CP violation and the widthZ→b \bar b

We discuss the effect of CP-violatingZb $\bar b$ Zb $\bar b$ G andZb $\bar b$ γ couplings on the width Γ(Z→b $\bar b$ X). The presence of such couplings leads in a natural way to an increase of this width relative to the prediction of the standard model. Various strategies of a direct search for such CP-violating couplings by using CP-odd observables are outlined. The number ofZ bosons required to obtain significant information on the couplings in this way is well within the reach of present LEP experiments.     

Efficient syntheses of new chiral peptidomimetic macrocycles through a configurationally driven preorganization

A new family of 32-membered ring peptidomimetic macrocycles has been efficiently obtained in a simple one-pot two-step reductive amination reaction, from easily prepared precursors. The structural and stereochemical variables have been explored in order to rationalize the obtained selectivity. The formation of the [2A+2B] tetraimine intermediate has been explained in terms of a very favorable configurationally driven preorganization as detected by NMR, CD and molecular modeling.     

Structure, 31P and 13C chemical shift anisotrophy of (CH3)3P, (CH3)3PO, (CH3)3PS and (CH3)3PSe as determined by liquid crystal NMR spectroscopy

The ¹³P and ¹³C spectra of the triply ¹³C labelled molecules (CH₃)₃P, (CH₃)₃PO, (CH₃)₃PS and (CH₃)₃PSe oriented in a nematic phase are reported. The CPC bond angles have been measured. The ¹³P chemical shift tensor shows a large anisotropy except in the case of (CH₃)₃P. The abnormal large value observed for the PSe bond length suggests a large anisotropy of the ¹J(PSe) spin coupling.     

The charge delocalised beta,beta-carotene dication--preparation, structure elucidation by NMR and reactions with nucleophiles

The reaction between beta,beta-carotene and BF3-etherates has been investigated, leading to structural elucidation of the blue product, formed in appropriate organic solvents, as a symmetrical charge delocalised dication (lambda(max) 985 nm at room temperature in CHCl3) with considerable stability. The reaction, monitored by EPR studies at -25 degrees C, occurred via free radical intermediates. A C40H56BF3 intermediate was captured by EIMS. The detailed structure of the dication was established by COSY, HSQC, HMBC and 1D and 2D ROESY NMR techniques (600 MHz, CDCl3, -20 degrees C) leading to complete assignments of 1H and 13C chemical shifts and 3J(H,H) coupling constants. The effects of the two delocalised charges on chemical shift (charge distribution) and bond distance (3J(H,H)) were considered. The results are consistent with charge delocalisation mainly in the C-5-C-9 and C-5'-C-9' regions and with bond inversion to retro shifted double bonds in the central C-13-C-13' region. A convention for denoting the charge delocalisation and bond types is presented. The experimental results are discussed relative to previous theoretical calculations of the beta,beta-carotene dication structure. (All-E) and (15-Z)-beta,beta-carotene provided the same dication. The NIR spectra and stability of dications prepared in the same manner from the related carotenes 20,20'-dinor-beta,beta-carotene, heptapreno-beta,beta-carotene and nonapreno-beta,beta-carotene were examined for comparison. Reactions of the beta,beta-carotene dication with selected nucleophiles provided products including isocryptoxanthin, isocarotene and mutatochrome with H2O as nucleophile, and isocryptoxanthin methyl ether, 8-methoxy-7,8-dihydro-beta,beta-carotene and isocarotene with CH3ONa as nucleophile. The formation of these products is rationalised from the structure assigned to the dication.     

Tuning the Regioselective Functionalization of Trifluoromethylated Dienes via Lanthanum-Mediated Single C−F Bond Activation

The development of new fluorine-containing building blocks and their efficient synthetic access is currently a challenging research field. Herein, the highly regio- and stereoselective addition of a large range of aldehydes onto trifluoromethylated benzofulvenes was achieved using a simple La/I₂/DIBAL-Cl system via a selective C−F bond activation process. This versatile methodology provided homodienyl alcohols bearing a terminal CF₂-alkene with potential further applications, as shown by the dehydration to the first benzofulvenes carrying a difluorovinyl group. In addition, for certain electron-poor aldehydes, unprecedented ipso substitution of the CF₃ group in a diene was observed, which, according to DFT studies, is related to the presence of the large, Lewis-acidic lanthanum metal.     

The influence of process conditions on the formation of thallium sulfide layers on polyethylene by the use of higher polythionic acid H2S33O6

Thallium sulfide layers of varying composition form on the surface of low-density polyethylene (PE) when the PE films have been sulfurized in a solution of higher polythionic acid H₂S₃₃O₆, and then immersed in the alkaline solution of thallium (I) sulfate. The concentration of sulfur sorbed-diffused into PE surface increases with the increase of the sulfurization time and concentration of higher polythionic acid solution. The concentration of thallium in the Tl _x S _y layers depends on the sulfur concentration sorbed-diffused into PE, the concentration, and temperature of thallium (I) sulfate solutions. By chemical analysis of the obtained sulfide layers it was determined that the values of x and y in the Tl_xS_y layers varies in the intervals: 1<x<3, 1<y<6. Two phases TlS, Tl₂S₂ were identified by X-ray diffraction analysis in thallium sulfide layers. Scanning Electron (SEM) and Atomic Force (AFM) microscopies were used to characterize surface morphology of thallium sulfide layers. The films deposited on the PE surface have a non-homogeneous structure, and consist of separated islands.      

How the First Partial Transpose was Written

We tell the tale of the first writing of a partial transpose, without guaranteeing historical authenticity. Dedicated to Prof. Asher Peres, Haifa, on the occasion of his 70th birthday.     

Nucleophilic reactions of charge delocalised carotenoid mono- and dications

In the present study insight was gained on the larger complexity of cationic mixtures of diaryl (phi,phi-carotene, isorenieratene) and aliphatic (psi,psi-carotene, lycopene) carotenes, prepared by reaction with BF3-etherate, compared with beta,beta-carotene. Chemical reactions of the mono- and dications prepared in situ from the allylic carotenols beta,beta-caroten-4-ol (isocryptoxanthin) and beta,beta-carotene-4,4'-diol (isozeaxanthin), and from isorenieratene and lycopene were investigated using selected O, N and S nucleophiles; water, methanol, azide and thioacetate. In total 22, including 18 new, neutral carotenoid products were isolated and identified by VIS, MS and NMR (in part) spectroscopy. Their structures were compatible with the structures of the cationic intermediates. The formal addition of hydride to the various dications, required to rationalise minor reaction products, is discussed in terms of more likely hydrogen radical or proton transfer in cationic reactions. Extensive E/Z isomerisation was observed for all quenching products. The potential use of carotenoid cations for the synthesis of 4,(4')-substituted beta,beta-carotenes and 7-oxabicyclo[2,2,1]heptane derivatives is discussed.