Quantitative analysis of fluorimated ethylchloroformate derivatives of non-protein amino acids using positive and negative chemical ionization gas chromatography-mass spectometry

The GC-MS characterization of the ethylchloroformate derivatives of amino acids in an aqueous medium has been applied to non-protein amino acids. Derivatization of non-protein amino acids using ethylchloroformate, trifluoroethanol, and pyridine produced strong [M + 1]⁺ and [M - 1]⁻ ions in positive and negative chemical ionization (CI) modes, respectively. Twenty-one out of the twenty-three non-protein amino acids studied produced detectable ion chromatograms in both ionization modes when methane was used as the CI reagent gas. Mass spectra of these non-protein amino acid derivatives showed characteristic [M - 19]⁺, [M + 1]⁺, [M + 29]⁺, and [M + 41]⁺ peaks in the positive chemical ionization mode, and [M - 1]⁻, and [M + 35]⁻ peaks in the negative chemical ionization mode. The detection limits and the linear dynamic range of trifluorethanol ethylchloroformate derivatives of non-protein amino acids were studied using positive chemical ionization. The detection limits are mostly in the femtomole range.     

A study of the gas-phase reaction between protonated acetaldehyde and methanol

Protonated acetaldehyde is methylated on the oxygen during interaction with methanol in the gas phase. The ionic product of the ion/molecule reaction between methanol and protonated acetaldehyde is identical with C-protonated methylvinyl ether (high-pressure ionization), and with the (M − C₂H₅)⁺ fragment ion of sec-butyl methyl ether (following electron ionization), and also with the (M − OCH₃)⁺ fragment ion of acetaldehyde dimethylacetal (following electron ionization). The structures of these ions and the mechanism of their formation were established by isotope-labeling experiments and collision-induced dissociation mass spectra of model compounds obtained with three different types of tandem mass spectrometers (BEQQ, triple-quadrupole, and a penta-quadrupole instrument). Gas phase synthesis of the product ion from [²H₃]-methanol or [²H₄]-acetaldehyde provided insight into its mode of formation and collision-induced dissociation.     

Role of the sulfhydryl group on the gas phase fragmentation reactions of protonated cysteine and cysteine containing peptides

The gas phase fragmentation reactions of protonated cysteine and cysteine-containing peptides have been studied using a combination of collisional activation in a tandem mass spectrometer and ab initio calculations [at the MP2(FC)/6-31G*//HF/6-31G* level of theory]. There are two major competing dissociation pathways for protonated cysteine involving: (i) loss of ammonia, and (ii) loss of the elements of [CH₂O₂]. MS/MS, MS/MS of selected ions formed by collisional activation in the electrospray ionization source as well as ab initio calculations have been carried out to determine the mechanisms of these reactions. The ab initio results reveal that the most stable [M + H − NH₃]⁺ isomer is an episulfonium ion (A), whereas the most stable [M + H − CH₂O₂]⁺ isomer is an immonium ion (B). The effect of the position of the cysteine residue on the fragmentation reactions of the [M + H]⁺ ions of all the possible simple dipeptide and tripeptide methyl esters containing one cysteine (where all other residues are glycine) has also been investigated. When cysteine is at the N-terminal position, NH₃ loss is observed, although the relative abundance of the resultant [M + H − NH₃]⁺ ion decreases with increasing peptide size. In contrast, when cysteine is at any other position, water loss is observed. The proposed mechanism for loss of H₂O is in competition with those channels leading to the formation of structurally relevant sequence ions.     

Matrix-assisted laser desorption/ionisation mass spectrometry of oligosaccharides and glycoconjugates

The technique of matrix-assisted laser desorption/ionization mass spectrometry (MALDI) is described and examples are given of its use for the examination of glycoproteins, glycopeptides, glycolipids and oligosaccharides. Abundant [M + H]⁺ ions are produced by the glycoproteins and glycopeptides, whereas glycolipids and oligosaccharides give mainly [M + Na]⁺ ions. Resolution on time-of-flight (TOF) instruments is poor but improved resolution can be obtained by use of ion cyclotron resonance or magnetic sector instruments. Although the technique gives mainly [M + Na]⁺ ions from neutral, underivatised oligosaccharides, with little fragmentation when implemented on TOF systems, the use of a reflectron enables fragment ions produced by post-source decay to be obtained. Acidic sugars give less satisfactory positive ion spectra with TOF analysers. but generally produce abundant negative ions. Extensive fragmentation is observed with these compounds when the spectra are recorded with magnetic sector instruments. Neutral glycolipids produce strong spectra from several matrices but acidic glycolipids show extensive fragmentation as the result of sialic acid loss.     

脯氨酸与Cu、Cu~+和Cu~(2+)配位体系的计算研究

运用M06-2X和ωB97XD方法分别在6-311++G(2d,p)和TZVP基组水平上,对脯氨酸(Pro)的15种构象与Cu、Cu+和Cu2+形成的多种配合物的几何结构、能量学特征、振动光谱和电子结构等进行计算研究.四种水平得到20种[Pro-Cu]、16种[Pro-Cu]+和16种[Pro-Cu]2+稳定结构.[Pro-Cu]和[Pro-Cu]+体系中出现12种Pro构象,而[Pro-Cu]2+体系中出现11种Pro构象,三种体系中最稳定的结构都不是由能量最低的Pro构象生成的.在结构CI3、CI4、CII7和CII8中,Pro的羧基氢转移到亚氨基氮形成两性离子与Cu双配位结合.[Pro-Cu]0/1+/2+体系四种水平计算相对能差范围逐渐增加,结合能分别在-60.0--5.0 kJ·mol-1、-340.0--170.0 kJ·mol-1和-1100.0--860.0 kJ·mol-1范围,配位体系中Pro的变形能逐渐增加.N―H和O―H键伸缩振动频率普遍发生红移,配位体系中部分电荷从Pro转移到Cu上,在[Pro-Cu]2+体系中单配位结构中电荷转移最多,约为单位负电荷.     

激光解吸电离飞行时间质谱下的银簇行为

近年来,对金属簇的研究已成为化学与物理学中最活跃的研究领域之一［１］．金属簇被认为是介于单个原子与固体之间的中间相［２］．深入地研究其结构、形成机理及物理与化学行为,对于寻找新的催化剂［３］,重新认识气相化学与凝聚相化学的关系［４］,都有非常重要的意...     

Electrospray ionization mass spectrometry of metal complexes. Gas phase formation of a binuclear copper(II)–5-Br-PADAP complex

The complexes formed from copper(II) and 2-(5-bromo-2-pyridylazo)-5-diethylaminophenol (5-Br-PADAP or HL) in aqueous methanol solution was studied by electrospray ionization mass spectrometry. The solution of a 1:1 complex of Cu(II) with 5-Br-PADAP showed five peaks assignable to a binuclear complex [Cu₂L₂(AcO)]⁺ and mononuclear complexes [CuL]⁺, [CuL(H₂O)]⁺, [CuL(AcOH)]⁺ and [CuL(HL)]⁺ (AcO=acetate). Collision activated dissociation revealed the relative order of bonding strengths; Cu–L>Cu–HL>CuL–AcOH>CuL–H₂O. The peak intensities of the binuclear complex showed second-order dependency on those of the mono complex. As for the solution of Ni(II)–5-Br-PADAP, no binuclear complex was observed in the mass spectra. Thus, it was suggested that [Cu₂L₂(AcO)]⁺ was formed by the fast gas phase reaction: 2[CuL]⁺+AcO⁻[Cu₂L₂(AcO)]⁺.     

Das perfluortriazinium-kation als oxidationsmittel in der metallorganischen synthese—ein neuer weg zur darstellung von [Cp2MCl2](M = Mo

The oxidation of Cp₂MCl₂ (M= Mo, W) with perfluortriazinium tetrafluoroborate, [(FCN)₃F]⁺[BF₄]⁻, in the presence of a flouride ion acceptor (BF₃ or PF₅) in SO₂ solution yielded the cationic metallocene complexes [Cp₂MCl ₂]²⁺[BF₄]⁻ or [C_p2MCl₂] ²⁺[BF₄]⁻[PF₆]⁻ (M = Mo, W), respectively. In these reactions, for the first time the perfluortriazinium cation has proved to be easy to handle and a useful oxidizer in organometallic chemistry. The oxidizer strength of three fluorotriazinium cations, [(XCN)₃F]⁺ (X = F, Cl, H), has been computed ab initio (HF/6 − 31 + G) and calibrated on literature data which were obtained by local density functional calculations. It was anchored to its F⁺ zero point by an experimental value for KrF⁺. ab]Die Oxidation von Cp²MCl₂ mit (M = MO, W) Perfluortriaziniumtetrafluoroborat, [(FCN)₃F]⁺[BF₄]⁻, in Anwesenheit eines Fluoridionenakzeptors (BF₃ oder PF₅) führte in SO₂-Lösung zur Bildung der kationischen Metallocen-Komplexe [Cp₂MCl₂₊]²⁺[BF₄]₂⁻ bzw. [Cp₂MCl₂]²⁺[BF₄]⁻ [PF₆]⁻ (M = Mo, W). In diesen Reaktionen konnte erstmals gezeigt werden, daß Perfluortriazinium-Kationen einfach zu handhabende und nützliche Oxidationsmittel im Bereich der metallorganischen Synthese darstellen. Das (Mdationsvermögen von drei Fluorotriazinium-Kationen, [(XCN)₃F]⁺(X = F, Cl, H), wurde ab initio berechnet (HF/6 − 31 + G) und mit Hilfe von Literaturdaten, die mittels local density functional-Berechnungen erhalten und am experimentellen Wert von KrF ⁺ bezüglich des F⁺ Nullpunktes verankert wurden, kalibriert.     

Optically active coordination compounds---XLVIII. Synthesis, resolution and interconversions of isomers of tris-salicylatocobaltate(III)

Stable aqueous solutions of the green ion [Co(sa1)₃]³⁻ (sa1 = dianion, C₆H₄( )(CO ), of salicylic acid, 2-hydroxybenzoic acid) are obtained from [Co(NH₃)₅ C1]C1₂ and an excess of salicylic acid. Several salts, [C][Co(sa1)₃] have been characterized, where C = [Co(NH₃)₆]³⁺ and [M(en)₃]³⁺ (M = Co or Rh, EN = 1,2-diamino-ethane). By using (+)-[Rh(en)₃]³⁺, optical resolution via less soluble diastereoisomeric salts has been achieved, and isomerization and racemization have been studied. Resolved tris-malonatocobaltate(III) has been used as a model. A novel thermochromism (77-293 K) in solid Δ(+)-[Rhen₃]Λ[Co(sa1)₃ is described.     

Kinetics and mechanisms of the redox reaction of hexaaquotitanium(III) and the ethylenediamine tetraacetato titanium(III) complex by aqueous solutions of bromine

At 25°C, I = 1.0 M (CF₃SO₃⁻Li⁺+CF₃SO₃H), [H⁺] = 0.034–0.274 M and λ = 453 nm, the rate equation for the oxidation of Ti(H₂O), ₆³⁺ by bromine was found to be: −d/[Br₂]T/dt=kK/[Br₂][Ti^III]/[H⁺]+K+kK/[Br₃⁻][Ti^III]/[H⁺+K, where k = 9.2 × 10⁻³ M ⁻¹ s ⁻¹ and K = 4.5 × 10⁻³ M. At [H⁺] = 1.0 M, [Br⁻] = 0.05–0.4 M, the apparent second-order rate constant decreases as [Br⁻] increases.

The pH-dependence of the oxidation of Ti^III-edta by bromine is interpreted in terms of the change in identity of the Ti^III-edta species as the pH of the reaction medium changes. The second-order rate constants were fitted using a non-linear least-square computer program with (1/k₀^edta)² weighting into an equation of the form: k₀^edta =k₁+k₂K₁[H⁺]⁻¹+k₃K₁K₂[H⁺]^−2/1+K₁[H⁺[H⁺⁻¹+K₁K₂[H⁺]⁻², with K₁ and K₂ fixed as earlier determined at 9.55 × 10⁻³ and 2.29 × 10⁻⁹ M, respectively, for the oxidation of bromine. k₁=k₂=(3.1±0.32)×10³M⁻¹s⁻¹ k₃=(2.3±0.45)×10⁶N⁻¹s⁻¹.

It is proposed that these electron transfer reactions proceed by univalent changes with the production of Br₂^.− as a transient intermediate. An outer-sphere mechanism is proposed for these reactions. The homonuclear exchange rate for Ti^III-edta+Ti^IV-edta is estimated at 32 M⁻¹ s⁻¹.     

碱金属离子与三肽复合物的气相裂解反应

为了探索侧链R基团对碱金属离子与多肽复合物气相裂解反应的影响, 采用电喷雾电离质谱法研究了碱金属离子Li⁺, Na⁺和K⁺分别与甘氨酸三肽(GGG)、 甘氨酰-苯丙氨酰-甘氨酸三肽(GFG)和甘氨酰-甘氨酰-苯丙氨酸三肽(GGF)形成的复合物的气相裂解反应. 质谱定性实验结果表明, Li⁺, Na⁺和K⁺与GGG, GFG或GGF在气相中可以形成稳定的复合物, 配合比为1∶1或2∶1. 竞争反应质谱图显示, GGG, GFG或GGF与碱金属离子形成的复合物的质谱峰丰度按Li⁺, Na⁺, K⁺顺序依次下降, 表明随着碱金属离子半径的增加, 它们与三肽的结合强度依次减弱. 碰撞诱导解离显示, 母体离子[GGG+Na]⁺, [GGF+Na]⁺和[GFG+Na]⁺ 的质心碰撞能量E(CM)₅₀数值分别为1.94, 1.76和1.63 eV. 通过质谱滴定法测得[GGG+Na]⁺, [GFG+ Na]⁺和[GGF+Na]⁺ 的结合常数lg\begin{array}{c}{K}_{a_1}\end{array}分别为5.30, 5.25和5.17. 质谱法定量结果进一步确认复合物的稳定性顺序为[GGG+Na]⁺>[GGF+Na]⁺>[GFG+Na]⁺, 表明由于空间位阻的影响, 侧链R基团含有苄基的GFG或 GGF与Na⁺的键合强度要小于侧链R全部为H的GGG. 串级质谱分析结果显示, 碱金属化的GGG断裂位点较多, 可解离出丰富的金属化a₂, b和y型碎片离子, 而碱金属化的GGF和GFG解离出的金属化y型离子较多, b型离子其次, 金属化a型离子几乎没有. 此外, 双碱金属化的GGF可解离出较多金属化y型离子. 复合物[GGF+Na]⁺的裂解曲线显示, 当碰撞能量为25 eV时, [y₂+Na-H]⁺ 和[b₂+Na+OH]⁺为主要碎片离子, 当碰撞能量>40 eV时, 只有[b₂+Na+OH]⁺ 碎片离子占有优势数量. 根据质子化三肽裂解机理可以推测, 钠化GFG裂解后生成含噁唑酮的[b₂+Na]⁺离子, 该离子经过一系列过渡态生成[a₂+Na]⁺(2-苄基-4-咪唑酮), 而不是常见的亚胺离子.     

二苯并噻吩及其氧化物与离子液体相互作用的理论研究

采用密度泛函理论方法比较了DBT/DBTO₂和[BMIM]⁺[PF₆]^-/[BMIM]⁺[BF₄]^-的相互作用。对最稳定的[BMIM]⁺[PF₆]^-、[BMIM]⁺[PF₆]^--DBT、[BMIM]⁺[PF₆]^--DBTO₂、[BMIM]⁺[BF₄]^-、[BMIM]⁺[BF₄]^--DBT、[BMIM]⁺[BF₄]^--DBTO₂进行了NBO和AIM分析。结果表明,DBT和[BMIM]⁺[PF₆]^-/[BMIM]⁺[BF₄]^-中的咪唑环彼此相互平行,NBO和AIM分析表明它们之间发生了π-π相互作用。H1'和H9'形成的F…H氢键有利于π-π堆积作用的形成。DBTO₂倾向于趋近C2-H2和甲基基团形成O…H相互作用;DBTO₂优先吸附在[BMIM]⁺[PF₆]^-/[BMIM]⁺[BF₄]^-。在模拟油中,[BMIM]⁺[PF₆]^-和[BMIM]⁺[BF₄]^-离子液体对DBTO₂的萃取能力大于DBT,其原因是可能是DBTO₂具有较大的极性和O…H与F…H的氢键作用。     

Capillary column gas chromatography-ammonia and deuterated ammonia chemical ionization mass spectrometry of sulfur vesicants

Capillary column gas chromatography-ammonia and deuterated ammonia chemical ionization mass spectrometry was found to be a highly specific technique for the detection and identification of three long-chain sulfur vesicants, 2-chloroethyl (2-chloroethoxy)ethyl sulfide, sesquimustard and bis[(2-chloroethylthio)ethyl]ether. All three vesicants exhibited significant (M + NX₄)⁺ (where X = H or ²H) pseudo-molecular ions and structurally significant chemical ionization fragmentation ions during capillary column gas chromatographic-ammonia chemical ionization mass spectrometric analysis. This method was utilized during analysis of contaminated painted panels circulated during the 3rd round robin verification exercise (1991). Chemical ionization data obtained during this exercise complemented the electron impact data obtained for sesquimustard and bis[(2-chloroethylthio)ethyl]ether and the specificity of the technique enabled the confirmation of 2-chloroethyl (2-chloroethyoxy)ethyl sulfide, a compound masked by hydrocarbons in the painted panel extracts.     

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.     

Synthesis and resonance raman study of conductive iodinated materials derived from [M(dmit)(phen)] complexes [M = Pd(II), Pt(II)]

The synthesis and characterization of the [M(dmit)(phen)] complexes [M = Pd(II), Pt(II); H₂dmit = 4,5-dimercapto-1,3-dithiole-2-thione; PHEN = 1,10-phenanthroline) and of the iodinated [M(dmit)(phen)]I compounds are described. The conductivity of [M(admit)(phen)] increases upon oxidation by a factor of 10⁶, and is ca. 5 × 10⁻³ ohm⁻ cm⁻ for the [M(admit)(phen)]I compounds. The nature of the iodine species in these solids is determined by UV-visible and resonance Raman spectroscopies. The only polyiodide present is I⁻₃ and, thus, the charge distribution can be expressed as [M(dmit) (phen)^0.33+[I⁻₃]_0.33.     

The coordinatively unsaturated cluster cations [Pt3{M(CO)3}(μ-Ph2PCH2PPh2)3] (M = Re, Mn)

The coordinatively unsaturated cluster [Pt₃(μ₃-CO)(μ-dppm)₃]²⁺ (1, dppm = Ph₂PCH₂PPh₂) reacts with Na⁺[M(CO)₅]⁻ to give the mixed metal clusters [Pt₃{M(CO)₃}(μ-dppm)₃]⁺ (M = Re, 2; Mn, 3). The new clusters are characterized by spectroscopic methods and, for M = Re, by an X-ray structure determination. The Pt₃Re core in 2 is tetrahedral with particularly short metal-metal distances.     

α-氨基酸及其酯化物侧链对其β-环糊精复合物稳定常数的影响

为了探索α-氨基酸及其酯化物的侧链R基团对其与环糊精非共价复合物结合强度的影响, 将一定摩尔比的β-环糊精(β-CD)分别与L型正缬氨酸(n-Val)、 亮氨酸(Leu)、 苯丙氨酸(Phe)、 天冬氨酸(Asp)、 天冬氨酸-4-苄酯(Asp-4-benzyl ester)和天冬氨酸-4-叔丁酯(Asp-4-t-butyl ester)在室温下混合, 反应平衡后采用电喷雾电离质谱进行竞争反应检测, 并以改进的质谱滴定结合曲线拟合法计算结合常数. 结果表明, 它们均可形成摩尔比为1∶1的非共价复合物. 在2组竞争反应中, 复合物的结合强度顺序分别为[β-CD∶Asp-4-benzyl ester+H]⁺>[β-CD∶Asp-4-t-butyl ester+H]⁺>[β-CD∶Asp+H]⁺以及[β-CD∶Phe+H]⁺>[β-CD∶Leu+H]⁺>[β-CD∶n-Val+H]⁺. 质谱滴定曲线拟合法测得[β-CD∶n-Val+H]⁺, [β-CD∶Asp+H]⁺, [β-CD∶Asp-4-t-butyl ester+H]⁺, [β-CD∶Asp-4-benzyl ester+H]⁺, [β-CD∶Leu+H]⁺和[β-CD∶Phe+H]⁺的稳定常数(lgK_st)分别为1.81, 2.54, 3.14, 3.26, 3.36和3.67, 结合强度依次增强. 竞争反应的定性分析结果与质谱滴定定量法测得结合强度结果的趋势一致. 由于所选用的α-氨基酸及其酯化物客体的羧基端(—COOH)和氨基端(—NH₂)均相同, 且都为亲水基团, 仅有侧链R基团不同, 因此在溶液中客体分子受疏水驱动与β-CD主体靠近并结合时, 侧链R基团的疏水力和极性2个因素起重要作用. 由于客体分子体积小, 其碳端的羧基还可与β-CD大口或小口边缘的羟基形成氢键, 使复合物更加稳定.     

Acetogenic isoquinoline alkaloids: CXII. Separation and identification of dimeric naphthylisoquinoline alkaloids by liquid chromatography coupled to electrospray ionization mass spectrometry

The atropodiastereomeric dimeric naphthylisoquinoline alkaloids, michellamines A (1a), B (1b) and C (1c), together with their monomers, korupensamines A (2a) and B (2b), were investigated using electrospray ionization tandem mass spectrometry coupled to liquid chromatography (LC–ESI-MS–MS). From the spectra obtained, characteristic product ions were chosen to monitor the chromatographic separation achieved on an RP-18 column. Under acidic conditions required for chromatographic analysis, the monomeric alkaloids 2a and 2b yielded protonated molecules [M+H]⁺, while the dimers, the michellamines, exhibited doubly protonated [M+2H]²⁺ molecules. In addition, the coeluting alkaloids 1b and 2b were identified unambiguously by means of tandem mass spectrometry. Thus, together with the retention times of the alkaloids, the product ion spectra allowed us the identification of michellamines in the presence of their presumed biogenetic monomeric precursors. Application of the HPLC–MS–MS method successfully proved the enzymatic formation of michellamine C (1c) by in vitro dimerization of korupensamine B (2b).     

PMBP与中性磷萃取剂对铽(Ⅲ)的协同萃取

本文研究了1-苯基-3-甲基-4-苯甲酰基吡唑啉酮-5(PMBP)与丁基膦酸二丁酯(DBBP)或磷酸三丁酯(TBP)的氯苯溶液在硝酸介质中对铽(Ⅲ)的协同萃取。测得了萃合物的组成及其萃取平衡常数,讨论了萃合物的可能结构式及协同萃取机理。     

Thermodynamics of formation of magnesium(II), calcium(II), strontium(II) and barium(II)—succinate complexes in aqueous solution

The formation constants for the complexes Mg²⁺ -, Ca²⁺ -, Sr²⁺ - and Ba²⁺ - succinate (succ²⁻) have been determined by potentiometric measurements, in aqueous solution, at different temperatures and ionic strengths. The species [M(succ)]⁰ and [M(succ)H]⁺ were found for all systems. For the stability constant the ionic strength dependence has been found, and general parameters for the relation log β = f(I) have been obtained. From the temperature dependence of stability constants ΔH values have been deduced. The procedure adopted in calculating all the thermodynamic parameters for the systems under study, where weak complexes are formed, is discussed. The stability of the complexes follows the order Mg < Ca Sr ≈ Ba.