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11.
Sasidhar Maddula Lars Mathias Blank Andreas Schmid Jörg Ingo Baumbach 《Analytical and bioanalytical chemistry》2009,394(3):791-800
Detection and immediate quantification of microbial metabolic activities is of high interest in fields as diverse as biotechnology
and infection biology. Interestingly, the most direct signals of microbial metabolism, the evolution of volatile metabolites,
is largely ignored in the literature, and rather, metabolite concentrations in the microbial surrounding or even disruptive
methods for intracellular metabolite measurements (i.e., metabolome analysis) are favored. Here, the development of a multi
capillary column coupled ion mobility spectrometer (MCC-IMS) was described for the detection of volatile organic compounds
from microbes and the MCC-IMS was used for characterization of metabolic activity of growing Escherichia coli. The MCC-IMS chromatogram of the microbial culture off-gas of the acetone-producing E. coli strain BL21 pLB4 revealed four analytes that positively correlated with growth, which were identified as ethanol, propanone
(acetone), heptan-2-one, and nonan-2-one. The occurrence of these analytes was cross-validated by solid-phase micro-extraction
coupled with gas chromatography mass spectrometry analysis. With this information in hand, the dynamic relationship between
the E. coli biomass concentration and the metabolite concentrations in the headspace was measured. The results suggest that the metabolic
pathways of heptan-2-one and nonan-2-one synthesis are regulated independent of each other. It is shown that the MCC-IMS in-line
off-gas analysis is a simple method for real-time detection of microbial metabolic activity and discussed its potential for
application in metabolic engineering, bioprocess control, and health care. 相似文献
12.
Vishal Kandathil Manjunatha Kempasiddaiah Sanna Kotrappanavar Nataraj Sasidhar Balappa Somappa Siddappa A. Patil 《应用有机金属化学》2020,34(3):e5357
The utilization of deoxyribonucleic acid (DNA) in nanotechnology is a promising area of research wherein the distinct properties of DNA are exploited for the design and development of new materials and applications. The biodegradability and natural profusion of DNA makes it highly suitable for use in various fields. In this report, we have treated DNA as a bioligand, supported on functionalized magnetite for the grafting of palladium (Pd) nanoparticles to make Pd-DNA bio-nanocatalyst. The Pd-DNA was subjected to Fourier-transform infrared spectroscopy, field-emission scanning electron microscopy, transmission electron microscopy, X-ray powder diffraction, Brunauer–Emmett–Teller, energy dispersive X-ray spectroscopy, vibrating sample magnetometry, X-ray photoelectron spectroscopy, and inductively coupled plasma optical emission spectrometry analysis. The prepared Pd-DNA was found to be highly efficient in catalyzing Suzuki–Miyaura cross-coupling reaction with excellent yields when compared with commercially available palladium-based catalysts. Also, the Pd-DNA could be easily recovered from the reaction mass using an external magnet and recycled up to six times without substantial loss of activity. Furthermore, Felbinac, a non-inflammatory drug, was synthesized in quantitative yields using the Pd-DNA bio-nanocatalyst. 相似文献
13.
Adusumilli Srikrishna Vijendra H. Pardeshi Konda Mahesh 《Tetrahedron: Asymmetry》2010,21(23):2830-2833
Enantiospecific total synthesis of two epimeric sesquiterpenes 11-hydroxyguaiadienes has been accomplished starting from the readily available monoterpene (R)-limonene, which confirmed the structure and absolute configuration of the natural products. 相似文献
14.
Alexander Bunkowski Sasidhar Maddula Antony N. Davies Michael Westhoff Patrick Litterst Bertram Bödeker Jorg Ingo Baumbach 《International Journal for Ion Mobility Spectrometry》2010,13(3-4):141-148
Ion mobility Spectrometry is used to detect volatile analytes within human breath directly. Many volatile organic compounds (VOC) show significant day-to-day variation in the signal height related to the concentration of the analyte, although the breath collection had been performed under the same conditions with respect to similar sampling procedure, similar dead volume, similar measurement time, and measurement conditions. Variations of 8 different analytes are investigated over a time period of 11 months in the exhaled breath of the same person in the same room environment. The individual variability is reported for Benzothiazole; D-Limonene; Eucalyptol; Decamethylcyclopentasiloxane; Decanal; 1-Hexanol, 2-ethyl-; Cyclohexanone, 5-methyl-2-(1-methylethyl) and Nonanal. The paper shows, that the individual variability must be taken into consideration to relate the findings to medical questions. Therefore, the room air concentration of VOCs must be taken into account, so that the difference between exhaled and inhaled air has to be used as indicator. Finally, starting with individual variabilities, the normal variation related to the specific analyte should be considered in addition. 相似文献
15.
During the transient period of facilitated transport of a permeant across a thin liquid film, the ratio of the concentrations of the carrier at the two ends of the film as a function of time has a shape which is sensitive to the values of the physicochemical parameters. In certain systems involving ionic carriers, the above concentration ratio can be related to a conveniently measurable electrical potential difference, ΔV, across a pair of electrodes attached to the two faces of the liquid film. Bdzil et al. measured ΔV vs. time for NO FeCl2FeCl3—formamide system and observed that it goes through a maximum (ΔVmax), before reaching the asymptotic value corresponding to the steady state, ΔVs.In the present paper, we solve numerically the species conservation equations, which describe the transients of the facilitated transport in the film, when the reversible reaction occurring in the film is of the form: A↑ + B = P (where A is the permeant and B and P are the carrier and permeant—carrier complex, respectively). The analysis takes into account: (i) the electrical effects which arise when B and P are ions of different diffusion coefficients and (ii) the effect of a second electrolyte added to the film to provide the cations which participate in an electrode reaction with the carrier ions. On this basis, an explanation is provided for the overshoot observed experimentally by Bdzil et al. in the ΔV vs. time curve. Such a maximum is exhibited by systems for which the time scales of diffusion and backward reaction in the film are of comparable magnitude. (Of course, for viable facilitation, the characteristic times of the forward and backward reactions should also be comparable.)The profile of ΔVvs. time is very sensitive to the values of the kinetic constants as well as the diffusion coefficients of the species A, B, and P. Therefore, measurements of ΔV vs. time (or equivalently the ratio of concentrations of the carrier on the two sides of the film as a function of time) can provide a more accurate method of determining the above parameters than those based on flux measurements. 相似文献
16.
Efficient hydrolysis of cellulose-to-glucose is critically important in producing fuels and chemicals from renewable feedstocks. Cellulose hydrolysis in aqueous media suffers from slow reaction rates because cellulose is a water-insoluble crystalline biopolymer. The high-crystallinity of cellulose fibrils renders the internal surface of cellulose inaccessible to the hydrolyzing enzymes (cellulases) as well as water. Pretreatment methods, which increase the surface area accessible to water and cellulases are vital to improving the hydrolysis kinetics and conversion of cellulose to glucose. In a novel technique, the microcrystalline cellulose was first subjected to an ionic liquid (IL) treatment and then recovered as essentially amorphous or as a mixture of amorphous and partially crystalline cellulose by rapidly quenching the solution with an antisolvent. Because of their extremely low-volatility, ILs are expected to have minimal environmental impact. Two different ILs, 1-n-butyl-3-methylimidazolium chloride (BMIMC1) and 1-allyl-3-methylimidazolium chloride (AMIMC1) were investigated. Hydrolysis kinetics of the IL-treated cellulose is significantly enhanced. With appropriate selection of IL treatment conditions and enzymes, the initial hydrolysis rates for IL-treated cellulose were up to 90 times greater than those of untreated cellulose. We infer that this drastic improvement in the "overall hydrolysis rates" with IL-treated cellulose is mainly because of a significant enhancement in the kinetics of the "primary hydrolysis step" (conversion of solid cellulose to soluble oligomers), which is the rate-limiting step for untreated cellulose. Thus, with IL-treated cellulose, primary hydrolysis rates increase and become comparable with the rates of inherently faster "secondary hydrolysis" (conversion of soluble oligomers to glucose). 相似文献
17.
S. S. Kumar M. V. Sivaiah K. A. Venkatesan R. M. Krishna G. S. Murthy P. Sasidhar 《Journal of Radioanalytical and Nuclear Chemistry》2003,258(2):321-327
A composite mixture of zirconium molybdate and zirconium tungstate was prepared and studied for the sorption of cesium and strontium as a function of nitric acid, metal ion concentration, time and temperature. The distribution coefficient (Kd) of 7000 ml/g (~90% sorption) and 70 ml/g (~20% sorption) was obtained for the sorption of cesium and strontium in 0.1M nitric acid, respectively. Experimental sorption capacity, b for cesium was found to be 50 mg/g from 0.1M HNO3 and 30 mg/g for strontium from 0.001M nitric acid. The sorption of strontium on the sorbent was accompanied by the absorption of heat but the sorption of Cs+ results in the liberation of heat. Column studies were conducted by following a breakthrough (BT) curve of cesium and strontium up to C/C0=1 and the results are reported. 相似文献
18.
Zhao F Ponnaiyan TK Graham CM Schall CA Varanasi S Anderson JL 《Analytical and bioanalytical chemistry》2008,392(7-8):1271-1275
The application of ionic liquids (ILs) as nonderivatizing solvents for the pretreatment and regeneration of cellulose is a growing area of research. Here we report the development of a rapid and simple method for the determination of residual ethanol content in two hydrophilic ILs, 1-butyl-3-methylimidazolium chloride and 1-ethyl-3-methylimidazolium acetate. The method utilizes headspace solid-phase microextraction coupled with gas chromatography at elevated extraction temperatures, resulting in rapid equilibration times. The effect of IL water content on the ethanol extraction efficiency is presented. Recovery experiments carried out in real samples gave recoveries ranging from 96.8 to 98.2%. 相似文献
19.
Of the sugars recovered from lignocellulose, d-glucose can be readily converted into ethanol by baker’s or brewer’s yeast (Saccharomyces cerevisiae). However, xylose that is obtained by the hydrolysis of the hemicellulosic portion is not fermentable by the same species
of yeasts. Xylose fermentation by native yeasts can be achieved via isomerization of xylose to its ketose isomer, xylulose.
Isomerization with exogenous xylose isomerase (XI) occurs optimally at a pH of 7–8, whereas subsequent fermentation of xylulose
to ethanol occurs at a pH of 4–5. We present a novel scheme for efficient isomerization of xylose to xylulose at conditions
suitable for the fermentation by using an immobilized enzyme system capable of sustaining two different pH microenvironments
in a single vessel. The proof-of-concept of the two-enzyme pellet is presented, showing conversion of xylose to xylulose even
when the immobilized enzyme pellets are suspended in a bulk solution whose pH is sub-optimal for XI activity. The co-immobilized
enzyme pellets may prove extremely valuable in effectively conducting “simultaneous isomerization and fermentation” (SIF)
of xylose. To help further shift the equilibrium in favor of xylulose formation, sodium tetraborate (borax) was added to the
isomerization solution. Binding of tetrahydroxyborate ions to xylulose effectively reduces the concentration of xylulose and
leads to increased xylose isomerization. The formation of tetrahydroxyborate ions and the enhancement in xylulose production
resulting from the complexation was studied at two different bulk pH values. The addition of 0.05 M borax to the isomerization
solution containing our co-immobilized enzyme pellets resulted in xylose to xylulose conversion as high as 86% under pH conditions
that are suboptimal for XI activity. These initial findings, which can be optimized for industrial conditions, have significant
potential for increasing the yield of ethanol from xylose in an SIF approach. 相似文献