X-ray crystallographic studies were carried out for seven
conglomerates, seventeen racemic compounds,
and four enantiomerically pure salts of chiral primary amines with
achiral monocarboxylic acids. The crystal structures
of the conglomerate salts revealed that these crystals can be regarded
as being an assembly of a characteristic columnar
hydrogen-bond network in which the ammonium cations and the carboxylate
anions are aligned around a 2-fold
screw axis (21-column). On the other hand, the crystal
structures of the racemic-compound salts could be broadly
classified into two types. One type is a crystal consisting of
21-columns; the other type is a crystal consisting of
a
different type of columnar hydrogen-bond network in which the ammonium
cations and the carboxylate anions are
related by inversion centers (i-column). Our results
suggest that both the formation and the assembly of
21-columns
are essential in the formation of conglomerates from these salts, and
that the difference in the packing of
21-columns
between conglomerate salts and racemic-compound salts is governed by
van der Waals interaction between the
21-columns.
We report the preparation and features of environmentally friendly "Green Dynamers" (GDs), dynamic polymers presenting sequential double-degradation features, chemical and biological. They were obtained by connecting biodegradable oligomers (such as small units of polybutylene adipate, PBA, and polybutylene succinate, PBS) through chemically degradable reversible imine bonds. The GDs possess water disintegratability, mendability and biodegradability. Their degradation rate may be modulated through and increases with the number of imine groups in the polymeric chain. The GDs were thermodynamically stable and maintained their molecular weight and their mechanical strength in air. However, when they were contacted with water, the imine bonds easily hydrolyzed, breaking up the polymer chains into oligomers. After such water disintegration, the residual oligomers were biodegraded into CO 2 and water. In addition, the imine bonds were restored by evaporation of the water, leading to recovery of the molecular weight and of the mechanical properties of the GDs. The present GDs may be considered to represent a class of doubly-degradable polymers, combining chemical and biological degradability features, that operate in mild environmental conditions. This concept may contribute to solve the problem of waste elimination associated with the use of non-degradable polymeric materials.
Optically active polyamides, derived from (-)-anti head-to-head coumarin dimer and , -alkanediamines, possess possible interaction sites for chiral recognition. Their chiral recognition ability was evaluated by using them as chiral stationary phases for high-performance liquid chromatography; they were found to be highly dependent on the methylene number in the diamine components. The polyamides, consisting of a diamine with an even methylene number, showed a sufficient chiral recognition ability, while the polyamides with an odd methylene number did not at all. This odd-even discrimination in chiral recognition was in good agreement with the crystallizability of the polyamides; i.e., only crystallizable polyamides showed a chiral recognition ability. The chiral recognition ability was also closely related to the degree of crystallinity and to the superstructure of the polyamides. The degree of crystallinity of the polyamides coated on the surface of silica gel was significantly influenced by the poor solvent for washing and by the quantity of a residual coating solvent.
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