Hadronic colliders as probes of the proton spin structure

We perform a systematic analysis of different processes with high energy polarized proton beams: jets, direct photon, lepton pairs (Drell-Yan) andWZ production. Different sets of polarized partonic densities are used that fit EMC and SLAC polarized deep inelastic scattering data with variable amount of quark and gluon components of the proton spin. The case of the future Relativistic Heavy Ion Collider (RHIC) used as a polarized collider at a maximum energy of \(\sqrt s = 500\) GeV is analyzed in detail.     

A mass spectrometric investigation on some 3-[2-(Nitroxy)alkyl]-2H-1,3-benzoxazin-4-(3H)-one derivatives

The electron ionization mass spectrometric behaviour of ten 3-[2-(nitroxy)alkyl]-2H-1,3-benzoxazin-4-(3H)-one derivatives has been studied by means of metastable ion studies. By mass-analysed ion kinetic energy spectrometry of the related molecular ions, clear differences have been evidenced between the 5-methyl derivative and the other compounds, consisting of a highly favoured loss of NO₂ radical. The same methodology has allowed easy characterization of isomeric compounds.     

Isolation and structure determination of bioactive isoflavones from callus culture of Dipteryx odorata

Crude extracts of callus and roots of Dipteryx odorata were analyzed by HPLC to detect and quantify isoflavone contents. Based on spectroscopic and X-ray crystallography data the structures of two isoflavones were elucidated as 7-hydroxy-4',6-dimethoxyisoflavone and 3',7-dihydroxy-4',6-dimethoxyisoflavone. The production of dry biomass of 7-hydroxy-4',6-dimethoxyisoflavone in cultured callus was 4.12 mg/g, approximately eleven fold higher than the amount accumulated in roots of D. odorata wild-growing plants. The 7-hydroxy-4',6-dimethoxyisoflavone was effective against glyceraldehyde-3-phosphate dehydrogenase from Trypanosoma cruzi. This is the first report on those bioactive isoflavones accumulated in callus of D. odorata.     

Electron impact mass spectrometry of ethyl esters of halogenated acetic acids

The behaviour of a series of differently halogenated acetic acid ethyl esters was studied using electron impact and metastable ion techniques. The presence of different halogens strongly influences the fragmentation pathways and also the kinetic energy release values associated with some decomposition routes. By mass-analysed ion kinetic energy spectrometry, a composite metastable peak was detected for the transition CF₂BrCO⁺ → CF₂Br⁺, and rationalized on the basis of two different structures for the precursor ion.     

Structural identification of fatty acid methyl esters by collision spectra of their [M ? H]− species

Negative ion chemical ionization linked to collisionally activated decomposition (CAD) experiments has proved to be an efficient analytical tool in mass spectrometric characterization of fatty acids. The CAD mass-analysed ion kinetic energy spectra of [M ? H]^? species, obtained by OH^? reaction with a selection of six C₁₈ fatty acid methyl esters, reveal useful correlations with the original structure of the neutrals, giving evidence of both chain branching and double bond positions.     

Identification of aminophospholipid stereomers by positive-ion fast atom bombardment combined with collisional activation mass-analysed ion kinetic energy analysis and high-performance liquid chromatography

Two methods for the identification of aminophospholipid stereomers are described. After a chemical derivatization, 9-fluorenylmethoxycarbonyl derivatives of diacyl-sn-2- and diacyl-sn-3-phosphoserine and diacyl-sn-2- and diacyl-sn-3-phosphoethanolamine can be characterized by positive-ion fast atom bombardment combined with collisional activation mass-analysed ion kinetic energy analysis based on the differentiation of relative abundances [M + H + diethanolamine ? 89]⁺ and [M + H]⁺ fragments derived from [M + H + diethanolamine]⁺ ions, the protonated solvated molecules, and normal phase high-performance liquid chromatography on the basis of different elution times of the derivatives of the aminophospholipid stereomers on an aminopropyl-bonded column.     

New model for a theoretical density functional theory investigation of the mechanism of the carbonic anhydrase: how does the internal bicarbonate rearrangement occur?

A theoretical density functional theory (DFT, B3LYP) investigation has been carried out on the catalytic cycle of the carbonic anhydrase. A model system including the Glu106 and Thr199 residues and the "deep" water molecule has been used. It has been found that the nucleophilic attack of the zinc-bound OH on the CO(2) molecule has a negligible barrier (only 1.2 kcal mol(-1)). This small value is due to a hydrogen-bond network involving Glu106, Thr199, and the deep water molecule. The two usually proposed mechanisms for the internal bicarbonate rearrangement have been carefully examined. In the presence of the two Glu106 and Thr199 residues, the direct proton transfer (Lipscomb mechanism) is a two-step process, which proceeds via a proton relay network characterized by two activation barriers of 4.4 and 9.0 kcal mol(-1). This pathway can effectively compete with a rotational mechanism (Lindskog mechanism), which has a barrier of 13.2 kcal mol(-1). The fast proton transfer found here is basically due to the effect of the Glu106 residue, which stabilizes an intermediate situation where the Glu106 fragment is protonated. In the absence of Glu106, the barrier for the proton transfer is much larger (32.3 kcal mol(-1)) and the Lindskog mechanism becomes favored.     

Mono-N-methylation of primary amines with alkyl methyl carbonates over Y faujasites. 2. Kinetics and selectivity

In the presence of a Na-exchanged Y faujasite, the reaction of primary aromatic amines 1 with 2-(2-methoxyethoxy)methylethyl carbonate [MeO(CH(2))(2)O(CH(2))(2)OCO(2)Me, 2a] yields the corresponding mono-N-methyl derivatives ArNHMe with selectivity up to 95%, at substantially quantitative conversions. At 130 degrees C, the reaction can be run under diffusion-free conditions and is strongly affected by the solvent polarity: for instance, in going from xylene (epsilon(r) = 2.40) to triglyme (epsilon(r) = 7.62) as the solvent, the pseudo-first-order rate constant for the aniline (1a) disappearance shows a 5-fold decrease. In DMF (epsilon(r) = 38.25), the same reaction does not occur at all. Competitive adsorption of the solvent and the substrate onto the catalytic sites accounts for this result. The behavior of alkyl-substituted anilines ZC(6)H(4)NH(2) [Z = p-Me, p-Et, p-Pr, p-(n-Bu) (1b-e); Z = 3,5-di-tert-butyl- and 2,4,6-tri-tert-butylanilines (1f,g)] and p-alkoxyanilines p-ZC(6)H(4)NH(2) [Z = OMe, OEt, OPr, O-n-Bu (1b'-e')] clearly indicates a steric effect of ring substituents: as diffusion of the amine into the catalytic pores is hindered, the reaction hardly proceeds and the mono-N-methyl selectivity (S(M/D)) drops as well. Moreover, the strength of adsorption of the amine onto the catalyst influences the rate and the selectivity as well: the reaction of p-anisidine and p-toluidine-despite the higher nucleophilicity of these compounds-is slower and even less selective with respect to aniline. From a mechanistic viewpoint, the intermediacy of carbamates ArN(Me)CO(2)R [R = MeO(CH(2))(2)O(CH(2))(2)] is suggested. At 90 degrees C, the reaction of benzylamine (7)-a model for aliphatic amines-with dimethyl carbonate shows that the reaction outcome can be improved by tuning the amphoteric properties of the catalyst: in going from CsY to the more acidic LiY zeolite, methylation is not only more selective (S(M/D) ratio increases from 77% to 84%) but even much faster (CsY, conversion of 36% after 22 h; LiY, conversion of 43% after 7 h).     

A Total Synthesis of Aphidicolin: Stereospecific Synthesis of (±)-3α, 18-Dihydoxy-17-Noraphidicolan-16-one

A simple, efficient, and stereospecific total synthesis of (±)-3α, 18-dihydroxy-17-noraphidicolan-16-one (2) , by solvolytic rearrangement of the endo-bicyclo-[2.2.2]oct-5-en-2-yl methanesulfonate 16 , is described. Since aphidicolin (1) has already been obtained from 2 , the preparation of the latter formally constitutes a new total synthesis of 1 .     

Reaction of 2-dimethylaminomethylene-1,3-diones with dinucleophiles. III. Synthesis of 5-acylpyrimidines and 7,8-dihydroquinazolin-5(6H)-ones

The reaction of open-chain and cyclohexane sym-2-dimethylaminomethylene-1,3-diones with amidines and guanidine in refluxing ethanol gave, generally in good yields, a series of 5-acylpyrimidines and 7,8-dihydroquinazolin-5(6H)-ones, respectively. With formamidine (and in part acetamidine), 2-formylimino-1,3-diones were formed in general, as sole products or mixtures with the corresponding pyrimidines or dihydroquinazolinones.