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134.
应用循环伏安和紫外光谱法研究杨梅酮氧化还原性质及其稳定性.结果表明:在B-R缓冲溶液中玻碳电极上,杨梅酮的氧化还原表现为两步氧化反应和两步还原反应.氧化反应对应于B环4-′OH和C环3-OH的氧化,还原反应对应于C环4位羰基还原为中间体自由基之后再进一步还原生成羟基.以上各步反应均为单电子单质子电极过程.杨梅酮的氧化还原反应与溶液pH关系密切,但其原因来自于去质子化作用,并导致它的抗氧化能力增强,但其最终氧化产物没有电化学活性,并吸附在电极表面,阻碍了电极过程电子传递.在pH 7.45~12.00范围内,杨梅酮也因去质子化作用导致紫外光谱Ⅰ带和Ⅱ带随pH增加,而发生红移,分解作用加剧.同时分解作用还与放置时间有关. 相似文献
135.
Prenesti E Fisicaro P Berto S Ferrara E Daniele PG 《Analytical and bioanalytical chemistry》2007,387(7):2595-2600
This paper reports evaluation of the behaviour of different combined glass electrodes applied to measurement of the pH of
a primary, 0.01 mol kg−1, tetraborate buffer. Measurements were first performed by use of a primary Harned cell (at 15, 25, and 37 °C); these results
were then compared with those obtained for the same solution by use of three combined glass electrodes (25 °C) with different
membranes and liquid-junction designs, calibrated by use of commercial pH-metric buffers. The pH of the same solution was
also measured in terms of the molal concentration of hydrogen ions, using acid–base titration to evaluate the formal potential
difference K of each cell at fixed ionic strength, I, adjusted by addition of KCl or Et4NI (tetraethylammonium iodide). The reference value from primary measurement, paH = 9.171, was slightly closer to the mean value obtained by determination of concentration, rather than that obtained by
direct measurement of activity; the differences were smaller than the extended uncertainty characteristics of the secondary
measurements. The importance of evaluation of the ionic strength of the solution under study is emphasised. We verified that
for tetraborate buffer slight modification of the value of I used to calculate γ
i
(the activity coefficient of a single ion) in the calculation of paH from the acidity function at zero molality of chloride can significantly affect the reference value of the calibrator tool.
This is true, in general, for low values of the ionic strength, such as those considered in this work; an approximate value
of I can then cause distortions along the pH traceability chain. Application of the concepts of thermodynamics to this traceability
chain is discussed. 相似文献
136.
P. Fini L. Catucci M. Castagnolo P. Cosma V. Pluchinotta A. Agostiano 《Journal of inclusion phenomena and macrocyclic chemistry》2007,57(1-4):663-668
The interaction of Rose Bengal (RB) with hydroxypropyl-α-cyclodextrin (HP-α-CD), hydroxypropyl-β-cyclodextrin (HP-β-CD) and
hydroxypropyl-γ-cyclodextrin (HP-γ-CD) has been studied in water and in acetate buffer at pH 4.5 by UV–Vis absorption, fluorescence
spectroscopy and Induced Circular Dichroism at 298 K. Evidence of the complex formation between the RB and all HP-CDs have
been obtained both in water and in buffer. Binding constants and stoichiometry of RB/HP-CD complexes in water have been determined
by applying the modified Benesi-Hildebrand equation to the fluorescence measurements. 相似文献
137.
The effect of carbon nanotubes on the electrochemical response of the pH sensing, redox-active copolymer poly(vinylanthracene-co-vinylferrocene) has been studied. A clear increase in the linear response of the anthracene moiety with pH is observed in the presence of carbon nanotubes. 相似文献
138.
Responsive polymers have been the focus of many studies during the past decade because of their ability to change according to environmental stimuli. In this paper, we report on the development of a method to synthesize a pH/temperature‐sensitive linear copolymer, poly(N‐isopropylacrylamide‐ co‐acrylic acid)(poly(NIPAAm‐co‐AAc)), with a molecular weight of about 106–105 Da in water using azobisisobutyronitrile (AIBN) as the initiator. The effects of the following on the lower critical solution temperature (LCST) of the copolymer and homopolymer of NIPAAm were investigated: the type of buffer salts and pH changes of test solutions, molecular weight and concentration of homopolymer/copolymer solutions, and AAc monomer molar feed ratio (mol%). The effects of different synthesis methods on the molecular weight and on the AAc content were also evaluated. The mechanism of action in environments with different pH values is discussed. Copyright © 2007 John Wiley & Sons, Ltd. 相似文献
139.
New copper(II) complexes of the hydrazone ligands H2salhyhb, H2salhyhp, and H2salhyhh, derived from salicylaldehyde and ω‐hydroxy carbonic acid hydrazides, have been synthesized and physically characterized. Two fundamental structures were found in solid state depending on the pH‐value of the reaction solution. Acidic conditions lead to the formation of the di‐μ‐phenoxo‐bridged dicationic complex dimers [{Cu(Hsalhyhb)}2]2+ ( 1a ), [{Cu(Hsalhyhp)}2]2+ ( 2a ), and [{Cu(Hsalhyhh)}2]2+ ( 3a ), isolated as perchlorate salts. The dimeric complexes show strong antiferromagnetic coupling with J = ?399 ( 1a ), ?410 ( 2a ), and ?311 cm?1 ( 3a ). Higher pH‐values resulted in the aggregation of neutral copper ligand fragments to the one‐dimensional coordination polymers [{Cu(salhyhb)}n] ( 1b ), [{Cu(salhyhp)}n] ( 2b ), and [{Cu(salhyhh)}n] ( 3b ). 3b has been examined by means of X‐ray crystallography and represents the first example of a structurally characterized neutral copper(II) N‐salicylidenehydrazide complex without additional ligands. The magnetic interactions in the polymers are also antiferromagnetic with J = ?125 ( 1b ), ?136 ( 2b ), and ?148 cm?1 ( 3b ), but strongly reduced compared to the corresponding dimeric complexes. The two basic structure types can be reversibly interconverted simply by pH‐control. 相似文献
140.
In this study, preparation of novel pH-sensitive N-doped carbon dots (NCDs) using glucose and urea is reported. The prepared NCDs present strong excitation-dependent fluorescence changes towards the pH that is a new behavior from these nanomaterials. By taking advantage of this unique behavior, two separated ratiometric pH sensors using emission spectra of the NCDs for both acidic (pH 2.0 to 8.0) and basic (pH 7.0 to 14.0) ranges of pH are constructed. Additionally, by considering the entire Excitation–Emission Matrix (EEM) of NCDs as analytical signal and using a suitable multivariate calibration method, a broad range of pH from 2.0 to 14.0 was well calibrated. The multivariate calibration method was independent from the concentration of NCDs and resulted in a very low average prediction error of 0.067 pH units. No changes in the predicted pH under UV irradiation (for 3 h) and at high ionic strength (up to 2 M NaCl) indicated the high stability of this pH nanosensor. The practicality of this pH nanosensor for pH determination in real water samples was validated with good accuracy and repeatability. 相似文献