Electronic and Steric Tuning of Catalytic H2 Evolution by Cobalt Complexes with Pentadentate Polypyridyl-Amine Ligands.

Structural modifications of molecular cobalt catalysts have provided important insights into the structure-function relationship for the hydrogen evolution reaction. We have shown that replacement of equatorial pyridines with more basic and conjugate isoquinoline groups of a pentadentate ligand results in lower overpotential and higher catalytic activity for electro- and photolytic H2 production in aqueous solutions. To fully understand the electronic and steric effects of the axial group that lies trans to the proposed cobalt hydride intermediate, isoquinoline groups were introduced in two new pentadentate ligands, N, N-bis(2-pyridinylmethyl)[3-(2-pyridinyl)isoquinoline)]-1-methanamine (DPA-1-MPI) and N, N-bis(2-pyridinylmethyl)[1-(2-pyridinyl)-isoquinoline)]-3-methanamine (DPA-3-MPI). Despite a slight structural difference of the introduced isoquinoline group, the resulting cobalt complexes display drastic changes in their electro- and photochemical properties. There are positive shifts of 290 and 260 mV, respectively, for the CoII/CoI and CoIII-H/CoII-H couples from [Co(DPA-1-MPI)(H2O)](PF6)3 to [Co(DPA-3-MPI)(H2O)](PF6)3, with the former being ∼32 times as active as the latter in photocatalytic H2 production. Density functional theory (DFT) calculations show that the protonation of CoI to yield the CoIII-H species is energetically more favorable for [Co(DPA-1-MPI)(H2O)](PF6)3 than that of [Co(DPA-3-MPI)(H2O)](PF6)3. Both experimental results and DFT computations suggest that the presence of a planar conjugate bipyridyl unit or its isoquinoline derivative is a key feature for stabilizing low valent CoI species toward proton binding. The incorporation of an electron-donating group trans to the proposed Co-H species also facilitates proton binding and H-H bond formation, which is proposed to occur by the heterolytic coupling of CoII-H species. The overall catalytic H2 evolution is presented as the modified electron transfer (E)-proton transfer (C)-electron transfer (E)-proton transfer (C) (mod-ECEC) pathway. This study provides important new insight into the electronic and steric factors controlling catalytic H2 production by Co complexes with pentadentate ligands.

Atlantoaxial Instability in a Patient with Neck Pain and Ankylosing Spondylitis.

The purpose of this report is to describe the evaluation and treatment of a patient with neck pain and ankylosing spondylitis who had underlying atlantoaxial instability. The patient was a 31-yr-old man diagnosed with ankylosing spondylitis 1 yr prior who was referred to a physical therapist for the treatment of chronic, worsening low back and hip pain. He also had secondary complaints of neck, upper back, and shoulder pain. The patient worked as a military pilot. As part of the patient's physical examination, a Sharp-Purser test was performed, which was positive for excessive motion. Diagnostic imaging confirmed the atlantoaxial instability; it was also determined that the patient's atlanto-occipital joints were fused. Despite evidence of atlantoaxial instability, it was determined the patient would be managed through nonsurgical interventions. The patient was prescribed etanercept by his rheumatologist and the physical therapist developed a comprehensive rehabilitation program that addressed relevant impairments of the spine, hips, and shoulders. At 3 yr following his initial evaluation with the physical therapist, the patient continued to report minimal bodily pain and no limitations in his functional capabilities. Additionally, the patient had earned a high profile flying position with an aggressive flying schedule and he successfully completed his first running marathon. It is important for clinicians to have an understanding of the clinical findings associated with atlantoaxial instability, as these findings provide guidance for diagnostic imaging and specialist referral prior to initiating conservative management strategies, such as physical therapy.

Differences in quadriceps femoris muscle torque when using a clinical electrical stimulator versus a portable electrical stimulator.

BACKGROUND AND PURPOSE: There have been conflicting views and evidence reported in the literature concerning differences in muscle torque-generating capacities between clinical ("plug-in") console devices whose power source is provided by an electrical outlet (60 Hz, alternating current-driven) and portable electrical muscle stimulators (smaller, battery-operated stimulators). The purpose of this study was to compare the torque-generating capacity of the quadriceps femoris muscle during neuromuscular electrical stimulation (NMES) between a clinical neuromuscular electrical stimulator (VersaStim 380) and a portable neuromuscular electrical stimulator (Empi 300PV). SUBJECTS: Forty volunteer subjects with no known knee, neurological, or cardiovascular pathology (22 male, 18 female) participated in the study. METHODS: All subjects were tested with the clinical and portable stimulators on 2 separate days. Peak isometric torque of the quadriceps femoris muscle was measured using a Biodex dynamometer. Peak isometric quadriceps femoris muscle torque achieved during NMES and the average quadriceps femoris muscle torque integral produced over 10 NMES contractions were measured for each stimulator. Subjects also rated the amount of pain they experienced during the 10 NMES contractions using a numeric pain scale. Paired t tests were used to compare mean differences in measured variables between stimulator conditions. RESULTS: There were no differences in the peak torque or numeric pain ratings during the electrically stimulated contractions between stimulator conditions. The Empi 300PV produced a greater average torque integral compared with the VersaStim 380 during 10 electrically stimulated contractions (Empi 300PV=988.6-/+330.4 N.m-s, Versastim 380=822.7-/+292.6 N.m-s). DISCUSSION AND CONCLUSION: The portable Empi 300PV stimulator produced comparable levels of average peak torque at comparable levels of discomfort to those produced by the VersaStim 380 clinical stimulator. The Empi 300PV maintained greater amounts of torque production during a 10-contraction training session compared with the VersaStim 380. Based on these data, we believe that the Empi 300PV has the potential to produce adequate levels of torque production for NMES quadriceps femoris muscle performance training. Further study is needed to determine the effectiveness of using the Empi 300PV for quadriceps femoris muscle performance training.