The use of physical and virtual infrastructures for the validation of algal cryopreservation methods in international culture collections

Two cryopreservation methods, colligative cryoprotection coupled with controlled cooling and vitrification-based, encapsulation-dehydration were validated by five members of the EU research infrastructure consortium, COBRA, and two independent external validators. The test strain Chlorella vulgaris SAG 211-11b was successfully cryopreserved using two-step cooling employing passive (Mr Frosty) and Controlled Rate Freezers (CRF) attaining the desired recovery target within 15% of the median viability level (94%). Significant differences (p < 0.05) between cooling regimes were observed where Mr Frosty was more variable (Inter-Quartile Range being 21.5%, versus 13.0% for CRF samples). Viability assessment using fluorescein diacetate gave significantly (P < 0.0001) higher survival than growth in agar with median values being 96% and 89%, respectively. On employing encapsulation-dehydration, greater variability between some validators was observed, with six labs observing recovery in 100% of the beads (84-95% of cells surviving) and one lab observing survival in 80% of the treated beads. Bead disruption followed by algal growth in agar was considered the most reliable and accurate method of assessing cell survival for encapsulation-dehydration.     

Effect of influent nitrogen concentration on feasibility of short-cut nitrification during wastewater treatment in activated sludge systems

The inhibitory effect of free ammonia and free nitrous acid on nitrite-oxidising bacteria (NOB) was studied in a laboratory-scale sequencing batch reactor with a suspended microbial culture. The reactor was operated at 15°C, with a dissolved oxygen concentration in excess of 5 mg L^?1 and a nitrogen-loading rate of 0.2 kg m^?3 d^?1. Diluted reject water with varying total ammonia nitrogen (TAN) concentrations was used as influent. N-NO₂^? represented more than 90 % of all of the oxidised nitrogen, with influent TAN concentrations of 600 mg L^?1, 300 mg L^?1 and 150 mg L^?1, respectively. With a TAN concentration of 75 mg L^?1, a gradual increase in N-NO₃^? concentration was detected, indicating the threshold value enabling short-cut nitrification (SN) to be between 150 mg L^?1 and 75 mg L^?1 under the pertaining conditions. Next, the influent concentration of TAN was gradually increased from 75 mg L^?1 to 1000 mg L^?1 but the nitrite accumulation was not restored. This indicates that once NOB are established in the suspended microbial culture, even high TAN concentrations are not sufficient for NOB inhibition.     

Improving the Stability of Maleimide–Thiol Conjugation for Drug Targeting

Maleimides are essential compounds for drug conjugation reactions via thiols to antibodies, peptides and other targeting units. However, one main drawback is the occurrence of thiol exchange reactions with, for example, glutathione resulting in loss of the targeting ability. A new strategy to overcome such retro-Michael exchange processes of maleimide–thiol conjugates by stabilization of the thiosuccinimide via a transcyclization reaction is presented. This reaction enables the straightforward synthesis of stable maleimide–thiol adducts essential in drug-conjugation applications.     

On the Reactivity of NHCtBuAuCl towards Rb6Cs6Si17: The First Gold-Silicon Cluster [(NHCtBuAu)6(η2-Si4)]Cl2·7NH3 and an Imide Capped Gold Triangle (NHCtBuAu)3NHCl

Crystals of the two new compounds (NHC^tBuAu)₃NHCl and [(NHC^tBuAu)₆(η²-Si₄)]Cl₂ · 7NH₃ could be isolated from the reaction of Rb₆Cs₆Si₁₇ with NHC^tBuAuCl in the presence of [2.2.2]-cryptand in liquid ammonia. Both compounds were characterized by single-crystal X-ray diffraction and crystallize trigonally without any alkali metals or chelating ligands. Additionally, the crystal of [(NHC^tBuAu)₆(η²-Si₄)]Cl₂ · 7NH₃ was further interpreted by means of ELF and NBO calculations. In the case of (NHC^tBuAu)₃NHCl, NMR experiments provided an exceptional insight into the reaction processes in solution and allowed for the detection of sequential precursors. In the class of capped gold triangles (NHC^tBuAu)₃NHCl impresses with its unique characteristics of being capped by an imide and bound to N-heterocyclic carbenes as ligands instead of the ubiquitously employed phosphines. The gold capped silicon tetrahedron [(NHC^tBuAu)₆(η²-Si₄)]Cl₂ · 7NH₃ represents the first known silicide-gold compound, as well as the first known functionalized Zintl anion, crystallized with a cationic central moiety.     

High Temperature Stable Maghemite Nanoparticles Sandwiched between Hectorite Nanosheets

Maghemite (γ-Fe₂O₃) is a metastable iron oxide phase and usually undergoes fast phase transition to hematite at elevated temperatures (>350 °C). Maghemite nanoparticles were synthesized by the polyol method and then intercalated into a highly swollen (>100 nm separation) nematic phase of hectorite. A composite of maghemite nanoparticles sandwiched between nanosheets of synthetic hectorite was obtained. The confinement of the nanoparticles hampered Ostwald ripening up to 700 °C and consequently the phase transition to hematite is suppressed. Only above 700 °C γ-Fe₂O₃ nanoparticles started to grow and undergo phase transition to α-F₂O₃. The structure and the phase transition of the composite was evaluated using X-ray diffraction, TEM, SEM, physisorption, TGA/DSC, and Mößbauer spectroscopy.     

In vivo MR spectroscopy and MR imaging on non-anaesthetized marine fish: techniques and first results

In vivo Magnetic Resonance Imaging (MRI) and Spectroscopy (MRS) experiments were carried out in non-anaesthetized marine fish with a maximum body length of 40 cm using a 4.7 T horizontal magnet. In flow-through animal chambers long-term investigations could be carried out for several days in a sessile benthic zoarcid species, the eelpout Zoarces viviparus, as well as in a pelagic gadid species, the cod Gadus morhua. Sea water adapted probes and optimised excitation and refocusing pulse shapes reduced the negative effects of the highly conductive medium. In both species, in vivo 31P-NMR spectra were collected within 5 minutes with a reasonable signal to noise ratio (PCr/Pi ratio > 40 in cod) and typical line widths in the range of 20 to max. 40 Hz. Magnetic resonance images were recorded in the sessile species without movement artefacts. In these fish it was even possible to measure the blood flow of different vessels with a flow compensated gradient echo sequence and to carry out localized in vivo 1H-NMR spectroscopy in different organs.     

A construction of polynomial lattice rules with small gain coefficients

In this paper we construct polynomial lattice rules which have, in some sense, small gain coefficients using a component-by-component approach. The gain coefficients, as introduced by Owen, indicate to what degree the method improves upon Monte Carlo. We show that the variance of an estimator based on a scrambled polynomial lattice rule constructed component-by-component decays at a rate of N ^{−(2α+1)+δ} , for all δ > 0, assuming that the function under consideration has bounded variation of order α for some 0 < α ≤ 1, and where N denotes the number of quadrature points. An analogous result is obtained for Korobov polynomial lattice rules. It is also established that these rules are almost optimal for the function space considered in this paper. Furthermore, we discuss the implementation of the component-by-component approach and show how to reduce the computational cost associated with it. Finally, we present numerical results comparing scrambled polynomial lattice rules and scrambled digital nets.