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排序方式: 共有196条查询结果,搜索用时 15 毫秒
1.
Leda M. F. Gottschalk Ronaldo Nobrega Elba P. S. Bon 《Applied biochemistry and biotechnology》2003,108(1-3):799-807
The effect of aeration on lignin peroxidase production by Streptomyces viridosporus T7A was studied in a bench-scale bioreactor using a previously optimized growth medium (0.65% yeast extract and 0.1% corn
oil, pH7.0) at 37°C and natural pH. Airflow rates of 0.3, 1.0, and 1.5 vvm and a fixed agitation of 200 rpm were initially
studied followed by 1.0 vvm and 200, 300, 400, and 500 rpm. The use of 1.0 vvm and 400 rpm increased enzyme concentration
1.8-fold (100–180 U/L) and process productivity 4.8-fold (1.4–6.7 U/[L·h]) in comparison with the use of 200 rpm and 0.3 vvm.
The inexpensive corn oil, used as carbon source, besides its antifoam properties, proved to be nonrepressive for enzyme production. 相似文献
2.
Manolis Stratakis Christos Raptis Nikoletta Sofikiti Constantinos Tsangarakis Giannis Kosmas Ioannis-Panagiotis Zaravinos Dimitris Kalaitzakis Dimitris Stavroulakis Constantinos Baskakis Aggeliki Stathoulopoulou 《Tetrahedron》2006,62(46):10623-10632
Depending on the nature of the substituents on the stereogenic carbon atom, the ene reaction of singlet oxygen with several chiral alkenes by confinement within thionin-supported zeolite NaY, may exhibit significant changes on facial selectivity by comparison to their photooxygenation reaction in solution. It is proposed that, apart from the conformational consequences as a result of the alkene confinement within the zeolite cavities, a synergism between Na+-π interactions and singlet oxygen-Na+ interactions plays a significant role in the transition states of ene hydroperoxidation. Within NaY, the diastereoselectivity may significantly depend on the site selectivity, as probed through specific deuterium labelling of trisubstituted alkenes bearing a gem-dimethyl group. In certain cases, a remote stereogenic centre relative to the reacting double bond may induce enhanced diastereoselection and regioselectivity. 相似文献
3.
Christos Kokkinos Anastasios Economou Ioannis Raptis Constantinos E. Efstathiou Thanasis Speliotis 《Electrochemistry communications》2007,9(12):2795-2800
This work describes a novel type of bismuth electrode for stripping voltammetry based on coating a silicon substrate with a thin bismuth film by means of sputtering. The bismuth-based sensors were characterized by optical methods (scanning electron microscopy (SEM), atomic force microscopy (AFM) and X-ray diffraction (XRD)) and as well as by linear sweep voltammetry. Subsequently, the electrodes were tested for the detection of low concentrations of trace metals (Cd(II), Pb(II) and Ni(II)) by stripping voltammetry. Well-formed stripping peaks were observed for trace concentrations of the target analytes demonstrating “proof-of-principle” for these sensors. This type of electrochemical device, utilizing thin-film technology for the formation of the bismuth film, holds promise for future applications in trace metal analysis. 相似文献
4.
Dionysios Raptis Charalampos Livas George Stavroglou Rafaela Maria Giappa Emmanuel Tylianakis Taxiarchis Stergiannakos George E. Froudakis 《Molecules (Basel, Switzerland)》2022,27(11)
The interaction strength of nitrogen dioxide (NO2) with a set of 43 functionalized benzene molecules was investigated by performing density functional theory (DFT) calculations. The functional groups under study were strategically selected as potential modifications of the organic linker of existing metal–organic frameworks (MOFs) in order to enhance their uptake of NO2 molecules. Among the functional groups considered, the highest interaction energy with NO2 (5.4 kcal/mol) was found for phenyl hydrogen sulfate (-OSO3H) at the RI-DSD-BLYP/def2-TZVPP level of theory—an interaction almost three times larger than the corresponding binding energy for non-functionalized benzene (2.0 kcal/mol). The groups with the strongest NO2 interactions (-OSO3H, -PO3H2, -OPO3H2) were selected for functionalizing the linker of IRMOF-8 and investigating the trend in their NO2 uptake capacities with grand canonical Monte Carlo (GCMC) simulations at ambient temperature for a wide pressure range. The predicted isotherms show a profound enhancement of the NO2 uptake with the introduction of the strongly-binding functional groups in the framework, rendering them promising modification candidates for improving the NO2 uptake performance not only in MOFs but also in various other porous materials. 相似文献
5.
G. Knapp S. E. Raptis G. Kaiser G. Tölg P. Schramel B. Schreiber 《Fresenius' Journal of Analytical Chemistry》1981,308(2):97-103
Summary A partially mechanized apparatus made of quartz (Trace-0-Mat) is described that permits the complete mineralization of up to 1 g of organic or biological solid samples. The combustion takes place in pure oxygen in a very small burning chamber (ca. 75 cm3) to subsequently determine metallic and nonmetallic trace elements (1 ng/g) with high reliability. The controllable incineration is started with an IR-radiator system. All volatile trace elements (e.g. Hg, Se, Te, As, Sb, I) are condensed together with the products of the combustion process in a cooling system filled with liquid nitrogen that is mounted on top of the burning chamber. Subsequent refluxing with a suitable acid in a quartz test tube mounted below the burning chamber collects both the volatilized elements from the cooled areas and nonvolatile elements in the ashing residue. The volume of the acid is about 2 ml.The recoveries of the elements following the decomposition process that takes 50–60 min for one sample was checked using 7 NBS-Standard Reference Materials for the elements B, Cr, Cu, Fe, Mn, Zn (ICP-emission spectrometry), Cd, Pb (ETA-AAS), Hg (AAS-cold vapor technique), As (AAS-hydride method) and Se (XRF). Very good agreement with the certified values was observed. This furnished evidence that this new and very general decomposition method is not only poor in blanks but also avoids substantially losses of the elements to be determined by volatilization, adsorption or even baking in the quartz surface. The easy handling of the apparatus offers the best premises for a reliable determination of trace elements in the g/g and ng/g range in most non-volatile organic matrices.
Teilmechanisiertes System zur Verbrennung organischer Proben im Sauerstoffstrom mit quantitativer Wiedergewinnung der Spurenelemente
Zusammenfassung Ein teilmechanisiertes aus Quarz bestehendes System (Trace-0-Mat) wird beschrieben, das die vollständige Mineralisation fester organischer oder biologischer Proben bis zu Mengen von 1 g gestattet. Die Verbrennung findet dabei in reinem Sauerstoff in einer sehr kleinen Verbrennungskammer (etwa 75 cm3) statt, so daß anschließend die metallischen und nichtmetallischen Spurenelemente mit hoher Zuverlässigkeit bestimmt werden können. Die steuerbare Veraschung wird durch ein System von IR-Strahlern gestartet. Alle flüchtigen Spurenelemente (z. B. Hg, Se, Te, As, Sb, I) werden zusammen mit den Verbrennungsprodukten in einem Kühlsystem kondensiert, das mit flüssigem Stickstoff gefüllt und über der Verbrennungskammer angeordnet ist. Die sich an den gekühlten Flächen befindlichen flüchtigen sowie die in der Asche vorhandenen nichtflüchtigen Elemente werden durch Rückflußbehandlung mit einer kleinen Säuremenge (2 ml) gelöst und in einem Quarzglas unterhalb der Verbrennungskammer gesammelt.Die Wiederfindung der Elemente nach dem Aufschlußprozeß (50–60 min) wurde mit Hilfe von 7 NBS-Referenzmaterialien für folgende Elemente geprüft: B, Cr, Cu, Fe, Mn, Zn (ICP-Emissionsspektrometrie), Cd, Pb (ETA-AAS), Hg (AAS-Kaltdampftechnik), As (AAS-Hydridmethode) und Se (Röntgenfluorescenz). Es ergab sich sehr gute Übereinstimmung mit den zertifizierten Werten. Diese neue und sehr allgemein anwendbare Aufschlußmethode weist nicht nur geringe Blindwerte auf, sondern vermeidet auch wesentliche Verluste der zu bestimmenden Elemente durch Verflüchtigung, Adsorption oder Zusammenbacken an der Quarzoberfläche. Durch die einfache Handhabung der Apparatur ist eine zuverlässige Bestimmung von Spurenelementen im g/g- und ng/g-Bereich für die meisten nichtflüchtigen organischen Matrices gewährleistet.相似文献
6.
The seeds of Clitoria fairchildiana provided a new rotenoid, 6-hydroxy-2,3,9-trimethoxy-[1]benzopyrano[3,4-b][1]benzopyran-12(6H)-one. The structural elucidation was performed using detailed analyses of H- and 13C-NMR spectra including 2DNMR spectroscopic techniques (1H-13CHETCOR) and by comparison with spectrometric data from the literature. The anti-inflammatory activity was investigated using a capillary permeability assay. 相似文献
7.
8.
The Caribbean alcyonacean Pseudopterogorgia kallos is shown to contain a novel rearranged pseudopterane diterpene, kallosin A (1), possessing several unusual structural features. In addition to having two distinct 2(3H)- and 2(5H)-furanone moieties, kallosin A is based on a new carbon skeleton. The structural assignment of 1 was based mainly on 1D and 2D NMR spectral data and was further supported by accurate mass measurement and single-crystal X-ray diffraction analysis. 相似文献
9.
10.
A locally finite, causal, and quantal substitute for a locally Minkowskian principal fiber bundle
of modules of Cartan differential forms over a bounded region X of a curved C
-smooth spacetime manifold M with structure group G that of orthochronous Lorentz transformations L
+ := SO(1,3), is presented.
is usually regarded as the kinematical structure of classical Lorentzian gravity when the latter is viewed as a Yang-Mills type of gauge theory of a sl(2, {})-valued connection 1-form
. The mathematical structure employed to model this replacement of
is a principal finitary spacetime sheaf
of quantum causal sets
with structure group G
n, which is a finitary version of the continuous group G of local symmetries of General Relativity, and a finitary Lie algebra g
n-valued connection 1-form
on it, which is a section of its subsheaf
.
is physically interpreted as the dynamical field of a locally finite quantum causality, whereas its associated curvature
as some sort of finitary and causal Lorentzian quantum gravity. 相似文献