Positive and negative ions generated by laser-based ionization methods from three gold:thiolate cluster compounds are mass analyzed by time-of-flight mass spectrometry. The three compounds have similar inorganic core masses ( approximately 29 kDa, approximately 145 Au atoms) but different n-alkanethiolate ligands associated with each cluster compound (Au:SR, R = butane, hexane, dodecane). Irradiation of neat films (laser desorption/ionization) and films generated by dilution of the cluster compounds in an organic acid matrix (matrix-assisted laser desorption/ionization) with a nitrogen laser (337 nm) produced distinct ion abundances that are relevant to different structural aspects of the cluster compound.
View Article and Find Full Text PDFRapid Commun Mass Spectrom
January 2004
An ion trap mass analyzer has been attached to an organic secondary ion microprobe. A pressure differential >100 can be maintained between the ion trap and microprobe. The well-focused secondary ion beam can transit a small (2 mm) diameter tube, but gas flow from ion trap to microprobe is impeded.
View Article and Find Full Text PDFMachine vision refers to computer programs consisting of a collection of pattern recognition and digital image processing algorithms (Fabel, G. Motion Control 2000, 53-54). A version of machine vision has been applied to correlating digital images generated by optical microscopy and secondary ion mass spectrometry (SIMS).
View Article and Find Full Text PDFOrganic secondary ion mass spectrometry (SIMS) and matrix-assisted laser desorption/ionization (MALDI) mass spectrometry can be used to produce molecular images of samples. This is achieved through ionization from a clearly identified point on a flat sample, and performing a raster of the sample by moving the point of ionization over the sample surface. The unique analytical capabilities of mass spectrometry for mapping a variety of biological samples at the tissue level are discussed.
View Article and Find Full Text PDFThe parent ions of human hemoglobin beta-chain ranging in charge from 2+ to 17+ have been subjected to ion trap collisional activation. The highest charge-state ions (17+ to 13+) yielded series of products arising from dissociation of adjacent residues. The intermediate charge-state ions (12+ to 5+) tended to fragment preferentially at the N-terminal sides of proline residues and the C-terminal sides of acidic residues.
View Article and Find Full Text PDFThe gas phase H/D exchange reactions of bradykinin (M + 3H)3+ ions with D2O and DI were monitored in a quadrupole ion trap mass spectrometer. The H/D exchange kinetics of both chemical probes (D2O and DI) indicate the presence of two noninterconverting reactive gas phase ion populations of bradykinin (M + 3H)3+ at room temperature. The H/D exchange involving DI, however, generally proceeds faster than that involving D2O.
View Article and Find Full Text PDFThis report describes how the electrochemical double-layer capacitances of nanometer-sized alkanethiolate monolayer-protected Au clusters (MPCs) dissolved in electrolyte solution depend on the alkanethiolate chain length (C4 to C16). The double-layer capacitances of individual MPCs (C(CLU)) are sufficiently small (sub-attoFarad, aF) that their metal core potentials change by >0.1 V increments for single electron transfers at the electrode/solution interface.
View Article and Find Full Text PDFThe kinetics of attachment of hydroiodic acid (HI) to the (M + 6H)6+ ions of native and reduced forms of bovine pancreatic trypsin inhibitor (BPTI) in the quadrupole ion trap environment are reported. Distinctly nonlinear (pseudo first-order) reaction kinetics are observed for reaction of the native ions, indicating two or more noninterconverting structures in the parent ion population. The reduced form, on the other hand, shows very nearly linear reaction kinetics.
View Article and Find Full Text PDFA transition from metal-like double-layer capacitive charging to redox-like charging was observed in electrochemical ensemble Coulomb staircase experiments on solutions of gold nanoparticles of varied core size. The monodisperse gold nanoparticles are stabilized by short-chain alkanethiolate monolayers and have 8 to 38 kilodaltons core mass (1.1 to 1.
View Article and Find Full Text PDFCis and trans isomers of two dinuclear platinum complexes, [cis-¿Pt(NH3)2Cl¿2 mu-(NH2(CH2)nNH2)](NO3)2 (1,1/c,c) and [trans-¿Pt(NH3)2Cl¿2 mu-(NH2(CH2)nNH2)](NO3)2 (1,1/t,t), where the diamine was 1,4-butanediamine (n = 4) or 1,6-hexanediamine (n = 6), were studied using electrospray ionization surface-induced dissociation (ESI/SID) tandem mass spectrometry (MS/MS). The same fragment ions were observed for both the cis and trans isomers of each complex (n = 4 or 6), but the relative intensities were dependent on the isomer studied. The ESI/SID data and energy-resolved mass spectra show that the position of the chloride plays a significant role in the fragmentation of these ions.
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