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251.
Junker BH Mann Z Seeley A Zhang J Greasham R 《Applied biochemistry and biotechnology》2002,97(2):63-78
A defined medium and fed-batch feeding process for the production of a yeast biocatalyst, developed at the 23-L scale, was scaled up to the 600-L pilot scale. Presterilized 100-L-vol plastic bags were implemented for the pilot-scale nutrient feeding. Medium of increased concentration Oqs implemented at the pilot scale, and equivalent dry cell weights were reached with a medium 80% more concentrated than that used at the laboratory scale. The higher medium concentration was believed to be necessary at the pilot scale owing to the additional heat stresses on key components (e.g., complexing of magnesium sulfate with phosphate), increased dilution during sterilization, lower evaporation rate owing to the lower vessel volume per minute air flow rate, and increased dilution owing to nutrient feeding or shot additions. Peak cell density was found to be somewhat insensitive to variations in residual glucose levels. These results suggest that defined medium developed at the laboratory scale may need to be further optimized at the pilot scale for equivalent performance. 相似文献
252.
Hemaka A. Rajapakse Mary Beth Young Samantha Charlton Nancy N. Tsou 《Tetrahedron letters》2005,46(51):8909-8912
An asymmetric route to dihydroquinazolinones via the addition of ortho metalated substrates to tert-butanesulfinyl imines is reported. The scope of the nucleophile and electrophile components and the absolute stereochemical outcome are presented. 相似文献
253.
Abstract— Ultraviolet radiation produces free radicals in Skh-1 mouse skin, contributing to photoaging and carcinogenesis. If a mouse model is a general indicator of free radical processes in human skin photobiology, then radical production observed in mouse and human skin should be directly comparative. In this work we show that UV radiation (Λ > 300 nm, 14 μW/cm2 UVB; 3.5 mW/cm2 UVA) increases the ascorbate free radical (Asc.-) electron paramagnetic resonance (EPR) signal in both Skh-1 mouse skin (45%) and human facial skin biopsies (340%). Visible light (Λ > 400 nm; 0.23 mW/cm2 UVA) also increased the Asc.- signal in human skin samples (45%) but did not increase baseline mouse Asc.-, indicating that human skin is more susceptible to free radical formation and that a chromophore for visible light may be present. Using EPR spin-trapping techniques, UV radiation produced spin adducts consistent with trapping lipid alkyl radicals in mouse skin (α-[4-pyridyl 1-oxide]-N-tert-butyl nitrone/alkyl radical adduct; aN= 15.56 G and aH= 2.70 G) and lipid alkoxyl radicals in human skin (5,5-dimethylpyrroline-l-oxide/alkoxyl radical adduct; aN= 14.54 G and aH= 16.0 G). Topical application of the iron chelator Desferal to human skin significantly decreases these radicals (±50%), indicating a role for iron in lipid peroxidation; Desferal has previously been shown to decrease radical production in mouse skin. This work supports the use of the Skh-1 mouse as a predictive tool for free radical formation in human skin. These results provide the first direct evidence for UV radiation-induced free radical formation at near physiological temperatures in human skin and suggest that iron chelators may be useful as photoprotective agents. 相似文献
254.
The electrical conductivity of nominally pure K2FeCl5·H2O and anhydrous K2AlF5 has been studied from 300 to 690°K. K2FeCl5·H2O exhibits mixed ionic and electronic conduction, whereas K2AlF5 is a pure ionic conductor. The mass and charge transport processes in K2FeCl5·H2O seem to be governed by deviations from both molecularity and stoichiometry. At elevated temperatures both potassium and chloride ions are mobile in K2FeCl5·H2O. 相似文献
255.
Wolfgang A. Herrmann John M. Huggins Christine Bauer Manfred L. Ziegler Heike Pfisterer 《Journal of organometallic chemistry》1984,262(2):253-262
The μ-ethylidene complex (μ-CHCH3)[(η5-C5Me5)Co(μ-CO)]2 (Me CH3) accessible along the diazoalkane route from [(η5-C5Me5)Co(μ-CO)]2 and diazoethane exhibits both in solution (IR spectroscopy) and in the crystalline state (X-Ray diffraction) a nearly Cs-symmetrical structure with a triply bridged metal—metal bond. This compound thus differs from the parent μ-methylene complex of analogous composition, which latter compound exists as a mixture of the isomers A and B with terminal and edge-bridging carbonyl ligands, respectively (IR spectra, X-Ray diffraction). A structural comparison with closely related alkylidene- and carbonyl-bridged derivatives reveals a striking lack of correlation between metal—metal bond lengths and formal bond orders as they result from the EAN rule. 相似文献
256.
Gerald De Leeuw John S. Field Raymond J. Haines Beth McCullouch Elsie Meintjies Christiaan Monberg Kandasamy G. Moodley Gillian M. Olivier Clifford N. Sampson Nick D. Steen 《Journal of organometallic chemistry》1982,228(3):C66-C70
Bis- and, in particular, tetra-substituted ditertiary phosphine and diphosphazane derivatives of [Fe2(CO)9] and [Ru2(CO)9], readily synthesised by reaction of the appropriate bidentate ligand with [Fe2(CO)9] and [Ru3(CO)12], respectively, are very susceptible to electrophilic attack by reagents such as halogens and protons; the solid state structure of one of the products [Fe2(μ-Br)(CO)4 {μ-(PhO)2PN(Et)P(OPh)2}2]PF6 has been determined by X-ray crystallography. 相似文献
257.
(4Z)-9-(5-Carboxypentyl)-2,3,7,8-tetramethyl-(10H)-dipyrrin- 1-one (1, semirubin), a new dipyrrinone model for one-half of bilirubin, the yellow-orange neurotoxic pigment of jaundice, was synthesized following Friedel-Crafts acylation of 2,3,7, 8-tetramethyl-(10H)-dipyrrin-1-one (5) with the half-ester acid chloride of adipic acid. Unlike other dipyrrinone models for bilirubin, such as the xanthobilirubic acids, which engage only in intermolecular hydrogen bonding, 1 is unique in having been designed and found to engage in intramolecular hydrogen bonding, between the carboxylic acid and the dipyrrinone lactam and pyrrole. This important conformation-determining structural characteristic, shared by 1 and bilirubin, renders them less polar than their methyl esters and leaves them monomeric in nonpolar solvents, where their esters are dimeric. The corresponding 10-oxo analogue (3) of 1 serves as a model for 10-oxo-bilirubin, a presumed bilirubin metabolite in alternate pathways for bilirubin excretion. Like 1, 3 is found to engage in intramolecular hydrogen bonding. Unlike the methyl ester of 1, the ethyl ester of 3 is not intermolecularly hydrogen bonded in nonpolar solvents. 相似文献
258.
Keith G. Orrell Vladimir Šik Carl H. Brubaker Beth McCulloch 《Journal of organometallic chemistry》1984,276(2):267-279
The stereodynamics of ferrocenylsulphide-palladium(II) and -platinum(II) complexes, Fe(C5H4SR)2MX2, (M = PdII, PtII; X = Cl, Br; R = Ph, i-Pr and i-Bu), have been examined by variable temperature NMR. At temperatures down to ca. ?100° C, the pyramidal inversion of the S atoms could be slowed down sufficiently to yield accurate energy data, while the reversal of the ferrocenophane ring remained fast on the NMR time scale. ΔG≠ data for the S inversion process were in the range 47 to 65 kJ mol?1 and were influenced to varying extents by the nature of the transition metal, the halogen, and the R substituent on the sulphur. 相似文献
259.
Bender R Braunstein P Dedieu A Ellis PD Huggins B Harvey PD Sappa E Tiripicchio A 《Inorganic chemistry》1996,35(5):1223-1234
Two isomers of the phosphido-bridged platinum cluster Pt(3)(&mgr;-PPh(2))(3)Ph(PPh(3))(2) (2 and 3) have been isolated, and their structures have been solved by single-crystal X-ray diffraction. Compound 2 crystallizes in the orthorhombic space group Cmc2(1) with a = 22.192(10) ?, b = 17.650(9) ?, c = 18.182(8) ?, and Z = 4. Compound 3 crystallizes with 2 molecules of dichloromethane in the monoclinic space group C2/c with a = 21.390(10) ?, b = 18.471(9) ?, c = 19.021(11) ?, beta = 105.27(5) degrees, and Z = 4. The two isomers differ essentially in their metal-metal distances and Pt-(&mgr;-PPh(2))-Pt angles. Thus 2, having an imposed C(s) symmetry, contains a bent chain of metal atoms with two short Pt-Pt distances of 2.758(3) ? and a long separation of 3.586(2) ?. In 3, which has an imposed C(2) symmetry, the metal atoms form an isosceles triangle with two Pt-Pt distances of 2.956(3) ? and one of 3.074(4) ?. These isomers can be smoothly interconverted by changing the crystallization solvents. Solution and solid-state (31)P NMR studies have been performed in order to assign the resonances of the different P nuclei and relate their chemical shifts with their structural environments. Raman spectroscopy was used to assign the nu(Pt-Pt) modes of the two structural isomers. Theoretical studies based on extended Hückel calculations and using the fragment molecular orbital approach show that the isomer with the three medium Pt-Pt distances is slightly more stable, in agreement with earlier theoretical predictions. Cluster core isomerism remains a rare phenomenon, and the present example emphasizes the role and the importance of flexible phosphido bridges in stabilizing clusters as well as the unprecedented features which can be observed in phosphine phosphido-rich metal clusters. 相似文献
260.
Dr. Mary K. Burdette-Trofimov Beth L. Armstrong Dr. Ryan P. Murphy Luke Heroux Dr. Mathieu Doucet Stephen E. Trask Alexander M. Rogers Dr. Gabriel M. Veith 《Chemphyschem》2021,22(11):1049-1058
This work probes the slurry architecture of a high silicon content electrode slurry with and without low molecular weight polymeric dispersants as a function of shear rate to mimic electrode casting conditions for poly(acrylic acid) (PAA) and lithium neutralized poly(acrylic acid) (LiPAA) based electrodes. Rheology coupled ultra-small angle neutron scattering (rheo-USANS) was used to examine the aggregation and agglomeration behavior of each slurry as well as the overall shape of the aggregates. The addition of dispersant has opposing effects on slurries made with PAA or LiPAA binder. With a dispersant, there are fewer aggregates and agglomerates in the PAA based silicon slurries, while LiPAA based silicon slurries become orders of magnitude more aggregated and agglomerated at all shear rates. The reorganization of the PAA and LiPAA binder in the presence of dispersant leads to a more homogeneous slurry and a more heterogeneous slurry, respectively. This reorganization ripples through to the cast electrode architecture and is reflected in the electrochemical cycling of these electrodes. 相似文献