Momentum dependent vertices σγγ, σργ and σρρ the NJL scalar hidden by chiral symmetry

We calculate the momentum dependence of three particle verticesσγγ, σργ andσρρ in the context of a Nambu Jona Lasinio type model. We show how they influence the processesγγ→σ→ππ, ρ→γσ andγγ→ρρ and how chiral symmetry shadows the presence of theσ.     

Pion,sigma and nucleon propagators in the linear σ-model

We study the pion, sigma and nucleon propagators of the linear -model in the one-loop approximation. We show that in the renormalized model the meson propagators exhibit imaginary poles. Such nonphysical poles disappear when a cutoff is introduced. The maximum of this cutoff value is shown to be of the order _c1.2 Gev. Once this value is fixed it is possible to find a set of parameters which allow for a selfconsistent interpretation of physical properties associated with the propagators. A 400 MeV wide resonance appears in the sigma propagator, the nucleon is a bound state and in its continuum two Roper resonances can be identified.Work supported in part by CNPq and FAPEMIG (Brasil) and CERN project no. PCERN/C/FAE/74/91     

A possible construction of a complex chemical reaction network

A procedure is suggested for the construction of chemical reaction networks. We define the kinetic communication as a transfer of atoms or atomic groups between two species and determine all the kinetic communications occurring in the possible mechanism of a complex chemical process. The set of kinetic communications is the basis of the communication matrices resulting in the complete network of the overall reaction.Limiting the consideration for certain types of kinetic communications we obtain the reaction subnetworks and selecting arbitrarily species among those participating in the possible mechanism we introduced the concept of the partial subnetworks which correspond to subsets of the complete network.By the simple analysis of the subnetworks it is easy to obtain the sequence network indicating the pathways via which the selected species are formed in the course of the overall process, by the transfer of chosen atoms or atomic groups.     

Tandem Sonogashira coupling: an efficient tool for the synthesis of diarylalkynes

[reaction: see text] The tandem Sonogashira coupling reaction of aryl halides provides an efficient method for the synthesis of diarylalkynes. Several aryl halides were coupled with 2-methyl-3-butyn-2-ol as acetylene source in the presence of PdCl2(PPh3)2 and CuI. Following the deprotection of the acetylene moiety in the same pot using a strong base, the Sonogashira coupling of a second aryl halide led to the formation of the appropriate diarylakyne. The established protocoll was successfully extended to the preparation of compound libraries.     

Reaction of a superoxochromium(III) ion with nitrogen monoxide: kinetics and mechanism.

The kinetics of the rapid reaction between Cr(aq)OO(2+) and NO were determined by laser flash photolysis of Cr(aq)NO(2+) in O(2)-saturated acidic aqueous solutions, k = 7 x 10(8) M(-1) s(-1) at 25 degrees C. The reaction produces an intermediate, believed to be NO(2), which was scavenged with ([14]aneN(4))Ni(2+). With limiting NO, the Cr(aq)OO(2+)/NO reaction has a 1:1 stoichiometry and produces both free NO(3)(-) and a chromium nitrato complex, Cr(aq)ONO(2)(2+). In the presence of excess NO, the stoichiometry changes to [NO]/[Cr(aq)OO(2+)] = 3:1, and the reaction produces close to 3 mol of nitrite/mol of Cr(aq)OO(2+). An intermediate, identified as a nitritochromium(III) ion, Cr(aq)ONO(2+), is a precursor to a portion of free NO(2)(-). In the proposed mechanism, the initially produced peroxynitrito complex, Cr(aq)OONO(2+), undergoes O-O bond homolysis followed by some known and some novel chemistry of Cr(aq)O(2+) and NO(2). The reaction between Cr(aq)O(2+) and NO generates Cr(aq)ONO(2+), k > 10(4) M(-1) s(-1). Cr(aq)OO(2+) reacts with NO(2) with k = 2.3 x 10(8) M(-1) s(-1).     

Disproportionation of aquachromyl(IV) ion by hydrogen abstraction from coordinated water

In aqueous solutions, the aquachromyl(IV) ion, Cr(aq)O(2+), disproportionates to Cr(aq)(3+) and HCrO(4)(-). The reaction exhibits second-order kinetics with an inverse [H(+)] dependence, -d[Cr(aq)O(2+)]/dt = 38.8[Cr(aq)O(2+)](2)[H(+)](-1) at 25 degrees C. The combination of the rate law and substantial kinetic isotope effect, k(H)/k(D) = 6.9, suggests a mechanism whereby a hydrogen atom is abstracted from a coordinated molecule of water or hydroxo group within a singly deprotonated transition state. The buildup of chromate is more complicated and somewhat slower than the loss of chromyl, suggesting the involvement of intermediates.     

ESR study of the reaction of substituted nitrosobenzenes with aliphatic and saturated alkylaromatic hydrocarbons

We have found that nitrosobenzenes spontaneously react with saturated hydrocarbons in the absence of oxygen and light. For interpretation of this general phenomenon a new reaction pathway has been assumed. In light of these results special care should be taken when applying nitrosobenzenes for inhibition and spin trapping as well as organic synthesis in saturated organic solvents, which are supposed to be inert.

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The effect of mineral composition on the sorption of cesium ions on geological formations

The sorption of cesium-137 on rock samples, mainly on clay rocks, is determined as a function of the mineral composition of the rocks. A relation between the mineral groups (tectosilicates, phyllosilicates, clay minerals, carbonates) and their cesium sorption properties is shown. A linear model is constructed by which the distribution coefficients of the different minerals can be calculated from the mineral composition and the net distribution coefficient of the rock. On the basis of the distribution coefficients of the minerals the cesium sorption properties of other rocks can be predicted.