Molecular States of p-Dimethylaminobenzonitrile Coground with .BETA.-Cyclodextrin Investigated Using Solid-State Fluorescence Spectroscopy

Abstract

NoteCyclodextrin (CD) molecules with hydrophobic cavities form inclusion complexes with hydrophobic guest molecules.1) b-CD in particular can include a wide range of guest molecules, so b-CD has widely been utilized in formulations for medicines and food.2,3) p-Dimethylaminobenzonitrile (DMABN) is known as a model probe for determining the mechanisms of inclusion in a solution.4) DMABN molecules have been reported to adopt two different conformation, planar and twisted, in a solution. The two structures have been reported to lead to different fluorescence emission peaks, with DMABN molecules in a planar structure producing a fluorescence emission peak at a shorter wavelength, and DMABN molecules in a twisted structure in a twisted intramolecular charge-transfer (TICT) state producing a peak at a longer wavelength. 5,6) TICT state emission has been reported to be caused by an electron transfer of the dimethylamino group from a nitrogen atom to the cyano group, or to the entire benzonitrile group, because of the twist. 7) Since DMABN adopts different structures depending on the molecular environment, e.g. different CD cavity diameters, and DMABN's molecular state is reflected in the fluorescent spectrum, DMABN is an interesting research probe for intermolecular interactions with CDs. 8) As a probe, DMABN was coprecipitated or coground with b-CD in this study to analyze the solid-state fluorescence emission spectrum of the inclusion complexes, as well as the excitation spectrum, and fluorescence lifetime by time-resolved fluorometry, and to examine the changes in DMABN's molecular state. ExperimentalMaterials p-Dimethylaminobenzonitrile (DMABN) was purchased from Tokyo Chemical Industry Co., Ltd. (Japan). b-Cyclodextrin (b-CD) was obtained from Mercian Co., Ltd., Japan. Crystalline cellulose (CC: PH-101) was obtained from Asahi Chemical Industrial Co., Ltd., Japan. b-CD and CC were used after they were dried under reduced pressure at 110°C for 3 h. All other chemicals used were of reagent grade.Preparation of a Physical Mixture and a Ground Mixture A physical mixture of DMABN and b-CD (molar ratio of DMABN/b-CDϭ1/1) or CC (DMABN content 11.4%) was prepared by kneading in a mortar for 10 s. A ground mixture was prepared by grinding the physical mixture (2.0 g) using a vibrating mill (Heiko Seisakusho, TI200, Japan).Preparation of Complexes by Coprecipitation b-CD (2.0ϫ10 Ϫ3 mol) and DMABN (6.0ϫ10 Ϫ3 mol) were dissolved in distilled water and diethyl ether, respectively. The 2 solutions were mixed well. Each solution was slowly cooled to 4.0°C to allow coprecipitation. The coprecipitate obtained in the aqueous phase was filtered out with filter paper and dried under reduced pressure at 120°C for 6 h.Powder X-Ray Diffractometry Powder X-ray diffraction patterns were measured using a Rigakudenki 2027 diffractometer (Japan). The measurement conditions were as follows: target, Cu; filter, Ni; voltage, 30 kV; current, 15 mA; time constant, 0.5 s; scanning speed, 4 degree/min.Thermal Analysis Thermogravimetry-differentia...

Physicochemical Characterization of Cyclodextrin–Drug Interactions in the Solid State and the Effect of Water on These Interactions

“…85,[90][91][92] Planar DMABN molecules produce a fluorescence emission peak at a shorter wavelength than their twisted conformers, which exhibit a twisted intramolecular charge-transfer (TICT) state. [90][91][92] A TICT emission was observed at 475 nm for DMABN crystals, and freeze-dried "-CD-DMABN, $-CD-DMABN, and (-CD-DMABN samples displayed emissions peaks at 450, 380, and 393 nm, respectively. Therefore, DMABN molecules were proposed to exist in a twisted conformation in the "-CD cavity and a plane structure in those of $-CD and (-CD.…”

“…That indicates the ground mixtures have crystallized into typical inclusion complexes under humid conditions. In solution, DMABN molecules have been reported to adopt planar or twisted conformations that lead to different fluorescence emission peaks . Planar DMABN molecules produce a fluorescence emission peak at a shorter wavelength than their twisted conformers, which exhibit a twisted intramolecular charge‐transfer (TICT) state .…”

“…In solution, DMABN molecules have been reported to adopt planar or twisted conformations that lead to different fluorescence emission peaks . Planar DMABN molecules produce a fluorescence emission peak at a shorter wavelength than their twisted conformers, which exhibit a twisted intramolecular charge‐transfer (TICT) state . A TICT emission was observed at 475 nm for DMABN crystals, and freeze‐dried α‐CD–DMABN, β‐CD–DMABN, and γ‐CD–DMABN samples displayed emissions peaks at 450, 380, and 393 nm, respectively.…”