Oxidation of allylic and benzylic alcohols to aldehydes and carboxylic acids

An oxidation of allylic and benzylic alcohols to the corresponding carboxylic acids is effected by merging a Cu-catalyzed oxidation using O2 as a terminal oxidant with a subsequent chlorite oxidation (Lindgren oxidation). The protocol was optimized to obtain pure products without chromatography or crystallization. Interception at the aldehyde stage allowed for Z/E-isomerization, thus rendering the oxidation stereoconvergent with respect to the configuration of the starting material

Photo-responsive hydrogels based on a ruthenium complex: synthesis and degradation

We report the synthesis of a photo responsive metallo-hydrogel based on a ruthenium(II) complex as a functional cross-linker. This metal complex contains reactive 4AAMP (= 4-(acrylamidomethyl)pyridine) ligands, which can be cleaved by light-induced ligand substitution. Ru[(bpy)2(4AAMP)2] cross-links 4-arm-PEG-SH macromonomers by thia-Michael-addition to the photocleavable 4AAMP ligand for the preparation of the hydrogel. Irradiation with green light at 529 nm leads to photodegradation of the metallo-hydrogel due to the ligand dissociation, which can be adjusted by adjusting the Ru[(bpy)2(4AAMP)2] concentration. The ligand substitution forming [Ru(bpy)2(L)2]2+ (L = H2O and CH3CN) can be monitored by 1H NMR spectroscopy and UV-visible absorption. The control of degradation by light irradiation plays a significant role in modulating the elasticity and stiffness of the light sensitive metallo-hydrogel network. The photo-responsive hydrogel is a viable substrate for cell cultures

Lignin Upconversion by Functionalization and Network Formation

Lignin, a complex and abundant biopolymer derived from plant cell walls, has emerged as a promising feedstock for sustainable material development. Due to the high abundance of phenylpropanoid units, aromatic rings, and hydroxyl groups, lignin is an idealcandidate for being explored in various material applications. Therefore, the demand on lignin valorization for development of value-added products is significantly increasing. This mini-review provides an overview of lignin upconversion, focusing on its functionalization through chemical and enzymatic routes, and its application in lignin-based polymer resins, hydrogels, and nanomaterials. The functionalization of lignin molecules with various chemical groups offers tailored properties and increased compatibility with other materials, expanding its potential applications. Additionally, the formation of lignin-based networks, either through cross-linking or blending with polymers, generates novel materials with improved mechanical, thermal, and barrier properties. However, challenges remain in optimizing functionalization techniques, preserving the innate complexity of lignin, and achieving scalability for industrial implementation. As lignin's potential continues to be unlocked, it is poised to contribute significantly to the shift towards more eco-friendly and resource-efficient industries

Conversion of Pyridine <i>N</i>‑Oxides to Tetrazolopyridines

An efficient and convenient procedure for the conversion of pyridine <i>N</i>-oxides to tetrazolopyridines by treatment with 4-toluene sulfonyl chloride and sodium azide in toluene at elevated temperature is described

Nitrene–nitrene rearrangement under thermal, photochemical, and electron-impact conditions: the 2-azidopyridines/tetrazolo[1,5-a]pyridines

N-15-Labeling demonstrates that the two nitrogen atoms in the 2-pyridylnitrene radical cation 2(+) become equivalent prior to fragmentation in the mass spectrometer. Furthermore, the mass spectra of 6- and 7-tetrazolo[1,4-a]pyridine are identical, as are those of 5- and 8-tetrazolo[1,5-a]pyridine, thereby again demonstrating interconversion of the nitrogen atoms in 2-pyridylnitrenes. These rearrangements parallel the reactions established under thermal (flash vacuum pyrolysis) and photochemical condition. Calculations of the energies of ground and transition states at the CASPT2(7,8) level support the notion that 2-pyridylnitrenes undergo very easy and exothermic ring expansion to 1,3-diazacycloheptatetraene 3, both in the neutrals and the radical cations. In addition, the ring opening to 4-cyanobutadienylnitrene 4 can take place in both the neutrals and the radical cations with modest activation barriers

Palladium-Catalyzed Directed Halogenation of Bipyridine <i>N</i>‑Oxides

The palladium-catalyzed directed C–H halogenation of bipyridine <i>N</i>-oxides was investigated. Using NCS or NBS (<i>N</i>-chloro- or <i>N</i>-bromosuccinimide) and 5 mol % Pd­(OAc)₂ in chlorobenzene (0.10 molar) at 110 °C, pyridine-directed functionalization took place and 3-chloro- or 3-bromobipyridine <i>N</i>-oxides were obtained in high yields. The reaction is sensitive to steric hindrance by 4- and 6′-substituents. Only in the latter case, where coordination of palladium by the pyridine is hindered, 3′-halogenation directed by the <i>N</i>-oxide function was observed. The halogenated products were deoxygenated by PCl₃ or PBr₃

Palladium-Catalyzed Directed Halogenation of Bipyridine <i>N</i>‑Oxides

The palladium-catalyzed directed C–H halogenation of bipyridine <i>N</i>-oxides was investigated. Using NCS or NBS (<i>N</i>-chloro- or <i>N</i>-bromosuccinimide) and 5 mol % Pd­(OAc)₂ in chlorobenzene (0.10 molar) at 110 °C, pyridine-directed functionalization took place and 3-chloro- or 3-bromobipyridine <i>N</i>-oxides were obtained in high yields. The reaction is sensitive to steric hindrance by 4- and 6′-substituents. Only in the latter case, where coordination of palladium by the pyridine is hindered, 3′-halogenation directed by the <i>N</i>-oxide function was observed. The halogenated products were deoxygenated by PCl₃ or PBr₃

Monitoring the Transmembrane Proton Gradient Generated by Cytochrome <i>bo</i>₃ in Tethered Bilayer Lipid Membranes Using SEIRA Spectroscopy

Membrane proteins act as biocatalysts or ion/proton pumps to convert and store energy from ubiquitous environmental sources. Interfacing these proteins to electrodes allows utilizing the energy for enzymatic biofuel cells or other auspicious biotechnological applications. To optimize the efficiency of these devices, appropriate membrane models are required that ensure structural and functional integrity of the embedded enzymes and provide structural insight. We present a spectroelectrochemical surface-enhanced infrared absorption (SEIRA) and electrical impedance spectroscopy (EIS) study of the bacterial respiratory ubiquinol/cytochrome <i>bo</i>₃ (cyt <i>bo</i>₃) couple incorporated into a tethered bilayer lipid membrane (tBLM). Here, we employed a new lipid tether (WK3SH, dihydrocholesteryl (2-(2-(2-ethoxy)­ethoxy)­ethanethiol), which was synthesized using a three-step procedure with very good yield and allowed measuring IR spectra without significant spectral interference of the tBLM. The functional integrity of the incorporated cyt <i>bo</i>₃ was demonstrated by monitoring the enzymatic O₂ reduction current and the formation of the transmembrane proton gradient. Based on a SEIRA-spectroscopic redox titration, a shift of the pH-dependent redox potential of the ubiquinones under turnover conditions was correlated with an alkalinization of the submembrane reservoir by +0.8 pH units. This study demonstrates the high potential of tBLMs and the SEIRA spectroscopic approach to study bioenergetic processes