In this study, ion mobility separation coupled with tandem mass spectrometry （IM-tandem MS） was utilized to investigate the ionization behaviors of two amino acids including leucine and isoleucine. Under the electro...In this study, ion mobility separation coupled with tandem mass spectrometry （IM-tandem MS） was utilized to investigate the ionization behaviors of two amino acids including leucine and isoleucine. Under the electrospray ionization （ESI） mode, two protonation sites in each molecular sturcture caused two forms of protomer. One arose from the amino being protonated （amino-protomer） and the other from the carboxyl being protonated （car- boxyl-protomer）. In the two-dimensional （drift time, m/z） spectrum, the protomers had the same mass, but the dis- tinguishable drift times and fragmentation patterns. For the characterization purpose, the theoretical collision cross section （CCS） values of the protomers were calculated and proven to be consistent with the experimental. Moreover, the quantified relationship between the amino acids and their protomers was evaluated. It showed that the abun- dance of the carboxyl-protomer was proportional to the concentration of the amino acid, whereas that of the amino- protomer did not have the same trend. Under the atmospheric pressure chemical ionization （APCI） mode, only the carboxyl-protomer was observed. In addition, the amino-protomer and the cluster ions observed under ESI were absent completely. The results demonstrate that the ionization mode impacts heavily on the ionization behaviors of leucine and isoleucine not only on the form of therir protomers but also On the quantified relationship.展开更多
Over the past 15 years,ambient ionization mass spectrometry has rapidly developed,greatly expanding the applications of single-cell analysis,food and agricultural,envi-ronmental,chemical analysis,biomedical analysis,m...Over the past 15 years,ambient ionization mass spectrometry has rapidly developed,greatly expanding the applications of single-cell analysis,food and agricultural,envi-ronmental,chemical analysis,biomedical analysis,mass spectrometry imaging,among other areas.Real time mass spectrometry evaluations of living sample,such as in vivo direct analysis for single cell,clinical applications,metabolic monitoring of living species and transient intermediates in organic reactions,have demonstrated the power and potential significance of ambient ionization mass spectrometry.Here-in,we want to introduce a partial of our works atmospheric ionization mass spec-trometry,related to ambient ionization mass spectrometry.展开更多
β-H elimination is an intrinsic problem in transition metal-catalyzed reactions.We describe herein an interesting ligand effect for Et2Zn acting as either ethyl provider or H provider,respectively:by applying SPhos o...β-H elimination is an intrinsic problem in transition metal-catalyzed reactions.We describe herein an interesting ligand effect for Et2Zn acting as either ethyl provider or H provider,respectively:by applying SPhos or Gorlos-Phos as the ligand,β-H elimination has been successfully controlled in the corresponding Negishi coupling reaction affording different poly-substituted allenes in good yields and excellent selectivities.SAESI-MS (Solvent Assisted Electrospray Ionization Mass Spectrometry) has been applied to successfully capture the highly reactive organometallic intermediates,which show the different coordination behaviors of Pd with SPhos or Gorlos-Phos as the ligand in the catalytic cycle.In addition,the different reactivities of Int 1 and Int 2 towards the formation of the final allene products have been demonstrated via SAESI-MS/MS experiments.These MS studies visualized the whole catalytic cycle for the Negishi coupling reaction while nicely explain the observed reactivity and selectivity.展开更多
In the traditional research of volatile compounds, some trace-level compounds could not be identified by gas chromatography-mass spectrometry. Target and post-targeted methods were applied in the investigation of trac...In the traditional research of volatile compounds, some trace-level compounds could not be identified by gas chromatography-mass spectrometry. Target and post-targeted methods were applied in the investigation of trace-level volatile compounds in fresh turf crop （Lolium perenne L.） based on gas chromatography in combination with hybrid quadrupole time-of-flight mass spectrometry. According to literatures published, a target analysis was performed by using retention index, accurate masses of characteristic ions and second-stage mass spectra （MS2 spectra）. And a series of experiments showed that low electron impact energy was beneficial to the improvement of the abundances of low abundance molecular ion peak. peak was beneficial to qualitative analysis. Totally, 60 Enhancing the abundances of low abundance molecular ion volatile compounds were identified, the great majority cornpounds of which were benzeneacetaldehyde （14.8%）, 2,5-dimethyl-pyrazine （9.6%）, and hexanal （9.3%）. Identification was complied by mass spectral search, retention index and accurate masses of characteristic ions.展开更多
Degradation of the highly reactive hypervalent trifluoromethylation iodine reagent PhI（OAc）（CF3）, which can only be generated in situ with mixing PhI（OAc）2 and TMSCF3 in the presence of CsF, was studied by ESI-M...Degradation of the highly reactive hypervalent trifluoromethylation iodine reagent PhI（OAc）（CF3）, which can only be generated in situ with mixing PhI（OAc）2 and TMSCF3 in the presence of CsF, was studied by ESI-MS and GC-MS combined with ~9F-NMR. The important transient intermediate PhlCF3＋ was determined by ESI-MS, and the major volatile products containing CF3 were identified with the authentic compounds by using GC-MS, such as trifluoromethylbenzene, 2-iodobenzotrifluoride, 3-iodobenzotrifluoride, 4-iodobenzotrifluoride. Meanwhile, more evidences obtained with 19F-NMR were given for such degradation reaction. A possible rapid CF3 radical transfer reaction pathway was proposed to clarify such degradation progress based on the experimental results. Therefore, this study may be helpful in elucidating the intrinsic reactivity of PhI（OAc）（CF3） and the possible competing side reactions caused by such self-degradation pathway.展开更多
The sustainable development of synthetic reactions catalyzed by earth-abundant metals is one of the principal goals in homogeneous catalysis.However,so far most of the protocols are still plagued by sophisticated liga...The sustainable development of synthetic reactions catalyzed by earth-abundant metals is one of the principal goals in homogeneous catalysis.However,so far most of the protocols are still plagued by sophisticated ligands,hazardous activators,high catalyst loading(1—10 mol%)and/or multistep synthesis of the metal complexes in the process development.Consequently,the development of earth-abundant metal catalysts with high activity from commercially available metal salts is highly desirable for practical utilization of base metal catalyzed synthetic methodology.Herein,we report the catalyst generated in situ from a mixture of catalytic amounts of Ni(acac)_(2)(as low as 0.005 mol%)and CsF,which is found highly active for Markovnikov-selective hydroboration of vinylarenes,including 1,1-disubstituted vinylarenes and internal olefins,affording a wide range of secondary and tertiary alkyl boronates in excellent yields.Mechanistic experiments indicate that the key to the success of this catalysis is the use of CsF,which in combination with pinacolborane acts as an effective activator for Ni(acac)_(2),probably generating metastable Ni nanoparticles in situ that demonstrate high activity in the catalytic hydroboration(TON up to 18800).展开更多
A method for rapid identification and quantification of phthalate plasticizers in beverages was developed.A number of 15 phthalate plasticizers which covered all the phthalates concerned in the US Consumer Product Saf...A method for rapid identification and quantification of phthalate plasticizers in beverages was developed.A number of 15 phthalate plasticizers which covered all the phthalates concerned in the US Consumer Product Safety Improvement Act(CPSIA),European Union legislations and Chinese national standards(GB)were analyzed.By a combined solid-phase micro-extraction(SPME)and direct analysis in real time mass spectrometry(DART-MS)approach,phthalates at sub-ng•mL^(−1)levels can be qualitatively and quantitatively analyzed in a short time.The use of ultrahigh-resolving power and the accurate mass measurement capacity naturally provided by Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR-MS)minimizes the matrix interferences and thus enables the evaluation of phthalates in a complex matrix without extensive sample handlings or preparations.The limits of quantification(LOQs)were estimated to be at 0.3-5.0 ng•mL^(−1),lower than the Maximum Residue Limit(MRL)regulated by the European Union legislations(2007/19/EC)in foods,beverages,food packaging and toys(0.3-30 ng•mL^(−1)).This rapid and easy-to-use SPME-DART-FT-ICR-MS method provided a relatively high-throughput and powerful analytical approach for quick testing and screening phthalates in beverages and water samples to ensure food safety.展开更多
文摘In this study, ion mobility separation coupled with tandem mass spectrometry （IM-tandem MS） was utilized to investigate the ionization behaviors of two amino acids including leucine and isoleucine. Under the electrospray ionization （ESI） mode, two protonation sites in each molecular sturcture caused two forms of protomer. One arose from the amino being protonated （amino-protomer） and the other from the carboxyl being protonated （car- boxyl-protomer）. In the two-dimensional （drift time, m/z） spectrum, the protomers had the same mass, but the dis- tinguishable drift times and fragmentation patterns. For the characterization purpose, the theoretical collision cross section （CCS） values of the protomers were calculated and proven to be consistent with the experimental. Moreover, the quantified relationship between the amino acids and their protomers was evaluated. It showed that the abun- dance of the carboxyl-protomer was proportional to the concentration of the amino acid, whereas that of the amino- protomer did not have the same trend. Under the atmospheric pressure chemical ionization （APCI） mode, only the carboxyl-protomer was observed. In addition, the amino-protomer and the cluster ions observed under ESI were absent completely. The results demonstrate that the ionization mode impacts heavily on the ionization behaviors of leucine and isoleucine not only on the form of therir protomers but also On the quantified relationship.
基金The authors would like to acknowledge the financial support from the National Key Research and Development Program of China(No.2016YFC0800704)the National Natural Science Foundation of China(Grant Nos.21532005,21472228,and 21874144).
文摘Over the past 15 years,ambient ionization mass spectrometry has rapidly developed,greatly expanding the applications of single-cell analysis,food and agricultural,envi-ronmental,chemical analysis,biomedical analysis,mass spectrometry imaging,among other areas.Real time mass spectrometry evaluations of living sample,such as in vivo direct analysis for single cell,clinical applications,metabolic monitoring of living species and transient intermediates in organic reactions,have demonstrated the power and potential significance of ambient ionization mass spectrometry.Here-in,we want to introduce a partial of our works atmospheric ionization mass spec-trometry,related to ambient ionization mass spectrometry.
基金Financial supports from the National Natural Science Foundation of China(Grant No.21690063)the National Basic Re1search Program(2015CB856600)are greatly appreciated.
文摘β-H elimination is an intrinsic problem in transition metal-catalyzed reactions.We describe herein an interesting ligand effect for Et2Zn acting as either ethyl provider or H provider,respectively:by applying SPhos or Gorlos-Phos as the ligand,β-H elimination has been successfully controlled in the corresponding Negishi coupling reaction affording different poly-substituted allenes in good yields and excellent selectivities.SAESI-MS (Solvent Assisted Electrospray Ionization Mass Spectrometry) has been applied to successfully capture the highly reactive organometallic intermediates,which show the different coordination behaviors of Pd with SPhos or Gorlos-Phos as the ligand in the catalytic cycle.In addition,the different reactivities of Int 1 and Int 2 towards the formation of the final allene products have been demonstrated via SAESI-MS/MS experiments.These MS studies visualized the whole catalytic cycle for the Negishi coupling reaction while nicely explain the observed reactivity and selectivity.
文摘In the traditional research of volatile compounds, some trace-level compounds could not be identified by gas chromatography-mass spectrometry. Target and post-targeted methods were applied in the investigation of trace-level volatile compounds in fresh turf crop （Lolium perenne L.） based on gas chromatography in combination with hybrid quadrupole time-of-flight mass spectrometry. According to literatures published, a target analysis was performed by using retention index, accurate masses of characteristic ions and second-stage mass spectra （MS2 spectra）. And a series of experiments showed that low electron impact energy was beneficial to the improvement of the abundances of low abundance molecular ion peak. peak was beneficial to qualitative analysis. Totally, 60 Enhancing the abundances of low abundance molecular ion volatile compounds were identified, the great majority cornpounds of which were benzeneacetaldehyde （14.8%）, 2,5-dimethyl-pyrazine （9.6%）, and hexanal （9.3%）. Identification was complied by mass spectral search, retention index and accurate masses of characteristic ions.
基金The authors are grateful for financial supports from the National Natural Science Foundation of China （NSFC Grant Nos. 21475145 and 21472228） and Youth Innovation Promotion Association CAS （201317 !）.
文摘Degradation of the highly reactive hypervalent trifluoromethylation iodine reagent PhI（OAc）（CF3）, which can only be generated in situ with mixing PhI（OAc）2 and TMSCF3 in the presence of CsF, was studied by ESI-MS and GC-MS combined with ~9F-NMR. The important transient intermediate PhlCF3＋ was determined by ESI-MS, and the major volatile products containing CF3 were identified with the authentic compounds by using GC-MS, such as trifluoromethylbenzene, 2-iodobenzotrifluoride, 3-iodobenzotrifluoride, 4-iodobenzotrifluoride. Meanwhile, more evidences obtained with 19F-NMR were given for such degradation reaction. A possible rapid CF3 radical transfer reaction pathway was proposed to clarify such degradation progress based on the experimental results. Therefore, this study may be helpful in elucidating the intrinsic reactivity of PhI（OAc）（CF3） and the possible competing side reactions caused by such self-degradation pathway.
基金The authors acknowledge financial support from the National Natural Science Foundation of China(No.21821002).
文摘The sustainable development of synthetic reactions catalyzed by earth-abundant metals is one of the principal goals in homogeneous catalysis.However,so far most of the protocols are still plagued by sophisticated ligands,hazardous activators,high catalyst loading(1—10 mol%)and/or multistep synthesis of the metal complexes in the process development.Consequently,the development of earth-abundant metal catalysts with high activity from commercially available metal salts is highly desirable for practical utilization of base metal catalyzed synthetic methodology.Herein,we report the catalyst generated in situ from a mixture of catalytic amounts of Ni(acac)_(2)(as low as 0.005 mol%)and CsF,which is found highly active for Markovnikov-selective hydroboration of vinylarenes,including 1,1-disubstituted vinylarenes and internal olefins,affording a wide range of secondary and tertiary alkyl boronates in excellent yields.Mechanistic experiments indicate that the key to the success of this catalysis is the use of CsF,which in combination with pinacolborane acts as an effective activator for Ni(acac)_(2),probably generating metastable Ni nanoparticles in situ that demonstrate high activity in the catalytic hydroboration(TON up to 18800).
基金support from National Natural Science Foundation of China(Nos.21172250 and 21275155).
文摘A method for rapid identification and quantification of phthalate plasticizers in beverages was developed.A number of 15 phthalate plasticizers which covered all the phthalates concerned in the US Consumer Product Safety Improvement Act(CPSIA),European Union legislations and Chinese national standards(GB)were analyzed.By a combined solid-phase micro-extraction(SPME)and direct analysis in real time mass spectrometry(DART-MS)approach,phthalates at sub-ng•mL^(−1)levels can be qualitatively and quantitatively analyzed in a short time.The use of ultrahigh-resolving power and the accurate mass measurement capacity naturally provided by Fourier transform ion cyclotron resonance mass spectrometry(FT-ICR-MS)minimizes the matrix interferences and thus enables the evaluation of phthalates in a complex matrix without extensive sample handlings or preparations.The limits of quantification(LOQs)were estimated to be at 0.3-5.0 ng•mL^(−1),lower than the Maximum Residue Limit(MRL)regulated by the European Union legislations(2007/19/EC)in foods,beverages,food packaging and toys(0.3-30 ng•mL^(−1)).This rapid and easy-to-use SPME-DART-FT-ICR-MS method provided a relatively high-throughput and powerful analytical approach for quick testing and screening phthalates in beverages and water samples to ensure food safety.
