26
French also reported the preparation, isolation, and partial characterization of large
cyclodextrins with 9, 10, 11, and 12 glycosyl units in the macrocycle (Pulley and
French 1961), identified during the preparation of α-, β-, and γ-dextrins like
Freudenberg.
In the mid-1950s, Cramer also investigated the enzymatic production of cyclodextrins, their separation and purification, and characterization (Cramer 1955, 1956;
Cramer and Steinle 1955; Cramer and Henglein 1957a, b). Cramer described an easy
protocol to separate α-, β-, and γ-cyclodextrins from the digest by selective precipitation using appropriate organic compounds and optimize parameters, e.g., pH = 6 and
temperature = 40 °C (Cramer 1956). The three cyclodextrins are precipitated by addition of a tetrachloroethylene-tetrachloroethane mixture, followed by the addition of
p-cumene. α-Cyclodextrin was isolated by selective precipitation with cyclohexane,
β-cyclodextrin with fluorobenzene, and γ-cyclodextrin with anthracene. Cramer
explained his results by the difference in the sizes of cavities of the three cyclodextrins
and concluded that the superiority of his method over previous procedures, particularly those of French, resided in the technical ease and the completeness of
precipitation.
To summarize, during the periods of reaching maturity from 1935 to 1950 and of
exploration from 1950 to 1970, the separation and the purification of the mixture
were difficult (Crini 2014; Crini et al. 2018). The period of reaching maturity was
also marked by several contradictory results, due, at least in part, to differences in the
protocols used for the preparation of Schardinger dextrins and dubious purity of the
samples (Thoma and Stewart 1965; Caesar 1968; Szejtli 1998). The work during
these periods was even marred by hot debate between the different laboratories, especially those of Freudenberg and Cramer and of French. In addition, in the early
1950s, researchers had not fully realized the potential of cycloamyloses and had little
faith in their complexation properties (Szejtli 1998). The three main cyclodextrins
were considered just laboratory curiosities difficult to produce. In 1963, French was
the first to propose the preparation of cycloamyloses on a larger-than- laboratory
scale (French et al. 1963). However, at the end of the 1960s, French concluded that
“cycloamyloses were very promising molecules although they remained very expensive products, available only in small amounts as fine chemicals, and also toxic.”
1.3.6 The Action of Amylases on Cycloamyloses
Up to 1939, the Schardinger dextrins were known only as products of the bacterial
breakdown of starch. For Freudenberg’s opinion, Bacillus macerans was able to
transform starch structure into cyclic and linear breakdown products, and starch was
based upon a cyclic Schardinger nucleus with side branches which would be broken
in the bacterial breakdown (Fig. 1.11). During the same period, Tilden and Hudson
(1942), studying the bacteria that produced the dextrins, also concluded that the
resulting Schardinger dextrins were derived from some basic configuration
N. Morin-Crini et al.
French also reported the preparation, isolation, and partial characterization of large
cyclodextrins with 9, 10, 11, and 12 glycosyl units in the macrocycle (Pulley and
French 1961), identified during the preparation of α-, β-, and γ-dextrins like
Freudenberg.
In the mid-1950s, Cramer also investigated the enzymatic production of cyclodextrins, their separation and purification, and characterization (Cramer 1955, 1956;
Cramer and Steinle 1955; Cramer and Henglein 1957a, b). Cramer described an easy
protocol to separate α-, β-, and γ-cyclodextrins from the digest by selective precipitation using appropriate organic compounds and optimize parameters, e.g., pH = 6 and
temperature = 40 °C (Cramer 1956). The three cyclodextrins are precipitated by addition of a tetrachloroethylene-tetrachloroethane mixture, followed by the addition of
p-cumene. α-Cyclodextrin was isolated by selective precipitation with cyclohexane,
β-cyclodextrin with fluorobenzene, and γ-cyclodextrin with anthracene. Cramer
explained his results by the difference in the sizes of cavities of the three cyclodextrins
and concluded that the superiority of his method over previous procedures, particularly those of French, resided in the technical ease and the completeness of
precipitation.
To summarize, during the periods of reaching maturity from 1935 to 1950 and of
exploration from 1950 to 1970, the separation and the purification of the mixture
were difficult (Crini 2014; Crini et al. 2018). The period of reaching maturity was
also marked by several contradictory results, due, at least in part, to differences in the
protocols used for the preparation of Schardinger dextrins and dubious purity of the
samples (Thoma and Stewart 1965; Caesar 1968; Szejtli 1998). The work during
these periods was even marred by hot debate between the different laboratories, especially those of Freudenberg and Cramer and of French. In addition, in the early
1950s, researchers had not fully realized the potential of cycloamyloses and had little
faith in their complexation properties (Szejtli 1998). The three main cyclodextrins
were considered just laboratory curiosities difficult to produce. In 1963, French was
the first to propose the preparation of cycloamyloses on a larger-than- laboratory
scale (French et al. 1963). However, at the end of the 1960s, French concluded that
“cycloamyloses were very promising molecules although they remained very expensive products, available only in small amounts as fine chemicals, and also toxic.”
1.3.6 The Action of Amylases on Cycloamyloses
Up to 1939, the Schardinger dextrins were known only as products of the bacterial
breakdown of starch. For Freudenberg’s opinion, Bacillus macerans was able to
transform starch structure into cyclic and linear breakdown products, and starch was
based upon a cyclic Schardinger nucleus with side branches which would be broken
in the bacterial breakdown (Fig. 1.11). During the same period, Tilden and Hudson
(1942), studying the bacteria that produced the dextrins, also concluded that the
resulting Schardinger dextrins were derived from some basic configuration
N. Morin-Crini et al.