Embryonic stem cells (ESC) are both a potential source of cells for tissue replacement therapies and an accessible tool to model early embryonic development. Chemical factors such as soluble growth factors and insoluble components of the extracellular matrix are known to affect the differentiation of murine ESCs. However, there is also evidence to suggest that undifferentiated cells can both sense the mechanical properties of their environment and differentiate accordingly. By growing ESCs on flexible polydimethylsiloxane substrates with varying stiffness, we tested the hypothesis that substrate stiffness can influence ESC differentiation. While cell attachment was unaffected by the stiffness of the growth substrate, cell spreading and cell growth were all increased as a function of substrate stiffness. Similarly, several genes expressed in the primitive streak during gastrulation and implicated in early mesendoderm differentiation, such as Brachyury, Mixl1 and Eomes, were upregulated in cell cultures on stiffer compared to softer substrates. Finally, we demonstrated that osteogenic differentiation of ESCs was enhanced on stiff substrates compared to soft substrates, illustrating that the mechanical environment can play a role in both early and terminal ESC differentiation. Our results suggest a fundamental role for mechanosensing in mammalian development and illustrate that the mechanical environment should be taken into consideration when engineering implantable scaffolds or when producing therapeutically relevant cell populations in vitro.

Environmental Context. Arsenic is of significant environmental concern in much of the world because of its contamination of waters, from mining, industry, sewage disposal, and agriculture. The environmental mobility of arsenic is controlled primarily by adsorption onto metal oxides, especially iron. Humic substances (natural organic matter), which are ubiquitous in aquatic and soil environments, may interfere with this adsorption and arsenic mobility may be increased. Thus, even if it is assumed that humic substances sorb arsenic less strongly than hydrous iron oxides, they may, nevertheless, influence arsenic sorption and mobility, particularly when the iron oxide content in the environment is low. Abstract. The environmental mobility of arsenic is primarily controlled by adsorption onto metal oxide surfaces, particularly iron, aluminium, and manganese. Humic acid (HA) may interfere with this adsorption, thereby increasing arsenic mobility. This study has characterized the interaction of arsenic with HA in a system consisting of HA with As(iii), As(v), and dimethylarsinic acid (DMAA). Three sets of batch experiments were performed at varying pH (3–12), ionic strength (0–0.4 mol dm−3), concentration of each arsenic species (0–100 mg dm−3), and HA concentration (0–10 g dm−3). Arsenic species were shown to react with humic acid. The interaction is postulated to involve bridging metals and deprotonated functional groups within the HA. The association is dependent on pH, ionic strength, and arsenic concentration. The extent of the interaction was greater in the pH range 8–10 for As(v) and DMAA, while it extended to pH 12 for As(iii). The strong pH dependency is probably due to the aqueous speciation of arsenic. The logarithmic conditional association constants for the reactions were found to be 1.97 ± 0.02, 1.58 ± 0.07, and 1.50 ± 0.10 for As(v), As(iii), and DMAA respectively. These values indicate the formation of weak complexes with humic acid.

Radionuclide solubility is one of the factors that can determine the 'source term' for potential migration to the far field. Hence, the mechanisms of immobilisation of radionuclides in cements need close study in order to quantify the nature of the binding. The nature of the binding forces in a cement matrix is very species sensitive, so it is difficult to produce a general description. This review summarises the main sorption mechanisms and then details immobilisation mechanisms for many elements.

Citation: KHAN, M.H., WARWICK, P. and EVANS, N., 2006. Spectrophotometric determination of uranium with arsenazo-III in perchloric acid. Chemosphere, 63, 2006Chemosphere, 63, , pp. 1165Chemosphere, 63, -1169 Additional Information:• AbstractA short, sensitive and reliable spectrophotometric method, which has advantages over all known "wet chemistry" methods for uranium determination with regard to tolerance to common interferences, has been developed for the determination of uranium. Selectivity, molar absorptivity and the determination range of uranium have been enhanced by using 0.07 % arsenazo-III as a chromogenic reagent. The use of 3 mol dm -3 perchloric acid as a medium of determination was found to be excellent in terms of good solvent compatibility on dilution, destruction of organic contamination and simplicity of operation. The uranium-arsenazo-III complex formed instantly, and was found to be stable for more than 3 weeks with constant absorbance. Beer's law was obeyed up to a uranium concentration of 16 μg g -1 , with Other cations studied did not affect the absorbance up to a 50 fold excess. The accuracy was checked by determining uranium from standard solutions in the range 10-50 μg g -1 . It was found to be accurate with a 96.0-98.6.% recovery rate. The method has been successfully applied to standard reference materials and ore samples at μg g -1 levels.

We explore the effect of magnetic field on chiral condensation in QCD via a simple bottom up holographic model which inputs QCD dynamics through the running of the anomalous dimension of the quark bilinear. Bottom up holography is a form of effective field theory and we use it to explore the dependence on the coefficients of the two lowest order terms linking the magnetic field and the quark condensate. In the massless theory, we identify a region of parameter space where magnetic catalysis occurs at zero temperature but inverse magnetic catalysis at temperatures of order the thermal phase transition. The model shows similar non-monotonic behaviour in the condensate with B at intermediate T as the lattice data. This behaviour is due to the separation of the meson melting and chiral transitions in the holographic framework. The introduction of quark mass raises the scale of B where inverse catalysis takes over from catalysis until the inverse catalysis lies outside the regime of validity of the effective description leaving just catalysis.

Complexation / Uranium / Isosaccharinic acid / Reducing conditions / Solubility product / Gluconic acid Summary. Conditional and pH independent stability constants have been determined for U(IV) α-isosaccharinic acid (ISA) and gluconic acid (Gl) complexes, under anaerobic and carbonate-free conditions, from pH 3 to 14. The constants are needed for nuclear waste repository performance assessment purposes. The constants were obtained by developing an approach based on the solubility product of amorphous UO 2 ·2H 2 O. The derived pH independent log β values for U(OH) 4 ISA and U(OH) 4 Gl were 49 ± 2 and 50 ± 1 respectively.

SummaryNickel reactions with gluconic acid (Gl) and

SummaryThe coherence of actinide(IV) complexation by humic substances (HS) is reviewed and new data are proposed. In a first attempt, the values of independent data from literature on Th(IV), U(IV), and Pu(IV) are collected, selected, and compiled. The data obtained follow the “classical” trend of increasing conditional formation “constants” with pH, led both by the increasing ionisation of HS and by the extensive hydrolysis of the tetravalent actinides. Even though a fair agreement is evident, the experimental uncertainties do not permit a full analogy between the actinides(IV) to be ascertained. In a second attempt, the experiments from which the original data are available were reinterpreted using only one hydrolysis constant set for U(IV) as an example, considering that all actinides(IV) have analogous humic complexation behaviour. Hence, the obtained evolution of conditional formation “constants” is much more coherent and the uncertainties do not permit to distinguish an actinide(IV) from one another. The obtained data are then applied to independent laboratory and