Erica Brendler

Lignins are heterogeneous aromatic biopolymers whose structural complexity depends strongly on botanical origin and isolation process. Comprehensive characterization therefore typically relies on multiple complementary techniques, including gel permeation chromatography (GPC), Fourier transform infrared spectroscopy (FT-IR), pyrolysis-gas chromatography/mass spectrometry (Py-GC/MS), and nuclear magnetic resonance (NMR) spectroscopy, resulting in labor-intensive workflows and complex data integration. Here, ultrahigh-resolution Fourier transform ion cyclotron resonance mass spectrometry (FT-ICR-MS) is systematically benchmarked against these established methods using solvent-fractionated spruce kraft lignin as a model system. Complementary electrospray ionization (ESI) and graphite-assisted laser desorption/ionization (GALDI), combined with tandem mass spectrometry (MS/MS) and heterospectroscopic correlation analysis, reproduce fraction-dependent trends in oxygenation, aromatic condensation, and functional group distribution consistent with FT-IR, Py-GC/MS, and quantitative NMR data. While limitations remain for molar mass distributions and linkage quantification, FT-ICR-MS can serve as an advanced, high-throughput complementary screening platform that enables streamlined, comparative molecular-level lignin profiling with reduced analytical complexity.

Stimuli-responsive polymers have endowed soft matter research with numerous applications. Moving beyond classical stimuli like temperature or pH, we introduce an electrochemical approach to control block copolymer aggregation by shifting between bishydrophilic and amphiphilic states. The aqueous solutions of the nonionic-cationic block copolymers poly[N-(3-aminopropyl)methacrylamide]30-b-poly(N,N-dimethylacrylamide)120 (PAPMA30-b-PDMAA120), synthesized via RAFT polymerization, and poly(ethylene oxide)114-b-poly{[2-(methacryloyloxy)ethyl]diisopropylmethylammonium chloride}171 (i.e., PEO114-b-PDPAEMA171 with a quaternized poly(diisopropylaminoethyl methacrylate) block, abbreviated as qPDPAEMA), were investigated for micellization via Dynamic Light Scattering (DLS), Small Angle X-ray Scattering (SAXS), and Cryogenic Transmission Electron Microscopy (cryo-TEM). Both polymers exhibit selective aggregation with hexacyanoferrate species: PAPMA-b-PDMAA forms aggregates specifically in the presence of ferrocyanide ions ([Fe(CN)6]4–), while PEO-b-qPDPAEMA forms micelles with ferricyanide ions ([Fe(CN)6]3–). These polymer systems demonstrate both chemical and electrochemical reversibility, with the combined polymer system allowing selective control over the type of polymer that aggregates by modulating the ferricyanide/ferrocyanide ratio. Furthermore, the pH sensitivity of PAPMA-b-PDMAA allows the disintegration of the micellar state by increasing the pH (electro-)chemically. In total, these results demonstrate full control over the assembly state of complex polymer mixtures by electrochemical means. In addition, it is shown for PEO-b-qPDPAEMA that electrochemical switching as a soft trigger leads to the thermodynamically preferred micelle morphology, while rapid chemical redox leads to kinetically trapped, nonequilibrium micelles. Here, electrochemistry can act as a trigger to transform the trapped micelles toward the thermodynamically stable ones, which can be recycled back to the nonequilibrium micelles. The principle of this electrochemically triggered micellization could represent a significant step toward developing stimuli-sensitive materials for autonomous drug delivery, sensing, or even smart materials within a systems chemistry approach.

In dynamic equilibria, benzylsilicon pyridine-2-olate (BnSi(pyO)₃, L) and benzaldehyde react with addition of the Si(pyO) moieties to the PhHC=O carbonyl group and formation of compounds BnSi(–O–C(H,Ph)–N^(2-pyridone))_x(pyO)_3−x (L’, L’’, and L’’’, for x = 1, 2, 3, respectively). Addition of CuCl to a solution containing L, L’, L’’, and L’’’ results in the formation of BnSi(pyO)₃CuCl (LCuCl), shifting the equilibrium towards L with liberation of benzaldehyde. In THF as a solvent, the reaction of L in the presence of excess CuCl affords the complex LCuClCuCl. Upon dissolving in chloroform, it transforms into LCuCl with precipitation of CuCl. The solid state structure of LCuClCuCl features both the monomeric complex with CuClCuCl pattern and a dimer thereof with CuClCu(Cl)₂CuClCu pattern and a central Cu₂Cl₂ four-membered ring. This dimer of LCuClCuCl is the first crystallographically characterized representative of this Cu(I)-only Cu₄Cl₄ motif. The reaction of LCuCl and silver tosylate (AgOTos) in THF affords LCuOTos with precipitation of AgCl, whereas LAgOTos was obtained from L and AgOTos. In the crystal structure, LAgOTos features tetracoordinate Ag(I) in a distorted tetrahedral AgN₃O coordination sphere and a short Ag···Si trans-annular contact (3.3245(7) Å). ¹⁰⁹Ag NMR spectroscopy indicates a change in the coordination in solution, with δ ¹⁰⁹Ag = +551 and +419 ppm in the solid and in CDCl₃ solution, respectively. In combination, ²⁹Si NMR spectroscopy indicates changes in the Si coordination sphere, with δ ²⁹Si = −74.2 and −66.5 ppm in the solid and in CDCl₃ solution, respectively. Conversion of LAgOTos with tetraethylammonium chloride results in the precipitation of AgCl with release of L.

Xylans, a highly abundant type of hemicelluloses in plant-based biomass, are currently being investigated as a renewable substitute for fossil resources. Thus, understanding their properties and structure is crucial for efficient utilization. This study aims to develop analytical methods for characterizing the soluble and insoluble compounds of xylans, using graphite-assisted laser desorption/ionization combined with Fourier-transform ion cyclotron resonance mass spectrometry (GALDI-FT-ICR-MS). A beechwood xylan was utilized as a representative sample for this work. Infrared (IR) and nuclear magnetic resonance (NMR) spectroscopy were additionally used to obtain further structural information. The results from the MS analyses indicate that liquid- and solid-state GALDI-MS techniques can aid in the characterization of the xylan molecules, and both ionization modes were found to be essential for a comprehensive understanding of xylans. The findings of this study may contribute to a deeper understanding of the structural characteristics of xylans and assist in the efficient application of these polysaccharides.

The 1:1 stoichiometric reactions of α-amino isobutyric acid (H₂Aib) and diaminosilanes of the type SiRR′(NR¹R²)₂ (SiMe₂(imidazol-1-yl)₂, SiMe₂(NHnPr)₂, and SiRR′(pyrrolidin-1-yl)₂ with R,R′ = Me,Me, Me,H, Me,Vi, and Et,Et) afforded the pentacoordinate silicon complexes (Aib)SiRR′(HNR¹R²) with the release of one equivalent of HNR¹R². Single-crystal X-ray diffraction analyses confirmed the coordination of the N-donor Lewis base (i.e., imidazole, n-propylamine, and pyrrolidine, respectively) in an axial position of the distorted trigonal-bipyramidal Si-coordination sphere, trans to the carboxylate O atom of the Si-chelating Aib-dianion. The N–H moieties of the adduct-forming Lewis bases are involved in N–H⋯O hydrogen bonds with carboxylate groups of adjacent complex molecules, thus supporting the supramolecular structures of these adducts. The equatorially bound NH group of the Aib-dianion is involved in N–H⋯O hydrogen bonds in most cases, and it gives rise to residual dipolar coupling of the ¹⁴N nucleus with its directly bound atoms C and Si, thus causing characteristic shapes of both the ²⁹Si and ¹³C NMR signals of these two atoms in the solid-state spectra. In contrast to the adduct-formation reactions, the analogous conversion of H₂Aib and SiMe₂(NHtBu)₂ did not afford an amine adduct. Instead, a second equivalent of H₂Aib entered the reaction, and the ionic silicon complex [tBuNH₃]⁺[(Aib)₂SiMe]⁻ was obtained and characterized by crystallography and solution NMR spectroscopy.

Spongin is a fundamental biopolymer that has played a crucial role in the skeletogenesis of keratosan sponges for over 800 million years. This biomaterial had so far remained chemically unidentified and believed to be an enigmatic type of halogenated collagen-keratin-based bioelastomer. Here we show collagen I and III as the main structural components of spongin. Proteomics, ¹³C solid state NMR and Raman spectroscopy confirm the identity of collagenous domains in spongin with collagen from mammals. Using an HPLC-MS analysis, we found halogenated di- and tri-tyrosines as crosslinking agents in spongin. Using molecular dynamics modeling, we solvated the crystal structures of collagen mimetic peptides for type I and type III collagens in four different systems, including selected brominated crosslinks. The results underscore the complex interplay between the collagen structures and crosslinks, raising intriguing questions about the molecular mechanisms underlying collagen chemistry within spongin as an ancient biocomposite.