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| - Resorufin in the Channels of Zeolite L
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| - Zeolite L containing the resorufin anion(Res-) in its anionic framework can be prepared byincorporatingthe neutral resorufin molecule (ResH) from the gas phase and thenexchanging the protons with potassiumions which leads to dark violet colored microcrystals. Thereversibility of the deprotonation/protonationreaction of resorufin can be monitored by measuring the UV/visabsorption spectrum of the samples. Theabsorption spectra of Res- and ResH and their solventdependence was interpreted using the EHMO-EDiTtheory. While Res- is strongly fluorescent insolution, the fluorescence is completely quenched whenRes-is located inside the channels of potassium zeolite L. This allowsthe investigation of the exit kinetics of theresorufin molecules as a function of the size of the solvent moleculeswhich enter the zeolite channels anddisplace the incorporated resorufin molecules irreversibly. Thefollowing series was found for the displacementrate: water ≫ methanol > ethanol > 1-propanol ≳ 1-butanol.Three cases can be distinguished concerningthe mechanism of the displacement process: In case 1 the solventmolecules can pass a dye molecule insidethe channel easily. For this case the exit kinetics can beexplained by a homogeneous Markoff chain. Incase 2 the solvent molecules are considerably hindered when passing adye molecule inside the channel, andin case 3 the solvent molecules are too large to pass a dye moleculeand, hence, the exit rate of dye moleculesis zero. While water corresponds to case 1, 1-butanol can beassigned to case 3 and may therefore be usedto remove resorufin molecules or molecules with similar properties fromthe outer surfaces of zeolite L withoutdisplacing the intercalated molecules.
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