氮氧自由基的研究(Ⅰ)——哌啶类氮氧自由基的合成与反应

本文报导了从4-氧-2,2,6,6-四甲基派啶氧化成4-氧-2,2,6,6-四甲基哌啶-1-氧自由基的一个改进方法,它具有收率高、反应时间短的优点。还对4-氧-2,2,6,6-四甲基哌啶-1-氧与羟胺盐酸盐在不同pH条件下的反应进行了研究:在碱性条件(pH 9-11)下得到该自由基的肟,在近中性条件(pH7-8)下,得到自由基肟的Beckmann重排产物,在酸性条件(pH2-5)下,得多一非自由基产物的盐酸盐,其分子式为C₉H₁₈N₂O₂·HCl.4-氧-2,2,6,6-四甲基哌啶-1-氧自由基很容易与抗坏血酸反应,被还原为1-羟基-4-氧-2,2,6,6-四甲基哌啶。对几种氮氧自由基在固态的顺磁共振谱及质谱也进行了测定。     

钙钛矿型复合氧化物CaVO3的制备及对氧还原反应的电催化性能

以五氧化二钒、硝酸钙、柠檬酸和草酸为原料,采用溶胶-凝胶法制备出CaVO₃的前驱体,在氩气保护下1000 ℃煅烧2 h,成功制备出目标产物CaVO₃.对前驱体和目标产物分别进行了傅里叶变换红外(FTIR)光谱、热重(TG)分析、X射线衍射(XRD)和电导率等表征.在1 mol·L^-1的KOH电解质溶液中测试了样品的氧还原反应(ORR)催化性能.结果表明,修饰电极上(ORR)的电子转移数是1.5-1.7,发生的是2电子还原.     

Formation of diagnostic product ions from cyanobacterial cyclic peptides by the two-bond fission mechanism using ion trap liquid chromatography/multi-stage mass spectrometry

Product ions obtained by tandem mass spectrometry (MS/MS) are quite effective for the amino acid sequencing of linear peptides. However, in the case of cyclic peptides, the fragmentation pattern is complicated because the cleavages occur randomly and product ions are generated as a(n), b(n), c(n), x(n), y(n) and z(n) series ions; therefore, the authors have never obtained sufficient sequence information. In order to overcome this problem, we applied ion trap liquid chromatography/multi-stage mass spectrometry (LC/MS(n)) and characterized the product ions obtained from anabaenopeptins and aeruginopeptins as the cyclic peptides. For the anabaenopeptins, MS(2) analysis did not provide sufficient sequence information on the cyclic structure, and MS(3) analysis was applied to sequence the constituent amino acids. Diagnostic product ions were obtained by the MS(3) analysis and were quite effective for obtaining the sequence information of the constituent amino acids. MS(2) analysis was, however, sufficient to obtain the sequence information of the aeruginopeptins. In both cases, the resulting product ions obtained from the cyclic structures were formed by the two-bond fission mechanism of the precursor ion, in which an initial fission of the cyclic structure to a linear one and subsequent fission(s) at the peptide bonds are included. The fragmentations were similar for the structurally related compounds, indicating that the cleavages occurred at definite peptide bonds. In addition, the resulting product ions are generated as b(n) series ions and the mass difference facilitates the amino acid sequencing. Thus, ion trap LC/MS(n) provides sequence information, and the resulting product ions are reproducible among the structurally related compounds and reliable for the sequencing of the constituent amino acids of the cyclic structure.     

Confirmation of sulfamethazine, sulfathiazole, and sulfadimethoxine residues in condensed milk and soft-cheese products by liquid chromatography/tandem mass spectrometry

A liquid chromatography/tandem mass spectrometry method (LC/MS/MS) is described for the simultaneous detection of 3 sulfonamide drug residues at 1.25 ppb in condensed milk and soft-cheese products. The 3 sulfonamide drugs of interest are sulfathiazole (STZ), sulfamethazine (SMZ), and sulfadimethoxine (SDM). The method includes extraction of the product with phosphate buffer, centrifugation of the diluted product, and application of a portion of the extract onto a polymeric solid-phase extraction cartridge. The cartridge is washed with water, and the sulfonamides are eluted with methanol. After evaporation, the residue is dissolved in 0.1% formic acid solution, and the solution is filtered before analysis by LC/MS/MS. The LC/MS/MS program involved a series of time-scheduled selected-reaction monitoring transitions. The transitions of MH+ to the common product ions at m/z 156, 108, and 92 were monitored for each residue. In addition, SMZ and SDM had a fourth significant and unique product ion transition that could be measured. Validation was performed with control and fortified-control condensed bovine milk with 2.5, 5, and 10 ppb sulfonamides. This method was applied to imported flavored and unflavored condensed milk and cream cheese bars. The presence of STZ and SMZ residues was confirmed in 3 out of 6 products.     

The mechanism of pyrolysis of polycycloalkyl sulfonates : The homo-retroene reaction in the noradamantane, adamantane and diamantane series

The minor product, 4-protoadamantene (5), from the gas phase pyrolysis of 2-adamantyl mesylate (3) was shown by labelling experiments not to arise from the major product, 2,4-dehydroadamantane (4), but rather by a concerted process (homo-retroene reaction). In the formation of 4, 1,3-elimination is favored by at least a 92:8 margin over a competitive route involving -elimination to a carbene and then C-H insertion. Equatorial and axial 2-noradamantyl mesylates pyrolyze to give predominantly 4-brendene (11) and triaxane (12), respectively, as required by concerted 1,3-eliminations, and not by an ion pair mechanism. The cross-over product appears in each case to result from the epimerizarion of the starting material by a wall-catalyzed process. In agreement with the results of the noradamantyl substrates, pyrolysis of 3-diamantyl mesylate (16) gave results which suggest that product stability helps to determine the course of the reaction. The products with the least amount of strain were obtained, namely 3,5-dehydrodiamantane (17) and pentacyclo[8.3.1.0^2,8.0^4,13.0^7,12]tetradec-5-ene (19, protodiamantene). The ease of separation of the cyclopropanic and olefinic products makes these reactions synthetically useful.     

Influence of mobile phase composition and thermodynamics on the normal phase chromatography of echinocandins

In the normal phase preparative HPLC of fermentation derived echinocandins, resolution of key impurities from the product of interest, pneumocandin B(o), is accomplished using a ternary ethyl acetate/methanol/water mobile phase with silica gel as the sorbent. In this work, previous characterization of the system is extended to define the impact and role of water content on the separation efficiency and retention of pneumocandin B(o). Experimental results indicate that column efficiency, measured using both the product of interest and small molecule tracers (compounds used for pulse tests), is good despite the use of an irregular silica and unusually high levels (greater than 6%) of water in the mobile phase. In contrast to column efficiency measurements using small molecules (MEK and toluene), measurements performed with the product itself indicate improved efficiency with increasing water content of the mobile phase. Building on these results, a scale-up/scale-down protocol was developed based on measurements of column efficiency using theoretical plate counts determined with pneumocandin B(o). Since the solubility of pneumocandin B(o) in the ternary mobile phase is relatively low, a higher strength solvent with higher levels of methanol and water is employed for dissolution of the crude product at concentrations of up to 40g/L. The mismatch between the high strength solvent used for the feed introduction and the mobile phase has the potential to affect column performance. The impact of this mismatch using plate count measurements with the product at both analytical and semi-preparative scales was found not to be significant. Finally, a van't Hoff analysis was performed to characterize the thermodynamics of adsorption of pneumocandin B(o) on silica. The analysis shows that the adsorption process for pneumocandin B(o) on silica in the ternary solvent system is endothermic (DeltaH(ads)>0), implying that the adsorption is entropically driven. Results from an overall water balance across the column indicate significant enrichment of adsorbed water on the silica surface. These results further emphasize the importance of selective partitioning of water between the bulk mobile phase and the silica as a dominant factor in controlling retention.     

Influence of Isotope Effects on Product Polarizations of N(2D)+D2, N(2D)+H2 and N(2D)+HD Reactive Systems

To figure out the influence of isotope effect on product polarizations of the N(²D)+D₂ reactive system and its isotope variants, quasi-classical trajectory(QCT) calculation was performed on Ho’s potential energy surface(PES) of ²A″ state. Product polarizations such as product distributions of P(θ_r), P(φ_r) and P(θ_r,φ_r), as well as the generalized polarization-dependent differential cross sections(PDDCSs) were discussed and compared in detail among the four product channels of the title reactions. Both the intermolecular and intramolecular isotope effects were proved to be influential on product polarizations.     

Photodissociation at 193 nm of some singly protonated peptides and proteins with m/z 2000-9000 using a tandem time-of-flight mass spectrometer equipped with a second source for delayed extraction/post-acceleration of product ions

A tandem time-of-flight mass spectrometer was built for photodissociation (PD) of singly protonated peptides and small proteins generated by matrix-assisted laser desorption/ionization. PD was performed in a second source after deceleration of precursor ions. The delayed extraction/post-acceleration scheme was used for the product ions. For the PD at 193 nm of small singly protonated peptides, the present instrument showed much better sensitivity and resolution for product ions than the previous one (Moon JH, Yoon SH, Kim MS, Bull. Korean Chem. Soc. 2005; 26: 763) even though the overall spectral patterns obtained with the two instruments were similar. The present instrument was inferior in precursor ion selection and background noise level. PD was achieved for precursor ions as large as the singly protonated ubiquitin (m/z 8560.63), indicating that the photoexcitation is capable of supplying a sufficient amount of internal energy to dissociate large singly protonated proteins. As the precursor ion m/z increased, however, product ion signals deteriorated rather rapidly. As in the PD of small peptide ions with m/z around 1000, the types of the product ions generated from singly protonated peptides with m/z in the range 2000-4000 were mostly determined by the positions of arginine residues. Namely, a(n) and d(n) ions dominated when an arginine residue(s) was near the N-terminus while v(n), w(n), x(n) and y(n) dominated when the same residue(s) was near the C-terminus. In addition, d(n), v(n) and w(n) ions were generated according to the correlation rules previously observed in the collisionally activated dissociation. Isoleucine and leucine isomers could be easily distinguished based on the w(n) and d(n) ions.     

'N-in-one' strategy for metabolite identification using a liquid chromatography/hybrid triple quadrupole linear ion trap instrument using multiple dependent product ion scans triggered with full mass scan

This paper describes a new strategy that utilizes the fast trap mode scan of the hybrid triple quadrupole linear ion trap (QqQ(LIT)) for the identification of drug metabolites. The strategy uses information-dependent acquisition (IDA) where the enhanced mass scan (EMS), the trap mode full scan, was used as the survey scan to trigger multiple dependent enhanced product ion scans (EPI), the trap mode product ion scans. The single data file collected with this approach not only includes full scan data (the survey), but also product ion spectra rich in structural information. By extracting characteristic product ions from the dependent EPI chromatograms, we can provide nearly complete information for in vitro metabolites that otherwise would have to be obtained by multiple precursor ion scan (prec) and constant neutral loss (NL) analysis. This approach effectively overcomes the disadvantages of traditional prec and NL scans, namely the slow quadrupole scan speed, and possible mass shift. Using nefazodone (NEF) as the model compound, we demonstrated the effectiveness of this strategy by identifying 22 phase I metabolites in a single liquid chromatography/tandem mass spectrometry (LC/MS/MS) run. In addition to the metabolites reported previously in the literature, seven new metabolites were identified and their chemical structures are proposed. The oxidative dechlorination biotransformation was also discovered which was not reported in previous literature for NEF. The strategy was further evaluated and worked well for the fast discovery setting when a ballistic gradient elution was used, as well as for a simulated in vivo setting when the incubated sample (phase I metabolites) was spiked to control human plasma extract and control human urine.     

Microwave-assisted extraction of phenolics from Canarium album L. and identification of the main phenolic compound

Microwave-assisted extraction (MAE) was applied in the extraction of phenolics from Canarium album L. Effects of various conditions including the solvent, solvent to material ratio, microwave power and irradiation time on extraction yield of phenolics were investigated. In terms of the optimal conditions of MAE, it was concluded that 70% (v/v) of ethanol was the proper extraction solvent, the solvent to material ratio was 10 : 1 (mL : g), and the microwave power and irradiation time were 600 W and 15 s, respectively. Compared with normal stirring extraction and ultrasound-assisted extraction, the MAE of phenolics from C. album L. was more time efficient and gave a high extraction rate. More than 1.2% extraction yield was achieved with MAE, and the purity of the phenolics in the extract product was up to 25%. In addition, by ultraviolet-visible (UV) spectrometry and electrospray ionised mass spectrometry (ESI/MS), the main phenolic compound in the extract product was identified as gallic acid.     

Synthesis and Characterization of the Monomer 2,2′ diallylbisphenol-A (ABFA) for obtaining Proton Exchange Membranes based on Crosslinked Sulphonated Poly(Arylene ether sulphone)s

Summary: In the present work, a methodology of synthesis and characterization of the monomer 2,2′ diallylbisphenol-A (ABFA) was developed, aiming at getting a precursor, with adequate purity, for obtaining cross-linked membranes based on sulphonated poly(arylene ether sulphone)s. The monomer synthesis involved the synthesis of 2,2′ bis(4-allyloxiphenyl)propane (Bisphenol-A, diallyl ether - BFAAE), from Bisphenol-A (BFA), followed by Claisen rearrangement of BFAAE, for the production of the target compound 2,2′ diallylbisphenol-A (ABFA). All the compounds, reagent BFA and obtained products, intermediate product BFAAE and final product ABFA, were characterized by FTIR (Fourier Transform infrared spectroscopy), TGA (Thermo-gravimetric analysis) and HPLC (High-performance liquid chromatography). The compound BFAAE was obtained with a yield of 94.5% and a purity of 97.3%, the latter characterized by TGA and by HPLC. The structure of the product was confirmed by FTIR. The thermal Claisen rearrangement process was conducted by using Differential Scanning Calorimetry (DSC) technique, from a factorial experiment planning, with two factors and three levels, with temperature and time being the variables. The above cited techniques were used for monitoring the Claisen rearrangement and for the characterization of the final product. The best results yield ABFA purity between 85 and 90%, approximately, for 220 °C/60min, 230 °C/30min and 210 °C/90min conditions. The obtained results suggest that, in the studied range, polymerization and degradation of the monomer ABFA occur, simultaneously to its formation.     

Regiochemistry of N‐substitution of some 4(5)‐substituted imidazoles under solvent‐free conditions

Imidazole‐4(5)‐carboxaldehyde and 4(5)‐cyanoimidazole were N‐benzylated and N‐methylated using benzyl chloride and methyl iodide on zinc oxide (ZnO), alumina, and KF/alumina under basic conditions without solvent. Triethylamine (Et₃N) or potassium carbonate was added as base in the reactions on ZnO and alumina. Imidazole‐4(5)‐carboxaldehyde was also benzylated on silica and carbon nanotubes. The effect of bases and solids on the product distribution of 1,4‐ and 1,5‐substituted compounds was investigated. In some cases, the product ratios were different for imidazole‐4(5)‐carboxaldehyde and 4(5)‐cyanoimidazole. In the reactions on KF/alumina the 1,4‐product was favored for both compounds. The combination of Et₃N and ZnO favored the 1,5‐product, however for the nitrile effect was not so pronounced. When N‐benzylation and methylation of the aldehyde were performed in the presence of catalytic amount of zinc chloride with Et₃N as base, the product distributions were the same as in the reactions on ZnO. Nitrile gave different product ratios on ZnO and in the presence of ZnCl₂. In addition, a mixture of N‐benzylimidazole and 1,3‐dibenzylimidazolium was produced when imidazole was benzylated on KF/alumina. Only the latter product was afforded when two equivalents of benzyl chloride were used.     

十二烷基硫酸钠对原位晶化制备小晶粒NaY的影响

研究了十二烷基硫酸钠对原位晶化制备小晶粒NaY的影响,并以包含小晶粒NaY的原位晶化产物为母体,通过铵交换和稀土离子交换制备出了REUSY催化剂.采用X射线衍射(XRD)、扫描电镜(SEM)、X射线荧光(XRF)及N₂物理吸附-脱附等手段对样品进行了表征,采用微反活性评价装置和小型固定流化床(ACE)评价了所制备催化剂在重油催化裂化反应中的催化性能.结果表明:在原位晶化合成NaY的体系中,添加高岭土微球质量5%的十二烷基硫酸钠,可以将分子筛的平均晶粒尺寸由540 nm减小到250 nm.相比于常规的原位晶化型流化催化裂化(FCC)催化剂,以包含小晶粒NaY的原位晶化产物为母体所制备出的催化剂,在反应原料的转化率、裂化产物的选择性以及抗积碳性能等方面均有明显的提高或改善.     

PHOTOOXYGENATION OF MESO-TETRAPHENYLPORPHYRIN METAL COMPLEXES

Abstract Cadmium(II), zinc(II), magnesium(II), and bis-[thallium(I)] complexes of meso -tetraphenyl-porphyrin undergo unsensitized photooxygenation to yield a bilitriene derivative as the final product. The reaction has previously been shown to involve singlet oxygen (Matsuura et al. , 1980); on the basis of mass spectrometry of products from ¹⁶O₂ and ¹⁸O₂ experiments, and characterization of the initial photoproduct, the reaction is shown to proceed by a mechanism in which one oxygen molecule adds to the metalloporphyrin to give a metallobilitriene. In the subsequent work-up, demetalation and addition of two hydrogen atoms gives the final product.     

无金属参与的二乙酸碘苯促进吲哚C3—H乙酸化反应

研究了无金属参与的二乙酸碘苯和吲哚的C3—H乙酸化反应, 通过对取代基效应、 温度以及二乙酸碘苯用量等因素的考察, 建立了反应的最佳条件: 反应温度60 ℃, 乙酸(HOAc)为溶剂. 在无需任何添加剂条件下, 以中等到良好的收率获得一系列C3位乙酸化的吲哚衍生物. 采用红外光谱、 核磁共振波谱、 高分辨质谱及X射线单晶衍射分析对目标化合物进行了结构表征, 并推测了可能的反应机理. 该催化体系对于克量级规模反应均能获得很好的结果.     

The 2-norbornyl cation via the fragmentations of exo- and endo-2-norbornyloxychlorocarbenes: distinction without much difference

exo- and endo-2-norbornyloxychlorocarbenes (7) were generated photochemically from the corresponding diazirines (6). Both carbenes fragmented to [2-norbornyl cation (carbon monoxide) chloride] ion pairs in MeCN or 1,2-dichloroethane solutions. Products included exo-norbornyl chloride (8), endo-norbornyl chloride (9), norbornene (10), and nortricyclene (11). Fragmentation activation energies were very low (< approximately 4 kcal/mol) and, as a result, the (laser flash photolytic) rate constants for fragmentation were essentially identical for exo-7 and endo-7 ( approximately 5 x 10(5) s(-1) in MeCN). Due to chloride return within the ion pairs, product distributions from exo- and endo-7 differed, with more endo-chloride formed from the endo-carbene: the 8/9 product ratio in MeCN was approximately 41 from exo-7, but only 4.6 from endo-7. Norbornene, formed by proton transfer to Cl(-) within the ion pairs, was a major product in both cases (44% from exo-7 and 62% from endo-7). In MeOH/MeCN, up to 28% of exo-2-norbornyl methyl ether formed at the expense of some of the norbornene, but even in 100% MeOH, the norbornyl chloride products of ion pair return still accounted for 46% and 31% of the exo-7 and endo-7 product mixtures (accompanied by 26-32% of norbornene). Electronic structure calculations on the ground states and fragmentation transition states of exo-7 and endo-7 are presented.     

反相胶束介质对2,3-二氨基吩嗪的荧光增敏作用研究

研究了反相胶束介质丁二酸双(2-乙基己基)酯磺酸钠(AOT)/正辛烷(n-octane)对漆酶催化氧化邻苯二胺的产物2,3-二氨基吩嗪(DAP)光谱性质的影响.试验表明,AOT/n-octane对DAP吸光性质稍有增敏作用,而对其荧光具有强烈的增敏作用,使DAP荧光量子产率提高近30倍,并进一步研究了微环境对荧光性质的影响和反相胶束介质AOT/n-octane对DAP荧光的增敏机理.     

高效液相色谱法测定水产品中四环素类抗生素残留

建立了一种高效液相色谱法测定水产品中土霉素、四环素、去甲基金霉素、金霉素、脱氧土霉素的分析方法。样品用5.0%高氯酸溶液提取,上清液用OasisHLB固相萃取柱净化,用紫外检测器于355nm测定。土霉素、四环素、去甲基金霉素检测限为0.01mg/kg,金霉素、脱氧土霉素检出限为0.02mg/kg。5种药物的回收率在74.8%~89.3%之间,相对标准偏差为3.95%~9.95%。方法适用于水产品中四环素类抗生素残留的检测。     

Gas-phase fragmentation study of novel synthetic 1,5-benzodiazepine derivatives using electrospray ionization tandem mass spectrometry

The fragmentation patterns of a series of three novel synthesized 3-hydroxy-4-phenyl-tetrahydro-1,5-benzodiazepin-2-ones (1-3), possessing the same backbone structure, were investigated using electrospray ionization mass spectrometry (ESI-MS) and tandem mass spectrometry (MS/MS) techniques. A simple methodology, based on the use of ESI (positive ion mode) and by increasing the declustering potential in the atmospheric pressure/vacuum interface, collision-induced dissociation (CID), was used to enhance the formation of the fragment ions. In general, the novel synthetic 1,5-benzodiazepine derivatives afforded, in the gas phase, both protonated and sodiated molecules. This led to the confirmation of the molecular masses and chemical structures of the studied compounds. Exact accurate masses were measured using a high-resolution ESI-quadrupole orthogonal time-of-flight (QqToF)-MS/MS hybrid mass spectrometer instrument.The breakdown routes of the protonated molecules were rationalized by conducting low-energy collision CID-MS/MS analyses (product ion- and precursor ion scans) using a conventional quadrupole-hexapole-quadrupole (QhQ) tandem mass spectrometer. All the observed major fragmentations for the 1,5-benzodiazepines occurred in the saturated seven-membered ring containing the nitrogen atoms. These formed a multitude of product ions by different breakdown routes. All the major fragmentations involved cleavages of the N-1-C-2 and C-3-C-4 bonds. These occurred with concomitant eliminations of glyoxal, benzene and ethyl formate, forming the product ion at m/z 119, which was observed in all the studied compounds. In addition, an unique simultaneous CID-MS/MS fragmentation was noticed for the 1,5-benzodiazepines 1 and 3, which occurred by a pathway dictated by the substituent located on the N-1-position. It was evident that the aromatic ring portion of the 1,5-benzodiazepines was resistant to CID-MS/MS fragmentation. Re-confirmation of the various geneses of the product ions was achieved by conducting a series of precursor ion scans. ESI-MS and CID-MS/MS analyses have thus proven to be a specific and very sensitive method for the structural identification of these novel 1,5-benzodiazepine derivatives.     

光氧化反应研究 Ⅸ.N-叔丁基苯甲叉亚胺的光氧化反应

对于含C=C和N=N双键化合物的光化学与光物理迄今已进行了广泛的研究,而介于其间的C=N双键类亚胺(imines)的光化学与光物理的探讨,由于视黄醛等涉及亚胺C=N键光化学的进展,而于近来得到重视.已知的C=N双键的光化学大多涉及环加成、重排、异构化和还原反应等^[1],而亚胺的光氧化反应则报道较少.