Inclusion Of β-Cyclodextrin And Its Polylactide-grafted Copolymer With Some Aromatic Amino Acids And Insulin

Cyclodextrin and their derivatives have the hydrophobic cavities and hydrophilic wall. As the molecular host they are well known to have the property of forming inclusion complexes with organic, inorganic and biological molecules which possess suitable polarity and dimension. As the excellent enzyme model and molecule receptor, cyclodextrins have been widely used in many fields in science and technology. And peptides and proteins are composed of amino acids. The study on the inclusion behaviors of cyclodextrins with amino acids, peptides and proteins would help us to recognize the essence of life, the conception of self-assembly, molecular recognition and so on in the supramolecular chemistry. In our laboratory, supramolecular inclusion behaviors of polylactide- grafted copolymer of 3 梒yclodextrin with peptides and proteins were investigated so as to evaluated the possibilities of polylactide grafted copolymer of 3 梒yclodextrin as a carrier of pept.ide drug delivery system.The inclusion behaviors of B -cyclodextrin with some aromatic amino acids such as L-phenylalanine, L-tyrosine and L-tryptophan were studied via ultraviolet and fluorescent spectrometry. The results indicated that inclusion complexes of β-cyclodextrin with aromatic amino acids could be formed and the inclusion behaviors were affected by the amount of β-cyclodextrin, temperature and pH value. With the increase of β-cyclodextrin concentration, the decrease of temperature and prolongation of time, the inclusion complexes of β-cyclodextrin with these aromatic ami no acids became more stable. These results showed that the inclusion was a reversible equilibrium process and the inclusion of β-cyclodextrin with these aromatic amino acids was exothermic. The 1:1 inclusion complexes of β-cyclodextrin with phenylalanine and tyrosine were formed; but 2:1 complex was afford from β-cyclodextrin with tryptophan owing to the various sites and chaps of different amino acids.The inclusion behaviors of β-cyclodextrin and its polylactide-garfted copolymer with insulin were also studied via ultraviolet and fluorescent spectrometry. It was observed that the inclusion complexes of 3 -cyclodextrin and its polylactide-garfted copolymer with insulin could be formed and the inclusion behaviors were affected by the amount of 3 -cyclodextrin, temperature as well as pH value. The formation mechanism of the supramolecular systems between 3 -cyclodextrin and insulin was the similar to that between 3 -cyclodextrin and the above-mentioned aromatic amino acids. Because of the three-dimensional structure of insulin and the exterior polar groups of its aggregates, the molecular recognition and inclusion of 3 -cyclodextrin with insulin were hindered. As a result, there was a weak interaction between 3 -cyclodextrin and insulin. However, the interaction of polylactide-garfted copolymer of 0 -cyclodextrin with insulin was much stronger owing to the polymer effects of cyclodextrin polymer. The polymeric effects of polylactide-garfted copolymer of β-cyclodextrin, including cooperation effect, neighboring effect and polymer chain effect were discussed. Such a result suggested that polylactide-garfted copolymer of β-cyclodextrin would be a carrier of drug delivery system for peptides and proteins with high loading capacity.