Assessment of Carcinogenic Risk and the Delaney Clause: The Search for a Better Standard

This article will focus upon the legislative history and subsequent case law dealing with the Delaney Clause and it will include the rationale and limitations of the provision. In order to regulate carcinogens one must have a clear understanding of the cancer processes. Therefore a brief discussion of the biological parameters involved is warranted. The purpose of this discussion is to find a more rational alternative to the Delaney Clause. The use of quantitative risk assessment as an approach to regulate carcinogens found in food is also discussed. By combining the purposes of the original (and current statutory provisions with current technologies), a more efficient and workable regulation of carcinogens may be effectuated

Unexpected Multiple Coordination Modes in Silyl-Bridged Bis(phosphinine) Complexes

The bis­(phosphinine) [bis­{3-methyl-6-(tri­methyl­silyl)­phosphinine-2-yl}­dimeth­yl­silane] (1) was synthesized and its coordination chemistry explored. Molybdenum and chromium carbonyl complexes were crystallographically characterized featuring 1 bound η6 through one phosphinine [Mo­(CO)3­(η6-1)] (2Mo), η6 through both phosphinines to two metal centers [{M­(CO)3}2­(μ-η6:​η6-1)] (3M2, M = Cr, Mo), and chelating with η1 coordination through both phosphines [M­(CO)4­(κ:η1:​η1-1)] (4M, M = Cr, Mo). However, only 3Mo2 could be isolated analytically pure. Heating species 3Mo2 in the presence of [Pd­(COD)­Cl2] removed one CO ligand and generated [{Mo­(CO)2}­(μ-κ:​η1η6-η6-1)­{Mo­(CO)3}] (5), which is the first crystallized example of a bis­(phos­phinine) featuring chelating η1 and η6 coordination, as well as a metal center bound to two phosphinines with different binding modes. In order to enforce a chelating bis-η1 binding mode, the Ru complex [Ru­(Cp*)­(Cl)­(κ:η1:η1-1)] (6) was prepared, demonstrating that judicious choice of metal fragment can dictate the coordination mode of a bis­(phos­phinine). Conversion of 6 to the hydride species [Ru­(Cp*)­(H)­(κ:η1:​η1-1)] (7) afforded the first crystallographically characterized example of a complex with both phosphinine and hydride ligands at the same metal center

Synthesis, reactivity, and electronic structure of molecular uranium nitrides

The study of metal-ligand multiple bonding offers insight into the electronic structure and bond of metal systems. Until recently, for uranium, such systems were limited to uranyl, and terminal chalcogenide, imide and carbene complexes. In 2012, this was extended to nitrides with the first preparation of a uranium–nitride (U≡N) species isolable under standard conditions, namely [U(TrenTIPS)(N)][Na(12C4)2] (52), which is prepared by the two-electron reduction of sodium azide with a trivalent uranium(III) precursor [U(TrenTIPS)] (15), and the subsequent sequestration and encapsulation of the loosely bound sodium cations. In order to then fully explore the bonding within this newly isolated fragment, alternative routes to prepare uranium–nitrides were investigated, in order to both expand the family of known uranium–nitrides, as well as remove the synthetic bottleneck that occurs due to issues in scale-up. The reduction of the pre-installed azide ligand of [U(TrenTIPS)(N3)] (13) with one-electron external reductants, namely the alkali powders or metals (lithium and sodium, rubidium and caesium) and potassium graphite, affords the dinuclear uranium(V)–nitride species of the form [{U(TrenTIPS)(µ-N)(µ-M)}2] (M = Li, Na, K, Rb, Cs; 51, 106 – 109). Analogously to the preparation of the first terminal uranium–nitride system, encapsulation of the cation affords separated ion pair species of the form [U(TrenTIPS)(N)][M(crown)2] (M = Na, K, Rb, Cs; 52, 114 – 117), or if a slightly larger co-ligand is utilised, capped uranium–nitrides of the form [U(TrenTIPS){(µ-N)(µ-M)(crown)}] (M = Li, Na, K, Rb, Cs; 53, 111 – 113, 118, 119). Oxidation of the separated ion pair nitrides affords the neutral uranium(VI)–nitride, [U(TrenTIPS)(N)] (54). Attempts to prepare dinuclear uranium–nitrides by the reduction of 13 with benzyl potassium (KCH2Ph) afforded instead the cyclometallated species [U{CH2CH(Me)Si(iPr)2NCH2CH2N(CH2CH2NSiiPr3)2}] (110). Unexpectedly, in an inversion of the anticipated reactivity trend, attempts to prepare a thorium congener of 110 did not initially form a cyclometallated species, with the reaction of [Th(TrenTIPS)(I)] (123) and KCH2Ph affording [Th(TrenTIPS)(CH2Ph)] (124); and cyclometallation was thermolytically induced. Computational calculations indicate that this is due to the stabilisation of the σ bond metathesis transition state in the uranium case. A combination of experimental and computational studies allows for the determination of the electronic structure of the families of uranium(V)–nitrides, by considering all the spectroscopic data available for the dinuclear, terminal separated ion pair and capped species in conjunction with ab initio calculations. This approach then leads to a description of the ground and excited states of Tren–uranium(V) nitrides, where [{U(TrenTIPS)(µ-N)(µ-K)}2] (107) and [U(TrenTIPS){(µ N)(µ Na)(15C5)}] (53) exhibit a jz ≈ ±5/2 ground state doublet, with a jz ≈ ±3/2 first excited state doublet, in contrast to all other nitrides studied, where the reverse is the case. The excited states can be derived from spectroscopic data (EPR and UV-vis-NIR), which corroborate these findings. A series of investigations into the small molecule activation chemistry of uranium–nitrides were instigated. The reaction of Tren–uranium(VI) or uranium(V)–nitrides (54, with carbon monoxide resulted in two-electron reductive carbonylation to afford the corresponding uranium(IV)– and uranium(III)–isocyanates, [U(TrenTIPS)(NCO)] (135), [U(TrenTIPS)(NCO)][K(Bn 15C5)2] (136), [U(TrenTIPS){(µ NCO)(µ K)(18C6)}] (137). Reduction of 135 with potassium graphite afforded complete nitrogen atom transfer to eliminate KOCN and generate 15. In the presence of crown, the uranium–nitrogen bond is retained and 136 or 137 can be isolated. A synthetic cycle for the conversion of NaN3 to NaOCN was investigated employing the UIII-UV redox couple by the reaction of 15, NaN3 and CO in pyridine, where one turnover was observed. DFT calculations were used to model these reactions, and they provided evidence for nucleophilic behaviour and explained the difference in the rates of reaction. The reaction of heteroallenes (CE2, E = O, S) with Tren–uranium nitrides was also investigated. It was found that terminal uranium–nitrides react with CO2 to afford uranium–oxo–isocyanates, with retention of uranium oxidation state. In the case of uranium(V), [U(TrenTIPS)(O)(NCO)][K(Bn-15C5)2] (138) is stable, though for uranium(VI), [U(TrenTIPS)(O)(NCO)] (139), a cyanate radical is extruded, which decomposes via diisooxocyan to afford N2 and CO, preparing [U(TrenTIPS)(O)] (122). With CS2, uranium(V)–nitrides undergo overall disproportionation to afford uranium(IV)–trithiocarbonates [U(TrenTIPS)(κ2-CS3)][K(Bn-15C5)2] (140) and [{U(TrenTIPS)(µ-κ2:κ1-CS3)(µ-K)(Bn2-18C6)}2(µ-C6H6)] (141), and uranium(VI)–nitride (54), alongside the formation of [K(crown)n][SCN]. The reaction of 54, which cannot engage in disproportionation chemistry, with CS2 prepares a uranium(IV)–isothiocyanate, [U(TrenTIPS)(NCS)] (142), by the elimination of sulfur, which can be scavenged by triphenylphosphine. Calculations reproduced experimental outcomes, and show that while uranium(V)–nitrides (115) engage in outer sphere type reactivity, uranium(VI)–nitrides (54) instead react via inner sphere mechanisms

Marketing alder and other hardwoods

Many landowners have hardwood trees that appear to be of marketable size. Some of these landowners may want to replace the hardwoods with conifers immediately.Keywords: marketing forest products, hardwoods, AlderFacts and recommendations in this publication may no longer be valid. Please look for up-to-date information in the OSU Extension Catalog: http://extension.oregonstate.edu/catalo

Selling timber and logs : seven steps to success

Published June 1992. Facts and recommendations in this publication may no longer be valid. Please look for up-to-date information in the OSU Extension Catalog: http://extension.oregonstate.edu/catalo

Catalytic peptide hydrolysis by mineral surface: Implications for prebiotic chemistry

Abstract The abiotic polymerization of amino acids may have been important for the origin of life, as peptides may have been components of the first self-replicating systems. Though amino acid concentrations in the primitive oceans may have been too dilute for significant oligomerization to occur, mineral surface adsorption may have provided a concentration mechanism. As unactivated amino acid polymerization is thermodynamically unfavorable and kinetically slow in aqueous solution, we studied mainly the reverse reaction of polymer degradation to measure the impact of mineral surface catalysis on peptide bonds. Aqueous glycine (G), diglycine (GG), diketopiperazine (DKP), and triglycine (GGG) were reacted with minerals (calcite, hematite, montmorillonite, pyrite, rutile, or amorphous silica) in the presence of 0.05 M, pH 8.1, KHCO 3 buffer and 0.1 M NaCl as background electrolyte in a thermostatted oven at 25, 50 or 70°C. Below 70°C, reaction kinetics were too sluggish to detect catalytic activity over amenable laboratory time-scales. Minerals were not found to have measurable effects on the degradation or elongation of G, GG or DKP at 70°C in solution. At 70°C pyrite was the most catalytic mineral with detectible effects on the degradation of GGG, although several others also displayed catalytic behavior. GGG degraded $1.5-4 times faster in the presence of pyrite than in control reactions, depending on the ratio of solution concentration to mineral surface area. The rate of pyrite catalysis of GGG hydrolysis was found to be saturable, suggesting the presence of discrete catalytic sites on the mineral surface. The mineral-catalyzed degradation of GGG appears to occur via a GGG ? DKP + G mechanism, rather than via GGG ? GG + G, as in solution-phase reactions. These results are compatible with many previous findings and suggest that minerals may have assisted in peptide synthesis in certain geological settings, specifically by speeding the approach to equilibrium in environments where amino acids were already highly concentrated, but that minerals may not significantly alter the expected solution-phase equilibria. Thus the abiotic synthesis of long peptides may have required activating agents, dry heating at higher temperatures, or some form of phase separation

The market for waterfowl hunting on private agricultural land in western Oregon

Trends in fee hunting in Oregon are examined, with particular emphasis on waterfowl in the western part of the state. Farmers with potential or existing waterfowl habitat in western Oregon were surveyed about their views on managing their lands for waterfowl. As incentives to such practices, they listed the financial returns from leasing access to hunting, aesthetic appreciation of waterfowl, and personal enjoyment from waterfowl hunting. As deterrents, they listed negative attitudes toward hunters and concerns over lawsuits by hunters. They also identified damage to crops by waterfowl as a source of friction between wildlife agencies and landowners

Managing a fee-recreation enterprise on private lands

Revised November 1995. Facts and recommendations in this publication may no longer be valid. Please look for up-to-date information in the OSU Extension Catalog: http://extension.oregonstate.edu/catalo

The medical student

The Medical Student was published from 1888-1921 by the students of Boston University School of Medicine

Molecular and electronic structure of terminal and alkali metal-capped uranium(V) nitride complexes

Determining the electronic structure of actinide complexes is intrinsically challenging because inter-electronic repulsion, crystal field, and spin–orbit coupling effects can be of similar magnitude. Moreover, such efforts have been hampered by the lack of structurally analogous families of complexes to study. Here we report an improved method to U≡N triple bonds, and assemble a family of uranium(V) nitrides. Along with an isoelectronic oxo, we quantify the electronic structure of this 5f1 family by magnetometry, optical and electron paramagnetic resonance (EPR) spectroscopies and modelling. Thus, we define the relative importance of the spin–orbit and crystal field interactions, and explain the experimentally observed different ground states. We find optical absorption linewidths give a potential tool to identify spin–orbit coupled states, and show measurement of UV···UV super-exchange coupling in dimers by EPR. We show that observed slow magnetic relaxation occurs via two-phonon processes, with no obvious correlation to the crystal field