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41.
T. L. Luke H. Mohan V. M. Manoj P. Manoj J. P. Mittal C. T. Aravindakumar 《Research on Chemical Intermediates》2003,29(4):379-391
Reactions of sulphate radical anion (SO·4
-) with 4,6-dihydroxy-2-methyl pyrimidine (DHMP), 2,4-dimethyl-6-hydroxy pyrimidine (DMHP), 6-methyl uracil (MU) and 5,6-dimethyl uracil (DMU) have been studied by pulse radiolysis at pH 3 and at pH 10. The transient intermediate spectra were compared with those from the reaction of hydroxyl radical (·OH). It is proposed that SO·4
- produces radical cations of these pyrimidines in the initial stage. These radical cations are short-lived except in the case of DMHP where a relatively longer lived radical cation is proposed to be formed. When there is a hydrogen atom attached to the N(1) or N(3) position, a deprotonation from these sites is highly favored. When there is no hydrogen attached to these sites, deprotonation from a substituted methyl group is favored. At acidic pH, deprotonation from nitrogen is observed for DHMP, MU and DMU. At basic pH, the radical cation reacts with OH- leading to the formation of OH adducts. 相似文献
42.
NMR spectroscopy plays an important part in the determination of the structures of organic compounds. The parameters of importance here are the chemical shifts of the 1H and 13C nuclei and the spin-spin interactions both between 1H nuclei and between 1H and 13C nuclei. Couplings between 13C nuclei were almost completely neglected until a few years ago, since they were extremely difficult to observe because of the low natural abundance of 13C. However, it is these couplings which afford information directly on the carbon-carbon connectivities in the molecule. It is now possible to use a special NMR pulse sequence to make these couplings more readily visible: the result of using this sequence is a 13C-NMR spectrum from which the carbon skeleton concerned can be directly read off. Two-dimensional spectra in particular are very easy to evaluate. The pulse sequence involved, which bears the somewhat puzzling name INADEQUATE, produces double-quantum coherences from which the NMR signals of the coupled carbon nuclei can be obtained. In this article the principle of double-quantum coherence is described and a number of examples for the application of the INADEQUATE pulse sequences to problems in synthetic organic chemistry, biosynthesis and natural products chemistry are presented; in addition, the possibility of applying the INADEQUATE method to other nuclei is considered. 相似文献
43.
在甲烷氧化偶联制C2烃的研究中,人们发现碱土金属与稀土金属组成的复合氧化物催化剂具有高的催化活性[1,2].稀土化合物作为有希望的工业催化剂之一,已受到广泛的关注.一般认为,它们含有的氧空位对活化甲烷的有效氧物种有利.Debey等在1%Sr/La2O... 相似文献
44.
The electrochemical reduction of antifouling agent 2-thiocyanomethylthiobenzothiazole (TCMTB) was investigated by cyclic and pulse differential voltammetry. The irreversible electrode reduction of TCMTB proceeded by ECEC reaction mechanism by two electrons transfer with one irreversible wave. Upon the basis of electrochemical evidence, the electrodic reaction mechanism was suggested to formation of mercaptobenzothiazole (MTB) in solution.Subsequently, a pulse differential method is described for the formation of TCMTB based on this electroreduction. Having been obtained a detection limit of 1.0 × 10−7 mol L−1 and recovery to 98% to concentration of 2.0 × 10−6 mol L−1. Therefore, the proposed method in this study is practical, sensitive and accurate for the analysis of TCMTB in tannery wastewater samples. 相似文献
45.
A novel and easy post modification method, pulse chemical vapor deposition (pulse CVD), was developed to tailor the pore-opening
of SBA-15 while largely keeping its surface area and pore volume. By using acetylene as carbon precursor and nitrogen as carrier
gas, the pore-mouth of SBA-15 was effectively reduced from 8.1 nm to 5.1 nm within 5 min while maintaining the pore body at
8.1 nm. This ink-bottle-structured SBA-15/carbon composite only losses 12% BET specific surface area and 16% total pore volume,
respectively. The SBA-15/carbon composite is highly hexagonally ordered and has similar particle morphology as the original
SBA-15. The effect of three pore modification factors—the number of cycles of pulse CVD, the ratio of acetylene/nitrogen and
the feeding time of carbon precursor, on the final pore structure of the SBA-15/carbon composite is also studied. 相似文献
46.
The partial molar isentropic pressure coefficients at infinite dilution, K
S,2
o
, have been determined for a number of dipeptides in aqueous solution at 25°C. For a series of dipeptides of sequence gly-X, where X is an amino acid with a neutral side chain, the K
S,2
o
values are all more negative than that for diglycine. The results are discussed in terms of the hydration of the side chains. There are significant differences in the K
S,2
o
values for sequence isomeric dipeptides. These differences can be rationalized in terms of the mutual interactions between the side chain and the ionic end groups in the dipeptides. Possible relationships between K
S,2
o
and V
2
o
, the partial molar volume at infinite dilution, were investigated. For the dipeptides of sequence gly-X there is an interesting linear relationship between K
S,2
o
/V
2
o
and V
2
o
. 相似文献
47.
Based on the theory of stochastic resonance, a new method carried on the quantitive analysis to weak chromatographic signal of glyburide in plasma, which was embedded in the noise background and the signal-to-noise ratio (SNR) of HPLC-UV is enhanced remarkably. This method enhances the quantification limit to 1 ng ml−1, which is the same as HPLC-MS, and makes it possible to detect the weak signal accurately by HPLC-UV, which was not suitable before. The results showed good recovery and linear range from 1 to 50 ng ml−1 of glyburide in plasma and the method can be used for quantitative analysis of glyburide. 相似文献
48.
《Arabian Journal of Chemistry》2020,13(2):4082-4091
In present study, an investigation was carried out to develop and validate an analytical method for the selective extraction and determination of griseofulvin (GSF) from plasma samples. For this purpose, a rational approach was made to synthesize and characterize the surface molecularly imprinted polymers (SMIPs). The SMIPs were utilized as solid phase extraction (SPE) sorbents. The SMIPs were prepared by using GSF as template molecule on the surface of modified silica particles through a non-covalent technique. The particles demonstrated high adsorption capacity (119.1 µg/mL), fast adsorption equilibrium time (30 min) and good recognition selectivity for the template drug. The scanning electron microscopy and infrared spectroscopy were used to explain the structural and morphological characteristics of the SMIPs and surface non-imprinted polymers. The SPE method was combined with HPLC for plasma analysis. The method validation results demonstrated that the established method possessed good linearity for GSF ranging from 0.1 to 50 µg/mL (R2 = 0.997). The limit of detection for this method was 0.02 µg/mL for rat plasma samples. The recoveries of GSF from spiked plasma samples were (90.7–97.7%) and relative standard deviations were (0.9–4.5%). Moreover, the SMIPs as selective SPE sorbent can be reused more than 8 times which is a clear advantage over commercial SPE sorbents. Finally, the usefulness of the proposed strategy was assessed by extraction and detection of GSF in real rat plasma samples. 相似文献
49.
50.