Dynamically assisted gated trapping for Fourier transform ion cyclotron mass spectrometry

Lithium monoxide anion: a ground-state triplet with the strongest base to date

Lithium monoxide anion (LiO(-)) has been generated in the gas phase and is found to be a stronger base than methyl anion (CH(3)(-)). This makes LiO(-) the strongest base currently known, and it will be a challenge to produce a singly charged or multiply charged anion that is more basic. The experimental acidity of lithium hydroxide is DeltaH degrees (acid) = 425.7 +/- 6.1 kcal.mol(-1) (1 kcal = 4.184 kJ) and, when combined with results of high-level computations, leads to our best estimate for the acidity of 426 +/- 2 kcal.mol(-1).

A novel workflow control system for Fourier transform ion cyclotron resonance mass spectrometry allows for unique on-the-fly data-dependent decisions

In this paper a novel workflow-based data acquisition and control system for Fourier transform ion cyclotron resonance mass spectrometry (FTICR-MS) is presented that facilitates a fast on-the-fly decision-making process for a wide variety of data-dependent experiments. Several new workflow implementations demonstrate the flexibility and benefit of this approach for rapid dynamic experimental design on a chromatographic timescale. The different sequence, evaluation, decision and monitoring modules are described using a selected set of examples. During a tandem liquid chromatography (LC)/FTICR-MS experiment the system is used to dynamically switch between various dissociation techniques such as electron capture dissociation (ECD) and sustained off-resonance irradiation (SORI) depending on the charge state of a tryptic peptide peak. The use of this workflow-based system for imaging FTICR-MS using a desorption electrospray ionization (DESI) source demonstrates the possibility of external control of the workflow by feedback from an imaging sample stage.

Are Carboxyl Groups the Most Acidic Sites in Amino Acids? Gas-Phase Acidity, H/D Exchange Experiments, and Computations on Cysteine and Its Conjugate Base

Hydrogen-deuterium exchange experiments were carried out on the conjugate base of cysteine with four different deuterated alcohols. Three H/D exchanges are observed to take place in each case, and a relay mechanism which requires the SH and CO2H groups to have similar acidities and subsequently proceeds through a zwitterionic intermediate is proposed. Gas-phase acidity measurements also were carried out in a quadrupole ion trap using the extended kinetic method and in a Fourier transform mass spectrometer by an equilibrium determination. The results are in excellent accord with each other and high-level ab initio and density functional theory calculations and indicate that the side-chain thiol in cysteine is more acidic than the carboxyl group by 3.1 kcal mol-1. Deprotonated cysteine is thus predicted to be a thiolate ion. A zwitterionic species also was located on the potential energy surface, but it is energetically unfavorable (+10.1 kcal mol-1).