Clemens Schwarzinger

Air-stable organic semiconductors based on 6,6′-dithienylindigo and polymers thereof

Herein we report on the synthesis and properties of 6,6′-dithienylindigo (DTI), as well as its solubilized N,N′-di(tert-butoxy carbonyl) derivative (tBOC-DTI). tBOC-DTI can be electropolymerized and thermally interconverted into films of poly(DTI). Thin films of DTI afford quasi-reversible 2-electron reduction and oxidation electrochemistry, and demonstrate ambipolar charge transport in organic field-effect transistors with a hole mobility of up to 0.11 cm2 V−1 s−1 and an electron mobility of up to 0.08 cm2 V−1 s−1. Operation of the p-channel shows excellent air stability, with minimal degradation over a 60 day stressing study. Poly(DTI) can be reversibly oxidized and reduced over hundreds of cycles while remaining immobilized on the working electrode surface, and additionally shows a pronounced photoconductivity response in a diode device geometry. This work shows the potential of extended indigo derivatives for organic electronic applications, demonstrating impressive stability under ambient conditions.

Levoglucosan, cellobiose and their acetates as model compounds for the thermally assisted hydrolysis and methylation of cellulose and cellulose acetate

Levoglucosan (1,6-anhydro-β-d-glucopyranose), cellobiose (β-d-glucopyranosyl-[1→4]-d-glucopyranose), tri-O-acetyl-levoglucosan (1,6-anhydro-β-d-glucopyranose-2,3,4-triacetate) and cellobiose octaacetate have been studied with regard to their suitability as model compounds for thermally assisted hydrolysis and methylation with tetramethylammonium hydroxide of cellulose and cellulose acetate. In addition, the results of analytical pyrolysis of methyl cellulose were compared with those of thermally assisted hydrolysis and methylation, to distinguish between products arising from alkaline hydrolysis and pyrolytic cleavage, respectively. Parameters such as surplus of tetramethylammonium hydroxide, water content prior to pyrolysis and pyrolysis temperature were varied to find the optimal thermochemolysis procedure for cellulosic samples.

Improved analysis of melamine-formaldehyde resins by capillary zone electrophoresis-mass spectrometry using ion-trap and quadrupole-time-of-flight mass spectrometers.

An improved method based on capillary zone electrophoresis (CZE) coupled to either ion-trap (IT) mass spectrometry (MS) or quadrupole-time-of-flight (Q-TOF) MS for the analysis of melamine-formaldehyde condensates is presented. Employing a formic acid-based electrolyte containing 50% acetonitrile (ACN) and MS detection up to 13 compounds could be determined in lab-made resins, synthesized by mixing formaldehyde and melamine in different ratios ranging from 1:1.5 to 1:4. The use of a Q-TOF-MS for detection allowed the assignment of molecular formulas for all 13 substances with high accuracy.

Electrocatalytic Reduction of Carbon Dioxide to Carbon Monoxide by a Polymerized Film of an Alkynyl‐Substituted Rhenium(I) Complex

The alkynyl‐substituted ReI complex [Re(5,5′‐bisphenylethynyl‐2,2′‐bipyridyl)(CO)3Cl] was immobilized by electropolymerization onto a Pt‐plate electrode. The polymerized film exhibited electrocatalytic activity for the reduction of CO2 to CO. Cyclic voltammetry studies and bulk controlled‐potential electrolysis experiments were performed by using a CO2‐saturated acetonitrile solution. The CO2 reduction, determined by cyclic voltammetry, occurs at approximately −1150 mV versus the normal hydrogen electrode (NHE). Quantitative analysis by GC and IR spectroscopy was used to determine a Faradaic efficiency of approximately 33 % for the formation of CO. Both values of the modified electrode were compared to the performance of the homogenous monomer [Re(5,5′‐bisphenylethynyl‐2,2′‐bipyridyl)(CO)3Cl] in acetonitrile. The polymer formation and its properties were studied by using SEM, AFM, and attenuated total reflectance (ATR) FTIR and UV/Vis spectroscopy.

An Analysis of Diet Quality, How It Controls Fatty Acid Profiles, Isotope Signatures and Stoichiometry in the Malaria Mosquito Anopheles arabiensis

Background Knowing the underlying mechanisms of mosquito ecology will ensure effective vector management and contribute to the overall goal of malaria control. Mosquito populations show a high degree of population plasticity in response to environmental variability. However, the principle factors controlling population size and fecundity are for the most part unknown. Larval habitat and diet play a crucial role in subsequent mosquito fitness. Developing the most competitive insects for sterile insect technique programmes requires a “production” orientated perspective, to deduce the most effective larval diet formulation; the information gained from this process offers us some insight into the mechanisms and processes taking place in natural native mosquito habitats. Methodology/Principal Findings Fatty acid profiles and de-novo or direct assimilation pathways, of whole-individual mosquitoes reared on a range of larval diets were determined using pyrolysis gas chromatograph/mass spectrometry. We used elemental analysis and isotope ratio mass spectrometry to measure individual-whole-body carbon, nitrogen and phosphorous values and to assess the impact of dietary quality on subsequent population stoichiometry, size, quality and isotopic signature. Diet had the greatest impact on fatty acid (FA) profiles of the mosquitoes, which exhibited a high degree of dietary routing, characteristic of generalist feeders. De-novo synthesis of a number of important FAs was observed. Mosquito C:N stoichiometry was fixed in the teneral stage. Dietary N content had significant influence on mosquito size, and P was shown to be a flexible pool which limited overall population size. Conclusions/Significance Direct routing of FAs was evident but there was ubiquitous de-novo synthesis suggesting mosquito larvae are competent generalist feeders capable of survival on diet with varying characteristics. It was concluded that nitrogen availability in the larval diet controlled teneral mosquito size and that teneral CN ratio is a sex- and species-specific fixed parameter. This finding has significant implications for overall mosquito competitiveness and environmental management.

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometric imaging of synthetic polymer sample spots prepared using ionic liquid matrices.

RATIONALE Polymer sample spots for matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) prepared by the dried-droplet method often reveal ring formation accompanied by possible segregation of matrix and sample molecules as well as of the polymer homologs itself. Since the majority of sample spots are prepared by this simple and fast method, a matrix or sample preparation method that excludes such segregation has to be found. METHODS Three different ionic liquid matrices based on conventionally used aromatic compounds for MALDI-TOF MS were prepared. The formation of ionic liquids was proven by (1) H NMR spectroscopy. MALDI-Imaging mass spectrometry was applied to monitor the homogeneity. RESULTS Our results show a superior sample spot homogeneity using ionic liquid matrices. Spots could be sampled several times without visible differences in the mass spectra. A frequently observed loss of matrix in the mass spectrometer vacuum was not observed. The necessary laser irradiance was reduced, which resulted in less polymer fragmentation. CONCLUSIONS Ionic liquid matrices can be used to overcome segregation, a typical drawback of conventional MALDI dried-droplet preparations. Homogeneous sample spots are easy to prepare, stable in the MS vacuum and, thereby, improve the reproducibility of MALDI.

Quantitative Analysis of Polymer Additives with MALDI-TOF MS Using an Internal Standard Approach

MALDI-TOF MS is used for the qualitative analysis of seven different polymer additives directly from the polymer without tedious sample pretreatment. Additionally, by using a solid sample preparation technique, which avoids the concentration gradient problems known to occur with dried droplets and by adding tetraphenylporphyrine as an internal standard to the matrix, it is possible to perform quantitative analysis of additives directly from the polymer sample. Calibration curves for Tinuvin 770, Tinuvin 622, Irganox 1024, Irganox 1010, Irgafos 168, and Chimassorb 944 are presented, showing coefficients of determination between 0.911 and 0.990.

THM-GC/MS analysis of model uronic acids of pectin and hemicelluloses

Abstract The thermally assisted hydrolysis and methylation (THM) reaction of hexuronic acids and xylobiose using tetramethylammonium hydroxide (TMAH) was studied. The results were compared to the THM of the corresponding matrix polymers. Glucuronic and galacturonic acids—which we take as model substances—produce unique products, namely 2,4,6-tri- O -methyl-3-deoxy-glucaric acid dimethyl ester and tri- O -methyl-3-deoxy-galactaric acid dimethyl ester, respectively, together with their epimers. The EI mass spectrum, as well as a proposed fragmentation pathway, are presented. These markers, however, are not detectable in the THM of the corresponding polymers, i.e. the hemicellulose xylan and pectin.

Pyrolysis GC/MS and IR spectroscopy in chitin analysis of molluscan shells.

Chitin is an insoluble component in the shells of several molluscan species. It is thought to play important roles, in biomineralization and shell structure. To date, however, reports are scarce and sometimes contradictory, and suffer from methodological problems. Only in a single cephalopod species has the chitin been identified as β-chitin. We present data on chitin occurrence in 22 species of shell-bearing Mollusca (Conchifera) and Polyplacophora, including the first evidence for scaphopods, based on pyrolysis gas chromatography, mass spectrometry (GC-MS), and infrared spectroscopy (IR). Pyrolysis GC-MS detected chitin in every tested member of the Conchifera. IR spectroscopy before and after chitinase treatment revealed at least three distinct patterns of peak changes. The contents of the insoluble shell organics included not only chitin and proteins, but also insoluble polysaccharides, e.g., glucan. We conclude that chitin was present in the last common ancestor of the Conchifera and that its abundance in the shell matrix depends on the differentiation of the shell.

On the mechanism of thermally assisted hydrolysis and methylation of carbohydrates: the contribution of aldol and retroaldol reactions

Abstract The thermally assisted hydrolysis and methylation (THM) analysis of glycolaldehyde produces a series of methylated C3 to C6 metasaccharinic acids by aldol reactions. The contribution of aldol and retro aldol reactions was investigated by analysis of 1-13C-glycolaldehyde, 1-13C-glucose, and 6-13C-glucose. It could be shown that carbohydrates undergo retro aldol cleavage under strong alkaline conditions, as they are in THM, and that these cleavage products subsequently produce higher molecular weight condensation products by aldol reactions. The cleavage occurs more readily close to the reducing end of the carbohydrate and recombination of these fragments may account for up to 30% of the saccharinic acid products formed.