Ding Chuanfan

A collinear tandem time-of-flight mass spectrometer for infrared photodissociation spectroscopy of mass-selected ions

An apparatus based on collinear tandem time-of-flight mass spectrometer has been designed for the measurement of infrared photodissociation spectroscopy of mass-selected ions in the gas phase. The ions from a pulsed laser vaporization supersonic ion source are skimmed and mass separated by a Wiley-McLaren time-of-flight mass spectrometer. The ion of interest is mass selected, decelerated and dissociated by a tunable IR laser. The fragment and parent ions are reaccelerated and mass analyzed by the second time-of-flight mass spectrometer. A simple new assembly integrated with mass gate, deceleration and reacceleration ion optics was designed, which allows us to measure the infrared spectra of mass selected ions with high sensitivity and easy timing synchronization.

Investigation of the Non-Covalent Interactions between Fragment Peptides of Bradykinin by Mass Spectrometry

To explore the important factors affecting the stability of gas phase bradykinin (R1P2P3G4F5S6P7F8R9), the non-covalent interactions between fragment peptides of bradykinin were investigated by electrospray ionization mass spectrometry (ESI-MS). The fracture sites are S 6 P 7 (mode1) and F5S6 (mode2). The fragment peptides of bradykinin and its des-arginine analogues were synthesized. ESI-MS results showed that the fragment peptides of bradykinin obtained in the two modes can easily react by non-covalent interactions. In fracture mode 1, when R 9 was removed, the peptide PF seldom bound to any other fragment peptide. While in fracture mode 2, non-covalent binding still occurred between fragment peptides when either R1 or R9 was removed, which indicates that serine is likely to be at the position of the β-turn. The collision induced dissociation (CID) revealed that the binding strength between RPPGFS and PFR, or RPPGF and SPFR, is stronger than for the peptides without R. For the complexes of RPPGFS with PFR, and RPPGF with SPFR, the binding constant (Kst) values determined by mass spectrometric titrations were 3.53×10 3 and 3.16×10 3 , respectively, which are greater than the K st value (1.25×103) of the complexesof PPGF with SPF. The mass spectrometric titrations confirmed the results from CID, indicating that the hydrogen bonds between the arginine residues of the two terminals of bradykinin play an important role in stabilizing the conformation of gas phase bradykinin.

Effect of Alkali Metal Ions on the Dissociation of Glycine Pentapeptide in the Gas Phase

To obtain more structural information of polypeptides,glycine pentapeptide(simplified as GGGGG or G5)was chosen as a model to investigate the impact of alkali metal ions on the dissociation of GGGGG in the gas phase.Stoichiometric G5 and alkali metal salt solutions,including Li+ ,Na+ ,K+ ,Rb+ , were mixed,respectively,and then the solutions were left to stand at room temperature for 10 h to reach equilibrium.The mass spectrometric results indicated that the alkali metal ions and G5 could form 1:1 or 2: 1 non-covalent complexes in solution.The energy of the collision induced dissociation(CID)was 25 eV. The gas phase CID results demonstrate that in the 1:1 complexes,the extent of fragmentation decreases according to the order:Li+ ,Na+ ,K+ ,Rb+ .Moreover,the unusual c,z ions were observed in the Rb + complex. In the 2:1 non-covalent complexes,the extent of fragmentation increases according to the order:Li+ ,Na+ , K+ ,Rb+ .The gas phase dissociation of the Na+ ,K+ ,Rb+ 2:1 complexes are easier than their 1:1 complexes. Except for Li+ ,the activation abilities of the double metal ions to G5 are stronger than that of the single metal ion to G5,which can induce more dissection sites in the glycine pentapeptide and lead to the formation of more kinds of fragment ions.

Probing Non-Covalent Complexes of Glutathione with D-Amino Acids by Mass Spectrometry

To investigate the non-covalent interaction between glutathione and D-amino acids, stoichiometric reduced glutathione (GSH) and three D-amino acids, including D-phenylalanine (D-Phe), D-histidine (D-His), and D-glutamine (D-Gln), were mixed respectively, and then incubated at room temperature for 1 h to reach equilibrium. The electrospray ionization mass spectrometry (ESI-MS) results indicated that glutathione and three D-amino acids could form non-covalent complexes in physiological pH conditions, respectively. The binding of glutathione to D-amino acid was further confirmed by collision-induced dissociation (CID) in a tandem mass spectrometer. Additionally, the complexes exhibited different features and properties from the reactants in UV spectroscopy, which also confirmed the results of ESI-MS. To avoid distinct ionization efficiency discrepancy and signal suppression in ESI-MS measurements, the interaction between glutathione (GSH) and D-glutamine (Gln) was quantitatively evaluated. A series of samples with different initial concentrations of glutathione and D-amino acids were mixed, and then series of peak intensities for different species in the mixture were achieved by ESI-MS. The dissociation constants of three complexes formed by glutathione and D-amino acids were calculated. The calculation results revealed that the reduced tripeptide γ-glutathione could interact with D-amino acids to form non-covalent complexes with different affinities, the stabilities of the three complexes increased gradually according to the order of D-glutamine, D-phenylalanine, and D-histidine.

The Measurement of the Ionization Potential and the Bond Energy Si(CH 3 ) 2 Cl 2

The vacuum ultraviolet photoionization spectrum of Si(CH3)(2)Cl-2 has been obtained with synchrotron radiation source. The adiabatic ionization potential of Si(CH3)(2)Cl-2 is 10.62 +/- 0.03eV (0.37eV lower than reported by PES), and the appearance potentials for Si(CH3)Cl-2(+), Si(CH3)(2)Cl+, SiCH3+ and SiCl+ are 11.25 +/- 0.03eV, 12.69 +/- 0.04eV, 15.1 +/- 0.1eV and 21.16eV +/- 0.1eV respectively. From these results, we estimate D(Si(CH3)Cl-2(+)-CH3)=0.63 +/- 0.03eV and D(Si(CH3)(2)Cl+-Cl))=2.07 +/- 0.04eV.