A mixed culture was enriched from surface soil obtained from an eastern United States site highly contaminated with chromate. Growth of the culture was inhibited by a chromium concentration of 12 mg/L. Another mixed culture was enriched from subsurface soil obtained from the Hanford reservation, at the fringe of a chromate plume. The enrichment medium was minimal salts solution augmented with acetate as the carbon source, nitrate as the terminal electron acceptor, and various levels of chromate. This mixed culture exhibited chromate tolerance, but not chromate reduction capability, when growing anaerobically on this medium. However, this culture did exhibit chromate reduction capability when growing anaerobically on TSB. Growth of this culture was not inhibited by a chromium concentration of 12 mg/L. Mixed cultures exhibited decreasing diversity with increasing levels of chromate in the enrichment medium. An in situ bioremediation strategy is suggested for chromate contaminated soil and groundwater.
UV photoelectron spectra (UPS) of the cyclic aromatic ethers (1; R = H, n = 1, 2) are compared with each other and with those of non-cyclic ethers. The spectrum of the chroman (1; R = H, n = 2) is clearly distinguishable from those of all the other ethers. The differences in the spectra have been interpreted in terms of differing conjugative effects of oxygen and of “hyperconjugative” effects of methylene with the aromatic ring. These conclusions are supported by MO calculations. The bearing of these differing conjugative effects on reactivity of cyclic aromatic ethers is discussed and the conclusion reached that the orientational preferences customarily explained by the “Mills-Nixon effect” do not depend upon variation of bond lengths or bond angles in the aromatic ring but upon cross-conjugation effects in “Wheland” transition states. 相似文献
The contributions of solute-solute dispersion interactions to binding thermodynamics have generally been thought to be small, due to the surmised equality between solute-solvent dispersion interactions prior to the interaction versus solute-solute dispersion interactions following the interaction. The thermodynamics of binding of primary alcohols to the major urinary protein (MUP-I) indicate that this general assumption is not justified. The enthalpy of binding becomes more favorable with increasing chain length, whereas the entropy of binding becomes less favorable, both parameters showing a linear dependence. Despite the hydrophobicity of the interacting species, these data show that binding is not dominated by the classical hydrophobic effect, but can be attributed to favorable ligand-protein dispersion interactions. 相似文献
Summary Consider estimating the mean vector from dataNn(,2I) withlq norm loss,q1, when is known to lie in ann-dimensionallp ball,p(0, ). For largen, the ratio of minimaxlinear risk to minimax risk can bearbitrarily large ifp. Obvious exceptions aside, the limiting ratio equals 1 only ifp=q=2. Our arguments are mostly indirect, involving a reduction to a univariate Bayes minimax problem. Whenp, simple non-linear co-ordinatewise threshold rules are asymptotically minimax at small signal-to-noise ratios, and within a bounded factor of asymptotic minimaxity in general. We also give asymptotic evaluations of the minimax linear risk. Our results are basic to a theory of estimation in Besov spaces using wavelet bases (to appear elsewhere). 相似文献
Three compounds, thieno[3,2-b]pyridine 4-oxide, 7-nitrothieno[3,2-b]pyridine 4-oxide ( 1 c), and 6-cyano-thieno[2,3-b]pyridine, undergo nitration by means of a mixture of nitric and sulfuric acids to yield 3,7-dinitro-thieno[3,2-b]pyridine (3%), 3,7-dinitrothieno[3,2-b]pyridine 4-oxide ( 1d ) (26%), and 6-carbamoyl-5-nitrothieno[2,3-b]pyridine ( 6b ) (11%), respectively. Structures of the products were ascertained by spectral means, notably infrared, 1H nmr, and 13C nmr. It is proposed that 1d exists (at least in part) as a tricyclic structure and that 6b may result from an intramolecular mechanism of nitration. An attempt to de-N-oxygenate 1c with excess triphenylphosphine removes more than one oxygen atom per molecule (as triphenylphosphine oxide) without producing an identified thienopyridine product. 相似文献
Abstract Attempts to synthesize N-phenylbenzeneselenena mide always produced the isomeric p-aminodiphenyl selenide, probably as a result of an acid catalyzed rearrangement. The ease with which this rearrangement occurs is contrasted with the forcing conditions required for the analogous rearrangement of sulfenamides. 相似文献
Technetium tetrachloride and β-TcCl3, synthesized from the reaction of Tc metal and Cl2(g) in sealed tubes, were characterized by X-ray absorption fine structure spectroscopy. Extended X-ray absorption fine structure (EXAFS) spectroscopy measurements are in good agreement with the X-ray diffraction structures of the two compounds. For TcCl4, the absorbing Tc atom is surrounded by Cl atoms at 2.34(2) Å and Tc atoms at 3.66(4) Å. For β-TcCl3, the absorbing Tc atom is surrounded by Cl atoms at 2.40(2) Å and Tc atoms at 2.81(3), 3.66(4) and 5.71(6) Å. EXAFS spectroscopy indicates that the TcCl4 and β-TcCl3 samples obtained by sealed tube reactions are single phase. The X-ray absorption near edge structure spectra of TcCl4 and β-TcCl3 were recorded; the positions of the Tc K-edges of β-TcCl3 (21,050.5 eV) and TcCl4 (21,053.0 eV) are compared to the ones measured for α-TcCl3 (21,051.0 eV) and TcCl2 (21,048.8 eV). A correlation between the positions of the Tc K-edges and the oxidation state of the Tc atom in technetium binary chlorides was determined. 相似文献
The mixed organic–inorganic title salt, C7H18N2O2+·C2HO4−·Cl−, forms an assembly of ionic components which are stabilized through a series of hydrogen bonds and charge‐assisted intermolecular interactions. The title assembly crystallizes in the monoclinic C2/c space group with Z = 8. The asymmetric unit consists of a 4‐(3‐azaniumylpropyl)morpholin‐4‐ium dication, a hydrogen oxalate counter‐anion and an inorganic chloride counter‐anion. The organic cations and anions are connected through a network of N—H...O, O—H...O and C—H...O hydrogen bonds, forming several intermolecular rings that can be described by the graph‐set notations R33(13), R21(5), R12(5), R21(6), R23(6), R22(8) and R33(9). The 4‐(3‐azaniumylpropyl)morpholin‐4‐ium dications are interconnected through N—H...O hydrogen bonds, forming C(9) chains that run diagonally along the ab face. Furthermore, the hydrogen oxalate anions are interconnected via O—H...O hydrogen bonds, forming head‐to‐tail C(5) chains along the crystallographic b axis. The two types of chains are linked through additional N—H...O and O—H...O hydrogen bonds, and the hydrogen oxalate chains are sandwiched by the 4‐(3‐azaniumylpropyl)morpholin‐4‐ium chains, forming organic layers that are separated by the chloride anions. Finally, the layered three‐dimensional structure is stabilized via intermolecular N—H...Cl and C—H...Cl interactions. 相似文献