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- ItempH- and Temperature-Dependent Kinetics of the Oxidation Reactions of OH with Succinic and Pimelic Acid in Aqueous Solution(Basel, Switzerland : MDPI AG, 2020) Schaefer, Thomas; Wen, Liang; Estelmann, Arne; Maak, Joely; Herrmann, HartmutRate constants for the aqueous-phase reactions of the hydroxyl radical with the dicarboxylic acids, succinic acid and pimelic acid were determined using the relative rate technique over the temperature range 287 K ≤ T ≤ 318 K and at pH = 2.0, 4.6 or 4.9 and 8.0. OH radicals were generated by H2O2 laser flash photolysis while thiocyanate was used as a competitor. The pH values were adjusted to obtain the different speciation of the dicarboxylic acids. The following Arrhenius expressions were determined (in units of L mol-1 s-1): succinic acid, k(T, AH2) (2.1 x 0.1) ± 1010 exp[(-1530 x 250 K)/T], k(T, AH-) (1.8 x 0.1) ± 1010 exp[(-1070 x 370 K)/T], k(T, A2-) (2.9 x 0.2) ± 1011 exp[(-1830 x 350 K)/T] and pimelic acid, k(T, AH2) (7.3 x 0.2) ± 1010 exp[(-1040 x 140 K)/T], k(T, AH-) (1.8 x 0.1) ± 1011 exp[(-1200 x 240 K)/T], k(T, A2-) (1.4 x 0.1) ± 1012 exp[(-1830 x 110 K)/T]. A general OH radical reactivity trend for dicarboxylic acids was found as k(AH2) < k(AH-) < k(A2-). By using the pH and temperature dependent rate constants, source and sinking processes in the tropospheric aqueous phase can be described precisely. © 2020 by the authors.
- ItemPrintability study of metal ion crosslinked PEG-catechol based inks(Bristol : Institute of Physics Publishing, 2020) Włodarczyk-Biegun, M.K.; Paez, J.I.; Villiou, M.; Feng, J.; Del Campo, A.In this paper we explore the printability of reversible networks formed by catechol functionalized PEG solutions and metal cations (Al3+, Fe3+ or V3+). The printability and shape fidelity were dependent on the ink composition (metal ion type, pH, PEG molecular weight) and printing parameters (extrusion pressure and printing speed). The relaxation time, recovery rate and viscosity of the inks were analyzed in rheology studies and correlated with thermodynamic and ligand exchange kinetic constants of the dynamic bonds and the printing performance (i.e. shape fidelity of the printed structures). The relevance of the relaxation time and ligand exchange kinetics for printability was demonstrated. Cells seeded on the materials crosslinked with Al3+, Fe3+ ions were viable and revealed well-spread morphologies during 7 day culture, indicating the potential of the formulations to be used as inks for cell encapsulation. The proposed dynamic ink design offers significant flexibility for 3D bioprinting, and enables straightforward adjustment of the printable formulation to meet application-specific needs.