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41.
A practical biosensor system has been developed for the determination of urinary glucose using a flow-injection analysis (FIA)
amperometric detector and ion-exchange chromatography. Glucose oxidase was immobilized onto porous aminopropyl glass beads
via glutaraldehyde activation to form an immobilized enzyme column. On the basis of its negative charge at pH 5.5, endogenous
urate in urine samples was effectively retained by an upstream anion-exchange resin column. The biosensor system possessed
a sensitivity of 160 ±2.4 RU μM-1 (RU or relative unit is defined as 2.86 μV at the detection output) for glucose with a minimum detection level of 10 μM.
When applied for the determination of urinary glucose, the result obtained compared very well with that of the widely accepted
hexokinase assay. The immobilized glucose oxidase could be reused for more than 1000 repeated analyses without losing its
original activity. The reuse of the acetate anion-exchange column before replacement would be about 25–30 analyses. Acetaminophen
and ascorbic acid were also effectively adsorbed by the acetate anion exchanger. The introduction of this type of anion exchanger
thus greatly improved the selectivity of the FIA biosensor system and fostered its applicability for the determination of
glucose in urine samples. 相似文献
42.
Keith B. Male John H. T. Luong Michael Trani 《Applied biochemistry and biotechnology》1994,44(1):91-100
Water-soluble 2-hydroxypropyl-β-cyclodextrin (Hp-β-CyD), a cyclic and nonreducing oligosaccharide was used to enclose a hydrophobic guest molecule 1,1′-dimethylferrocene (DMF) to form a water-soluble yellow complex. At high concentrations (300 mM), Hp-β-CyD enclosed up to 100 mM DMF. The yellow complex was electrochemically oxidized (platinum vs Ag/AgCl poised at +450 mV) to form a blue dye, 1,1′-dimethylferricinium (DMF+). This is a one-electron transfer process and the ferricinium cation formed exhibited an absorption peak at 650 nm. The concentrated DMF+ was stable for at least 4 mo at 4°C and insensitive to a wide pH variation (pH 2–11). Application of the novel DMF+ complex as a colorimetric dye for the determination of uric acid in urine was successfully demonstrated. The reaction between the dye and uric acid is almost instantaneous and decrease in absorbance caused by the reduction of 1,1′-dimethylferricinium to 1,1′-dimethylferrocene can be followed at 650 nm. The results obtained agreed well with those of the reference reversed-phase HPLC method. 相似文献
43.
OK Yoon WG Hwang JC Choe MS Kim 《Rapid communications in mass spectrometry : RCM》1999,13(14):1515-1521
A technique to investigate photodissociation kinetics on a nanosecond time scale has been devised for molecular ions generated by multiphoton ionization (MPI) using mass-analyzed ion kinetic energy spectrometry. The branching ratio or rate constant has been determined for the photodissociation of the n-butylbenzene, bromobenzene, iodobenzene, and aniline molecular ions generated by MPI at 266 nm. The ion internal energies have been estimated by comparing the measured kinetic data with the previous energy dependence data. The analysis has shown that only those molecular ions generated by two-photon ionization contribute to the photodissociation signals. Around half of the available energy has been found to remain as molecular ion internal energy in the two-photon ionization process. Copyright 1999 John Wiley & Sons, Ltd. 相似文献
44.
Florent Benaych-Georges Alice Guionnet Camille Male 《Communications in Mathematical Physics》2014,329(2):641-686
We show central limit theorems (CLT) for the linear statistics of symmetric matrices with independent heavy tailed entries, including entries in the domain of attraction of α-stable laws and entries with moments exploding with the dimension, as in the adjacency matrices of Erdös-Rényi graphs. For the second model, we also prove a central limit theorem of the moments of its empirical eigenvalues distribution. The limit laws are Gaussian, but unlike the case of standard Wigner matrices, the normalization is the one of the classical CLT for independent random variables. 相似文献
45.
Dr. Marie Betou Dr. Louise Male Prof. Jonathan W. Steed Dr. Richard S. Grainger 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(21):6505-6517
In an approach to the biologically important 6‐azabicyclo[3.2.1]octane ring system, the scope of the tandem 4‐exo‐trig carbamoyl radical cyclization—dithiocarbamate group transfer reaction to ring‐fused β‐lactams is evaluated. β‐Lactams fused to five‐, six‐, and seven‐membered rings are prepared in good to excellent yield, and with moderate to complete control at the newly formed dithiocarbamate stereocentre. No cyclization is observed with an additional methyl substituent on the terminus of the double bond. Elimination of the dithiocarbamate group gives α,β‐ or β,γ‐unsaturated lactams depending on both the methodology employed (base‐mediated or thermal) and the nature of the carbocycle fused to the β‐lactam. Fused β‐lactam diols, obtained from catalytic OsO4‐mediated dihydroxylation of α,β‐unsaturated β‐lactams, undergo semipinacol rearrangement via the corresponding cyclic sulfite or phosphorane to give keto‐bridged bicyclic amides by exclusive N‐acyl group migration. A monocyclic β‐lactam diol undergoes Appel reaction at a primary alcohol in preference to semipinacol rearrangement. Preliminary investigations into the chemo‐ and stereoselective manipulation of the two carbonyl groups present in a representative 7,8‐dioxo‐6‐azabicyclo[3.2.1]octane rearrangement product are also reported. 相似文献
46.
Jasna Malešič Martin Šala Vid Simon Šelih Drago Kočar 《Cellulose (London, England)》2014,21(4):2925-2936
Iron gall ink was the most widely used writing ink for paper from the Middle Ages to the twentieth century. Unfortunately, the ink ingredients contain corrosive transition metal ions and acids that cause severe damage to the paper carrier. New or improved paper conservation methods for iron gall ink stabilization are constantly sought. The aim of the study was evaluation of a recently proposed stabilization treatment, adapted to lower relative humidity, applied to various model and historical paper samples containing iron gall ink. The effect of stabilization treatment on paper samples during artificial thermal aging was followed by the determination of the molecular weight distribution by size exclusion chromatography and colorimetry. Migration of iron and copper compounds from the ink lines was monitored by laser ablation inductively coupled plasma mass spectrometry. The results demonstrate that effective stabilization of iron gall ink-containing paper can be successfully achieved by interleaving with papers impregnated with the antioxidant tetrabutylammonium bromide and alkaline buffer under experimental conditions. Negative side effects of the stabilization treatment, such as migration of iron or copper ions from the ink lines and changes of color after the treatment and after accelerated thermal degradation, were limited, proving that the proposed stabilization treatment can be considered for future use by conservators. 相似文献
47.
Keith B. Male Mahsa HamzehJohnny Montes Alfred C.W. LeungJohn H.T. Luong 《Analytica chimica acta》2013
Titanium dioxide (TiO2) nanoparticles (NPs) with different sizes and structures were probed for plausible cytotoxicity using electric cell-substrate impedance sensing (ECIS), a non-invasive and on-line procedure for continuous monitoring of cytotoxicity. For insect cells (Spodoptera frugiperda Sf9), the ECIS50 values, i.e., the concentration required to achieve 50% inhibition of the response, differed depending on the size and shape of the TiO2 nanostructure. The lowest ECIS50 value (158 ppm) was observed for the needle shaped rutile TiO2 (10 nm × 40 nm, 15.5 nm nominal particle size), followed by 211 ppm for P-25 (34.1 nm, 80% anatase and 20% rutile), 302 ppm for MTI5 (5.9 nm, 99% anatase) and 417 ppm for Hombitan LW-S bulk TiO2 (169.5 nm, 99% anatase). Exposure of TiO2 NPs to UV light at 254 nm or 365 nm exhibited no significant effect on the ECIS50 value due to the aggregation of TiO2 NPs with diminishing photocatalytic activities. Chinese hamster lung fibroblast V79 cells, exhibited no significant cytotoxicity/inhibition up to 400 ppm with P25, MTI5 and bulk TiO2. However, a noticeable inhibitory effect was observed (ECIS50 value of 251 ppm) with rutile TiO2 as cell spreading on the electrode surface was prevented 相似文献
48.
Jason T Miller John H Bartley Hereward JC Wimborne Aisha L Walker David C Hess William D Hill James E Carroll 《BMC neuroscience》2005,6(1):63
Background
Stromal cell-derived factor 1 (SDF-1 or CXCL12) is chemotaxic for CXCR4 expressing bone marrow-derived cells. It functions in brain embryonic development and in response to ischemic injury in helping guide neuroblast migration and vasculogenesis. In experimental adult stroke models SDF-1 is expressed perivascularly in the injured region up to 30 days after the injury, suggesting it could be a therapeutic target for tissue repair strategies. We hypothesized that SDF-1 would be expressed in similar temporal and spatial patterns following hypoxic-ischemic (HI) injury in neonatal brain. 相似文献49.
Vundać Vjera Bilušić Maleš Željan Plazibat Miško Golja Petra Cetina-Čižmek Biserka 《平面色谱法杂志一现代薄层色谱法》2005,18(4):269-273
JPC – Journal of Planar Chromatography – Modern TLC - Stachys is a large genus belonging to the family Lamiaceae. In common with many other representatives of this family, the aerial... 相似文献
50.