBERG Institute of Physical C h e m i s t r y , Cniversity of Upsala, r p s a l a , Sweden Received A u g u s t 8 , 1946
I n the early days of colloid chemistry polydispersity m s regarded as the rule. Monodisperse systems could be obtained by special fractionation procedures (Perrin’s gamboge suspensions, OdBn’s sulfur sols) or to a certain degree by the nuclear method (Zsigmondy’s gold sols). This was still the generally recognized opinion at the time of the First Colloid Symposium, which was held here in hladison in June 1923. Three years later it was shoivn that a large group of colloids, the proteins, are, as a rule, monodisperse. During the following twenty years the physical chemistry of the protein molecules has been estensively studied in many laboratories (lG). One of the chief centers of such studies has been here in Madison. The fact that upon denaturation many proteins become polydisperse has often been taken as an indication that monodispersity is a characteristic of native high-molecular compounds. To a certain extent this is probably true, but polydispersity has now been found t o be the rule in a t least one large group of native organic colloide, viz., the polysaccharides. The degree of polydispersity is, hovever, less high than in synthetic high polymers produced in the laboratory, such as the polyethylenes and rubbers. I n the following report a short summary will be given of the investigations carried out in Upsala on the physical chemistry of the polysaccharide molecules, especially cellulose (2, 3 , 4, 5, 6,17). The chief experimental methods used by us are n-ell known and lvill therefore be referred t o only briefly. ULTRACEKTRIFUG.AL SEDIMESTATIOS
Work of this type Tyas started in hladison in 1923, and the method was further developed in Upsala and in American laboratories. The type of apparatus used in Cpsala and also here in Madison for high-speed sedimentation is shown in figures 1 and 2 . The solution t o be studied is enclosed in a sector-shaped cell with plane parallel windows and spun in a suitable rotor at constant speed and constant temperature. One of the chief difficulties has been the avoiding of convection currents in the solution, owing to slight thermal disturbances. I n the oilturbine ultracentrifuge this is achieved by running the rotor in hydrogen a t about 15 mm. pressure, thus reducing the friction considerably and a t the same I Presented a t the Twentieth Sational Colloid Symposium, which was held a t Madison, Wisconsin, May 28-29, 1946.
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THE CXiLLULObL YOLECCLE
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For memiirmwnts of sedimentation equilibrium
