10-hydroxy-10,9-boroxarophenanthrenes: versatile synthetic intermediates to 3,4-benzocoumarins and triaryls

10-Hydroxy-10,9-boroxarophenanthrenes were obtained as unexpected major products upon BBr(3)-mediated O-demethylation of 2-methoxybiaryls. The formation likely proceeds via intramolecular electrophilic aromatic cyclization of a reactive dibromoaryloxyborane intermediate. Essentially quantitative yields of 10-hydroxy-10,9-boroxarophenanthrenes were also obtained from 2-hydroxybiaryl and BCl(3)/AlCl(3) with use of a modified literature procedure. As synthetic intermediates, 10-hydroxy-10,9-boroxarophenanthrenes were efficiently converted to 3,4-benzocoumarins and triaryls through Pd-catalyzed CO insertion and Suzuki reaction.     

Structure and phase behaviour of the ternary system water, n-heptane and the nonionic surfactant Igepal® CA520

The phase behavior of the system water, n-heptane and the nonionic surfactant Igepal^® CA520 has been studied by visual inspection, high-performance liquid chromatography, polarizing microscopy and freeze-fracture electron microscopy. The phase diagram at 25?°C contains two large homogeneous microemulsion phases, an extended region of a lamellar liquid crystalline structure and some two- and three-phase regions. The oil-rich part of the phase diagram has been investigated by static and dynamic light scattering in order to examine the behavior of the collective diffusion coefficient and the scattering intensity in the presence of increasing concentrations of water, starting from the binary system of n-heptane and Igepal^® CA520. The results suggested that at a very low water content the aggregates of the microemulsion are small. With the exception of this region the structure is bicontinuous.     

Molecular control of recombination dynamics in dye-sensitized nanocrystalline TiO2 films: free energy vs distance dependence

In this paper we address the dependence of the charge recombination dynamics in dye-sensitized, nanocrystalline TiO2 films upon the properties of the sensitizer dye employed. In particular we focus upon dependence of the charge recombination kinetics upon the dye oxidation potential E0(D+/D), determined electrochemically, and the spatial separation r of the dye cation HOMO orbital from the metal oxide surface, determined by semiempirical calculations. Our studies employed a series of ruthenium bipyridyl dyes in addition to porphyrin and phthalocyanine dyes. A strong correlation is observed between the recombination dynamics and the spatial separation r, with variation in r by 3 A resulting in a more than 10-fold change in the recombination half-time t(50%). This correlation is found to be in agreement with electron tunneling theory, t(50%) proportional, variant exp(-betar) with beta = 0.95 +/- 0.2 A-1. In contrast, the recombination dynamics were found to be relatively insensitive to variations in E0D+/D), indicative of the recombination reaction lying near the peak of the Marcus free energy curve, DeltaG approximately lambda, and with lambda approximately 0.8 eV. A correlation is also observed between the recombination half-time and the temporal shape of the kinetics, with faster recombination dynamics being more dispersive (less monoexponential). Comparison with numerical Monte Carlo type simulations suggests this correlation is attributed to a shift from fast recombination dynamics primarily limited by dispersive electron transport within the metal oxide film to slower dynamics primarily limited by the interfacial electron-transfer reaction. We conclude that the primary factor controlling the charge recombination dynamics in dye-sensitized, nanocrystalline TiO2 films is the spatial separation of the dye cation from the electrode surface. In particular, we show that for the Ru(dcbpy)2NCS2 dye series, the use of X = NCS rather than X = CN results in a 2 A shift in the dye cation HOMO orbital away from the electrode surface, causing a 7-fold retardation of the recombination dynamics, resulting in the remarkably slow recombination dynamics observed for this sensitizer dye.     

β-Lactam Derivatives as Enzyme Inhibitors: Peptidic Derivatives of (<Emphasis Type="Italic">RS</Emphasis>)-2-Oxo-4-phenylazetidine-1-alkanoic Acids

Summary. 4-Phenylazetidine-2-one was transformed into 4-phenylazetidine-1-alkanoic acids, which were reacted in the presence of diphenylphosphoroazidate with amino acid esters and dipeptide esters yielding β-lactam peptides with different spacers between the lactam ring and the peptide moiety. All structures were established by elementary analyses, HPLC, optical rotation, and spectroscopic data and all new compounds were tested as inhibitors of PPE using standard procedures. Four compounds exhibited a weak activity compared with the standard inhibitor trifluoroacetyl-l-val-l-tyr-l-val.     

The Green function for uniformly elliptic equations

The authors discuss a generalization of the usual Green function to equations with only measurable and bounded coefficients. The existence and uniqueness as well as several other important properties are shown. Such a Green function proves useful in connection with quasilinear elliptic systems of diagonal type.     

A direct determination of the proton electron mass ratio

The cyclotron frequencies of free protons and electrons in a magnetic field of 5.81 Tesla with superimposed electrostatic quadrupole field have been measured. The increase of energy connected with a transition at cyclotron frequency is detected by the measurement of the time of flight through an inhomogeneous magnetic field. From the ratio of the measured cyclotron frequencies of both particles the proton electron mass ratio is deduced. The resultm _p /m _e =1,836.1527(11) agrees within the limits of error (0.6 ppm) with the value of the indirect determination.