TY - JOUR A1 - Wagner, Sabine A1 - Zapata, Carlos A1 - Wan, Wei A1 - Gawlitza, Kornelia A1 - Weber, M. A1 - Rurack, Knut T1 - Role of Counterions in Molecularly Imprinted Polymers for Anionic Species N2 - Small-molecule oxoanions are often imprinted noncovalently as carboxylates into molecularly imprinted polymers (MIPs), requiring the use of an organic counterion. Popular species are either pentamethylpiperidine (PMP) as a protonatable cation or tetraalkylammonium (TXA) ions as permanent cations. The present work explores the influence of the TXA as a function of their alkyl chain length, from methyl to octyl, using UV/vis absorption, fluorescence titrations, and HPLC as well as MD simulations. Protected phenylalanines (Z-L/D-Phe) served as templates/analytes. While the influence of the counterion on the complex stability constants and anion-induced spectral changes shows a monotonous trend with increasing alkyl chain length at the prepolymerization stage, the cross-imprinting/rebinding studies showed a unique pattern that suggested the presence of adaptive cavities in the MIP matrix, related to the concept of induced fit of enzyme−substrate interaction. Larger cavities formed in the presence of larger counterions can take up pairs of Z-X-Phe and smaller TXA, eventually escaping spectroscopic detection. Correlation of the experimental data with the MD simulations revealed that counterion mobility, the relative distances between the three partners, and the hydrogen bond lifetimes are more decisive for the response features observed than actual distances between interacting atoms in a complex or the orientation of binding moieties. TBA has been found to yield the highest imprinting factor, also showing a unique dual behavior regarding the interaction with template and fluorescent monomer. Finally, interesting differences between both enantiomers have been observed in both theory and experiment, suggesting true control of enantioselectivity. The contribution concludes with suggestions for translating the findings into actual MIP development. KW - Anion receptors KW - Fluorescence sensing KW - Molecular dynamics simulations KW - Molecularly imprinted polymers KW - Rational design PY - 2018 U6 - https://doi.org/10.1021/acs.langmuir.8b00500 SN - 0743-7463 VL - 34 IS - 23 SP - 6963 EP - 6975 PB - American Chemical Society CY - Washington, D.C. AN - OPUS4-45399 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER - TY - JOUR A1 - Wagner, Sabine A1 - Bell, Jérémy A1 - Biyikal, Mustafa A1 - Gawlitza, Kornelia A1 - Rurack, Knut T1 - Integrating fluorescent molecularly imprinted polymer (MIP) sensor particles with a modular microfluidic platform for nanomolar smallmolecule detection directly in aqueous samples N2 - Fluorescent sensory MIP (molecularly imprinted polymer) particles were combined with a droplet-based 3D microfluidic system for the selective determination of a prototype small-molecule analyte of environmental concern, 2,4-dichlorophenoxyacetic acid or 2,4-D, at nanomolar concentration directly in water samples. A tailor-made fluorescent indicator cross-linker was thus designed that translates the binding event directly into an enhanced fluorescence signal. The phenoxazinone-type cross-linker was co-polymerized into a thin MIP layer grafted from the surface of silica microparticles following a RAFT (reversible addition-fragmentation chain transfer) polymerization protocol. While the indicator cross-linker outperformed its corresponding monomer twin, establishment of a phase-transfer protocol was essential to guarantee that the hydrogen bond-mediated signalling mechanism between the urea binding site on the indicator cross-linker and the carboxylate group of the analyte was still operative upon real sample analysis. The latter was achieved by integration of the fluorescent core-shell MIP sensor particles into a modular microfluidic platform that allows for an in-line phasetransfer assay, extracting the analyte from aqueous sample droplets into the organic phase that contains the sensor particles. Real-time fluorescence determination of 2,4-D down to 20 nM was realized with the system and applied for the analysis of various surface water samples collected from different parts of the world. KW - Molecular imprinting KW - Microfluidics KW - Fluorescence KW - Core-shell particles KW - Droplets PY - 2018 U6 - https://doi.org/10.1016/j.bios.2017.07.053 SN - 0956-5663 VL - 99 IS - 1 SP - 244 EP - 250 PB - Elsevier B.V. CY - Amsterdam AN - OPUS4-42258 LA - eng AD - Bundesanstalt fuer Materialforschung und -pruefung (BAM), Berlin, Germany ER -