Sequential Observation of Alkali-halide Gas Phase Clusters in High Resolution TOF-MS and Prediction of Their Structures

Alkali halide clusters are interesting model systems that can provide information about how crystal properties evolve. To study these properties, a high-resolution atmospheric pressure inlet time-of-flight mass spectrometry （APi-TOF-MS） study of the sequential sodium halides series, C1-（NaC1）n and Br-（NaBr）m, has been reported, and the viability of the APi-TOF- MS equipped with an electrospray ionization source in determining cluster compositions has been demonstrated. The isotopic patterns were well resolved, as n=4 and 7 were determined to be the magic numbers for C1-（NaC1）n clusters, which were particularly abundant in the mass spectra. A global minimum search based on density functional theory enabled basin hopping yield the most stable structures for the mentioned series. The structures exhibit several distinct motifs which can be roughly categorized as linear chain, rock salt, and hexag- onal ring. This work provides an effective way to discover and elucidate the nonstoichiometry sodium halide clusters. These clusters possess very high vertical detachment energies and are generally called as superhalogens, which play important roles in chemistry because they are widely used in the synthesis of new classes of charge-transfer salts.     

一类新型硼氢阴离子BnH-m的激光产生

硼烷是最典型也是迄今研究得最系统的非金属原子簇化合物.目前已知的硼烷有闭式、开式和网式三种典型的结构,其通式分别为B_nH_n~(2-)、B_nH_(n+4)、和B_nH_(n+6),对这些硼烷的结构研究极大地丰富了原子簇化学。最近,我们在自制的装置上以脉冲激光束作用于NaBH_4,产生了一类组成与结构均与已知硼烧不同的单电荷硼氢阴离子,记录了它们的飞行时间质谱。     

Molar Mass Distribution and Chain Conformation of Polysaccharides from Fortunella margarita （Lour.） Swingle

In order to study the effects of different extraction methods on the molar mass distribution and chain conformation of Fortunella margarita(Lour.) Swingle polysaccharides(FP), we used extraction by hot water(WFP), ultrasonic-assisted treatment(UFP), microwave-assisted treatment(MFP) and ultrasonic/microwave-assisted treatment(UMFP), and then Fourier transform infrared(FT-IR) spectroscopy as well as 1H and 13 C nuclear magnetic resonance(NMR) spectroscopy to characterize the structural properties of FP extracted. The molar weight(Mw), polydispersity index(Mw/Mn), root-mean-square(RMS) turning radius(Rg), molar mass distribution and chain conformation of FP were studied systematically using size-exclusion chromatography(SEC), multi-angle laser light-scattering(MALLS) and refractive index(RI). WFP, UFP, MFP and UMFP are all typical carbohydrates according to 1H NMR, 13 C NMR and FT-IR measurements. The type of glycosidic linkage is mainly a β-glycosidic bond with a small amount of α-glycosidic bond. The results obtained by the SEC-MALLS-RI system showed the molar masses of WFP and UMFP were distributed mainly in the range of 5.0×106~1.0×107 g·mol–1 and they accounted for 57.80% and 56.84% of total FP, respectively. The molar masses of UFP and MFP were distributed mainly in the 1.0×106~5.0×106 g·mol–1 range, which accounted for 38.24% and 52.39% of FP, respectively. WFP and UMFP in water were uniform spherical polymers; UFP and MFP were typical highly branched polymers and the degree of branching for MFP was higher compared to UFP. These results indicated the ultrasonic- and microwave-assisted extraction methods caused a significant decrease of the molar mass of FP but the ultrasonic/microwave synergistic extraction method had no effect.     

纳秒强光场下呋喃的激光电离中高价离子的产生

The photo ionization of furan by an intense 25 ns Nd:YAG 532 nm laser has been studied by time-of-flight mass spectrometry. At the laser intensity of 1010～1011 W/cm2, multi-charged ions Can+ (n=2～4) and Ohm+ (m=2～3) appeared in the mass spectra when argon was used as the carrier gas. From the peak splitting and the numeric analysis, the most probable kinetic energies of C2+, C3+ and C4+ were confirmed to be 21、63 and 100 eV respectively, and the most probable kinetic energies of O2+ and O3+ were confirmed to be 20 and 40 eV respectively. It is proposed that the multi-charged ions come from the Coulomb explosion of furan cluster ions produced by multi photon ionization of neutral furan cluster.     

Photoionization mass spectrometry of kinetic energy-selected ions. The translational energy distribution of N /N2 in the inner-shell ionization energy range

An ion retarding potential difference (IRPD) method has been used to investigate the ion yield and kinetic energy distributions of N⁺/N₂ produced by photoionization mass specrometry using synchrotron radiation. Photoion yield curves of energy selected N⁺ ions are deduced. Translational energy distribution of N⁺ at energies of the N(1s)→π*, N(1s)→(nl)¹ and above the N(1s)⁻¹ threshold are determined. Comparison is made with previous photoin-photoelectron coincidence work using time-of-flight (TOF) measurements.     

Reactive scattering of Sn from Cl2 and Br2 and a lower limit on D00 (SnBr)

Laboratory (lab) angular and time-of-flight (TOF) recoil velocity spectra of SnCl product formed by crossing a thermal Sn beam with a Cl₂ nozzle beam have been measured in a molecular beam apparatus equipped with an electron bombardment ionizer—quadrupole mass filter detector unit. Product center of mass (c.m.) recoil angle and energy distributions have been fit to the data by convoluting the c.m. → lab transformation over measured beam speed distributions and the instrumental TOF resolution. The inferred distributions for the Sn + Cl₂ reaction are strikingly similar to those reported for the Li + Cl₂ reaction. In addition, SnBr product was observed from crossed beams of Sn and Br2 which establishes a lower limit for D⁰₀ (SnBr) of 131 kJ/mole.     

氯甲烷分子在13至17 eV激发能量范围内的电离解离

利用阈值光电子-光离子符合飞行时间质谱研究了氯甲烷分子在13至17eV激发能量范围内的光电离和光解离动力学.在此能量范围内,电离产生的CH3Cl+离子处于A2A1和B2E电子激发态.两电子态均为完全解离态,可生成CH3+和CH2Cl+碎片离子,其中CH3+是最主要的解离产物.拟合CH3+离子的符合飞行时间质谱峰形,可以得到CH3Cl+离子解离过程中释放的平动能分布,结果显示CH3Cl+离子A2A1态解离生成CH+3的过程接近直接解离机理,而B2E态的解离过程则具有统计解离的特征.此外,结合理论计算的势能面信息,我们推测在A2A1态出现的CH2Cl+碎片离子来源于CH3Cl分子自电离产生高振动激发的CH3Cl+(X2E)离子统计解离过程.     

Photodissociation spectroscopy of Mg—Ar

Mg⁺—Ar ion—molecule complexes are produced in a pulsed supersonic nozzle cluster source. The complexes are mass selected and studied with laser photodissociation spectroscopy in a reflectron time-of-flight mass spectrometer system. An electronic transition assigned as X ²Σ⁺ → ²Π is observed with an origin at 31387 cm⁻¹ (vac) for ²⁴Mg⁺—Ar. The ²⁴Mg⁺—Ar spectrum is characterized by a 15 member progression with a frequency (ω′_e) of 272 cm⁻¹. An extrapolation of this progression fixes the excited state dissociation energy (D′_o) at 5552 cm⁻¹. The corresponding ground-state value (D″_o) is 1270 cm⁻¹ (3.6 kcal/mol). The ²Π _, spin—orbit splitting is 76 cm⁻.     

Quantification of [Dmt1]DALDA in ovine plasma by on-line liquid chromatography/quadrupole time-of-flight mass spectrometry

The synthetic peptide [Dmt(1)]DALDA (Dmt-D-Arg-Phe-Lys-NH(2); Dmt = 2',6'-dimethyltyrosine; 'super-DALDA') is a mu opioid-receptor agonist. On-line liquid chromatography/quadrupole time-of-flight mass spectrometry and the corresponding stable isotope-incorporated synthetic peptide internal standard were used to quantify [Dmt(1)]DALDA that had been extracted from ovine plasma samples. The [M+2H](2+) ion was used to construct the calibration curve, and the product ion was used for verification of the peptide. The detection sensitivity for the [Dmt(1)]DALDA [M+2H](2+) ion was 12.5 fmol and 50 fmol for the m/z 432.3 product ion. The concentration profile of [Dmt(1)]DALDA was determined from a set of ovine plasma samples. The molecular specificity of the peptide quantification was confirmed by tandem mass spectrometry (MS/MS).     

Development of LC-IMS-CID-TOFMS techniques: Analysis of a 256 component tetrapeptide combinatorial library

Recent improvements in ion mobility/time-of-flight mass spectrometry techniques have made it possible to incorporate nano-flow liquid chromatography and collision induced dissociation techniques. This combination of approaches provides a new strategy for detailed characterization of complex systems—such as, combinatorial libraries. Our work uses this technology to provide a detailed analysis of a tetrapeptide library having the general form Xxx₁-Xxx₂-Xxx₃-Xxx₄ where Xxx₁ = Glu, Phe, Val, Asn; Xxx₂ = Glu, Phe, Val, Tyr; Xxx₃ = Glu, Phe, Val, Thr; and Xxx₄ = Glu, Phe, Val, Leu—a system that is expected to contain 256 different peptide sequences. The results corroborate the presence of many expected peptide sequences and indicate that some synthetic steps appear to have failed. Particularly interesting is the observation of a t-butyl protecting group on the tyrosine (Tyr) residue. It appears that most Tyr containing peptides that have this t-butyl group attached favor formation of [2M + 2H]²⁺ dimers, which can be readily distinguished from [M + H]⁺ monomers based on differences in their gas-phase mobilities. In this case, we demonstrate the use of the mobility differences between [2M + 2H]²⁺ and [M + H]⁺ ions as a signature for a failure of a synthetic step.     

Fragmentation study of a 8-C-glycosyl isoflavone, puerarin, using electrospray ion trap time-of-flight mass spectrometry at high resolution

A mass spectrometry method that combines electrospray with an ion trap time-of-flight mass analyzer has been used to characterize puerarin (7,4'-dihydroxyisoflavone-8-C-beta-D-glucoside). MS(n) spectra (n 相似文献   

激光产生的碳原子簇负离子及其质谱研究

自80年代中叶以来,Bloomfield等人以脉冲激光结合超声分子束的方式产生碳原子簇,尤其在Smalley等发现被认为具有足球形超稳定结构的C_(60)以来,碳原子簇的激光产生与研究已经吸引了越来越多的化学家的兴趣.然而迄今为止,研究的手段仍以质谱为主,而且多     

Role of the hydroxyl-water hydrogen-bond network in structural transitions and selectivity toward cesium in Cs0.38(D1.08H0.54)SiTi2O7.(D0.86H0.14)2O crystalline silicotitanate

The crystal structure of the selective Cs+ ion exchanger D1.6H0.4Ti2SiO7.D2.66H0.34O1.5, known as crystalline silicotitanate or CST, has been determined in both native (D-CST) and in the Cs+-exchanged forms ((Cs, D)-CST) from angle-dispersive and time-of-flight neutron diffraction studies. The final fully exchange Cs+ form transformed from D-CST with unit cell parameters a = 11.0704(3) A c = 11.8917(5) A and space group P42/mbc, to one with a = 7.8902(1) A c = 11.9051(4) A and space group P42/mcm. Rietveld structure refinements of both D-CST and (Cs, D)-CST suggest the transition, and ultimately the selectivity, is driven by changes in the positions of water molecules, in response to the initial introduction of Cs+. The changes in water position appear to disrupt the D-O-O-D dihedral associated with the CST framework in space group P42/mbc which ultimately leads to the structural transition. The new geometric arrangement of the water-deuteroxyl network in (Cs, D)-CST suggests that Dwater-Ddeuteroxyl repulsion forced by Cs+ exchange drives the structural transformation.     

Structural Changes and Phase Transitions in Whitlockite-Like Phosphates

New compounds with a g -Ca 3 (PO 4 ) 2 structure type were found in three systems: Sr 9+ x M 1.5 m x (PO 4 ) 7 ( M = Mn, Fe, Co, Ni, Cu, and Cd; space group R 3 m ; Z = 3), Sr 9 R (PO 4 ) 7 ( R = Al, Sc, Cr, Fe, Ga, In, and Gd-Lu; space group P 2/ c , Z = 4), and Sr 9+2 x M 1+ x A 1 m 6 x (PO 4 ) 7 ( M = Mn, Ni, Cd; space group R 3 c and Z = 6 for A = Na, K; space group P 2/ m and Z = 4 for A = Li). Crystal structures of these compounds were determined by time-of-flight neutron, synchrotron X-ray, and laboratory X-ray powder diffraction. Reversible polar-to-centrosymmetric phase transitions ( R 3 c {\begin{array}{c}\\[-14pt]\hspace*{.5pt}\to\\[-7pt]\hspace*{-.5pt}\gets \end{array}} R 3 m ) were observed at high temperatures in Ca 3 m x Sr x (PO 4 ) 2 (0 h x h 12/7), Ca 10.5 m 1.5 x Fe x (PO 4 ) 7 (0 h x h 1), and Ca 9 R (PO 4 ) 7 . Solid solutions Ca 3 m x Sr x (PO 4 ) 2 (13/7 h x h 16/7) are centosymmetric with space group R 3 m at room temperature. These phase transitions were studied by high-temperature X-ray diffraction, second-harmonic generation, DSC, electric-conductivity and dielectric measurements.     

Formation and Photodissociation of Transition Metal-Sulfur Binary Cluster Ions

Transition metal-sulfur binary cluster ions were produced by direct laser ablation and analyzed with the first stage time-of-flight mass spectrometer (TOF-MS). It was found that the distribution of the strong peaks of the stable cluster ions in the TOF-MS were not appreciably affected by the composition of the sample. The composition of the most stable metal-sulfur cluster ions, M_nS_m are different for various transition metals: Cu, n = 2m + I and n = 2m; Zn, m = n; Mn, m = n; Fe, m = n, m = n ?1 and m = n ? 2; Co, m = n ? 1, m = n ? 2, m = n ? 3, m = n ? 4 and m = n ? 5; Cr, m = n and m = n + 1; Ta, m = n + 1 and m = n + 2. Cluster ions can be selected by a mass gate, and photolyzed by an excimer laser. The photodissociation product ions were analyzed with the second stage TOF-MS. These product ions were mainly the more stable cluster ions as those given in the first stage TOF-MS.     

Intracluster ion-molecule reactions of Ti+ with C2H5OH and CF3CH2OH clusters: influence of fluorine substituents on chemical reactivity

A laser ablation-molecular beam/reflectron time-of-flight mass spectrometric technique was used to investigate the ion-molecule reactions that proceed within Ti+(ROH)n (R = C2H5, CF3CH2) heterocluster ions. The mass spectra exhibit a major sequence of cluster ions with the formula Ti+(OR)m(ROH)n (m = 1, 2), which is attributed to sequential insertions of Ti+ into the O-H bond of C2H5OH or CF3CH2OH molecules within the heteroclusters, followed by H eliminations. The TiO+ and TiOH+ ions produced from the reactions of Ti+ with C2H5OH are interpreted as arising from insertion of Ti+ into the C-O bond, followed by C2H5 and C2H6 eliminations, respectively. When Ti+ reacted with CF3CH2OH, by contrast, considerable contributions from TiFOH+, TiF2+, and TiF2OH+ ions were observed in the mass spectrum of the reaction products, indicating that F and OH abstractions are the dominant product channels. Ab initio calculations of the complex of Ti+ with 2,2,2-trifluoroethanol show that the minimum energy structure is that in which Ti+ is attached to the O atom and one of the three F atoms of 2,2,2-trifluoroethanol, forming a five-membered ring. Isotope-labeling experiments additionally show that the chemical reactivity of heterocluster ions is greatly influenced by the presence of fluorine substituents and cluster size. The reaction energetics and formation mechanisms of the observed heterocluster ions are discussed.     

5-乙酰(苯甲酰)基-4-芳基-3,4-二氢嘧啶-2(1H)-酮的质谱裂解规律

Using high resolution capabilities of a time-of-flight instrument and ion trap tandem technique, electron impact mass spectra of 5-acetyl (benzoyl)-4-aryl-3,4-dihydropyrimidin-2 (1H)-ones 1-5 were studied. The molecular ion (M) peaks for 1-3 can be found in the spectra with high abundances, but very weak for 4 and 5,in which strong electron-attracting substituents are attached to the benzene ring. The main fragmentation pathways for 1-5 include the cleavage of (M-Ar) + with high intensity, (M-RCO) + with moderate abundance, (M-H) +with high intensity for the compounds without strong electron-attracting substituent in the aromatic ring, and the pyrimidine ring cleavage (loss of neutral NH=C=X). In addition, a prominent cation (Ph + , m/z 77) can be found in the low mass region of the spectra for all the compounds, which give rise by different pathways between 1- 2 and 3-5. Several additional fragmentations for individual compounds are proposed.     

三唑仑苯二氮(艹卓)类药物的电喷雾质谱裂解特征

采用电喷雾/四极杆飞行时间质谱(ESI-QqTOF)联用技术,对3种三唑仑苯二氮(艹卓)类药物进行CID研究,并以质子化准分子离子[M+H]+作为内标物,对碎片离子进行了准确质量测定,确认了这些碎片离子的元素组成,探讨了该类化合物的质谱裂解规律.研究发现,它们的ESI-MS2(源内)和ESI-MS3质谱分别生成脱去N2分子、HCN或CH3CN分子和Cl原子的碎片离子,其中m/z 205为3种药物共有的碎片离子,这些特征可用于三唑仑苯二氮(艹卓)类药物的体内代谢转化和定量研究.     

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometric analysis of phospholipase A2 and fibrinolytic enzyme, two enzymes obtained from Chinese Agkistrodon blomhoffii Ussurensis venom

Matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOFMS) was used to analyze two enzymes, phospholipase A2 and fibrinolytic enzyme isolated from Chinese Agkistrodon blomhoffii Ussurensis venom. Using sinapinic acid as the matrix, positive ion mass spectra of the enzymes were obtained. In addition to the dominant protein [M + H]+ ions, multimeric and multiply charged ions were also observed in the mass spectra. The higher the concentration of the enzymes, the more multiply charged polymer and multimeric ions were detected. Our results indicate that MALDI-TOFMS can provide a rapid and accurate method for molecular weight determination of snake venom enzymes. Mass accuracies of 0.1 and 0.3% were achieved by analysis of highly dialyzed phospholipase A2 and fibrinolytic enzyme, and these results are much better than those obtained using sodium dodecyl sulfate-polyacrylamide gel electrophoresis. MALDI-TOFMS thus provides a reliable method to determine the purity and molecular weight of these enzymes, which are of potential use as therapeutants.     

闭式十二顶双镍十硼烷簇合物[(μ-Cl)(Ph_2PC_6H_4)_2Ni_2B_(10)H_6Cl(PPh_3)]的合成与结构

研究了[NiX_2(PPh_3)_2](X=F, Cl, SCN)在二氯甲烷中与B_(10)H_(10)~(2-) 的反应,对形成的产物[(μ-Cl)(Ph_2PC_6H_4)_2-Ni_2B_(10)H_6Cl(PPh_3)]·0. 25CH_2Cl_2 (1)通过元素分析、红外光谱、飞行时间二次离子质谱等进行了表征, 并通过单晶X射线衍射测定了簇合物的结构。1的晶体学数据：单斜晶系,空间群 P2_1/c,a = 1.1703(2)nm, b = 2.1082(4) nm, c = 2.2068 (8) nm, β = 99.98 (2) °, V = 5.3622(2)nm~3, Z = 4, F(000) = 2274, D_(calcd)=1.373g/cm~3. R_1 = 0.0358, wR_2 = 0.0807. 1为闭式十二项双镍十硼烷簇合物,具有两个邻 位环化的Ni-P-C-C-B五元环,镍-镍之间还存在氯桥。结构分析表明：邻位环化增 强了镍与硼之间的成键作用。