Biomedical subjects

Yuichi Tozuka

Publications and source records attributed to Yuichi Tozuka.

24 records · Page 2Linked to original sources

PubMed2002

Effects of dehydration temperature on water vapor adsorption and dissolution behavior of carbamazepine.

Anhydrous carbamazepine was prepared by heating carbamazepine dihydrate at 60, 80, 100, 120, and 140 degrees C and used to investigate the effects of dehydration temperature on water vapor adsorption and dissolution behavior. The hydration rate of anhydrous carbamazepine at 75, 83, and 95% relative humidity and 25 degrees C decreased with increasing heating temperature. From the dissolution study by the rotating disk method, the calculated solubility of anhydrous carbamazepine was about 2.5 times higher than that of the dihydrate. The rate of phase transformation from the anhydrous form into the dihydrate during the dissolution process decreased with an increase in sample preparation temperature. These phenomena were further studied by thermal analysis, specific surface area measurement, density measurement, small-angle X-ray scattering, and wide-angle powder X-ray diffraction. As the heating temperature was raised, the specific surface area was reduced and the density was increased; furthermore, the average of the solid part calculated by the Debye method with small-angle X-ray scattering increased. The anhydrous carbamazepine prepared at lower heating temperatures was found to have a more porous structure and was seen by wide-angle powder X-ray diffraction to comprise both anhydrous forms I and II.

Adsorption↗

PubMed2002

Solid-state fluorescence study of naphthalene adsorption on porous material.

Naphthalene adsorption profile on porous materials was studied using solid-state fluorescence spectroscopy. When naphthalene crystals were simply mixed with porous crystalline cellulose (PCC), excimer emission of naphthalene was observed after 1 min of mixing, suggesting a drastic change in the naphthalene molecular environment during the mixing procedure. For the naphthalene-octadesyl silane (ODS)-80A or naphthalene-ODS-2 systems, the changes in adsorption profiles and fluorescence spectral pattern of naphthalene were similar to those of the naphthalene-PCC system. The final amounts of naphthalene adsorbed to ODS-80A and ODS-2 were 0.05 and 0.024 g/g adsorbent, respectively, even though the two materials had comparable values of specific surface area. The relative emission intensity (I(excimer)/I(monomer)) in the ODS-80A system was higher than that in the ODS-2 system when compared at the same amount of naphthalene adsorbed. It was concluded that the pore size of porous materials affected the naphthalene excimer formation on the surface.

Adsorption↗

PubMed2002

Formation of fine drug particles by cogrinding with cyclodextrins. I. The use of beta-cyclodextrin anhydrate and hydrate.

PURPOSE: To improve the micromeritical properties of pranlukast (PRK) hydrate, a cogrinding process with cyclodextrin was used, and the formation of fine drug particles was investigated. METHODS: PRK crystals were ground with either beta-cyclodextrin (beta-CD) anhydrate or beta-CD hydrate crystals at a mixing molar ratio of 2:1 (beta-CD:PRK) to prepare the ground mixtures (GMs). Powder X-ray diffraction measurement and particle size analysis were performed. RESULTS: The two GMs differed from one another in appearance, wettability, and fine particle production. Quantitative determination demonstrated that when the beta-CD hydrate/PRK GM was dispersed in water, 96% of PRK loaded in GM became fine particles smaller than 0.8 microm. In contrast, only 1.4% of PRK in GM transformed to fine particles in the case of beta-CD anhydrate/PRK GM. The PRK fine particles were considered to be dispersed as small crystals. The stability of PRK particles in the aqueous solution was improved by the addition of a water-soluble polymer. CONCLUSION: Cogrinding with a beta-CD of higher water content can be an effective method to prepare fine drug particles at the submicron level.

Chemistry, Pharmaceutical↗

PubMed2002

Crystal structure of the alcoholates and the ansolvate of PNU-97018, an angiotensin II receptor antagonist.

The title compound, PNU-97018 [systemic name: 2-butyl-3,6,7,8,9,11-hexahydro-6,9-dimethyl-3-([2'-(2H-tetrazol-5-yl)[1,1'-biphenyl]-4-yl]methyl)-6,9-ethano-4H-imidazo[4,5-d]-pyridazino[1,2-a]pyridazin-4-one] is a newly developed angiotensin II receptor antagonist. The compound and its methanolate and ethanolate were characterized by X-ray crystallography and thermal analysis. The methanolate and ethanolate crystals have an almost identical molecular conformation and crystal packing. In both alcoholates, each alcohol molecule is fixed to the compound with a molar ratio of 1 : 1 by a hydrogen bond between the hydroxyl group of the alcohol molecule and the tetrazole group of the compound. The hydroxyl group of each alcohol molecule further links with the imidazole ring of the neighboring compound by hydrogen bond to form a hydrogen-bond network in both alcoholates. A tunnel-like structure that includes alcohol molecules is formed in each alcoholate. The ansolvate crystal showed completely different thermal and X-ray crystallographic characteristics from the alcoholates, where the compound molecules were directly linked by hydrogen bonds between the tetrazole group of a molecule and the imidazole ring of the neighboring molecule. The position of the hydrogen atom in the tetrazole ring was different between the ansolvate and alcoholates. Unlike alcoholates, a layer structure stacked on the b-c plane was observed in the ansolvate crystal. It was concluded that the molecular conformation and the arrangement of the compound molecules were largely different between ansolvate and alcoholate crystals.

Alcohols↗

PubMed2002

Characterization and quantitation of clarithromycin polymorphs by powder X-ray diffractometry and solid-state NMR spectroscopy.

Characterization of clarithromycin polymorph was performed by solid-state cross polarization and magic angle spinning (CP/MAS) 13C-NMR spectroscopy. Two polymorphs, form II and form I, of clarithromycins indicated characteristic resonances of C1 carbonyl carbon at 176.2 and 175.2 ppm, respectively. Since each peak of C1 carbon was well separated in the spectrum of the two polymorphs, we performed quantitative analysis of the polymorphic fraction from the peak area of these peaks. The peak area of form I was found to linearly increase with an increase of its content, with a correlation coefficient of above 0.99. Solid-state NMR was found to be a useful technique to determine the characteristics of the polymorphic forms.

Clarithromycin↗

PubMed2002

Elucidation of solid-state complexation in ground mixtures of cholic acid and guest compounds.

The solid-state complexation between cholic acid (CA) and either methyl p-hydroxybenzoate (MPB) or ibuprofen (IBP) was investigated. Powder X-ray diffractometry, IR spectroscopy and thermal analysis suggested the complex formation between CA and MPB as well as between CA and IBP by co-grinding method. The stoichiometry of CA-MPB was 1 : 1 while that of CA-IBP was 2 : 1, reflecting the effect of guest size on complex formation. The guest compounds were assumed to be included in the channel of complexes formed by hydrogen bonds among CA molecules.

Calorimetry, Differential Scanning↗