New method to measure oxygen isotopic concentration ratios18O/16O by gamma-activation analysis,especially in biological media

The photonuclear reactions used for this isotopic analysis are as follows:¹⁶O(γ, n)¹⁵O threshold energy 15.7 MeV;¹⁸O(γ, p)¹⁷N threshold energy 16.3 MeV.¹⁵O is a pure β⁺ emitter of half-life 2.03 minutes, whereas¹⁷N presents a 4.2 second neutron emission. The principle of the method is founded on the simultaneous measurement of the above characteristic radioactivities, the intensities of which are proportional to the respective quantities of¹⁶O and¹⁸O present in the irradiated sample. The potentialities of this new oxygen isotope analysis method, based on the use of an electron accelerator, are described. Detection limit of 0.1 μg¹⁸O is easily attainable. The equipment designed and built to industrialise this technique is described. It allows a hundred samples to be analysed automatically, the accelerator, detection instruments and pneumatic transfer circuits being controlled by a logic system linked to an electronic chronometer.     

Ordered binary crystals via cocrystallisation of quasiracemic Pd(II) complexes in a borderline regime between inertness and lability

Square planar complexes of the type [2-(1-aminoethyl)phenyl-kappa(2)C(1),N]chloro(py-kappaN)palladium(II)(py = pyridine derivative) have been prepared by cyclopalladation of 1-phenylethylamine. When opposite enantiomers of the chiral amine and different pyridine ligands were coordinated to the metal, quasiracemic complexes were obtained. The racemisation speed of solutions containing equimolar amounts of such quasiracemic complexes was used to test the compounds for inertness: slow ligand exchange was found for methylated pyridines. Enantiomerically pure complexes of opposite chirality with the electron rich ligands 2,6-collidine and 2,4,6-lutidine were successfully cocrystallised: they form a well-ordered binary solid in which four independent molecules, two of each constituent, are related by pseudo symmetry operations. This quasiracemate as well as its components and the true racemates of the latter were characterised by single crystal X-ray diffraction. The heterochiral crystals, both the cocrystal as well as the racemates, show better space filling than the homochiral solids.     

Comparison of inductively coupled plasma mass spectrometry techniques in the determination of platinum in urine: quadrupole vs. sector field

In recent years the increasing use of platinum (Pt) both in medical and in industrial applications has caused its growing anthropogenic emission and spread in the environment. Pt is released into the atmosphere by exhaust catalytic converters, and Pt compounds are often used in antitumour therapies. As a consequence, significant amounts of Pt can be detected in hospital wastewaters. This can lead to an increase in the exposure levels to Pt, especially in urban areas. It is therefore necessary to determine Pt reference values in the general population, by using suitable procedures able to achieve adequate analytical performances. Several measurements of Pt in biological fluids have been reported, but the analytical methods used for the determination of Pt often lack information about the uncertainty of the results, especially for low concentrations of urinary Pt in non-occupationally exposed subjects. The present paper considers the measurement of urinary Pt levels in a general population group from central Italy, by both quadrupole (Q) and sector field (SF) inductively coupled plasma mass spectrometry (ICP-MS). The two procedures were validated and their expanded uncertainties were evaluated. The limits of detection (LODs), calculated taking into account dilution factors, were 0.18 and 0.05 ng L(-1) of Pt for the Q and SF procedures, respectively. The median value observed was 4.13 ng L(-1) of Pt in urine, while the relative combined uncertainty at 5 ng L(-1) was below 20% with both ICP-MS techniques. These data are in good agreement with those reported in the literature for similar studies.     

Mechanical properties of hexylene- and phenylene-bridged polysilsesquioxane aerogels and xerogels

Bridged polysilsesquioxanes are increasingly used to prepare protective coatings, particulate chromatographic materials, and adsorbents. However, little is known about the mechanical properties of the materials and how they are influenced by the nature of the bridging group. In this paper, we have prepared monolithic xerogels and aerogels of hexylene- and phenylene-bridged polysilsesquioxanes and have measured their flexural strength and modulus. Consistent with their compact structure, the porous, glassy phenylene- and hexylene-bridged xerogels were hundreds of stronger than the analogous aerogels. The nature of the bridging group did not appear to affect the mechanical properties of the xerogels, in contrast, it presented a profound effect on the mechanical properties of the aerogels. Phenylene-bridged aerogels were brittle and 30% stronger than silica aerogels of the same density. However, the opaque hexylene-bridged aerogels were found to be elastic and appreciably weaker than the phenylene-bridged or silica aerogels.     

Polymorph formation from solvate desolvation

Spironolactone (C₂₄H₃₂O₄S) usually crystallizes into an orthorhombic phase, named Form II. Another orthorhombic phase, named Form I, is also known but seems difficult to obtain. Studies of the kinetics of desolvation of the ethanol solvate at room temperature showed that these two forms can be obtained through different mechanisms of desolvation.     

α-Well-posedness for Nash Equilibria and For Optimization Problems with Nash Equilibrium Constraints

We present the concepts of α-well-posedness for parametric noncooperative games and for optimization problems with constraints defined by parametric Nash equilibria. We investigate some classes of functions that ensure these types of well-posedness and the connections with α-well-posedness for variational inequalities and optimization problems with variational inequality constraints.