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  • Author or Editor: X. Cheng x
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To understand the molecular details of T-DNA integration, the left border (LB) sequences and flanking plant DNA of 16 independent T-DNA insertions in transgenic cry1Ab rice were analyzed by an inverse PCR approach. DNA sequencing indicated that five of the 16 fragments (31%) were found to have simple or rearranged tandem repeats of right border sequences in a head to tail fashion. Mirror truncations of LB of the T-DNA, as well as mirror rearrangements, such as point mutations, small deletions and inversions were found in the region close to the LB breakpoints in some inserts. Host plant DNA flanking the T-DNA endpoints were also sequenced. The A+T contents in the plant DNA within 50 bp adjacent to the T-DNA endpoints were between 30–76% (average 52.5%), not different from the average genome value. Despite minor mutations and some rearrangements, it appears that T-DNA, harbouring a synthetic cry1Ab coding sequence of 49% GC (as well as uidA and hph ), still carries such a foreign gene into ‘transcriptionally active regions’ of the rice genome, which are 55.8% GC on average as predicted from the rice genome sequence.

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A novel method for the determination of rate constants of reactions, the time-variable method, is proposed in this paper. The method needs only three time points (t), peak heights () and pre-peak areas (), obtained from the measured thermoanalytical curve. It does not require the thermokinetic reaction to be completed. It utilizes data-processing on a computer to give the rate constants. Four reaction systems, including a first-order reaction, second-order reactions (with equal concentrations and with unequal concentrations) and a third-order reaction, were studied with this method. The method was validated and its theoretical basis was verified by the experimental results.

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DSC and TG-DTA techniques were used to investigate micro-sized silver powder particles and the adsorption of ethyl cellulose on these particles in a solution of ethyl acetate. The apparent specific heat of the silver particles was determined, and the kinetics of temperature-programmed desorption (TPD) of these adsorbed silver particles was investigated. Results show that the apparent specific heat and desorption kinetic parameters obtained by thermal analysis techniques could be used to characterize certain physico-chemical properties of such a particulate system.

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Summary

1,7-Dihydroxy-3,8-dimethoxyxanthone (X1) and 1,8-dihydroxy-3,7-dimethoxyxanthone (X2) are two important xanthones of the Tibetan medicinal plant Gentianopsis paludosa (Hook. f.) Ma. They are very similar in structure, the only difference being exchange of OH and OCH3 at the 7 and 8 positions. By calculations based on the geometry of the molecules using the MM+ force field, the different distances between the hydroxyl groups of the two xanthones were obtained (4.64774 Å for X2 and 7.19412 Å for X1), therefore, the two hydroxyl groups of X1 should freely interact with more water molecules than those of X2 in aqueous solution. In other words, X2 is more hydrophobic than X1. Micellar electrokinetic capillary chromatography (MEKC) was therefore chosen for separation of the compounds. The optimum separation conditions were: 20 mm borate + 20 mm SDS (pH 9.8) as running buffer, 17.5 kV applied potential, and detection wavelength 260 nm. The two xanthones were well separated in 9.0 min, with Gaussian peak shapes. The repeatability of the MEKC method (expressed as RSD) for X1 and X2 was 0.9 and 1.1%, respectively, for migration time, and 3.1 and 1.4% for peak area. The limits of detection (S/N = 3) were 0.41 μg mL−1 for X1 and 0.82 μg mL−1 for X2. The recovery of the MEKC method for the two xanthones was also satisfactory.

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Effects of pH, ionic strength and fulvic acid on sorption of radiocobalt on montmorillonite and its Al-pillared and cross-linked samples were studied using batch technique. The results indicate that the sorption of cobalt is strongly dependent on pH values and independent of ionic strength. Fulvic acid enhances the sorption of cobalt slightly at low pH, but has no influence at high pH values. Surface complexation is considered the main mechanism of cobalt sorption to montmorillonite. The sequences of FA/Co2+ additions to the system did not affect cobalt sorption.

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The inclusion complex of benzaldehyde (BA) with β-cyclodextrin (β-CD) was prepared and was studied by thermal analysis and X-ray diffractometry. The composition of the complex was identified by TG and elemental analysis as β-CDBA9H2O. TG and DSC studies showed that the thermal dissociation of β-CDBA9H2O took place in three stages: dehydration in the range 70-120C; dissociation of β-CDBA in the range 235-270C; and decomposition of β-CD above 280C. The kinetics of dissociation of β-CDBA in flowing dry nitrogen was studied by means of TG both at constant temperature and at linearly increasing temperature. The results showed that the dissociation of β-CDBA was dominated by a one-dimensional random nucleation and subsequent growth process (A2). The activation energy E was 124. 8 kJ mol-1, and the pre-exponential factor A 5.041011 min-1.

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The stability of β-cyclodextrinethyl benzoate6H2O(β-CDC6H5COOC2H56H2O) was investigated by TG and DSC. The mass loss takes place in three stages: the dehydration occurs at 50-120C; the dissociation of β-CDC6H5COOC2H5occurs at 200-260C; the decomposition of β-CD begins at 280C. The kinetics of the dissociation of β-CDC6H5COOC2H5in a dry nitrogen flow was studied by means of thermogravimetry both at constant temperature and linearly increasing temperature. The results show that the dissociation of β-CDC6H5COOC2H5is dominated by a three-dimensional diffusion process (D3). The activation energy E is 116.19 kJ mol-1and the pre-exponential factor A 6.5358109min-1. Cyclodextrin is able to form inclusion complexes with a great variety of guest molecules, and the studies focus on the energy of binding between cyclodextrin and the guest molecule. In this paper, the β-cyclodextrinethyl benzoate inclusion complex was studied by fluorescence spectrophotometry and infrared absorption spectroscopy, and the results show that the stable energy of inclusion complexes of β-CD with weakly polar guest molecules consists mainly of van der Waals interaction.

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Abstract  

This paper presents a novel data processing method for thermokinetics of faster first-order reaction on the basis of the double-parameter theoretical model of a conduction calorimeter, in which the rate constant of a first-order reaction can be calculated from only four peak height data from the same thermoanalytical curve without using any peak-area. The saponifications of ethyl acetate and methyl acetate in aqueous solution and ethyl benzoate in aqueous alcohol have been studied to test the validity of this method. The rate constants calculated with this method are in fair agreement with those in literature; hence the validity of this method is demonstrated.

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Changes in microbial population, pH, sugar, organic acid, anthocyanins, total soluble phenolics, and anti-glucosidase contents were measured during fermentation of mulberry juice at 30 °C by probiotic Leuconostoc mesenteroides showing rapid growth after an approximately 1-day lag phase and reaching a maximum of 8.6 log CFU ml−1 after 4 d. During the rapid growth phase, the main mulberry juice sugars, glucose and fructose, were largely consumed, and the acidic metabolites, lactic acid and acetic acid, were produced accordingly. A slow decrease in the concentration of the main organic acid, citric acid, was also observed during fermentation. After 4 d fermentation, anthocyanin content showed a 44.4% reduction, but the total amount of soluble phenolics and α-glucosidase inhibitory activity showed no significant changes (P>0.05). This suggests that L. mesenteroides fermentation of mulberry juice is a good strategy to enhance its probiotic value and to decrease the sugar content without changing the anti-glucosidase activity, which is required to reduce postprandial rise in blood glucose.

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