Substituent Effects on Torsional Strain in Cyclopentene Derivatives: A Computational Study.

Density functional theory calculations were used to create a library of ring strain energies (RSEs) for 73 cyclopentene derivatives with potential use as monomers for ring-opening metathesis polymerization (ROMP). An overarching goal was to probe how substituent choice may influence torsional strain, which is the driving force for ROMP and one of the most understudied types of RSEs. Potential trends investigated include substituent location, size, electronegativity, hybridization, and steric bulk. Using traditional and recently developed homodesmotic equations, our results show that the size and substitution (bulk) of the atom directly bonded to the ring have the greatest influence on torsional RSE. A complex interplay between bond length, bond angle, and dihedral angle dictates the relative eclipsed conformations between the substituent and its neighboring hydrogens and was found to be responsible for the notable differences in RSEs. Furthermore, substituents placed on the homoallylic position resulted in higher RSEs than the same substituent placed on the allylic position due to increased eclipsing interactions. Different levels of theory were also assessed, and it was determined that consideration of electron correlation in calculations increased RSEs by ∼2-5 kcal mol-1. Further increasing the level of theory did not significantly change RSEs, indicating that the increased computational cost and time may not be necessary for improved accuracy.

Novel parallelized quadrupole/linear ion trap/Orbitrap tribrid mass spectrometer improving proteome coverage and peptide identification rates.

Proteome coverage and peptide identification rates have historically advanced in line with improvements to the detection limits and acquisition rate of the mass spectrometer. For a linear ion trap/Orbitrap hybrid, the acquisition rate has been limited primarily by the duration of the ion accumulation and analysis steps. It is shown here that the spectral acquisition rate can be significantly improved through extensive parallelization of the acquisition process using a novel mass spectrometer incorporating quadrupole, Orbitrap, and linear trap analyzers. Further, these improvements to the acquisition rate continue to enhance proteome coverage and general experimental throughput.