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abstracts
Vapochromic materials, which show color change induced by vapors, are expected to be applied to the sensing of volatile organic compounds or humidity. As for the metal complex crystals, many vapochromic crystals are reported, however, vapochromic organic crystals are not common. Therefore, it is important to find vapochromic organic crystals and to reveal the mechanistic aspects of structure transformations and color change based on the crystal structures. Pale brown Enoxacin-3,5-Diaminobenzoic Acid (ENO-3,5DABA) dihydrate cocrystal changed to yellow on exposure to four kinds of alcohol solvent vapors (methanol, ethanol, 1-propanol, 2-propanol), and these yellow crystals returned to pale brown dihydrate crystal by humidity, which is called vapochromism. The single crystals recrystallized from water (pale brown) and methanol (yellow) are equal to the dihydrate and the methanol vapor applied forms, respectively, and their crystal structure determination revealed that the cocrystals are 1:1 salt of ENO and 3,5DABA. Surprisingly, in the methanol vapor applied from, the crystalline solvent was changed to 0.5-methanol-0.5-water solvate (composition is ENO:3,5DABA:MeOH:H2O=2:2:1:1). Thus the dihydrate cocrystal undergoes solvent exchange transformation on exposure to methanol vapor and the color changes from pale brown to yellow. Because the XRD patterns of the yellow 0.5-methanol-0.5-water solvate cocrystal and the forms exposed to other alcohol solvent vapors shows high similarity, they are isostructure crystals. The color change is caused by the π...π interaction formation between the ENO molecule and 3,5DABA molecule in alcohol solvate form via solvent exchange transformations.
abstracts
Photochromic materials have attracted attention in recent years, however, in situ control of the photochromic reactivities still challenging. In order to realize dynamic control of photochromic property in crystal, we designed and created new dual photoisomeric type cobaloxime complexes, in which the reactivity of photochromic ligand changes by contact with surrounding photoreactive ligands. In this study, salicylideneaniline derivatives (SAP) are used as photochromic ligands, and the relationships between their photochromic reactivity and structural changes induced by crystalline-state photoisomerization of alkyl group of cobaloxime complex were investigated. As a salicylideneaniline (SAP) type cobaloxime complex, (3-cyanopropyl)(N-(3,5-di-tert-butylsalicylidene)-3-aminopyridine)cobaloxime was successfully synthesized. In the crystal, the SAP moiety which had a twisted conformation (dihedral angle of rings, 30.0(6)0)showed the photochromism upon UV irradiation. Also the 3-1 photoisomerization of the 3-cyanopropyl group in the cobaloxime moiety occurred with retention of the single-crystal form upon visible light irradiation. After crystalline-state 3-1 photoisomerization of the alkyl group by visible light, the photochromic property was examined to show the lifetime of colored species became significantly longer than before the reaction. It would be explained that the reaction cavity around the SAP moiety was modified by solid-state photoisomerization of alkyl group of the surrounding cobaloxime complexes, which successfully enabled the control of the photochromism. Moreover, other several derivatives are investigated similarly and their results were discussed together.
abstracts
Hydration/dehydration phase transitions of active pharmaceutical ingredients (API) are often accompanied with changes of physicochemical properties, such as solubility, stability, and bioavailability. Therefore, three dimensional structural investigation of the hydration / dehydration mechanism of API is important for pharmaceutical research and development. By relative humidity control, Cefaclor hydrate crystal dehydrates non-stoichiometrically from dihydrate to anhydrous form A. Unexpectedly, its monohydrate form transformed into new 1.9 hydrate by slurry treatment (methanol / water) which dehydrated into another anhydrous form B through hemihydrate by heating. In this study, these hydration and dehydration presudo-polymorphic transitions of Cefaclor are investigated by the crystal structure analyses. Crystal structures of anhydrous and partially dehydrated forms were determined by structure determination from powder diffraction data technique because such dehydration phase transitions were resulted in a disintegration of single crystal form. In the first dehydration route, hydrates and the anhydrous form A have similar crystal structure, which is referred as `isomorphic desolvation'. Interestingly, the anhydrous form A has void spaces which corresponds to the water molecule position in the hydrate form. Thus, in hydration / dehydration phase transitions, water molecules move in and out of the void without changing the crystal structures, and the anhydrous form A can hydrate even in low R.H. condition. In the second route, the 1.9 hydrate, hemihydrate and the anhydrate form B have three crystallographically independent molecules forming similar T-shape building block pattern. There are tunnel spaces along b axis between the blocks. In the hydration / dehydration process, the blocks slide each other to open and close the channel. This mechanism explains another non-stoichiometric dehydration in this route.
