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2018 Volume 76 Issue 10
2018, 76(10): 739-748
doi: 10.6023/A18080340
Abstract:
The extreme environment resistance materials can be normally used under severe conditions (e.g. T ≤ -50℃ or T ≥ 200℃, 1000 h exposed to UV light etc.), which common hydrocarbon materials cannot tolerate. It was found that fluorine atoms can effectively enhance the extreme environment resistance property of materials. The reason why fluorine atoms have such ability is mainly due to two key factors:first, fluorine and carbon elements are in the same cycle of the periodic table, the electronegativity of fluorine is large (4.0) and its atomic radius is small; second, polarization of fluorine atom is extremely low. The C-F bond is the strongest chemical single bond (≥ 116 kcal/mol) in which the carbon atom participates. It is a short bond and highly polarized. This paper makes brief introduction to the development and present situation of fluorine-containing materials with extreme environment resistance. In the field of fluorination methods, the history of fluorine chemistry since 1970s, the researches on the formation and fracture of carbon-fluorine bond, the influence of fluorine on the formation of carbon-carbon bond and the related researches on polyfluoro-arylation methods are introduced. This paper also introduces the important results of fluorine-containing materials in lithium isotope extraction, thermo-stable fluoropolymers which can be applied in aviation, aerospace, automobile and other fields, as well as the preparation of high-performance fluorine-containing materials with low dielectric constant in electronic equipment and communication fields. In the future, how to further develop and optimize the fluorine-containing materials with extreme environment resistance and put the research results into large-scale use is the working direction for researchers.
The extreme environment resistance materials can be normally used under severe conditions (e.g. T ≤ -50℃ or T ≥ 200℃, 1000 h exposed to UV light etc.), which common hydrocarbon materials cannot tolerate. It was found that fluorine atoms can effectively enhance the extreme environment resistance property of materials. The reason why fluorine atoms have such ability is mainly due to two key factors:first, fluorine and carbon elements are in the same cycle of the periodic table, the electronegativity of fluorine is large (4.0) and its atomic radius is small; second, polarization of fluorine atom is extremely low. The C-F bond is the strongest chemical single bond (≥ 116 kcal/mol) in which the carbon atom participates. It is a short bond and highly polarized. This paper makes brief introduction to the development and present situation of fluorine-containing materials with extreme environment resistance. In the field of fluorination methods, the history of fluorine chemistry since 1970s, the researches on the formation and fracture of carbon-fluorine bond, the influence of fluorine on the formation of carbon-carbon bond and the related researches on polyfluoro-arylation methods are introduced. This paper also introduces the important results of fluorine-containing materials in lithium isotope extraction, thermo-stable fluoropolymers which can be applied in aviation, aerospace, automobile and other fields, as well as the preparation of high-performance fluorine-containing materials with low dielectric constant in electronic equipment and communication fields. In the future, how to further develop and optimize the fluorine-containing materials with extreme environment resistance and put the research results into large-scale use is the working direction for researchers.
2018, 76(10): 749-756
doi: 10.6023/A18060248
Abstract:
High-performance electrolyte is one of the key materials for achieving secondary batteries with high energy density, long cycle life and good safety. Traditional organic and aqueous systems, however, due to many restrictions (such as narrow potential window, low ionic conductivity, dendrite, gas expansion and corrosion, etc.), are unable to meet the demand of the further development for secondary batteries. In recent years, ionic liquid-inorganic particle hybrid electrolytes (IL-NPHE) have attracted much attention due to their high stabilities, non-combustibilities and various synergistic characteristics. This paper focuses on the latest research progress of IL-NPHE, and summarizes the physicochemical and electrochemical properties of this electrolyte system. Additionally, the synergistic mechanism between ionic liquid and inorganic particles is systematically summarized. Based on the above discussion, the future development trend and direction of IL-NPHE are prospected.
High-performance electrolyte is one of the key materials for achieving secondary batteries with high energy density, long cycle life and good safety. Traditional organic and aqueous systems, however, due to many restrictions (such as narrow potential window, low ionic conductivity, dendrite, gas expansion and corrosion, etc.), are unable to meet the demand of the further development for secondary batteries. In recent years, ionic liquid-inorganic particle hybrid electrolytes (IL-NPHE) have attracted much attention due to their high stabilities, non-combustibilities and various synergistic characteristics. This paper focuses on the latest research progress of IL-NPHE, and summarizes the physicochemical and electrochemical properties of this electrolyte system. Additionally, the synergistic mechanism between ionic liquid and inorganic particles is systematically summarized. Based on the above discussion, the future development trend and direction of IL-NPHE are prospected.
2018, 76(10): 757-773
doi: 10.6023/A18060250
Abstract:
The emission of volatile organic compounds (VOCs) causes serious harm to the natural environment and human health. Adsorption and catalytic oxidation are effective methods to control VOCs. With the large specific surface area, the uniform and controllable structure, and the surface acid sites, the zeolite is very suitable as the adsorbing materials and the catalyst carrier materials. It has been widely used in the fields of separation, adsorption and catalysis. This paper summarizes the recent research progress in the removal of different VOCs, such as alkanes, aromatic hydrocarbons, aldehydes, ketones, acids, esters, alcohols, and chlorinated hydrocarbons, over different zeolites and their various supported catalysts. The results show that the pore structure and surface properties of zeolite, the species, polarity and hydrophilicity of volatile organic compounds, have important effects on the adsorption properties of zeolite. The surface acidity of zeolite, the types and distribution of active catalysts, the types of VOCs, are the important factors for catalytic oxidation of volatile organic compounds. The synergistic effect between the zeolite and the active component allows the supported catalyst to exhibit excellent catalytic activity. Compared with zeolite-supported metal oxide catalysts, zeolite-supported noble metal catalysts have better catalytic activity for different VOCs, but noble metal catalysts are very expensive. The catalytic activity of zeolite-supported catalysts can be significantly improved by rationally designing multi-component metal oxides. In addition, the further research on the removal of VOCs by zeolite and its supported catalysts both is prospected.
The emission of volatile organic compounds (VOCs) causes serious harm to the natural environment and human health. Adsorption and catalytic oxidation are effective methods to control VOCs. With the large specific surface area, the uniform and controllable structure, and the surface acid sites, the zeolite is very suitable as the adsorbing materials and the catalyst carrier materials. It has been widely used in the fields of separation, adsorption and catalysis. This paper summarizes the recent research progress in the removal of different VOCs, such as alkanes, aromatic hydrocarbons, aldehydes, ketones, acids, esters, alcohols, and chlorinated hydrocarbons, over different zeolites and their various supported catalysts. The results show that the pore structure and surface properties of zeolite, the species, polarity and hydrophilicity of volatile organic compounds, have important effects on the adsorption properties of zeolite. The surface acidity of zeolite, the types and distribution of active catalysts, the types of VOCs, are the important factors for catalytic oxidation of volatile organic compounds. The synergistic effect between the zeolite and the active component allows the supported catalyst to exhibit excellent catalytic activity. Compared with zeolite-supported metal oxide catalysts, zeolite-supported noble metal catalysts have better catalytic activity for different VOCs, but noble metal catalysts are very expensive. The catalytic activity of zeolite-supported catalysts can be significantly improved by rationally designing multi-component metal oxides. In addition, the further research on the removal of VOCs by zeolite and its supported catalysts both is prospected.
2018, 76(10): 774-778
doi: 10.6023/A18070281
Abstract:
Recently the research work concerning B(C6F5)3 catalyzed reductive and amination of aldehydes and ketones revealed that this extremely electron-deficient borane is, actually, a rather water-tolerant catalyst. This fact considerably broadens the scope of the water/base tolerant FLP chemistry. In this project, an efficient one pot reductive amination method has been developed by reaction of aldehydes and alkoxyamines with hydrosilanes as the hydride sources and B(C6F5)3 as catalyst without cleavage of the N-O bond. This protocol can be used to prepare the secondary and tertiary alkoxyamines by starting from the primary and secondary ones, respectively. A special attention has been paid to elucidate the role of water in the reductive amination. When benzaldehyde reacts with benzoxylamine, only the condensation product oxime ether could be observed. Whereas surprisingly when excess amount of water is added, the reductive amination goes successfully like the alkoxyamine hydrochloride works. The detailed NMR data has shown that a transformation of the intermediate oximes ArCH=NOR to the "ammonium borates"[ArCH=NHOR]+[X-B(C6F5)3]-(X=Cl, OH) can take place in the reaction system, while the latter can be converted into the well-known active intermediate "ammonium hydroborates"[ArCH=NHOR]+[H-B(C6F5)3]- to reduce the C=N bond under mild condition in the presence of hydrosilanes. That means the deprotonation reaction of the Lewis acid water adduct H2O-B(C6F5)3 could be a key step for the B(C6F5)3 catalyzed reaction under moist condition. In this case the adduct H2O-B(C6F5)3 acts as a Brønsted acid as HCl does. Meanwhile a simulative experiment under different ratio of water has been fulfilled to prove this speculation. The C=N bond of Benzalaniline (PhCH=NPh) and Benzyloxy oxime ether (PhCH=NOCH2Ph) could be reduced only in presence of 2 equiv. H2O rather than equivalent. Based on this study it has shown that in the frustrated Lewis pair (FLP) chemistry, the Lewis acid B(C6F5)3 is not only a highly effective and water tolerant catalyst, the "disfavored" deprotonation of H2O-B(C6F5)3 adductis possibly playing an important role in reductive amination reaction. To clarify in detail the actual role of water in the reductive amination reaction under the "moist" conditions would enable the further development of FLP and related catalyzed reactions.
Recently the research work concerning B(C6F5)3 catalyzed reductive and amination of aldehydes and ketones revealed that this extremely electron-deficient borane is, actually, a rather water-tolerant catalyst. This fact considerably broadens the scope of the water/base tolerant FLP chemistry. In this project, an efficient one pot reductive amination method has been developed by reaction of aldehydes and alkoxyamines with hydrosilanes as the hydride sources and B(C6F5)3 as catalyst without cleavage of the N-O bond. This protocol can be used to prepare the secondary and tertiary alkoxyamines by starting from the primary and secondary ones, respectively. A special attention has been paid to elucidate the role of water in the reductive amination. When benzaldehyde reacts with benzoxylamine, only the condensation product oxime ether could be observed. Whereas surprisingly when excess amount of water is added, the reductive amination goes successfully like the alkoxyamine hydrochloride works. The detailed NMR data has shown that a transformation of the intermediate oximes ArCH=NOR to the "ammonium borates"[ArCH=NHOR]+[X-B(C6F5)3]-(X=Cl, OH) can take place in the reaction system, while the latter can be converted into the well-known active intermediate "ammonium hydroborates"[ArCH=NHOR]+[H-B(C6F5)3]- to reduce the C=N bond under mild condition in the presence of hydrosilanes. That means the deprotonation reaction of the Lewis acid water adduct H2O-B(C6F5)3 could be a key step for the B(C6F5)3 catalyzed reaction under moist condition. In this case the adduct H2O-B(C6F5)3 acts as a Brønsted acid as HCl does. Meanwhile a simulative experiment under different ratio of water has been fulfilled to prove this speculation. The C=N bond of Benzalaniline (PhCH=NPh) and Benzyloxy oxime ether (PhCH=NOCH2Ph) could be reduced only in presence of 2 equiv. H2O rather than equivalent. Based on this study it has shown that in the frustrated Lewis pair (FLP) chemistry, the Lewis acid B(C6F5)3 is not only a highly effective and water tolerant catalyst, the "disfavored" deprotonation of H2O-B(C6F5)3 adductis possibly playing an important role in reductive amination reaction. To clarify in detail the actual role of water in the reductive amination reaction under the "moist" conditions would enable the further development of FLP and related catalyzed reactions.
2018, 76(10): 779-784
doi: 10.6023/A18070258
Abstract:
Rotaxanes, composed of macrocyclic wheel and linear axle, have been used in areas such as molecular machines, stimuli-responsive materials, information storage, supramolecular catalysts. The macrocyclic host and its noncovalent interaction are key for the rotaxanes. Pillar[n]arenes (n=5~10) have drew much attention as widely-used hosts. Their facile synthesis, unique rigid structure, versatile functionalization, and interesting host-guest properties enable pillar[n]arenes to build various supramolecular architectures including rotaxanes. Currently, the research of pillararene-based rotaxanes mainly focuses on the synthesis, the responsiveness to temperature and solvent, and the application as catalyst, however, reports of emissive pillararene-based rotaxanes are very rare. Besides, higher-ordered[n]rotaxanes (n ≥ 3) based on pillararene remain rarely explored limited by the poor synthetic yield, despite their fascinating structure and potential applications in molecular devices. Herein, we report two pillararene-based rotaxanes ([3]R and [3]R') incorporating naphthalene diimide with red fluorescence in solid state. The 1, 4-diethoxypillar[5]arene (EtP5A) was chosen as the wheel, diamino-substituted naphthalene diimides (NDI) were used as the axle containing two separated linear guest parts for EtP5A. The addition reaction of NDI-precursor S1/S2 and the stopper 3, 5-dimethylphenyl isocyanate with the presence of EtP5A afforded [3]R and[2]R (byproduct as model compound)/[3]R', respectively, with high yield of 45% for [3]R and 62% for [3]R'. The structures of rotaxanes were confirmed by 1H NMR spectroscopy, ROESY (rotating frame Overhause enhancement spectroscopy), and HR-ESI-MS. Limited by the length of linear chains, EtP5As are adjacent tightly to NDI in [3]R, whereas EtP5As stay four-atom distance away from NDI in 3[R]'. The optical properties of rotaxanes in various solvents and in powders were detected. [3]R and [3]R' show bright red fluorescence not only in solution but also in solid state, which distinguishes [3]R and [3]R' from [2]R and most of NDI-based fluorescent compounds. The increased fluorescence in solid state of [3]R and [3]R' benefits from the bulky EtP5As hindering the π-π interaction and suppressing the self-quenching of NDI. We suspect that [3]R and [3]R' may have potential applications in red-emitting materials and optoelectronic devices.
Rotaxanes, composed of macrocyclic wheel and linear axle, have been used in areas such as molecular machines, stimuli-responsive materials, information storage, supramolecular catalysts. The macrocyclic host and its noncovalent interaction are key for the rotaxanes. Pillar[n]arenes (n=5~10) have drew much attention as widely-used hosts. Their facile synthesis, unique rigid structure, versatile functionalization, and interesting host-guest properties enable pillar[n]arenes to build various supramolecular architectures including rotaxanes. Currently, the research of pillararene-based rotaxanes mainly focuses on the synthesis, the responsiveness to temperature and solvent, and the application as catalyst, however, reports of emissive pillararene-based rotaxanes are very rare. Besides, higher-ordered[n]rotaxanes (n ≥ 3) based on pillararene remain rarely explored limited by the poor synthetic yield, despite their fascinating structure and potential applications in molecular devices. Herein, we report two pillararene-based rotaxanes ([3]R and [3]R') incorporating naphthalene diimide with red fluorescence in solid state. The 1, 4-diethoxypillar[5]arene (EtP5A) was chosen as the wheel, diamino-substituted naphthalene diimides (NDI) were used as the axle containing two separated linear guest parts for EtP5A. The addition reaction of NDI-precursor S1/S2 and the stopper 3, 5-dimethylphenyl isocyanate with the presence of EtP5A afforded [3]R and[2]R (byproduct as model compound)/[3]R', respectively, with high yield of 45% for [3]R and 62% for [3]R'. The structures of rotaxanes were confirmed by 1H NMR spectroscopy, ROESY (rotating frame Overhause enhancement spectroscopy), and HR-ESI-MS. Limited by the length of linear chains, EtP5As are adjacent tightly to NDI in [3]R, whereas EtP5As stay four-atom distance away from NDI in 3[R]'. The optical properties of rotaxanes in various solvents and in powders were detected. [3]R and [3]R' show bright red fluorescence not only in solution but also in solid state, which distinguishes [3]R and [3]R' from [2]R and most of NDI-based fluorescent compounds. The increased fluorescence in solid state of [3]R and [3]R' benefits from the bulky EtP5As hindering the π-π interaction and suppressing the self-quenching of NDI. We suspect that [3]R and [3]R' may have potential applications in red-emitting materials and optoelectronic devices.
2018, 76(10): 785-792
doi: 10.6023/A18070293
Abstract:
In this work, the adsorption performance of 6013 computation-ready, experimental metal-organic frameworks (CoRE-MOFs) for the capture of H2S and CO2 from natural gas mixture (CH4, C2H6, C3H8, H2S and CO2) is calculated by high-throughput screening of grand canonical Monte Carlo (GCMC) simulation in 298 K and 10 bar. For the comprehensive consideration of both adsorption capacities and selectivities of H2S+CO2, first, we compare three different tradeoff methods (α tradeoff method (Tradeoff between SH2S+CO2/C1-C3 and NH2S+CO2, TSN), standard normal method (SNM), β tradeoff method (Tradeoff between selectivity and capacity, TSC)). The effect of selectivity on the new tradeoff variables are appropriately reduced by these tradeoff methods, because some of selectivities are very high. Thus, the new tradeoff variables can comprehensively evaluate the adsorption performance of CoRE-MOFs. Moreover, the correlation of each MOF descriptor (including the largest cavity diameter (LCD), void fraction (φ), surface area (VSA) and isosteric heat (Qst0)) with three tradeoff variables are analyzed by Pearson correlation coefficient, respectively. The LCDs are calculated by Zeo++ software, but the φ and VSA are simulated by RASPA using probes of He and N2, respectively. The Qst0 of each adsorbate gas are calculated at infinite dilution condition using NVT-MC method. All GCMC simulations for the screening are carried out using RASPA software. The results show that TSC has the best correlation with four MOF descriptors and the linear model could sufficiently describe the relationship between TSC and four MOF descriptors. Pearson correlation coefficients of four descriptors were -0.613, -0.717, -0.673 and 0.536 on TSC, respectively. Multiple linear regression is applied to quantitatively determine the influencing degree of four descriptors on performance, respectively. Among the four descriptors, Qst0, φ, and LCD have larger standardized regression coefficients compared with VSA. This indicates that Qst0, φ, and LCD are more useful in describing the performances of the MOFs. Thus, these three descriptors are used in the decision tree modeling to define an effective path for screening high-performance MOFs. It is concluded that a maximum probability (77.6%) of finding the good MOFs can be obtained from the three descriptors. Finally, the 20 best MOFs stand out from the whole database, and find that the alkali or alkaline earth metals in MOFs could effectively enhance the separation performance of H2S and CO2. The microscopic insights and guidelines by this computational study can provide significant theoretical guidance for the development of adsorbent for the purification of natural gas.
In this work, the adsorption performance of 6013 computation-ready, experimental metal-organic frameworks (CoRE-MOFs) for the capture of H2S and CO2 from natural gas mixture (CH4, C2H6, C3H8, H2S and CO2) is calculated by high-throughput screening of grand canonical Monte Carlo (GCMC) simulation in 298 K and 10 bar. For the comprehensive consideration of both adsorption capacities and selectivities of H2S+CO2, first, we compare three different tradeoff methods (α tradeoff method (Tradeoff between SH2S+CO2/C1-C3 and NH2S+CO2, TSN), standard normal method (SNM), β tradeoff method (Tradeoff between selectivity and capacity, TSC)). The effect of selectivity on the new tradeoff variables are appropriately reduced by these tradeoff methods, because some of selectivities are very high. Thus, the new tradeoff variables can comprehensively evaluate the adsorption performance of CoRE-MOFs. Moreover, the correlation of each MOF descriptor (including the largest cavity diameter (LCD), void fraction (φ), surface area (VSA) and isosteric heat (Qst0)) with three tradeoff variables are analyzed by Pearson correlation coefficient, respectively. The LCDs are calculated by Zeo++ software, but the φ and VSA are simulated by RASPA using probes of He and N2, respectively. The Qst0 of each adsorbate gas are calculated at infinite dilution condition using NVT-MC method. All GCMC simulations for the screening are carried out using RASPA software. The results show that TSC has the best correlation with four MOF descriptors and the linear model could sufficiently describe the relationship between TSC and four MOF descriptors. Pearson correlation coefficients of four descriptors were -0.613, -0.717, -0.673 and 0.536 on TSC, respectively. Multiple linear regression is applied to quantitatively determine the influencing degree of four descriptors on performance, respectively. Among the four descriptors, Qst0, φ, and LCD have larger standardized regression coefficients compared with VSA. This indicates that Qst0, φ, and LCD are more useful in describing the performances of the MOFs. Thus, these three descriptors are used in the decision tree modeling to define an effective path for screening high-performance MOFs. It is concluded that a maximum probability (77.6%) of finding the good MOFs can be obtained from the three descriptors. Finally, the 20 best MOFs stand out from the whole database, and find that the alkali or alkaline earth metals in MOFs could effectively enhance the separation performance of H2S and CO2. The microscopic insights and guidelines by this computational study can provide significant theoretical guidance for the development of adsorbent for the purification of natural gas.
2018, 76(10): 793-801
doi: 10.6023/A18080317
Abstract:
Sevoflurane is an excellent volatile anaesthetic which has been widely in clinical use. However, it was found that sevoflurane is a potent green-house gas with a significant global warming potential. Atmospheric degradation of sevoflurane is desired for its long-term application. The reaction of sevoflurane with hydroxyl radicals (OH·) produces two radical species, namely, (CF3)2C(·)OCH2F and (CF3)2CHOC(·)HF, which have different reactivity. Under the low-NO atmospheric conditions, it was found that both radical fragments enable to initialize the regeneration of OH·radicals in the presence of molecular oxygen (O2). Microscopic mechanisms for the reactions of the two radicals with O2 have been investigated for the first time in this work. Geometries of various intermediates and transition states on the doublet potential energy surfaces were optimized at the M06-2X/6-311++G (d, p) level of theory. Moreover, the single-point calculations were carried out using the composite model CBS-Q to refine the reaction energetics to the chemical accuracy. It was revealed that the formation of peroxy intermediate (RO2·) undergoes via the definitive barriers of 1.3 or 1.8 kcal·mol-1, in contrast to the barrierless association between the alkyl radicals and O2. Apparently, the association of the fluorinated alkyl radicals with O2 takes place more slowly due to the substitute effect. Although the addition of O2 to the fluorine-rich radical site is more preferable than that to the fluorine-poor site, the latter is more exothermic in view of the exothermicity of the intermediates RO2·. The barriers for the subsequent H-migration of RO2·to form the QOOH intermediates are 17.9 and 21.5 kcal·mol-1, respectively. Both barriers lie well below the reactant asymptote, indicating the isomerization paths are energetically favorable. Decomposition of QOOH takes place via three competitive mechanisms, including the step-wise bond fission, the three-body concerted cleavage, and the four-center intramolecular SN2 reaction, to produce OH·radicals predominantly. All the reaction pathways could be competitive for (CF3)2C(OC(·)HF)OOH because the energies of the corresponding barriers are close. In contrast, only the SN2 displacement energetic route is dominant for (CF3)2C(·)OC(HF)(OOH). Neither step-wise nor three-body pathways is important because the barrier height is roughly 7 kcal·mol-1 higher than that for the SN2 pathway. The isomerization of QOOH to alkoxy intermediate is of little importance due to the significant barrier even though it is highly exothermic. Implication of the current theoretical findings in the OH·radicals recycling reaction in atmosphere has been illustrated.
Sevoflurane is an excellent volatile anaesthetic which has been widely in clinical use. However, it was found that sevoflurane is a potent green-house gas with a significant global warming potential. Atmospheric degradation of sevoflurane is desired for its long-term application. The reaction of sevoflurane with hydroxyl radicals (OH·) produces two radical species, namely, (CF3)2C(·)OCH2F and (CF3)2CHOC(·)HF, which have different reactivity. Under the low-NO atmospheric conditions, it was found that both radical fragments enable to initialize the regeneration of OH·radicals in the presence of molecular oxygen (O2). Microscopic mechanisms for the reactions of the two radicals with O2 have been investigated for the first time in this work. Geometries of various intermediates and transition states on the doublet potential energy surfaces were optimized at the M06-2X/6-311++G (d, p) level of theory. Moreover, the single-point calculations were carried out using the composite model CBS-Q to refine the reaction energetics to the chemical accuracy. It was revealed that the formation of peroxy intermediate (RO2·) undergoes via the definitive barriers of 1.3 or 1.8 kcal·mol-1, in contrast to the barrierless association between the alkyl radicals and O2. Apparently, the association of the fluorinated alkyl radicals with O2 takes place more slowly due to the substitute effect. Although the addition of O2 to the fluorine-rich radical site is more preferable than that to the fluorine-poor site, the latter is more exothermic in view of the exothermicity of the intermediates RO2·. The barriers for the subsequent H-migration of RO2·to form the QOOH intermediates are 17.9 and 21.5 kcal·mol-1, respectively. Both barriers lie well below the reactant asymptote, indicating the isomerization paths are energetically favorable. Decomposition of QOOH takes place via three competitive mechanisms, including the step-wise bond fission, the three-body concerted cleavage, and the four-center intramolecular SN2 reaction, to produce OH·radicals predominantly. All the reaction pathways could be competitive for (CF3)2C(OC(·)HF)OOH because the energies of the corresponding barriers are close. In contrast, only the SN2 displacement energetic route is dominant for (CF3)2C(·)OC(HF)(OOH). Neither step-wise nor three-body pathways is important because the barrier height is roughly 7 kcal·mol-1 higher than that for the SN2 pathway. The isomerization of QOOH to alkoxy intermediate is of little importance due to the significant barrier even though it is highly exothermic. Implication of the current theoretical findings in the OH·radicals recycling reaction in atmosphere has been illustrated.
2018, 76(10): 802-806
doi: 10.6023/A18070297
Abstract:
In vivo, free radical damage of disulfide bonds in proteins affects the structure and function of proteins, and has an important relationship with cell aging. Therefore, studying the mechanism of the interaction between free radicals and disulfide bonds, and understanding the interaction process between free radicals and disulfide bonds, is important for the cleavage or proteciton of disulfide bond. In this paper, liquid-assisted surface desorption atmospheric pressure chemical ionization technology is adopted (LA-DAPCI), to construct a two-channel ion source device, obtaining high abundance water radical cations (H2O)n+· (n=2~4). Using linear ion trap mass spectrometer, combining with Density Functional Theory, the interaction process between (H2O)n+· and bis(2-hydroxyethyl) disulfide (HEDS) in mass spectrometer and thermodynamic process of the interaction were studied. The results indicated that (H2O)n+· interacted with HEDS, forming a radical complex (M+H2O)+· (m/z 172) without covalent bond, and H2O in complex (M+H2O)+· (m/z 172) is derived from (H2O)n+·, not from the H2O of sample solution. Furthermore, thermodynamic theoretical calculation results demonstrated that H on the β-hydroxyl group of HEDS structure forms a weak hydrogen bond with S in the form of an intramolecular five-membered ring. During the interaction process, (H2O)n+· preferentially binds to the hydroxyl group of HEDS, forming a radical complex (M+H2O)+·, whose disulfide bond will be difficult to be cleaved. In conclusion, the β-hydroxyl group has a protective effect on the disulfide bond of HEDS during the interaction with water radical cations.
In vivo, free radical damage of disulfide bonds in proteins affects the structure and function of proteins, and has an important relationship with cell aging. Therefore, studying the mechanism of the interaction between free radicals and disulfide bonds, and understanding the interaction process between free radicals and disulfide bonds, is important for the cleavage or proteciton of disulfide bond. In this paper, liquid-assisted surface desorption atmospheric pressure chemical ionization technology is adopted (LA-DAPCI), to construct a two-channel ion source device, obtaining high abundance water radical cations (H2O)n+· (n=2~4). Using linear ion trap mass spectrometer, combining with Density Functional Theory, the interaction process between (H2O)n+· and bis(2-hydroxyethyl) disulfide (HEDS) in mass spectrometer and thermodynamic process of the interaction were studied. The results indicated that (H2O)n+· interacted with HEDS, forming a radical complex (M+H2O)+· (m/z 172) without covalent bond, and H2O in complex (M+H2O)+· (m/z 172) is derived from (H2O)n+·, not from the H2O of sample solution. Furthermore, thermodynamic theoretical calculation results demonstrated that H on the β-hydroxyl group of HEDS structure forms a weak hydrogen bond with S in the form of an intramolecular five-membered ring. During the interaction process, (H2O)n+· preferentially binds to the hydroxyl group of HEDS, forming a radical complex (M+H2O)+·, whose disulfide bond will be difficult to be cleaved. In conclusion, the β-hydroxyl group has a protective effect on the disulfide bond of HEDS during the interaction with water radical cations.
2018, 76(10): 807-812
doi: 10.6023/A18050201
Abstract:
Dual-functional thin films simultaneously demonstrating antireflective and antibacterial properties have important practical values in the fields of medicine and health. Unfortunately, related studies have so far been very limited. This work chose a quaternary ammonium salt with the longest carbon chain of C18 as antibacterial agent, and used it to modify an acid-catalyzed silica sol via chemical bonding. The obtained quaternary ammonium salt modified acid-catalyzed silica sol (Q-ASNs) was subsequently mixed with a hollow silica nanospheres sol (HSNs) followed by stirring for 6 h to obtain a mixed sol. The volume percentage of Q-ASNs was varied as 3.1%, 4.9%, 6.7%, and 8.4%, respectively. In detail, Q-ASNs were synthesized as follows:1 mL tetraethyl orthosilicate (TEOS), 0.6 mL quaternary ammonium salt methanol solution (65 wt%), 13.6 mL ethanol, 0.45 mL water and 21 μL HCl were mixed followed by stirring at room temperature for 4 h and aging for at least one day. HSNs were prepared according to the following procedure:0.1 g poly(acrylic acid) (PAA) was dissolved in 4.5 mL ammonium hydroxide, and then it was mixed with 90 mL absolute ethanol under stirring. This was followed by the injection of 800 μL TEOS under vigorous magnetic stirring at room temperature in 40 min. After 10 h, a HSNs sol containing~30 nm hollow silica nanospheres formed. Before mixing Q-ASNs and HSNs, the HSNs were stirred in a ventilating cabinet for more than 24 h to remove ammonia. Antireflective/antibacterial dual-functional thin films were fabricated by dip-coating from the mixed sol of Q-ASNs and HSNs. The optical properties of the films were optimized by regulating the mixing ratio of the above-mentioned two sols. The optimal thin film coated glass substrate presented high transmittance (Tmax=99.2%, Tave=98.6%) in the visible wavelength range of 400~800 nm. The HSNs and the mixed sol were observed by transmission electron microscopy. The fabricated thin films were characterized by scanning electron microscopy, atomic force microscopy, transmission/reflection spectroscopy, X-ray photoelectron spectroscopy, and confocal laser scanning microscopy using a live/dead reagent. The current method is simple and easy for large-area coating without any high-temperature heat treatment, and is thus promising for practical applications.
Dual-functional thin films simultaneously demonstrating antireflective and antibacterial properties have important practical values in the fields of medicine and health. Unfortunately, related studies have so far been very limited. This work chose a quaternary ammonium salt with the longest carbon chain of C18 as antibacterial agent, and used it to modify an acid-catalyzed silica sol via chemical bonding. The obtained quaternary ammonium salt modified acid-catalyzed silica sol (Q-ASNs) was subsequently mixed with a hollow silica nanospheres sol (HSNs) followed by stirring for 6 h to obtain a mixed sol. The volume percentage of Q-ASNs was varied as 3.1%, 4.9%, 6.7%, and 8.4%, respectively. In detail, Q-ASNs were synthesized as follows:1 mL tetraethyl orthosilicate (TEOS), 0.6 mL quaternary ammonium salt methanol solution (65 wt%), 13.6 mL ethanol, 0.45 mL water and 21 μL HCl were mixed followed by stirring at room temperature for 4 h and aging for at least one day. HSNs were prepared according to the following procedure:0.1 g poly(acrylic acid) (PAA) was dissolved in 4.5 mL ammonium hydroxide, and then it was mixed with 90 mL absolute ethanol under stirring. This was followed by the injection of 800 μL TEOS under vigorous magnetic stirring at room temperature in 40 min. After 10 h, a HSNs sol containing~30 nm hollow silica nanospheres formed. Before mixing Q-ASNs and HSNs, the HSNs were stirred in a ventilating cabinet for more than 24 h to remove ammonia. Antireflective/antibacterial dual-functional thin films were fabricated by dip-coating from the mixed sol of Q-ASNs and HSNs. The optical properties of the films were optimized by regulating the mixing ratio of the above-mentioned two sols. The optimal thin film coated glass substrate presented high transmittance (Tmax=99.2%, Tave=98.6%) in the visible wavelength range of 400~800 nm. The HSNs and the mixed sol were observed by transmission electron microscopy. The fabricated thin films were characterized by scanning electron microscopy, atomic force microscopy, transmission/reflection spectroscopy, X-ray photoelectron spectroscopy, and confocal laser scanning microscopy using a live/dead reagent. The current method is simple and easy for large-area coating without any high-temperature heat treatment, and is thus promising for practical applications.
