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971.
An experiment was developed as a simple alternative to existing analytical methods for the simultaneous quantitation of glucose (substrate) and glucuronic acid (main product) in the bioprocesses Kombucha by using FTIR spectroscopy coupled to multivariate calibration (partial least-squares, PLS-1 and artificial neural networks, ANNs). Wavelength selection through a novel ranked regions genetic algorithm (RRGA) was used to enhance the predictive ability of the chemometric models. Acceptable results were obtained by using the ANNs models considering the complexity of the sample and the speediness and simplicity of the method. The accuracy on the glucuronic acid determination was calculated by analysing spiked real fermentation samples (recoveries ca. 115%). 相似文献
972.
The present work demonstrates the importance of the ionic composition in the BGE for enantioseparation. (-)-2,3:4,6-di-O-Isopropylidene-2-keto-L-gulonic acid ((-)-DIKGA) has been used as the chiral selector in methanolic and ethanolic BGEs. The influence of added alkali metal hydroxides on the EOF and the chiral separation of amines (atenolol, isoprenaline, pindolol and propranolol) have been studied. The ion-pair formation constants in ethanol were determined by precision conductometry for the enantiomers of pindolol with (-)-DIKGA, for Li(+), Na(+) and Cs(+) with (-)-DIKGA, and also for the corresponding alkali metal hydroxides. The effective mobilities and the enantiomeric mobility differences were affected by the type of alkali metal hydroxide (LiOH, NaOH, KOH, RbOH or CsOH) added to the BGE. The effective mobility and mobility difference were increased with decrease in solvated radius of the alkali metal cation. These differences could partly be correlated to the ion-pair formation constants of the alkali metal cations with the chiral selector, affecting the equilibrium concentration of the free selector. The electroosmosis was also affected by the alkali metal hydroxide added to the BGE. The cathodic electroosmosis decreased with decreasing solvated radius of the alkali metal cation added to the BGE. Interestingly, the cathodic EOF was even reversed, i.e. became anodic in the ethanolic BGEs containing KOH, RbOH or CsOH and the methanolic ones with RbOH and CsOH. 相似文献
973.
Lindberg P Dahlin AP Bergström SK Thorslund S Andrén PE Nikolajeff F Bergquist J 《Electrophoresis》2006,27(11):2075-2082
This study presents a microbead-packed PDMS microchip with an integrated electrospray emitter for sample pretreatment prior to sheathless ESI-MS. We prove the concept of analytical functions integrated onto a cm-sized area of a single bulk material. The microchip consists of two PDMS substrates replicated from SU-8 fabricated silicon wafer masters, bonded together after oxidation by corona discharge treatment. The channel within the microchip contains a grid structure that was used to trap 5 microm hypercross-linked polystyrene beads. The beads acted as a medium for sample desalting and enrichment. Electrical contact for the sheathless ESI process was achieved by coating the integrated emitter with conductive graphite powder after applying a thin layer of PDMS as glue. The coating as well as the bond of the PDMS structures showed excellent durability. A continuous spray was obtained from the microchip for over 800 h in a long-term electrospray stability experiment. Desalting and enrichment of neuropeptides from a physiological salt solution was successful by loading the sample onto the packed beads, followed by a washing and an eluting step. The results were obtained and evaluated using a TOF MS. An LOD of approximately 20 fmol (loaded onto the beads) for angiotensin II was obtained from a sample of neuropeptides dissolved in physiological salt solution. 相似文献
974.
[STRUCTURE: SEE TEXT] The rates of oxidative addition of phenyl bromide to [Pd(BINAP)2] have been measured in the presence and absence of added amine to assess a previous hypothesis that addition to [Pd(BINAP)(amine)] is faster than addition to [Pd(BINAP)]. These data show that addition to the amine complex is not faster than addition to [Pd(BINAP)]. Instead, they are consistent with oxidative addition, even in the presence of amine, to [Pd(BINAP)] as the major pathway. These data underscore the value of studying the stoichiometric reactions of isolated complexes when assessing the mechanism of a catalytic process. 相似文献
975.
Sennbro CJ Olin M Edman K Hansson G Gunnarsson PO Svensson LD 《Rapid communications in mass spectrometry : RCM》2006,20(22):3313-3318
Laquinimod (ABR-215062) is a synthetic compound currently undergoing clinical development for oral treatment of multiple sclerosis. The present paper describes the development, validation and clinical application of two rapid and sensitive methods for the determination of ABR-215062 in human plasma. Both methods use liquid chromatography/tandem mass spectrometry (LC/MS/MS) with electrospray ionization in positive mode and a stable isotope (13C6)-labeled ABR-215062 as internal standard for calibration. The selected reaction monitoring was based on the transitions m/z 357.1 --> 236.1 for ABR-215062, and either m/z 363.2 --> 236.1 or 365.2 --> 238.1 for 13C6-ABR-215062. Method 1, aimed and validated for low level determinations (0.4-100 nmol/L) of ABR-215062, utilizes solid-phase extraction followed by isocratic elution. Method 2, aimed and validated for wide range determinations (0.75-15000 nmol/L) of ABR-215062, utilizes protein precipitation followed by fast gradient elution. The methods were validated with respect to selectivity, lower limit of quantification (LLOQ), dynamic range, precision, accuracy, extraction recovery and ruggedness. Furthermore, the stability of low level ABR-215062 in plasma was investigated. The methods were also applied in clinical trials. The LLOQs were 0.4 and 0.75 nmol/L for methods 1 and 2, respectively. The intra- and inter-day precision for the methods were 1.6-3.5% and 2.1-5.7%. The extraction recoveries were 90-97% for both methods. ABR-215062 was stable in plasma for at least 3 months when stored at -20 degrees C. In conclusion, our developed methods were found to be selective, sensitive, robust and suitable for applications in clinical pharmacokinetic profiling. 相似文献
976.
Heegaard NH Hansen MZ Sen JW Christiansen M Westermark P 《Journal of separation science》2006,29(3):371-377
Transthyretin (TTR) is a small serum protein that is involved in distinct phenotypes of amyloidosis with different tissue localization, age of onset, and rate of progression. Some types of TTR-amyloidosis (such as familial amyloid polyneuropathy) are associated with various amino acid point mutations, while cardiac amyloid myopathy may also be associated with precipitation of the wild-type molecules, e.g., in senile systemic amyloidosis. Because of the unsettled relationship between circulating and precipitated TTR we here explore on-line immunoaffinity (IA) chromatography-MS and immunoprecipitation (IP)-MS methods for characterizing the circulating TTR population in normal individuals and in patients with known TTR-amyloidosis. It was found necessary to reduce the samples, e.g., with DTT, prior to ESI-TOF-MS. This reversed oxidative modifications to sufficiently resolve the two mass peaks isolated from sera of heterozygous patients. A simple IP technique without the use of centrifugal filtration was found to be convenient for the assessment of the TTR population in serum as demonstrated for both normal and variant (the Met111Leu mutation) TTR. This approach also readily allowed the identification of oxidation, S-sulfation, and S-cysteinylation in unreduced samples, while these modifications were less well resolved in the on-line IA chromatography-MS approach. 相似文献
977.
Jonas Lindh Jonas Sävmarker Peter Nilsson Dr. Per J. R. Sjöberg Dr. Mats Larhed Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(18):4630-4636
One Heck of a reaction : Treatment of arylboronic acids or aryltrifluoroborates with vinyl acetate by using a palladium(II) catalyst gives the corresponding styrenes (see scheme). No palladium reoxidant is needed and the vinylation is performed under non‐inert conditions
978.
Mounir Andaloussi Dr. Jonas Lindh Jonas Sävmarker Per J. R. Sjöberg Dr. Mats Larhed Prof. 《Chemistry (Weinheim an der Bergstrasse, Germany)》2009,15(47):13069-13074
The first PdII‐catalyzed P arylation has been performed by using palladium acetate, the rigid bidentate ligand dmphen (dmphen=2,9‐dimethyl‐1,10‐phenanthroline), and without the addition of base or acid. Couplings of arylboronic acids or aryl trifluoroborates with H‐phosphonate dialkyl esters were conducted in 30 min with controlled microwave (MW) heating under non‐inert conditions. Aryl phosphites were also synthesized at room temperature with atmospheric air as the sole reoxidant. The arylated phosphonates were isolated in 44–90 % yields. The excellent chemoselectivity of the method was illustrated in the synthesis of a Mycobacterium tuberculosis glutamine synthetase (MTB‐GS) inhibitor. Online ESIMS was used to detect cationic palladium species in ongoing reactions directly, and a catalytic cycle has been proposed based on these results. 相似文献
979.
Strength and barrier properties of MFC films 总被引:1,自引:0,他引:1
The preparation of microfibrillar cellulose (MFC) films by filtration on a polyamide filter cloth, in a dynamic sheet former
and as a surface layer on base paper is described. Experimental evidence of the high tensile strength, density and elongation
of films formed by MFC is given. Typically, a MFC film with basis weight 35 g/m2 had tensile index 146 ± 18 Nm/g and elongation 8.6 ± 1.6%. The E modulus (17.5 ± 1.0 GPa) of a film composed of randomly oriented fibrils was comparable to values for cellulose fibres with
a fibril angle of 50°. The strength of the films formed in the dynamic sheet former was comparable to the strength of the
MFC films prepared by filtration. The use of MFC as surface layer (0–8% of total basis weight) on base paper increased the
strength of the paper sheets significantly and reduced their air permeability dramatically. FEG-SEM images indicated that
the MFC layer reduced sheet porosity, i.e. the dense structure formed by the fibrils resulted in superior barrier properties.
Oxygen transmission rates (OTR) as low as 17 ml m−2 day−1 were obtained for films prepared from pure MFC. This result fulfils the requirements for oxygen transmission rate in modified
atmosphere packaging. 相似文献
980.
Summary Rule-based ensemble modelling has been used to develop a model with high accuracy and predictive capabilities for distinguishing
between four different modes of toxic action for a set of 220 phenols. The model not only predicts the majority class (polar
narcotics) well but also the other three classes (weak acid respiratory uncouplers, pro-electrophiles and soft electrophiles)
of toxic action despite the severely skewed distribution among the four investigated classes. Furthermore, the investigation
also highlights the merits of using ensemble (or consensus) modelling as an alternative to the more traditional development
of a single model in order to promote robustness and accuracy with respect to the predictive capability for the derived model. 相似文献