Spontaneous symmetry breaking in an O(2) invariant scalar theory

A simple variational principle for an O(2) invariant scalar theory, within the framework of gaussian wave functionals, is presented. The conditions for the occurrence of spontaneous symmetry breaking are discussed. The limits of validity of the gaussian approximation are also analyzed in detail.     

Fluoride ion induced reactions of organosilanes with electrophiles

Benzyl- 4-picolyl- and phenylallyl(trimethyl)silanes react with electrophiles in the presence of KF/18-crown-6 or silica-TBAF under mild conditions.     

Thermodynamic characterization of the acetylacetone-trichloroethylene system

Delfini, M., Gironi, F. and Variali, G., 1984. Thermodynamic characterization of the acetylacetone-trichloroethylene system. Fluid Phase Equilibria, 18: 69–82.Vapor-liquid equilibria have been measured for the system acetylacetone-trichloroethylene at 100, 200, 400 and 760 mm Hg. The influence of trichloroethylene on the keto-enol equilibrium of acetylacetone has been elucidated by ¹H NMR spectroscopy.A semiempirical model taking into account the “true” chemical species involved (the enol and keto tautomers of acetylacetone, and trichloroethylene) is used for thermodynamic reduction of the experimental data.     

Side-chain silylation of heterocyclic derivatives. The sythesis of 3-methyl-5-(trimethylsilylmethyl)-1,2,4-oxa-diazole and the atttempted synthesis of 3-methyl-4-nitro-5(trimethylsilymethyl)isoxazole via organolithium reagents

Silylation of activated heterocyclic systems via treatment with organolithium reagents followed by coupling with Me₃SiCl, leads to the expected product in the case of 3,5-dimethyl-1,2,4-oxadiazole, whereas for 3,5-dimethyl-4-nitroiso-xazole the predominant reaction is addition of the lithiating agent, to give after work-up 3,5-dimethyl-5-butyl-4-nitro-4,5-isoxazoline.     

Some molecular aspects of the radiation-induced oxidative degradation of glutathione

Glutathione (GSH) is well known to have an important role as natural antioxidant. Some aspects of GSH degradation following the capture of water primary radicals in aerated or deaerated medium were investigated after -irradiation and by pulse radiolysis.___TAGSTART___BR___TAGEND___ Some relevant reactions involved in the GSH oxidation mechanism, leading to GSOO-related products, were evidenced by pulse radiolysis experiments.___TAGSTART___BR___TAGEND___ From the quantitative determinations of the GSH degradation and the GSSG formation, useful indications on the fate of thiyl radicals (GS), the most preminent sulfur centred intermediates, were drawn out in anaerobic and aerobic conditions.     

Hammett correlations in the photosensitized oxidation of 4-substituted thioanisoles

Singlet oxygen is quenched by a series of 4-substituted thioanisoles (methoxy to nitro), with rate constant k(t) = 7 x 10(4) to 7 x 10(6) M(-)(1) s(-)(1), close to the value observed for the myoglobin-catalyzed sulfoxidation of the same sulfides. Correlations with sigma (rho = -1.97) and with E(ox) (slope -3.9 V(-)(1)) are evidence for an electrophilic mechanism. In methanol sulfoxides are formed (85%) via an intermediate quenched by diphenyl sulfoxide; competing minor paths lead to arylthiols, arylsulfenic acid, and aryl sulfoxides. In aprotic solvents, the sulfoxidation is quite sluggish, but carboxylic acids (mostly 100. The protonated persulfoxide is formed in this case and acts as an electrophile with sulfides, again with a rate constant correlating with sigma (rho = -1.78).     

Translocation of bioactive peptides across cell membranes by carbon nanotubes

Functionalised carbon nanotubes are able to cross the cell membrane and to accumulate in the cytoplasm or reach the nucleus without being toxic for the cell up to 10 [micro sign]M.     

Gaseous ion activation dynamics: the role of the bulk gas in the racemization of chiral oxonium ions.

The kinetics of the inversion of configuration of a family of chiral oxonium ions, that is, O-protonated 1-aryl-1-methoxyethanes [YMe+], were investigated in two different gaseous media (in CH3X with X=F and X=Cl) at 720 torr of pressure and in the temperature range: 25-140 degrees C. The activation parameters of the [YMe+] inversion reaction were found to obey two different isokinetic relationships (IKR), depending on the nature and the position of the substituents in the oxonium ions and on the nature of the bulk gas employed. The observation of two IKR for the same family of reactions was related to a switchover in the resonant vibrational energy exchange between the reactants' critical mode, active in the transition state (omega), and the discrete vibrational levels v of the bulk gas. In CH3F, this vibrational-vibrational coupling switchover concerns the out-of-plane C-F...H-O bending) the phi family) and the H3C-F stretching (the gamma family) modes in the proton-bound [CH3F.YMe+] complex. In CH3Cl, the coupling switchover concerns the out-of-plane C-Cl...H-O bending (the phi family) and the H3C-Cl methyl group rocking (the gamma family) modes in the proton-bound [CH3Cl.YMe+] complex. The [YMe+] activation dynamics also determine the inversion dynamics. The [YMe+]ret<==>[YMe+]inv isomerization for the phi family involves the same "thermodynamically most favorable" transition state in both the CH3F and the CH3Cl media, whereas the same process for the gamma family proceeds through different, dynamically favored transition states.     

The influence of the boat-to-chair conversion on the demetallation of the nickel(II) complex of an open-chain tetramine containing a piperazine fragment

The nickel(II) complex with an open chain tetramine containing a piperazine fragment (1) displays an unusual resistance to demetallation in acidic solution and exhibits a lifetime of about five minutes in a solution 0.1 M in HClO4 and 7.0 M in NaClO4. Sluggishness with respect to the demetallation is ascribed to the occurrence of the boat-to-chair conformational conversion of the piperazine fragment, which implies the passage through the highly energetic half-boat transition state. The use of a high concentration of the inert electrolyte induces a 'salting out' effect on both thermodynamics (stability of metal complexes is enhanced) and kinetics (resistance to demetallation is increased).     

Unexpected formation of a copper(II) 12-metallacrown-4 with (S)-glutamic-gamma-hydroxamic acid: a thermodynamic and spectroscopic study in aqueous solution

The equilibria of copper(II) with (S)-glutamic-gamma-hydroxamic acid (H2L) were investigated in aqueous solution by different techniques: glass electrode potentiometry; calorimetry; VIS and CD spectrophotometry; and ES-MS. An unexpected pentacopper(II) 12-metallacrown-4 [Cu5L4H(-4)](2-) was detected, analogous to those well known formed by alpha- and beta-aminohydroxamic acids, but of lower stability. Another five species were found: [CuLH]+; [CuL2H2]; [Cu2L2]; [CuL2H]-; and [CuL2]2-. Their structures are proposed based on both spectroscopic and calorimetric data.