In vitro formation of Ca-oxalates and the mineral glushinskite by fungal interaction with carbonate substrates and seawater

This study investigates the in vitro formation of Ca-oxalates and glushinskite through fungal interaction with carbonate substrates and seawater as a process of biologically induced metal recycling and neo-mineral formation. The study also emphasizes the role of the substrates as metal donors. In the first experiment, thin sections prepared from dolomitic rock samples of Terwagne Formation (Carboniferous, Viséan, northern France) served as substrates. The thin sections placed in Petri dishes were exposed to fungi grown from naturally existing airborne spores. In the second experiment, fungal growth and mineral formation was monitored using only standard seawater (SSW) as a substrate. Fungal growth media consisted of a high protein/carbohydrates and sugar diet with demineralized water for irrigation. Fungal growth process reached completion under uncontrolled laboratory conditions. The newly formed minerals and textural changes caused by fungal attack on the carbonate substrates were investigated using light and scanning electron microscopy (SEM-EDX), x-ray diffraction (XRD) and Raman spectroscopy. The fungal interaction and attack on the dolomitic and seawater substrates resulted in the formation of Ca-oxalates (weddellite CaC2O4·2(H2O), whewellite (CaC2O4·(H2O)) and glushinskite MgC2O4·2(H2O) associated with the destruction of the original hard substrates and their replacement by the new minerals. Both of Ca and Mg were mobilized from the experimental substrates by fungi. This metal mobilization involved a recycling of substrate metals into newly formed minerals. The biochemical and diagenetic results of the interaction strongly marked the attacked substrates with a biological fingerprint. Such fingerprints are biomarkers of primitive life. The formation of glushinskite is of specific importance that is related, besides its importance as a biomineral bearing a recycled Mg, to the possibility of its transformation through diagenetic pathway into an Mg carbonate. This work is the first report on the in vitro formation of the mineral glushinskite through fungal interaction with carbonate and seawater substrates. Besides recording the detailed Raman signature of various crystal habits of Mg- and Ca-oxalates, the Raman spectroscopy proved two new crystal habits for glushinskite. The results of this work document the role of microorganisms as metal recyclers in biomineralization, neo-mineral formation, sediment diagenesis, bioweathering and in the production of mineral and diagenetic biomarkers. They also reveal the capacity of living fungi to interact with liquid substrates and precipitate new minerals

Proprioceptive changes impair balance control in individuals with chronic obstructive pulmonary disease

Copyright @ 2013 Janssens et al. This is an open-access article distributed under the terms of the Creative Commons Attribution License, which permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.Introduction: Balance deficits are identified as important risk factors for falling in individuals with chronic obstructive pulmonary disease (COPD). However, the specific use of proprioception, which is of primary importance during balance control, has not been studied in individuals with COPD. The objective was to determine the specific proprioceptive control strategy during postural balance in individuals with COPD and healthy controls, and to assess whether this was related to inspiratory muscle weakness. Methods: Center of pressure displacement was determined in 20 individuals with COPD and 20 age/gender-matched controls during upright stance on an unstable support surface without vision. Ankle and back muscle vibration were applied to evaluate the relative contribution of different proprioceptive signals used in postural control. Results: Individuals with COPD showed an increased anterior-posterior body sway during upright stance (p=0.037). Compared to controls, individuals with COPD showed an increased posterior body sway during ankle muscle vibration (p=0.047), decreased anterior body sway during back muscle vibration (p=0.025), and increased posterior body sway during simultaneous ankle-muscle vibration (p=0.002). Individuals with COPD with the weakest inspiratory muscles showed the greatest reliance on ankle muscle input when compared to the stronger individuals with COPD (p=0.037). Conclusions: Individuals with COPD, especially those with inspiratory muscle weakness, increased their reliance on ankle muscle proprioceptive signals and decreased their reliance on back muscle proprioceptive signals during balance control, resulting in a decreased postural stability compared to healthy controls. These proprioceptive changes may be due to an impaired postural contribution of the inspiratory muscles to trunk stability. Further research is required to determine whether interventions such as proprioceptive training and inspiratory muscle training improve postural balance and reduce the fall risk in individuals with COPD.This work was supported by the Research Foundation – Flanders (FWO) grants 1.5.104.03, G.0674.09, G.0598.09N and G.0871.13N

Cleavage of the Oxanorbornene Oxygen Bridge with Lewis Acids: Computation and Experiment

Since the discovery of the biological activity of aminophosphonates, research started on the synthesis of more constraint azaheterocyclic phosphonates. We developed a route via an intramolecular Diels-Alder reaction towards α-aminophosphonates 1. [1] The obtained oxanorbornene skeleton is a valuable synthetic intermediate that has been used in various natural product syntheses. [2] An important synthetic transformation involves the cleavage of the oxygen bridge, used to construct substituted arenes and cyclohexenes. We wanted to investigate the ring opening of adducts 1 using different Lewis acids experimentally and get more insight in the reaction pathways towards the different products via computational experiments. In this presentation the results obtained with TiCl4 and FeCl3 catalyst are shown. The computational study started with the catalysts and their multiplicity. Next, the complexation energy with different binding sites was calculated. Therefore, a level of theory study was done using an ONIOM QM/QM approach. This shows the importance of the inclusion of electron correlation effects. B3LYP geometries and energies can be used as a good approximation. Bidentate coordination towards the most electronegative phosphonate oxygen and the oxygen bridge is favoured for both catalysts. Then, different reaction pathways were investigated via a static, gas-phase approach. The energy barrier towards the transition state using the TiCl4 catalyst, shown in Figure 1, is much lower than for the FeCl3 catalyst and very different products are formed. The computational results were compared with the experiments

Asymptotics for the Partition Function in Two-Cut Random Matrix Models

We obtain large N asymptotics for the Hermitian random matrix partition function $$Z_N(V)=\int_{\mathbb R^N}\prod_{i<j}(x_i-x_j)^2 \prod_{j=1}^N e^{-N V(x_j)}dx_j,$$ in the case where the external potential $V$ is a polynomials such that the random matrix eigenvalues accumulate on two disjoint intervals (the two-cut case). We compute leading and sub-leading terms in the asymptotic expansion for $\log Z_N(V)$, up to terms that are small as $N$ goes to infinity. Our approach is based on the explicit computation of the first terms in the asymptotic expansion for a quartic symmetric potential $V$. Afterwards, we use deformation theory of the partition function and of the associated equilibrium measure to generalize our results to general two-cut potentials $V$. The asymptotic expansion of $\log Z_N(V)$ as $N$ goes to infinity contains terms that depend analytically on the potential $V$ and that have already appeared in the literature. In addition our method allows to compute the $V$-independent terms of the asymptotic expansion of $\log Z_N(V)$ which, to the best of our knowledge, had not appeared before in the literature. We use rigorous orthogonal polynomial and Riemann-Hilbert techniques which had so far been successful to compute asymptotics for the partition function only in the one-cut case.Comment: 75 pages. To appear in Comm. Math. Physic

Critical behavior in Angelesco ensembles

We consider Angelesco ensembles with respect to two modified Jacobi weights on touching intervals [a,0] and [0,1], for a < 0. As a \to -1 the particles around 0 experience a phase transition. This transition is studied in a double scaling limit, where we let the number of particles of the ensemble tend to infinity while the parameter a tends to -1 at a rate of order n^{-1/2}. The correlation kernel converges, in this regime, to a new kind of universal kernel, the Angelesco kernel K^{Ang}. The result follows from the Deift/Zhou steepest descent analysis, applied to the Riemann-Hilbert problem for multiple orthogonal polynomials.Comment: 32 pages, 9 figure

On the origin of the 1/f noise in shallow germanium p(+)-n junctions

The low-frequency noise of shallow germanium p(+)-n junctions is studied, for diodes with or without a nickel-germanide Ohmic contact. It is shown that the application of NiGe not only reduces the series resistance, resulting in a higher forward current, but also results in a lower 1/f noise at forward bias. From the observed geometry dependence, it is concluded that germanidation suppresses the 1/f noise generated in the series resistance, leaving surface-state-assisted generation-recombination at the junction perimeter as the dominant flicker noise source