Substituent effects in the fragmentation reactions of acetanilides and phenyl acetates

The mass spectra of a group of m- and p-substituted acetanilides were measured to determine the effect of the substituents, if any, on the rate of C₂H₂O expulsion (rearrangement) vs. the rate of [CH₃CO]⁺ formation (simple cleavage). Our results agree with observations of others in that substituents which raise the ionization potential of the aromatic ring appear to localize, on the average, less charge density on this locus, and conversely. The atomic composition of the substituent, however, irrespective of its position, seems to determine the relative rates of the competing reaction. Although in several cases Z_m/Z_p values were close to unity, rearrangement of isomeric molecular ions to a common species is shown not to occur.     

Yields of Br* (4P1/2) as a function of wavelength in the photodissociation of Br2 and IBr

A flashlamp-pumped tunable dye laser has been used to study the photochemical production of Br* (4²P_1/2) atoms from Br₂ and IBr exc     

Neutron scattering study of pentanol solubilization in sodium octanoate micelles

We extend a previous small-angle neutron scattering study of sodium octanoate (NaC₈) micelles to the ternary system sodium octanoate/pentanol/water. The use of contrast variation through selective deuteration of individual components together with explicit computation of interference effects, permits us to deduce the location of pentanol (C₅OH) in the micelles. Our main conclusion is that, although the micelles grow as (C₅OH) is solubilised, there is no concomitant variation in the NaC₈ aggregation number. At low alcohol concentrations, the C₅OH is located near the NaC₈ polar heads, while at higher concentration the -OH groups are distributed throughout the micellar core.     

Electrochemical oxidation of 6-hydroxy-1,2,3,4-tetrahydro-β-carboline in aqueous solution

The electrochemical oxidation of 6-hydroxy-1,2,3,4-tetrahydro-β-carboline (1), an alkaloid which occurs naturally in the mammalian brain, has been studied in aqueous solution particularly at physiological pH. The first voltammetric oxidation peak of 1 observed at the pyrolytic graphite electrode generates a radical intermediate which dimerizes to give 5,5′-bi-(6-hydroxy-1,2,3,4-tetrahydro-β-carboline) (3). However, the putative radical intermediate can also be further oxidized (1e) to give a C(5)-centered carbocation which can either dimerize in an ion-substrate reaction to give 3 or be attacked by water to give 5,6-dihydroxy-1,2,3,4-tetrahydro-β-carboline (8) which is rapidly oxidized further to 1,2,3,4-tetrahydro-β-carboline-5,6-dione (9). In the presence of glutathione dione 9 forms the 8-S-glutathionyl conjugate of 8 which is easily oxidized to the 8-S-glutathionyl conjugate of 9. It is suggested that 1 might be an alkaloid which is elevated in the brain as a result of chronic alcoholism, and the roles of the oxidative transformations of this compound in some of the addictive and neurophathological consequences of ethanol consumption are discussed.     

Cycloalkene budding: mass spectrometric studies of competitive and dual cycloalkene extrusion reactions from doubly unsaturated aldehyde N,N-dimethylhydrazones

Mass spectral fragmentation pathways of four doubly unsaturated aldehyde N,N-dimethylhydrazones were investigated using EI-MS and tandem mass spectrometry (MS/MS) under electron ionization and collisionally activated decomposition (CAD) conditions. Cyclopentene extrusion was found to be slightly favored over cyclohexene loss in a hydrazone capable of losing either cycloalkene. Evidence for the regeneration of a chain-shortened iminium radical cation as a result of cycloalkene extrusion was provided by studying substrates capable of undergoing successive cycloalkene budding sequences. EI-MS of these compounds shows sequential loss of both cyclopentene and cyclohexene, in accord with expectations for a cascade mechanism. Although these MS/MS experimental results are also compatible with alternative mechanisms which would entail the simultaneous loss of both neutral cycloalkenes or of a macrocyclic diene, a rapid cascade of cycloalkene budding accounts best for the experimental observations.     

Simultaneous microbatch screening of enantiorecognition on solid chiral selectors using selected mixtures of test-racemates: a case study on cellulose tris(alpha-phenylpropionate) with configurational diversity

An improved methodology for microbatch screening in the liquid-solid enantioselective adsorption of racemates by solid chiral selector is presented and illustrated by the evaluation of a series of six cellulose tris(alpha-phenylpropionate) presenting a configurational diversity and cellulose tris (4-methylbenzoate). Analyses were performed on 5 mg scale of chiral selector and 150 microL of supernatant containing a mixture of three test-racemates. Fifteen test-racemates were chosen according to their molecular diversity using a hierarchical clustering approach for seven selected three-dimensional molecular properties. The 15 racemates were sorted in five test mixtures composed of three racemates each according to the following constraints: each triplet of test-racemates can be analyzed without peak overlap on a commercially available chiral stationary phase (CSP). The designed five groups of three racemates may be used for the evaluation of other chiral selectors in view of the preparation of CSPs. This methodology improves the throughput of the evaluation and could be automated.     

Concentration dependence of the surface tension of ternary systems

A surface tension isotherm equation for ternary systems was derived based on general thermodynamic expressions with consideration for the concentration dependence of the molar surface area. Within the experimental errors, the equation describes the properties of ternary systems with smooth surface tension isotherms.     

Electrodeposition of fluorine-doped lead dioxide

The electrocatalytic properties of PbO₂ may be increased by incorporation of some ions such as F⁻. In this review, the preparation of fluorine-doped PbO₂ in the presence of some additives of fluorine-containing compounds (F⁻, potassium salt of nonafluoro-1-butanesulfonic acid C₄F₉O₃SK and Nafion^®) is reported. The mechanism of electrodeposition is discussed. The amount of additives in the deposit depends on the experimental conditions: potential, current density and charge of additive species in the plating solution. The physicochemical properties of doped oxide are very different from those of undoped oxide, accounting for the different electrocatalytic activity of the materials.