Hermitian symmetric polynomials and CR complexity

Properties of Hermitian forms are used to investigate several natural questions from CR Geometry. To each Hermitian symmetric polynomial we assign a Hermitian form. We study how the signature pairs of two Hermitian forms behave under the polynomial product. We show, except for three trivial cases, that every signature pair can be obtained from the product of two indefinite forms. We provide several new applications to the complexity theory of rational mappings between hyperquadrics, including a stability result about the existence of non-trivial rational mappings from a sphere to a hyperquadric with a given signature pair.Comment: 19 pages, latex, fixed typos, to appear in Journal of Geometric Analysi

Catalytic Activity and Fluxional Behavior of Complexes Based on RuHCl(CO)(PPh₃)₃ and Xantphos-Type Ligands

With RuHCl(CO)(PPh3)3 as the starting material, the complexes RuHCl(CO)(PPh3)(L) were prepared for L = Xantphos and closely related ligands. Their catalytic activity in the direct amination of cyclohexanol showed large differences depending on the different backbone structures. In those complexes the Xantphos-type ligand backbones are slightly bent and display fluxionality, studied by VT-NMR. This was assigned to the "flipping" of the backbone via the bridging atoms in the xanthene backbone. Via line shape analysis of the peaks, the Gibbs free energy of activation of the flipping movement was found to be around 56 kJ/mol in all cases. However, the activation enthalpy and entropy differed considerably. Employing RuCl2(PPh3)3 as the precursor resulted in the trans-coordinated complexes RuCl2(PPh3)(L) for L = Xantphos, Sixantphos. Fluxionality was no longer observed, due to the fact that in these complexes the O atom in the backbone also coordinates to the Ru

Using fractionation and diffusion ordered spectroscopy to study lignin molecular weight

This work was supported by EPSRC Ph.D. studentships EP/1654168 (JRDM). EP/1654168/1. Raw data files can be found at: https://doi.org/10.6084/m9.figshare.8034680Recent reports demonstrate that applications of the biopolymer lignin can be helped by the use of a portion of the lignin which has an optimal molecular weight range. Unfortunately, the current methods used to determine lignin’s molecular weight are inconsistent or not widely accessible. Here, an approach that relies on 2D DOSY NMR analysis is described that provides a measure of lignin’s molecular weight. Consistent results were obtained using this well-established NMR technique across a range of lignins.Publisher PDFPeer reviewe

Use of bisulfite processing to generate high-β-O-4 content water-soluble lignosulfonates

This work was supported by EPSRC grants (EP/1518175), the Industrial Biotechnology Innovation Centre (IBioIC) (DMB Ph.D. studentship) and an EPSRC Doctoral Prize Fellowship (CSL).With lignin-first biorefineries likely to become a reality, controlled depolymerization of high-quality lignin streams to high value products has become a priority. Using bisulfite chemistry, access to a high-β-O-4 content water-soluble lignosulfonate has been achieved, allowing follow-on procedures in water to be conducted. We show that phenolic β-O-4 units preferential-ly react under acidic bisulfite conditions, whilst non-phenolic β-O-4 units react much more slowly. Exploiting this improved chemical understanding and inherent selectivity, a softwood lignosulfonate has been prepared in which phenolic β-O-4 α-sulfonation has occurred leaving significant native β-O-4 content. Use of an O-benzoylation protocol with lignin coupled with advanced 2D NMR methods has allowed detailed analysis of this and other commercial and industrial lignosulfonates. Conversion of the native β-O-4 to benzylic- oxidized β-O-4 units was followed by a selective reductive cleavage to give a premium aromatic monomer in pure form.Publisher PDFPeer reviewe

The synthesis and analysis of lignin-bound Hibbert ketone structures in technical lignins

This work was supported by EPSRC Ph.D. studentships (EP/1518175 (DMB), EP/1517938 (AN)), the Industrial Biotechnology Innovation Centre (Ph.D. studentship to DMB), CRITICAT Centre for Doctoral Training (Ph.D. studentship to IP; EP/L016419/1), EPSRC grants EP/J018139/1 and EP/K00445X/1 (SOJO) and an EPSRC Doctoral Prize Fellowship (CSL).Understanding the structure of technical lignins resulting from acid-catalysed treatment of lignocellulosic biomass is important for their future applications. Here we report an investigation into the fate of lignin under acidic aqueous organosolv conditions. In particular we examine in detail the formation and reactivity of non-native Hibbert ketone structures found in isolated organosolv lignins from both Douglas fir and beech woods. Through the use of model compounds combined with HSQC, HMBC and HSQC-TOCSY NMR experiments we demonstrate that, depending on the lignin source, both S and G lignin-bound Hibbert ketone units can be present. We also show that these units can serve as a source of novel mono-aromatic compounds following an additional lignin depolymerisation reaction.PostprintPeer reviewe

Ribe na početku života

This work was supported by EPSRC (grants EP/J018139/1, EP/K00445X/1 (NJW), the EPSRC funded CRITICAT Centre for Doctoral Training (Ph.D. studentship to IP; EP/L016419/1) and EPSRC Doctoral Prize Fellowship (CSL)A new method has been developed to enable the modification of the organosolv technical lignin. Using a walnut shell butanol alkoxasolv lignin as a source of high β-O-4 content material, the β-O-4 γ-position has been selectively modified via tosylation, azidation and copper-catalyzed azide-alkyne triazole formation . In addition, extensive model studies were used to aid the detailed characterization of the modified lignin structure. The copper catalyzed click reaction was used to attach modified PEG chains and the resulting lignin-based co-polymer displayed improved thermal stability. This protocol was also used to incorporate a novel BODIPY-type fluorophore, generating a fluorescent lignin. Copper catalytic loadings were effective as low as 0.3 weight% and were found to catalyze the cycloaddition efficiently. This efficient and generic approach to preparing lignin-derived polymers is relevant to the core societal challenge of improving biorefinery efficiency.PostprintPeer reviewe

Preparation and reactivity of biomass-derived dihydro-dioxins

This work was supported by EPSRC PhD studentships EP/1654168 (JRDM) and EP/1518175 (DMMB) and the Industrial Biotechnology Innovation Centre (DMMB).The depolymerisation of the biopolymer lignin can give pure aromatic monomers but selective catalytic approaches remain scarce. Here, an approach was re-routed to deliver an unusual phenolic monomer. This monomer’s instability proved challenging but a degradation study identified strategies to overcome this. Heterocycles and a useful synthetic intermediate were prepared. The range of aromatics available from the b-O-4 unit in lignin was extended.PostprintPeer reviewe

Simple and inexpensive method for the detection of carbon monoxide released from thermal cheletropic decarbonylation reactions

This work presents a simple protocol that demonstrates the use of an inexpensive household carbon monoxide detector as a useful tool to detect the release of carbon monoxide gas from thermal cheletropic decarbonylation reactions. The carbon monoxide detection method described has been employed in a short series of reactions used in a university teaching laboratory setting, and full procedures for these are outlined. In each case, the procedure to isolate and identify the decarbonylation products has also been provided.PostprintPeer reviewe