Despite having ligands with almost identical conformations, the structures of the AgI complexes of 1 and 2 differ significantly: ligand 1 forms a double‐helical complex of P chirality, and 2 gives a triple‐helical complex (depicted on the right). The reason for the difference appears to be the existence of strong interligand stacking in the latter case.
Many and varied are the effects which control the self‐assembly of silver helicates, as illustrated schematically: besides the structure of the ligand and the coordination preferences of the metal, conditions such as the nature of the solvent and the concentration may also exert an influence.
Trotz nahezu identischer Konformation der Liganden im Komplex sind die Strukturen der Ag1‐Komplexe von 1 und 2 deutlich verschieden: eine Doppelhelix mit P‐Chiralität bzw. eine Tripelhelix (siehe rechts). Der Grund dürften starke Stapelwechselwirkungen der Liganden im zweiten Fall sein.
Abstract:The investigations on a variety of proteins present in corn zein, wheat gluten, milk whey and soya have shown that these proteins possess the ability to form films which can be used in food packaging. We, therefore, selected cowpea (Vigna unguiculata), a cereal abundantly available in Sri Lanka, to investigate its polymer film forming ability. Our studies have shown that the choice of a suitable solvent, pH of the medium and the use of a plasticizer were essential to obtain useful films. In this study polyethylene glycol and glycerol were used as plasticizers. The extracted cowpea protein and the plasticizers were dissolved in hot aqueous ethanol to obtain a viscous solution. The casting technique was used to fabricate the films. A series of films were made by varying the pH from 8 to 11. For each pH a series of films was prepared by varying the concentration of polyethylene glycol from 2.5 to 10% (w/v). The fabricated films were tested for transparency, glass transition temperature, tensile strength and water vapour permeability. The pH of the medium and the concentration of the plasticizer were found to have a considerable effect on the physico-chemical properties of the film. The film fabricated at pH 10 with 2.5% (w/v) of polyethylene glycol and 2% glycerol was found to possess the desired tensile strength, water vapour permeability, transparency and glass transition temperature, making the film suitable to be used as an edible food packaging material.
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