Thermodynamic and biodistribution studies of Zn(II), Ca(II), Gd(III) and Cu(II) complexes of 3,3,9,9-tetramethyl-4,8-diazaundecane-2,10-dione dioxime

The thermodynamic equilibria of copper(II), zinc(II), calcium(II) and gadolinium(III) with 3,3,9,9-tetramethyl-4,8-diazaundecane-2,10-dione dioxime (L1) have been studied at 25 degrees C and an ionic strength of 0.15 mol dm(-3). Copper and gadolinium form stable complexes with the ligand while the corresponding zinc species are more than 9 log units less stable. No complexes between calcium and the ligand were detected. The low binding strength of L1 towards zinc is attributed to the square-planar coordination geometry forced on the metal ion by the ligand as revealed by molecular mechanics calculations and molecular dynamics simulations. Speciation calculations, using a computer model of blood plasma, indicate that, despite the high concentration of zinc(II) and calcium(II) in vivo, L1 is able to increase the low-molecular-mass fraction of copper in plasma. Octanol/water partition coefficient of [CuL1H(-1)] indicates that although this species is largely hydrophilic, approximately 6% of the complex goes into the octanol phase and hence may promote dermal absorption of copper by the same amount. The dermal penetration rate is calculated to be 4.0 x 10(-4) mm h(-1). The [CuL1H(-1)] complex, which predominates at pH 7.4, is a poor mimic of native copper-zinc superoxide dismutase. Biodistribution experiments using the 64Cu-labelled [CuL1H(-1)] complex indicate an initial high uptake of this species in the liver followed by redistribution into muscle. Only a small amount is excreted through the urine.     

Chemical mass shifts in resonance ejection experiments in the quadrupole ion trap

Chemical mass shifts were measured in a Paul ion trap operated in the mass-selective instability scan with resonance ejection using a custom-built instrument. These shifts, which can be as much as 2%, decrease with increasing endcap electrode separation owing to changes in the higher order contributions to the electric field. They also decrease with decreasing helium buffer gas pressure. Both of these effects are analogous to those found with boundary ejection. This suggests that the previously proposed chemical mass shift mechanism based on compound-dependent collisional modification of the ejection delay produced by field faults near the endcap electrode apertures holds true also for resonance ejection. The influence of the resonance frequency on chemical mass shifts was also investigated and it is shown that at certain working points (values of the Mathieu parameter q(z) and a(z)) non-linear resonances greatly reduce the ejection delay for all ions, regardless of their chemical structures, and thus reduce the magnitude of the chemical mass shift. Energetic collisions leading to dissociation can take place at an earlier stage during the ejection process in the mass analysis scan when using resonance ejection compared with boundary ejection. This leads to even larger chemical mass shifts of fragile ions in resonance ejection. Increasing the resonance voltage amplitude can enhance this effect. The chemical mass shifts of fragile ions increase with increase in the resonance voltage amplitude, whereas negligible changes occur for structurally stable ions.     

Quantitative and bioluminescent assay to measure efficacy of conventional and DNA vaccinations against Helicobacter pylori

Vaccination against Helicobacter pylori using DNA sequences encoding Urease A and B subunits was compared to immunization with urease antigen and MTP-PE in a liposome formulation. To determine the effectiveness of a vaccine against H. pylori in a mouse model it is essential to quantify the number of H. pylori remaining in the stomachs following challenge with an inoculum of live bacteria. Culture assays and enzymatic assays produce inconsistent results often unsuitable to conclude if vaccine candidates are protective. To overcome this problem, we developed two assays: 1) a competitive quantitative PCR using a colorimetric readout and 2) a non-competitive direct quantitative PCR using a highly sensitive bioluminescent readout. The competitive PCR requires coamplification of a segment of the urease C sequence and an internal control standard in a competitive manner using a single set of primers. PCR products were quantified colorimetrically by an enzyme-linked immunosorbent assay and compared with known quantities of the internal control standard added to the PCR reaction. The highly sensitive, bioluminescent assay measures the amplified DNA directly using a flash-type luminescent tag and a specific probe. The Sydney strain of H. pylori was used for the mouse infection model. Quantification of H. pylori by either the bioluminescent assay or the competitive PCR was reliable, specific and sensitive compared to quantitative growth assays which often gave false results. The bioluminescent assay was much more sensitive and less labor/time intensive than the competitive PCR. The bioluminescent assay was able to quantitate as few as 100 bacteria, while the competitive assay could not detect less than 10(3) bacteria per mouse stomach. Quantification of H. pylori by bioluminescent assay was superior to the competitive assay and may be used for research applications, such as the development of vaccines, pathogenesis of gastric disease and monitoring of antibiotic treatment.     

Theoretical calculation of electrode potentials: Electron-withdrawing compounds

The electrode potential of 2,3-dicyanobenzoquinone in aqueous solution has been calculated relative to parabenzoquinone using a thermodynamic cycle approach that includes accurate gasphase ab initio calculations and calculation of differences in free energies of hydration using the free-energy perturbation method. The discrepancy between the calculated and experimental electrode potential is disappointingly large (99 mV) compared to previous studies using this approach. This, along with the experimental evidence, suggests that the experimental value itself is too large and that theoretical approaches may indeed be as reliable as experimental ones for determining redox properties of molecules such as 2,3-dicyanobenzoquinone. In the light of this discrepancy we have examined the variation of the results with the basis set, inclusion of electron correlation and changes in the parameters used in the molecular dynamics free-energy simulations. The results are shown to be dependent upon the torsional parameters and especially dependent upon the basis set or semiempirical method used to obtain the electrostatic potential-derived charges. The best charge set was determined using the ab initio criteria of completeness—as far as it can be applied to large molecules—and also by studying the effect of hydration on these charges. This was done by allowing the solvent to perturb the wave function prior to the electrostatic potential determination. Thus, 3-21G and 6-31G * basis sets were found to give satisfactory results. Similar results were obtained using semiempirical and ab initio geometries.     

Synthesis of some pyridylamino-1,4-disubstituted phthalazines

Two general procedures involving the condensation of phthalonitrile or 1,3-diiminoisoindoline with various aminopicolines, followed by ring expansion with hydrazine to the corresponding phthalazine are described. Syntheses are reported of 1, 4-di(3′-methyl-2′-pyridyl) aminophthalazine, 1,4-di(5′-methyl-2′-pyridyl)aminophthalazine, and 1,4-di(4′, 6′-dimethyl-2′-pyridyl)aminophthalazine.     

Brucine salts of l‐α‐hydr­oxy acids: brucinium hydrogen (S)‐malate penta­hydrate and anhydrous brucinium hydrogen (2R,3R)‐tartrate at 130 K

The structures of two brucinium (2,3‐dimeth­oxy‐10‐oxostrychnidinium) salts of the α‐hydr­oxy acids l ‐malic acid and l ‐tartaric acid, namely brucinium hydrogen (S)‐malate penta­hydrate, C₂₃H₂₇N₂O₄⁺·C₄H₅O₅⁻·5H₂O, (I), and anhydrous brucinium hydrogen (2R,3R)‐tartrate, C₂₃H₂₇N₂O₄⁺·C₄H₅O₆⁻,(II), have been determined at 130 K. Compound (I) has two brucinium cations, two hydrogen malate anions and ten water mol­ecules of solvation in the asymmetric unit, and forms an extensively hydrogen‐bonded three‐dimensional framework structure. In compound (II), the brucinium cations form the common undulating brucine sheet substructures, which accommodate parallel chains of head‐to‐tail hydrogen‐bonded tartrate anion species in the inter­stitial cavities.     

Solvent Effect and Reactivity Trend in the Aerobic Oxidation of 1,3‐Propanediols over Gold Supported on Titania: NMR Diffusion and Relaxation Studies

In recent work, it was reported that changes in solvent composition, precisely the addition of water, significantly inhibits the catalytic activity of Au/TiO₂ catalyst in the aerobic oxidation of 1,4‐butanediol in methanol due to changes in diffusion and adsorption properties of the reactant. In order to understand whether the inhibition mechanism of water on diol oxidation in methanol is generally valid, the solvent effect on the aerobic catalytic oxidation of 1,3‐propanediol and its two methyl‐substituted homologues, 2‐methyl‐1,3‐propanediol and 2,2‐dimethyl‐1,3‐propanediol, over a Au/TiO₂ catalyst has been studied here using conventional catalytic reaction monitoring in combination with pulsed‐field gradient nuclear magnetic resonance (PFG‐NMR) diffusion and NMR relaxation time measurements. Diol conversion is significantly lower when water is present in the initial diol/methanol mixture. A reactivity trend within the group of diols was also observed. Combined NMR diffusion and relaxation time measurements suggest that molecular diffusion and, in particular, the relative strength of diol adsorption, are important factors in determining the conversion. These results highlight NMR diffusion and relaxation techniques as novel, non‐invasive characterisation tools for catalytic materials, which complement conventional reaction data.