Insoluble Salt of Memantine with a Unique Fluorescence Phenomenon

Alzheimer's disease is a chronic disease, and the long-termtreatment of chronic diseases has always been a concern. Memantine(Mem) is approved by the US Food and Drug Administration for thetreatment of moderate to severe Alzheimer's disease. In this study, reactionsof memantine (Mem) with pamoic acid (Pam) were carried out to forminsoluble salts (Mem-Pam). Four polymorphic forms (Forms I-IV) ofMem-Pam were successfully obtained through polymorphic screening,which were systematically characterized by X-ray powder diffraction(PXRD), thermal analysis (TGA and DSC), single-crystal X-ray diffraction(SXRD), and solid-statefluorescence. Compared with the hydrochlorideform, the dissolution and release rates of these four forms are lower. Thepresence of pamoic acid reduces the release rate of memantine and makes itpossible to achieve a sustained release of the drug. Interestingly, because ofthe presence of memantine, each polymorphic solid crystal of Mem-Pam has uniquefluorescence emission. Therefore, memantineand pamoic acid have a synergistic effect on thefluorescence performance and can be expected to be used for real-time monitoring incontinuous and controlled release drug delivery systems. In addition, the polymorphic solid crystals also exhibit reversiblemechanochromic luminescence under the fumigation of acetonitrile vapor, which has a guiding role in thefluorescence design andsynthesis of Pam substances and is expected to be used for information security, visual inspection of organic substances, etc.