Combining selective sequential extractions,X-ray absorption spectroscopy,and principal component analysis for quantitative zinc speciation in soil

Selective sequential extractions (SSE) and, more recently, X-ray absorption fine-structure IXAFS) spectroscopy have been used to characterize the speciation of metal contaminants in soils and sediments. However, both methods have specific limitations when multiple metal species coexist in soils and sediments. In this study, we tested a combined approach, in which XAFS spectra were collected after each of 6 SSE steps, and then analyzed by multishell fitting, principal component analysis (PCA) and linear combination fits (LCF), to determine the Zn speciation in a smelter-contaminated, strongly acidic soil. In the topsoil, Zn was predominately found in the smelter-emitted minerals franklinite (60%) and sphalerite (30%) and as aqueous or outer-sphere Zn2+ (10%). In the subsoil, aqueous or outer-sphere Zn2+ prevailed (55%), but 45% of Zn was incorporated by hydroxy-Al interlayers of phyllosilicates. Formation of such Zn-bearing hydroxy-interlayers, which has been observed here for the first time, may be an important mechanism to reduce the solubility of Zn in those soils, which are too acidic to retain Zn by formation of inner-sphere sorption complexes, layered double hydroxides or phyllosilicates. The stepwise removal of Zn fractions by SSE significantly improved the identification of species by XAFS and PCA and their subsequent quantification by LCF. While SSE alone provided excellent estimates of the amount of mobile Zn species, it failed to identify and quantify Zn associated with mineral phases because of nonspecific dissolution and the precipitation of Zn oxalate. The systematic combination of chemical extraction, spectroscopy, and advanced statistical analysis allowed us to identify and quantify both mobile and recalcitrant species with high reliability and precision.     

Trapped Pore Waters in the Open Proton Channel HV1

The voltage-gated proton channel, H_V1, is crucial for innate immune responses. According to alternative hypotheses, protons either hop on top of an uninterrupted water wire or bypass titratable amino acids, interrupting the water wire halfway across the membrane. To distinguish between both hypotheses, the water mobility for the putative case of an uninterrupted wire is estimated. The predicted single-channel water permeability 2.3 × 10⁻¹² cm³ s⁻¹ reflects the permeability-governing number of hydrogen bonds between water molecules in single-file configuration and pore residues. However, the measured unitary water permeability does not confirm the predicted value. Osmotic deflation of reconstituted lipid vesicles reveals negligible water permeability of the H_V1 wild-type channel and the D174A mutant open at 0 mV. The conductance of 1400 H⁺ s⁻¹ per wild-type channel agrees with the calculated diffusion limit for a ≈2 Å capture radius for protons. Removal of a charged amino acid (D174) at the pore mouth decreases H⁺ conductance by reducing the capture radius. At least one intervening amino acid contributes to H⁺ conductance while interrupting the water wire across the membrane.     

Molecular Insights into an Antibiotic Enhancer Action of New Morpholine-Containing 5-Arylideneimidazolones in the Fight against MDR Bacteria

In the search for an effective strategy to overcome antimicrobial resistance, a series of new morpholine-containing 5-arylideneimidazolones differing within either the amine moiety or at position five of imidazolones was explored as potential antibiotic adjuvants against Gram-positive and Gram-negative bacteria. Compounds (7–23) were tested for oxacillin adjuvant properties in the Methicillin-susceptible S. aureus (MSSA) strain ATCC 25923 and Methicillin-resistant S. aureus MRSA 19449. Compounds 14–16 were tested additionally in combination with various antibiotics. Molecular modelling was performed to assess potential mechanism of action. Microdilution and real-time efflux (RTE) assays were carried out in strains of K. aerogenes to determine the potential of compounds 7–23 to block the multidrug efflux pump AcrAB-TolC. Drug-like properties were determined experimentally. Two compounds (10, 15) containing non-condensed aromatic rings, significantly reduced oxacillin MICs in MRSA 19449, while 15 additionally enhanced the effectiveness of ampicillin. Results of molecular modelling confirmed the interaction with the allosteric site of PBP2a as a probable MDR-reversing mechanism. In RTE, the compounds inhibited AcrAB-TolC even to 90% (19). The 4-phenylbenzylidene derivative (15) demonstrated significant MDR-reversal “dual action” for β-lactam antibiotics in MRSA and inhibited AcrAB-TolC in K. aerogenes. 15 displayed also satisfied solubility and safety towards CYP3A4 in vitro.     

LTI models for 3-iodothyronamine time dynamics: a multiscale view

3-Iodothyronamine (T(1)AM) is a novel relative of thyroid hormone that plays a role in critical body regulatory processes such as glucose metabolism, thermal regulation, and heart beating. This paper was aimed at characterizing time dynamics of T(1)AM and its catabolite 3-iodothyroacetic acid (TA(1)) in different biological scales with linear time-invariant models. Culture medium samples coming from culture of H9c2 murine cells and perfusion liquid samples from perfused rat heart were collected after the injection of a T(1)AM bolus. T(1)AM and TA(1) concentrations in the samples were assayed with high-performance liquid chromatography coupled to tandem mass spectrometry. Kinetic constants relative to T(1)AM transport and conversion were estimated with weighted least-squares method. We found that these constants can be related with an allometric power law depending on mass, with a negative exponent of -0.27 ± 0.19, implying that the velocity of conversion and internalization of T(1)AM decreases with increasing of system mass.     

Fast analysis of proteins in wines by capillary gel electrophoresis

Wine proteins play an important role in different characteristics of wine (e.g., aroma and body, foaming in sparkling wines). They can also cause a number of technological problems during vinification and may be responsible for the appearance of turbidity in bottled wine. These important features of proteins in wine have made necessary the development of new and fast analytical methods that can provide deeper knowledge about these biopolymers. However, separation and characterization of wine proteins is difficult and time-consuming mainly due to their low concentration and large number of interfering compounds. Besides, long sample preparation protocols can bring about protein decomposition. This paper proposes a new and fast method for carrying out the analysis of the protein fraction of wines. The procedure consists of direct treatment of wine using a centrifugal filter device (CFD), denaturation of the proteinaceous fraction with sodium dodecyl sulfate (SDS) and 2-mercaptoethanol, and subsequent CGE analysis of SDS-proteins. Results on the molecular weight (Mw) and relative quantity of proteins of wines are attained in about 1 h with this procedure. The method is applied to analyze different wines from Canary Islands. To our knowledge, this is the first report of separation of wine proteins according to their Mw by CGE.     

Chemical and near-infrared determination of moisture,fat and protein in tuna fishes

Moisture, protein, free fat and total fat were determined in Tuna Fishes (38) skipjack (Katsuwonus pelamis) (20) and yellow fin (Thunnus albacares) (18) by chemical methods. Moisture was determined by freeze-drying or lyophilization, oven-dry methods and by using electronic moisture analyzer. Protein content was determined using Gerhardt semi-micro Kjeldahl and combustion methods. Total fat was determined using acid-hydrolysis method and free fat was determined by Soxhlet method. Near-infrared spectra of the fishes (28) and partial least square regression with the reference methods namely lyophilization method for moisture, combustion method for proteins, acid-hydrolysis method for total fat and Soxhlet method for free fat were used to set a calibration model. This regression model was then used for quantifying the named components of the fishes (5), considered as unknowns, from their near-infrared spectra. There is a good comparison between the results from the different chemical methods and the components quantified using the near-infrared spectroscopy method. An outcome of this work is that near-infrared spectroscopy can serve as an accurate and fast method for quantifying the components of fishes.