Eigenvibrations of the expanding universe

A theoretical interpretation of the observed periodicity of large-scale (128 Mpc) correlations of galaxies is proposed as due to eigenvibrations of the closed expanding universe. Eigensolutions of the equations of motion for a scalar field in an inflationary model allow one to compute the energy density, interpreted as matter density. Isotropic eigensolution give rise to a matter density distribution having a periodic structure centered at the north pole of the closed Robertson-Walker universe represented by S³/Z₂. It is able to reproduce well the striking periodicity of the observational data, in the galactic north-south directions. The dipole and quadrupole eigensolutions and the location of the co-moving observer in a point of S³/Z₂ different from the center of the vibrational structure would imply, in a theoretically well predictable way, a decrease of the observed periodicity in some other directions.Partially supported by the State Committee for Scientific Research, Grant No. 2-0206-91-01.     

Studies in organic mass spectrometry. Part 15 [1]. Electron ionization mass spectra of some 5-nitro-3-thiophenecarboxanilides

The study of the electron ionization mass spectra of 5-nitro-3-thiophenecarboxanilides 1-24 has shown peculiar effects induced by the 5-nitro group on the fragmentation of molecular ions M and the thenoyl cation a (Scheme 1). A comparison of the abundances of the important fragment ions for 5-nitro-3-thiophene-carboxanilides with those of the corresponding 3-thiophenecarboxanilides shows that the extent of C-N amide bond cleavage decreases in the former series as a consequence of the increased bond strength. The produced ion a does not eliminate carbon monoxide as 2- and 3-thenoyl cations usually do. Again this behaviour depends on the electronic effects of the nitro group which strongly destabilizes the 5-nitro-3-thienyl cation and consequently strengthens the carbon-3 carbonyl carbon bond. Recalling the behavior of the previously studied 2- and 3-thiophenecarboxanilides most of the 2′-substituted 5-nitro-3-thiophenecarboxanilides give loss of the ‘ortho’ substituent of the phenyl ring furnishing the cyclic ion g(Scheme 2). In the instance of 2′-alkyl substituted derivatives the formation of abundant ions h' by loss of 5-nitrothenoyl radical from M (Scheme 3) was observed, thus confirming the occurrence of a cryptic ‘ortho’ effect. The results are also discussed in relation to those obtained on some related benzoylanilides.     

The crystal structure of triphenylallyltin

The crystal structure of (C₆H₅)₃SnCH₂CHCH₂ has been determined. The asymmetric unit consists of two molecules of triphenylallyltin having virtually the same conformation. Their geometrical parameters exclude p_π-d_π bonding between the metal and the allyl double bond, and seem to be in a better agreement with a σ-π conjugation effect.     

Ion chromatographic determination of sulfide and cyanide in real matrices by using pulsed amperometric detection on a silver electrode

The determination of free sulfide and cyanide by pulsed amperometric detection (PAD) at a silver-working electrode was improved through a deep de-oxygenation (at least 10 min) of both standard and real solutions containing the two analytes and adopting a two-potential waveform able to eliminate Ag working electrode fouling. The waveform stepped around the oxidation of Ag in the presence of 0.1-0.4 M hydroxyl ion, from -0.1 to 0.1 V versus saturated calomel electrode (SCE). The eluent composition (0.4 M NaOH plus 7.5 mM oxalate solution) allowed a very good column efficiency and selectivity. The presence of a polysulfide species was hypothesized in sulfide solutions that had not been de-oxygenated and aged. The polysulfide eluted just before sulfide and was confirmed by a chemical test with SO3(2-) producing the elimination of the polysulfide peak. Detection limits, according to the Hubaux-Vos method, were 1.0 and 2.0 microg/l for S2- and CN , respectively. We demonstrated good performance of the optimized method by repeatedly injecting standard solutions and by analyzing different real matrices. The method exhibited very good accuracy and repeatability (10 microg/l and a 500 microl injection loop, had a repeatability better than 3% for sulfide and 100 microg/l had a repeatability better than 1% for cyanide). The two-potential waveform ensured long-term stability of the electrode surface that required no manual polishing procedure for at least 1 month (20 analysis per day).     

Cyclohexanones derived from dihydrocarvone as precursor of chiral dioxiranes for epoxidation of olefins

New ketones having an axial α-fluorine atom and substituents other than fluorine at C8, derived from commercially available (+)-dihydrocarvone, have been prepared and used for epoxidations of trans stilbene, trans methyl p-methoxy cinnamate, trans cinnamyl alcohol and derivatives. It was found that replacement of the H at C8 by a substituent containing an oxygen atom increases the enantioselectivities in all cases. It was also shown that protic substituents (hydroxyl groups) provide a decrease in enantioselectivity in the case of cinnamates probably because of H-bonding dioxirane-substrate. It is noted that the absolute configurations of the various epoxides obtained hold with the usual model involving a spiro-approach on the dioxirane conformation C1 having the α-fluorine axial. Moreover, sub-stoichiometric amounts (0.3 equiv) of ketone can be used in all cases as these ketones do not undergo Baeyer-Villiger oxidation and are recovered.     

Determination of ochratoxin A in Portuguese rice samples by high performance liquid chromatography with fluorescence detection

A sensitive and accurate analytical method for the determination of ochratoxin A (OTA) in rice, based on extraction with phosphate-buffered saline/methanol, an immunoaffinity column (IAC) for clean-up, and high performance liquid chromatography with fluorescence detection (HPLC-FD), is described. The limit of quantification of the proposed method was 0.05 g kg^–1. Recovery of OTA from rice samples spiked at 0.05 g kg^–1 was 92%, with a within-day RSD of 5.4%. The proposed method was applied to 42 rice samples from Portugal and the presence of OTA was found in six samples at concentrations ranging from 0.09 to 3.52 g kg^–1. The identification of OTA was confirmed by methyl ester derivatization and then HPLC analysis. The daily intake of OTA by the Portuguese population was also estimated.     

Voltammetric probe of milk samples by using a platinum microelectrode

Milk is a complex heterogeneous fluid containing many components in several states of dispersion. When used as a bulk solvent for studying electrochemical processes of some of the electroactive species present, it displayed mainly aqueous solution properties. With microelectrodes (25 μm in diameter) some typical constituents can be detected and the reproducibility of the processes studied was found to be satisfactory, with relative standard deviations (r.s.d.s.) lower than 2%, whereas measurements with conventional-sized platinum electrode (3 mm in diameter) gave r.s.d.s, of about 10%. Moreover, because of enhanced mass transport associated with the smallest electrodes, it was possible to diagnose the formation of precipitates of calcium phosphates on the electrode surface, as a consequence of a CEC electrode process at ?0.920 V vs. SCE, involving protons released by H₂PO^?₄, HPO^2?₄ formed in the electrode reaction and Ca²⁺. The reduction of acidic groups from casein, the oxidation of ascorbate and oxygen effects were also studied.     

A study of the OH- -induced beta-elimination reactions of 2-(4-chloroethyl)pyridine, 2-(2-chloroethyl)pyridine, 1-methyl-2-(4-chloroethyl)pyridinium iodide and 1-methyl-2-(2-chloroethyl)pyridinium iodide in acetonitrile/water

Second-order rate constants have been determined for the title reactions in OH(-)/H(2)O and in OH(-)/ (CH(3)CN/H(2)O) [30/70, 60/40, and 85/15 (v/v) mixtures]. A relatively small increase in reactivity is observed for the four substrates upon increasing the percentage of CH(3)CN in the solvent mixture. The methyl activating factors (/) are also slightly affected by the solvent composition. On the other hand, the high acceleration of the reaction by methylation of the pyridine ring amounts to 10(4)-10(6) according to an E1cb mechanism.     

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.     

Asymmetric aminolysis of aromatic epoxides: a facile catalytic enantioselective synthesis of anti-beta-amino alcohols

[reaction: see text] The first asymmetric aminolysis of trans-aromatic epoxides with anilines is described. The process affords enantioenriched anti-beta-amino alcohols in up to 99% ee. The complete regio- and diastereoselectivity observed uses commercially available [Cr(Salen)Cl] as a Lewis acid catalyst and in combination with a very simple experimental procedure renders the present reaction a facile and practical tool for the synthesis of chiral nonracemic anti-beta-amino alcohols.