Size of the Schardinger Dextrins

Molecular Size from Measurements of CoUigative Properties 

Schardinger himself did not attempt molecular-weight determinations of the crystalline dextrins. The first molecular-weight determinations were based on freezing-point depressions in water or on osmotic-pressure measurements. Other measurements were based on dialysis rates or on cryoscopic measurements rvith the acetates, nitrates, and methyl ethers. In some cases microisopiestic methods were used. - 

In most of the early work the importance of low molecular-weight impurities (such as alcohol or salts of crystallization) appears to have been ignored. Further, the necessity of extrapolation to infinite dilution has not always been appreciated, or in some cases the extrapolations were along curved lines,  

Although early workers had arrived at a hexasaccharide character for one modification of a-dextrin ( a-hexaamylose ) this result was of questionable significance because of the simultaneous findings that compounds now regarded merely as different crystalline modifications or complexes of a-dextrin were reported as a-diamylose, a-tetraamylose, a-octaamylose, a-amylosan, a-isoamylosan, and so on. If there was an element of truth here, it was well concealed by the surrounding confusion. 

The basic principle of the method is to determine by x-ray diffraction the volume of the crystal unit-cell. This, together with the measured crystal density gives directly the mass of the contents of a unit cell, and hence the mass of an integral number of molecules of the material. In most cases of complex organic molecules the number of molecules per cell is small (2-6) and fixed by the crystallographic symmetry and the symmetry of the molecule. 

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Paper Chromatography, Optical Rotation, and Miscellaneous Observations Bearing on the Molecular Size of the Schardinger Dextrins.241... 

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