The kinetics of reduction of nitroxides including 4-hydroxy-TEMPO, 4-methoxy-TEMPOand 4-hexanoyloxy-TEMPO, which are of different lipophilicities, by vitamin C in cationic,non-ionic and anionic micelles, i. e. CTAB, T...The kinetics of reduction of nitroxides including 4-hydroxy-TEMPO, 4-methoxy-TEMPOand 4-hexanoyloxy-TEMPO, which are of different lipophilicities, by vitamin C in cationic,non-ionic and anionic micelles, i. e. CTAB, Triton X-100 and SDS, respectively, have beenstudied by ESR spectroscopy by a stopped-flow technique. A mechanism for the reactionconducted in micelles is proposed and the rate constants for the elementary reactions areevaluated. It is found that the rates of single electron transfer reactions involving the ni-troxides are dependent on the nature of the micelle and the lipophilicity of the nitroxide.The rates are increased in CTAB, decreased in SDS, whereas unaffected in Triton X-100.And the greater the lipophilicity of the nitroxide, the more pronounced the rate variation.As high as a 3600-fold increase in the rate was observed for 4-hexanoyloxy-TEMPO in CTABover that in SDS. The micellar effects are rationalized on the basis of analysis of parame-ters and line shape of the ESR spectra for the nitroxides in the micelles.展开更多
The effects of aliphatic alcohol on the twisted intramolecular charge transfer (TICT) of p-N, N-dimethylaminobenzoic acid (DMABOA) in cetyltrimethylammonium bromide (CTMAB) micelle were examined by the TICT-typical du...The effects of aliphatic alcohol on the twisted intramolecular charge transfer (TICT) of p-N, N-dimethylaminobenzoic acid (DMABOA) in cetyltrimethylammonium bromide (CTMAB) micelle were examined by the TICT-typical dual fluorescence. The introduction of aliphatic alcohol (CnH2n+10H, n=1, 2, 3, 4, 6, 8, 14, 16, 18) to CTMAB Ancellar solution does not change the positions of the dual fluorescence bands of DMABOA,but results in a decrease in the fluorescence intensities with that of the longer-wavelength TICT band (a band) more repidly, the latter is demonstrated by a linear decrease of the fluorescence intensity ratio of a band to b band (shorter-wavelength normal band) with the concentration of the alcohol added. The logarithm of the absolute value of the linear slope is positively linearly correlated with the carbon number(n) of the alkyl chain in the alcohol molecule when the chain is relatively short (<8), whereas a negatively linear correlation is observed when the chain length (n=14, 16, 18) is comparable with that of CTMAB. In pure aqueous solution, the intensities and positions of the dual fluorescence bands are not varied by the same concentration of added alcohol. The decrease of the charge density of micellar surface due to the solubilization of alcohol in micelle is considered to be the cause of the alcohol effects on the TICT in charged micelle.展开更多
A study was made of magnetic field effects (MFEs) on the photoreduction reaction of 2-methyl-1,4-naphthoqui- none (MNQ) in Brij 35 micellar solution containing 4-lauroylamino-TEMPO (2,2,6,6-tetramethylpiperidine-1-oxy...A study was made of magnetic field effects (MFEs) on the photoreduction reaction of 2-methyl-1,4-naphthoqui- none (MNQ) in Brij 35 micellar solution containing 4-lauroylamino-TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) radical (L-R) under magnetic fields below 1.75 T by a nanosecond laser flash photolysis technique. The triplet MNQ mainly underwent the hydrogen abstraction from Brij 35 molecule to give a radical pair. The escaped radical yield increased with magnetic fields from 0 to 0.62 T and then saturated from 0.62 to 1.75 T. MFEs for both sys-tems can be explained by the relaxation mechanism. However, it was supposed that additional radical, L-R affected the MFEs mainly through enhancing the spin-spin interactions of radical pairs. The effect of the micelle size on MFEs of the studying system was also discussed.展开更多
基金the National Natural Science Foundation of China.
文摘The kinetics of reduction of nitroxides including 4-hydroxy-TEMPO, 4-methoxy-TEMPOand 4-hexanoyloxy-TEMPO, which are of different lipophilicities, by vitamin C in cationic,non-ionic and anionic micelles, i. e. CTAB, Triton X-100 and SDS, respectively, have beenstudied by ESR spectroscopy by a stopped-flow technique. A mechanism for the reactionconducted in micelles is proposed and the rate constants for the elementary reactions areevaluated. It is found that the rates of single electron transfer reactions involving the ni-troxides are dependent on the nature of the micelle and the lipophilicity of the nitroxide.The rates are increased in CTAB, decreased in SDS, whereas unaffected in Triton X-100.And the greater the lipophilicity of the nitroxide, the more pronounced the rate variation.As high as a 3600-fold increase in the rate was observed for 4-hexanoyloxy-TEMPO in CTABover that in SDS. The micellar effects are rationalized on the basis of analysis of parame-ters and line shape of the ESR spectra for the nitroxides in the micelles.
文摘The effects of aliphatic alcohol on the twisted intramolecular charge transfer (TICT) of p-N, N-dimethylaminobenzoic acid (DMABOA) in cetyltrimethylammonium bromide (CTMAB) micelle were examined by the TICT-typical dual fluorescence. The introduction of aliphatic alcohol (CnH2n+10H, n=1, 2, 3, 4, 6, 8, 14, 16, 18) to CTMAB Ancellar solution does not change the positions of the dual fluorescence bands of DMABOA,but results in a decrease in the fluorescence intensities with that of the longer-wavelength TICT band (a band) more repidly, the latter is demonstrated by a linear decrease of the fluorescence intensity ratio of a band to b band (shorter-wavelength normal band) with the concentration of the alcohol added. The logarithm of the absolute value of the linear slope is positively linearly correlated with the carbon number(n) of the alkyl chain in the alcohol molecule when the chain is relatively short (<8), whereas a negatively linear correlation is observed when the chain length (n=14, 16, 18) is comparable with that of CTMAB. In pure aqueous solution, the intensities and positions of the dual fluorescence bands are not varied by the same concentration of added alcohol. The decrease of the charge density of micellar surface due to the solubilization of alcohol in micelle is considered to be the cause of the alcohol effects on the TICT in charged micelle.
基金Project supported by the Scientific Research Foundation for the Returned Overseas Chinese Scholars State Education Ministry+1 种基金 and the Scientific Research Foundation for the Returned Overseas University of Science and Technology of China (No. 2047308
文摘A study was made of magnetic field effects (MFEs) on the photoreduction reaction of 2-methyl-1,4-naphthoqui- none (MNQ) in Brij 35 micellar solution containing 4-lauroylamino-TEMPO (2,2,6,6-tetramethylpiperidine-1-oxyl) radical (L-R) under magnetic fields below 1.75 T by a nanosecond laser flash photolysis technique. The triplet MNQ mainly underwent the hydrogen abstraction from Brij 35 molecule to give a radical pair. The escaped radical yield increased with magnetic fields from 0 to 0.62 T and then saturated from 0.62 to 1.75 T. MFEs for both sys-tems can be explained by the relaxation mechanism. However, it was supposed that additional radical, L-R affected the MFEs mainly through enhancing the spin-spin interactions of radical pairs. The effect of the micelle size on MFEs of the studying system was also discussed.
