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Item type:Publication, Access status: without files , Carboxylic Groups via Postpolymerization Modification of Polythiophene and their Influence on the Performance of a Polymeric MALDI Matrix(2023-01-01); ; ; ; Matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) requires a matrix, and traditionally small organic matrices (SOMs) carrying acidic or basic functional groups are used. However, the analyte ionization via secondary processes in the gas-phase seems to be more important than primary processes. For conjugated polymeric matrices, an even more complicated picture emerges due to their apolar and aprotic nature, high molecular weight, and low tendency to desorb. Poly(3-dodecylthiophene-2,5-diyl) (P3DDT), a good matrix for low-molecular weight (LMW) analytes, does not give matrix-related peaks in the LMW area. Here, carboxylic acid (-COOH) side-chains are introduced via postpolymerization modification. The polymers are characterized by NMR, FT-IR, CV, MALDI MS, and, when possible, GPC. The electron withdrawing side-chains serve three functions; i) raising the ionization potential (IP), ii) improving the absorption maximum, and iii) acting as a source of protons. When measuring basic amines, this results in the occurrence of additional [Analyte + H+]+ signals compared to polymers without acidic groups, where only radical cations [Analyte]+• are detected. Similarly, estradiol and testosterone, compounds with high IPs, are not detected by polythiophenes without acidic groups, while P3DDT-COOH enables detection as protonated species.Publicationtype: Journal Article29 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Synthesis of linear unsubstituted poly(4,4′-triphenylamine) via Suzuki-Miyaura coupling of an asymmetric AB monomer(2022-06-15); ; ; ; Polytriarylamines (PTAAs) are amorphous polymers that can be reversibly oxidized to generate stable radical cations. Despite exhibiting a low charge carrier mobility, PTAAs are widely used as hole-transporting layers in perovskite solar cells due to their excellent stability under ambient conditions. The highest occupied molecular orbital (HOMO) energy levels of PTAA are generally in the range of −5.1 to −5.2 eV, and therefore slightly too high for an optimal alignment with perovskites. Most linear PTAAs carry two or three methyl substituents per repeating unit. While these prevent crosslinking of chains and thus provide reaction control, the electron-donating substituents raise the energy level of the HOMO. Unsubstituted PTAA on the other hand is usually obtained crosslinked via oxidative polymerization, while nickel-catalyzed Grignard polycondensation leads to inclusion of impurities. We report the synthesis of linear unsubstituted PTAA using Suzuki-Miyaura coupling of a novel asymmetric monomer, 4-((4-bromophenyl)(phenyl)amino)phenyl)boronic acid M1. Based on matrix-assisted laser desorption/ionization-time of flight (MALDI-TOF) and 1H NMR analysis, we can conclude that the hydrogen-terminated linear polymer is obtained. The determined HOMO energy level of −5.47 eV is a favorable match for many perovskite systems.Publicationtype: Journal Article16 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Polymerization as a Strategy to Improve Small Organic Matrices for Low-Molecular-Weight Compound Analytics with MALDI MS and MALDI MS Imaging(2021-08-13); ; ; ; Matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) and the corresponding visualizing technique MALDI MS imaging (MSI) are potent and widely used analytical methods in medical and pathological research. In recent years, the investigation of low-molecular-weight compounds (LMWCs) such as metabolites has moved increasingly into the focus. MALDI techniques require a matrix system, and small organic matrices (SOMs) are commonly used. While SOMs offer multiple advantages, such as broad analyte scopes and high ionization efficiencies, they also suffer from drawbacks, e.g., strong background interferences in the low-mass area (m/z < 1000) and low vacuum stability, which is particularly detrimental for LMWC analytics with high vacuum (HV) MALDI MS and MSI. Here, we apply polymerization as a strategy to alleviate these drawbacks while retaining the multiple advantages of SOMs. Vinyl groups were introduced to two SOMs, the state-of-the-art positive mode matrix 2,5-dihydroxybenzoic acid (DHB) as well as one of the few known dual polarity mode matrices, 7-methoxy-1-methyl-9H-pyrido[3,4-b]indole (harmine), and radical polymerization was performed to obtain polyethylene-based P(SOMs) carrying the corresponding SOMs as side chains. Compared to the corresponding SOMs, the synthesized P(SOMs) maintain optical properties in the solid state and have competitive performances regarding analyte scopes, ionization efficiencies, and dual polarity mode suitability. Additionally, both P(SOMs) are HV stable (μ10-7 mbar) and reveal no background interferences in the low-mass area (MALDI-silent). To assess a potential application in a clinical workflow, the P(SOMs) were applied on breast cancer xenografts and MALDI MSI measurements were carried out, demonstrating their ability to produce and spatially resolve positive and negative tissue-related ions directly from the cancer tissue. Polymerization is shown to be a promising strategy to make state-of-the-art SOMs MALDI silent and vacuum stable and yield easily handled matrices for clinical workflows.Publicationtype: Journal Article16 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , MALDI Matrices for the Analysis of Low Molecular Weight Compounds: Rational Design, Challenges and Perspectives(2021-04-19); The analysis of low molecular weight (LMW) compounds is of great interest to detect small pharmaceutical drugs rapidly and sensitively, or to trace and understand metabolic pathways. Matrix-assisted laser desorption/ionization mass spectrometry (MALDI MS) plays a central role in the analysis of high molecular weight (bio)molecules. However, its application for LMW compounds is restricted by spectral interferences in the low m/z region, which are produced by conventional organic matrices. Several strategies regarding sample preparation have been investigated to overcome this problem. A different rationale is centred on developing new matrices which not only meet the fundamental requirements of good absorption and high ionization efficiency, but are also vacuum stable and “MALDI silent”, i. e., do not give matrix-related signals in the LMW area. This review gives an overview on the rational design strategies used to develop matrix systems for the analysis of LMW compounds, focusing on (i) the modification of well-known matrices, (ii) the search for high molecular weight matrices, (iii) the development of binary, hybrid and nanomaterial-based matrices, (iv) the advance of reactive matrices and (v) the progress made regarding matrices for negative or dual polarity mode.Publicationtype: Journal ArticleScopus© Citations 33 21 - Some of the metrics are blocked by yourconsent settings
Item type:Publication, Access status: without files , Poly(3-hexylthiophene)s Functionalized with N-Heterocyclic Carbenes as Robust and Conductive Ligands for the Stabilization of Gold Nanoparticles(2021-02-19); ; ; ; Recently, N-heterocyclic carbenes (NHCs) are explored as anchor groups to bind organic ligands to colloidal gold (i.e. gold nanoparticles, Au NPs), yet these efforts are confined to non-conjugated ligands so far—that is, focused solely on exploiting the stability aspect. Using NHCs to link Au NPs and electronically active organic components, for example, conjugated polymers (CPs), will allow capitalizing on both the stability as well as the inherent conductivity of the NHC anchors. Here, we report three types of Br-NHC-Au-X (X=Cl, Br) complexes, which, when used as starting points for Kumada polymerizations, yield regioregular poly(3-hexylthiophenes)-NHC-Au (P3HTs-NHC-Au) with narrow molecular weight distributions. The corresponding NPs are obtained via direct reduction and show excellent thermal as well as redox stability. The NHC anchors enable electron delocalization over the gold/CP interface, resulting in an improved electrochromic response behavior in comparison with P3HT-NHC-Au.Publicationtype: Journal ArticleScopus© Citations 19 18