Scoping review of nonsurgical treatment options for macular holes.

Macular holes (MH) are full-thickness retinal defects affecting central vision. While vitrectomy with inner limiting membrane (ILM) peel is the conventional MH treatment, non-surgical alternatives are gaining interest to mitigate surgical risks. This study conducted a comprehensive literature review and analysis of nonsurgical MH management. A systematic literature search was conducted on PubMed, Embase, Scopus, and the Cochrane Library from January 1, 1973, to September 13, 2023. Treatments included laser therapy, carbonic anhydrase inhibitors (CAIs), nonsteroidal antiinflammatory drugs (NSAIDs), steroids (topical, subtenons, peribulbar, intravitreal), intravitreal gas, anti-vascular endothelial growth factors and ocriplasmin injections. Data extraction covered study details, patient characteristics, MH features, treatment outcomes, and recurrence rates. The initial search yielded 3352 articles, refined to 83 articles that met inclusion criteria following screening. Overall reported anatomical closure rates were 36% with laser photocoagulation, 37% with intravitreal ocriplasmin, 55% with intravitreal gas. Closures were more frequently observed with topical NSAIDs (79%), steroids (84%) and CAIs (73%). Closures were more often observed in patients with smaller MH and in the presence of cystic macular oedema. Although non-surgical MH management approaches show potential for conservative therapy, evidence is limited to support routine use. Stage 1 and traumatic MH may benefit from a short period of observation, but the gold standard approach for full-thickness MH remains to be vitrectomy with ILM peel.

Electronic Structure and Reactivity of Mononuclear Nonheme Iron-Peroxo Complexes as a Biomimetic Model of Rieske Oxygenases: Ring Size Effects of Macrocyclic Ligands.

We report the macrocyclic ring size-electronic structure-electrophilic reactivity correlation of mononuclear nonheme iron(III)-peroxo complexes bearing N-tetramethylated cyclam analogues (n-TMC), [FeIII(O2)(12-TMC)]+ (1), [FeIII(O2)(13-TMC)]+ (2), and [FeIII(O2)(14-TMC)]+ (3), as a model study of Rieske oxygenases. The Fe(III)-peroxo complexes show the same δ and pseudo-σ bonds between iron and the peroxo ligand. However, the strength of these interactions varies depending on the ring size of the n-TMC ligands; the overall Fe-O bond strength and the strength of the Fe-O2 δ bond increase gradually as the ring size of the n-TMC ligands becomes smaller, such as from 14-TMC to 13-TMC to 12-TMC. MCD spectroscopy plays a key role in assigning the characteristic low-energy δ → δ* LMCT band, which provides direct insight into the strength of the Fe-O2 δ bond and which, in turn, is correlated with the superoxo character of the iron-peroxo group. In oxidation reactions, reactivities of 1-3 toward hydrocarbon C-H bond activation are compared, revealing the reactivity order of 1 > 2 > 3; the [FeIII(O2)(n-TMC)]+ complex with a smaller n-TMC ring size, 12-TMC, is much more reactive than that with a larger n-TMC ring size, 14-TMC. DFT analysis shows that the Fe(III)-peroxo complex is not reactive toward C-H bonds, but it is the end-on Fe(II)-superoxo valence tautomer that is responsible for the observed reactivity. The hydrogen atom abstraction (HAA) reactivity of these intermediates is correlated with the overall donicity of the n-TMC ligand, which modulates the energy of the singly occupied π* superoxo frontier orbital that serves as the electron acceptor in the HAA reaction. The implications of these results for the mechanism of Rieske oxygenases are further discussed.

Topical carbonic anhydrase inhibitors closing bilateral secondary macular holes and a review of literature.

PURPOSE: To present a rare occurrence of bilateral macular hole secondary to vitrectomy that was successfully treated with topical carbonic anhydrase inhibitors and to review the literature for this phenomenon. METHODS: Monthly clinical examination and optical coherence tomography (OCT) was conducted before and after eight weeks of topical 2% dorzolamide administered twice a day. RESULTS: A 62-year-old male that had bilateral giant retinal tears which were repaired with vitrectomy subsequently presented with bilateral small macular holes of size 74 and 78 microns. Patient was trialled on 2% topical dorzolamide twice a day and reviewed monthly with OCT scans. Macular hole closure was identified after four weeks of topical treatment. Conclusion: Clinical improvement with conservative measures suggests a potential first line approach to the treatment of macular holes avoiding surgery and its risk profile. We also present a review of literature regarding macular holes treated with topical carbonic anhydrase inhibitors and its mechanism of action in treating macular holes.

The elusive active species in nickel(II)-mediated oxidations of hydrocarbons by peracids: a NiII-oxyl species, an aroyloxy radical, or a NiII-peracid complex?

Nonheme nickel(II)-mediated oxidations of hydrocarbons by meta-chloroperbenzoic acid (mCPBA) show promising activity and selectivity; however, the active species and the reaction mechanism of these reactions are still elusive after decades of efforts. Herein, a novel free radical chain mechanism of the Ni(II)-mediated oxidation of cyclohexane by mCPBA is investigated using density functional theory calculations. In this study, we rule out the involvement of a long speculated NiII-oxyl species. Instead, an aroyloxy radical (mCBA˙) and a NiIII-hydroxyl species formed by a rate-limiting O-O homolysis of a NiII-mCPBA complex are active species in the C-H bond activation to form a carbon-centered radical R˙, where mCBA˙ is more robust than the NiIII-hydroxyl species. The nascent R˙ radical either reacts with mCPBA to form a hydroxylated product and a mCBA˙ radical to propagate the radical chain or reacts with the solvent dichloromethane to form a chlorinated product. In addition, the NiII-mCPBA complex is found for the first time to be a robust oxidant in hydroxylation of cyclohexane, with an activation energy of 13.4 kcal mol-1. These mechanistic findings support the free radical chain mechanism and enrich the mechanistic knowledge of metal-peracid oxidation systems containing transition metals after group 8 in periodic table of elements.

Optimising vitrectomy operation note coding with machine learning.

BACKGROUND: The accurate encoding of operation notes is essential for activity-based funding and workforce planning. The aim of this project was to evaluate the procedural coding accuracy of vitrectomy and to develop machine learning, natural language processing (NLP) models that may assist with this task. METHODS: This retrospective cohort study involved vitrectomy operation notes between a 21-month period at the Royal Adelaide Hospital. Coding of procedures were based on the Medicare Benefits Schedule (MBS)-the Australian equivalent to the Current Procedural Terminology (CPT®) codes used in the United States. Manual encoding was conducted for all procedures and reviewed by two vitreoretinal consultants. XGBoost, random forest and logistic regression models were developed for classification experiments. A cost-based analysis was subsequently conducted. RESULTS: There were a total of 1724 procedures with individual codes performed within 617 vitrectomy operation notes totalling $1 528 086.60 after manual review. A total of 1147 (66.5%) codes were missed in the original coding that amounted to $736 539.20 (48.2%). Our XGBoost model had the highest classification accuracy (94.6%) in the multi-label classification for the five most common procedures. The XGBoost model was the most successful model in identifying operation notes with two or more missing codes with an AUC of 0.87 (95% CI 0.80-0.92). CONCLUSIONS: Machine learning has been successful in the classification of vitrectomy operation note encoding. We recommend a combined human and machine learning approach to clinical coding as automation may facilitate more accurate reimbursement and enable surgeons to prioritise higher quality clinical care.

Ophthalmology Operation Note Encoding with Open-Source Machine Learning and Natural Language Processing.

INTRODUCTION: Accurate assignment of procedural codes has important medico-legal, academic, and economic purposes for healthcare providers. Procedural coding requires accurate documentation and exhaustive manual labour to interpret complex operation notes. Ophthalmology operation notes are highly specialised making the process time-consuming and challenging to implement. This study aimed to develop natural language processing (NLP) models trained by medical professionals to assign procedural codes based on the surgical report. The automation and accuracy of these models can reduce burden on healthcare providers and generate reimbursements that reflect the operation performed. METHODS: A retrospective analysis of ophthalmological operation notes from two metropolitan hospitals over a 12-month period was conducted. Procedural codes according to the Medicare Benefits Schedule (MBS) were applied. XGBoost, decision tree, Bidirectional Encoder Representations from Transformers (BERT) and logistic regression models were developed for classification experiments. Experiments involved both multi-label and binary classification, and the best performing model was used on the holdout test dataset. RESULTS: There were 1,000 operation notes included in the study. Following manual review, the five most common procedures were cataract surgery (374 cases), vitrectomy (298 cases), laser therapy (149 cases), trabeculectomy (56 cases), and intravitreal injections (49 cases). Across the entire dataset, current coding was correct in 53.9% of cases. The BERT model had the highest classification accuracy (88.0%) in the multi-label classification on these five procedures. The total reimbursement achieved by the machine learning algorithm was $184,689.45 ($923.45 per case) compared with the gold standard of $214,527.50 ($1,072.64 per case). CONCLUSION: Our study demonstrates accurate classification of ophthalmic operation notes into MBS coding categories with NLP technology. Combining human and machine-led approaches involves using NLP to screen operation notes to code procedures, with human review for further scrutiny. This technology can allow the assignment of correct MBS codes with greater accuracy. Further research and application in this area can facilitate accurate logging of unit activity, leading to reimbursements for healthcare providers. Increased accuracy of procedural coding can play an important role in training and education, study of disease epidemiology and improve research ways to optimise patient outcomes.

Use of Singlet Oxygen in the Generation of a Mononuclear Nonheme Iron(IV)-Oxo Complex.

Nonheme iron(III)-superoxo intermediates are generated in the activation of dioxygen (O2) by nonheme iron(II) complexes and then converted to iron(IV)-oxo species by reacting with hydrogen donor substrates with relatively weak C-H bonds. If singlet oxygen (1O2) with ca. 1 eV higher energy than the ground state triplet oxygen (3O2) is employed, iron(IV)-oxo complexes can be synthesized using hydrogen donor substrates with much stronger C-H bonds. However, 1O2 has never been used in generating iron(IV)-oxo complexes. Herein, we report that a nonheme iron(IV)-oxo species, [FeIV(O)(TMC)]2+ (TMC = tetramethylcyclam), is generated using 1O2, which is produced with boron subphthalocyanine chloride (SubPc) as a photosensitizer, and hydrogen donor substrates with relatively strong C-H bonds, such as toluene (BDE = 89.5 kcal mol-1), via electron transfer from [FeII(TMC)]2+ to 1O2, which is energetically more favorable by 0.98 eV, as compared with electron transfer from [FeII(TMC)]2+ to 3O2. Electron transfer from [FeII(TMC)]2+ to 1O2 produces an iron(III)-superoxo complex, [FeIII(O2)(TMC)]2+, followed by abstracting a hydrogen atom from toluene by [FeIII(O2)(TMC)]2+ to form an iron(III)-hydroperoxo complex, [FeIII(OOH)(TMC)]2+, that is further converted to the [FeIV(O)(TMC)]2+ species. Thus, the present study reports the first example of generating a mononuclear nonheme iron(IV)-oxo complex with the use of singlet oxygen, instead of triplet oxygen, and a hydrogen atom donor with relatively strong C-H bonds. Detailed mechanistic aspects, such as the detection of 1O2 emission, the quenching by [FeII(TMC)]2+, and the quantum yields, have also been discussed to provide valuable mechanistic insights into understanding nonheme iron-oxo chemistry.

High-sensitivity NH3 gas sensor using pristine graphene doped with CuO nanoparticles.

A highly sensitive and selective NH3 gas sensor was developed based on single-layer pristine graphene doped with copper(II) oxide (CuO) nanoparticles of a specific size. High-quality single-layer graphene was grown using chemical vapor deposition. Approximately 15 nm-sized CuO colloidal nanoparticles were fabricated by a microwave-assisted thermal method using copper acetate as the precursor, and dimethylformamide as the reducing and stabilizing agent. Pristine graphene was doped with an aqueous suspension of CuO nanoparticles at a coating speed of 1500 rpm using a simple spin coater. CuO nanoparticle doping induces changes in the electronic properties of graphene; in particular, p-type doping significantly altered graphene resistivity in the presence of NH3 gas. Upon exposure of the pristine graphene surface to NH3 gas, NH3 reacted with O2-/ O-/ O2- species on the graphene surface and released electrons into graphene. This caused a change in the concentration of charge carriers in the valence channel of graphene and an increase in graphene resistivity, facilitating real-time NH3 monitoring with quick response and rapid recovery at 25 ℃ and ~ 55% relative humidity. Our results indicated that graphene doped with ~ 15 nm-sized CuO nanoparticles can sense NH3 gas selectively with a resistivity response of ~ 83%. Moreover, the sensor exhibited good reusability, fast response (~ 19 s), and rapid recovery (~ 277 s) with a detection limit of 0.041 ppm and a relative standard deviation of 0.76%.

Seeing the cis-Dihydroxylating Intermediate: A Mononuclear Nonheme Iron-Peroxo Complex in cis-Dihydroxylation Reactions Modeling Rieske Dioxygenases.

The nature of reactive intermediates and the mechanism of the cis-dihydroxylation of arenes and olefins by Rieske dioxygenases and synthetic nonheme iron catalysts have been the topic of intense research over the past several decades. In this study, we report that a spectroscopically well characterized mononuclear nonheme iron(III)-peroxo complex reacts with olefins and naphthalene derivatives, yielding iron(III) cycloadducts that are isolated and characterized structurally and spectroscopically. Kinetics and product analysis reveal that the nonheme iron(III)-peroxo complex is a nucleophile that reacts with olefins and naphthalenes to yield cis-diol products. The present study reports the first example of the cis-dihydroxylation of substrates by a nonheme iron(III)-peroxo complex that yields cis-diol products.

Can we safely place the distal volar locking plate screws into the subchondral zone of a distal radius fracture using a 45° supination oblique view under fluoroscopic guidance?

INTRODUCTION: Careful distal locking screw insertion into the subchondral zone is necessary to obtain proper mechanical strength of unstable distal radius fractures using volar locking plating. However, subchondral zone screw insertion increases the risk of intra-articular screw penetration, which may remain unrecognized during surgery due to complex distal radial anatomy. The purpose of this study was to evaluate the role of fluoroscopic guidance with a 45° supination oblique view technique for placing distal screws into the subchondral zone during volar locking plating for unstable distal radius fractures and to explore the factors associated with poor screw placement. METHODS: We retrospectively analyzed 171 wrists of 169 patients treated with variable-angle volar locking plates for unstable radius fractures. The subchondral zone was defined as the metaphyseal area within 4 mm of the articular margin of the distal radius. The location of the distal locking screws and radiographic parameters, including the teardrop angle, were measured using computed tomography scans and X-rays. Clinical and radiographic factors were examined to determine their possible associations with screw placement failure. RESULTS: Of 581 distal screws inserted, 559 screws (96.2%) were inserted into the subchondral zone and 17 screws into the metaphyseal zone (2.9%). Five screws (0.7%) in three wrists showed intra-articular placement: four screws were placed into the lunate fossa and one into the scaphoid fossa. These three wrists also exhibited significantly reduced teardrop angles. The distal screws were significantly closer to the joint line in the lunate fossa than the scaphoid fossa (1.9 ± 0.9 mm vs. 2.8 ± 1 mm, P < 0.000). CONCLUSION: The 45° supination oblique view technique is a useful fluoroscopic guiding technique for accurate and safe distal screw placement in the subchondral zone in volar locking plate fixation for distal radial fractures. However, a decreased teardrop angle or extended lunate fossa should be corrected before distal screw insertion to avoid intra-articular screw placement.

A Contrasting Effect of Acid in Electron Transfer, Oxygen Atom Transfer, and Hydrogen Atom Transfer Reactions of a Nickel(III) Complex.

There have been many examples of the accelerating effects of acids in electron transfer (ET), oxygen atom transfer (OAT), and hydrogen atom transfer (HAT) reactions. Herein, we report a contrasting effect of acids in the ET, OAT, and HAT reactions of a nickel(III) complex, [NiIII(PaPy3*)]2+ (1) in acetone/CH3CN (v/v 19:1). 1 was synthesized by reacting [NiII(PaPy3*)]+ (2) with magic blue or iodosylbenzene in the absence or presence of triflic acid (HOTf), respectively. Sulfoxidation of thioanisole by 1 and H2O occurred in the presence of HOTf, and the reaction rate increased proportionally with increasing concentration of HOTf ([HOTf]). The rate of ET from diacetylferrocene to 1 also increased linearly with increasing [HOTf]. In contrast, HAT from 9,10-dihydroanthracene (DHA) to 1 slowed down with increasing [HOTf], exhibiting an inversely proportional relation to [HOTf]. The accelerating effect of HOTf in the ET and OAT reactions was ascribed to the binding of H+ to the PaPy3* ligand of 2; the one-electron reduction potential (Ered) of 1 was positively shifted with increasing [HOTf]. Such a positive shift in the Ered value resulted in accelerating the ET and OAT reactions that proceeded via the rate-determining ET step. On the other hand, the decelerating effect of HOTf on HAT from DHA to 1 resulted from the inhibition of proton transfer from DHA•+ to 2 due to the binding of H+ to the PaPy3* ligand of 2. The ET reactions of 1 in the absence and presence of HOTf were well analyzed in light of the Marcus theory of ET in comparison with the HAT reactions.

Role of conservative therapy prior to surgery in xanthogranulomatous mastitis: a case report.

Background: Xanthogranulomatous mastitis is an extremely rare condition that is characterised by the infiltration of the breast parenchyma by foamy histiocytes. There have been only 26 reported cases amongst 10 publications. The clinical and radiological presentation of xanthogranulomatous mastitis often causes diagnostic confusion due to its similarity to breast cancer and other forms of chronic inflammatory mastitis. A histological diagnosis is often required either by core needle biopsy or excisional biopsy. Upon review of the literature, surgical excision was the most predominant mode of management. Case Description: We present a case of xanthogranulomatous mastitis in a 40-year-old female who presented with clinical and radiological features of breast malignancy. This was a significantly large mass with a dimension of 90.7 mm by 36.4 mm, which if surgically excised, would have led to permanent cosmetic changes. Multiple core needle biopsies were completed to consider other differentials of histiocytic lesions including cystic neutrophilic granulomatous mastitis, histiocytoid lobular breast carcinoma, Rosai-Dorfman disease and Erdheim-Chester disease. Conclusions: Clinical improvement was noted with reduction in size from prolonged antibiotic therapy suggesting an initial conservative approach in the management of xanthogranulomatous mastitis. By contributing our experience with xanthogranulomatous mastitis, we also present a review of literature on its aetiology, clinical features, and management of this pathology.

Enthalpy-Entropy Compensation Effect in Oxidation Reactions by Manganese(IV)-Oxo Porphyrins and Nonheme Iron(IV)-Oxo Models.

"Enthalpy-Entropy Compensation Effect" (EECE) is ubiquitous in chemical reactions; however, such an EECE has been rarely explored in biomimetic oxidation reactions. In this study, six manganese(IV)-oxo complexes bearing electron-rich and -deficient porphyrins are synthesized and investigated in various oxidation reactions, such as hydrogen atom transfer (HAT), oxygen atom transfer (OAT), and electron-transfer (ET) reactions. First, all of the six Mn(IV)-oxo porphyrins are highly reactive in the HAT, OAT, and ET reactions. Interestingly, we have observed a reversed reactivity in the HAT and OAT reactions by the electron-rich and -deficient Mn(IV)-oxo porphyrins, depending on reaction temperatures, but not in the ET reactions; the electron-rich Mn(IV)-oxo porphyrins are more reactive than the electron-deficient Mn(IV)-oxo porphyrins at high temperature (e.g., 0 °C), whereas at low temperature (e.g., -60 °C), the electron-deficient Mn(IV)-oxo porphyrins are more reactive than the electron-rich Mn(IV)-oxo porphyrins. Such a reversed reactivity between the electron-rich and -deficient Mn(IV)-oxo porphyrins depending on reaction temperatures is rationalized with EECE; that is, the lower is the activation enthalpy, the more negative is the activation entropy, and vice versa. Interestingly, a unified linear correlation between the activation enthalpies and the activation entropies is observed in the HAT and OAT reactions of the Mn(IV)-oxo porphyrins. Moreover, from the previously reported HAT reactions of nonheme Fe(IV)-oxo complexes, a linear correlation between the activation enthalpies and the activation entropies is also observed. To the best of our knowledge, we report the first detailed mechanistic study of EECE in the oxidation reactions by synthetic high-valent metal-oxo complexes.

A Mononuclear Non-heme Iron(III)-Peroxo Complex with an Unprecedented High O-O Stretch and Electrophilic Reactivity.

A mononuclear non-heme iron(III)-peroxo complex, [Fe(III)(O2)(13-TMC)]+ (1), was synthesized and characterized spectroscopically; the characterization with electron paramagnetic resonance, Mössbauer, X-ray absorption, and resonance Raman spectroscopies and mass spectrometry supported a high-spin S = 5/2 Fe(III) species binding an O2 unit. A notable observation was an unusually high νO-O at ∼1000 cm-1 for the peroxo ligand. With regard to reactivity, 1 showed electrophilic reactivity in H atom abstraction (HAA) and O atom transfer (OAT) reactions. In the HAT reaction, a kinetic isotope effect (KIE) value of 5.8 was obtained in the oxidation of 9,10-dihydroanthracene. In the OAT reaction, a negative ρ value of -0.61 in the Hammett plot was determined in the oxidation of p-X-substituted thioanisoles. Another interesting observation was the electrophilic reactivity of 1 in the oxidation of benzaldehyde derivatives, such as a negative ρ value of -0.77 in the Hammett plot and a KIE value of 2.2. To the best of our knowledge, the present study reports the first example of a mononuclear non-heme iron(III)-peroxo complex with an unusually high νO-O value and unprecedented electrophilic reactivity in oxidation reactions.

Ligand Architecture Perturbation Influences the Reactivity of Nonheme Iron(V)-Oxo Tetraamido Macrocyclic Ligand Complexes: A Combined Experimental and Theoretical Study.

Iron(V)-oxo complexes bearing negatively charged tetraamido macrocyclic ligands (TAMLs) have provided excellent opportunities to investigate the chemical properties and the mechanisms of oxidation reactions of mononuclear nonheme iron(V)-oxo intermediates. Herein, we report the differences in chemical properties and reactivities of two iron(V)-oxo TAML complexes differing by modification on the "Head" part of the TAML framework; one has a phenyl group at the "Head" part (1), whereas the other has four methyl groups replacing the phenyl ring (2). The reactivities of 1 and 2 in both C-H bond activation reactions, such as hydrogen atom transfer (HAT) of 1,4-cyclohexadiene, and oxygen atom transfer (OAT) reactions, such as the oxidation of thioanisole and its derivatives, were compared experimentally. Under identical reaction conditions, 1 showed much greater reactivity than 2, such as a 102-fold decrease in HAT and a 105-fold decrease in OAT by replacing the phenyl group (i.e., 1) with four methyl groups (i.e., 2). Then, density functional theory calculations were performed to rationalize the reactivity differences between 1 and 2. Computations reproduced the experimental findings well and revealed that the replacement of the phenyl group in 1 with four methyl groups in 2 not only increased the steric hindrance but also enlarged the energy gap between the electron-donating orbital and the electron-accepting orbital. These two factors, steric hindrance and the orbital energy gap, resulted in differences in the reduction potentials of 1 and 2 and their reactivities in oxidation reactions.

Organ donation after controlled circulatory death (Maastricht classification III) following the withdrawal of life-sustaining treatment in Korea: a suggested guideline.

The "Act on hospice and palliative care and decisions on life-sustaining treatment for patients at the end of life" was enacted in February 2018 in Korea. Therefore, we suggest a Korean guideline for organ donation after circulatory death (DCD) category III after the withdrawal of life-sustaining treatment (WLST). Implementation of WLST includes stopping ventilation, extubation, discontinuation of inotropics and vasoconstrictors, cessation of continuous renal replacement therapy, and cessation of extracorporeal membrane oxygenation. Medical staff involved in organ procurement or transplantation surgery cannot participate in the WLST process. Following cardiac arrest, 5 minutes of "no touch time" should pass, after which circulatory death can be declared. The procurement team can enter the room after the declaration of death. The final procurement decision is made after the surgeon visually checks the organ condition. DCD category III activation in Korea will help increase organ donation and reduce the demand-supply mismatch of organ transplantation.

Catalytic Four-Electron Reduction of Dioxygen by Ferrocene Derivatives with a Nonheme Iron(III) TAML Complex.

A mononuclear nonheme iron(III) complex with a tetraamido macrocyclic ligand (TAML), [(TAML)FeIII]- (1), is a selective precatalyst for four-electron reduction of dioxygen by ferrocene derivatives in the presence of acetic acid (CH3COOH) in acetone. This is the first work to show that a nonheme iron(III) complex catalyzes the four-electron reduction of O2 by one-electron reductants. An iron(V)-oxo complex, [(TAML)FeV(O)]- (2), was produced by oxygenation of 1 with O2 via the formation of triacetone triperoxide (TATP), acting as an autocatalyst that shortened the induction time for the generation of 2. Decamethylferrocene (Me10Fc) and octamethylferrocene (Me8Fc) reduced 2 to 1 by two electrons in the presence of CH3COOH to produce decamethylferrocenium cation (Me10Fc+) and octamethylferrocenium cation (Me8Fc+), respectively. Then, 1 was oxygenated by O2 to regenerate 2 via the formation of TATP. In the cases of ferrocene (Fc), bromoferrocene (BrFc) and 1,1'-dibromoferrocene (Br2Fc), initial electron transfer from ferrocene derivatives to 2 occurred; however, neither a second proton-coupled electron transfer from ferrocene derivatives to 2 nor a catalytic four-electron reduction of O2 occurred.

Proton-promoted disproportionation of iron(V)-imido TAML to iron(V)-imido TAML cation radical and iron(IV) TAML.

The present study reports the first example of a proton-promoted disproportionation reaction of a non-heme iron(v)-imido TAML (1) complex to give an iron(v)-imido TAML cation radical (2) and an iron(iv) TAML (3) upon addition of acids. Detailed mechanistic investigations revealed that two molecules of 1 react with one proton to yield 2 and [FeIV(NHTs)(TAML)]- (4), followed by the reaction of 4 with another proton to afford 3 and NH2Ts.

Enhanced Redox Reactivity of a Nonheme Iron(V)-Oxo Complex Binding Proton.

Acid effects on the chemical properties of metal-oxygen intermediates have attracted much attention recently, such as the enhanced reactivity of high-valent metal(IV)-oxo species by binding proton(s) or Lewis acidic metal ion(s) in redox reactions. Herein, we report for the first time the proton effects of an iron(V)-oxo complex bearing a negatively charged tetraamido macrocyclic ligand (TAML) in oxygen atom transfer (OAT) and electron-transfer (ET) reactions. First, we synthesized and characterized a mononuclear nonheme Fe(V)-oxo TAML complex (1) and its protonated iron(V)-oxo complexes binding two and three protons, which are denoted as 2 and 3, respectively. The protons were found to bind to the TAML ligand of the Fe(V)-oxo species based on spectroscopic characterization, such as resonance Raman, extended X-ray absorption fine structure (EXAFS), and electron paramagnetic resonance (EPR) measurements, along with density functional theory (DFT) calculations. The two-protons binding constant of 1 to produce 2 and the third protonation constant of 2 to produce 3 were determined to be 8.0(7) × 108 M-2 and 10(1) M-1, respectively. The reactivities of the proton-bound iron(V)-oxo complexes were investigated in OAT and ET reactions, showing a dramatic increase in the rate of sulfoxidation of thioanisole derivatives, such as 107 times increase in reactivity when the oxidation of p-CN-thioanisole by 1 was performed in the presence of HOTf (i.e., 200 mM). The one-electron reduction potential of 2 (Ered vs SCE = 0.97 V) was significantly shifted to the positive direction, compared to that of 1 (Ered vs SCE = 0.33 V). Upon further addition of a proton to a solution of 2, a more positive shift of the Ered value was observed with a slope of 47 mV/log([HOTf]). The sulfoxidation of thioanisole derivatives by 2 was shown to proceed via ET from thioanisoles to 2 or direct OAT from 2 to thioanisoles, depending on the ET driving force.