Theoretical Investigation of Transient Species Following Photodissociation of Ironpentacarbonyl in Ethanol Solution.

Photodissociation of ironpentacarbonyl [1Fe(CO)5] in solution generates transient species in different electronic states, which we studied theoretically. From ab initio molecular dynamics simulations in ethanol solution, the closed-shell parent compound 1Fe(CO)5 is found to interact weakly with the solvent, whereas the irontetracarbonyl [Fe(CO)4] species, formed after photodissociation, has a strongly spin-dependent behavior. It coordinates a solvent molecule tightly in the singlet state [1Fe(CO)4] and weakly in the triplet state [3Fe(CO)4]. From the simulations, we have gained insights into intersystem crossing in solvated irontetracarbonyl based on the distinct structural differences induced by the change in multiplicity. Alternative forms of coordination between 1Fe(CO)4 and functional groups of the ethanol molecule are simulated, and a quantum chemical investigation of the energy landscape for the coordinated irontetracarbonyl gives information about the interconversion of different transient species in solution. Furthermore, insights from the simulations, in which we find evidence of a solvent exchange mechanism, challenge the previously proposed mechanism of chain walking for under-coordinated metal carbonyls in solution.

Photochemical Formation and Electronic Structure of an Alkane σ-Complex from Time-Resolved Optical and X-ray Absorption Spectroscopy.

C-H bond activation reactions with transition metals typically proceed via the formation of alkane σ-complexes, where an alkane C-H σ-bond binds to the metal. Due to the weak nature of metal-alkane bonds, σ-complexes are challenging to characterize experimentally. Here, we establish the complete pathways of photochemical formation of the model σ-complex Cr(CO)5-alkane from Cr(CO)6 in octane solution and characterize the nature of its metal-ligand bonding interactions. Using femtosecond optical absorption spectroscopy, we find photoinduced CO dissociation from Cr(CO)6 to occur within the 100 fs time resolution of the experiment. Rapid geminate recombination by a fraction of molecules is found to occur with a time constant of 150 fs. The formation of bare Cr(CO)5 in its singlet ground state is followed by complexation of an octane molecule from solution with a time constant of 8.2 ps. Picosecond X-ray absorption spectroscopy at the Cr L-edge and O K-edge provides unique information on the electronic structure of the Cr(CO)5-alkane σ-complex from both the metal and ligand perspectives. Based on clear experimental observables, we find substantial destabilization of the lowest unoccupied molecular orbital upon coordination of the C-H bond to the undercoordinated Cr center in the Cr(CO)5-alkane σ-complex, and we define this as a general, orbital-based descriptor of the metal-alkane bond. Our study demonstrates the value of combining optical and X-ray spectroscopic methods as complementary tools to study the stability and reactivity of alkane σ-complexes in their role as the decisive intermediates in C-H bond activation reactions.

Evaluation of operating room inefficiencies and their impact on operating room duration using a surgical app.

BACKGROUND: Efficient utilization of the operating room (OR) is essential. Inefficiencies are thought to cause preventable delays. Our goal was to identify OR incidents causing delays and estimate their impact on the duration of various general surgery procedures. MATERIALS: Three trained observers prospectively collected intraoperative data using the ExplORer Surgical app, a tool that helped capture incidents causing delays. The impact of each incident on case duration was assessed using multivariable analysis. RESULTS: 151 general surgery procedures were observed. The mean number of incidents was 2.7 per each case that averaged 109min. On average, each incident caused a 2.8 â€‹min delay (p â€‹< â€‹0.001), however, some incidents were associated with longer delays. The procedural step of each procedure most susceptible to incidents was also defined. CONCLUSION: The identification of the type of incidents and the procedural step during which they occur may allow targeted interventions to optimize OR efficiency and decrease operative time.

Accessing metal-specific orbital interactions in C-H activation with resonant inelastic X-ray scattering.

Photochemically prepared transition-metal complexes are known to be effective at cleaving the strong C-H bonds of organic molecules in room temperature solutions. There is also ample theoretical evidence that the two-way, metal to ligand (MLCT) and ligand to metal (LMCT), charge-transfer between an incoming alkane C-H group and the transition metal is the decisive interaction in the C-H activation reaction. What is missing, however, are experimental methods to directly probe these interactions in order to reveal what determines reactivity of intermediates and the rate of the reaction. Here, using quantum chemical simulations we predict and propose future time-resolved valence-to-core resonant inelastic X-ray scattering (VtC-RIXS) experiments at the transition metal L-edge as a method to provide a full account of the evolution of metal-alkane interactions during transition-metal mediated C-H activation reactions. For the model system cyclopentadienyl rhodium dicarbonyl (CpRh(CO)2), we demonstrate, by simulating the VtC-RIXS signatures of key intermediates in the C-H activation pathway, how the Rh-centered valence-excited states accessible through VtC-RIXS directly reflect changes in donation and back-donation between the alkane C-H group and the transition metal as the reaction proceeds via those intermediates. We benchmark and validate our quantum chemical simulations against experimental steady-state measurements of CpRh(CO)2 and Rh(acac)(CO)2 (where acac is acetylacetonate). Our study constitutes the first step towards establishing VtC-RIXS as a new experimental observable for probing reactivity of C-H activation reactions. More generally, the study further motivates the use of time-resolved VtC-RIXS to follow the valence electronic structure evolution along photochemical, photoinitiated and photocatalytic reactions with transition metal complexes.

Accidental triplet harvesting in donor-acceptor dyads with low spin-orbit coupling.

We present an accidental mechanism for efficient intersystem crossing (ISC) between singlet and triplet states with low spin-orbit coupling (SOC) in molecules having donor-acceptor (D-A) moieties separated by a Sigma bond. Our study shows that SOC between the lowest singlet excited state and the higher-lying triplet states, together with nuclear motion-driven coupling of this triplet state with lower-lying triplet states during the free rotation about a Sigma bond, is one of the possible ways to achieve the experimentally observed ISC rate for a class of D-A type photoredox catalysts. This mechanism is found to be the dominant contributor to the ISC process with the corresponding rate reaching a maximum at a dihedral angle in the range of 72°-78° between the D-A moieties of 10-(naphthalen-1-yl)-3,7-diphenyl-10H-phenoxazine and other molecules included in the study. We have further demonstrated that the same mechanism is operative in a specific spirobis[anthracene]dione molecule, where the D and A moieties are interlocked near to the optimal dihedral angle, indicating the plausible effectiveness of the proposed mechanism. The present finding is expected to have implications in strategies for the synthesis of new generations of triplet-harvesting organic molecules.

Simulating Non-Adiabatic Dynamics of Photoexcited Phenyl Azide: Investigating Electronic and Structural Relaxation en Route to the Formation of Phenyl Nitrene.

Excited state molecular dynamics simulations of the photoexcited phenyl azide have been performed. The semi-classical surface hopping approximation has enabled an unconstrained analysis of the electronic and nuclear degrees of freedom which contribute to the molecular dissociation of phenyl azide into phenyl nitrene and molecular nitrogen. The significance of the second singlet excited state in leading the photodissociation has been established through electronic structure calculations, based on multi-configurational schemes, and state population dynamics. The investigations on the structural dynamics have revealed the N-N bond separation to be accompanied by synchronous changes in the azide N-N-N bond angle. The 100 fs simulation results in a nitrene fragment that is electronically excited in the singlet manifold.

A Δ-learning strategy for interpretation of spectroscopic observables.

Accurate computations of experimental observables are essential for interpreting the high information content held within x-ray spectra. However, for complicated systems this can be difficult, a challenge compounded when dynamics becomes important owing to the large number of calculations required to capture the time-evolving observable. While machine learning architectures have been shown to represent a promising approach for rapidly predicting spectral lineshapes, achieving simultaneously accurate and sufficiently comprehensive training data is challenging. Herein, we introduce Δ-learning for x-ray spectroscopy. Instead of directly learning the structure-spectrum relationship, the Δ-model learns the structure dependent difference between a higher and lower level of theory. Consequently, once developed these models can be used to translate spectral shapes obtained from lower levels of theory to mimic those corresponding to higher levels of theory. Ultimately, this achieves accurate simulations with a much reduced computational burden as only the lower level of theory is computed, while the model can instantaneously transform this to a spectrum equivalent to a higher level of theory. Our present model, demonstrated herein, learns the difference between TDDFT(BLYP) and TDDFT(B3LYP) spectra. Its effectiveness is illustrated using simulations of Rh L3-edge spectra tracking the C-H activation of octane by a cyclopentadienyl rhodium carbonyl complex.

Simulations of the Aqueous "Brown-Ring" Complex Reveal Fluctuations in Electronic Character.

Ab initio molecular dynamics (AIMD) simulations of the aqueous [Fe(H2O)5(NO)]2+ "brown-ring" complex in different spin states, in combination with multiconfigurational quantum chemical calculations, show a structural dependence on the electronic character of the complex. Sampling in the quartet and sextet ground states show that the multiplicity is correlated with the Fe-N distance. This provides a motivation for a rigid Fe-N scan in the isolated "brown-ring" complex to investigate how the multiconfigurational wave function and the electron density change around the FeNO moiety. Our results show that subtle changes in the Fe-N distance produce a large response in the electronic configurations underlying the quartet wave function. However, while changes in spin density and potential energy are pronounced, variations in charge are negligible. These trends within the FeNO moiety are preserved in structural sampling of the AIMD simulations, despite distortions present in other degrees of freedom in the bulk solution.

Excited-State (Anti)Aromaticity Explains Why Azulene Disobeys Kasha's Rule.

Fluorescence exclusively occurs from the lowest excited state of a given multiplicity according to Kasha's rule. However, this rule is not obeyed by a handful of anti-Kasha fluorophores whose underlying mechanism is still understood merely on a phenomenological basis. This lack of understanding prevents the rational design and property-tuning of anti-Kasha fluorophores. Here, we propose a model explaining the photophysical properties of an archetypal anti-Kasha fluorophore, azulene, based on its ground- and excited-state (anti)aromaticity. We derived our model from a detailed analysis of the electronic structure of the ground singlet, first excited triplet, and quintet states and of the first and second excited singlet states using the perturbational molecular orbital theory and quantum-chemical aromaticity indices. Our model reveals that the anti-Kasha properties of azulene and its derivatives result from (i) the contrasting (anti)aromaticity of its first and second singlet excited states (S1 and S2, respectively) and (ii) an easily accessible antiaromaticity relief pathway of the S1 state. This explanation of the fundamental cause of anti-Kasha behavior may pave the way for new classes of anti-Kasha fluorophores and materials with long-lived, high-energy excited states.

Wave packet theory for non-resonant x-ray emission and non-resonant Auger electron emission in molecules.

We present a time-dependent theory for non-resonant x-ray emission spectrum (XES) and normal Auger spectrum (NAS) calculation, based on a fully quantum description of nuclear dynamics using the vibrational wave packet concept. We compare two formulations of the time-dependent theory, either employing a two-time propagation scheme or using spectral integration over the electron energy continuum. We find that the latter formulation is more efficient for numerical simulations, providing a reasonable accuracy when the integration step is shorter than the lifetime broadening of the core-ionized state. We demonstrate our approach using the example of non-resonant x-ray emission from a water molecule, considering the lowest core-ionized K-1 and first core-ionized shake-up K-1V-1V1 intermediate states. These channels exemplify the developed theory on bound-bound, bound-continuum, continuum-bound, and continuum-continuum transitions. Our results suggest that the time-dependent approach is efficient for simulating XES involving dissociative states, whereas the time-independent approach, based on Franck-Condon factors, is more efficient for bound-bound transitions expressed as discrete frequency dependence in the energy domain. The methods and discussion have general applicability, including both NAS and more complex systems, such as liquid water.

Tracking C-H activation with orbital resolution.

Transition metal reactivity toward carbon-hydrogen (C-H) bonds hinges on the interplay of electron donation and withdrawal at the metal center. Manipulating this reactivity in a controlled way is difficult because the hypothesized metal-alkane charge-transfer interactions are challenging to access experimentally. Using time-resolved x-ray spectroscopy, we track the charge-transfer interactions during C-H activation of octane by a cyclopentadienyl rhodium carbonyl complex. Changes in oxidation state as well as valence-orbital energies and character emerge in the data on a femtosecond to nanosecond timescale. The x-ray spectroscopic signatures reflect how alkane-to-metal donation determines metal-alkane complex stability and how metal-to-alkane back-donation facilitates C-H bond cleavage by oxidative addition. The ability to dissect charge-transfer interactions on an orbital level provides opportunities for manipulating C-H reactivity at transition metals.

Patient perspectives on the usefulness of the MBSAQIP Bariatric Surgical Risk/Benefit Calculator: a randomized controlled trial.

BACKGROUND: The Metabolic and Bariatric Surgery Accreditation and Quality Improvement Program (MBSAQIP) Bariatric Surgical Risk/Benefit Calculator uses procedure-specific prediction models to generate individualized surgical risk/outcome estimates. This tool helps guide informed consent and operative selection. We hypothesized that calculator use would influence patient procedure choice. OBJECTIVE: To assess patient perspectives on the bariatric surgical calculator. SETTING: A randomized controlled trial at an MBSAQIP-accredited center. METHODS: During the preoperative bariatric surgical office consultation, patients were randomized into 2 groups: the control group received conventional surgeon-led counseling, whereas surgeons used the risk/benefit calculator to guide decision making for the calculator group. Surveys were completed by patients following consultations to evaluate satisfaction and perceived impact of the risk/benefit calculator on operative selection. RESULTS: Between 2020 and 2022, 61 patients were randomized to the calculator group and 68 patients to the control group. The percentage of patients whose procedure of choice changed following consultation was similar in the calculator versus control group (44.3% versus 41.2%; P = .723). However, calculator group patients were less likely to perceive surgeon counseling as very important for their decision making (43.3% versus 76.5%; P < .001). Eighty-five percent of calculator group patients rated the calculator as useful or very useful, and only 1.7% found it not very important. The reasons patients changed procedure choice were similar between the groups (P = .091); the most common cause was to improve their anticipated outcome (48.7% versus 54.8%). CONCLUSIONS: While the risk/benefit calculator was perceived as a helpful tool by most patients, its use did not influence their procedure choice. However, the patient-reported usefulness and importance of the calculator during surgeon counseling suggest that the information provided has weight in patient decision making.

Spectroscopic Signature of Dynamical Instability of the Aqueous Complex in the Brown-Ring Nitrate Test.

The chemistry of the brown-ring test has been investigated for nearly a century. Though recent studies have focused on solid state structure determination and measurement of spectra, mechanistic details and kinetics, the aspects of solution structure and dynamics remain unknown. We have studied structural fluctuations of the brown-ring complex in aqueous solution with ab-initio molecular dynamics simulations, from which we identified that the classically established pseudo-octahedral [Fe(H2 O)5 (NO)]2+ complex is present along with a square-pyramidal [Fe(H2 O)4 (NO)]2+ complex. Based on the inability in multi-reference calculations to reproduce the experimental UV-vis spectra in aqueous solution by inclusion of thermal fluctuations of the [Fe(H2 O)5 (NO)]2+ complex alone, we propose the existence of an equilibrium between pseudo-octahedral and square-pyramidal complexes. Despite challenges in constructing models reproducing the solid-state UV-vis spectrum, the advanced spectrum simulation tool motivates us to challenge the established picture of a sole pseudo-octahedral complex in solution.

Electronic Structure Changes of an Aromatic Amine Photoacid along the Förster Cycle.

Photoacids show a strong increase in acidity in the first electronic excited state, enabling real-time studies of proton transfer in acid-base reactions, proton transport in energy storage devices and biomolecular sensor protein systems. Several explanations have been proposed for what determines photoacidity, ranging from variations in solvation free energy to changes in electronic structure occurring along the four stages of the Förster cycle. Here we use picosecond nitrogen K-edge spectroscopy to monitor the electronic structure changes of the proton donating group in a protonated aromatic amine photoacid in solution upon photoexcitation and subsequent proton transfer dynamics. Probing core-to-valence transitions locally at the amine functional group and with orbital specificity, we clearly reveal pronounced electronic structure, dipole moment and energetic changes on the conjugate photobase side. This result paves the way for a detailed electronic structural characterization of the photoacidity phenomenon.

Photoinduced bond oscillations in ironpentacarbonyl give delayed synchronous bursts of carbonmonoxide release.

Early excited state dynamics in the photodissociation of transition metal carbonyls determines the chemical nature of short-lived catalytically active reaction intermediates. However, time-resolved experiments have not yet revealed mechanistic details in the sub-picosecond regime. Hence, in this study the photoexcitation of ironpentacarbonyl Fe(CO)5 is simulated with semi-classical excited state molecular dynamics. We find that the bright metal-to-ligand charge-transfer (MLCT) transition induces synchronous Fe-C oscillations in the trigonal bipyramidal complex leading to periodically reoccurring release of predominantly axial CO. Metaphorically the photoactivated Fe(CO)5 acts as a CO geyser, as a result of dynamics in the potential energy landscape of the axial Fe-C distances and non-adiabatic transitions between manifolds of bound MLCT and dissociative metal-centered (MC) excited states. The predominant release of axial CO ligands and delayed release of equatorial CO ligands are explained in a unified mechanism based on the σ*(Fe-C) anti-bonding character of the receiving orbital in the dissociative MC states.

The Role of Copper Salts and O2 in the Mechanism of C≡N Bond Activation for Facilitating Nitrogen Transfer Reactions.

C≡N bond scission can be a potential avenue for the functionalization of chemical bonds. We have conducted a computational study, using density functional theory (DFT) and ab initio multireference CASSCF methods, to unravel the intricate mechanistic pathways traversed in the copper-promoted, dioxygen-assisted reaction for the formation of aryl isocyanate species from aryl aldehyde. This aryl isocyanate species acts as an active species for C≡N bond cleavage of coordinated cyanide anion enabling nitrogen transfer to various aldehydes. Electronic structure analysis revealed that under all the reaction conditions radical-based pathways are operative, which is in agreement with the experimental findings. The major driving force is a CuII/I redox cycle initiated by single-electron transfer from the carbon center of the nitrile moiety. Our study reveals that the copper salts act as the "electron pool" in this unique nitrogen transfer reaction forming an aryl isocyanate species from aryl aldehydes.

Chylous ascites in the setting of internal hernia: a reassuring sign.

BACKGROUND: Chylous ascites is often reported in cases with lymphatic obstruction or after lymphatic injuries such as intraabdominal malignancies or lymphadenectomies. However, chylous ascites is also frequently encountered in operations for internal hernias. We sought to characterize the frequency and conditions when chylous ascites is encountered in general surgery patients. METHODS: Data from patients who underwent operations for CPT codes related to open and laparoscopic abdominal and gastrointestinal surgery in our tertiary hospital from 2010 to 2019 were reviewed. Patients with the postoperative diagnosis of internal hernia were identified and categorized into three groups: Internal Hernia with chylous ascites, non-chylous ascites, and no ascites. Demographics, prior surgical history, CT findings, source of internal hernia, open or laparoscopic surgery, and preoperative labs were recorded and compared. RESULTS: Fifty-six patients were found to have internal hernias and were included in our study. 80.3% were female and 86% had a previous Roux-en-Y gastric bypass procedure (RYGBP). Laparoscopy was the main approach for all groups. Ascites was present in 46% of the cases. Specifically, chylous ascites was observed in 27% of the total operations and was exclusively (100%) found in patients with gastric-bypass history. Furthermore, it was more commonly associated with Petersen's defect (p < 0.001), while the non-chylous fluid group was associated with herniation through the mesenteric defect (p < 0.001). CONCLUSIONS: Chylous ascites is a common finding during internal hernia operations. Unlike other more morbid conditions, identification of chylous ascites during an internal hernia operation appears innocuous. However, in the context of a patient with a history of RYGBP, the presence of chylous fluid signifies the associated small bowel obstruction is likely related to an internal hernia through a patent Petersen's defect.

Postoperative 4-Year Outcomes in Septuagenarians Following Bariatric Surgery.

BACKGROUND: Bariatric surgery is the most effective treatment for obesity; however, its utilization in older patients remains low. There is a dearth of literature on long-term effectiveness and safety of bariatric surgery in septuagenarian patients. The aim of this study was to compare the short- and long-term outcomes of bariatric surgery in this population. METHODS: Patients who underwent primary laparoscopic Roux-en-Y gastric bypass (LRYGB) or laparoscopic sleeve gastrectomy (LSG) at our institution between 2011 and 2015 were included. Patients were divided into two age groups: < 70 and ≥ 70 years. Outcomes included postoperative hospital length of stay (LOS), 30-day complications, up to 4-year complications, 90-day mortality, comorbidity resolution, and 4-year weight loss (BMI change-ΔΒΜΙ). The groups were also compared using multivariable analyses adjusting for potential confounders (gender, preoperative BMI, and type of procedure). RESULTS: Twenty-nine septuagenarians who underwent 21 LRYGB (72.4%) and 8 LSG (27.6%) were compared to 1016 patients aged < 70 years operated on during the same time period. Additionally, following the multivariable analyses, the septuagenarians had higher LOS (3 vs 2.3 days, p = 0.01), 4-year complications (38% vs 23%, p = 0.012), and less comorbidities' resolution but similar 4-year ΔBMI (- 8.6 vs - 10, p = 0.421), and 30-day complications (10% vs 6%, p = 0.316). CONCLUSION: Bariatric surgery in carefully selected septuagenarians can be accomplished with acceptable safety and comparable postoperative weight loss at 4 years. Surgeons may consider broadening their selection criteria to include this patient subgroup but may allow the patients to reap its benefits if offered earlier in life.

Bariatric Surgery is Safe for Patients After Recovery from COVID-19.

BACKGROUND: Studies of patients who have undergone surgery while infected with COVID-19 have shown increased risks for adverse outcomes in both pulmonary complications and mortality. It has become clear that the risk of complications from perioperative COVID-19 infection must be weighed against the risk from delayed surgical treatment. Studies have also shown that prior bariatric surgery conveys protection against mortality from COVID-19 and that obesity is the biggest risk factor for mortality from COVID-19 infection in adults under 45 years of age. Studies in patients who have fully recovered from COVID-19 and underwent elective surgery have not become widely available yet. OBJECTIVES: This multi-institutional case series is presented to highlight patients who developed COVID-19, fully recovered, and subsequently underwent elective bariatric surgery with 30-day outcomes available. SETTING: Nine bariatric surgery centers located across the United States. METHODS: This multicenter case series is a retrospective chart review of patients who developed COVID-19, recovered, and subsequently underwent bariatric surgery. Fifty-three patients are included, and 30-day morbidity and mortality were analyzed. RESULTS: Thirty-day complications included esophageal spasm, dehydration, and ileus. There were no cardiovascular, venous thromboembolism (VTE) or respiratory events reported. There were no 30- day mortalities. CONCLUSIONS: Bariatric surgery has been safely performed in patients who made a full recovery from COVID-19 without increased complications due to cardiovascular, pulmonary, venous thromboembolism, or increased mortality rates.

Postoperative Dysphagia Following Esophagogastric Fundoplication: Does the Timing to First Dilation Matter?

BACKGROUND: Postoperative dysphagia after anti-reflux surgery typically resolves in a few weeks. However, even after the initial swelling has resolved at 6 weeks, dysphagia can persist in 30% of patients necessitating esophageal dilation. The purpose of this study was to investigate the effect of esophageal dilation on postoperative dysphagia, the recurrence of reflux symptoms, and the efficacy of pneumatic dilations on postoperative dysphagia. METHODS: A prospectively collected database was reviewed for patients who underwent partial/complete fundoplication with/without paraesophageal hernia repair between 2006 and 2014. Patient age, sex, BMI, DeMeester score, procedure type, procedure duration, length of stay, postoperative dysphagia, time to first pneumatic dilation, number of dilations, and the need for reoperations were collected. RESULTS: The study included 902 consecutive patients, 71.3% females, with a mean age of 57.8 ± 14.7 years. Postoperative dysphagia was noted in 26.3% of patients, of whom 89% had complete fundoplication (p < 0.01). Endoscopic dilation was performed in 93 patients (10.3%) with 59 (63.4%) demonstrating persistent dysphagia. Recurrent reflux symptoms occurred in 35 (37.6%) patients who underwent endoscopic dilation. Patients who underwent a dilation for symptoms of dysphagia were less likely to require a revisional surgery later than patients who had dysphagia but did not undergo a dilation before revisional surgery (17.2% vs 41.7%, respectively, p < 0.001) in the 4-year follow-up period. The duration of initial dilation from surgery was inversely related to the need for revisional surgery (p = 0.047), while more than one dilation was not associated with additive benefit. CONCLUSION: One attempt at endoscopic dilation of the esophagogastric fundoplication may provide relief in patients with postoperative dysphagia and can be used as a predictive factor for the need of revision. However, there is an increased risk for recurrent reflux symptoms and revisional surgery may ultimately be indicated for control of symptoms.