On carboxylate as a leaving group at the active site of Mo nitrogenase: electrochemical reactions of some MO and W carboxylates, formation of mono-, di- and tri-hydrides and the detection of an MoH2(N2) intermediate

A carboxylate ligand can function as a leaving group at a reduced molybdenum dihydride centre and this exposes a site at which dinitrogen or other small molecules can bind ; dihydrogen loss occurs after substrate binding ; protic attack intercepts carboxylate loss affording a trihydride intermediate which can partake in a hydrogen evolution cycle : it is suggested that carboxylate loss from the reduced Mo centre of nitrogenase might similarly lead to substrate binding and thence obligatory evolution of H₂.     

Synthesis of 5H[l]benzopyrano[3,4-b]pyridin-5-one and its derivatives

3-Aminocoumarin undergoes the Skraup reaction to give a new ring system, 5H[l]benzo-pyrano[3,4-b]pyridin-5-one (IVa). When 3-aminocoumarin was condensed with the ethoxy methylene derivatives of active methylene compounds, ethyl acetoacetate, and dimethyl acetylenedicarboxylate, the intermediates Vla-VIf were formed which on thermal cyclizations afforded other derivatives of 5H[l ]benzopyrano[3,4-b]pyridin-5-one (IVb-IVf). The nitration of IVa gave IVg.     

Use of ion exchange membranes in preparative organic electrochemistry: New processes for electrolysis

2-Amino 5-nitro pyridinc (ANP) adsorbs strongly at an electrochemically roughened silver surface and gives an intense surface-enhanced Raman (SER) spectrum which identifies the adsorbate as the [ANP]^? ion [C₅H₄N₃O₂]^?. Coulometric and spectrophotometric methods are used to provide an in situ measurement of the surface molecular concentration of this adsorbate. This is shown to be linearly dependent upon the anodic roughening charge transfer in 0.1 M KCl over the range 0–150 mC cm^?2 for double-potential-step roughening cycles. A quantitative measure of the surface Raman enhancement factor for this adsorbate is obtained, and this is shown to reach a maximum of 1.5 × 10⁴ for surface roughening involving the passage of 25 mC cm^?2. For this amount of roughening or greater, it is concluded that the surface roughness further increases the total SER intensity by a factor of 10 or more due to the resulting high effective surface concentration of the adsorbate.     

Use of a fluorescent phosphoprotein dye to characterize oxidative stress-induced signaling pathway components in macrophage and epithelial cultures exposed to diesel exhaust particle chemicals

A large body of evidence has shown that exposure to ambient particulate matter (PM) leads to asthma exacerbation through an excitation of allergic inflammation. Utilizing diesel exhaust particles (DEPs) as a model air pollutant, we and others have demonstrated that PM contains redox-active chemicals that generate inflammation through an oxidative stress mechanism. Recently, the strengths of proteomics have enabled us to demonstrate that organic DEP extracts induce a hierarchical expression pattern of oxidative stress-induced proteins in macrophages and epithelial cells. As a further extension of this work, we now employ a new phosphosensor fluorescent dye, Pro-Q Diamond, to elucidate the induction of phosphoproteins and intracellular signaling cascades that may play a role in DEP-induced inflammation. We demonstrate that DEPs induced the phosphorylation of several phosphoproteins that belong to a number of signaling pathways as well as other oxidative stress pathways. In combination with cytokine array, phosphoproteome analysis using Pro-Q Diamond allowed us to characterize the aromatic and polar chemicals of DEPs that are involved in the activation of three different mitogen-activated protein (MAP) kinase signaling pathways.     

Detection and identification of thyreostats in the thyroid gland by gas chromatography-mass spectrometry

Because thyreostatic compounds, also named thyreostats, are banned in Europe (directive 86/469/EEC), methods have to be developed to prevent the illegal use of these substances. The analytical procedure described herein involves the detection and identification at the low ng g⁻¹ level of the main thyreostats known to be used for growth promotion by gas chromatography coupled to mass spectrometry (GC-MS). The assay is based on a liquid/liquid extraction of the thyroid gland, derivatization with pentafluorobenzyl bromide (PFBBr), purification on a silica solid phase extraction column and finally a trimethylsilylation prior to GC-MS. Good thyreostat recoveries were obtained (from 40% to 70%) as well as at acceptable repeatability. The target analytes were detectable below the 1 ng g⁻¹ level on a quadrupole mass spectrometer with negative chemical ionization (NCI) using ammonia as reagent gas and the selected ion monitoring (SIM) acquisition mode. This limit of detection was also reached in the SIM high resolution mode. An improved specificity (more diagnostic ions) was obtained under electronic impact (EI) conditions and positive chemical ionization (PCI) with methane as reagent gas. Identification of thyreostats according to the EU (European Union) criteria (93/256/EEC decision) was made on the basis of two independent GC-MS techniques; the limit of identification was close to 5 ng g⁻¹ for most thyreostats, which represents a real improvement for their control.     

Single molecule modulation spectroscopy of conjugated polymers

This paper describes a new single molecule spectroscopy approach for the investigation of triplet-triplet and singlet-triplet interactions in conjugated polymers. The technique involves the irradiation of isolated single, mulitchromophoric, conjugated polymer molecules by a repetitive sequence of variable-intensity microsecond time scale excitation pulses. The fluorescence intensity is synchronously time-averaged for thousands of cycles of the pulse sequence to yield a high signal-to-noise fluorescence transient on the microsecond time scale. The transient can be analyzed with kinetic models to obtain quantitative information about the kinetics of triplet-triplet exciton annihilation and the quenching of singlet excitons by triplet excitons in conjugated polymers.     

Quantum bits with polyacetylene

The dynamics of a polyacetylene single chain as a system for possible physical implementations of quantum bits is determined. This novel proposition is studied by varying intensity and duration of application of an electric field as well as the intensity, number, and position in the polymer chain of impurity molecules. The behavior of soliton pairs, whose associated energy levels form the quantum bit, is analyzed. The chain is modeled by a modified Pariser-Parr-Pople Hamiltonian extended to include the effects of an external electric field and the parameters of the impurity molecules. The effect of the variation of the field and impurities on the separation of the energy levels associated with soliton pairs is analyzed by numerical integration of the equations of motion. Two different approaches for controlling the separation of levels are presented, and their features compared. First, the use of changes in the electric field to control the distance (and ultimately coupling) between two solitons moving freely on the chain or captured by the potential generated by the impurity molecules. Second, the change in the intensity of the impurities alone, with no application of an external field. We have found that the effect of the use of the field on the separation of levels is much smaller than the one obtained by changes in the parameters of the impurity molecules, which eventually led us to achieve quantum bit behavior in a polyacetylene chain. The influence of the field and impurity parameters in the energy levels is determined, as well as their role in the coupling of the two solitons on the chain. Critical values for distance between solitons, intensity of field, and impurities that determine whether a pair of solitons can work as a quantum bit are obtained.     

Controlled clustering and enhanced stability of polymer-coated magnetic nanoparticles

The clustering and stability of magnetic nanoparticles coated with random copolymers of acrylic acid, styrenesulfonic acid, and vinylsulfonic acid has been studied. Clusters larger than 50 nm are formed when the coatings are made using too low or too high molecular weight polymers or using insufficient amounts of polymer. Low-molecular-weight polymers result in thin coatings that do not sufficiently screen van der Waals attractive forces, while high-molecular-weight polymers bridge between particles, and insufficient polymer results in bare patches on the magnetite surface. The stability of the resulting clusters is poor, but when an insufficient polymer is used as primary coating, and a secondary polymer is added to coat remaining bare magnetite, the clusters are stable in high salt concentrations (>5 M NaCl), while retaining the necessary cluster size for efficient magnetic recovery. The magnetite cores were characterized by TEM and vibrating sample magnetometry, while the clusters were characterized by dynamic light scattering. The clustering and stability are interpreted in terms of the particle-particle interaction forces, and the optimal polymer size can be predicted well on the basis of these forces and the solution structure and hydrophobicity of the polymer. The size of aggregates formed by limited polymer can be predicted with a diffusion-limited colloidal aggregation model modified with a sticking probability based on fractional coating of the magnetite cores.     

A mathematical electron

A particle (m) is represented by a Ricci-flat Schwarzschild-basedanalytic enerel (“energy+ ixelectric charge”) geometry X with fundamental form:ds ²=g _αβ dx ^β =(1-2m/r)dt²?(1?2m/r)^?1 dr ² ?r ²(dθ²+sin²θd?²), wherex ^γ=(t, r, θ,?), m=m+ie isenerel, m is rest energy (or mass), and e is electric charge. A unitary vectoru _α and a scalarφ are defined inX by means of the postulated constitutive equation: φu _αβ u ^β+φ_α=0. The normalization condition is postulated as: $$m = \kappa \smallint _0^\pi \smallint _0^\pi \smallint _{ - a}^a \phi \rho g^{{1 \mathord{\left/ {\vphantom {1 2}} \right. \kern-\nulldelimiterspace} 2}} u^0 dr{\text{ }}d\theta {\text{ }}d\varphi $$ whereρ=(R _αβγδ R ^αβγδ )^1/2 is an enerel density function,?=m ²/?c is a normalization constant and also a fine-structure constant,gdetg _αβ =?r ⁴sin² θ, andR _αβγδ is the Riemann curvature tensor formed with complexg _αβ . These equations yield the charge e=0.0855115... of a purely mathematicaleltron (m)=(ie) of radiusa.     

Complexes of Zn(2+), Cd(2+), and Hg(2+) with 2-(alpha-Hydroxybenzyl)thiamine Monophosphate Chloride

The binding sites of Zn(2+), Cd(2+), and Hg(2+) in complexes with 2-(alpha-hydroxybenzyl)thiamine monophosphate chloride, (LH)(+)Cl(-), have been investigated in the solid state [2-(alpha-hydroxybenzyl)thiamin monophosphate chloride monoprotonated at the phosphate group and protonated at N(1)' is denoted as (LH)(+)Cl(-); therefore, the ligand monoprotonated at the phosphate group and deprotonated at N(1)' is L]. Complexes of formulae MLCl(2), M(LH)Cl(3), and (MCl(4))(2)(-)(LH)(2)(+) (M = Zn(2+), Cd(2+), and Hg(2+)) were isolated in aqueous and methanolic solutions, depending on pH. The crystal structure of the complex of formula HgL(2)Cl(2) was solved, together with that of the free ligand (LH)(+)Cl(-), by X-ray crystallography. HgL(2)Cl(2) crystallizes in C2/c, with a = 32.968(6) ?, b = 7.477(2) ?, c = 21.471(4) ?, beta = 118.19(1) degrees, V = 4665(2) ?(3), and Z = 4. (LH)(+)Cl(-) crystallizes in Cc, with a = 10.951(3) ?, b = 17.579(4) ?, c = 13.373(3) ?, beta = 105.36(2) degrees, V = 2482.4(10) ?(3), and Z = 4. Mercury(II) binds to the N(1') of the pyrimidine ring. Both ligands are in the S conformation [Phi(T) = -98.1(9) degrees and Phi(P) = 176.1(10) degrees for HgL(2)Cl(2) and Phi(T) = 104.1(5) degrees and Phi(P) = 171.9(6) degrees for (LH)(+)Cl(-)]. (31)P and (13)C NMR spectra, together with vibrational spectra (IR/Raman), are used to deduce the binding sites of the metal and the protonation states of the ligand at various pH values. It is found that solid-state (31)P NMR spectroscopy is particularly useful in characterizing these complexes as the (31)P shielding tensors are sensitive to the state of the phosphate group. On the other hand, the (31)P NMR spectra indicate that direct bonding between Zn(2+) and Cd(2+) to the phosphate can occur under certain preparation conditions. Solid-state (13)C NMR and vibrational (IR/Raman) spectroscopic results are also in agreement with the other techniques.