Ground state oxygen in synthesis of cyclic peroxides. Part 1: Benzo fused ketals

A thiol-olefin-cooxygenation (TOCO) radical chain reaction involving ground state molecular oxygen converts 2′-isopropenyl acetophenones directly into cyclic peroxy hemiketal products with three new bonds. Starting with 4-t-butylbenzenethiol, this TOCO process proceeds reproducibly on gram scale in 86% yield. Hemiketal→ketal and sulfide→sulfone transformations finally provide a series of sulfonyl cyclic peroxy ketals. The in vitro antimalarial activities of some of these structurally simple benzo-fused cyclic peroxides are reported.     

Kinetics and Thermodynamics of Hydrogen Atom Exchange Reactions in Sterically Hindered Hydroxylamine-Nitroxyl Radical Systems

Rate constants and activation energies were determined for the forward and reverse hydrogen exchange reactions in systems involving a sterically hindered hydroxylamine and a nitroxyl radical of dihydroquinoline, tetrahydroquinoline, diphenylamine, imidazoline, pyrrolidine, or piperidine. The equilibrium constants and heats of these reactions were determined, and the dissociation energies of the NO-H bonds in the hydroxylamines were estimated.     

Immobilization of α-chymotrypsin into the poly(N,N-diallyl-N,N-didodecyl ammonium bromiae)/surfactant nanocapsules

The biocatalytic systems from nanocapsules containing α-chymotrypsin in the inner aqueous cavities have been prepared. They can act in both the organic solvent and the aqueous medium. For such encapsulation, the reversed hydrated micelles from N,N-diallyl-N,N-didodecyl ammonium bromide (DDAB) in cyclohexane (w₀ = 22), including α-chymotrypsin, have been polymerized by UV initiation. After precipitation by acetone, these nanocapsules were moved into the aqueous medium with the aid of ionic, AOT, or nonionic, Brij-97, surfactants. In this case, the unilamellar liposomes were formed. They have the inner monolayer from the poly-DDAB network, and the outer one predominantly from surfactant molecules. According to the light-scattering data, the average outer diameter of nanocapsules equals to 20 nm. The vesicular “coated” α-chymotrypsin was used for study of enzymatic activity. It has been shown using the integral form of the Michaelis-Menten equation, that by encapsulation of α-chymotrypsin the value of the Michaelis constant, K_m, increases by a factor of 1.8 by the ATEE hydrolysis. However, the value of the maximal velocity, V_max, decreases by a factor of 1.7. Encapsulated α-chymotrypsin has a high thermostability keeping its own activity up to 80°C. The polymer network blocks the conformational transitions of enzyme molecule by heating of a system.     

Carbon-13 NMR substituent effects in para-substituted benzophenones

The carbon-13 NMR spectra for a series of benzophenones was obtained and analyzed, using the dual substituent parameter (DSP) equation. The DSP analysis indicates that transmission of the substituent effect to the substituted ring is primarily resonance controlled while the transmission to the second phenyl ring involves a π-bond polarization mechanism. The DSP analysis of the C'₄ chemical shifts (para carbon in ring B) was found to compare very favorably with the fluorine “tag” data for analogous systems. Data for some para-para' benzophenones is also given.     

Fragmentation of some even-electron nitroaromatic ions: The question of the nitrotropylium ion

The behavior of the even-electron mass 150 ions, (presumably nitrobenzoyl cations) generated by simple α-cleavage of m- and p-nitrobenzoic acid derivatives, undergo two competing secondary fragmentations to yield odd-electron ions by the expulsion of NO and NO₂. Expulsion of NO from the mass 150 ions from p-nitro compounds is far greater than expulsion of NO from those generated from m-nitro compounds. In addition, the behavior of the even-electron mass 136 ions, generated from m- and p-nitrobenzyl compounds, was compared to that of the mass 150 ions and they were found to decompose in a similar fashion. From our results we conclude that the decomposing mass 136 ions produced from either the m- or p-nitrobenzyl compounds, or both, do not have the nitropylium structure; our data are more consistent with the decomposing ions having nitrobenzyl structures.     

Photorefractive Properties of a Polyimide Containing Thiacarbocyanine Dye J-Aggregates

The photorefractive properties of a polyimide containing J-aggregates of a thiacarbocyanine dye were examined. Measurements were made with a holographic apparatus at Ar–Kr laser wavelengths of 647 and 514 nm. The J-aggregate and the monomeric form of the dye, respectively, are responsible for the photoelectric sensitivity at these wavelengths. It was shown that the J-aggregates are also responsible for the nonlinear optical properties of the polymeric system. The combination of these features determines the photorefractive characteristics of the polymer composite: under interference conditions, the intensity of one of the interacting beams (signal beam) increases at the expense of extinction of the other (pumping) beam. The difference between the beam-coupling gain coefficient and the absorption coefficient increases at 647 nm from 217 to 361 cm^–1 with the increasing strength of a constant electric field E ₀ applied to the layer from 16 to 123 V/m. Only the samples containing J-aggregates display the photorefractive effect at 514 nm.     

Differentiating action of solvents on the strength of CH-acids

The reasons for the differentiating action of solvents on the relative kinetic acidity of CH-acids (hydrocarbons and their derivatives), determined by measuring the kinetics of the isotopic exchange of hydrogen, have been examined. The effect is associated with deviations from Brönsted's relationship, which depend on the characteristic features of the structure and differences in the solvation of the acids, their anions, or the transition states of the reactions is which the acids are taking part. It has been shown that the differentiating effect is observed for a large number of substances with different structures (aliphatic-aromatic hydrocarbons, benzene derivatives, and five-membered heterocyclic compounds and their derivatives) when the relative kinetic acidities of the substances in solvents belonging to different groups are compared. One group includes t-butyl alcohol, liquid ammonia, and cyclohexylamine, and the second includes dimethyl sulfoxide and methyldi(methoxymethyl)phospine oxide. The solvents differ in their proton-donating properties and in the values of their dipole moments and dielectric constants. Different values are obtained for the deuterium—tritium kinetic isotopic effects for reactions carried out in solvents belonging to different groups.     

Charge exchange spectra of simple ketones

Charge exchange spectra of three simple 2-ketones are reported. Comparison of charge exchange data with low voltage electron-impact spectra provides information on the nature of the electron-impact energy distribution. The existence of high energy molecular ions which do not decompose in the mass spectral time scale led us to postulate that isolated states or photon emission reactions are operative in the present system.