Mass spectrometric characterization of 3'-imino[60]fulleryl-3'-deoxythymidine by collision-induced dissociation

The primary structure of 3'-imino[60]fulleryl-3'-deoxythymidine ions is studied using mass spectrometry both in the positive and negative modes. Interaction between the subunits is discussed using collision-induced dissociation (CID) spectra. Collisional activation with argon of the sodiated cations leads to the cleavage of the glycosidic bond and the transfer of a radical hydrogen from the deoxyribose to the thymine. The sodiated thymine is the only fragment observed for low collision energies in the positive mode. In the negative mode, two different ionization mechanisms take place, reduction and deprotonation in the presence of triethylamine. The 2.7 eV electron affinity of C60 and its huge cross section compared to the small cross section and predicted 0.44 eV electron affinity of the thymidine subunit most likely localize the radical electron on the fullerene. On the other hand, deprotonation of the 3'-azido-3'-deoxythymidine (AZT) is known to occur in N-3, the most acidic site of the nucleobase. Consequently, deprotonation causes the negative charge to be initially localized on the thymine. Both types of parent anions give the radical anion C60*- as fragment. The other fragments detected are the dehydrogenated 3'-imino[60]fulleryl-3'-deoxyribose anion, C60NH2-, C60N- and C60H-. Since in negative ion mass spectrometry all fragments include the [60]fullerene unit, this suggests that the fragmentation is driven by the electron affinity of the [60]fullerene, likely responsible for a charge transfer between the deprotonated thymine and the C60.     

C alpha-C backbone fragmentation dominates in electron detachment dissociation of gas-phase polypeptide polyanions

Fragmentation of peptide polyanions by electron detachment dissociation (EDD) has been induced by electron irradiation of deprotonated polypeptides [M-nH](n-) with >10 eV electrons. EDD has been found to lead preferentially to a* and x fragment ions (C(alpha)-C backbone cleavage) arising from the dissociation of oxidized radical anions [M-nH]((n-1)-*. We demonstrate that C(alpha)-C cleavages, which are otherwise rarely observed in tandem mass spectrometry, can account for most of the backbone fragmentation, with even-electron x fragments dominating over radical a* ions. Ab initio calculations at the B3 LYP level of theory with the 6-311+G(2 p,2 d)//6-31+G(d,p) basis set suggested a unidirectional mechanism for EDD (cleavage always N-terminal to the radical site), with a*, x formation being favored over a, x* fragmentation by 74.2 kJ mol(-1). Thus, backbone C(alpha)-C bonds N-terminal to proline residues should be immune to EDD, in agreement with the observations. EDD may find application in mass spectrometry for such tasks as peptide sequencing and localization of labile post-translational modifications, for example, those introduced by sulfation and phosphorylation. EDD can now be performed not only in Fourier transform mass spectrometry, but also in far more widely used quadrupole (Paul) ion traps.     

In-source collision induced dissociation of inorganic explosives for mass spectrometric signature detection and chemical imaging

The trace detection, bulk quantification, and chemical imaging of inorganic explosives and components was demonstrated utilizing in-source collision induced dissociation (CID) coupled with laser desorption/ionization mass spectrometry (LDI-MS). The incorporation of in-source CID provided direct control over the extent of adduct and cluster fragmentation as well as organic noise reduction for the enhanced detection of both the elemental and molecular ion signatures of fuel-oxidizer mixtures and other inorganic components of explosive devices. Investigation of oxidizer molecular anions, specifically, nitrates, chlorates, and perchlorates, identified that the optimal in-source CID existed at the transition between fragmentation of the ionic salt bonds and molecular anion bonds. The chemical imaging of oxidizer particles from latent fingerprints was demonstrated, including both cation and anion components in positive and negative mode mass spectrometry, respectively. This investigation demonstrated LDI-MS with in-source CID as a versatile tool for security fields, as well as environmental monitoring and nuclear safeguards, facilitating the detection of elemental and molecular inorganic compounds at nanogram levels.     

Differences between collisionally activated and electron-transfer dissociations found for CH(2)X(2)(X = Cl, Br, and I) by using alkali-metal targets

High-energy collisionally activated dissociation (HE-CAD) and high-energy electron- transfer dissociation (HE-ETD) on collisions with alkali-metal targets (Cs, K, and Na) were investigated for CH(2)X(2) (+) (X = Cl, Br, and I) ions by tandem mass spectrometry (MS/MS). In the HE-CAD spectra observed, peaks associated with CH(2)X(+) ions formed by a loss of a halogen atom are always predominant regardless of precursor ions and target metals. The observation of the predominant CH(2)X(+) ions is explained by the lowest energy levels of the fragments of CH(2)X(+) + X among the possible fragment energy levels and internal-energy distribution in HE-CAD. In the charge-inversion spectra, relative peak intensities of the negative ions formed by HE-ETD strongly depend on the precursor ions and the target metals. While the CHCl(2) (-) ion was predominant in the spectra of CH(2)Cl(2) (+) regardless of target species, the most intense peaks in those of CH(2)Br(2) (+) and CH(2)I(2) (+) were ascribed to either Br(-) or CH(2)Br(-) and either I(-) or I(2) (-), respectively, depending on the target metals. The dependence of the relative intensities of the fragment ions by HE-ETD on the precursor ions and target species are discussed on the basis of the energy levels of the neutral fragments and the narrow internal-energy distribution resulting from the near-resonant neutralization. It was demonstrated that HE-ETD using the alkali-metal targets provided rich information on the dissociation of the neutral species.     

Formation and Optical Absorption of Clusters of the p-tert-butylcalix[8]arene:C60 Complex

Depending on the initial concentrations of fullerene (C₆₀) and p-tert-butyl calix[8]arene (C[8]A) in toluene, two regimes of their interaction were distinguished. The changes in optical absorption of C₆₀:C[8]A mixed solutions observed over a period of time suggest that the following consecutive processes take place upon interaction between C₆₀ and C[8]A in toluene: (1) molecular inclusion, and (2) growth and sedimentation of the insoluble C₆₀/C[8]A clusters. At increased concentrations of the components, process (2) is suppressed and stable C₆₀/C[8]A colloids can be formed. Spectral features of these colloids in different solvents clearly indicate the difference between self-aggregated C₆₀ and small clusters of the complex. A specific influence of the C[8]A cage on the entrapped C₆₀ molecules is also confirmed by IR spectroscopy of the complex in the solid state.     

Bulk polymerization of N-vinylcarbazole initiated by C60

In this communication, we first used [60]fullerene as initiator to initiate the bulk polymerization of N-vinylcarbazole (NVC) monomer at 70°C (slightly higher than the melting point temperature, 65°C, of NVC). A reasonable polymerization reaction pathway via C₆₀-NVC ion-radical pairs is suggested. © 1999 John Wiley & Sons, Inc. J Polym Sci A: Polym Chem 37: 3745–3747, 1999     

Reaction of D2 with palladium fulleride C60Pd4.9

Fullerene deuteride was obtained by the reaction of deuterium with solid palladium fulleride C₆₀Pd_4.9 under fairly mild conditions. The compound was identified by FD-MS, UV-Vis and IR spectroscopies, and TLC.Translated from Izvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 483–484, February, 1996     

Electrochemical behavior of the C60–γ-cyclodextrin inclusion complex (1:1) on HMDE in an aqueous solution

The electrochemical behavior of the water-soluble C₆₀–γ-CD (1:1) inclusion complex has been studied on the hanging mercury drop electrode. A one-electron reversible adsorptive electroreduction and three irreversible adsorptive electroreductions were detected by cyclic voltammetry. The amount of C₆₀–γ-CD adsorbed at saturation is 1.73 × 10⁻¹¹ mol/cm², the diffusion coefficient is 5.81 × 10⁻⁶ cm²/s, and the standard rate constant of the surface reaction k_s are 0.888 s⁻¹, 0.853 s⁻¹ and 1.032 s⁻¹, respectively.     

Chemiluminecsence in the oxidation of Na2C60 by the (NH4)2Ce(NO3)6 complex in THF

Chemiluminescence (_max = 790 nm) in the oxidation of fulleride Na₂C₆₀ by the (NH₄)₂Ce(NO₃)₆ complex in THF was found. The ³C₆₀* triplet of fullerene formed in the transfer of an electron from the intermediate C₆₀ ^– anion to Ce^IV was suggested to be the chemiluminescence emitter.     

Intervalence charge transfer transition in mixed valence complexes synthesised from RuIII(edta)- and FeII(CN)5-cores

Intervalence charge transfer properties were studied for a set of mixed valence complexes incorporating Ru(III) and Fe(II)-centres linked by various saturated and unsaturated bridging ligands (BL). Studies reveal that degree of ground state electronic interaction and coupling between Ru(III) and Fe(II)-centrescanbe attenuated by changing the nature of the bridging ligand. Further, inclusion of the bridging ligand with interrupted π-electron system in a β-CD cavity initiate an optical electron transfer from Fe(II) to Ru(III) which is otherwise not observed.     

Fluorimetric and molecular mechanics study of the inclusion complex of 2-quinoxalinyl-phenoxathiin with β-cyclodextrin

The complex formed by the inclusion of the polarity-sensitive fluorescent probe 2-[2′-quinoxalinyl]-phenoxathiin (QP) into β-cyclodextrin (β-CD) was investigated by steady-state fluorescence spectroscopy in order to confirm the previously stated intramolecular charge transfer nature of the first excited singlet state of QP. A decrease in the emission intensity in the presence of β-CD was observed and explained on this basis. The 1:1 stoichiometry of the inclusion complex and its association constant of 2,223 M⁻¹ were computed. The QP–β-CD complex was further studied by molecular mechanics (MM+ force field), in order to determine its structure and the type of interactions between QP and β-CD. All possible ways QP could penetrate the β-CD cavity were considered and several structures were generated and optimized. The interaction, binding (van der Waals and electrostatic contributions) and perturbation energies were also calculated. The results have showed that the β-CD cavity incorporates the central part of QP and that complexation is mainly due to van der Waals host–guest interactions.     

NMR characterization of the host-guest inclusion complex between beta-cyclodextrin and doxepin

The interaction between doxepin, a member of the tricyclic antidepressant (TCA) class of drugs, with beta-cyclodextrin (beta-CD) was investigated using NMR. Several TCAs have been reported to form a complex with beta-CD having 1:1 stoichiometry. Previous results from UV-visible spectroscopy, fluorescence measurements, and molecular modeling indicated that for imipramine, desipramine, and amitriptyline, the TCA aliphatic tail is included in the cyclodextrin cavity with apparently no interaction of the tricyclic ring. An alternative view of the doxepin-beta-CD complex is presented in this work using analysis of complexation-induced chemical shifts (CICSs), the method of continuous variation (Job's analysis), and analysis of ROESY spectra. The Job's plot derived from the NMR spectral data confirms that the complex formed has 1:1 stoichiometry. The largest changes in the CICS data were observed for the aromatic protons of one of the doxepin rings, with much smaller chemical shift changes observed for the protons of the other aromatic ring and the doxepin tail. Perhaps the most significant evidence for inclusion of the doxepin tricyclic ring is the strong ROESY cross peaks between the doxepin aromatic resonances and the protons located inside the beta-CD cavity. Changes in the doxepin (1)H NMR spectrum and the behavior of ROESY exchange cross peaks suggest that inclusion complex formation decreases the rate of internal motions of doxepin.     

2,5—双（4—羟基苯亚甲基）环戊酮中双电荷离子存在的串联质谱证据

应用串联质谱的碰撞诱导解离和联动扫描技术，研究了２，５－双（４－羟基苯亚甲基）环戊酮的质谱解离特征，提供了双电荷离子存在的实验证据。进一步对双电荷离子（ｍ／ｚ１４６）的碰撞诱导解离碎裂进行了讨论。     

Morphological change of poly (ε‐caprolactone) with a wide range of molecular weight via formation of inclusion complex with α‐cyclodextrin

The effect of molecular weight of poly(ε‐caprolactone) (PCL) on the formation and stability of inclusion complexes (ICs) between α‐cyclodextrin (α‐CD) and PCL was investigated by FTIR, WAXD, and DSC measurements. ICs between α‐CD and PCLs with a wide range of number‐average molecular weight, M_n = 1.21 × 10⁴ – 1.79 × 10⁵, were prepared by mixing the aqueous solution of CD and acetone solution of PCL followed by stirring at 60 °C for 1h and at the room temperature for 1 day. FTIR, WAXD, and DSC measurement showed the PCL chains were included into the α‐CD cavity, and the crystallization of PCL was suppressed in the α‐CD cavity. Stoichiometry and yield of each IC varied with the molecular weight of guest PCL, and the effect of IC formation on the crystallization behaviour of guest polymer decreased with the increase of molecular weight of guest polymer. © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 1433–1440, 2005     

1-甲基环丙烯与α-环糊精包合物的合成

采用溶液包结法利用α-环糊精(α-CD)对1-甲基环丙烯(1-MCP)进行包合,将气态的1-MCP固态化形成白色粉末状的1-MCP/α-CD稳定包合物,使之便于保存和应用。利用拉曼光谱(Raman)、X射线粉末衍射光谱(XRD)、气质联用测试仪(GC-MS)、核磁谱仪(NMR)等测试技术对所得包合物的结构和组成进行表征,证明了包合物的形成,同时提出了1-MCP/α-CD包合物中1-MCP含量的快速测定方法,以该法测定的包合物中1-MCP的有效质量分数约为3.6%。对1-MCP和α-CD的包合机理进行了探讨,认为1-MCP和α-CD按摩尔比1∶1进行包合。     

电喷雾质谱法研究人参皂苷与溶菌酶的相互作用

用电喷雾质谱法研究了溶菌酶与人参皂苷Rg1和Re的非共价相互作用。非共价复合物的解离常数可以由溶菌酶和复合物的峰高直接计算得到。由各个体系得到的溶菌酶与Rg1和Re的一级解离常数KD, 1是一致的，但是二级解离常数KD, 2的差别较大。由此可以推断出复合物的峰高越强，结果的精密度越好。当固定溶菌酶的浓度不变时，复合物的解离常数会随着人参皂苷的浓度的增加而略微的增大。而当固定人参皂苷的浓度时，复合物的解离常数会随着溶菌酶的浓度的增加而减小。计算结果还证明了人参皂苷Rg1与溶菌酶的结合能力大于Re。     

Mass spectrometric study of thermal stability of copper(II) bis(dipivaloylmethanate) vapour

The processes of thermal destruction of copper(II) bis(dipivaloylmethanate) (Cu(dpm)₂) in the temperature range 150°–550°C were studied by using a two-temperature variant of a double chamber Knudsen cell, with mass spectrometric recording of the gas-phase composition. The temperature range of stability of the vapour of the complex in vacuum was determined, as were those of its mixtures with oxygen in different proportions. The temperature dependence of the rate constant of the thermolysis of (Cu(dpm)₂) vapour was obtained. The thermal stability of Hdpm vapour and the influence of oxygen on the thermolysis of the ligand were studied.

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Zusammenfassung Unter Verwendung einer Zweitemperaturenvariante der Knudsenschen Doppelkammerzelle wurde mittels MS-Untersuchung der Gasphasenzusammensetzung im Temperaturbereich 150°–550°C der thermische Abbau von Kupfer(II)-bis(dipivaloylmethanat) (Cu(dpm)₂) untersucht. Es wurde der Temperaturbereich für die Stabilität der gasförmigen Komplexe in Vakuum sowie in Gemischen mit Sauerstoff in verschiedenen Verhältnissen bestimmt. Dabei wurde die Temperaturabhängigkeit der Geschwindigkeitskonstante für die Thermolyse von Cu(dpm)₂ ermittelt. Weiterhin wurde die thermische Stabilität von Hdpm-Dampf sowie der Einfluß von Sauerstoff auf die Thermolyse der Liganden bestimmt.