Quantification of Four Isoflavones in Forages with UPLC®-MS/MS,Using the Box–Behnken Experimental Design to Optimize Sample Preparation

A performant method for the simultaneous quantification of daidzein, genistein, formononetin, and biochanin A in forages using an UPLC^®-MS/MS was developed and fully validated. The ultrasound-assisted extraction and enzymatic hydrolysis used in the sample preparation step were optimized using the Box–Behnken experimental design. The optimal extraction conditions used for a representative mix of forage plants were 80 °C, 10 min, and 55 % methanol, and for hydrolysis, they were 20 °C, 18 h, and pH = 6. The chromatographic separation was achieved using an Acquity UPLC^® HSS T3 column, with a water/methanol linear gradient containing 0.01 % of formic acid at a 0.55 mL min⁻¹ flow rate. The four isoflavones were detected by ESI mass spectrometry in positive ion MRM mode. The method allows high throughput analyses of samples and showed an adequate linear regression model for all isoflavones over a range from 5 to 125 ng mL⁻¹. There were good intra- and inter-day precisions (≤8.2 and ≤7.6 %) and accuracy (≤11.4 and ≤7.1 %). The recovery rates were in an acceptable range of 70–120 %, except for biochanin A, where the rate was about 50 %. Good method repeatability was also observed, and there was no matrix effect or carryover problem. The sample extracts were stable for at least 6 days of storage at -21 and 6 °C. The method proved to be sensitive, precise, and accurate for discriminating a wide variety of forages likely to be grazed by ruminants according to their isoflavone contents and to observe the impact of storage process on isoflavone content in forages.

     

Fast gas chromatography characterisation of purified semiochemicals from essential oils of Matricaria chamomilla L. (Asteraceae) and Nepeta cataria L. (Lamiaceae)

The chemical composition of Matricaria chamomilla L. and Nepeta cataria L. essential oils was determined by GC-MS on an apolar stationary phase by comparison of the characteristic fragmentation patterns with those of the Wiley 275L database. The GC-MS chromatograms were compared with those obtained by fast GC equipped with a direct resistively heated column (Ultra Fast Module 5% phenyl, 5 mx 0.1 mm, 0.1 microm film thickness). Analytical conditions were optimised to reach a good peak resolution (split ratio=1:100), with analysis time lower than 5 min versus 35-45 min required by conventional GC-MS. The fast chromatographic method was completely validated for the analysis of mono- and sesquiterpene compounds. Essential oils were then fractionated by column chromatography packed with silica gel. Three main fractions with high degree of purity in E-beta-farnesene were isolated from the oil of M. chamomilla. One fraction enriched in (Z,E)-nepetalactone and one enriched in beta-caryophyllene were obtained from the oil of N. cataria. These semiochemical compounds could act as attractants of aphid's predators and parasitoids.     

Survival of Freeze-dried Leuconostoc mesenteroides and Lactobacillus plantarum Related to Their Cellular Fatty Acids Composition during Storage

Lactic acid bacteria strains Lactobacillus plantarum CWBI-B534 and Leuconostoc ssp. mesenteroïdes (L. mesenteroïdes) Kenya MRog2 were produced in bioreactor, concentrated, with or without cryoprotectants. In general, viable population did not change significantly after freeze-drying (p?>?0.05). In most cases, viable population for cells added with cryoprotectants was significantly lower than those without (p?16:0), palmitoleic (C_16:1), stearic (C_18:0), oleic (C_18:1), linoleic (C_18:2), and linolenic (C_18:3) acids were identified. Four of them, C_16:0, C_16:1, C_18:0, and C_18:1, make up more than 94% or 93% of the fatty acids in L. mesenteroides and L. plantarum, respectively, with another one, namely, C18:3, making a smaller (on average 5–6%, respectively) contribution. The C_18:2 contributed very small percentages (on average?≤?1%) to the total in each strain. C_16:0 had the highest proportion at most points relative to other fatty acids. Moisture content and water activity (a _w) increased significantly during the storage period. It was observed that C_16:1/C_16:0, C_18:0/C_16:0 and C_18:1/C_16:0 ratios for freeze-dried L. mesenteroides or L. plantarum, with or without cryoprotectants, did not change significantly during the storage period. According to the packaging mode and storage temperatures, C_18:2/C_16:0 and C_18:3/C_16:0 ratios for freeze-dried L. mesenteroides and L. plantarum with or without cryoprotectants decreased as the storage time increased. However, a higher C_18:2/C_16:0 or C_18:3/C_16:0 ratio for L. mesenteroides and L. plantarum was noted in the freeze-dried powder held at 4 °C or under vacuum and in dark than at 20 °C or in the presence of oxygen and light.     

Enzymatically prepared n-alkyl esters of glucuronic acid: the effect of freeze-drying conditions and hydrophobic chain length on thermal behavior

In this work, some of the physicochemical properties of enzymatically prepared n-alkyl esters of glucuronic acid are presented. Two questions are addressed. The first concerns the influence of post-purification freeze-drying conditions on octyl glucuronate thermotropic behavior. Depending on the amount of water added before freeze-drying, the alpha/beta anomeric ratio determined by (1)H NMR is affected and differences are observed in DSC thermograms probably due to polymorphism. The second question concerns the effect of hydrophobic chain length on the thermal behavior. An increase of both transition temperature and transition enthalpy is observed by increasing the number of carbon atoms in the alkyl chain (C8相似文献   

A chemoselective ligation for the synthesis of amino acid derivatives of virginiamycin M1

An efficient chemoselective ligation approach using an oxime bond was developed for the synthesis of amino acid derivatives of virginiamycin M₁, a highly sensitive streptogramin antibiotic.     

A fast and reliable chromatographic procedure for the purification of virginiamycin M1 factor

Summary The goal of this study was to develop a simple, fast and reliable procedure for the preparation of highly purified virginiamycin M₁ factor using readily available and low cost laboratory equipment. This was achieved by purifying M₁ by reversed-phase flash chromatography after clean-up of the bulk sample by filtration on a silica gel cake. The purity of the final product determined by RP-HPLC was 99% and its identity was confirmed by IR spectroscopy and ESI mass spectrometry.     

Development and validation by accuracy profile of a method for the analysis of monoterpenes in indoor air by active sampling and thermal desorption-gas chromatography-mass spectrometry

The technique of thermal desorption (TD)-GC/MS was evaluated for the measurement of monoterpenes in indoor air. The validation strategy was intentionally oriented towards routine use and the reliability of the method rather than extreme performance. For this reason, validation by accuracy profile was chosen. The accuracy profile procedure, which is based on the concept of total error (bias + standard deviation), guarantees that a known proportion of future results obtained with the method will be within acceptance limits. For all the compounds tested in the present study, α-pinene, α-terpineol, β-pinene, d-limonene, Δ³-carene, camphene, 1,8-cineole, p-cymene, linalool, but not in the case of carvone, the accuracy profile procedure established that at least 95% of the future results obtained would be within the ±15% acceptance limits of the validated method over the whole defined concentration range. Other parameters, such as selectivity, recovery, repeatability, stability of the molecules of interest and the effect of temperature, were also determined. The performance of the described method was finally evaluated by the analysis of indoor air from new timber frame constructions.     

Enzymatically prepared n-alkyl esters of glucuronic acid: the effect of hydrophobic chain length on surface properties

N-isopropylacrylamide (NIPA) homopolymers having carboxylic acid-end groups were synthesized by using mercaptoacetic acid (MAA) as the chain transfer agent. Polymerization was achieved in ethanol using azobisisobutyronitrile (AIBN) as the initiator. Average molecular weight of the homopolymer estimated by titration was 1958. This carboxylic acid-ended poly(NIPA) was then copolymerized with polyethylenimine (PEI, M(W)-2000) using a water soluble carbodiimide (EDAC). With respect to carboxyl-ended poly(NIPA), the block copolymers exhibited a pH dependent-temperature sensitivity and higher LCST values in acidic pH. Scanning tunneling microscopy (STM) images of both the homopolymer and the copolymer were obtained at 25 and 45 degrees C with tip-sample bias voltages of up to 800 mV and tunneling currents approximately 1 nA. These images showed that STM can be used to visualize both the formation of copolymer chains and their structure, and also their stimuli-responsive behavior.