Y are available in the database of your authors at the Faculty of Materials Varespladib web Science and Engineering. Acknowledgments: This analysis was supported by Basic Science Analysis System by means of the National Investigation Foundation of Korea (NRF) funded by the Ministry of Education (NRF2020R1F1A1072616). Conflicts of Interest: The authors declare no conflict of interest.
Citation: R duc , M.; M d lan, A.M. a a a a Cocrystals versus Salts of Fluorescein. Crystals 2021, 11, 1217. https://doi. org/10.3390/cryst11101217 Academic Editors: Younes Hanifehpour and Neil Champness Received: 22 September 2021 Accepted: six October 2021 Published: 9 OctoberPublisher’s Note: MDPI stays neutral with regard to jurisdictional claims in published maps and institutional affiliations.Copyright: 2021 by the authors. N-Acetylcysteine amide MedChemExpress Licensee MDPI, Basel, Switzerland. This article is definitely an open access report distributed beneath the terms and conditions of your Inventive Commons Attribution (CC BY) license (https:// creativecommons.org/licenses/by/ four.0/).Fluorescein is really a xanthene derivative extensively made use of as platform for designing several chromogenic or fluorogenic probes [1]. Fluorescein derivatives can serve as fluorescent chelators for Zn(II) [2,3], Cu(II) [4], Co(II), Ni(II) [5], Hg(II) or Ag(I) [6] metal ions. As biological applications on the fluorescein derivatives we can also mention detection of nitric oxide production in some tissues [7], detection of homocysteine and cysteine [8], detection of hypochlorite [9], study of serotonin receptors [10], enzymes [11] and live bacteria detection [12]. The chromogenic mechanism of fluorescein is according to protonation eprotonation reactions. As a result of the biological applications in the fluorescein dyes, solution studies have attracted particular consideration. The ionization equilibria of fluorescein are presented in Scheme 1. Depending on pH, in solution may be identified cationic (H3 Fl+ ), neutral (H2 Fl) or anionic species (HFl- and Fl2- ). The neutral type (H2 Fl) presents in remedy three tautomers: zwitterion (H2 Flz), quinonoid (H2 Flq) and lactone (H2 Fll). For the monoanionic kind (HFl- ), the phenolate tautomer appears in compact quantities only in pure solvents for example DMSO, acetonitrile or acetone [13]. In solid state, the three tautomers with the neutral form are characterized by various colors: the zwitterionic type is yellow, the quinonoid kind is red and also the lactonoid type of fluorescein is colorless. The crystal structures of H2 Flq and H2 Flz have been determined by powder X-ray diffraction [14,15]. The crystal structure of your pure lactonoid type of fluorescein has not been reported. The lactonoid kind crystallizes with solvent molecules, plus the methanol [16], acetone [15,17] and 1,4-dioxane [15,18] solvates had been structurally characterized by X-ray diffraction on a single crystal. The lactone (H2 Fll) can also cocrystallize with nitrogen-containing heteroaromatic molecules: acridine, phenanthiridine and pyrazine [19]. The use of basic nitrogen-containing molecules as partners for cocrystallization provides the theoretical possibility of proton transfer with all the formation of organic salts. Such salts were reported for eosin (2 ,4 ,five ,7 tetrabromofluorescein) with 4-aza-1-azoniabicyclo[2.two.2]octane [20] and guanidiumCrystals 2021, 11, 1217. https://doi.org/10.3390/crysthttps://www.mdpi.com/journal/crystalstals 2021, 11, x FOR PEER Review Crystals 2021, 11,2 of2 oftetrabromofluorescein) with 4-aza-1-azoniabicyclo[2.two.2]octane [20] and guanidi.
