Gregor Alexander Groß

Cationic heteroarylstilbenes, such as the furanyl-indolinium chromophore, represent a class of watersoluble, visible-light-responsive photoswitches. However, their photochemical behaviour under physiologically relevant pH conditions remains insufficiently understood. In this study, four derivatives were synthesized and systematically investigated, with particular emphasis on their photoswitching properties at three pH values using phosphate-buffered media. The visible-light-induced E/Z photoisomerization kinetics were analysed by UV/Vis spectroscopy, while the structures of the resulting isomers were confirmed by NMR spectroscopy. A key result is the pronounced pH dependence of the thermal Z→E back-isomerization in phosphate buffer, whereas the photoinduced E→Z switching is only weakly affected. The apparent thermal recovery is superimposed by a competing dark-decay process, which was quantified independently to separate concurrent degradation from the actual thermal back-isomerization kinetics. The derivatives differ in their chemical stability. The methyl-substituted derivative is comparatively robust, whereas the nitro-substituted derivative shows pronounced degradation. These results show that water solubility alone does not guarantee robust photoswitching under biologically relevant conditions and that both pH-dependent switching kinetics and chemical stability must be considered in the design of cationic heteroarylstilbene photoswitches.

Ortho-Nitrobenzyl (oNB) esters are widely employed as photolabile protecting groups and linkers in diverse applications ranging from materials science to chemical biology. While their photochemical decomposition mechanism has been well studied, a comprehensive understanding of the structure–property relationships governing their photolysis kinetics remains lacking. In this study, the synthesis and kinetic analysis of 11 novel oNB esters with varying ester and aromatic substituents are reported. Using time-resolved NMR spectroscopy, we determined first-order rate constants for the photochemical cleavage of each compound under UV irradiation. A clear correlation between the reaction rate and the acidity (pK _a) of the corresponding acid anion, with more acidic leaving groups yielding faster decomposition, was found. In contrast, the nature of the substituents on the aromatic ring shows no strong correlation with Hammett parameters or steric hindrance, quantified by Sterimol parameters. A multilinear model incorporating both steric and electronic parameters confirms this observation. Our findings highlight the critical role of the ester moiety in tuning photolysis rates while suggesting that aromatic substitution can be strategically employed for functionalization (e.g., polymer cross-linking) without substantially affecting reactivity. These insights lay the foundation for the rational design of photoresponsive oNB-based linkers for advanced materials and chemical applications.

A microfluidic transfer tool (MTT) was designed to pick objects and store them intermediately in a droplet sequence before placement. Overall system achieved a significantly increased throughput when sorting 50 μm polymer beads or 20 μm plant pollen.

Here, we present a protocol for the one-step synthesis of the title compound in quantitative yield using adapted Vilsmeier conditions. The product was characterized by ¹H-,²H-,¹³C-NMR-, as well as IR and Raman spectroscopy. Spectral data are given in detail.

Alkyd resins are oil-based polymers that have been widely used for generations in the surface coating industry and beyond. Characterization of these resins is of high importance to understand the influence of its components on its behavior, compatibility with other resins, and final quality to ensure high durability. Here, NMR spectroscopy and GPC were used for characterizing differences in the chemical structure, molecular distribution, and dispersity between oil-based and fatty acid-based alkyd polymers made from sacha inchi and linseed oils. Sancha inchi (Plukentia volubilis L.) is a fruit-bearing plant native to South America and the Caribbean, and has a rich unsaturated fatty acid content. The effect of vegetable oil and polyol selection on the synthesis of alkyd resins for coating applications was analyzed. The influence of two different synthesis methods, monoglyceride and fatty acid processes, was also compared. Important structural differences were observed using NMR: one-dimensional spectra revealed the degree of unsaturated fatty acid chains along the polyester backbone, whereas, 2D NMR experiments facilitated chemical shift assignments of all signals. GPC analysis suggested that alkyd resins with homogeneous and high molecular weights can be obtained with the fatty acid process, and that resins containing pentaerythritol may have uniform chain lengths.

Droplet-based microfluidic screening techniques can benefit from interfacing established microtiter plate-based screening and sample management workflows. Interfacing tools are required both for loading preconfigured microtiter-plate (MTP)-based sample collections into droplets and for dispensing the used droplets samples back into MTPs for subsequent storage or further processing. Here, we present a collection of Digital Microfluidic Pipetting Tips (DMPTs) with integrated facilities for droplet generation and manipulation together with a robotic system for its operation. This combination serves as a bidirectional sampling interface for sample transfer from wells into droplets (w2d) and vice versa droplets into wells (d2w). The DMPT were designed to fit into 96-deep-well MTPs and prepared from glass by means of microsystems technology. The aspirated samples are converted into the channel-confined droplets’ sequences separated by an immiscible carrier medium. To comply with the demands of dose-response assays, up to three additional assay compound solutions can be added to the sample droplets. To enable different procedural assay protocols, four different DMPT variants were made. In this way, droplet series with gradually changing composition can be generated for, e.g., 2D screening purposes. The developed DMPT and their common fluidic connector are described here. To handle the opposite transfer d2w, a robotic transfer system was set up and is described briefly.

Real-time monitoring of bioanalytes in organotypic cell cultivation devices is a major research challenge in establishing stand-alone diagnostic systems. Presently, no general technical facility is available that offers a plug-in system for bioanalytics in diversely available organotypic culture models. Therefore, each analytical device has to be tuned according to the microfluidic and interface environment of the 3D in vitro system. Herein, we report the design and function of a 3D automated culture and analysis device (3D-ACAD) which actively perfuses a custom-made 3D microbioreactor, samples the culture medium and simultaneously performs capillary-based flow ELISA. A microstructured MatriGrid^® has been explored as a 3D scaffold for culturing HepaRG cells, with albumin investigated as a bioanalytical marker using flow ELISA. We investigated the effect of acetaminophen (APAP) on the albumin secretion of HepaRG cells over 96 h and compared this with the albumin secretion of 2D monolayer HepaRG cultures. Automated on-line monitoring of albumin secretion in the 3D in vitro mode revealed that the application of hepatotoxic drug-like APAP results in decreased albumin secretion. Furthermore, a higher sensitivity of the HepaRG cell culture in the automated 3D-ACAD system to APAP was observed compared to HepaRG cells cultivated as a monolayer. The results support the use of the 3D-ACAD model as a stand-alone device, working in real time and capable of analyzing the condition of the cell culture by measuring a functional analyte. Information obtained from our system is compared with conventional cell culture and plate ELISA, the results of which are presented herein.

Droplet-based microfluidics is a versatile tool to reveal the dose–response relationship of different effectors on the microbial proliferation. Traditional readout parameter is the temporal development of the cell density for different effector concentrations. To determine nonlinear or unconventional dose–response relationships, data with high temporal resolution and dense concentration graduation are essential. If microorganisms with slow microbial growth kinetics are investigated, a sterile and evaporation-free long-term incubation technique is required. Here, we present a modular droplet-based screening system which was developed to solve these issues. Beside relevant technical aspects of the developed modules, the procedural workflow, and exemplary dose–response data for 1D and 2D dose–response screenings are presented.

The defined formation and expansion of droplets are essential operations for droplet-based screening assays. The volumetric expansion of droplets causes a dilution of the ingredients. Dilution is required for the generation of concentration graduation which is mandatory for many different assay protocols. Here, we describe the design of a microfluidic operation unit based on a bypassed chamber and its operation modes. The different operation modes enable the defined formation of sub-µL droplets on the one hand and the expansion of low nL to sub-µL droplets by controlled coalescence on the other. In this way the chamber acts as fluidic interface between two fluidic network parts dimensioned for different droplet volumes. Hence, channel confined droplets of about 30–40 nL from the first network part were expanded to cannel confined droplets of about 500 to about 2500 nL in the second network part. Four different operation modes were realized: (a) flow rate independent droplet formation in a self-controlled way caused by the bypassed chamber design, (b) single droplet expansion mode, (c) multiple droplet expansion mode, and (d) multiple droplet coalescence mode. The last mode was used for the automated coalescence of 12 droplets of about 40 nL volume to produce a highly ordered output sequence with individual droplet volumes of about 500 nL volume. The experimental investigation confirmed a high tolerance of the developed chamber against the variation of key parameters of the dispersed-phase like salt content, pH value and fluid viscosity. The presented fluidic chamber provides a solution for the problem of bridging different droplet volumes in a fluidic network.