Only one crystal form of metoprolol succinate (Form I) was reported during previous researches and production. In this study, a new polymorph of metoprolol succinate (here named as Form II) was discovered and investigated by X-ray diffraction, thermoanalysis and infrared spectroscopy. The results show its crystal structure and thermal properties are significantly different with Form I. Compared with Form I, Form II exhibits specific diffraction pattern, lower melting temperature and weaker hydrogen bond effect. The thermostability testing suggests Form II is a metastable crystal form and will gradually transform into Form I undergoing treatment of high temperature and humidity. Metastable crystal form generally has better dissolubility than its corresponding stable form. Subsequent measurement also verified that Form II can dissolve in the water more quickly than Form I.
The enhancement of speech degraded by non-stationary interferers is a highly relevant and difficult task for many signal processing applications. In this study, we present a monaural speech enhancement method based on spectral subtraction and Kalman filtering (KF) by extracting the Liljencrants–Fant (LF) excitation during voiced speech, in which the nature of glottal flow can be maintained. Therefore, the approach could preserve the glottal pulse's nature characteristic in Kalman filtering and thus achieve significant improvements on objective quality. The quality of the enhanced speech has been evaluated by perceptual evaluation of speech quality (PESQ) score. The results indicate that the proposed algorithm could improve the output speech quality compared with the conventional KF algorithm and sub-band spectral subtraction
An efficient and practical route for the synthesis of (-)-tasimelteon from 2,3-bis(2-hydroxyethyl)phenol has been developed. The product was prepared in seven steps in overall 16.4% yield using highly stereoselective cyclopropanation reaction of the intermediate as the key step.
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