Iota-carrageenan/casein micelles interactions: evidence at different scales

The effect of temperature on the behaviour of iota-carrageenan (CI) 0.1 wt.%/casein micelles (CM) 0–5 wt.% mixtures has been studied using three techniques: confocal laser scanning microscopy (CLSM), differential scanning calorimetry (DSC) and spectrophotometry. The microscopy clearly shows that those mixed systems separate in two phases, one being enriched in CM. It has been shown that the CM concentration seems to have an effect on the extent of the phase separation phenomenon. The DSC experiments show that addition of CM modifies the helix to coil transition temperature of carrageenan. The enthalpy of melting of helices decreases as the CM concentration increases, and the peak is shifted towards higher temperature. Local electrostatic interactions between carrageenan chains and CM have been studied by a spectrophotometric method using methylene blue (MB) properties of absorption. The absorption spectra of MB in presence of CI and CM were compared with the one of MB in presence of carrageenan alone at temperatures above and below the carrageenan coil to helix transition. The modifications of the spectrum by addition of CM are discussed in terms of interactions and rigidification of the carrageenan chains.     

Optically pumped14NH3 laser and its stark tuning at 10.78 μm

Infrared (ir) emissions from a TEA-CO₂-laser-pumped NH₃ laser are reported. Superfluorescent emissions and selective single-line oscillations have been obtained in the range from 11 to 13 m. The results make possible the design of a NH₃ Stark cell allowing a 1 GHz shift of the 10.78 m NH₃ emission line.     

Selective 1H-13C correlation by low power single frequency off-resonance decoupling assisted by exhaustive simulation techniques

Selectivity in the ¹H-¹³C correlation for assignments of ¹³C spectra is enhanced by recording single frequency off-resonance ¹³C NMR spectra with low decoupling field strength (? 2J_o), distortion of signal patterns is avoided by submitting the spin system to a previous noise broad band decoupling. Correlation is obtained by comparison of observed and simulated 2-D spectra (π ¹³C vs decoupler frequency) joined to fitting of the curve J_R = f (decoupler frequency) with the equation of Freeman and Anderson.₁     

The coupling constant averaged exchange–correlation energy density

ABSTRACT

The exchange–correlation energy, central to density-functional theory, may be represented in terms of the coupling constant averaged (CCA) exchange–correlation energy density. We present an approach to calculate the CCA energy density using accurate ab initio methods and its application to simple atomic systems. This function provides a link between intrinsically non-local, many-body electronic structure methods and simple local and semi-local density-functional approximations (DFAs). The CCA energy density is resolved into separate exchange and correlation terms and the features of each compared with those of quantities commonly used to construct DFAs. In particular, the more complex structure of the correlation energy density is found to exhibit features that align well with those present in the Laplacian of the density, suggesting its role as a key variable to be used in the construction of improved semi-local correlation functionals. The accurate results presented in this work are also compared with those provided by the Laplacian-dependent Becke–Roussel model for the exchange energy.     

Determinations of Uranium(VI) Binding Properties with some Metalloproteins (Transferrin,Albumin, Metallothionein and Ferritin) by Fluorescence Quenching

The interactions between uranium and four metalloproteins (Apo-HTf, HSA, MT and Apo-EqSF) were investigated using fluorescence quenching measurements. The combined use of a microplate spectrofluorometer and logarithmic additions of uranium into protein solutions allowed us to define the fluorescence quenching over a wide range of [U]/[Pi] ratios (from 0.05 to 1150) at physiologically relevant conditions of pH. Results showed that fluorescence from the four metalloproteins was quenched by UO₂²⁺. Stoichiometry reactions, fluorescence quenching mechanisms and complexing properties of metalloproteins, i.e. binding constants and binding sites densities, were determined using classic fluorescence quenching methods and curve-fitting software (PROSECE). It was demonstrated that in our test conditions, the metalloprotein complexation by uranium could be simulated by two specific sites (L₁ and L₂). Results showed that the U(VI)–Apo-HTf complexation constant values (log K₁ = 7.7, log K₂ = 4.6) were slightly higher than those observed for U(VI)–HSA complex (log K₁ = 6.1, log K₂ = 4.8), U(VI)–MT complex (log K₁ = 6.5, log K₂ = 5.6) and U(VI)–Apo-EqsF complex (log K₁ = 5.3, log K₂ = 3.9). PROSECE fitting studies also showed that the complexing capacities of each protein were different: 550 moles of U(VI) are complexed by Apo-EqSF while only 28, 10 and 5 moles of U(VI) are complexed by Apo-HTf, HSA and MT, respectively.     

Forazoline A: Marine‐Derived Polyketide with Antifungal In Vivo Efficacy

Forazoline A, a novel antifungal polyketide with in vivo efficacy against Candida albicans, was discovered using LCMS‐based metabolomics to investigate marine‐invertebrate‐associated bacteria. Forazoline A had a highly unusual and unprecedented skeleton. Acquisition of ¹³C–¹³C gCOSY and ¹³C–¹⁵N HMQC NMR data provided the direct carbon–carbon and carbon–nitrogen connectivity, respectively. This approach represents the first example of determining direct ¹³C–¹⁵N connectivity for a natural product. Using yeast chemical genomics, we propose that forazoline A operated through a new mechanism of action with a phenotypic outcome of disrupting membrane integrity.     

Bacterial Autoimmune Drug Metabolism Transforms an Immunomodulator into Structurally and Functionally Divergent Antibiotics

Tapinarof is a stilbene drug that is used to treat psoriasis and atopic dermatitis, and is thought to function through regulation of the AhR and Nrf2 signaling pathways, which have also been linked to inflammatory bowel diseases. It is produced by the gammaproteobacterial Photorhabdus genus, which thus represents a model to probe tapinarof structural and functional transformations. We show that Photorhabdus transforms tapinarof into novel drug metabolism products that kill inflammatory bacteria, and that a cupin enzyme contributes to the conversion of tapinarof and related dietary stilbenes into novel dimers. One dimer has activity against methicillin‐resistant Staphylococcus aureus (MRSA) and vancomycin‐resistant Enterococcus faecalis (VRE), and another undergoes spontaneous cyclizations to a cyclopropane‐bridge‐containing hexacyclic framework that exhibits activity against Mycobacterium. These dimers lack efficacy in a colitis mouse model, whereas the monomer reduces disease symptoms.     

Rheological properties of starch suspensions using a rotational rheometer fitted with a starch stirrer cell

The rheological properties of a starch suspension are usually studied through two viscosity measurements-pasting behavior and flow behavior of the resulting starch pastes-performed separately with two different tools and demanding rather high starch concentrations (6–10 wt %). This study focused on the feasibility of using a rheometer fitted with a starch stirrer cell to characterize, in a single experiment, the starch suspension’s behavior during and after pasting, all the while involving only low concentrations (2–4 wt %), more representative of a real-food context. A calibration of the starch stirrer cell in comparison to the coaxial cylinders one was done using model fluids (Newtonian and shear-thinning). A link between torque, rotational speed, and rheological properties was determined through two recalculated conversion factors (shear rate and shear stress). An operating diagram was then set indicating the laminar flow and good sensitivity domain for this cell. The accuracy of those constants to starch suspensions in the concentration range 2–4 wt % was demonstrated. The pasting behaviors of 2 wt % starch suspensions were followed successfully at two selected shear rates (13.5 and 135 s^?1). The impact of the level of turbulence on the profiles obtained was stressed, a result that is not limited to low-concentration starch suspensions. Finally, the method developed was used to compare the pasting behaviors of 2 wt % native and modified waxy maize starch suspensions.