Sparsely substituted chlorins as core constructs in chlorophyll analogue chemistry. I. Synthesis

Five routes to stable chlorins bearing 0 or 1 meso substituents have been investigated, among which reaction of a 9-bromo-1-formyldipyrromethane and 2,3,4,5-tetrahydro-1,3,3-trimethyldipyrrin proved most effective. Application of this route afforded metallochlorins [Cu(II), Zn(II), and Pd(II)] including the chlorin lacking any β-pyrrole and meso substituents.     

Reductive activation of nitrate reductases

Protein film voltammetry of Paracoccus pantotrophus respiratory nitrate reductase (NarGH) and Synechococcus elongatus assimilatory nitrate reductase (NarB) shows that reductive activation of these enzymes may be required before steady state catalysis is observed. For NarGH complementary spectroscopic studies suggest a structural context for the activation. Catalytic protein film voltammetry at a range of temperatures has allowed quantitation of the activation energies for nitrate reduction. For NarGH with an operating potential of ca. 0.05 V the activation energy of ca. 35 kJ mol-1 is over twice that measured for NarB whose operating potential is ca. -0.35 V.     

The different steric environments of the 5-exo- and 5-endo- substituent for a pair of isomeric tricarbonyl(methoxycyclohexa-1,-diene)irons

A shift reagent has been employed to demonstrate the sterically-hindered environment of the methoxy group in tricarbonyl(5-endo-methoxycyclohexa-1,-diene)iron relative to that of the methoxy group in the 5-exo analogue.     

An improved microwave plasma torch for atomic spectrometry

The analytical performance of a microwave plasma torch was improved through mechanical alterations. Several problems reported in earlier designs were addressed: the ignition and stabilization of a helium plasma in the MPT was difficult; high powers were required to both ignite and operate the plasma; otherwise, the plasma would erratically change from an annular to a filament type discharge. In the new torch, the helium discharge was stabilized by replacing the copper central tube with one made of quartz. In addition, air entrainment was alleviated through use of a sheathing gas. This modification simplified the background mass spectrum and raised the effective ionization temperature of the discharge. A detailed schematic diagram of the new microwave plasma torch is presented.     

Ring-opening metathesis/oxy-cope rearrangement: a new strategy for the synthesis of bicyclic medium ring-containing compounds

Ring-opening/ring-closing metathesis on cyclobutene-containing substrates with angular oxygen functionality provides a stereospecific introduction of 1,5-bis-dienes required for an anion-accelerated oxy-Cope rearrangement. The reaction sequence offers generally a stereocontrolled preparation of a variety of medium ring-containing bicyclic ring systems, while rearrangement to the bicyclo[7,3,0]dodecane (9-5) system leads to a mixture of olefin isomers.     

Tricarbonyliron complexes of some blocked cyclohexadienes

Complexation commencing with some substituted 1,3- or 1,4-cyclohexadienes with Fe(CO)₅ indicates that the steric direction is controlled by classical hindrance with groups such as alkyl, but probably involves transmission of the entering group through intermediate complexation with CO₂Me. The results help to define methods of obtaining desired stereoisomers in the series.     

Development of an in situ fiber optic Raman system to monitor hydrothermal vents

The development of a field portable fiber optic Raman system modified from commercially available components that can operate remotely on battery power and withstand the corrosive environment of the hydrothermal vents is discussed. The Raman system is designed for continuous monitoring in the deep-sea environment. A 785 nm diode laser was used in conjunction with a sapphire ball fiber optic Raman probe, single board computer, and a CCD detector. Using the system at ambient conditions the detection limits of SO(4)(2-), CO(3)(2-) and NO(3)(-) were determined to be approximately 0.11, 0.36 and 0.12 g l(-1) respectively. Mimicking the cold conditions of the sea floor by placing the equipment in a refrigerator yielded slightly worse detection limits of approximately 0.16 g l(-1) for SO(4)(-2) and 0.20 g l(-1) for NO(3)(-). Addition of minerals commonly found in vent fluid plumes also decreased the detection limits to approximately 0.33 and 0.34 g l(-1) respectively for SO(4)(-2) and NO(3)(-).     

Crystal engineering of novel cocrystals of a triazole drug with 1,4-dicarboxylic acids

Cocrystals of the poorly soluble antifungal drug cis-itraconazole (1) with 1,4-dicarboxylic acids have been prepared. The crystal structure of the succinic acid cocrystal with 1 was determined to be a trimer by single-crystal X-ray. The trimer is comprised of two molecules of 1 oriented in antiparallel fashion to form a pocket with a triazole at either end. The extended succinic acid molecule fills the pocket, bridging the triazole groups through hydrogen-bonding interactions rather than interacting with the more basic piperazine nitrogens. The solubility and dissolution rate of some of the cocrystals are approximately the same as those of the amorphous drug in the commercial formulation and are much higher than those for the crystalline free base. The results suggest that cocrystals of drug molecules have the possibility of achieving the higher oral bioavailability common for amorphous forms of water-insoluble drugs while maintaining the long-term chemical and physical stability that crystal forms provide.     

The 'Trinity' helix: synthesis and structural characterisation of a C3-symmetric tris-bidentate ligand and its coordination to Ag(I)

The synthesis and structural characterisation of a novel C3-symmetric tris-bidentate ligand, L, featuring a triphenylamine core appended by pyridylimine coordination sites is reported: 1H NMR compleximetric titration studies with Ag(I) and ESMS indicate the presence of [Ag3L2]3+ species in solution, consistent with the formation of a trinuclear double helicate complex: the Trinity helix.