Hydnellins A and B, nitrogen-containing Terphenyls from the mushrooms Hydnellum suaveolens and Hydnellum geogerirum

Fractionation of methanol extracts of the fruit bodies of two inedible mushrooms Hydnellum suaveolens and Hydnellum geogerirum (Thelephoraceae) resulted in isolation of two new p-terphenyl derivatives named hydnellins A and B and sarcodonin delta possessing N-oxide. Their structures were determined by 2D NMR, IR, UV spectroscopy, and chemical reaction. These terphenyls showed moderate antioxidant activity.     

Evolving P450pyr hydroxylase for highly enantioselective hydroxylation at non-activated carbon atom

Directed evolution of a monooxygenase to achieve very high enantioselectivity for hydroxylation at non-activated carbon atoms is demonstrated for the first time, where a triple mutant of P450pyr hydroxylase is obtained via determination of enzyme structure, iterative saturation mutagenesis, and high-throughput screening with a MS-based ee assay to increase the product ee from 53% to 98% for the hydroxylation of N-benzyl pyrrolidine to (S)-N-benzyl 3-hydroxypyrrolidine.     

Effective pressure-sensitive elastoplastic behavior of particle-reinforced composites and porous media under isotropic loading

The composite under investigation consists of an elastoplastic matrix reinforced by elastic particles or weakened by pores. The material forming the matrix is pressure-sensitive. The Drucker–Prager yield criterion and a one-parameter non-associated flow rule are employed to formulate the yield behavior of the matrix. The objective of this work is to estimate the effective elastoplastic behavior of the composite under isotropic tensile and compressive loadings. To achieve this objective, the composite sphere assemblage model of Hashin [Z. Hashin, The elastic moduli of heterogeneous materials, ASME J. Appl. Mech. 29 (1962) 143–150] is used. Exact solutions are thus derived as estimations for the effective secant and tangent bulk moduli of the composite. The effects of the loading modes and phase properties on the effective elastoplastic behavior of the composite are analytically and numerically evaluated.     

Two-stage dilute-acid pretreatment of softwoods

Whole treechips obtained from softwood forest thinnings were pretreated via single-and two-stage dilute-sulfuric acid pretreatment. Whole-tree chips were impregnated with dilute sulfuric acid and steam treated in a 4-L steam explosion reactor. In single-stage pretreatment, wood chips were treated using a wide range of severity. In two-stage pretreatment, the first stage was carried out at low severity tomaximize hemicellulose recovery. Solubilized sugars were recovered from the first-stage prehydrolysate by washing with water. In the second stage, water-insoluble solids from first-stage prehydrolysate were impregnated with dilute sulfuric acid, then steam treated at more severe conditions to hydrolyze a portion of the remaining cellulose to glucose and to improve the enzyme digestibility. The total sugar yields obtained after enzymatic hydrolysis of two-stage dilute acid-pretreated samples were compared with sugar yields from single-stage pretreatment. The overall sugar yield from two-stage dilute-acid pretreatment was approx 10% higher, and the net enzyme requirement was reduced by about 50%. Simultaneous saccharification and fermentation using an adapted Saccharomyces cerevisiae yeast strain further improved cellulose conversion yield and lowered the enzyme requirement.     

Soft magnetic properties and giant magneto-impedance effect of Fe73.5−xCrxSi13.5B9Nb3Au1 (x=1–5) alloys

In this paper, the effect of microstructural and surface morphological developments on the soft magnetic properties and giant magneto-impedance (GMI) effect of Fe_73.5−xCr_xSi_13.5B₉Nb₃Au₁ (x=1, 2, 3, 4, 5) alloys was investigated. It was found that the Cr addition causes slight decrease in the mean grain size of α-Fe(Si) grains. AFM results indicated a large variation of surface morphology of density and size of protrusions along the ribbon plane due to structural changes caused by thermal treatments with increasing Cr content. Ultrasoft magnetic properties such as the increase of magnetic permeability and the decrease of coercivity were observed in the samples annealed at 540 °C for 30 min. Accordingly, the GMI effect was also observed in the annealed samples.     

Oxidation – Reduction Reactions of Tetrachloroaurate(III) Anion with Triphenyl Derivatives of Group V Elements

The reduction of the tetrachloroaurate (III) anion by L (L = PPh₃, AsPh₃, SbPh₃) is quantitative in non-aqueous solution. The products are the gold(I)-complexes AuClL (L = AsPh₃, SbPh₃) and Au(PPh₃)⁺₂ together with the corresponding oxidation product LCl₂. Kinetic studies show that the reactions are first order in AuCl^?₁ and L. In addition a path independent of PPh₃ was found in dichloromethane. These data are interpreted in terms of mechanisms which involve reduction of AuCl^?₄ to AuCl^?₂ followed by equilibrium formation of AuClL for L = AsPh₃ and SbPh₃. For PPh₃, the data are consistent with a chloride replacement by PPh₃ to give AuCl₃ PPh₃, which is followed by a rapid reduction by a second mole of PPh₃. Equilibrium formation constants are reported for several Au(I) complexes.     

Effects of temperature and moisture on dilute-acid steam explosion pretreatment of corn stover and cellulase enzyme digestibility

Corn stover is emerging as a viable feedstock for producing bioethanol from renewable resources. Dilute-acid pretreatment of corn stover can solubilize a significant portion of the hemicellulosic component and enhance the enzymatic digestibility of the remaining cellulose for fermentation into ethanol. In this study, dilute H₂SO₄ pretreatment of corn stover was performed in a steam explosion reactor at 160°C, 180°C, and 190°C, approx 1 wt% H₂SO₄, and 70-s to 840-s residence times. The combined severity (Log₁₀ [R _o ] - pH), an expression relating pH, temperature, and residence time of pretreatment, ranged from 1.8 to 2.4. Soluble xylose yields varied from 63 to 77% of theoretical from pretreatments of corn stover at 160 and 180°C. However, yields >90% of theoretical were found with dilute-acid pretreatments at 190°C. A narrower range of higher combined severities was required for pretreatment to obtain high soluble xylose yields when the moisture content of the acid-impregnated feedstock was increased from 55 to 63 wt%. Simultaneous saccharification and fermentation (SSF) of washed solids from corn stover pretreated at 190°C, using an enzyme loading of 15 filter paper units (FPU)/g of cellulose, gave ethanol yields in excess of 85%. Similar SSF ethanol yields were found using washed solid residues from 160 and 180°C pretreatments at similar combined severities but required a higher enzyme loading of approx 25 FPU/g of cellulose.     

Polychloroprene. I. Etude de la microstructure par RMN 1H

The microstructure of polychloroprenes was studied by ¹H-NMR at high field (350 MHz). An examination with two solvents, CDCl₃ and C₆D₆, was necessary to show all the addition modes. The complementary information obtained made possible the quantitative determination of head-to-tail, head-to-head, tail-to-tail, trans-1–4, and cis-1–4, 1–2, and 3–4 additions.     

Gas-phase ion–molecule reactions of thioic and dithioic acid derivatives. Condensation reactions with alkenes and alkynes

A Fourier transform–ion cyclotron resonance study of thioacyl compounds as binary mixtures with unsaturated hydrocarbons has revealed that thioacetylium ions CH₃CS⁺ generated by electron fragmentation fail to thioacyl-ate even the most reactive aromatic hydrocarbons. Among the hydrocarbons studied, only 3-hexyne and 2,4-dimethyl-2,5-hexadiene were observed to react with CH₃CS⁺. Apart from proton-transfer reactions, the major ionic reaction of thioesters with arenes, alkynes and alkenes is condensation of the molecular ion of one component, usually the ester, with a neutral molecule of the other, resulting in the cleavage of the S? C_alkyl bond of the thioester. The nature of this reaction is discussed and a possible mechanism is suggested.