Reversible O-H Bond Activation by Tripodal tris(Nitroxide) Aluminum and Gallium Complexes.

Herein, we report the preparation and characterization of the Group 13 metal complexes of a tripodal tris(nitroxide)-based ligand, designated (TriNOx3-)M (M = Al (1), Ga (2), In (3)). Complexes 1 and 2 both activate the O-H bond of a range of alcohols spanning a ∼10 pKa unit range via an element-ligand cooperative pathway to afford the zwitterionic complexes (HTriNOx2-)M-OR. Structures of these alcohol adduct products are discussed. We demonstrate that the thermodynamic and kinetic aspects of the reactions are both influenced by the identity of the metal, with 1 having higher reaction equilibrium constants and proceeding at a faster rate relative to 2 for any given alcohol. These parameters are also influenced by the pKa of the alcohol, with more acidic alcohols reacting both to more completion and faster than their less acidic counterparts. Possible mechanistic pathways for the O-H activation are discussed.

Initial Evidence for Reliable and Valid Use of Scores on the 8-Item Econ-QOL Short Form to Measure Economic Quality of Life in Caregivers of Persons With Traumatic Brain Injury.

OBJECTIVE: To provide reliability and validity data to support the clinical utility of Economic Quality of Life Measure (Econ-QOL) scores in caregivers of civilians and service members/veterans with traumatic brain injury (TBI). DESIGN: Cross-sectional survey study. SETTING: Three academic medical centers and a Veterans Affairs treatment facility. PARTICIPANTS: 376 caregivers of civilians (n=213) and service members/veterans (n=163) with TBI (N=376). INTERVENTIONS: N/A. MAIN OUTCOME MEASURES: Econ-QOL and several patient-reported outcome measures (Traumatic Brain Injury Caregiver Quality of Life Caregiver-Specific Anxiety and Caregiver Strain, Patient-Reported Outcomes Measurement Information System sleep-related impairment, Neurological Quality of Life Measurement System positive affect and well-being) and measures of financial status (self-reported income). RESULTS: Internal consistency reliability of the Econ-QOL Short Form scores were excellent (all Cronbach's alphas ≥.92). There were no floor or ceiling effects for scores. There was evidence of convergent and discriminant validity, with the Econ-QOL scores having the strongest relationships with self-reported income (convergent validity evidence) and weak relationships with the other measures (discriminant validity evidence). Individuals with scores that were "below or possibly below" the poverty line (according to 2016 federal government poverty level thresholds) reported worse economic quality of life relative to those individuals who were definitely above the poverty line, supporting known-groups validity. CONCLUSIONS: This article establishes the clinical utility of scores on the Econ-QOL Short Form in caregivers of persons with TBI and provides evidence that it is valid and appropriate to use such scores not only in a variety of different disability populations (eg, spinal cord injury, stroke) but also in caregivers.

Biomarkers and their association with bacterial illnesses in hypothermic infants.

OBJECTIVES: To describe the association of biomarkers with serious bacterial infection (SBI; urinary tract infection [UTI], bacteremia and/or bacterial meningitis) in hypothermic infants presenting to the emergency department (ED). METHODS: We performed a cross sectional study in four academic pediatric EDs from January 2015 through December 2019, including infants ≤90 days old presenting with a rectal temperature of ≤36.4 °C. We constructed receiver operating characteristic (ROC) curves to evaluate the accuracy of blood biomarkers including white blood cell count (WBC), absolute neutrophil count (ANC) and platelets for identifying SBI, with exploratory analyses evaluating procalcitonin and band counts. RESULTS: Among 850 included infants (53.5% males; median days of age 13 [IQR 5-58 days]), SBI were found in 55 (6.5%). For infants with SBI, the area under the curve (AUC; 95% confidence interval) for WBC was 0.70 (0.61-0.78) with sensitivity 0.64 (0.50-0.74) and specificity 0.77 (0.74-0.80). The AUC for ANC was 0.77 (0.70-0.84) with sensitivity 0.69 (0.55-0.81) and specificity 0.77 (0.74-0.8). For platelets, the AUC was 0.6 (0.52-0.67) with sensitivity 0.73 (0.59-0.84) and specificity 0.5 (0.46-0.53). Both the WBC and ANC were minimally accurate for identifying hypothermic infants with SBI. When looking at the accuracy of these biomarkers for identifying invasive bacterial infection (IBI; bacteremia and/or bacterial meningitis), ANC again showed minimal accuracy with an AUC of 0.70 (0.55-0.85). CONCLUSIONS: Biomarkers commonly used as part of an infectious workup are generally poor at identifying SBI in hypothermic infants. Our findings from this cohort of hypothermic infants are similar to those reported from febrile infants, suggesting similarities in the bioresponse to infection between hypothermic and febrile infants. Additional research is required to improve risk stratification for hypothermic infants, and to better guide evaluation and management.

Temperature threshold in the screening of bacterial infections in young infants with hypothermia.

BACKGROUND: Young infants with hypothermia presenting to the emergency department (ED) are at risk for serious bacterial infections (SBI), however there is no consensus temperature to prompt evaluation for SBI among these children. We sought to statistically derive a temperature threshold to guide detection of SBI in young infants with hypothermia presenting to the ED. METHODS: We performed a cross-sectional study of infants ≤90 days old presenting to four academic paediatric EDs in the United States of America from January 2015 through December 2019 with a rectal temperature of ≤36.4°C. Our primary outcomes were SBI, defined as urinary tract infection (UTI), bacteraemia and/or bacterial meningitis, and invasive bacterial infections (IBI, limited to bacteraemia and/or bacterial meningitis). We constructed receiver operating characteristic (ROC) curves to evaluate an optimally derived cutpoint for minimum ED temperature and presence of SBI or IBI. RESULTS: We included 3376 infants, of whom SBI were found in 62 (1.8%) and IBI in 16 (0.5%). The most common infection identified was Escherichia coli UTI. Overall, cohort minimum median temperature was 36.2°C (IQR 36.0°C-36.4°C). Patients with SBI and IBI had lower median temperatures, 35.8°C (IQR 35.8°C-36.3°C) and 35.4°C (IQR 35.7°C-36.3°C), respectively, compared with those without corresponding infections (both p<0.05). Using an outcome of SBI, the area under the ROC curve (AUROC) was 61.0% (95% CI 54.1% to 67.9%). At a cutpoint of 36.2°C, sensitivity was 59.7% and specificity was 59.2%. When using an outcome of IBI, the AUROC was 65.9% (95% CI 51.1% to 80.6%). Using a cutpoint of 36.1°C in this model resulted in a sensitivity of 68.8% and specificity of 60.1%. CONCLUSION: Young infants with SBI and IBI presented with lower temperatures than infants without infections. However, there was no temperature threshold to reliably identify SBI or IBI. Further research incorporating clinical and laboratory parameters, in addition to temperature, may help to improve risk stratification for these vulnerable patients.

Development of cross-service training and job performance criterion measures for the U.S. Military.

As part of an effort to provide standardized criterion measures across the Armed Services, the current research effort developed a set of service-wide criterion measures for first-term enlisted personnel using a recently developed model of cross-service job performance. Two concurrent work streams developed criterion measures which provide complete construct coverage of the cross-service performance model. Using existing service-specific instruments, methods for development of the Cross-Service Situational judgment Test (CSSJT), the Cross-Service Job Performance Ratings Scales (CSPRS), and two cross-service self-report measures (end of training and in unit surveys) are described and discussed.

Variability in fitness effects can preclude selection of the fittest.

Evolutionary biologists often predict the outcome of natural selection on an allele by measuring its effects on lifetime survival and reproduction of individual carriers. However, alleles affecting traits like sex, evolvability, and cooperation can cause fitness effects that depend heavily on differences in the environmental, social, and genetic context of individuals carrying the allele. This variability makes it difficult to summarize the evolutionary fate of an allele based solely on its effects on any one individual. Attempts to average over this variability can sometimes salvage the concept of fitness. In other cases evolutionary outcomes can only be predicted by considering the entire genealogy of an allele, thus limiting the utility of individual fitness altogether. We describe a number of intriguing new evolutionary phenomena that have emerged in studies that explicitly model long-term lineage dynamics and discuss implications for the evolution of infectious diseases.

Synthesis and Characterization of Neutral Ligand α-Diimine Complexes of Aluminum with Tunable Redox Energetics.

The synthesis and full characterization of a series of neutral ligand α-diimine complexes of aluminum are reported. The compounds [Al(LAr)2Cl2)][AlCl4] [LAr = N, N'-bis(4-R-C6H4)-2,3-dimethyl-1,4-diazabutadiene] are structurally analogous, as determined by multinuclear NMR spectroscopy and solid-state X-ray diffraction, across a range of electron-donating [R = Me (2), tBu (3), OMe (4), and NMe2 (5)] and electron-withdrawing [R = Cl (6), CF3 (7), and NO2 (8)] substituents in the aryl side arm of the ligand. UV-vis absorption spectroscopy and electrochemistry were used to access the optical and electrochemical properties, respectively, of the complexes. Both sets of properties are shown to be dependent on the R substituent. Density functional theory calculations performed on the [Al(LPh)2Cl2)][AlCl4] complex (1) indicate primarily ligand-based frontier orbitals and were used to help support our discussion of both the spectral and electrochemical data. We also report the reaction of the LPh ligand with both AlBr3 and AlI3 and demonstrate a different reactivity profile for the heavier halide relative to the lighter members of the group.

Structure and function of anticoagulation clinics in the United States: an AC forum membership survey.

Many anticoagulation clinics have adapted their services to provide care for patients taking direct oral anticoagulants (DOAC) in addition to traditional warfarin management. Anticoagulation clinic scope of service and operations in this transitional environment have not been well described in the literature. A survey was conducted of United States-based Anticoagulation Forum members to inquire about anticoagulation clinic structure, function, and services provided. Survey responses are reported using summary or non-parametric statistics, when appropriate. Unique clinic survey responses were received from 159 anticoagulation clinics. Clinic structure and staffing are highly variable, with approximately half of clinics (52%) providing DOAC-focused care in addition to traditional warfarin-focused care. Of those clinics managing DOAC patients, this accounts for only 10% of their clinic volume. These clinics commonly have a DOAC follow up protocol (75%). Clinics assign a median of 190.5 (interquartile range 50-300) patients per staff full-time-equivalent, with more patients assigned in phone-based care clinics than in face-to-face based care clinics. Most clinics (68.5%) report receiving reimbursement, which occur either through a combination of patient and insurance provider billing (78.2%), insurance reimbursement only (19.5%) or patient reimbursement only (2.3%). There is wide heterogeneity in anticoagulation clinic structure, function, and services provided. Half of all survey-responding anticoagulation clinics provide care for DOAC-treated patients. Understanding how changes in healthcare policy and reimbursement have impacted these clinics remains to be explored.

What Does a Shoulder MRI Cost the Consumer?

BACKGROUND: More than 100 MRIs per 1000 inhabitants are performed in the United States annually, more than almost every other country. Little is known regarding the cost of obtaining an MRI and factors associated with differences in cost. QUESTIONS/PURPOSES: By surveying all hospital-owned and independent imaging centers in Iowa, we wished to determine (1) the cost to the consumer of obtaining a noncontrast shoulder MRI, (2) the frequency and magnitude of discounts provided, and (3) factors associated with differences in cost including location (hospital-owned or independent) and Centers for Medicare & Medicaid Services designation (rural, urban, and critical access). METHODS: There were 71 hospitals and 26 independent imaging centers that offered MRI services in Iowa. Each site was contacted via telephone and posed a scripted request for the cost of the technical component of a noncontrast shoulder MRI. Radiologists' reading fees were not considered. Statistical analysis was performed using standard methods and significance was defined as a probability less than 0.05. RESULTS: The mean technical component cost to consumers for an MRI was USD 1874 ± USD 694 (range, USD 500-USD 4000). Discounts were offered by 49% of imaging centers, with a mean savings of 21%. Factors associated with increased cost include hospital-owned imaging centers (USD 2062 ± USD 664 versus USD 1400 ± USD 441 at independent imaging centers; p < 0.001; mean difference, USD 662; 95% CI, USD 351-USD 893) and rural imaging centers, unless designated as a critical access hospital (USD 2213 ± USD 668 versus USD 1794 ± USD 680; p = 0.0202; mean difference, USD 419; 95% CI, USD 66-USD 772). CONCLUSIONS: In Iowa, the cost to the consumer of a shoulder MRI is significantly less at independent imaging centers compared with hospital-owned centers. Referring physicians and healthcare consumers should be aware that there may be substantial price discrepancies between centers that provide advanced imaging services. LEVEL OF EVIDENCE: Level IV, Economic and decision analysis.

Root Cause Analysis of Adverse Events in an Outpatient Anticoagulation Management Consortium.

BACKGROUND: A number of factors can lead to adverse events (AEs) in patients taking warfarin. Performing a root cause analysis (RCA) of serious AEs is one systematic way of determining the causes of these events. METHODS: Multidisciplinary teams were formed at Michigan Anticoagulation Quality Improvement Initiative (MAQI2) sites with organized anticoagulation management services (AMS). Medical records from patients who suffered serious AEs (major bleed, embolic stroke, venous thromboembolism) were reviewed, and AMS staff were interviewed to determine the root cause using the "5 Whys" technique. More than 600 patients had an AE and underwent screening by trained RNs. Of these, 79 required full review by a multidisciplinary panel. All potential contributing factors (comorbidities, concurrent medications, current protocols) were assessed to determine the main factor that caused the AE. RESULTS: Full RCA was completed in 79 cases. The main contributing factor was identified in 69/79 (87%) cases. Most identified AEs, 55/69 (80%), were due to patient-specific factors such as comorbidities. Patient-to-provider and provider-to-provider communication accounted for 16/69 (23%) of events and was the second most common cause. Other causes included protocol non-adherence and technology/equipment issues. After each detailed review, the multidisciplinary panel recommended system changes that addressed the primary cause. CONCLUSION: The majority of severe AEs for patients taking warfarin were related to nonmodifiable patient-related issues. The remaining AEs were primarily due to patient-to-provider and provider-to-provider communication issues. Methods for improving communication need to be addressed, and methods for more effective patient education should be investigated.

Eliminating degradation in solid oxide electrochemical cells by reversible operation.

One promising energy storage technology is the solid oxide electrochemical cell (SOC), which can both store electricity as chemical fuels (electrolysis mode) and convert fuels to electricity (fuel-cell mode). The widespread use of SOCs has been hindered by insufficient long-term stability, in particular at high current densities. Here we demonstrate that severe electrolysis-induced degradation, which was previously believed to be irreversible, can be completely eliminated by reversibly cycling between electrolysis and fuel-cell modes, similar to a rechargeable battery. Performing steam electrolysis continuously at high current density (1 A cm(-2)), initially at 1.33 V (97% energy efficiency), led to severe microstructure deterioration near the oxygen-electrode/electrolyte interface and a corresponding large increase in ohmic resistance. After 4,000 h of reversible cycling, however, no microstructural damage was observed and the ohmic resistance even slightly improved. The results demonstrate the viability of applying SOCs for renewable electricity storage at previously unattainable reaction rates, and have implications for our fundamental understanding of degradation mechanisms that are usually assumed to be irreversible.

Functional Responses of Salt Marsh Microbial Communities to Long-Term Nutrient Enrichment.

UNLABELLED: Environmental nutrient enrichment from human agricultural and waste runoff could cause changes to microbial communities that allow them to capitalize on newly available resources. Currently, the response of microbial communities to nutrient enrichment remains poorly understood, and, while some studies have shown no clear changes in community composition in response to heavy nutrient loading, others targeting specific genes have demonstrated clear impacts. In this study, we compared functional metagenomic profiles from sediment samples taken along two salt marsh creeks, one of which was exposed for more than 40 years to treated sewage effluent at its head. We identified strong and consistent increases in the relative abundance of microbial genes related to each of the biochemical steps in the denitrification pathway at enriched sites. Despite fine-scale local increases in the abundance of denitrification-related genes, the overall community structures based on broadly defined functional groups and taxonomic annotations were similar and varied with other environmental factors, such as salinity, which were common to both creeks. Homology-based taxonomic assignments of nitrous oxide reductase sequences in our data show that increases are spread over a broad taxonomic range, thus limiting detection from taxonomic data alone. Together, these results illustrate a functionally targeted yet taxonomically broad response of microbial communities to anthropogenic nutrient loading, indicating some resolution to the apparently conflicting results of existing studies on the impacts of nutrient loading in sediment communities. IMPORTANCE: In this study, we used environmental metagenomics to assess the response of microbial communities in estuarine sediments to long-term, nutrient-rich sewage effluent exposure. Unlike previous studies, which have mainly characterized communities based on taxonomic data or primer-based amplification of specific target genes, our whole-genome metagenomics approach allowed an unbiased assessment of the abundance of denitrification-related genes across the entire community. We identified strong and consistent increases in the relative abundance of gene sequences related to denitrification pathways across a broad phylogenetic range at sites exposed to long-term nutrient addition. While further work is needed to determine the consequences of these community responses in regulating environmental nutrient cycles, the increased abundance of bacteria harboring denitrification genes suggests that such processes may be locally upregulated. In addition, our results illustrate how whole-genome metagenomics combined with targeted hypothesis testing can reveal fine-scale responses of microbial communities to environmental disturbance.

Patient-Reported Allergies Predict Worse Outcomes After Hip and Knee Arthroplasty: Results From a Prospective Cohort Study.

BACKGROUND: Retrospective analyses have demonstrated correlation between patient-reported allergies and negative outcomes after total joint arthroplasty. We sought to validate these observations in a prospective cohort. METHODS: One hundred forty-four patients undergoing total hip arthroplasty and 302 patients undergoing total knee arthroplasty were prospectively enrolled. Preoperatively, patients listed their allergies and completed the Medical Outcomes Study Short Form 36 (SF-36) and the Charlson Comorbidity Index (CCI) Questionnaire. At a mean of 17 months (range 12-25 months) postoperatively, SF-36, CCI, and Western Ontario and McMaster Universities Osteoarthritis Index (WOMAC) were obtained by telephone survey. Regression analysis was used to determine the strength of correlation between patient age, comorbidity burden, and number of allergies and outcome measurements. RESULTS: In 446 patients, 273 reported at least 1 allergy. The number of allergies reported ranged from 0 to 33. Penicillin or its derivative was the most frequently reported allergy followed by sulfa, environmental allergen, and narcotic pain medication. Patients reporting at least 1 allergy had a significantly lower postoperative SF-36 Physical Component Score compared to those reporting no allergies (51.3 vs 49.4, P = .01). The SF-36 postoperative Mental Component Score was no different between groups. Multivariate regression analysis showed that age and patient reported allergies, but not comorbidities, were independently associated with worse postoperative SF-36 Physical Component Summary (PCS) and WOMAC score. Patients with allergies experienced the same improvement in SF-36 PCS as those without an allergy. Comorbidities did not correlate with patient-reported function postoperatively. CONCLUSION: Patients who report allergies have lower postoperative outcome scores but may experience the same increment in improvement after total joint arthroplasty.

Natural selection promotes antigenic evolvability.

The hypothesis that evolvability - the capacity to evolve by natural selection - is itself the object of natural selection is highly intriguing but remains controversial due in large part to a paucity of direct experimental evidence. The antigenic variation mechanisms of microbial pathogens provide an experimentally tractable system to test whether natural selection has favored mechanisms that increase evolvability. Many antigenic variation systems consist of paralogous unexpressed 'cassettes' that recombine into an expression site to rapidly alter the expressed protein. Importantly, the magnitude of antigenic change is a function of the genetic diversity among the unexpressed cassettes. Thus, evidence that selection favors among-cassette diversity is direct evidence that natural selection promotes antigenic evolvability. We used the Lyme disease bacterium, Borrelia burgdorferi, as a model to test the prediction that natural selection favors amino acid diversity among unexpressed vls cassettes and thereby promotes evolvability in a primary surface antigen, VlsE. The hypothesis that diversity among vls cassettes is favored by natural selection was supported in each B. burgdorferi strain analyzed using both classical (dN/dS ratios) and Bayesian population genetic analyses of genetic sequence data. This hypothesis was also supported by the conservation of highly mutable tandem-repeat structures across B. burgdorferi strains despite a near complete absence of sequence conservation. Diversification among vls cassettes due to natural selection and mutable repeat structures promotes long-term antigenic evolvability of VlsE. These findings provide a direct demonstration that molecular mechanisms that enhance evolvability of surface antigens are an evolutionary adaptation. The molecular evolutionary processes identified here can serve as a model for the evolution of antigenic evolvability in many pathogens which utilize similar strategies to establish chronic infections.

First arrived takes all: inhibitory priority effects dominate competition between co-infecting Borrelia burgdorferi strains.

BACKGROUND: Within-host microbial communities and interactions among microbes are increasingly recognized as important factors influencing host health and pathogen transmission. The microbial community associated with a host is indeed influenced by a complex network of direct and indirect interactions between the host and the lineages of microbes it harbors, but the mechanisms are rarely established. We investigated the within-host interactions among strains of Borrelia burgdorferi, the causative agent of Lyme disease, using experimental infections in mice. We used a fully crossed-design with three distinct strains, each group of hosts receiving two sequential inoculations. We used data from these experimental infections to assess the effect of coinfection on bacterial dissemination and fitness (by measuring the transmission of bacteria to xenodiagnostic ticks) as well as the effect of coinfection on host immune response compared to single infection. RESULTS: The infection and transmission data strongly indicate a competitive interaction among B. burgdorferi strains within a host in which the order of appearance of the strain is the main determinant of the competitive outcome. This pattern is well described by the classic priority effect in the ecological literature. In all cases, the primary strain a mouse was infected with had an absolute fitness advantage primarily since it was transmitted an order of magnitude more than the secondary strain. The mechanism of exclusion of the secondary strain is an inhibition of the colonization of mouse tissues, even though 29% of mice showed some evidence of infection by secondary strain. Contrary to expectation, the strong and specific adaptive immune response evoked against the primary strain was not followed by production of immunoglobulins after the inoculation of the secondary strain, neither against strain-specific antigen nor against antigens common to all strains. Hence, the data do not support a major role of the immune response in the observed priority effect. CONCLUSION: The strong inhibitory priority effect is a dominant mechanism underlying competition for transmission between coinfecting B. burgdorferi strains, most likely through resource exploitation. The observed priority effect could shape bacterial diversity in nature, with consequences in epidemiology and evolution of the disease.

Kinetics of CO/CO2 and H2/H2O reactions at Ni-based and ceria-based solid-oxide-cell electrodes.

The solid oxide electrochemical cell (SOC) is an energy conversion technology that can be operated reversibly, to efficiently convert chemical fuels to electricity (fuel cell mode) as well as to store electricity as chemical fuels (electrolysis mode). The SOC fuel-electrode carries out the electrochemical reactions CO2 + 2e(-) ↔ CO + O(2-) and H2O + 2e(-) ↔ H2 + O(2-), for which the electrocatalytic activities of different electrodes differ considerably. The relative activities in CO/CO2 and H2/H2O and the nature of the differences are not well studied, even for the most common fuel-electrode material, a composite of nickel and yttria/scandia stabilized zirconia (Ni-SZ). Ni-SZ is known to be more active for H2/H2O than for CO/CO2 reactions, but the reported relative activity varies widely. Here we compare AC impedance and DC current-overpotential data measured in the two gas environments for several different electrodes comprised of Ni-SZ, Gd-doped CeO2 (CGO), and CGO nanoparticles coating Nb-doped SrTiO3 backbones (CGOn/STN). 2D model and 3D porous electrode geometries are employed to investigate the influence of microstructure, gas diffusion and impurities.Comparing model and porous Ni-SZ electrodes, the ratio of electrode polarization resistance in CO/CO2vs. H2/H2O decreases from 33 to 2. Experiments and modelling suggest that the ratio decreases due to a lower concentration of impurities blocking the three phase boundary and due to the nature of the reaction zone extension into the porous electrode thickness. Besides showing higher activity for H2/H2O reactions than CO/CO2 reactions, the Ni/SZ interface is more active for oxidation than reduction. On the other hand, we find the opposite behaviour in both cases for CGOn/STN model electrodes, reporting for the first time a higher electrocatalytic activity of CGO nanoparticles for CO/CO2 than for H2/H2O reactions in the absence of gas diffusion limitations. We propose that enhanced surface reduction at the CGOn/gas two phase boundary in CO/CO2 and in cathodic polarization can explain why the highest reaction rate is obtained for CO2 electrolysis. Large differences observed between model electrode kinetics and porous electrode kinetics are discussed.

Synthesis and Characterization of Aluminum Complexes of Redox-Active Pyridyl Nitroxide Ligands.

The aluminum complexes ((R)pyNO(-))2AlCl ((R)pyNO(-) = N-tert-butyl-N-(2-pyridyl)nitroxyl; R = H (1), CH3 (2), CF3 (3)) were prepared in 80-98% yield through the protonolysis reaction between the pyridyl hydroxylamine ligand precursors (R)pyNOH and dimethylaluminum chloride. Complex 1 was also prepared using a salt metathesis route in 92% yield. Complexes 1-3 were characterized using (1)H and (13)C NMR spectroscopies. Single-crystal X-ray diffraction analysis of the complexes revealed that 1-3 are isostructural, with the Al(III) cation in all cases being five coordinate with distorted square pyramidal geometries. The geometry of complex 1 was studied using DFT, which showed primarily ligand-based frontier molecular orbitals. Reaction of 1 with NaOt-Bu gave (pyNO(-))2AlOt-Bu (4), while reaction of 1 with AgBPh4 gave [(pyNO(-))2Al(THF)2][BPh4] (5) in 54% and 87% yields, respectively. Compounds 4 and 5 were both characterized using (1)H and (13)C NMR spectroscopies and compound 5 by X-ray diffraction. Complexes 1-5 were also characterized by UV-vis electronic absorption spectroscopy and electrochemistry. The cyclic voltammograms of the complexes show two separate oxidation process, the potentials of which are dependent on both the substitution pattern of the (R)pyNO(-) ligands and the anion that completes the aluminum coordination sphere. A correlation was determined between the chemical shift of the t-Bu of the (R)pyNO(-) ligand in the (1)H NMR spectroscopy and the potentials of the redox events for complexes 1-4.

Synthesis and Characterization of α-Diimine Complexes of Group 13 Metals and Their Catalytic Activity toward the Epoxidation of Alkenes.

Complexes of group 13 metal (Al, Ga, In) ions with neutral α-diimine ligands have been prepared and characterized. The Al(III) and Ga(III) [M(α-diimine)2Cl2][MCl4] complexes catalyze the epoxidation of alkenes by peracetic acid under ambient conditions. The two complexes display nearly identical reactivity, demonstrating that inexpensive and highly abundant aluminum is a viable catalytic metal for these reactions.

Synthesis and characterization of aluminum-α-diimine complexes over multiple redox states.

The aluminum complexes (LMes(2-))AlCl(THF) (3) and (LDipp(-))AlCl2 (4) (LMes = N,N'-bis[2,4,6-trimethylphenyl]-2,3-dimethyl-1,4-diazabutadiene, LDipp = N,N'-bis[2,6-diisopropylphenyl]-2,3-dimethyl-1,4-diazabutadiene) were prepared by direct reduction of the ligands with sodium metal followed by salt metathesis with AlCl3. The (LMes(-))AlCl2 (5) complex was prepared through one-electron oxidative functionalization of 3 with either AgCl or CuCl. Complex 3 was characterized using (1)H and (13)C NMR spectoscopies. Single-crystal X-ray diffraction analysis of the complexes revealed that 3-5 are all four-coordinate, with 3 exhibiting a trigonal pyramidal geometry, while 4 and 5 exist between trigonal pyramidal and tetrahedral. Notable in the LMes complexes 3 and 5 is a systematic lengthening of the C-Nimido bonds and shortening of the C-C bond in the N-C-C-N backbone with increased electron density on the ligand. The geometries of the complexes 3 and 5 were optimized using DFT, which showed primarily ligand-based frontier orbitals, supporting the analysis of the solid-state structural data. The complexes 3-5 were also characterized by electrochemistry. The cyclic voltamogram of complex 3 showed an oxidation processes at -0.94 and -0.03 V versus ferrocene, while complexes 4 and 5 exhibit both reduction (-1.37 and -1.34 V, respectively) and oxidation (-0.62 and -0.73 V, respectively) features.