Ion-pair reorganization regulates reactivity in photoredox catalysts.

Cyclometalated and polypyridyl complexes of d6 metals are promising photoredox catalysts, using light to drive reactions with high kinetic or thermodynamic barriers via the generation of reactive radical intermediates. However, while tuning of their redox potentials, absorption energy, excited-state lifetime and quantum yield are well-known criteria for modifying activity, other factors could be important. Here we show that dynamic ion-pair reorganization controls the reactivity of a photoredox catalyst, [Ir[dF(CF3)ppy]2(dtbpy)]X. Time-resolved dielectric-loss experiments show how counter-ion identity influences excited-state charge distribution, evincing large differences in both the ground- and excited-state dipole moment depending on whether X is a small associating anion (PF6-) that forms a contact-ion pair versus a large one that either dissociates or forms a solvent-separated pair (BArF4-). These differences correlate with the reactivity of the photocatalyst toward both reductive and oxidative electron transfer, amounting to a 4-fold change in selectivity toward oxidation versus reduction. These results suggest that ion pairing could be an underappreciated factor that modulates reactivity in ionic photoredox catalysts.

Efficacy of flexion and extension treatments incorporating braces for low-back pain patients with retrodisplacement, spondylolisthesis, or normal sagittal translation.

Radiographic instability seemingly enjoys the status of a well-defined clinical syndrome. The concept is widely used, and specific treatments, usually spinal fusion, are routinely performed based on the diagnosis. The minimum standards necessary to establish radiographic instability as a legitimate clinical syndrome have not been established, however. The primary purpose of this study was to determine if treatment involving bracing, exercise, and education controlling either flexion or extension postures, would result in a distinctive pattern of favorable or unfavorable results, depending on the type of radiographic instability (retrodisplacement or spondylolisthesis). Fifty-six patients meeting strict study inclusion and radiographic evaluation criteria were assigned signed to a bracing treatment (flexion, extension, placebo-control) according to a randomization scheme, designed to ensure equal representation of translation categories (retro, normal, spondy) across treatment groups, and assessed at admission and 1-month follow-up. The sample was relatively evenly divided between men (46%) and women (54%), and by age. Translation classification was related to both gender and age, with men more likely classified as retro and women more likely spondy and patients in their 20s having lower incidence of spondy and higher incidence of normal translation. Translation classification was not related to selected indices of low-back pain history. Brace treatments were not shown to reduce patient range of motion or lessen trunk strength. A significant treatment by time interaction for the modified pain interference (VAS) scale indicated improvement for patients in extension compared with patients in flexion and control-placebo treatments. In conjunction with no significant three-way interaction between treatment, translation classification, and time, it was hypothesized that radiographic instability might more appropriately be considered a corroborative sign of advanced discogenic problems. Improvement in extension treatment, regardless of the type of radiographic abnormality, suggests that the treating clinician might consider extension treatment for chronic low-back pain patients. Causes and implications for the failure of this study to provide support for considering radiographic instability as a clinical syndrome are considered and future directions for this area of research suggested.

Isolated L4-L5 fusions using the variable screw placement system: unilateral versus bilateral.

Thirty-six patients were retrospectively followed an average of 25.1 months to evaluate the relative effectiveness of unilateral (16 patients) versus bilateral (20 patients) variable screw placement (VSP) instrumentation in isolate L4-L5 fusions. Demographic variables and preoperative diagnoses were similar between treatment groups. Outcome was assessed primarily through evaluation of plain roentgenograms and self-report questionnaires. Use of VSP instrumentation at the L4-L5 level with autogenous posterolateral grafting achieved a successful fusion rate of 97% with minimal complications. Fusion results with unilateral instrumentation were nearly identical to those of bilateral; in both cases, results were better than most historical controls for noninstrumented fusions in situ. Clinical outcome, as obtained through standardized measurement techniques of pain and function, demonstrated 69% excellent and good results. Clinical outcome was similar between treatment groups yet was not significantly related to the fusion status obtained at follow-up.

Lumbar discography in normal subjects. A controlled, prospective study.

Major advances in the techniques of discography since 1968, in conjunction with major strides in the evaluation of pain in recent years, prompted a study in which Holt's work on the specificity of discography was replicated and extended. For the present study, seven patients who had low-back pain and ten volunteers who had been carefully screened, with a questionnaire and a physical examination, to ensure that they had no history of problems with the back, had an injection at three levels, and all sessions were videotaped. After each injection, the participant was interviewed about the pattern and intensity of the pain, and then the discs were imaged with computed tomography. Five raters, who were blind to the condition of the participant, graded each disc as normal or abnormal on the basis of findings on magnetic resonance images that had been made before the injection and computed tomography (discography) were done. There was only one disagreement between the ratings that were made on the basis of the magnetic resonance images and those that were made on the basis of the discograms. Each participant's pain-related response was evaluated independently by two raters who viewed the videotapes of the discography. Inter-rater reliability was 0.99, 0.93, and 0.88 for the evaluation of intensity of the pain, pain-related behavior, and similarity of the pain to pain that the subject had had before the injection. In the asymptomatic individuals, the discogram was interpreted as abnormal for 17 per cent (five) of the thirty discs and for five of the ten subjects.(ABSTRACT TRUNCATED AT 250 WORDS)

A new approach to the low-back physical examination. Behavioral assessment of mechanical signs.

UNLABELLED: A rationale for a new approach to the low-back physical examination was developed. A set of 21 tests, 17 assessing organic and four assessing nonorganic signs, were organized into an examination according to specified criteria, and the reliability of the patient-reported and examiner-observed measures within the examination assessed. Primary outcome measures included patient reports of their pain location, aggravation and examiner-observed pain behaviors resulting from the maneuvers. Two pain behavior composites, conceptualized as outcome measures, were developed, one based on the 17 organic tests and one based on the four nonorganic tests. DESIGN: The reliability of the physical examination was assessed using a short-term test-retest paradigm. Three raters, two experienced orthopaedic surgeons and an RN with no previous experience in administering physical examinations were trained in the examination methods. Patients were assigned to one of three rater pairs and examined twice within a single day. During each examination both raters evaluated each patient; however, rater role as examiner or observer was reversed across examination. RESULTS: Forty-two patients were examined. Average times of 13.9 and 11.6 minutes were required to complete examinations 1 and 2, respectively. In addition, the time required to complete the examination decreased as the examiners became more familiar with the procedure, suggesting that an experienced examiner would usually be able to complete the examination in approximately 10 minutes. Within-examination reliabilities for the patient-reported measures (pain location and aggravation) were universally high, as expected, since these rating required the rater only to correctly hear and code patient responses.(ABSTRACT TRUNCATED AT 250 WORDS)