Rapid determination of orotic acid in urine by a fast liquid chromatography/tandem mass spectrometric method

Quantification of orotic acid (uracil-6-carboxylic acid) in urine is an important tool to diagnose some inherited diseases, such as urea cycle disorder (OTCD) and hereditary orotic aciduria. New rapid analytical methods are necessary to provide high-throughput orotic acid analyses. A new analytical method has been developed for the rapid analysis of orotic acid in urine by liquid chromatography coupled with ion spray tandem mass spectrometry (LC/MS/MS). After a sample dilution 1:20, the analysis was performed in the selected reaction monitoring mode in which orotic acid was detected through the transition m/z 155 to 111. The retention time was 3.9 min in a 4.5-min analysis. Daily calibration between 0.5-5.0 micromol/L of orotic acid, corresponding to 10-100 micromol/L in urine before the 1:20 dilution, offered consistent linearity and reproducibility. Interassay coefficient of variance (c.v.) was 4.97% at a mean concentration of 10.99 micromol/L. The sensitivity and specificity of tandem mass spectrometry permitted a high volume of analyses of orotic acid. The sample preparation is simple, inexpensive and not time demanding.     

The Molecular and Crystal Structure of the Glycopeptide A-40926 Aglycone

The crystal structure of a glycopeptide antibiotic A–40926 aglycone was investigated by X-ray analysis at ?120°. A-40926 crystallises in the orthorhombic space group P2₁2₁2₁ with two monomers in the asymmetric unit, a = 21.774(4), b = 28.603(7), c = 29.757(4) Å. ‘Conventional’ direct methods approach failed to solve the structure, but a novel iterative real/reciprocal space procedure was successful. Refinement against 11248 F² data led to R1 = 13.3% for 6770 F > 4σ (F). The two monomers of A-40926 have similar conformations and are bound by antiparallel H-bonds to form a ‘chain’ structure of connecting dimers. The antibiotic molecule possesses a ‘binding pocket’ for the C-terminal carboxy group of the cell-wall protein, which is consisten with suggestions based on NMR data and the recently reported crystal structure of ureido-balhimycin. In A-40926 the monomers are polymerically linked by H-bonds, quite unlike the tight dimer formation observed in ureido-balhimycin.     

On the Landau-Teller approximation for energy exchanges with fast degrees of freedom

We revisit the Landau-Teller heuristic approach to adiabatic invariants and, following Rapp, use it to investigate the energy exchanges between the different degrees of freedom, in simple Hamiltonian systems describing the collision of fast rotating or vibrating molecules with a fixed wall. We critically compare the theoretical results with particularly accurate numerical computations (quite small energy exchanges, namely of one part over 10³⁰, are measured).     

Determination of platinum-group metals and lead in vegetable environmental bio-monitors by voltammetric and spectroscopic techniques: critical comparison

This paper reports voltammetric sequential determination of Pt(II), Pd(II), and Rh(III), by square-wave adsorption stripping voltammetry (SWAdSV), and Pb(II), by square-wave anodic stripping voltammetry (SWASV), in vegetable environmental matrices. Analytical procedures were verified by the analysis of the standard reference materials: Olive Leaves BCR-CRM 062 and Tomato Leaves NIST-SRM 1573a. Precision and accuracy, expressed as relative standard deviation and relative error, respectively, were always less than 6% and the limits of detection (LOD) for each element were below 0.096 g g^–1. Once set up on the standard reference materials, the analytical procedure was transferred and applied to laurel leaves sampled in proximity to a superhighway and in the Po river mouth area. A critical comparison with spectroscopic measurements is discussed.     

Gadolinium(III) Complexes of dota‐Derived N‐Sulfonylacetamides (H4(dota‐NHSO2R)=10‐{2‐[(R)sulfonylamino]‐2‐oxoethyl}‐1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic Acid): A New Class of Relaxation Agents for Magnetic Resonance Imaging Applications

Four new ligands for lanthanide ions based on the H₃do3a (=1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic acid) structure and bearing one N‐sulfonylacetamide arm were synthesized, i.e., H₄dota‐NHSO₂R=10‐{2‐[(R)sulfonylamino]‐2‐oxoethyl}‐1,4,7,10‐tetraazacyclododecane‐1,4,7‐triacetic acids 1a – e . A ¹⁵N‐NMR study of the ¹⁵N‐labelled Eu³⁺ complex of one such ligands, 1d , showed that the coordination of the N‐sulfonylacetamide arm involves the carbonyl O‐atom rather than the N‐atom. The relaxometric properties of the corresponding Gd³⁺ complexes were investigated as a function of pH and temperature. These complexes have relaxivities in the range 4.5–5.3 mM ^?1 s^?1, at 20 MHz and 25°, and are characterized by a single H₂O molecule in their inner coordination sphere. The mean residence lifetime of this molecule is relatively long (500–700 ns) compared to other anionic complexes. The slow rate of H₂O exchange can be justified by the extensive delocalization of the negative charge on the N‐sulfonylacetamide arm. The long residence time of the coordinated H₂O allowed the observation of the effect of the prototropic exchange on the relaxivity. The study of the interaction between the complex [Gd( 1e )]‐ and HSA revealed a weak affinity constant highlighting the importance of a localized negative charge on the complex to promote a strong interaction with the protein.     

Structural researches on the chelating behaviour of the biguanide ligand. The crystal structures of Co(C2H6N5)3 · 2H2O and Cu(C2H7N5)2CO3·4H20

Summary Crystals of the title compounds are both monoclinic, with unit cell dimensions:a = 9.293(5),b = 10.122(5),c = 16.737(7) Å. = 103.44(3)°,Z = 4, space groupP2₁/c for the cobalt derivative;a = 13.1ß5(7),b = 17.546(ß),c = 6.871(3) Å, = 107.01(4)°Z = 4, space groupP2₁/n for the copper derivative. The structures were solved from diffractometer data by the heavy-atom technique for the first compound and by direct methods for the second compound. Refinement by block diagonal least-squares gaveR = 5.9% for 3511 independent reflections andR = 8.8% for 2885 independent reflections for the cobalt and copper compound respectively. In both compounds the biguanide moiety behaves as a bidentate chelating ligand in a symmetrical tautomeric form, but it is deprotonated in the octahedral cobalt compound and neutral in the square planar copper compound.     

Palladium-catalyzed reaction of aryl iodides with acetic anhydride. A carbon monoxide-free synthesis of acetophenones

[reaction: see text] The palladium-catalyzed reaction of aryl iodides with acetic anhydride provides a straightforward and experimentally simple carbon monoxide-free route to acetophenones. The reaction tolerates a wide range of functionalized aryl iodides. Acetophenones are isolated in excellent yield with a variety of neutral, slightly electron-rich, and slightly electron-poor aryl iodides, whereas moderate yields are obtained with aryl iodides containing strongly electron-withdrawing substituents.     

Determination of the boiling-point distribution by simulated distillation from n-pentane through n-tetratetracontane in 70 to 80 seconds

This work presents the carrying out of boiling-point distributions by simulated distillation with direct-column heating rather than oven-column heating. Column-heating rates of 300 degrees C/min are obtained yielding retention times of 73 s for n-tetratetracontane. The calibration curves of the retention time versus the boiling point, in the range of n-pentane to n-tetratetracontane, are identical to those obtained by slower oven-heating rates. The boiling-point distribution of the reference gas oil is compared with that obtained with column oven heating at rates of 15 to 40 degrees C/min. The results show boiling-point distribution values nearly the same (1-2 degrees F) as those obtained with oven column heating from the initial boiling point to 80% distilled off. Slightly higher differences are obtained (3-4 degrees F) for the 80% distillation to final boiling-point interval. Nonetheless, allowed consensus differences are never exceeded. Precision of the boiling-point distributions (expressed as standard deviations) are 0.1-0.3% for the data obtained in the direct column-heating mode.     

Structural characterization techniques for the analysis of semiconductor strained heterostructures

A combined method for structural characterization of strained epitaxial heterostructures involving different techniques such as Rutherford backscattering spectrometry (RBS), multiple crystal X-ray diffractometry (MCD) and transmission electron microscopy (TEM) is presented. In order to obtain a complete characterization of the analysed structure, three different quantities are measured independently: the epilayer thickness, the density of misfit dislocations which may appear at the interface, and the significant components of the strain tensor, mainly the tetragonal distortion, affecting the epilayer lattice. In this way the thermodynamic state and the mechanisms of plastic deformation of the structures can be fully investigated. In this contribution we present and discuss the experimental results concerning a set of InP/GaAs samples having different layer thicknesses ranging from 5 to 500 nm. The thickness of the samples has been determined by RBS. Measurements of in-plane strain and tetragonal distortion have been performed by MCD and RBS-channelling respectively, finally TEM has been used for determining the defects densities and distribution.