Mononuclear anionic formyl complexes; synthesis and properties

A series of kinetically unstable mononuclear anionic formyl complexes have been prepared by the action of Li(C₂H₅)₃BH on neutral metal carbonyl precursors. One of these, Li⁺[(CO)₄Mn(COC₆H₅)(CHO)]^?, is shown to decompose by a hydride transfer disproportionation mechanism involving the by-product (C₂H₅)₃B.     

Eine Elektrophoresebestimmung von Kreatinin in Fleischextrakt, Fleisch und kohlenhydrathaltigen Fleischprodukten

Ohne Zusammenfassung     

Beryllium

Ohne Zusammenfassung     

Versatility of the dipolar filter selection: from 1H nuclear spin diffusion experiment to the measurement of nuclear Overhauser effect in homopolymer melts

Dipolar filters select ¹H magnetization according to local dipolar dephasing, which corresponds to site mobility in systems with heterogeneous molecular mobility. Combined with a conventional exchange experiment, it is usually applied to polymeric samples exhibiting structures on the nanometer length scale associated with a strong dynamic contrast. There, the resulting ¹H nuclear spin diffusion experiment yields the size of the structure. When the same experiment is applied to homopolymer melts exhibiting a weak dynamic contrast and dynamic heterogeneities on significant shorter length scales, the recorded magnetization decay is in agreement with decays expected from a heterogeneous nanostructure. However, dipolar filters actually can also select mobile parts of the repeat unit, e.g. the end of the alkyl side chains and the subsequent magnetization transfer then can occur via cross relaxation due to non coherent zero-quantum transitions (nuclear Overhauser effect, NOE). The difficulties of distinguishing these two cases are examined and it is demonstrated that NOE experiments exploiting magnetization selection via the dipolar filter allow quantifying the local dynamics of the side chains. This opens new possibilities for measurements of local dynamics in non isotopically labeled homopolymer melts.     

Improving the reproducibility of chemical reactions on the surface of cellulose nanocrystals: ROP of ε-caprolactone as a case study

In our group, we work on the surface modification of cellulose nanocrystals. During this work, we have encountered reproducibility issues when the same reactions were performed on nanocrystals from different hydrolysis batches, indicating a variable surface composition. Given the inherent purity of the nanoparticles themselves, this issue was believed to be due to the presence of adsorbed species at the surface of the nanocrystals blocking reactive sites. To investigate this in detail, nanocrystals from several batches were extracted with different solvents. The effect of these extractions on the surface composition of the nanowhiskers was investigated, followed by its effect on the Surface-Initiated Ring-Opening Polymerization (SI-ROP) of ε-caprolactone. The extracted impurities were analysed by NMR (¹H and ¹³C) and MS, showing a variety of adsorbed species which can be removed by solvent extraction. A Soxhlet extraction using ethanol before the reaction was shown to be the most effective in removing adsorbed low molecular weight organic compounds produced during the hydrolysis, resulting in improved reproducibility between reactions using nanocrystals from different batches, as confirmed by FTIR, elemental analysis and XPS. Extraction with ethanol should thus be performed before all reaction as these adsorbed species can be expected to interfere with all surface modification reactions.     

Absorption and emission spectroscopic characterisation of combined wildtype LOV1-LOV2 domain of phot from Chlamydomonas reinhardtii

An absorption and emission spectroscopic characterisation of the combined wild-type LOV1-LOV2 domain string (abbreviated LOV1/2) of phot from the green alga Chlamydomonas reinhardtii is carried out at pH 8. A LOV1/2-MBP fusion protein (MBP=maltose binding protein) and LOV1/2 with a His-tag at the C-terminus (LOV1/2-His) expressed in an Escherichia coli strain are investigated. Blue-light photo-excitation generates a non-fluorescent intermediate photoproduct (flavin-C(4a)-cysteinyl adduct with absorption peak at 390 nm). The photo-cycle dynamics is studied by dark-state absorption and fluorescence measurement, by following the temporal absorption and emission changes under blue and violet light exposure, and by measuring the temporal absorption and fluorescence recovery after light exposure. The fluorescence quantum yield, phi(F), of the dark adapted samples is phi(F)(LOV1/2-His) approximately 0.15 and phi(F)(LOV1/2-MBP) approximately 0.17. A bi-exponential absorption recovery after light exposure with a fast (in the several 10-s range) and a slow component (in the near 10-min range) are resolved. The quantum yield of photo-adduct formation, phi(Ad), is extracted from excitation intensity dependent absorption measurements. It decreases somewhat with rising excitation intensity. The behaviour of the combined wildtype LOV1-LOV2 double domains is compared with the behaviour of the separate LOV1 and LOV2 domains.