Quantum chemical study of the structure, spectroscopy and reactivity of NO+.(H2O) n=1-5 clusters

Quantum chemical methods including Møller-Plesset perturbation (MP2) theory and density functional theory (DFT) have been used to study the structure, spectroscopy and reactivity of NO⁺(H₂O) _n=1-5 clusters. MP2/6-311++G** calculations are shown to describe the structure and spectroscopy of the clusters well. DFT calculations with exchange-correlation functionals with a low fraction of Hartree-Fock exchange give a binding energy of NO⁺(H₂O) that is too high and incorrectly predict the lowest energy structure of NO⁺(H₂O)₂, and this error may be associated with a delocalization of charge onto the water molecule directly binding to NO⁺ Ab initio molecular dynamics (AIMD) simulations were performed to study the NO⁺(H₂O)₅ [Formula: see text] H⁺(H₂O)₄ + HONO reaction to investigate the formation of HONO from NO⁺(H₂O)₅ Whether an intracluster reaction to form HONO is observed depends on the level of electronic structure theory used. Of note is that methods that accurately describe the relative energies of the product and reactant clusters did not show reactions on the timescales studied. This suggests that in the upper atmosphere the reaction may occur owing to the energy present in the NO⁺(H₂O)₅ complex following its formation.This article is part of the theme issue 'Modern theoretical chemistry'.

Ankle-foot orthoses: effect on energy expenditure of gait in spastic diplegic children

This study examined the effect of conventional plastic bilateral ankle-foot orthoses (AFOs) on the energy expenditure of ambulation in spastic diplegic cerebral palsy patients. Eighteen subjects (aged 8.3 +/- 2.83 years) ambulated five minutes at freely chosen velocities with and without their AFOs. Heart rate (beats per minute) and distance (meters) ambulated were recorded for each minute. A physiologic cost index was calculated by determining the ratio of walking heart rate to velocity [(HRamb-HRrest) divided by meters per minute]. The mean physiologic cost indexes for the last three minutes of ambulation with and without orthoses were 1.34 +/- 0.69 beats per meter and 1.51 +/- 0.79 beats per meter, respectively (p less than 0.05). Ambulation heart rate, velocity and total distance traveled were not statistically different between the two trials. The results indicated that energy expenditure of ambulation at self-selected speeds in spastic diplegic children was reduced by the application of conventional AFOs. However, each child should be evaluated on a single-case basis because of individual differences.