Kinetics of iodine-catalyzed reduction of vanadium(V) by arsenic(III)

Summary The kinetics of the iodine-catalysed reaction of vanadium(V) with arsenious acid in dilute H₂SO₄, leading to the formation of vanadium(IV) and arsenic acid, have been investigated spectrophotometrically. Plausible pathways consistent with the experimental rate law are discussed. An iodine bridged activated complex between reactant and substrate species is proposed to explain the electron mobility from arsenic to vanadium by resonance transfer. Applying other criteria, the heterolytic dissociation of the vanadium-iodine bond of the activated complex is considered rate-controlling.     

Kinetics of dissociation of tris-1,10-phenanthroline-iron(II) complex cation in aqueous acetic acid solutions

The reaction under study is first order in the complex ion over the entire composition range of the mixed solvent. A minimum amount of mineral acid is needed for completion of the reaction (formation of colorless products), but the rate is practically acid-independent. The influence of solvent composition and some common ions on the reaction rate have been examined. A reaction mechanism consistent with the rate behavior is proposed where water is shown as an active participant in the dissociation process. A plausible explanation for the retardation effect of HSO₄ ⁻ as against the accelerating effect of Cl⁻ under water-scarce conditions is provided.     

Kinetics of the dissociation of tris(1,10-phenanthroline) iron(III) complex ion in aqueous acid solutions. A mechanistic model for product specificity

Summary The natural decay of Fe(phen) _f3 ^p3+ , where no Ce^IV is employed for scavenging the side reaction product, Fe(phen) _f3 ^p2+ , is now treated as a complex reaction involving two parallel processes, and the experimental kinetics are consistent with the rate laws derived from a mechanism that simultaneously explains the composition of the products as a function of acidity. In terms of the proposed mechanism the dissociation rate of the complex ion in acid solutions containing Ce^IV as scavenging agent is to be regarded as a Ce^IV retarded aquation rate, and OH^– is to be assigned a catalytic role in the kinetics of basic reduction.     

First results from the CERN axion solar telescope

Hypothetical axionlike particles with a two-photon interaction would be produced in the sun by the Primakoff process. In a laboratory magnetic field ("axion helioscope"), they would be transformed into x-rays with energies of a few keV. Using a decommissioned Large Hadron Collider test magnet, the CERN Axion Solar Telescope ran for about 6 months during 2003. The first results from the analysis of these data are presented here. No signal above background was observed, implying an upper limit to the axion-photon coupling g(agamma)<1.16x10(-10) GeV-1 at 95% C.L. for m(a) less, similar 0.02 eV. This limit, assumption-free, is comparable to the limit from stellar energy-loss arguments and considerably more restrictive than any previous experiment over a broad range of axion masses.     

Inclusive π0 production at the CERN p-p̄ collider

Inclusive π⁰ production has been measured at the CERN pp? collider, $\text{s}\text{=540}\text{GeV}$, for 90° production angle and in a range of transverse momenta between 1.5 and 4.5 GeV/c. The invariant production cross section is larger than that measured at $\text{s}\text{= 53}\text{GeV}$ for p-p collisions. The production of μ mesons aand of direct photons is also investigated.     

A study of high transverse momentum η and π0 mesons at the CERN ISR

The production of high transverse momentum η mesons from proton-proton collisions has been studied at the CERN ISR. The decay η→γγ was identified in an array of lead-glass ?erenkov counters. The preliminary results, obtained at a total centre-of-mass energy √s=52.7 GeV, show an η signal, which amounts to approximately one half of the π⁰ cross-section for centre-of-mass transverse momenta between 3 and 5 GeV/c. The production of high transverse momentum π⁰'s was also measured and compared with previous results.     

Chemoenzymatic total synthesis of paecilocin A and 3-butyl-7-hydroxyphthalide

A highly enantioselective total synthesis of paecilocin A and 3-butyl-7-hydroxyphthalide is described. The key steps involved in this synthesis are enzymatic kinetic resolution and Alder–Rickert reaction.     

Observation of high transverse momentum electrons at the CERN ISR

A search for high transverse momentum electrons directly produced in proton-proton collisions has been performed at the CERN ISR. The apparatus included a magnetic spectrometer with wire spark chambers, a lead-glass counter array, and a threshold gas ?erenkov counter. At a centre-of-mass energy √s = 52.7 GeV, a signal has been observed in the range $\text{1.6<p}{}_{\mathrm{T}}{}^1\text{<4.7}\text{GeV}\text{/c}$. The signal occurs at a level of approximately 10^?4 of the inclusive pion cross-section.     

Formal total synthesis of (−)-spongidepsin

The formal total synthesis of (−)-spongidepsin is described. Three fragments I, II, and III were first prepared from readily available starting materials and then assembled to the target compound. The key steps involved in the synthesis are asymmetric α-hydroxylation, Ender's alkylation, and ring-closing metathesis reactions. An alternative route for the fragment II is also achieved involving Sharpless asymmetric epoxidation and Gilman's alkylation as key reactions.     

Stereoselective formal total synthesis of the cyclodepsipeptide (−)-spongidepsin

The formal total synthesis of (−)-spongidepsin is achieved starting from easily available raw materials involving asymmetric α-hydroxylation, Enders alkylation, and RCM as key reactions.