Conformation with linkages

A number of substituted propane-l,3-diamine (64) compounds of the type [PtL2] and [PtX2L2] (X = Cl, Br, or NH3) have been described. Several of the latter species exhibited polymorphism which was attributed to either different H-bonded linkages or different chelate ring conformations in the two forms.In solution their n.m.r. spectra are consistent with a preference for a chair-type conformation with the Cl or OH axial.Similar n.m.r. spectral studies have also been reported for some related N-methyl substituted... 

These polymers have high intrinsic viscosities [e.g., about 22 (ml/g), for polyvinylpyrrolidone], which indicates that the macromolecules are swollen and extended in water. In contrast, serum albumin, with an intrinsic viscosity near 4 (ml/g), must be relatively compact. Promising approaches might be, therefore, to obtain a relatively compact conformation with a water-soluble polymer by introducing cross-linkages or by using a highly branched matrix. The latter has proved to be particularly fruitful. 

The final Klebsiella polysaccharide that will be mentioned specifically is KZS, whose chemical structure was determined by Niemann et al (24) (Figure 30). This polysaccharide is of particular interesT because its backbone consists of a similar alternating 1, 3 diequatorial, 1, 4 diequatorial glycosidic linkage geometry to that found in the connective tissue polysaccharides, hyaluronic acid, chondroitin sulphate and dermatan sulphate (25). All these three polysaccharides have exhibited 3-fold helical conformations with axially projected chemical repeats in the range 0.95 - 0.97 nm which is comparable to 0.97 nm found in K25 which also forms a 3-fold helix (14). Further, left-handed helices were found to be more favourable in K25 as has previously been observed in the connective tissue polysaccharides. The similarities between these various different structures is apparent in Figure 31 which shows projections down the axis of K25 and several of the connective tissue polysaccharides. 

The physicochemical uniqueness of trehalose originates from the presence of an a, a-1,1-linkage, which brings about the rigid conformation with a clam, shell-like shape. Because of the conformational rigidity, trehalose has a... 

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