Benefits of Pyrenemethanol as an Initiator for the ROP of Morpholine-2,5-Diones: Fluorescence Probing of Nanoparticle Degradation and Cellular Uptake

High Resolution Image Download MS PowerPoint Slide 1-Pyrenemethanol was used as an initiator for the ring-opening polymerization (ROP) of three morpholine-2,5-diones, which are based on the naturally occurring amino acids l -phenylalanine, l -isoleucine, and l -valine. A catalytic system consisting of 1,8-diazabicyclo[5.4.0]undec-7-ene (DBU) and 1-(3,5-bis(trifluoromethyl)phenyl)-3-cyclohexylthiourea (TU) was applied for the polymerizations at room temperature. Kinetic studies demonstrated controlled reaction conditions and the absence of transesterification under the selected parameters. By means of 1 H NMR spectroscopy and size exclusion chromatography (SEC), monomer conversion values of about 90% were observed during the considered reaction times of up to 1 h, whereby the dispersity remained below 1.15. The covalent attachment of the pyrene α-end group to the respective poly(morpholine-2,5-dione)s (PEAs) was proven by 1 H NMR spectroscopy, SEC using a diode array detector, matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS), and fluorescence spectroscopy. The PEAs formed spherical nanoparticles with uniform size distribution via nanoprecipitation, which were subjected to degradation studies using proteinase K. Due to the characteristic change in the vibronic fine structure of the fluorescence spectrum of pyrene with the changing molecular environment, this process could be observed by fluorescence spectroscopy. The received data were validated by dynamic light scattering (DLS) measurements. Furthermore, the pyrene end group served as a fluorescent label for cellular uptake studies in L929 cells monitored by confocal laser scanning microscopy (CLSM). This report demonstrates the added value of the introduction of the fluorescence-active pyrene into the polymer structure, enabling access to additional information about the polymer and its nanoparticles without additional synthesis effort.