Patrick R. R. Langridge-Smith

The bond length of silver dimer

Abstract The spectroscopy of the A–X system of disilver in a supersonic jet has been studied at 120 MHz resolution. The lowest rotational levels were observed and an unequivocal J-numbering was established for the first time. The following bond lengths were derived: ro(X, 107Ag109Ag)=2.53350 (48)A, re(A). The ground state bond length is compared with previous experimental and ab initio determinations.

EINSTEIN A-COEFFICIENTS AND TRANSITION DIPOLE-MOMENTS FOR SOME ION-PAIR TO VALENCE TRANSITIONS IN I2

The relative fluorescence intensities of all the strong electronic transitions from five of the first cluster of ion-pair (IP) states of I2 and from three states in the second cluster have been measured. The fluorescence, in most cases from ν′ = 0, was dispersed and comprised both discrete and continuous (bound → free) spectra. These were fitted and each simulated electronic spectrum integrated separately to give relative values of the Einstein A-coefficients (summed over final vibrational states) for each transition. Using previously reported lifetimes, transition dipoles for each of the parallel transitions from nine IP states are deduced, together with some of the stronger perpendicular transition dipole moments. At R e of the ion-pair states, μ‖ (five transitions observed) is almost constant at 0·2–0·3 D, but μ‖ ranges between 0·7 and 3·7 D. There is a marked difference in the parallel transition moments associated with some g/u pairs in the same cluster of IP states which can be accounted for by the ...

Precursor Ion Independent Algorithm for Top-Down Shotgun Proteomics

We present a precursor ion independent top-down algorithm (PIITA) for use in automated assignment of protein identifications from tandem mass spectra of whole proteins. To acquire the data, we utilize data-dependent acquisition to select protein precursor ions eluting from a C4-based HPLC column for collision induced dissociation in the linear ion trap of an LTQ-Orbitrap mass spectrometer. Gas-phase fractionation is used to increase the number of acquired tandem mass spectra, all of which are recorded in the Orbitrap mass analyzer. To identify proteins, the PIITA algorithm compares deconvoluted, deisotoped, observed tandem mass spectra to all possible theoretical tandem mass spectra for each protein in a genomic sequence database without regard for measured parent ion mass. Only after a protein is identified, is any difference in measured and theoretical precursor mass used to identify and locate post-translation modifications. We demonstrate the application of PIITA to data generated via our wet-lab approach on a Salmonella typhimurium outer membrane extract and compare these results to bottom-up analysis. From these data, we identify 154 proteins by top-down analysis, 73 of which were not identified in a parallel bottom-up analysis. We also identify 201 unique isoforms of these 154 proteins at a false discovery rate (FDR) of <1%.

Energy-dependent electrospray ionisation mass spectrometry: applications in transition metal carbonyl chemistry

Maps of electrospray mass spectrometry data, plotted as cone voltage versus mass-to-charge ratio, provide a clear and compact method of visualising the accompanying fragmentation processes, in this case applied to the sequential removal of ligands from transition-metal carbonyl complexes. The technique is described as energy-dependent electrospray ionisation mass spectrometry (EDESI-MS). Copyright 2000 John Wiley & Sons, Ltd.

Chemical transformations on the surface of [60]fullerene: Synthesis of [60]fullereno[1′,2′:4,5]oxazolidin-2-one

Abstract Base-induced α-elimination from substituted O -4-nitrophenylsulfonylhydroxamic acids has been used as a mild source of nitrenes for capture by [60]fullerene; rearrangment of the resulting [60]fullereno[1′,2′:2,3]aziridine bearing a N -ethoxycarbonyl grouping under the influence of phenol/chlorotrimethylsilane results in the quantitative formation of the title compound which can be cleaved to yield 1-hydroxy-2- N -methylamino[60]fullerene.

Investigation of Porphyrins and Metalloporphyrins Using Two-Step Laser Mass Spectrometry

Laser desorption time-of-flight mass spectrometry with laser postionization at 193 nm has been used to study a series of selected porphyrins and metalloporphyrins. Molecular ions are predominantly formed under soft ionization conditions, with extensive fragmentation of the peripheral substituents being observed under hard ionization conditions. Cu-octaethylporphyrin is found to exhibit anomalous demetallation at this ionization wavelength. At high ionization laser fluences it is also possible to observe extensive fragmentation of the porphyrin macrocycle. Much of the observed fragmentation can be understood with reference to previous studies using electron impact (EI) ionization. The stability of the porphyrin nucleus allows the fragmentation of the side chains to be examined. As in earlier EI studies dehydration products are observed in the mass spectra of hematoporphyrin IX. These products are shown to be thermally induced during infrared laser desorption, rather than fragments arising from photoionisation. The flexibility of this two-step laser mass spectrometric approach has allowed the analysis of chlorophyll a directly from an organic matrix. The data obtained suggest that information concerning the interaction between adsorbate and substrate can be extracted.

Aziridino[2′,3′ : 1,2][60]fullerene

Thermal elimination of isobutene and CO2 from N-tert-butoxycarbonylaziridino[2′,3′ : 1,2][60]fullerene 4 provides a clean and efficient route to aziridino[2′,3′ : 1,2][60]fullerene 1, an isolable and stable solid.

Destabilizing missense mutations in the tumour suppressor protein p53 enhance its ubiquitination in vitro and in vivo

p53 ubiquitination catalysed by MDM2 (murine double minute clone 2 oncoprotein) provides a biochemical assay to dissect stages in E3-ubiquitin-ligase-catalysed ubiquitination of a conformationally flexible protein. A mutant form of p53 (p53(F270A)) containing a mutation in the second MDM2-docking site in the DNA-binding domain of p53 (F270A) is susceptible to modification of long-lived and high-molecular-mass covalent adducts in vivo. Mutant F270A is hyperubiquitinated in cells as defined by immunoprecipitation and immunoblotting with an anti-ubiquitin antibody. Transfection of His-tagged ubiquitin along with p53(R175H) or p53(F270A) also results in selective hyperubiquitination in cells under conditions where wild-type p53 is refractory to covalent modification. The extent of mutant p53(R175H) or p53(F270A) unfolding in cells as defined by exposure of the DO-12 epitope correlates with the extent of hyperubiquitination, suggesting a link between substrate conformation and E3 ligase function. The p53(F270A:6KR) chimaeric mutant (where 6KR refers to the simultaneous mutation of lysine residues at positions 370, 372, 373, 381, 382 and 386 to arginine) maintains the high-molecular-mass covalent adducts and is modified in an MDM2-dependent manner. Using an in vitro ubiquitination system, mutant p53(F270A) and the p53(F270A:6KR) chimaeric mutant is also subject to hyperubiquitination outwith the C-terminal domain, indicating direct recognition of the mutant p53 conformation by (a) factor(s) in the cell-free ubiquitination system. These data identify an in vitro and in vivo assay with which to dissect how oligomeric protein conformational alterations are linked to substrate ubiquitination in cells. This has implications for understanding the recognition of misfolded proteins during aging and in human diseases such as cancer.

The electropolymerization and characterization of 5-cyanoindole

Abstract The electropolymerization of 5-cyanoindole in acetonitrile leads to the formation and deposition of a cyclic trimer. This trimer then undergoes further oxidation on the electrode surface to form polymeric species. The trimer and polymers can be separated by their differential solubility, and they have been structurally characterized. The structure of the trimer is analogous to that found when indole-5-carboxylic acid is polymerized, indicating that the trimer is formed by a similar mechanism. Electrochemical studies indicate that both free trimer and the trimer centres in the polymer are less easily oxidized than indole-5-carboxylic acid; this can be attributed to the increased electronegativity of the 5-cyano substituent which increases the energy of the oxidized form of the redox centre.

Bis-functionalisation of C60via thermal rearrangement of an isolable fulleroaziridine bearing a ‘solubilising’ supermesityl ester moiety

Heating of C60 with the novel azidoformate 3 bearing a highly solubilising supermesityl group affords the first example of a nitrogen-bridged fullerene 4, with a σ-homoaromatic closed 6,6-aziridine structure, which by further heating can be induced to undergo rearrangement on the fullerene surface to form as the sole product, the closed isomeric oxazole derivative 5 with O and N vicinally bound to the fullerene framework at a 6,6-ring juncture