Functional mimic of dioxygen-activating centers in non-heme diiron enzymes: mechanistic implications of paramagnetic intermediates in the reactions between diiron(II) complexes and dioxygen

Two tetracarboxylate diiron(II) complexes, [Fe(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)(C(5)H(5)N)(2)] (1a) and [Fe(2)(mu-O(2)CAr(Tol))(4)(4-(t)BuC(5)H(4)N)(2)] (2a), where Ar(Tol)CO(2)(-) = 2,6-di(p-tolyl)benzoate, react with O(2) in CH(2)Cl(2) at -78 degrees C to afford dark green intermediates 1b (lambda(max) congruent with 660 nm; epsilon = 1600 M(-1) cm(-1)) and 2b (lambda(max) congruent with 670 nm; epsilon = 1700 M(-1) cm(-1)), respectively. Upon warming to room temperature, the solutions turn yellow, ultimately converting to isolable diiron(III) compounds [Fe(2)(mu-OH)(2)(mu-O(2)CAr(Tol))(2)(O(2)CAr(Tol))(2)L(2)] (L = C(5)H(5)N (1c), 4-(t)BuC(5)H(4)N (2c)). EPR and M?ssbauer spectroscopic studies revealed the presence of equimolar amounts of valence-delocalized Fe(II)Fe(III) and valence-trapped Fe(III)Fe(IV) species as major components of solution 2b. The spectroscopic and reactivity properties of the Fe(III)Fe(IV) species are similar to those of the intermediate X in the RNR-R2 catalytic cycle. EPR kinetic studies revealed that the processes leading to the formation of these two distinctive paramagnetic components are coupled to one another. A mechanism for this reaction is proposed and compared with those of other synthetic and biological systems, in which electron transfer occurs from a low-valent starting material to putative high-valent dioxygen adduct(s).     

Efficient protiodesilylation of unactivated C(sp3)-SiMe2Ph bonds using tetrabutylammonium fluoride

[reaction: see text] The protiodesilylation of unactivated C(sp3)-SiMe2Ph bonds proceeds efficiently by treatment with tetrabutylammonium fluoride in wet DMF or THF via isolable dimethylsilanol intermediates.     

O=P(i‐PrNCH2CH2)3NCH3+: Novel effect of quaternization on the structural metrics of the bicyclic cage

The title cation features the longest distance between the bridgehead atoms (3.56 Å) so far recorded for phosphatrane cages despite a nontetrahedral CN_brigeheadC angle (∼114°). The 70.8° N_bridgeheadCCN torsion angles in the bridging moieties produce a substantial twist along the C₃ axis of the structure that does not easily allow racemization of the cage. The resulting rigidity of the twisted cage gives rise to AB patterns for the methylene protons of this cation and its analogues. © 1999 John Wiley & Sons, Inc. Heteroatom Chem 10:255–258, 1999     

Ion-molecule reactions of oxygenated chemical ionization reagents with vincamine

The ion-molecule reactions of ions from acetone, dimethyl ether, 2-methoxyethanol, and vinyl methyl ether with vincamine were investigated. Reactions with dimethyl ether result in [M+13]⁺ and [M+45]⁺ products, reactions with 2-methoxyethanol produce [M+13]⁺ and [M+89]⁺ ions, and reactions with acetone or vinyl methyl ether ions generate predominantly [M+43]⁺ ions. Collision-activated dissociation and deuterium labeling experiments allowed speculation about the product structures and mechanisms of dissociation. The methylene substitution process was shown to occur at the hydroxyl oxygen and the phenyl ring of vincamine for dimethyl ether reactions, but the methylene substitution process was not favored at the hydroxyl oxygen for the 2-methoxyethanol reactions, instead favored at the 12 phenyl position. The reaction site is likely different for the 2-methoxyethanol ion due to its capability for secondary hydrogen-bonding interactions. For the [M+45]⁺ and [M+89]⁺ ions, evidence suggests that charge-remote fragmentation processes occur from these products. In general, the use of dimethyl ether ions or 2-methoxyethanol ions for ionmolecule reactions prove highly diagnostic for the characterization of vincamine; both molecular weight and structural information are obtained. Limits of detection for vincamine with dimethyl ether chemical ionization via this technique on a benchtop ion trap gas chromatography-tandem mass spectrometer are in the upper parts per trillion range.     

Identification and Linkage of Tarballs from the Coasts of Vancouver Island and Northern California Using GC/MS and Isotopic Techniques

During January and February 1996, a significant number of tarball/patty incidents occurred along the coasts of Vancouver Island, Washington, Oregon, and California. Samples of the tarballs were collected from the affected beaches and analyzed by gas chromatography/mass spectrometry (GC/MS) and gas chromatography/flame ionization detector (GC/FID) using a tiered analytical approach developed for determining the origin of oils. Selected samples were further analyzed using a carbon isotopic technique. Also, the relative abundances of a large number of “source-specific marker” compounds, in particular alkylated series of polycyclic aromatic hydrocarbons within the same alkylation isomeric groups, were compared. Results of the analysis revealed that (1) California/Oregon samples were chemically similar and consistent with the same source. They were identified to be bunker type fuel; (2) The tarball samples collected from British Columbia and Ocean Shores, Washington were chemically similar and consistent with the same source (also bunker type fuel). They were found to be similar to but may have a source different than the California/Oregon samples; (3) The source of the tarball/patty samples was neither Alaska North Slope oil nor California Monterrey Miocene oil; (4) The spilled oil samples have been highly weathered since release, and the California samples were more heavily weathered than the British Columbia samples.     

Optimization of Graphene Layers Grown on Pt/Ti/SiO2 by Hot Filament Chemical Vapor Deposition

Large area single and bilayer graphene are grown on Pt/Ti/SiO₂ substrates by hot filament chemical vapor deposition (HFCVD) with and without the assistance of Cu foil. The quality and number of graphene layers deposited on the substrate are assessed by Raman Spectroscopy. Atomic Force Microscopy (AFM) is used for assessing the surface topography of the graphene films grown on the Pt/Ti/SiO₂ substrates. The microstructure and elemental analyses are performed by Scanning Electron Microscopy (SEM) and Energy Dispersive Spectroscopy (EDS). The results show that bilayer graphene growth is facilitated by a copper foil placed nearby Pt/Ti/SiO2 substrate and by a high filament temperature in the HFCVD reactor. Monolayer graphene grows only when no copper foil is placed near the Pt/Ti/SiO₂ substrate at a low filament temperature. The approach paves a novel pathway towards the layer-controlled growth of graphene on Pt/Ti/SiO₂ substrates by HFCVD for frontier applications.     

Internal pulsed valve sample introduction on a quadrupole ion trap mass spectrometer

A pulsed valve positioned just outside the ion trap electrodes (within the vacuum chamber) has been characterized. The observed gas pulse widths and the maximum ion intensities were found to decrease as the distance between the pulsed valve and the ion trap electrodes increased. An explanation is presented within. The pulsed valve was found to impart temporal separation in ion-molecule reactions by permitting the removal of interfering neutrals. Other factors that affect the degree of temporal separation also are presented.     

Strobovideolaryngoscopy in the management of acute laryngeal trauma

Surgical intervention in the management of acute laryngeal trauma can sometimes pose a difficult decision. The objective of this study is to evaluate the effectiveness of strobovideolaryngoscopy (SVL) in determining the course of management for patients sustaining acute laryngeal trauma. A 20-year retrospective study of patients presenting with acute laryngeal trauma was performed in order to determine if the addition of SVL during the study period changed the management of certain acute laryngeal injuries. Patients sustaining blunt laryngeal trauma evaluated at our institution from 1981 to the present were reviewed. There were 40 patients identified that were grouped by severity according to the Schaefer classification. Analysis included mechanism of injury, clinical presentation, assessment, treatment, and outcome. Group 1 injuries were the most common, with motor vehicle accident (MVA) the most frequent mechanism of injury. Initial assessment included fiberoptic laryngoscopy and computed tomography (CT) imaging in all patients not requiring immediate exploration. SVL was used in 20 patients, with 7 undergoing stroboscopy within 24 hours of presentation. All 7 patients were managed conservatively without surgical intervention or the need to establish an alternative airway. SVL improves the clinical assessment of patients with acute laryngeal injury. This study supports its use and found it to be an important factor in determining the need for surgical intervention. SVL may also shorten the hospital stay in these patients.     

Products of Hecke eigenforms

Let f(z) and g(z) be Hecke eigenforms for Γ₀(p), where p is a prime. If both f(z) and g(z) are non-cuspidal forms and p?7, then the product is a Hecke eigenform only if it comes trivially from a level 1 solution. If g(z) is a cuspform and p?5, then in addition to the level 1 solutions, there are 8 new cases where the product of Hecke eigenforms is a Hecke eigenform.     

Generalizing the notion of Koszul algebra

We introduce a generalization of the notion of a Koszul algebra, which includes graded algebras with relations in different degrees, and we establish some of the basic properties of these algebras. This class is closed under twists, twisted tensor products, regular central extensions and Ore extensions. We explore the monomial algebras in this class and we include some well-known examples of algebras that fall into this class.