Fourier transform ion cyclotron resonance study of multiply charged aggregates of small singly charged peptides formed by electrospray ionization

AbstractAggregates of singly protonated peptides formed with a nanoelectrospray ion source have been observed in the gas phase using Fourier transform ion cyclotron resonance (FT-ICR). Employment of “soft” ion sampling conditions in the source, which were developed previously to generate water clusters of biomolecules, provides significant yields of aggregates of singly protonated GGDPG ([2GGDPG + 2H]2+), GGEPG ([2GGEPG + 2H]2+), and VEPIPY (2VEPIPY + 2H]2+). With peptide mixtures, heteroaggregates, e.g., [GGDPG + GGEPG + 2H]2+ have also been observed along with the homoaggregates. These weakly bound noncovalent complexes undergo facile exothermic dissociation into the corresponding singly protonated monomer species with normal operation of the electrospray ion source. For example, the aggregates were not observed in FT-ICR experiments utilizing a conventional electrospray ionization (ESI) or fast atom bombardment source or with a quadrupolar ion trap mass spectrometer equipped with a conventional ESI source. The formation and metastability of these aggregates are dependent on highly specific intermolecular hydrogen bonding between the monomers. The amino acid sequence (DPG) of GGDPG mimics the well-known β reverse turn of proteins and semiempirical calculations show that it provides excellent hydrogen bonding sites for a protonated N-terminus amino group. Support for this conjecture is provided by the failure to observe aggregate formation of singly protonated peptides with several larger peptides, including hexaglycine and hexaalanine

Ionization Mechanism of the Ambient Pressure Pyroelectric Ion Source (APPIS) and Its Applications to Chemical Nerve Agent Detection

We present studies of the ionization mechanism operative in the ambient pressure pyroelectric ionization source (APPIS), along with applications that include detection of simulants for chemical nerve agents. It is found that ionization by APPIS occurs in the gas-phase. As the crystal is thermally cycled over a narrow temperature range, electrical discharges near the surface of the crystal produce energetic species which, through reactions with atmospheric molecules, result in reactant ions such as protonated water clusters or clusters of hydroxide and water. Reactant ions can be observed directly in the mass spectrometer. These go on to react with trace neutrals via proton transfer reactions to produce the ions observed in mass spectra, which are usually singly protonated or deprotonated species. Further implicating gas-phase ionization, observed product distributions are highly dependent on the composition of ambient gases, especially the concentration of water vapor and oxygen surrounding the source. For example, basic species such as triethylamine are observed as singly protonated cations at a water partial pressure of 10 torr. At a water pressure of 4 torr, reactive oxygen species are formed and lead to observation of protonated amine oxides. The ability of the APPIS source to detect basic molecules with high proton affinities makes it highly suited for the detection of chemical nerve agents. We demonstrate this application using simulants corresponding to VX and GA (Tabun). With the present source configuration pyridine is detected readily at a concentration of 4 ppm, indicating ultimate sensitivity in the high ppb range

Differential cell susceptibilities to kras(G12D) in the setting of obstructive chronic pancreatitis

BACKGROUND & AIMS: Activating mutation of the KRAS gene is common in some cancers, such as pancreatic cancer, but rare in other cancers. Chronic pancreatitis is a predisposing condition for pancreatic ductal adenocarcinoma (PDAC), but how it synergizes with KRAS mutation is not known. METHODS: We used a mouse model to express an activating mutation of Kras in conjunction with obstruction of the main pancreatic duct to recapitulate a common etiology of human chronic pancreatitis. Because the cell of origin of PDAC is not clear, Kras mutation was introduced into either duct cells or acinar cells. RESULTS: Although Kras(G12D) expression in both cell types was protective against damage-associated cell death, chronic pancreatitis induced p53, p21, and growth arrest only in acinar-derived cells. Mutant duct cells did not elevate p53 or p21 expression and exhibited increased proliferation driving the appearance of PDAC over time. CONCLUSIONS: One mechanism by which tissues may be susceptible or resistant to KRAS(G12D)-initiated tumorigenesis is whether they undergo a p53-mediated damage response. In summary, we have uncovered a mechanism by which inflammation and intrinsic cellular programming synergize for the development of PDAC

Reflection and the art of coaching: fostering high-performance in olympic ski cross

In preparation for the 2010 Vancouver Winter Olympic Games, the lead author engaged in systematic reflection in an attempt to implement coaching behaviours and create practice environments that promoted athlete development (psycho-social and physical performance). The research was carried out in relation to his work as head Ski Cross coach working with (primarily) three athletes in their quest for Olympic qualification and subsequent performance success in the Olympic Games. This project sought to examine coach-athlete interactions. Of particular interest were coach and athlete responses regarding the implementation of autonomy supportive coaching behaviours in a high context. Autonomy supportive coaching behaviours have previously been strongly associated with positive athlete psycho-social and performance outcomes, however, a paucity of research has examined its implementation in high-performance contexts. Through the use of participant ethnography, it was possible to gain considerable insights regarding athletes' perceptions of choice, implications of perceived athletic hierarchies, as well as cultural and experience-related influences on training and performance expectations

INFRARED MULTIPHOTON DISSOCIATION SPECTRUM OF CF3MN(CO)3(NO)-

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PROTON AFFINITY AND HEAT OF FORMATION OF SILYLENE

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THERMOCHEMISTRY OF SILAETHYLENE AND METHYLSILYLENE FROM EXPERIMENT AND THEORY

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PHOTOIONIZATION MASS-SPECTROMETRIC STUDIES OF THE METHYLSILANES SI(CH3)NH4-N (N = 0-3)

Photoionization efficiency curves for the low energy fragment ions (M - H)+, (M - H2)+, (M - CH3)+, and (M - CH4)+ for the series of methyl substituted silanes Si(CH3)nH4-n (n = 0-3) are reported. The molecular ions were undetectable except SiH4+. (M - H2)+ and (M - CH4)+ ions show sharp appearance onsets compared with (M - H)+ ions, which have distinct threshold curvature. (M - H2)+ ions are ascribed to silylene positive ions, SiR2+. The alternative silaethylene positive ion structure, CH2SiHR+, is unlikely because the fragmentation process yielding CH2SiD2+ with loss of HD is not observed in the photoionization mass spectrum of CH3SiD3. Thresholds are interpreted in terms of the thermochemistry of the various ionic and neutral silicon species and afford accurate calculation of hydride affinities of the silylene positive ions. The calculated hydride affinities for silylene positive ions are 263.4, 244.3 and 230.6 kcal mol-1 for SiH2+, SiMeH+ and SiMe2+, respectively. Within experimental error, the hydride affinities of the silylene positive ions are identical to those of the silicenium ions with the same number of methyl groups. The present results, combined with other available thermochemical data, lead to the critical assessment of the Si-H and Si-CH3 bond energies of the neutral and ionic fragments of methylsilanes, as well as ionization potentials of the silyl radicals and silylenes.X113229sciescopu