Hydrodeoxygenation of Lignin-Based Compounds over Ruthenium Catalysts Based on Sulfonated Porous Aromatic Frameworks.

Bifunctional catalysts are a major type of heterogeneous catalytic systems that have been widely investigated for biomass upgrading. In this work, Ru-catalysts based on sulfonated porous aromatic frameworks (PAFs) were used in the hydrodeoxygenation (HDO) of lignin-derived compounds: guaiacol, veratrole, and catechol. The relationship between the activity of metal nanoparticles and the content of acid sites in synthesized catalysts was studied. Herein, their synergy was demonstrated in the Ru-PAF-30-SO3H/5-COD catalyst. The results revealed that this catalytic system promoted partial hydrogenation of lignin-based compounds to ketones without any further transformations. The design of the Ru-PAF-30-SO3H/5-COD catalytic system opens a promising route to the selective conversion of lignin model compounds to cyclohexanone.

Mitigating of Thin-Film Composite PTMSP Membrane Aging by Introduction of Porous Rigid and Soft Branched Polymeric Additives.

This work was focused on the mitigation of physical aging in thin-film composite (TFC) membranes (selective layer ~1 µm) based on polymer intrinsic microporosity (PTMSP) by the introduction of both soft, branched polyethyleneimine (PEI), and rigid, porous aromatic framework PAF-11, polymer additives. Self-standing mixed-matrix membranes of thicknesses in the range of 20-30 µm were also prepared with the same polymer and fillers. Based on 450 days of monitoring, it was observed that the neat PTMSP composite membrane underwent a severe decline of its gas transport properties, and the resultant CO2 permeance was 14% (5.2 m3 (STP)/(m2·h·bar)) from the initial value measured for the freshly cast sample (75 m3 (STP)/(m2·h·bar)). The introduction of branched polyethyleneimine followed by its cross-linking allowed to us to improve the TFC performance maintaining CO2 permeance at the level of 30% comparing with day zero. However, the best results were achieved by the combination of porous, rigid and soft, branched polymeric additives that enabled us to preserve the transport characteristics of TFC membrane as 43% (47 m3 (STP)/(m2·h·bar) after 450 days) from its initial values (110 m3 (STP)/(m2·h·bar)). Experimental data were fitted using the Kohlrausch-Williams-Watts function, and the limiting (equilibrium) values of the CO2 and N2 permeances of the TFC membranes were estimated. The limit value of CO2 permeance for neat PTMSP TFC membrane was found to be 5.2 m3 (STP)/(m2·h·bar), while the value of 34 m3(STP)/(m2·h·bar) or 12,600 GPU was achieved for TFC membrane containing 4 wt% cross-linked PEI, and 30 wt% PAF-11. Based on the N2 adsorption isotherms data, it was calculated that the reduction of the free volume was 1.5-3 times higher in neat PTMSP compared to the modified one. Bearing in mind the pronounced mitigation of physical aging by the introduction of both types of fillers, the developed high-performance membranes have great potential as support for the coating of an ultrathin, selective layer for gas separation.

Cobalt(II) complexation with small biomolecules as studied by 57Co emission Mössbauer spectroscopy.

In the emission (57Co) variant of Mössbauer spectroscopy (EMS), the 57Co radionuclide (with a half-life of 9months) is used that undergoes a nuclear decay 57Co→57Fe via electron capture followed by the emission of a γ-quantum, the energy of which is modified by the chemical state and the close coordination environment of the parent 57Co atom. While EMS has been used largely in materials science and nuclear chemistry, its high sensitivity can also be of great advantage in revealing fine structural features and for speciation analysis of biological complexes, whenever the 57Co2+ cation can be used directly as the coordinating metal or as a substitute for native cobalt or other metal ions. As such EMS applications are yet rare, in order to reliably interpret emission spectra of sophisticated 57Co2+-doped biosystems, model EMS studies of simple cobalt biocomplexes are necessary. In this work, EMS spectroscopic data are analysed and discussed for 57Co2+ complexes with a range of small biomolecules of different structures, including 4-n-hexylresorcinol, homoserine lactone and a few amino acids (spectra measured in rapidly frozen dilute aqueous solutions or in the dried state at T=80K). The EMS data obtained are discussed with regard to the available literature data related to the coordination modes of the biocomplexes under study.

Instrumental analysis of bacterial cells using vibrational and emission Mössbauer spectroscopic techniques.

In biosciences and biotechnology, the expanding application of physicochemical approaches using modern instrumental techniques is an efficient strategy to obtain valuable and often unique information at the molecular level. In this work, we applied a combination of vibrational (Fourier transform infrared (FTIR), FT-Raman) spectroscopic techniques, useful in overall structural and compositional analysis of bacterial cells of the rhizobacterium Azospirillum brasilense, with 57Co emission Mössbauer spectroscopy (EMS) used for sensitive monitoring of metal binding and further transformations in live bacterial cells. The information obtained, together with ICP-MS analyses for metals taken up by the bacteria, is useful in analysing the impact of the environmental conditions (heavy metal stress) on the bacterial metabolism and some differences in the heavy metal stress-induced behaviour of non-endophytic (Sp7) and facultatively endophytic (Sp245) strains. The results show that, while both strains Sp7 and Sp245 take up noticeable and comparable amounts of heavy metals from the medium (0.12 and 0.13 mg Co, 0.48 and 0.44 mg Cu or 4.2 and 2.1 mg Zn per gram of dry biomass, respectively, at a metal concentration of 0.2 mM in the medium), their metabolic responses differ essentially. Whereas for strain Sp7 the FTIR measurements showed significant accumulation of polyhydroxyalkanoates as storage materials involved in stress endurance, strain Sp245 did not show any major changes in cellular composition. Nevertheless, EMS measurements showed rapid binding of cobalt(II) by live bacterial cells (chemically similar to metal binding by dead bacteria) and its further transformation in the live cells within an hour.

Monitoring of cobalt(II) uptake and transformation in cells of the plant-associated soil bacterium Azospirillum brasilense using emission Mössbauer spectroscopy.

Interaction of cobalt(II) at micromolar concentrations with live cells of the plant-growth-promoting rhizobacterium Azospirillum brasilense (strain Sp245) and further transformations of the metal cation were monitored using 57Co emission Mössbauer spectroscopy (EMS). Cell suspensions of the bacterial culture (2.4 x 10(8) cells ml(-1)) were doped with radioactive 57CoCl2 (1 mCi; final concentration 2 x 10(-6) M 57Co2+), kept under physiological conditions for various periods of time (from 2 min up to 1 hour) and then rapidly frozen in liquid nitrogen. Analysis of emission Mössbauer spectra of the frozen aqueous suspensions of the bacterial cell samples shows that the primary absorption of cobalt(II) at micromolar concentrations by the bacterial cells is rapid and virtually complete, giving at least two major forms of cobalt(II) species bound to the cells. Within an hour, the metal is involved in further metabolic transformations reflected by changes occurring in the spectra. The Mössbauer parameters calculated from the EMS data by statistical treatment were different for suspensions of live and dead (thermally killed) bacterial cells that had been in contact with 57Co2+ for 1 h, as well as for the cell-free culture medium containing the same concentration of 57Co2+. Chemical after-effects of the nuclear transition (57Co --> 5 7Fe), which provide additional information on the chemical environment of metal ions, are also considered. The data presented demonstrate that EMS is a valuable tool for monitoring the chemical state of cobalt species in biological matter providing information at the atomic level in the course of its uptake and/or metabolic transformations.

Structural characterization of glutamine synthetase from Azospirillum brasilense.

CD spectroscopic study of the secondary structure of partly adenylylated glutamine synthetase (GS) of the bacterium Azospirillum brasilense showed both the native and cation-free (EDTA-treated) enzyme to be highly structured (58 and 49% as alpha-helices, 10 and 20% as beta-structure, respectively). Mg(2+), Mn(2+), or Co(2+), when added to the native GS, had little effect on its CD spectrum, whereas their effects on the cation-free GS were more pronounced. Emission ((57)Co) Mössbauer spectroscopic (EMS) study of (57)Co(2+)-doped cation-free GS in frozen solution and in the dried state gave similar spectra and Mössbauer parameters for the corresponding spectral components, reflecting the ability of the Co(2+)-enzyme complex to retain its properties upon drying. The EMS data show that (a) A. brasilense GS has 2 cation-binding sites per active center and (b) one site has a higher affinity to Co(2+) than the other, in line with the data on other bacterial GSs.