Low-Temperature High-Resolution Solid-State (cryoMAS) NMR of Han Purple BaCuSi2O6

We present low-temperature (low-T, sub-liquid-N₂) high-speed high-resolution ²⁹Si solid-state (cryoMAS) nuclear magnetic resonance studies on a model 2D-BEC quantum magnet BaCuSi₂O₆, known also as Han Purple. We observe broadened ²⁹Si lines below the well-established 100 K structural phase transition confirming the existence of inhomogeneities at low temperatures. Interestingly, the low-T spectra of \({\mathrm{BaCuSi}}_{2}{\mathrm{O}}_{6}\) closely resemble those of the novel compound Ba₂CoSi₂O₆Cl₂ taken at room temperature. This suggests that the Co compound features structural modulations or inhomogeneities already at room temperature. The low-T crystal structure and magnetism of \({\mathrm{BaCuSi}}_{2}{\mathrm{O}}_{6}\) are more complex than previously believed, and deserve further investigation.     

Characterization of sulfate-reducing bacteria in yeast industry waste by microcalorimetry and PCR amplification

Sulfate-reducing bacteria (SRB) were isolated from anaerobic sludge of yeast factory wastewater treatment plant by cultivation on Postgate C medium. Microcalorimetry was used to monitor the anaerobic digestion processes and to measure the growth rates of sulfate-reducing bacteria. The maximum growth rates determined by microcalorimetry and ATP analysis were different—μ_max(dQ/dt) = 0.165 ± 0.008 h⁻¹ and μ_max(N_ATP) = 0.207 ± 0.013 h⁻¹. Experiments on the cultivation of SRB from yeast industry wastewater treatment plant in batch culture showed that during the first 20 h the concentration of sulfate decreased from 78.3 mM down to 62.2 mM while the increase of sulfide production was negligible. Perceptible amount of sulfide (7.82 mM) appeared on the 33.5 h of fermentation together with a peak on the power–time curve and considerable increase in the cell count (1.26 × 10⁹). First steps of sulfate metabolism (activation of sulfate by ATP sulfurylase, production of H₂) are accompanied by endothermic heat effects, therefore the values of thermal power remain moderate until the evolution of sulfide starts. The influence of green microalgae Chlorococcum sp. (preparation Biotreat 100) on the growth characteristics of microorganisms was also studied. Identification of one SRB strain was started by sequencing of PCR-amplified 16S rRNA gene. Two sets of primers were used for PCR amplification, both specific for domain Bacteria but giving different gene fragments. PCR-products were purified with JETQUICK kit according to the manufacturer instructions.     

Synthesis of DLC films by PLD from liquid target and dependence of film properties on the synthesis conditions

DLC (Diamond-like carbon films) were prepared by pulsed laser ablation of a liquid target at substrate temperatures from 18 to 600°C using 248 nm KrF excimer laser. The sp³ hybridization state carbon formation was additionally promoted by gaseous H₂O₂ flow through the reaction chamber and substrate excitation by the same laser beam. Deposited DLC films were characterised by Raman scattering spectroscopy and atomic force microscopy (AFM). Comparative AFM and Raman study shows that the increase in the content of sp³ type bonding in DLC is in correlation with the increase of the surface roughness of the samples prepared.     

Diamond-like phase formation in an amorphous carbon films prepared by periodic pulsed laser deposition and laser irradiation method

Diamond-like carbon (DLC) films were fabricated by pulsed laser ablation of a liquid target. During deposition process the growing films were exited by a laser beam irradiation. The films were deposited onto the fused silica using 248 nm KrF eximer laser at room temperature and 10⁻³ mbar pressure. Film irradiation was carried out by the same KrF laser operating periodically between the deposition and excitation regimes. Deposited DLC films were characterized by Raman scattering spectroscopy. The results obtained suggested that laser irradiation intensity has noticeable influence on the structure and hybridization of carbon atoms deposited. For materials deposited at moderate irradiation intensities a very high and sharp peak appeared at 1332 cm⁻¹, characteristic of diamond crystals. At higher irradiation intensities the graphitization of the amorphous films was observed. Thus, at optimal energy density the individual sp³-hybridized carbon phase was deposited inside the amorphous carbon structure. Surface morphology for DLC has been analyzed using atomic force microscopy (AFM) indicating that more regular diamond cluster formation at optimal additional laser illumination conditions (∼20 mJ per impulse) is possible.     

Development and Optimisation of HILIC-LC-MS Method for Determination of Carbohydrates in Fermentation Samples

Saccharides are the most common carbon source for Streptococcus thermophilus, which is a widely used bacterium in the production of fermented dairy products. The performance of the strain is influenced by the consumption of different saccharides during fermentation. Therefore, a precise measurement of the concentrations of saccharides in the fermentation media is essential. An 18-min long method with limits of quantitation in the range of 0.159–0.704 mg/L and with ¹³C labelled internal standards employing hydrophilic interaction chromatography coupled to mass spectrometric detection-(HILIC-LC-MS) allowed for simultaneous quantification of five saccharides: fructose, glucose, galactose, sucrose, and lactose in the fermentation samples. The method included a four-step sample preparation protocol, which could be easily applied to high-throughput analysis. The developed method was validated and applied to the fermentation samples produced by Streptococcus thermophilus.     

Comparison of the contents of various antioxidants of sea buckthorn berries using CE

The increased interest in sea buckthorn (Hippophae rhamnoides L.) made it possible to investigate the antioxidant content in it. To address this issue, the presence of following antioxidant compounds were analyzed: trans-resveratrol, catechin, myricetin, quercetin, p-coumaric acid, caffeic acid, L-ascorbic acid (AA), and gallic acid (linear range of 50-150 micromol/L) in six different varieties of sea buckthorn berries extracts (sea buckthorn varieties: "Trofimovskaja (TR)," "Podarok Sadu (PS)," and "Avgustinka (AV),") received from two local Estonian companies. Trans-Resveratrol, catechin, AA, myricetin, and quercetin were found in extracts of sea buckthorn. Moreover, AA, myricetin, and quercetin contents were quantified. The biggest average AA content was found in TR (740 mg/100 g of dried berries, respectively). Furthermore, the same varieties gave the biggest quercetin content 116 mg/100 g of dried berries, respectively. For analysis, CZE was used and the results were partly validated by HPLC. Statistically no big differences in levels of antioxidants were consistently found in different varieties of sea buckthorn extracts investigated in this work.     

Microcalorimetric Monitoring of Anaerobic Digestion Processes

Microcalorimetry was used for monitoring anaerobic digestion processes of heavily polluted industrial waste waters (from cheese industry, distilleries, yeast plant). Interpreting the thermal power-time curves by HPLC, some sub-processes in batch cultures were tentatively identified as acidogenic, acetogenic and methanogenic. Processes underlying power-time curves up to 10 h were different for different wastes. In the case of cheese whey and distillery waste it was acidogenesis, in the case of sulfate containing waste - presumably reduction of sulfates. The effect of Biotreat 100 (BimKemi Eesti Ltd.), a preparation for removing H₂S from waste water, was observed for these processes. This revised version was published online in July 2006 with corrections to the Cover Date.     

Structural study of TiO2 thin films by micro-Raman spectroscopy

The Raman spectroscopy method was used for structural characterization of TiO₂ thin films prepared by atomic layer deposition (ALD) and pulsed laser deposition (PLD) on fused silica and single-crystal silicon and sapphire substrates. Using ALD, anatase thin films were grown on silica and silicon substrates at temperatures 125–425 °C. At higher deposition temperatures, mixed anatase and rutile phases grew on these substrates. Post-growth annealing resulted in anatase-to-rutile phase transitions at 750 °C in the case of pure anatase films. The films that contained chlorine residues and were amorphous in their as-grown stage transformed into anatase phase at 400 °C and retained this phase even after annealing at 900 °C. On single crystal sapphire substrates, phase-pure rutile films were obtained by ALD at 425 °C and higher temperatures without additional annealing. Thin films that predominantly contained brookite phase were grown by PLD on silica substrates using rutile as a starting material.     

On-line coupling of a miniaturized bioreactor with capillary electrophoresis, via a membrane interface, for monitoring the production of organic acids by microorganisms

Capillary electrophoresis (CE) can be a valuable tool for on-line monitoring of bioprocesses. Production of organic acids by phosphorus-solubilizing bacteria and fermentation of UHT milk were monitored and controlled by use of a membrane-interfaced dialysis device and a home-made microsampler for a capillary electrophoresis unit. Use of this specially designed sampling device enabled rapid consecutive injections without interruption of the high voltage. No additional sample preparation was required. The time resolution of monitoring in this particular work was approximately 2 h, but could be reduced to 2 min. Analytes were detected at low microg mL(-1) levels with a reproducibility of approximately 10%. To demonstrate the potential of CE in processes of biotechnological interest, results from monitoring phosphate solubilization by bacteria were submitted to qualitative and quantitative analysis. Fermentation experiments on UHT milk showed that monitoring of the processes by CE can provide good resolution of complex mixtures, although for more specific, detailed characterization the identification of individual substances is needed.     

Solid-state NMR spectroscopy of molecular hydrogen trapped inside an open-cage fullerene

Solid-state 1H experiments were performed an open-cage fullerene hosting molecular hydrogen. The anisotropy of the molecular hydrogen rotation was studied by double-quantum magic-angle-spinning NMR. The time scale of the molecular hydrogen rotation was estimated by spin-lattice relaxation measurements as a function of temperature.