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2. Supramolecular effects in the dynamics of radicals in MFI zeolites: a direct EPR investigation

Author

Turro, Nicholas J., Jockusch, Steffen, and Lei, Xue-Gong

Subjects
Chemistry, Organic -- Research, Molecular dynamics -- Research, Zeolites -- Physiological aspects, Radicals (Chemistry) -- Physiological aspects, Electron paramagnetic resonance spectroscopy -- Usage, Photochemical research -- Analysis, Biological sciences, Chemistry
Abstract

Research has been conducted on the supramolecular complexes. Results indicate that the photolysis of these complexes leads to the radical supramolecular complexes detected by CW-EPR spectroscopy and provides radicals' dynamics information.

Published
2002

3. EPR investigation of persistent radicals produced from the photolysis of dibenzyl ketones adsorbed on ZSM-5 zeolites

Author

Turro, Nicholas J., Lei, Xue-gong, Jockusch, Steffen, Li, Wei, Liu, Zhiqiang, Abrams, Lloyd, and Ottaviani, M. Francesca

Subjects
Chemistry, Organic -- Research, Photochemical research -- Analysis, Zeolites -- Physiological aspects, Ketones -- Physiological aspects, Radicals (Chemistry) -- Physiological aspects, Benzene -- Physiological aspects, Biological sciences, Chemistry
Abstract

Research has been conducted on the carbon-centered radicals produced by ketone photolysis. The effect of the supramolecular structure and dynamics on persistence of these radicals has been investigated via ERP analysis and the details are presented.

Published
2002

7. Aggregation of l,3-di(α-naphthyl)propane and di(α-naphthylmethyl)ether in aqueous binary solvents

Author

Lei Xue‐Gong and Liu You-Cheng

Subjects
Hydrophobic effect, chemistry.chemical_compound, Monomer, Aqueous solution, chemistry, Molecule, Organic chemistry, Physical chemistry, Ether, General Chemistry, Chromophore, Ground state, Excimer
Abstract

The UV absorption and fluorescence spectra of 1,3-di (α-naphthyl) propane (1), di (α-naphthylmethyl) ether (2), and α-methylnaphthalene (3) in aqueous methanol, ethanol, and DMSO were recorded as a function of π value (fraction of water in binary solvents). The existence of two states, a metastable state (defined as m) and a stable stationary state (defined as s), of molecules 1 as well as 2 in the above cosolvents at high π was shown by the contrary fluorescence excimer to monomer intensity (Ie/Im) vs. π relationships of the samples prepared with different processes. On the basis of the π value, substrate concentration, and the temperature dependence of the UV spectra, fluorescence excitation and emission spectra, the chromophores of 1, 2 show the formation of aggregates in ground state at high π owing to the hydrophobic interaction. The m states consist of a supersaturated solution with aggregates, whereas the s states are suspended microcrystals or micro-oil-droplets with aggregates. The conformations of the molecules in the aggregates were discussed. Single crystal X-ray structure of 2 is reported.

Published
1990
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8. Microenvironmental control of photochemical reactions: II. Fluorescence quenching of naphthalene and 1,3-di-(α-naphthyl)propane by RNA and bases in aqueous methanol

Author

Liu You-Cheng, Xie Rui‐Qiang, and Lei Xue‐Gong

Subjects
chemistry.chemical_compound, Quenching (fluorescence), Monomer, Aqueous solution, chemistry, Molecule, Uracil, General Chemistry, Excimer, Photochemistry, Fluorescence, Naphthalene
Abstract

The fluorescence quenching of naphthalene (2) and 1,3-di(α-naphythyl)propane (1) by RNA and bases in methanol-water (v:v = 1:1) binary solvents in the presence or absence of cyclodextrin (CD) has been investigated. The results show that both the monomer and excimer fluorescence of 1 can be quenched by these quenchers. The quenching and rates depend on the quencher and temperature. It is shown that there is a critical temperature (Tc) for each quencher. Below Tc, the excimer fluorescence spectra show vibrational structures and the Stern-Volmer plots are straight lines (for uracil and cytosine); while above the Tc, the vibrational structures disappear and the Stern-Volmer plots deviate from linearity and curve upward. The former is a static process; while the latter is a mixture of both static and dynamic processes. The addition of α-CD has no effect on the fine structure; whereas β-CD prevents the appearance of this structure efficiently. The quenching rates both for the monomer and excimer of 1 by bases except cytosine in the presence of β-CD at ambient temperature are not changed; the quenching of fluorescence of 1 by RNA in the presence of β-CD, however, is hindered. Time-resolved fluorescence study shows that the excimer fine structures appear from the zero time. The intensity of fine structures depend on the fraction of water (π) in binary solvents, and it is independent of the pH value of the solvents. It is suggested that bases and RNA induced aggregates (perhaps microcrystal) are formed, in which the motion of molecules 1 is limited.

Published
1990
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16. Photochemical and magnetic resonance investigations of the supramolecular structure and dynamics of molecules and reactive radicals on the external and internal surface of MFI zeolites

Author

Turro, Nicholas J., Lei, Xue-Gong, Li, Wei, Liu, Zhiqiang, McDermott, Ann, Francesca Ottaviani, M., and Abrams, Lloyd

Subjects
Magnetic resonance -- Usage, Zeolites -- Research, Chemistry
Abstract

The supramolecular structure and dynamics of molecules and reactive radicals on MFI zeolites were studied using photochemical and magnetic resonance investigations.

Published
2000

29. In situ EPR investigation of the addition of persistent benzyl radicals to acrylates on ZSM-5 zeolites. Direct spectroscopic detection of the initial steps in a supramolecular photopolymerization

Author

Lei, Xue-gong, Jockusch, Steffen, Ottaviani, M. Francesca, and Turro, Nicholas J.

Abstract

Photolysis of dibenzyl ketone derivatives adsorbed on ZSM-5 zeolites produces persistent benzyl radicals (initiator radicals), which add to methyl acrylates (monomers) to generate persistent adduct radicals. Both initiator and adduct radicals are readily observable by conventional steady-state EPR spectroscopy at room temperature and are persistent for time periods ranging from seconds to many days. The rate of the formation and the amount of the adduct persistent radical formed depends on the structure of the initiator radical (benzyl radical derivative) and the structure of the monomer (acrylate derivative). The lifetimes of the initiator and adduct radicals depend on the supramolecular structure of the radical@zeolite complex and the diffusion and reaction dynamics of the radicals in the complex. The most intense signal and highest addition rate to methyl acrylate were observed for the smallest initiator radical, the benzyl radical, because of its high mobility and relatively rapid diffusion within the internal zeolite surface. With increasing length of an alkyl chain (methyl, ethyl, and pentyl) on either the initiator (α position of the radical) or monomer (alkyl group of acrylate ester), the rate of radical addition to the monomer decreased, a result that is consistent with the decreased mobility and diffusion of the initiator radical or monomer. Deuterium isotope experiments and variation of the methyl acrylate concentration demonstrated that the initial adduct radical from methyl acrylate adds to another methyl acrylate to generate a secondary adduct radical, which, in turn, can continue to propagate to form a polymer that is cross-linked to the zeolite crystals. The results demonstrate that EPR can be a powerful tool for the direct in situ analysis of supramolecular photochemistry involving radicals rendered persistent by supramolecular steric effects. The latter eliminate the need for sophisticated flash photolysis equipment to investigate the structure and dynamics of reactive radicals and require only the use of simpler steady-state lamps.

Published
2004

30. In situEPR investigation of the addition of persistent benzyl radicals to acrylates on ZSM-5 zeolites. Direct spectroscopic detection of the initial steps in a supramolecular photopolymerizationThis paper is dedicated to Professor Fred Lewis on the event of his 60th birthday.

Author

Lei, Xue-gong, Jockusch, Steffen, Francesca Ottaviani, M., and Turro, Nicholas J.

Abstract

Photolysis of dibenzyl ketone derivatives adsorbed on ZSM-5 zeolites produces persistent benzyl radicals initiator radicals, which add to methyl acrylates monomers to generate persistent adduct radicals. Both initiator and adduct radicals are readily observable by conventional steady-state EPR spectroscopy at room temperature and are persistent for time periods ranging from seconds to many days. The rate of the formation and the amount of the adduct persistent radical formed depends on the structure of the initiator radical benzyl radical derivative and the structure of the monomer acrylate derivative. The lifetimes of the initiator and adduct radicals depend on the supramolecular structure of the radicalzeolite complex and the diffusion and reaction dynamics of the radicals in the complex. The most intense signal and highest addition rate to methyl acrylate were observed for the smallest initiator radical, the benzyl radical, because of its high mobility and relatively rapid diffusion within the internal zeolite surface. With increasing length of an alkyl chain methyl, ethyl, and pentyl on either the initiator α position of the radical or monomer alkyl group of acrylate ester, the rate of radical addition to the monomer decreased, a result that is consistent with the decreased mobility and diffusion of the initiator radical or monomer. Deuterium isotope experiments and variation of the methyl acrylate concentration demonstrated that the initial adduct radical from methyl acrylate adds to another methyl acrylate to generate a secondary adduct radical, which, in turn, can continue to propagate to form a polymer that is cross-linked to the zeolite crystals. The results demonstrate that EPR can be a powerful tool for the direct in situanalysis of supramolecular photochemistry involving radicals rendered persistent by supramolecular steric effects. The latter eliminate the need for sophisticated flash photolysis equipment to investigate the structure and dynamics of reactive radicals and require only the use of simpler steady-state lamps.

Published
2004
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31. In situEPR investigation of the addition of persistent benzyl radicals to acrylates on ZSM-5 zeolites. Direct spectroscopic detection of the initial steps in a supramolecular photopolymerization

Author

Lei, Xue-gong, Jockusch, Steffen, Ottaviani, M. Francesca, and Turro, Nicholas J.

Abstract

Photolysis of dibenzyl ketone derivatives adsorbed on ZSM-5 zeolites produces persistent benzyl radicals (initiator radicals), which add to methyl acrylates (monomers) to generate persistent adduct radicals. Both initiator and adduct radicals are readily observable by conventional steady-state EPR spectroscopy at room temperature and are persistent for time periods ranging from seconds to many days. The rate of the formation and the amount of the adduct persistent radical formed depends on the structure of the initiator radical (benzyl radical derivative) and the structure of the monomer (acrylate derivative). The lifetimes of the initiator and adduct radicals depend on the supramolecular structure of the radical@zeolite complex and the diffusion and reaction dynamics of the radicals in the complex. The most intense signal and highest addition rate to methyl acrylate were observed for the smallest initiator radical, the benzyl radical, because of its high mobility and relatively rapid diffusion within the internal zeolite surface. With increasing length of an alkyl chain (methyl, ethyl, and pentyl) on either the initiator (α position of the radical) or monomer (alkyl group of acrylate ester), the rate of radical addition to the monomer decreased, a result that is consistent with the decreased mobility and diffusion of the initiator radical or monomer. Deuterium isotope experiments and variation of the methyl acrylate concentration demonstrated that the initial adduct radical from methyl acrylate adds to another methyl acrylate to generate a secondary adduct radical, which, in turn, can continue to propagate to form a polymer that is cross-linked to the zeolite crystals. The results demonstrate that EPR can be a powerful tool for the direct in situanalysis of supramolecular photochemistry involving radicals rendered persistent by supramolecular steric effects. The latter eliminate the need for sophisticated flash photolysis equipment to investigate the structure and dynamics of reactive radicals and require only the use of simpler steady-state lamps.

Published
2003
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32. Studies on the kinetics of decomposition of diacyl peroxides: VI. CIDNP in the products of thermolysis of lauroyl peroxide and 3,5,5-trimethylhexanoyl peroxide

Author

Lei Xue‐Gong, Liu You-Cheng, and Guo Qing-Xiang

Subjects
chemistry.chemical_compound, Reaction rate constant, chemistry, CIDNP, Kinetics, Thermal decomposition, Proton NMR, General Chemistry, Lauroyl peroxide, Photochemistry, Decomposition, Peroxide
Abstract

The 1H NMR spectra recorded during the thermolysis of lauroyl peroxide and of 3,5,5-trimethylhexanoyl peroxide in ODCB containing 2-iodopropane show CIDNP multiplet effect. It was observed that the relative concentrations of 1-iodoundecane and 2-iodopropane, both polarized and normal species, changed with time. The relaxation time T1 of the α-protons in 1-iodoundecane and vinyl protons of CH2 in 1-undecene, enhancement factor of the protons of polarized species and the rate constant of decomposition for lauroyl peroxide have been determined. The mechanism of the decomposition of the entitled peroxides is discussed in terms of the radical pair theory.

Published
1986
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33. Studies on the kinetics of decomposition of diacyl peroxides: III. Kinetics and mechanism of decomposition of 3, 5, 5-trimethylhexanoyl peroxide in benzene

Author

Lei Xue‐Gong and Liu You-Cheng

Subjects
chemistry.chemical_compound, chemistry, Galvinoxyl, Thermal decomposition, Kinetics, Organic chemistry, Molecule, Cage effect, General Chemistry, Benzene, Photochemistry, Peroxide, Scavenging
Abstract

The kinetics of decomposition of 3,5,5-trimethylhexanoyl peroxide (1) in benzene at 30, 40, and 50°C respectively have been studied and the cage effect, main products and the products obtained in scavenging experiment with galvinoxyl determined and characterized. The results show that the decomposition of 1, with initial concentration between 0.04 to 0.43 mol. L−1, followed first plus three halves order kinetics with cage effect of 0.6, and the mechanism of decomposition is basically the same as previously proposed for lauroyl peroxide (2).4 In comparison with 2, the decomposition of 1 at the same temperature showed a faster rate for spontaneous decomposition, a larger cage effect and lesser induced decomposition, which is attributed to the branching in molecule of 1, especially to the presence of β-methyl group, which caused a larger entropy increase between the peroxide molecule and the transition state for decomposition.

Published
1983
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34. Experimental studies on the antitumor action of free radicals: Antitumor action of galvinoxyl

Author

Ding Yu, Ma Rundi, Liu Yaohua, Liu You-Cheng, Yang Di-Lun, Duan Xuezhi, Lei Xue‐Gong, Yu Lijian, Zhang Aixian, and Liu Wenqin

Subjects
Male, Free Radicals, Radical, Antineoplastic Agents, Tumor cells, In Vitro Techniques, In vitro, Scavenger, Mice, chemistry.chemical_compound, Liver Neoplasms, Experimental, Galvinoxyl, chemistry, Biochemistry, In vivo, Medicine public health, Animals, Female, Benzhydryl Compounds, Sarcoma 180, Inhibitory effect, Cells, Cultured, Earth-Surface Processes
Abstract

Galvinoxyl is a long-lived free radical and a highly efficient scavenger of shorter-lived free radicals. In vitro studies demonstrated that galvinoxyl has an inhibitory effect on tumor cells of sarcoma 180 and ascitic form of hepatoma. The higher the concentration of galvinoxyl, the more remarkable its inhibiting effect. Growth of the hepatoma cells in vivo was also inhibited when they had been treated in vitro with galvinoxyl. Galvinoxyl showed an inhibition rate of 43.1%.

Published
1983
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