Three-photon near-threshold photoionization dynamics of isooctane

The electron survival probability following three-photon (9.3 eV total) near-threshold photoionization of neat isooctane is measured with sub-50 fs time resolution. The measured dynamics are nonexponential in time and are well described by a diffusion-controlled electron-cation recombination model. Excitation-power-dependent studies indicate that the unperturbed three-photon threshold ionization is only observed for pump irradiance below 0.5 TW cm2. At excitation fields above this level, the signal is no longer cubic in the excitation irradiance, and the observed electron survival probability dramatically changes, decaying as a single exponential in time.     

The chemistry of electrogenerated transition metals species - the insertion of olefins into a nickelcarbon bond

The nickel(1) complex, Ni(teta)⁺, formed by cathodic reduction of the corresponding nickel(11) complex, reacts rapidly with alkyl bromides to form an unstable intermediate containing a nickelcarbon bond. When the electrolysis medium also contains an activated olefin an insertion reaction occurs. The new metalcarbon bond is cleaved by further reduction and overall the reduction of Ni(teta)²⁺ in the presence of RBr and CH₂CHY leads to high yiels of RCH₂CH₂Y.     

Novel approaches to the analysis of the Maillard reaction of proteins

The Maillard reaction comprises a complex network of reactions which has proven to be of great importance in both food science and medicine. The majority of methods developed for studying the Maillard reaction in food have focused on model systems containing amino acids and monosaccharides. In this study, a number of electrophoretic techniques, including two-dimensional gel electrophoresis and capillary electrophoresis, are presented. These have been developed specifically for the analysis of the Maillard reaction of food proteins, and are giving important insights into this complex process.     

Ground states of molecules. 64.MNDO Calculations for compounds containing bromine

MNDO has been parametrized for bromine. Since d atomic orbitals (AOS) are not included, the calculations are restricted to Br^I. Heats of formation, molecular geometries, ionization energies, and dioole moments are reproduced with useful accuracy.     

Probing the formation of bicyclo[4.2.0]octan-1-ols

Reaction of lithium enolates of simple ketones with (+/-)-phenyl vinyl sulfoxide has potential for the convergent construction of complex fused ring systems containing a bicyclo[n.2.0]alkan-1-ol. The formation of sulfinylbicyclo[4.2.0]octan-1-ols 1-3 from the lithium enolate of cyclohexanone with (+/-)-phenyl vinyl sulfoxide or (R)-(+)-p-tolyl vinyl sulfoxide 18 was used to probe the mode of this novel cyclization reaction. Using phenyl vinyl sulfoxide, variations in the reaction lighting and solvent were investigated, in conjunction with radical trapping (TEMPO) and isotope labeling (deuterium) experiments. Cyclization to form sulfinylbicyclooctanols 1-3 is likely to proceed via an intermediate that ring closes to the bicycloalkanol anion 11 and was presently favored by the use of solvents such as THF or DME.     

Adsorption of organic matter at mineral/water interfaces. 6. Effect of inner-sphere versus outer-sphere adsorption on colloidal stability

The effects of the adsorption modes of several low molecular weight (LMW) organic anions (maleate, oxalate, and citrate) on the colloidal stability of corundum-water suspensions have been examined using electrokinetic and shear yield stress (tau(y)) measurements over a broad range of pH conditions and LMW organic anion concentrations. Consistent with previous studies, increasing concentrations of maleate, oxalate, and citrate progressively shift the electrokinetic isoelectric point and pH of the maximum shear yield stress (tau(y,max)) to more acidic conditions. Due to its predominant electrostatic driving force for adsorption, outer-spherically adsorbed maleate possesses a very limited ability to charge reverse the corundum-water interface or bind to the negatively charged corundum surface. By contrast, inner-spherically adsorbed oxalate and citrate can significantly charge reverse the corundum-water interface, with the extent of charge reversal being related to the relative binding strengths of the oxalate and citrate anions. Adsorbed maleate, oxalate, and citrate generate steric barriers to interparticle approach, leading to substantial reductions in the magnitude of tau(y,max) at low to intermediate concentrations of those LMW anions. At the highest anion concentrations investigated, however, increases in tau(y,max) are observed, and can be attributed to the formation of bridging Al(III)-organic surface precipitates, as suggested by in situ attenuated total reflectance Fourier transform infrared spectroscopic measurements of corundum-oxalate suspensions at high oxalate concentrations. The extent of precipitate formation is greatest for the corundum-oxalate system due to the strong dissolution-enhancing properties of the inner-spherically adsorbed oxalate anion (i.e., its ability to generate enhanced concentrations of dissolved Al(III) which can then participate in precipitate formation). The effects of the LMW organic anion adsorption modes on both the forms of the measured tau(y) versus pH data, and the ability to quantitatively compare tau(y) and zeta potential data measured at different corundum concentrations, are also discussed.     

Two pseudopolymorphic hydrates of brucine: brucine–water (1/4) and brucine–water (1/5.25) at 130 K

The structures of two pseudopolymorphic hydrates of brucine, C₂₃H₂₆N₂O₄·4H₂O, (I), and C₂₃H₂₆N₂O₄·5.25H₂O, (II), have been determined at 130 K. In both (I) and (II) (which has two independent brucine mol­ecules together with 10.5 water mol­ecules of solvation in the asymmetric unit), the brucine mol­ecules form head‐to‐tail sheet substructures, which associate with the water mol­ecules in the inter­stitial cavities through hydrogen‐bonding associations and, together with water–water associations, give three‐dimensional framework structures.     

1H and 199Hg NMR spectra of methylmercury(II) complexes. Effects of basicity and ortho substitution in pyridines(L) in complexes [MeHgL]NO3

Linear complexes [MeHgL]NO₃ (L = substituted pyridine) have been prepared and their ¹H and ¹⁹⁹Hg NMR spectra measured and compared with other complexes of this series reported previously. The coupling constant J(¹H?¹⁹⁹Hg) correlates directly with pKa and with the gas phase enthalpy of ionization [ΔG_i(g)] of LH⁺; with J(¹H?¹⁹⁹Hg) decreasing with increasing pKa or ΔG_i(g). The chemical shift, δ, for ¹⁹⁹Hg does not correlate with either pKa or ΔG_i(g). Complexes without substituents in the 2 position of pyridine have δ¹⁹⁹Hg ca. 80–100 ppm downfield from MeHgNO₃, those with one methyl group in the 2 position ca. 125–150 ppm, and those with methyl groups in the 2 and 6 position (or benzyl or 3′-methylpyridyl groups in the 2 position) ca. 160–200 ppm downfield from MeHgNO₃. The coupling constant J(¹H?¹⁹⁹Hg) is found to be more useful than δ¹⁹⁹Hg in determination of solution structures of MeHg(II) complexes of this type of ligand.