NMR and Mössbauer Studies Reveal a Temperature-Dependent Switch from S = 1 to 2 in a Nonheme Oxoiron(IV) Complex with Faster C-H Bond Cleavage Rates.

S = 2 FeIV═O centers generated in the active sites of nonheme iron oxygenases cleave substrate C-H bonds at rates significantly faster than most known synthetic FeIV═O complexes. Unlike the majority of the latter, which are S = 1 complexes, [FeIV(O)(tris(2-quinolylmethyl)amine)(MeCN)]2+ (3) is a rare example of a synthetic S = 2 FeIV═O complex that cleaves C-H bonds 1000-fold faster than the related [FeIV(O)(tris(pyridyl-2-methyl)amine)(MeCN)]2+ complex (0). To rationalize this significant difference, a systematic comparison of properties has been carried out on 0 and 3 as well as related complexes 1 and 2 with mixed pyridine (Py)/quinoline (Q) ligation. Interestingly, 2 with a 2-Q-1-Py donor combination cleaves C-H bonds at 233 K with rates approaching those of 3, even though Mössbauer analysis reveals 2 to be S = 1 at 4 K. At 233 K however, 2 becomes S = 2, as shown by its 1H NMR spectrum. These results demonstrate a unique temperature-dependent spin-state transition from triplet to quintet in oxoiron(IV) chemistry that gives rise to the high C-H bond cleaving reactivity observed for 2.

The Efficacy of Ketoconazole Containing Regimens in Castration-Resistant Prostate Cancer: A Systematic Review and Meta-Analysis.

Castration resistant prostate cancer (CRPC) is a challenging subset of prostate cancer associated with an extensive metastatic profile and high mortality. Ketoconazole is a nonselective steroid 17α-hydroxylase/17,20 lyase (CYP17A1) inhibitor and is employed as a second line treatment option for CRPC with an established efficacy profile in patients. The aim of this study is to assess the efficacy of ketoconazole containing regimens for CRPC in terms of prostate specific antigen (PSA) decline rate using a systematic review and meta-analysis. In this review, an electronic search was carried out on PubMed, Cochrane CENTRAL, Scopus, and Google Scholar to find relevant literature. Random effects model was used to assess pooled PSA decline rate and 95% CIs. Publication bias was assessed using the funnel plot symmetry and one-tailed Egger's and Begg's test. In all cases, P-value <.05 was indicative of significant results. The review is registered with PROSPERO: CRD42023466536. A total of 483 articles were retrieved after database searching, out of which 23 studies (having a total of 1315 patients) were included in the review based on prespecified criteria. The PSA decline rate was reported in the 14 observational studies (having 964 patients) and 9 experimental studies (having 351 patients). Pooled results revealed that 48.6% (95% CI 43.1-54.2; P-value <.001; I2 = 73.24%) of participants achieved more than 50% decline in PSA (602/1315 participants). Sensitivity analysis using the leave-one-out method revealed no substantial change in pooled effect estimates; (Risk Ratio) RR 47.2% to RR 49.8% demonstrating the robustness of our results. There was no evidence of publication bias as assessed from the funnel plot symmetry. Ketoconazole containing regimens have shown moderate efficacy in high risk CRPC patients as demonstrated by the pooled results. Hence, a ketoconazole based chemotherapy can be added to patients' regimen if there is a persistent rise in PSA levels after androgen deprivation therapy.

Can my surgeon scope? Trends in endoscopy training volume and experience among general surgery residents in the United States: a nationwide analysis.

INTRODUCTION: Endoscopy is a major part of surgical training. Accreditation Council for Graduate Medical Education (ACGME) has set standards regarding the minimum volume of endoscopy cases required for graduation. However, there is paucity of high-quality data on the number of cases that most surgical graduates perform. METHODS: We conducted a retrospective analysis of operative case logs of all general surgery residents graduating from ACGME-accredited programs from 2010 to 2023. Data on mean number of endoscopy cases, including mean in each subcategory, were retrieved. Mann-Kendall trend test was used to investigate trends in endoscopy experience. RESULTS: Between 2010 and 2023, the mean overall endoscopy procedures per resident remained stable, with 129.5 in 2010 and 132.1 in 2023 (t = 0.429; p-value = 0.037). The majority of these cases were performed as surgeon junior (76.6% in 2010; 80.9% in 2023), while the remaining cases were logged as surgeon chief. The most substantial contribution to the overall volume was from flexible colonoscopy (mean: 64.1 in 2010 and 67.2 in 2023). The volume for colonoscopy remained fairly stable (t = 0.429; p-value = 0.036). This was followed by esophagogastroduodenoscopy (mean: 35.3 in 2010 and 35.5 in 2023), which saw a significant increase in volume (t = 0.890; p-value ≤ 0.001). There was a significant increase in the number of overall upper endoscopic procedures (t = 0.791; p-value ≤ 0.001), while lower endoscopic procedures did not change significantly (t = 0.319; p-value = 0.125). The procedural volume for endoscopic retrograde cholangiography, sigmoidoscopy, cystoscopy/ureteroscopy, laryngoscopy, and bronchoscopy decreased significantly (p-value < 0.05 for all). CONCLUSION: The overall endoscopy volume for general surgery residents has largely remained stable, with a minor increase in esophagogastroduodenoscopy and no change in colonoscopy. Future research should investigate whether simulation-based exercises can bridge the gap between procedural volume and learning curve requirements for endoscopy.

Esophageal Adenocarcinoma: An Unusual Pericardial and Pulmonary Metastasis - A Case Report.

Introduction: Esophageal adenocarcinoma (EAC) manifests in the glandular cells present in the lining of the esophagus and usually forms in the distal portion of the esophagus. The metastasis of EAC has been reported to occur in surrounding lymphovascular structures, the liver, brain, and bones. Case Presentation: We present the rare case of a 52-year-old Hispanic male with EAC metastasis to the pericardium and lungs. The patient presented with shortness of breath off and on for the last 6 weeks without any usually reported symptoms of EAC like chest pain, vomiting, or chronic cough. Respiratory examinations of this patient were significant for bilateral bronchial breathing and coarse crackles. The patient had been given numerous courses of oral antibiotics over the previous weeks with the provisional diagnosis of atypical pneumonia. Cardiac tamponade pathophysiology was also observed in this patient, for which a pericardial window was created to relieve the patient's symptoms. A final diagnosis of EAC with an unusual metastasis in the lungs and pericardium was made based on radiological and pathological findings. The patient chose palliative care instead of curative care because of the advanced stage of this cancer. The patient received cancer diagnosis counseling and was sent to hospice care for further management. Conclusion: The metastasis of EAC to the pericardium and lungs instead of usual sites constitutes an important prognostic factor in the overall survival of patients.

Association between smoking status and inpatient outcomes of acute cholangitis in the United States: a propensity matched analysis.

Background: Acute cholangitis (AC) is an infection of the biliary tract superimposed on stasis. This study aimed to investigate the effects of smoking on inpatient outcomes of AC. Methods: We identified primary AC hospitalizations using the National Inpatient Sample database (2017-2020). Using a 1:1 matching method, we created a matched comparison cohort of AC patients who were non-smokers, based on demographics, hospital characteristics and comorbidities. Results: We matched 3960 smoker patients with 3960 non-smoker patients within the AC population. Non-smokers were older than smokers (70 vs. 59 years, P<0.001). Smokers had a stronger association with bile duct calculi (74.37% vs. 69.29%, P<0.001) and other bile duct disorders (clots, parasites, extrinsic compression and other rare disorders) (6.82% vs. 5.05%, P=0.011). No significant difference in inpatient mortality, median length of stay (LOS), or median inpatient cost (MIC) was found between the matched cohorts (P>0.05). However, smoking was associated with higher odds of complications, including sepsis without shock (0.88% vs. 0.51%, P=0.042), sepsis with shock (1.26% vs. 0.51%, P<0.001), biliary pancreatitis (6.57% vs. 4.42%, P<0.001) and myocardial infarction (6.19% vs. 3.54%, P<0.001), as well as a greater need for inpatient endoscopic retrograde cholangiopancreatography (ERCP) (72.85% vs. 63.76%, P<0.001) and early ERCP (50.76% vs. 42.32%, P<0.001) compared to non-smokers. Conclusions: This study found no difference in mortality, LOS, or MIC in acute cholangitis-related hospitalizations associated with smoking. However, smoking was associated with a higher risk of complications and a greater need for ERCP and early ERCP.

Increasing inpatient mortality of nonvariceal upper gastrointestinal bleeding during the COVID-19 pandemic: a nationwide retrospective cohort study.

Upper gastrointestinal bleeding results in significant morbidity, mortality, and healthcare burden. This study aimed to evaluate inpatient outcomes of nonvariceal upper gastrointestinal bleeding (NVUGIB) during the year 2020 of the COVID-19 pandemic. The National Inpatient Sample databases were used to identify NVUGIB-related hospitalizations. Outcomes of interest for the year 2019 were compared to 2020 and included inpatient mortality, length of stay, mean inpatient cost, odds of getting esophagogastroduodenoscopy (EGD), mean time to EGD, early EGD (within 1 day of hospitalization), endoscopic intervention for hemostasis, and the odds of developing complications. NVUGIB-related hospitalizations increased by 8.1% in 2020. NVUGIB-related hospitalizations in 2020 were also associated with an 11.1% higher mortality (adjusted odds ratio [aOR] = 1.11, confidence interval [CI] = 1.06-1.17, P < 0.01), 0.15-day longer mean time to EGD (aOR = 0.15, CI = 0.08-0.24, P < 0.01), 4% lower odds of getting an EGD (aOR = 0.96, CI = 0.93-0.99, P = 0.02), 8% lower odds of getting an early EGD (aOR = 0.92, CI = 0.89-0.96, P < 0.01), and $6340 higher mean inpatient cost (aOR = 6340, CI = 1762-10919, P = 0.01) compared to 2019. We conclude that there was an increase in NVUGIB-related hospitalizations and mortality in 2020 when the COVID-19 pandemic started.

10-year trends and inpatient outcomes of gastrointestinal angiodysplasia with bleeding in the United States: National Inpatient Sample, 2011 to 2020.

Gastrointestinal angiodysplasia (GIAD) is the presence of aberrant blood vessels in the gastrointestinal (GI) tract that can lead to GI bleeding. There has been an increase in the incidence of GI angiodysplasia, partly due to the availability of better diagnostic techniques. The cecum is known as the most common site for GIAD; therefore, GIAD is considered a frequent cause of lower GI bleeding. Studies have shown an increasing incidence of GIAD in the upper GI tract and jejunum. No population-based studies exist on inpatient outcomes of GIAD-bleeding (GIADB) in recent years, and no prior studies have compared the inpatient outcomes of upper vs lower GIADB. We identified 321,559 weighted hospitalizations and found a 32% increase in GIADB-related hospitalizations from 2011 to 2020. There were more hospitalizations for upper (57.38%) than lower GIADB (42.62%), indicating GIADB is an important cause of upper GI bleeding as well. No statistically significant difference in mortality was found between upper and lower GIADB cohorts; however, lower GIADB was associated with a 0.2-day longer length of stay (95% confidence interval 0.09-0.30, P < 0.001) and $3857 higher mean inpatient cost (95% confidence interval $2422-$5291, P < 0.001).

Leukocytoclastic Vasculitis Masquerading as Chronic Idiopathic Thrombocytopenic Purpura.

Background: Idiopathic thrombocytopenic purpura and leukocytoclastic vasculitis can present in a similar fashion and can be very hard to differentiate clinically without a biopsy. This can cause diagnostic dilemma and delay in management. A thorough evaluation is recommended to determine etiology, although about half are idiopathic. Case Presentation: A patient aged 79 years with longstanding thrombocytopenia secondary to chronic idiopathic thrombocytopenic purpura presented with a rash. Although it was thought to be secondary to idiopathic thrombocytopenic purpura, a biopsy revealed presence of leukocytoclastic vasculitis. Conclusions: Although most leukocytoclastic vasculitis cases are mild and resolve without intervention, many go undiagnosed due to biopsy delays. Health care professionals should determine and treat the underlying cause.

A Case of Severe Acute Respiratory Distress Syndrome Secondary to Atypical Amniotic Fluid Embolism.

Acute respiratory distress syndrome (ARDS) is a noncardiogenic pulmonary edema that leads to acute respiratory distress. It remains one of the major diagnoses requiring ICU admission and mechanical ventilation. We present a case of a 25-year-old gravida 3 para 2 female who was admitted for uncomplicated 38-week pregnancy and delivered a healthy male infant but developed acute onset dyspnea six hours after vaginal delivery. She required mechanical ventilation four hours after the onset of respiratory distress and had to be transferred to a higher level facility for extracorporeal membrane oxygenation (ECMO) within 24 hours of the symptom onset. She was diagnosed with severe ARDS. Even though she missed the other typical feature of amniotic fluid embolism, atypical amniotic fluid embolism remained the most likely explanation for her symptoms after the other causes of ARDS were excluded.

Allergic Bronchopulmonary Aspergillosis (ABPA) Diagnosis Missed in the Context of Asthma Exacerbation Due to Medication Nonadherence.

Allergic bronchopulmonary aspergillosis (ABPA) results from a hypersensitivity reaction to Aspergillus fumigatus colonization of airways in patients with asthma or cystic fibrosis. Our patient is a 47-year-old female with a history of asthma and nonadherence to medications who presented with frequent asthma exacerbations. She required intubation three times within six months, labeled as asthma exacerbation due to nonadherence to medications until she was finally diagnosed with and successfully treated for ABPA. She was tested for ABPA very late as the medication nonadherence was thought to be the sole cause of repeated asthma exacerbations during previous hospitalizations. This case illustrates the importance of maintaining a high index of suspicion for ABPA in recurrent asthma exacerbation even in the setting of medical nonadherence.

An Important Association With Lower Gastrointestinal Bleed: A Case of Heyde Syndrome.

The association between aortic stenosis and angiodysplastic gastrointestinal bleed is known as Heyde syndrome. It was first described in 1958 and has since received further medical attention. We present a case of an 86-year-old lady with a history of severe aortic stenosis that was admitted with gastrointestinal bleeding secondary to colonic angiodysplasia. A review of the literature showed mixed opinions with respect to the idea of causation versus coincidence; both theories are valid. However, studies that supported causation had a bigger study population and overall seem to be more plausible.

A Case Report of Successful Medical Management of Emphysematous Gastritis With Portal Venous Air.

Emphysematous gastritis is an uncommon yet life-threatening condition characterized by air in the gastric wall. It requires clinical and radiological findings for its diagnosis. Management is done either medically or surgically and requires early intervention with bowel rest, proton pump inhibitors, and antibiotics with or without gastrectomy secondary to the high mortality associated with the condition. We present a case of a 55-year-old male who responded well to medical therapy without the need for surgical intervention.

Sensory stimulation-based protection from impending stroke following MCA occlusion is correlated with desynchronization of widespread spontaneous local field potentials.

In a rat model of ischemic stroke by permanent occlusion of the medial cerebral artery (pMCAo), we have demonstrated using continuous recordings by microelectrode array at the depth of the ischemic territory that there is an immediate wide-spread increase in spontaneous local field potential synchrony following pMCAo that was correlated with ischemic stroke damage, but such increase was not seen in control sham-surgery rats. We further found that the underpinning source of the synchrony increase is intermittent bursts of low multi-frequency oscillations. Here we show that such increase in spontaneous LFP synchrony after pMCAo can be reduced to pre-pMCAo baseline level by delivering early (immediately after pMCAo) protective sensory stimulation that reduced the underpinning bursts. However, the delivery of a late (3 h after pMCAo) destructive sensory stimulation had no influence on the elevated LFP synchrony and its underpinning bursts. Histology confirmed both protection for the early stimulation group and an infarct for the late stimulation group. These findings highlight the unexpected importance of spontaneous LFP and its synchrony as a predictive correlate of cerebral protection or stroke infarct during the hyperacute state following pMCAo and the potential clinical relevance of stimulation to reduce EEG synchrony in acute stroke.

Diagnostic Accuracy of High-Resolution Computed Tomography of Chest in Diagnosing Sputum Smear Positive and Sputum Smear Negative Pulmonary Tuberculosis.

Introduction Pulmonary tuberculosis (PTB) is caused by species of organisms in the Mycobacterium tuberculosis complex. It is a major public health problem worldwide and is endemic in Pakistan. Various clinical and biochemical markers exist for its diagnosis. Radiology has an important role in the diagnosis of PTB. Initially, a chest radiograph is warranted for PTB evaluation. High-resolution computed tomography (HRCT) also has high sensitivity and specificity for PTB diagnosis. Features of primary TB include consolidation, lymphadenopathy, pleural effusion and miliary nodules whereas post-primary TB include apical consolidation, nodules and cavitation. The aim of this study was to determine the diagnostic accuracy of HRCT chest in diagnosing sputum smear positive and smear negative PTB. Methods A cross-sectional study was conducted at a large tertiary care teaching hospital. A retrospective review of medical records of patients who underwent HRCT chest and sputum acid-fast bacillus (AFB) direct smear and AFB culture for suspicion of PTB was undertaken. All HRCT chest examinations were performed on multislice computed tomography (CT) scanner. On HRCT, PTB was defined as the presence of consolidation, centrilobular nodules, branching nodules with tree in bud appearance with or without lymphadenopathy and pleural effusion. Diagnostic accuracy of HRCT including sensitivity, specificity, positive and negative predictive values was calculated using 2 x 2 table, taking findings of AFB culture as a gold standard. Results A total of 108 patients were included in this study with a mean age of 51.85 ± 16.86 years. Diagnostic accuracy of HRCT in diagnosing PTB was found to be 84.26% with sensitivity, specificity, positive predictive value (PPV) and negative predictive value (NPV) of 89.09%, 79.25%, 81.67%, and 87.50%, respectively. In sputum smear positive patients, HRCT has diagnostic accuracy, sensitivity, specificity, PPV and NPV of 87.50%, 88.57%, 84.62%, 93.94%, and 73.33%, respectively. In sputum smear negative patients, HRCT has diagnostic accuracy, sensitivity, specificity, PPV and NPV of 81.67%, 90.00%, 77.50%, 66.67%, and 93.94%, respectively. Conclusion HRCT has high sensitivity in diagnosing sputum smear positive and sputum smear negative PTB. The specificity of HRCT in diagnosing sputum smear positive PTB was high, whereas it was slightly low in diagnosing sputum smear negative PTB. Overall diagnostic accuracy of HRCT was high in diagnosing PTB.

Anomaly Detection of Moderate Traumatic Brain Injury Using Auto-Regularized Multi-Instance One-Class SVM.

Detection and quantification of functional deficits due to moderate traumatic brain injury (mTBI) is crucial for clinical decision-making and timely commencement of functional therapy. In this work, we explore magnetoencephalography (MEG) based functional connectivity features i.e. magnitude squared coherence (MSC) and phase lag index (PLI) to quantify synchronized brain activity patterns as a means to detect functional deficits. We propose a multi-instance one-class support vector machine (SVM) model generated from a healthy control population. Any dispersion from the decision boundary of the model would be identified as an anomaly instance of mTBI case (Glasgow Coma Scale, GCS score between 9 and 13). The decision boundary was optimized by considering the closest anomaly (GCS =13) from the negative class as a support vector. Validated against magnetic resonance imaging (MRI) data, the proposed model at high beta band yielded an accuracy of 94.19% and a sensitivity of 90.00%, when tested with our mTBI dataset. The results support the suggestion of multi-instance one-class SVM for the detection of mTBI.

Diagnostic Accuracy of Xpert MTB/RIF in Sputum Smear-Negative Pulmonary Tuberculosis.

Introduction Tuberculosis is a major health problem in Pakistan. The prevalence of pulmonary as well as extrapulmonary tuberculosis is quite high. Tuberculin skin test, radiological imaging, and sputum smear microscopy have limitations in the diagnosis of tuberculosis. Xpert MTB/RIF was recently approved for the diagnosis of pulmonary tuberculosis and has shown promising results. The aim of this study was to determine the diagnostic accuracy of Xpert MTB/RIF in sputum smear-negative pulmonary tuberculosis using acid-fast bacilli (AFB) culture as the gold standard. Materials and methods This cross-sectional study was conducted at Iqbal Yad Chest Clinic and Nazimabad Chest Clinic of Ojha Institute of Chest Diseases, Dow University of Health Sciences. Patients of either gender aged 18-65 years suspected to have pulmonary tuberculosis with at least two sputum samples negative for AFB underwent Xpert MTB/RIF testing. Early morning sputum samples were obtained and sent for AFB smear microscopy, Xpert testing and also for culture analysis. Results Mean age of the patients was 37.48 ±17.49 years. There were 84 (37.3%) females and 141 (62.7%) males. Positive findings on Xpert MTB/RIF were found in 147 (65.3%) patients whereas AFB culture showed positive findings in 174 (77.3%) patients. Sensitivity, specificity, positive predicted value, negative predicted value and overall diagnostic accuracy of Xpert MTB/RIF was found to be 84.48%, 100%, 100%, 65.38%, and 88%, respectively. Conclusion Xpert MTB/RIF has high sensitivity, specificity, and diagnostic accuracy in diagnosis of sputum smear-negative cases of pulmonary tuberculosis.

Acid pKa Dependence in O-O Bond Heterolysis of a Nonheme FeIII-OOH Intermediate To Form a Potent FeV═O Oxidant with Heme Compound I-Like Reactivity.

Protons play essential roles in natural systems in controlling O-O bond cleavage of peroxoiron(III) species to give rise to the high-valent iron oxidants that carry out the desired transformations. Herein, we report kinetic and mechanistic evidence that acids can control the mode of O-O bond cleavage for a nonheme S = 1/2 FeIII-OOH species [(BnTPEN)FeIII(OOH)]2+ (2, BnTPEN = N-benzyl-N,N',N'-tris(2-pyridylmethyl)-1,2-diaminoethane). Addition of acids having pKa values of >8.5 in CH3CN results in O-O bond homolysis, leading to the formation of hydroxyl radicals that give rise to alcohol/ketone (A/K) ratios of around 1 in the oxidation of cyclohexane. However, the introduction of acids with pKa values of <8.5 elicits a different outcome, namely the achievement of A/K ratios of as high as 9, the observation of rapid and catalytic hydroxylation of cyclohexane, and a million-fold acceleration in the decay rate of the FeIII-OOH intermediate at -40 °C. These results implicate the generation of a highly reactive FeV═O species via proton-assisted O-O bond heterolysis of the FeIII-OOH intermediate, which is unprecedented for nonheme iron complexes supported by neutral pentadentate ligands and serves as a nonheme analogue for heme enzyme compounds I.

Structural implications of the paramagnetically shifted NMR signals from pyridine H atoms on synthetic nonheme FeIV=O complexes.

Oxoiron(IV) motifs are found in important intermediates in many enzymatic cycles that involve oxidations. Over half of the reported synthetic nonheme oxoiron(IV) analogs incorporate heterocyclic donors, with a majority of them comprising pyridines. Herein, we report 1H-NMR studies of oxoiron(IV) complexes containing pyridines that are arranged in different configurations relative to the Fe = O unit and give rise to paramagnetically shifted resonances that differ by as much as 50 ppm. The strong dependence of 1H-NMR shifts on the different configurations and orientation of pyridines relative to the oxoiron(IV) unit demonstrates how unpaired electronic spin density of the iron center affects the chemical shifts of these protons.

NMR Reveals That a Highly Reactive Nonheme FeIV =O Complex Retains Its Six-Coordinate Geometry and S=1 State in Solution.

The [FeIV (O)(Me3 NTB)]2+ (Me3 NTB=tris[(1-methyl-benzimidazol-2-yl)methyl]amine) complex 1 has been shown by Mössbauer spectroscopy to have an S=1 ground state at 4 K, but is proposed to become an S=2 trigonal-bipyramidal species at higher temperatures based on a DFT model to rationalize its very high C-H bond-cleavage reactivity. In this work, 1 H NMR spectroscopy was used to determine that 1 does not have C3 -symmetry in solution and is not an S=2 species. Our results show that 1 is unique among nonheme FeIV =O complexes in retaining its S=1 spin state and high reactivity at 193 K, providing evidence that S=1 FeIV =O complexes can be as reactive as their S=2 counterparts. This result emphasizes the need to identify factors besides the ground spin state of the FeIV =O center to rationalize nonheme oxoiron(IV) reactivity.

Crystallographic Evidence for a Sterically Induced Ferryl Tilt in a Non-Heme Oxoiron(IV) Complex that Makes it a Better Oxidant.

Oxoiron(IV) units are often implicated as intermediates in the catalytic cycles of non-heme iron oxygenases and oxidases. The most reactive synthetic analogues of these intermediates are supported by tetradentate tripodal ligands with N-methylbenzimidazole or quinoline donors, but their instability precludes structural characterization. Herein we report crystal structures of two [FeIV (O)(L)]2+ complexes supported by pentadentate ligands incorporating these heterocycles, which show longer average Fe-N distances than the complex with only pyridine donors. These longer distances correlate linearly with log k2 ' values for O- and H-atom transfer rates, suggesting that weakening the ligand field increases the electrophilicity of the Fe=O center. The sterically bulkier quinoline donors are also found to tilt the Fe=O unit away from a linear N-Fe=O arrangement by 10°.