Two- and three-dimensional mid-infrared chemical imaging

This article describes the state-of-the-art in 2D and 3D tomographic mid-IR imaging and its current and potential applications in the imaging of material and biological systems with a focus on cells and tissues. 2D FTIR microscopy is first presented in terms of the basic experimental configurations of the technique, optics, data and image acquisition. This first section provides a basis for the ensuing discussion on 3D FTIR spectro-microtomography. In the second part, examples of 2D and 3D chemical imaging are given with a focus on the use of molecular chemical probes and probe-free applications, respectively

Solvent-Free Visible-Light Photocatalysis and Synthesis in Deep-Eutectic Solvents

Methods for solvent-free photocatalysis and the synthesis in deep-eutectic solvents were developed. Chapter 1 gives an overview about reported approaches on synthesis without conventional solvents driven by thermal, mechanical, and light energy. This includes reactions in the solid state, namely mechanochemistry and solid-state photochemistry, and in liquid mixtures, focusing on photocatalysis and thermal reactions. Furthermore, the application of unconventional solvents, namely ionic liquids and deep-eutectic solvents, is discussed. In Chapter 2, a method for the solvent-free oxidation of benzylic alcohols by visible-light photocatalysis is presented. A novel rod mill reactor was developed, based on the formation of thin films of the reaction mixture. Applying this reactor, several solid benzylic alcohols were oxidized to their corresponding carbonyl compounds under blue light irradiation with riboflavin tetraacetate as photocatalyst and oxygen as terminal oxidant. Chapter 3 presents a method for the solvent-free photocatalytic conversion of paste-like reaction mixtures in a novel rotating film reactor. By rotation of the reaction vessel, a thin film is generated from the reaction mixture, enabling an efficient excitation of the photocatalyst by blue light irradiation. The reactor was used for the coupling of aryl halides with pyrrole derivatives and phosphites, applying rhodamine 6G as the photocatalyst and DIPEA as the sacrificial electron donor. The necessary amounts of photocatalyst, trapping reagent, and sacrificial electron donor were reduced significantly compared to those for literature known reactions in solution and high mole fractions of the trapping reagent are achieved. In Chapter 4, the synthesis of propargyl amines from an aldehyde, an amine, and an alkyne (“A3-coupling”) in a deep-eutectic solvent is reported. The deep-eutectic solvent consists of zinc chloride and dimethylurea, acts simultaneously as catalyst and solvent and can be recycled. A variety of propargyl amines was isolated in moderate to very good yields. Chapter 5 reports on reductive coupling reactions and reductions applying zinc in acidic deep-eutectic solvents based on choline chloride. The Barbier reaction of benzaldehyde and allyl bromide proceeds in ChCl–lactic acid; other halide substrates showed no reaction or resulted in low conversion. Furthermore, the reduction of benzaldehyde proceeds in very good conversion in several deep-eutectic solvents investigated. However, other substrates, including ketones, alkynes, alkenes, nitriles, and N-heterocycles, did not react

Suitability of lectin binding studies for the characterization of redox-active microbial environmental biofilms

Aquatic environmental microbial biofilms grow in a broad range of redox environments from oxic to methanogenic, and they often also establish internal redox gradients. In technical applications, biofilms are also subjected to controlled redox conditions. Studies on biofilms often make use of fluorescence microscopic imaging techniques together with lectin binding analysis to gain insights into structure, composition, and functions of the biofilms. Here we studied the direct influence of redox potentials on fluorescence lectin binding analyses (FLBA) for two commonly used lectin-fluorophore conjugates. An effect of the electrical potential on signal intensity was observed and found to be statistically significant. The signal intensity changes however, remained within the range of a few percent total. A significant drop in intensity was only observed for extremely oxidizing potentials, typically not found under environmental conditions. Our results showed that the fluorophore itself and not the lectin binding to the respective glycoconjugate causes fluorescence changes. The two tested lectin-fluorophores are shown to be suitable for studying the distribution and composition of EPS in environmental biofilms or technical applications and under varying redox conditions. SUPPLEMENTARY INFORMATION: The online version contains supplementary material available at 10.1186/s13568-022-01479-7

Three-dimensional mid-infrared tomographic imaging of endogenous and exogenous molecules in a single intact cell with subcellular resolution

Microscopy in the mid-infrared spectral range provides detailed chemical information on a sample at moderate spatial resolution and is being used increasingly in the characterization of biological entities as challenging as single cells. However, a conventional cellular 2D imaging measurement is limited in its ability to associate specific compositional information to subcellular structures because of the interference from the complex topography of the sample. Herein we provide a method and protocols that overcome this challenge in which tilt-series infrared tomography is used with a standard benchtop infrared microscope. This approach gives access to the quantitative 3D distribution of molecular components based on the intrinsic contrast provided by the sample. We demonstrate the method by quantifying the distribution of an exogenous metal carbonyl complex throughout the cell and by reporting changes in its coordination sphere in different locations in the cell

Competing Sorption of Se(IV) and Se(VI) on Schwertmannite

Schwertmannite (SHM) is a naturally occurring mineral that has been shown to effectively scavenge oxyanions from contaminated water. In this study, Fourier-transform infrared spectroscopy and X-ray absorption spectroscopy techniques in combination with wet-chemical techniques were used to study the competitive sorption of Se(IV) and Se(VI) at pH 3. The experiments were conducted with three types of schwertmannite obtained from oxidative synthesis, biogenic synthesis and high-pressure compaction at different initial Se concentrations and mixing ratios for 48 h and 56 days, respectively. A threshold value for the uptake mechanisms was identified, which reflects the amount of easily exchangeable sulphate (~0.5 mmol/g). At adsorbate concentrations below this threshold, an inner-sphere corner-sharing bidentate binuclear complex forms upon exchange with sulphate. At higher concentrations, both oxyanions become bound to SHM through co-occurrence of mainly inner-sphere and partly outer-sphere corner-sharing bidentate binuclear complexes with Fe(III) containing surface sites. Single species experiments clearly indicate a higher affinity of SHM for Se(IV). However, in mixed species experiments, competitive sorption occurs with equal or even preferential uptake of Se(VI) at concentrations much lower than the threshold value, presumably due to geometrical similarity between selenate and sulphate, and increasing preference for Se(IV) at high Se concentrations

Spectral Control via Multi-Species Effects in PW-Class Laser-Ion Acceleration

Laser-ion acceleration with ultra-short pulse, PW-class lasers is dominated by non-thermal, intra-pulse plasma dynamics. The presence of multiple ion species or multiple charge states in targets leads to characteristic modulations and even mono-energetic features, depending on the choice of target material. As spectral signatures of generated ion beams are frequently used to characterize underlying acceleration mechanisms, thermal, multi-fluid descriptions require a revision for predictive capabilities and control in next-generation particle beam sources. We present an analytical model with explicit inter-species interactions, supported by extensive ab initio simulations. This enables us to derive important ensemble properties from the spectral distribution resulting from those multi-species effects for arbitrary mixtures. We further propose a potential experimental implementation with a novel cryogenic target, delivering jets with variable mixtures of hydrogen and deuterium. Free from contaminants and without strong influence of hardly controllable processes such as ionization dynamics, this would allow a systematic realization of our predictions for the multi-species effect.Comment: 4 pages plus appendix, 11 figures, paper submitted to a journal of the American Physical Societ

Modulation of visual processing of food by transcutaneous vagus nerve stimulation (tVNS)

Present project is concerned with the possibility to modulate the neural regulation of food intake by non-invasive stimulation of the vagus nerve. This nerve carries viscero-afferent information from the gut and other internal organs and therefore serves an important role in ingestive behavior. The electrical stimulation of the vagus nerve (VNS) is a qualified procedure in the treatment of drug-resistant epilepsy and depression. Since weight loss is a known common side effect of VNS treatment in patients with implanted devices, VNS is evaluated as a treatment of obesity. To investigate potential VNS-related changes in the cognitive processing of food-related items, 21 healthy participants were recorded in a 3-Tesla scanner in two counterbalanced sessions. Participants were presented with 72 food pictures and asked to rate how much they liked that food. Before entering the scanner subjects received a 1-h sham or verum stimulation, which was implemented transcutanously with a Cerbomed NEMOS® device. We found significant activations in core areas of the vagal afferent pathway, including left brainstem, thalamus, temporal pole, amygdala, insula, hippocampus, and supplementary motor area for the interaction between ratings (high vs low) and session (verum vs sham stimulation). Significant activations were also found for the main effect of verum compared to sham stimulation in the left inferior and superior parietal cortex. These results demonstrate an effect of tVNS on food image processing even with a preceding short stimulation period. This is a necessary prerequisite for a therapeutic application of tVNS which has to be evaluated in longer-term studies

Microplastics accumulate fungal pathogens in terrestrial ecosystems

Microplastic (MP) is a pervasive pollutant in nature that is colonised by diverse groups of microbes, including potentially pathogenic species. Fungi have been largely neglected in this context, despite their affinity for plastics and their impact as pathogens. To unravel the role of MP as a carrier of fungal pathogens in terrestrial ecosystems and the immediate human environment, epiplastic mycobiomes from municipal plastic waste from Kenya were deciphered using ITS metabarcoding as well as a comprehensive meta-analysis, and visualised via scanning electron as well as confocal laser scanning microscopy. Metagenomic and microscopic findings provided complementary evidence that the terrestrial plastisphere is a suitable ecological niche for a variety of fungal organisms, including important animal and plant pathogens, which formed the plastisphere core mycobiome. We show that MPs serve as selective artificial microhabitats that not only attract distinct fungal communities, but also accumulate certain opportunistic human pathogens, such as cryptococcal and Phoma-like species. Therefore, MP must be regarded a persistent reservoir and potential vector for fungal pathogens in soil environments. Given the increasing amount of plastic waste in terrestrial ecosystems worldwide, this interrelation may have severe consequences for the trans-kingdom and multi-organismal epidemiology of fungal infections on a global scale