18
comparison with that of straight-chain amylodextrin. French published protocols
for the methylation of Schardinger dextrins and showed that 2,3,6-tri- methylglucose
was the only product of methylation of cycloamyloses followed by hydrolysis
(French et al. 1950b), in agreement with the previous results published by Pringsheim
(Pringsheim 1924, 1925, 1926; Pringsheim and Beiser 1924) and Freudenberg
(Freudenberg and Meyer-Delius 1938; Freudenberg et al. 1938). French also published solubility data on cycloamyloses, especially in presence of organic liquids.
Solubility data of dextrins in water at room temperature were as follows: α-dextrin
14.5 g/100 mL, β-dextrin 1.8 g/100 mL, and γ-dextrin 23.2 g/100 mL (French et al.
1949a). Using data from periodate oxidation and methylation reactions, French
definitively demonstrated that Schardinger dextrins could not be open-chain compounds and they were regarded as conical cylinders (French and McIntire 1950;
Norberg and French 1950; French et al. 1950a, b). At that time, Schardinger dextrins were also found to be rather anomalous structures with interesting complexing
properties when compared with the linear oligosaccharides. French indeed suggested for the first time the fact that cycloamyloses were capable of forming particular complexes. The nature of the complexes between halogen and Schardinger
dextrins, particularly the iodine complexes, depended much on the amount of the
halides added. However, the cavity of dextrins was referred to as hydrocarbon in
nature by French. This result has been definitively abandoned in 1965 with the
advent of the modern conformational theory.
1.3.4 Molecular Structure of Schardinger Dextrins
Schardinger was the first to hypothesize that the crystalline substances were “cyclic
polysaccharides” (Schardinger 1907, 1909, 1911). However, he never managed to
elucidate their structure.
In 1920, Karrer was the first to suggest that the dextrins were made up of several
components (Karrer 1920), and 1 year later, he proved it using detailed acetolysis
data (Karrer 1921; Karrer and Nägeli 1921a, b; Karrer et al. 1921). In 1923, Karrer
was also the first to propose that dextrins are composed of maltose units only joined
by α-(1→4) glucosidic linkages (Karrer 1923, 1925), although Pringsheim (1922,
1924) remained unconvinced by Karrer’s conclusions. Figure 1.6 is a schematic
illustration of two glucopyranose units of a dextrin molecule showing details of the
α-(1→4) glucosidic/glycosidic linkage and the numbering systems employed to
describe the glucopyranose rings. Later, Miekeley (1930, 1932) also came to the
same conclusions as Karrer. In 1926, Pringsheim is finally convinced by Karrer’s
conclusions (Pringsheim 1926) although he continued to regard the polyamyloses
as the basic units of the starch “molecule” (Pringsheim 1928a, 1931a). However,
just like Schardinger, Karrer, and Miekeley, Pringsheim failed to elucidate the cyclic
structure of the dextrins.
From 1934 for a period of approximately 25 years, the main contributions toward
the molecular structure and size of the Schardinger dextrins were developed by
N. Morin-Crini et al.
comparison with that of straight-chain amylodextrin. French published protocols
for the methylation of Schardinger dextrins and showed that 2,3,6-tri- methylglucose
was the only product of methylation of cycloamyloses followed by hydrolysis
(French et al. 1950b), in agreement with the previous results published by Pringsheim
(Pringsheim 1924, 1925, 1926; Pringsheim and Beiser 1924) and Freudenberg
(Freudenberg and Meyer-Delius 1938; Freudenberg et al. 1938). French also published solubility data on cycloamyloses, especially in presence of organic liquids.
Solubility data of dextrins in water at room temperature were as follows: α-dextrin
14.5 g/100 mL, β-dextrin 1.8 g/100 mL, and γ-dextrin 23.2 g/100 mL (French et al.
1949a). Using data from periodate oxidation and methylation reactions, French
definitively demonstrated that Schardinger dextrins could not be open-chain compounds and they were regarded as conical cylinders (French and McIntire 1950;
Norberg and French 1950; French et al. 1950a, b). At that time, Schardinger dextrins were also found to be rather anomalous structures with interesting complexing
properties when compared with the linear oligosaccharides. French indeed suggested for the first time the fact that cycloamyloses were capable of forming particular complexes. The nature of the complexes between halogen and Schardinger
dextrins, particularly the iodine complexes, depended much on the amount of the
halides added. However, the cavity of dextrins was referred to as hydrocarbon in
nature by French. This result has been definitively abandoned in 1965 with the
advent of the modern conformational theory.
1.3.4 Molecular Structure of Schardinger Dextrins
Schardinger was the first to hypothesize that the crystalline substances were “cyclic
polysaccharides” (Schardinger 1907, 1909, 1911). However, he never managed to
elucidate their structure.
In 1920, Karrer was the first to suggest that the dextrins were made up of several
components (Karrer 1920), and 1 year later, he proved it using detailed acetolysis
data (Karrer 1921; Karrer and Nägeli 1921a, b; Karrer et al. 1921). In 1923, Karrer
was also the first to propose that dextrins are composed of maltose units only joined
by α-(1→4) glucosidic linkages (Karrer 1923, 1925), although Pringsheim (1922,
1924) remained unconvinced by Karrer’s conclusions. Figure 1.6 is a schematic
illustration of two glucopyranose units of a dextrin molecule showing details of the
α-(1→4) glucosidic/glycosidic linkage and the numbering systems employed to
describe the glucopyranose rings. Later, Miekeley (1930, 1932) also came to the
same conclusions as Karrer. In 1926, Pringsheim is finally convinced by Karrer’s
conclusions (Pringsheim 1926) although he continued to regard the polyamyloses
as the basic units of the starch “molecule” (Pringsheim 1928a, 1931a). However,
just like Schardinger, Karrer, and Miekeley, Pringsheim failed to elucidate the cyclic
structure of the dextrins.
From 1934 for a period of approximately 25 years, the main contributions toward
the molecular structure and size of the Schardinger dextrins were developed by
N. Morin-Crini et al.