Molecular weight determination, starch

Starch acetate solutions, because of their stability, are suited for osmotic pressure measurements and have been employed with considerable success for direct molecular weight determinations. 

At about the same time, Saposchnikoff attempted a molecular-weight determination on starch nitrate produced by dissolution in nitric acid, and arrived at the figure of 1845— agreeing best with the formula C36H430is-(N03)i7. This formula, wherein the DP is 6, is not unlikely, as the conditions used probably effected degradation. In Britain, Arnold and his associates were granted patents for the nitration of potato starch in mixed acids. The product was probably worthless, owing to the naive assumption that it was freed of acids by currents of fresh water. ... 

Synthetic amyloses have been prepared from maltopentaose and D-glucose 1-phosphate by the action of potato phosphorylase. The products were characterized by the analysis of the products of /3-amylolysis and were used as standards in the determination of the molecular weight of starches by gel chromatography. 

The initial proof of the existence of very large organic molecules was supplied by Raoult [1] and van t Hoff [2], who carried out cryoscopic molecular weight determinations on mbber, starch, and cellulose nitrate. By the methods developed by Raoult and by van t Hoff and by the formulation of solution laws, molecular weights of 10,000 0,000 were demonstrated. Unfortunately, chemists of that day failed to appreciate this evidence and refused to accept it. The main reason for such a response was the inability to distinguish macromolecules from colloidal substances that could be obtained in low molecular weights. The opinion of the majority of that day was that Raoul s solution does not apply to materials in colloidal state. ... 

The number-average molecular weights of starches have been determined by a procedure that involves oxidation of the polysaccharide with potassium hexa-cyanoferrate solution and potentiometric titration of ferrous ions with ceric sulphate. ... 

Thus, molecular weight determinations of acetylated starch give a minimal value of (CgHi(,Os)i8 for the starch molecule, but this may have been lowered by depolymerisation during acetylation. 

Molecular weight determinations made on whole stardies are of little value owing to the heterogeneity of the material, but reported values indicate that in contrast to cellulose, starches occur with a very broad spectrum of molecular weights. 

Poly(starch-g-(l-amidoethylene)) copolymer is not a polyelectrolyte and will be a smaller molecule in water than an equal molecular weight, partially hydrolyzed poly(l-amidoethylene). Polyelectrolyte effect should, however, cause the graft copolymer to expand in solution in the same way it causes poly(l -amidoethylene) to expand, so a series of hydrolyzed graft copolymers were prepared from poly(starch-g-(l-amidoethylene))(41-43) and these derivatives were tested to determine the effect of hydrolysis on copolymer properties in solution. 

V. Properties of the Starch Components in Solution 1. The Determination of Molecular Weight... 

Musculus and Meyer (12) measured the diffusion rates of some starches and dextrins in 1881. The work was designed to determine the relationship of these "isomeric or polymeric" forms to the simple sugars from which they were formed. They concluded that dextrin molecules must be much larger than those of the sugars. This work, however, preceeded Raoult s (13) development of the cryoscopic technique for the determination of the molecular weights of dissolved substances, and van t Hoff s (14) formulation of the solution laws. Further, since the vapor density method was obviously inapplicable, it was not possible for them to actually determine the degree of polymerization. 

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