Effects of 2-Hydroxypropyl-b-cyclodextrin on Polymorphic Transition of Chlorpropamide in Various Conditions: Temperature, Humidity and Moulding Pressure

The amorphous complex of 2-hydroxypropyl--cyclodextrin (HP--CyD) with an oral hypoglycemic agent, chlorpropamide (CPM), in a molar ratio of 1:1 was prepared by the spray-drying method. The effects of storage (temperature and humidity) and moulding pressure on the polymorphic transition of CPM in HP--CyD matrix were investigated, in comparison with those of the CPM polymorphs, Form A (stable form) and Form C (metastable form). The formation of an amorphous complex of CPM with HP--CyD was confirmed by powder X-ray diffractometry and differential scanning calorimetry. During storage at various temperature and humidity conditions, the metastable Form C of CPM converted to the stable Form A, where the conversion proceeded according to the Jander equation with an activation energy of 51 kJ/mol (25–60–°C) and a reaction-order of 1.55 with respect to water content (relative humidity (RH) 20–75%). No polymorphic transition of Form A crystals was observed under the experimental conditions. In the case of the amorphous HP--CyD complex, Form C crystals were slowly produced, but the further conversion of the resulting Form C to Form A was markedly suppressed in HP--CyD matrix. Upon compression (2000kg/cm²), Forms A and C were converted to amorphous CPM in a major portion and Forms C and A, respectively, in a minor portion. The polymorphic transition behavior was clearly reflected in the dissolution rate of CPM, i.e., (1) the dissolution rate was in the order of HP--CyD complex (Form C) Form A, and (2) the dissolution rate of Forms A and C after the compression increased because of the conversion to amorphous state, while the complex maintained the fast dissolving property even after the compression. The results indicated that HP--CyD is useful not only for converting crystalline CPM to an amorphous substance, but also for maintaining the metastable form with fast dissolution rate, Form C, over a long period.     

Design and evaluation of cyclodextrin-based drug formulation

The pharmaceutically useful cyclodextrins (CyDs) are classified into hydrophilic, hydrophobic, and ionic derivatives. Because of the multi-functional characteristics and bioadaptability, these CyDs are capable of alleviating the undesirable properties of drug molecules through the formation of inclusion complexes or the form of CyD/drug conjugates. This review outlines the current application of CyDs in design and evaluation of CyD-based drug formulation, focusing on their ability to enhance the drug absorption across biological barriers, the ability to control the rate and time profiles of drug release, and the ability to deliver a drug to a targeted site.     

Quasi-solid dye sensitised solar cells filled with ionic liquid--increase in efficiencies by specific interaction between conductive polymers and gelators

Photo-energy conversions for quasi-solid dye sensitised solar cells increased when gel electrolytes were combined with conductive polymers as counter electrodes and the conversion surpassed that for DSSCs equipped with conventional Pt counter electrodes.     

Temperature dependences of electrical resistivity and magnetic susceptibility in (SN)x single crystal

Pauli-paramagnetism is observed in high quality (SN)x single crystal. Density of state at Fermi level is estimated to be 0.14 ± 0.06 states/(eV spin molecule) from the observed magnetic susceptibility. Curie Weiss like laws are observed in γ-ray irradiated and low quality (SN)x crystals which show the resistivity minimum at 30–40 K. The resistivity minimum is discussed in terms of carrier scattering by localized paramagnetic centers.