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151.
The magneto-structural correlation between a Mn(ll) ion, coordinated in an octahedral environment, and two nitronyl nitroxide
radical ligands in trans- and cis-metal-radical complexes is investigated by the broken symmetry (BS) approach within density functional theory (DFT).
The dependences of coupling constants J on three structural parameters: (i) bond angle θ (Mn-O-N (nitroxide)); (ii) rotating angle ψ, defined by the nitronyl nitroxide radical plane rotating around the axial Mn-O (nitroxide); (iii) bond distance R (Mn-O (nitroxide)) are directly calculated. Our calculations showed that both trans- and cis-Mn(ll)-radical complexes behave a stronger antiferromagnetic interaction, consistent with experiments. In view of
molecular orbital theory, the direct exchanges, including σ-type and π-type exchanges, are responsible for the magnetic exchange
pathways. There is a preferable linear correlation between the calculated coupling constants J and the overlap integral squares S b between the local magnetic orbitals at the various rotating angle ψ at the fixed bond angle θ and bond distance R, in both trans- and cis-Mn(ll)-radical complexes. 相似文献
152.
A simplified high-pressure liquid chromatograhic method for determination of furosemide in plasma and urine has been developed using a fluorometric detector directly coupled to the column effluent. The method includes an ether extraction from acidified biologic samples. The mobile phase used for chromatography on a reversed-phase column (C15 hydrocarbon permanently bonded to silica particles) is sufficiently acidic to induce fluorescence of furosemide. The methylester of furosemide is employed as an internal standard. The sensitivity is 0.1 and 0.25 microgram per ml plasma and urine, respectively. The applicability to pharmacokinetic studies of furosemide is shown. 相似文献
153.
154.
Classifying wine according to geographical origin via quadrupole-based ICP–mass spectrometry measurements of boron isotope ratios 总被引:1,自引:0,他引:1
The potential of quadrupole-based ICP–MS as a tool for B-isotopic analysis of wines and its usefulness in provenance determinations
were assessed. A precision of 0.1–0.25% RSD (corresponding to a relative standard deviation of the mean of three replicate
measurements of 0.06–0.12%) was sufficient to establish small differences in the B isotope ratios in wines from different
geographical origins. Each sample measurement was bracketed by measurements of a standard and mass bias drift correction made
by interpolation. Sample preparation was kept to a minimum to avoid possible fractionation. Dilution of the wine samples by
a factor of 100 with 0.65% HNO3 was found to reduce matrix-induced mass discrimination substantially. Wines from three wine-producing regions, Stellenbosch,
Robertson, and Swartland, in the Western Cape Province of South Africa, and wines from specific regions in France (Bergerac)
and Italy (Valpolicella) were analyzed by ICP–QMS for their B-isotopic compositions. It was concluded that the 11B/10B ratios can be used to characterize wines from different geographical origins. Average 11B/10B ratios in red wines from South Africa (Stellenbosch), France (Bergerac), and Italy (Valpolicella) were found to differ by
between 0.5 and 1.5%. 相似文献
155.
Carnitine in Pregnancy 总被引:1,自引:0,他引:1
Alfred?LohningerEmail author H.?Karlic S.?Lohninger A.?Tammaa S.?Jinniate Hermann?Mascher Daniel?Mascher H.?Salzer 《Monatshefte für Chemie / Chemical Monthly》2005,136(8):1523-1533
Summary. By the 12th week of gestation, mean whole blood and plasma carnitine levels are already significantly (p<0.01) lower than those of controls, with a further significant (p<0.01) decrease up to parturition. Diminished carnitine levels may cause a downregulation of carnitine palmitoyltransferase1 (CPT1), both the liver isoform (CPT1A) and muscle isoform (CPT1B), carnitine palmitoyltransferase2 (CPT2), and carnitine acetyltransferase (CRAT) in white blood cells of pregnant women, as determined by real time PCR using the LightCyclerSYBR Green technology.L-Carnitine-L-tartrate supplementation of 2 g/d resulted in an up to 10-fold increase of the relative mRNA abundances of CPT1B, CPT2, and OCTN2 and a 5-fold increase of CPT1A, and CRAT.There is a relationship between the relative mRNA levels of CPT1A and CPT1B and the FFA plasma levels. The substitution of 2 g L-carnitine-L-tartrate/d resulted in significant (p<0.001) lower FFA levels compared to untreated controls and the groups substituted with 0.5 and 1 g L-carnitine/d although plasma carnitine levels were not significantly increased. The most substantial effect was the reduced portion of acylcarnitines on total carnitine in those women receiving 2 g L-carnitine-L-tartrate.Carnitine substitution resulted in an enhanced excretion of both, free carnitine and acylcarnitines, whereas acetylcarnitine accounts for 50–65% of total acylcarnitines.The results of the present study provide evidence that L-carnitine supplementation in pregnancy in sufficient doses avoids a striking increase of plasma FFAs, which are thought to be the main cause of insulin resistance and consequently gestational diabetes mellitus (GDM). 相似文献
156.
It is well known that porphyrin derivatives play a key role in the primary process of photo-synthesis[1], in which porphyrins directly absorb the sunlight or indirectly acquire excitation en-ergy from light-harvesting antenna system to reach their excited state, and then donate electrons to quinone acceptors to yield a series of charge-separated species. In general, only first singlet ex-cited state of porphyrins is involved in energy transfer process[2]. However, highly excited state (S2 stat… 相似文献
157.
Background
Kynureninase is a key enzyme on the kynurenine pathway of tryptophan metabolism. One of the end products of the pathway is the neurotoxin quinolinic acid which appears to be responsible for neuronal cell death in a number of important neurological diseases. This makes kynureninase a possible therapeutic target for diseases such as Huntington's, Alzheimer's and AIDS related dementia, and the development of potent inhibitors an important research aim. 相似文献158.
Summary In this paper an application is presented of the median molecule workflow to the de novo design of novel molecular entities with a property profile of interest. Median molecules are structures that are optimised to be similar to a set of existing molecules of interest as an approach for lead exploration and hopping. An overview of this workflow is provided together with an example of an instance using the similarity to camphor and menthol as objectives. The methodology of the experiments is defined and the workflow is applied to designing novel molecules for two physical property datasets: mean molecular polarisability and aqueous solubility. This paper concludes with a discussion of the characteristics of this method. 相似文献
159.
B. W. Wenclawiak Torsten Hees Corinna E. Z?ller Hans-Peter Kabus 《Fresenius' Journal of Analytical Chemistry》1997,358(4):471-474
An on-line system of supercritical fluid extraction (SFE) and high performance liquid chromatography (HPLC) via solid phase
extraction (SPE) is described for the determination of palladium and rhodium 2,2,6,6-tetramethyl-3,5-heptanedione-(thd) as
well as rhodium-acetylacetonate-(acac) and benzylacetonate-(bzac) chelates. The chelates were extracted with supercritical
CO2 from sand and humic acid, concentrated on SPE cartridges and analysed with HPLC. Two cartridge materials were tested and
compared to off-line trapping. The percentage of the breakthrough and cartridge retained material were measured in liquid
dichloromethane. The SFE conditions could be optimized to separate metal chelates during the extraction. The supercritical
fluid (SF) behaviour of different ligands on rhodium were investigated.
Received: 19 July 1996/Revised: 11 December 1996/Accepted: 14 December 1996 相似文献
160.
Arsenic (As) is a toxic trace element that occurs naturally in groundwater and soils. Understanding the reactions of arsenite
(As(III)) and arsenate (As(V)) with soil and mineral surfaces is critical for predicting the fate and transport of As in the
environment and developing better ways to remediate As-contaminated areas. This investigation uses X-ray absorption near edge
spectroscopy (XANES) to evaluate the solid phase oxidation state and mineral surface binding sites in three agricultural soil
samples from California, USA by fitting linear combinations of XANES spectra derived from several synthetic and well characterized
As(III)- and As(V)-treated model compounds (Fe and Al metal hydroxides and aluminosilicate illite clay mineral). The results
suggest that As(III) is either partially or completely oxidized to As(V) when reacted with soil in an aqueous, batch reaction.
The As(III)-treated Aiken soil was composed of 60% As(III) attached to surfaces similar to lepidocrocite (γ-FeOOH)) and 40%
As(V) attached to aluminosilicate (illite). The Fallbrook soil completely oxidized As(III) and the product was As(V) adsorbed
on Al hydroxide (gibbsite, γ-Al(OH)3) (62%), illite (16%), and lepidocrocite (γ-FeOOH) (22%). The reaction of As(III) with Wyo soil resulted in 42% As(III) adsorbed
on surface similar to goethite and 58% As(V) adsorbed on lepidocrocite. Arsenic(V) adsorption on soil resulted in stable As(V)
surface complexes that were well described by XANES spectra from As(V) adsorption complexes on gibbsite, illite, and lepidocrocite. 相似文献