Limiting viscosity number was measured for two alginate samples with different mannuronate (M)/guluronate (G) ratios in dilute aqueous salt solutions. Root mean square end-to-end distance <γ
2>
1/2 obtained was ca. 600Å for the M rich sample (M/G=1.85) having a viscosity average molecular weight M
V of 6.66×10
4 and ca. 480Å for the G rich sample (M/G=0.55) with M
V=2.82×10
4. The contribution from the M and G components to <γ
2> was estimated and the molecular length defined by <γ
M2>/P
M and <γ
G2>/P
G for the M and G residues, (i. e., the mean-square end-to-end distance per monomeric unit for each component) were estimated. Here <γ
M2>, <γ
G2> and P
M, P
G are mean-square end-to-end distances and degree of polymerization which are assigned to the M and G components in an alginate chain, respectively. The present investigation has revealed that the molecular extension of the G component is larger than that of the M component, and that the <γ
G2>/P
G value is ca. 2.2 times as large as the <γ
M2>/P
M value.
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