Measurement of the kinetic isotope effect for the oxidation of NADH at a poly(aniline)-modified electrode

Kinetic isotope measurements using [4,4-2H2]NADH and [4-1H, 4-2H]NADH have been used to investigate the mechanism of the electrochemical oxidation of NADH at poly(aniline)-poly(vinyl sulfonate)-modified electrodes. The experiments show a primary kinetic isotope effect for the reaction of 4.2. This is consistent with literature values for the corresponding isotope effect for the oxidation of NADH by two-electron oxidants in homogeneous solution. The result demonstrates that transfer of H from NADH to the modified electrode occurs in the rate-limiting step within the reaction complex.     

Synthèse partielle et propriétés oncostatiques des pseudo-tubulosines,analogues de l'émétine et de la tubulosine

Partial Synthesis and Oncostatic Properties of Pseudotubulosines, Analogues of Emetine and Tubulosine Pseudotubulosines, structural analogues of emetine and tubulosine, have been synthesized by either Pictet-Spengler or Bischler-Napieralski condensation from dihydrocorynantheal or corynantheidal. Spectral data, cytotoxic and oncostatic properties of these new alkaloids are described.     

MONOFUNCTIONAL ANGULAR FUROCOUMARINS: SEQUENCE SPECIFICITY IN DNA HOTOBINDING OF 6,4,4''-TRIMETHYLANGELICIN and OTHER ANGELICINS

The sequence specificity in the photoreaction (365 nm) of 6,4,4'-trimethylangelicin (TMA) with DNA fragments of the lac I gene of Escherichia coli was studied by using DNA sequencing methodology. In order to map the sites of TMA photoaddition, we took advantage of the (3'-5') exonuclease activity associated with T4 DNA polymerase, which is blocked by bulky adducts, such as furocoumarin photoadducts. A quantitative analysis of the sites of photoaddition is reported. TMA was demonstrated to photoreact with thymine and, to a lower extent, to cytosine. AT-rich sequences and TTT sites in a GC context are the most reactive sites towards TMA whereas TA, AT, CA, AC sites are weaker sites with similar reactivity. Cytosines in alternated CG sequences are also targets of TMA photobinding. We observed a less pronounced sequence specificity of TMA than that of other psoralen derivatives already studied (Sage and Moustacchi, 1987; Boyer et al., 1988). A comparison with other furocoumarins 4,4'-dimethylangelicin (4,4'-DMA), 4'-methylangelicin (4'-MA), angelicin, 4,5',8-trimethylpsoralen (TMP) and 8-methoxypsoralen (8-MOP) is also reported. The role of flanking sequence and consequently of the local conformation at the various sites of photoaddition is discussed. A preferential orientation of the TMA molecule during the intercalation in the dark is suggested. Hot alkali treatment of TMA-modified DNA did not reveal any DNA strand breakage due to photooxidized bases.     

Direct determination of the complete set of iron normal modes in a porphyrin-imidazole model for carbonmonoxy-heme proteins: [Fe(TPP)(CO)(1-MeIm)

Detailed Fe vibrational spectra have been obtained for the heme model complex [Fe(TPP)(CO)(1-MeIm)] using a new, highly selective and quantitative technique, Nuclear Resonance Vibrational Spectroscopy (NRVS). This spectroscopy measures the complete vibrational density of states for iron atoms, from which normal modes can be calculated via refinement of the force constants. These data and mode assignments can reveal previously undetected vibrations and are useful for validating predictions based on optical spectroscopies and density functional theory, for example. Vibrational modes of the iron porphyrin-imidazole compound [Fe(TPP)(CO)(1-MeIm)] have been determined by refining normal mode calculations to NRVS data obtained at an X-ray synchrotron source. Iron dynamics of this compound, which serves as a useful model for the active site in the six-coordinate heme protein, carbonmonoxy-myoglobin, are discussed in relation to recently determined dynamics of a five-coordinate deoxy-myoglobin model, [Fe(TPP)(2-MeHIm)]. For the first time in a six-coordinate heme system, the iron-imidazole stretch mode has been observed, at 226 cm(-)(1). The heme in-plane modes with large contributions from the nu(42), nu(49), nu(50), and nu(53) modes of the core porphyrin are identified. In general, the iron modes can be attributed to coupling with the porphyrin core, the CO ligand, the imidazole ring, and/or the phenyl rings. Other significant findings are the observation that the porphyrin ring peripheral substituents are strongly coupled to the iron doming mode and that the Fe-C-O tilting and bending modes are related by a negative interaction force constant.     

New reaction of formation of the fused tricyclic bispyrroloquinone ring system

A one-pot procedure to difunctionalized fused tricyclic bispyrroloquinone derivatives involving the condensation of N-tosylindoledione and α-ketoamines is described.     

Biomolecular Imaging with a C60-SIMS/MALDI Dual Ion Source Hybrid Mass Spectrometer: Instrumentation,Matrix Enhancement,and Single Cell Analysis

We describe a hybrid MALDI/C₆₀-SIMS Q-TOF mass spectrometer and corresponding sample preparation protocols to image intact biomolecules and their fragments in mammalian spinal cord, individual invertebrate neurons, and cultured neuronal networks. A lateral spatial resolution of 10 μm was demonstrated, with further improvement feasible to 1 μm, sufficient to resolve cell outgrowth and interconnections in neuronal networks. The high mass resolution (>13,000 FWHM) and tandem mass spectrometry capability of this hybrid instrument enabled the confident identification of cellular metabolites. Sublimation of a suitable matrix, 2,5-dihydroxybenzoic acid, significantly enhanced the ion signal intensity for intact glycerophospholipid ions from mammalian nervous tissue, facilitating the acquisition of high-quality ion images for low-abundance biomolecules. These results illustrate that the combination of C₆₀-SIMS and MALDI mass spectrometry offers particular benefits for studies that require the imaging of intact biomolecules with high spatial and mass resolution, such as investigations of single cells, subcellular organelles, and communities of cells. Graphical Abstract

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Spectroscopic and Computational Study of a Nonheme Iron Nitrosyl Center in a Biosynthetic Model of Nitric Oxide Reductase

A major barrier to understanding the mechanism of nitric oxide reductases (NORs) is the lack of a selective probe of NO binding to the nonheme Fe_B center. By replacing the heme in a biosynthetic model of NORs, which structurally and functionally mimics NORs, with isostructural ZnPP, the electronic structure and functional properties of the Fe_B nitrosyl complex was probed. This approach allowed observation of the first S=3/2 nonheme {FeNO}⁷ complex in a protein‐based model system of NOR. Detailed spectroscopic and computational studies show that the electronic state of the {FeNO}⁷ complex is best described as a high spin ferrous iron (S=2) antiferromagnetically coupled to an NO radical (S= 1/2) [Fe²⁺‐NO^.]. The radical nature of the Fe_B‐bound NO would facilitate N? N bond formation by radical coupling with the heme‐bound NO. This finding, therefore, supports the proposed trans mechanism of NO reduction by NORs.     

Replacement of the Cobalt Center of Vitamin B12 by Nickel: Nibalamin and Nibyric Acid Prepared from Metal-Free B12 Ligands Hydrogenobalamin and Hydrogenobyric Acid

The (formal) replacement of Co in cobalamin ( Cbl ) by Ni^II generates nibalamin ( Nibl ), a new transition-metal analogue of vitamin B₁₂. Described here is Nibl , synthesized by incorporation of a Ni^II ion into the metal-free B₁₂ ligand hydrogenobalamin ( Hbl ), itself prepared from hydrogenobyric acid ( Hby ). The related Ni^II corrin nibyric acid ( Niby ) was similarly synthesized from Hby , the metal-free cobyric acid ligand. The solution structures of Hbl , and Niby and Nibl , were characterized by spectroscopic studies. Hbl features two inner protons bound at N2 and N4 of the corrin ligand, as discovered in Hby . X-ray analysis of Niby shows the structural adaptation of the corrin ligand to Ni^II ions and the coordination behavior of Ni^II. The diamagnetic Niby and Nibl , and corresponding isoelectronic Co^I corrins, were deduced to be isostructural. Nibl is a structural mimic of four-coordinate base-off Cbls , as verified by its ability to act as a strong inhibitor of bacterial adenosyltransferase.