Solution conformation of the Pseudomonas syringae MSU 16H phytotoxic lipodepsipeptide Pseudomycin A determined by computer simulations using distance geometry and molecular dynamics from NMR data

Pseudomycin A is a cyclic lipodepsinonapeptide phytotoxin produced by a strain of the plant pathogenic bacterium Pseudomonas syringae. Like other members of this family of bacterial metabolites, it is characterised by a fatty acylated cyclic peptide with mixed chirality and lactonic closure. Several biological activities of Pseudomycin A are lower than those found for some of its congeners, a difference which might depend on the diverse number and distribution of charged residues in the peptide moiety. Hence, it was of interest to investigate its conformation in solution. After the complete interpretation of the two-dimensional NMR spectra, NOE data were obtained and the structure was determined by computer simulations, applying distance geometry and molecular dynamics procedures. The conformation of the large ring of Pseudomycin A in solution includes three rigid structural regions interrupted by three short flexible regions that act as hinges. The overall three-dimensional structure of the cyclic moiety is similar to that of previously studied bioactive lipodepsinonapeptides produced by other pseudomonads.     

Renal osteodystrophy in diabetic patients

To assess the effects of diabetes mellitus on renal osteodystrophy, we examined the database of 256 patients (45% on hemodialysis and 55% on peritoneal dialysis) who were prospectively studied in three Toronto dialysis centers between October of 1987 and 1989. All patients had serial documentation of their clinical, laboratory and risk parameters of bone disease, and completed a series of investigations that included the deferoxamine test, measurement of intact 1-84 PTH levels, and an iliac crest bone biopsy. Twenty-five percent of these patients were diabetic. When compared to non-diabetic patients, they were on dialysis for a shorter duration (2.4 +/- 0.3 vs. 4.7 +/- 0.3 years; P < 0.0002), used calcium carbonate as the only phosphate binder more frequently (40 vs. 25%; P < 0.007), and had lower parathyroid hormone levels (12 +/- 1.4 vs. 24 +/- 2.3 pmol/liter; P < 0.002). High-turnover bone disorders (that is, osteitis fibrosa and mixed disorder) were distinctly uncommon (8 vs. 33%; P < 0.01 by Fisher's exact test), while the mild (19 vs. 9%; P = NS) and the aplastic disorders (with mean stainable bone surface aluminum of 6.5 +/- 0.7%) (46 vs. 31%; P = NS) tended to be more common in diabetic patients. The prevalence of aluminum bone disease was the same in both groups (27%). Diabetic patients ingested a smaller cumulative dose of aluminum gels (3.7 +/- 0.6 vs. 9.3 +/- 1.1 kg; P < 0.005), yet had a higher rate of aluminium accumulation on bone surfaces than non-diabetic patients (1.5 +/- 0.19 vs. 0.96 +/- 0.10% per month on dialysis; P < 0.015).(ABSTRACT TRUNCATED AT 250 WORDS)     

Specific heat and critical field for some iron-containing superconductors

Specific heat measurements on superconductingLu ₂ Fe ₃ Si ₅ reveal a strong sample dependence of the residual specific heat contribution _s , belowT _c , effectively ruling out the possibility of a two-band model. Upper critical fieldH _c2 results for Lu₂Fe₃Si₅, Sc₂Fe₃Si₅, and LaFe₄P₁₂ show a very largeH _c2 with an unusual temperature dependence for Lu₂Fe₃Si₅, in contrast to the latter two compounds, implying a strongly sample-dependentH _c2 as well. Intrinsic magnetic impurities arising from structural disorder and defects are possibly the origin of these anomalous superconducting state properties of Lu₂Fe₃Si₅.     

An X-ray absorption spectroscopy study of Mo oxidation in Pb at elevated temperatures

The corrosion of fuel cladding and structural materials by lead and lead-bismuth eutectic in the liquid state at elevated temperatures is an issue that must be considered when designing advanced nuclear systems and high-power spallation neutron targets. In this work, lead corrosion studies of molybdenum were performed to investigate the interaction layer as a function of temperature by X-ray absorption spectroscopy. In situ X-ray absorption measurements on a Mo substrate with a 3-6 μm layer of Pb deposited by thermal evaporation were performed at temperatures up to 900 °C and at a 15° angle to the incident X-rays. The changes in the local atomic structure of the corrosion layer are visible in the difference extended X-ray absorption fine structure and the linear combination fitting of the X-ray absorption near-edge structure to as-deposited molybdenum sample and molybdenum oxide (MoO₂ and MoO₃) standards. The data are consistent with the appearance of MoO₃ in an intermediate temperature range (650-800 °C) and the more stable MoO₂ phase dominating at high and low temperatures.     

Using <Superscript>1</Superscript>H and <Superscript>13</Superscript>C NMR techniques and artificial neural networks to detect the adulteration of olive oil with hazelnut oil

The lack of any official analytical method to detect the adulteration of olive oil with a low percentage of hazelnut oil is explained by the similarities in the chemical compositions of both kinds of oils. To counter this problem, an artificial neural network based on ¹H-NMR and ¹³C-NMR data has been developed to detect olive oil adulteration, and the results from this ANN are presented here. A training set consisting of hazelnut oils, pure olive oils, and olive oils blended with 2–20% hazelnut oils was used to design and train a multilayer perceptron with 100% correct classifications. This mathematical model was also validated using an external validation set of blend samples (3–15%) and genuine samples. The detection limit of the model was around 8%.     

New formalism for the analysis of polarization evolution for radiation in a weakly nonuniform, fully anisotropic medium: a magnetized plasma

The evolution equation is obtained for the state of polarization of partially polarized radiation propagating in a medium that is nonuniform and fully anisotropic, i.e., that presents both linear and circular birefringence as well as dichroism. The treatment covers the general case in which the characteristic polarizations are not necessarily orthogonal, such as occurs for propagation in a magnetized, dissipative plasma. The differential Mueller matrix that appears in the evolution equation is obtained explicitly for two particular cases. The resulting formalism is convenient for numerical integration.     

Niobium speciation at the metal/oxide interface of corroded niobium-doped Zircaloys: A X-ray absorption near-edge structure study

X-ray absorption near-edge structure (XANES) spectroscopy is applied to Zr-based alloys ((Zr, x%Nb) with x  1 wt.%) corroded in steam at 415 °C to resolve the niobium speciation in the metal and the oxide parts of their metal/oxide interface. By combining these synchrotron X-ray measurements with additional ab initio calculations of Nb K-edge XANES spectra, this study reveals (i) the presence of Nb⁰ in the metal and of Nb atoms having valency between +2 and +4 in the oxide as well as (ii) the coexistence of Nb-doped monoclinic and Nb-doped tetragonal zirconia structures within the oxide of the (Zr, 1.0%Nb) alloy.