Investigation of the cooperative-effects of Lewis- and Brønstedt acids in homogeneously catalyzed OME fuel synthesis by inline-NMR monitoring.

Via inline-nuclear magnetic resonance measurements, the homogeneously catalyzed poly(oxymethylene dimethyl ether) fuel synthesis using trioxane and dimethoxy methane is investigated. Besides the Brønsted acid (BA) catalyst triflic acid (TfOH) different metal halides are studied as Lewis-acidic (LA) catalysts. Among the used LAs, MgCl2, the weakest based on electronegativity, reveals the highest catalytical activity. Additionally, the influence of the concentration of BA and LA is investigated. An increase in BA concentration leads to an exponential increase of the reaction rate, while increasing the concentration of the LA leads to a volcano plot with its optimum at a LA : BA ratio of 1 : 3. The influence of the LA on the electron density of the intermediate formaldehyde is concluded as the main factor for this behavior.

Evaluation of restricted access media for the purification of cell culture-derived Orf viruses.

Recently, multimodal chromatography using restricted access media (RAM) for the purification of nanoparticles, such as viruses has regained increasing attention. These chromatography resins combine size exclusion on the particle shell and adsorptive interaction within the core. Accordingly, smaller process-related impurities, for example, DNA and proteins, can be retained, while larger product viruses can pass unhindered. We evaluated a range of currently available RAM, differing in the shells' pore cut-off and the core chemistry, for the purification of a cell culture-derived clarified model virus, namely the Orf virus (ORFV). We examined impurity depletion and product recovery as relevant criteria for the evaluation of column performance, as well as scale-up robustness and regeneration potential for evaluating a multiple use application. The results indicate that some columns, for example, the Capto Core, enable both a high DNA and protein removal, while others, for example, the Monomix Core 60 (MC60), are more suitable for DNA depletion. Furthermore, column regeneration is facilitated by using columns with larger shell pores (5000 vs. 700 kDa) and weaker binding interactions (anion exchange vs. multimodal). According to these findings, the choice of RAM resins should be selected according to the respective feed sample composition and the planned number of application cycles.

Micro-flow size-exclusion chromatography for enhanced native mass spectrometry of proteins and protein complexes.

Size-exclusion chromatography (SEC) employing aqueous mobile phases with volatile salts at neutral pH combined with native mass spectrometry (nMS) is a valuable tool to characterize proteins and protein aggregates in their native state. However, the liquid-phase conditions (high salt concentrations) frequently used in SEC-nMS hinder the analysis of labile protein complexes in the gas phase, necessitating higher desolvation-gas flow and source temperature, leading to protein fragmentation/dissociation. To overcome this issue, we investigated narrow SEC columns (1.0 mm internal diameter, I.D.) operated at 15-µL/min flow rates and their coupling to nMS for the characterization of proteins, protein complexes and higher-order structures (HOS). The reduced flow rate resulted in a significant increase in the protein-ionization efficiency, facilitating the detection of low-abundant impurities and HOS up to 230 kDa (i.e., the upper limit of the Orbitrap-MS instrument used). More-efficient solvent evaporation and lower desolvation energies allowed for softer ionization conditions (e.g., lower gas temperatures), ensuring little or no structural alterations of proteins and their HOS during transfer into the gas phase. Furthermore, ionization suppression by eluent salts was decreased, permitting the use of volatile-salt concentrations up to 400 mM. Band broadening and loss of resolution resulting from the introduction of injection volumes exceeding 3% of the column volume could be circumvented by incorporating an online trap-column containing a mixed-bed ion-exchange (IEX) material. The online IEX-based solid-phase extraction (SPE) or "trap-and-elute" set-up provided on-column focusing (sample preconcentration). This allowed the injection of large sample volumes on the 1-mm I.D. SEC column without compromising the separation. The enhanced sensitivity attained by the micro-flow SEC-MS, along with the on-column focusing achieved by the IEX precolumn, provided picogram detection limits for proteins.

Oxymethylene Ether (OME) Fuel Catalyst Screening Using In Situ NMR Spectroscopy.

Online NMR measurements are introduced in the current study as a new analytical setup for investigation of the oxymethylene dimethyl ether (OME) synthesis. For the validation of the setup, the newly established method is compared with state-of-the-art gas chromatographic analysis. Afterwards, the influence of different parameters, such as temperature, catalyst concentration and catalyst type on the OME fuel formation based on trioxane and dimethoxymethane is investigated. As catalysts, AmberlystTM 15 (A15) and trifluoromethanesulfonic acid (TfOH) are utilized. A kinetic model is applied to describe the reaction in more detail. Based on these results, the activation energy (A15: 48.0 kJ mol-1 and TfOH: 72.3 kJ mol-1 ) and the order in catalyst (A15: 1.1 and TfOH: 1.3) are calculated and discussed.

Two-Dimensional Photosensitizer Nanosheets via Low-Energy Electron Beam Induced Cross-Linking of Self-Assembled RuII Polypyridine Monolayers.

Artificial photosynthesis for hydrogen production is an important element in the search for green energy sources. The incorporation of photoactive units into mechanically stable 2D materials paves the way toward the realization of ultrathin membranes as mimics for leaves. Here we present and compare two concepts to introduce a photoactive RuII polypyridine complex into ≈1 nm thick carbon nanomembranes (CNMs) generated by low-energy electron irradiation induced cross-linking of aromatic self-assembled monolayers. The photoactive units are either directly incorporated into the CNM scaffold or covalently grafted to its surface. We characterize RuII CNMs using X-ray photoelectron, surface-enhanced Raman, photothermal deflection spectroscopy, atomic force, scanning electron microscopy, and study their photoactivity in graphene field-effect devices. Therewith, we explore the applicability of low-energy electron irradiation of metal complexes for photosensitizer nanosheet formation.

Solution-Based Self-Assembly and Stability of Ruthenium(II) Tris-bipyridyl Monolayers on Gold.

Ruthenium(II) polypyridyl complexes are commonly applied as photosensitizers in the fields of artificial photosynthesis and light harvesting. Their immobilization on gold surfaces is also of interest for sensing and biological applications. Here, we report the self-assembly of [Ru(dmbpy)2(dcbpy)](PF6)2 complexes on gold substrates from solution (dmbpy: 4,4'-dimethyl-2,2'-bipyridine; dcbpy: 2,2'-bipyridine-4,4'-dicarboxylic acid). Applying X-ray photoelectron spectroscopy, we demonstrate the formation of self-assembled monolayers (SAMs) of the Ru(II) complexes upon loss of counterions with carboxylate groups oriented toward the gold surface. We investigate the stability of the formed SAMs toward the substitution in solvents with competing aliphatic and aromatic thiols such as 4'-nitro[1,1'-biphenyl]-4-thiol, [1,1'-biphenyl]-4-thiol, and 1-hexadecanethiol. We show that the exchange reactions may lead to both complete replacement of the Ru(II) complexes and controlled formation of mixed SAMs. Moreover, we demonstrate that thiol-based SAMs can also be replaced completely from gold via their immersion into solutions of [Ru(dmbpy)2(dcbpy)](PF6)2, indicating a relatively high stability for the Ru(II) complex SAMs. Our findings open up a variety of opportunities for applications of carboxylate-based SAMs on gold in nanotechnology.

Evaluation of hydrophobic-interaction chromatography resins for purification of antibody-drug conjugates using a mimetic model with adjustable hydrophobicity.

Antibody drug conjugates are cytotoxic pharmaceuticals, designed to destroy malignant cells. A cytotoxic molecule is attached to an antibody that binds specific to a cancer-cell surface. Given the high toxicity of the drugs, strict safety standards have to be kept. For this reason, an antibody drug conjugates model was developed with fluorescein 5-isothiocyanate as the nontoxic payload surrogate. Due to the similar hydrophobicity, this model is used to establish a suitable purification process and characterization method for antibody drug conjugates. Because of the pH dependent solubility of fluorescein, the hydrophobicity of conjugates can be modulated by the pH value. Based on the complex heterogeneity and hydrophobicity of the conjugates a chromatographic purification is challenging. Hydrophobic interaction chromatography is used for analytical as well as for preparative separation. Because of the increased hydrophobicity of the conjugates compared to native antibody, hydrophobic interaction chromatography often suffer from resolution and recovery problems. Conjugates were separated differing on the number of payloads attached to the antibody. For this matter, the drug-antibody ratio is determined and used as a quantitative term. The conjugates are purified at high recoveries and resolution by step gradients using suitable resins, allowing the separation of the target drug-antibody ratio.

Towards Covalent Photosensitizer-Polyoxometalate Dyads-Bipyridyl-Functionalized Polyoxometalates and Their Transition Metal Complexes.

A triol-functionalized 2,2'-bipyridine (bpy) derivative has been synthesized and used for the tris-alkoxylation of polyoxometalate (POM) precursors. The resultant POM-bpy conjugates of the Wells-Dawson- and Anderson-type feature a C-C bond as a linkage between the POM and bpy fragments. This structural motif is expected to increase the hydrolytic stability of the compounds. This is of particular relevance with respect to the application of POM-bpy metal complexes, as photocatalysts, in the hydrogen-evolution reaction (HER) in an aqueous environment. Accordingly, Rh(III) and Ir(III) complexes of the POM-bpy ligands have been prepared and characterized. These catalyst-photosensitizer dyads have been analyzed with respect to their electrochemical and photophysical properties. Cyclic and square-wave voltammetry, as well as UV/vis absorption and emission spectroscopy, indicated a negligible electronic interaction of the POM and metal-complex subunits in the ground state. However, emission-quenching experiments suggested an efficient intramolecular electron-transfer process from the photo-excited metal centers to the POM units to account for the non-emissive nature of the dyads (thus, suggesting a strong interaction of the subunits in the excited state). In-depth photophysical investigations, as well as a functional characterization, i.e., the applicability in the HER reaction, are currently ongoing.