1. Equilibrium constants have been measured for several methyl ammonium and anilinium water cluster ions using the electrospray ionization equilibrium gas phase ion molecule reaction approach. Satisfactory agreement with published values for sodium and potsassium ion water clusters confirmed equilibrium conditions within the ion source. Gibbs free energy values calculated from the equilibrium constants for methylammonium cation-water clusters showed clear trends of a) increasing energy for smaller numbers of water molecules on any cation and b) decreasing energy for any given number of waters as the extent of methyl substitution increased. 2. The CID threshold approach was used to determine energies of tetraethyl and tetramethyl ammonium water cluster ion fragmentation. This approach is equivalent of the inverse of water cluster build up of under equilibrium conditions. Using a simplified model for threshold behavior, the trend described in a) above was seen for the tetramethylammonium ion. These latter are the first energetics measurements for multiple water attachments to tetraalkyl ammonium ions. 3. Our previously reported observations of aging dependent conformation changes of the 1-40 residues portion of beta-amyloid protein have been incorporated into a model for conformational changes of the peptide consistent with both the mass spectrometric observations and other physical measurements using NMR and CD. The premise of the model is that an irreversible conformational change occurs in solution, and that this conformational change leads to large aggregates with relatively little surface exposure.
| Epstein, Jonathan A; Blank, Paul S; Searle, Brian C et al. (2016) ProteinProcessor: A probabilistic analysis using mass accuracy and the MS spectrum. Proteomics 16:2480-90 |
| Campbell, Jennifer M; Vestal, Marvin L; Blank, Paul S et al. (2007) Fragmentation of leucine enkephalin as a function of laser fluence in a MALDI TOF-TOF. J Am Soc Mass Spectrom 18:607-16 |
| Vieira, N E; Goans, R E; Weiss, G H et al. (2000) Calcium kinetics in children with osteogenesis imperfecta type III and IV: pre- and post-growth hormone therapy. Calcif Tissue Int 67:97-100 |
| Mauras, N; Hayes, V Y; Vieira, N E et al. (1999) Profound hypogonadism has significant negative effects on calcium balance in males: a calcium kinetic study. J Bone Miner Res 14:577-82 |
| Vieira, N E; Marini, J C; Hopkins, E et al. (1999) Effect of growth hormone treatment on calcium kinetics in patients with osteogenesis imperfecta type III and IV. Bone 25:501-5 |
