Time-resolved laser-induced fluorescence with high-performance liquid chromatography for analysis of polycyclic aromatic hydrocarbon mixtures

Time-resolved fluorescence is used to enhance the selectivity for polycyclic aromatic hydrocarbon mixtures by high-performance liquid chromatography. A pulsed laser is used as the excitation source. Only fluorophores with long fluorescence lifetimes (e.g. fluoranthene) are monitored if the delay between excitation and detection is sufficiently long. Limits of detection are of the order of 1–10 pg (5–50 fmol). The advantages are illustrated with a sample from the condensed steam distillate following a coal gasification experiment.     

Novel annulation reactions : the direct synthesis of cyclopentanes using a lewis acid activated bisfunctional annulating reagent

In a novel one-pot reaction 3,3-Dimethoxy-1-trimethylstannyl-propane (1) reacts in the presence of Lewis acids with O-silytated enolates in a [3+2] annulation to form fused cyclopentanes possessing a bridgehead hydroxy group.     

Chiroptical properties of S-alanine conformational isomers

The chiroptical properties of several S-alanine (zwitterionic and nonzwitterionic), S-alanine cation, and S-alanine anion structural isomers are calculated from LCAO-MO-SCF-CI wave functions constructed on the semiempirical CNDO MO model. Electronic excited states are constructed in the virtual orbital-configuration interaction approximation. We calculate and report the transition energies, dipole strengths, reduced rotatory strengths, and dissymmetry factors for the four lowest energy singlet-singlet transitions as a function of a single conformational variable (the angle between the C_αCOO′ plane and the CC_αN plane, where C ≡ carboxylate C atom, N ≡ ammonium or amino N atom, and C_α ≡ α-carbon atom) for zwitterionic and nonzwitterionic S-alanine, the S-alanine anion, and the S-alanine cation. The ground state dipole moments and first three ionization potentials are also computed and reported for the various S-alanine species. Electric dipole transition integrals are calculated in the dipole velocity formalism and all two-center contributions to these and the magnetic dipole transition integrals are included. The calculated rotatory strengths are compared with experimental circular dichroism spectra reported for S-alanine and with predictions based on sector rules which have been proposed for α-amino acids.     

CHEMILUMINESCENCE INVOLVING PEROXIDE DECOMPOSITIONS

Abstract— It is a reasonable assumption that many of the known cherniluminescent organic compounds react to give a carbonyl group in an excited state. By extension of this hypothesis we were led to test several substituted acridinium salts. Oxidation of these with hydrogen peroxide in the presence of base resulted in the formation of N-methylacridone in high yield, and the emission of light from an excited state of this ketone. Mechanisms for this process are discussed. Interest in indole derivatives aroused by the finding of a tryptamine residue in the luminescent cypridina luciferin, in conjunction with the hypothesis mentioned above, has led to an investigation of some indoles, and in particular, the important isolable peroxide of tetrahydrocarbazole. A preliminary account of this work is given.     

The use of high pressure freezing and freeze substitution to study host-pathogen interactions in fungal diseases of plants.

This article reports on the use of high pressure freezing followed by freeze substitution (HPF/FS) to study ultrastructural details of host-pathogen interactions in fungal diseases of plants. The specific host-pathogen systems discussed here include a powdery mildew infection of poinsettia and rust infections of daylily and Indian strawberry. The three pathogens considered here all attack the leaves of their hosts and produce specialized hyphal branches known as haustoria that invade individual host cells without killing them. We found that HPF/FS provided excellent preservation of both haustoria and host cells for all three host-pathogen systems. Preservation of fungal and host cell membranes was particularly good and greatly facilitated the detailed study of host-pathogen interfaces. In some instances, HPF/FS provided information that was not available in samples prepared for study using conventional chemical fixation. On the other hand, we did encounter various problems associated with the use of HPF/FS. Examples included freeze damage of samples, inconsistency of fixation in different samples, separation of plant cell cytoplasm from cell walls, breakage of cell walls and membranes, and splitting of thin sections. However, we believe that the outstanding preservation of ultrastructural details afforded by HPF/FS significantly outweighs these problems and we highly recommend the use of this fixation protocol for future studies of fungal host-plant interactions.     

Magnetic interactions in a vanadyl complex of an iminonitroxide radical

We have synthesized a complex in which a pyridyliminonitroxide radical is coordinated to a vanadyl ion. ESR studies of this complex show that the radical's unpaired spin is tightly coupled to the vanadium spin to form a ground singlet state with a thermally accessible triplet state. The vanadium hyperfine splitting in the triplet state of the complex is found to be one half of that of isolated vanadyl complexes.     

Rapid Access to Azabicyclo[3.3.1]nonanes by a Tandem Diverted Tsuji–Trost Process

A three-step synthesis of the 2-azabicyclo[3.3.1]nonane ring system from simple pyrroles, employing a combined photochemical/palladium-catalysed approach is reported. Substrate scope is broad, allowing the incorporation of a wide range of functionality relevant to medicinal chemistry. Mechanistic studies demonstrate that the process occurs by acid-assisted C−N bond cleavage followed by β-hydride elimination to form a reactive diene, demonstrating that efficient control of what might be considered off-cycle reactions can result in productive tandem catalytic processes. This represents a short and versatile route to the biologically important morphan scaffold.