Direct analysis of complex reaction mixtures: formose reaction

Complex reaction mixtures, like those postulated on early Earth, present an analytical challenge because of the number of components, their similarity, and vastly different concentrations. Interpreting the reaction networks is typically based on simplified or partial data, limiting our insight. We present a new approach based on online monitoring of reaction mixtures formed by the formose reaction by ion-mobility-separation mass-spectrometry. Monitoring the reaction mixtures led to large data sets that we analyzed by non-negative matrix factorization, thereby identifying ion-signal groups capturing the time evolution of the network. The groups comprised ≈300 major ion signals corresponding to sugar-calcium complexes formed during the formose reaction. Multivariate analysis of the kinetic profiles of these complexes provided an overview of the interconnected kinetic processes in the solution, highlighting different pathways for sugar growth and the effects of different initiators on the initial kinetics. Reconstructing the network's topology further, we revealed so far unnoticed fast retro-aldol reaction of ketoses, which significantly affects the initial reaction dynamics. We also detected the onset of sugar-backbone branching for C6 sugars and cyclization reactions starting for C5 sugars. This top-down analytical approach opens a new way to analyze complex dynamic mixtures online with unprecedented coverage and time resolutio

Hydrogen Bonding Effect on the Oxygen Binding and Activa-tion in Cobalt(III)-peroxo Complexes

Cobalt(III)peroxo complexes serve as model metal complexes mediating oxygen activation. We report a systematic study of the effect of the hydrogen bonding on the oxygen binding and on the O-O bond activation within the cobalt(III)-peroxo complexes. To this end, we prepared a series of tris(pyridin-2-ylmethyl)amine based cobalt(III)peroxo complexes having either none, one, two or three amino groups in the secondary coordination sphere. The hydrogen bonding between the amino group(s) and the peroxo ligand was investigated within the isolated complexes in the gas phase using helium tag-ging IR photodissociation spectroscopy, energy-resolved collision induced dissociation experiments and density func-tional theory. The results show that the hydrogen bonding stabilizes the cobalt(III)-peroxo core, but the effect is on the order of units of kcal mol-1. Introduction of the first amino group to the secondary coordination sphere has the largest stabilization effect; more amino groups do not change the results significantly. The amino group can transfer a hydrogen atom to the peroxo ligands which results in the O-O bond cleavage. This process is thermodynamically favored over the O2 elimination, but entropically disfavored

Aliphatic and Aromatic C-H Bond Oxidation by High-Valent Manganese(IV)-Hydroxo Species

The strong C-H bond activation of hydrocarbons is a difficult reaction in environmental and biological chemistry. Herein, a high-valent manganese(IV)-hydroxo complex, [MnIV(CHDAP-O)(OH)]2+ (2), was synthesized and character-ized by various physicochemical measurements, such as ultra-violet-visible (UV-vis), electrospray ionization-mass spectrome-try (ESI-MS), electron paramagnetic resonance (EPR), and helium-tagging infrared photodissociation (IRPD) methods. The one-electron reduction potential (Ered) of 2 was determined to be 0.93 V vs SCE by redox titration. 2 is formed via a transient green species assigned to a manganese(IV)-bis(hydroxo) complex, [MnIV(CHDAP)(OH)2]2+ (2 '), which performs intramolecular aliphatic C-H bond activation. The kinetic isotope effect (KIE) value of 4.8 in the intramolecular oxidation was observed, which indicates that the C-H bond activation occurs via rate-determining hydrogen atom abstraction. Further, complex 2 can activate the C-H bonds of aromatic compounds, anthracene and its derivatives, under mild conditions. The KIE value of 1.0 was obtained in the oxidation of anthracene. The rate constant (ket) of electron transfer (ET) from N,N '-dimethylaniline derivatives to 2 is fitted by Marcus theory of electron transfer to afford the reorganization energy of ET (lambda = 1.59 eV). The driving force dependence of log ket for oxidation of anthracene derivatives by 2 is well evaluated by Marcus theory of electron transfer. Detailed kinetic studies, including the KIE value and Marcus theory of outer-sphere electron transfer, imply that the mechanism of aromatic C-H bond hydroxylation by 2 proceeds via the rate-determining electron-transfer pathway

Enzyme-like reactivity for increasing selectivity in CO2 electrochemical reduction

The development of selective catalysts for the reduction of CO2 mostly focuses on electrocatalytic approaches and aims at increasing the selectivity of the reaction while keeping a high activity, which is difficult to achieve. Metalloporphyrins are good catalysts for CO2 reduction because they have favorable electronic properties and offer the possibility to make use of secondary coordination sphere effects. Here, we present a new approach to CO2 reduction, which is based on host-guest chemistry enabled by an iron porphyrin cage catalyst. When this iron porphyrin cage catalyst is immobilized on a conducting carbon support the selectivity for CO2 reduction to CO stays above 90 % in a wide range of overpotentials. The hosting of potassium ions in the cage of the catalyst decreases the overpotential of the reduction and increases the catalytical activity while retaining the high selectivity. DFT calculations show that the potassium ions assist the reduction of CO2 by making the 2-electron transfer from iron(0) to CO2 exothermic. Upon protonation, the Fe-COOH intermediates have been trapped by combining an electrochemical cell with an electrospray ionization mass spectrometer and their structure has been characterized by cryogenic ion spectroscopy

Kinetic enantio-recognition of chiral viologen guests by planar-chiral porphyrin cages

International audienceThe kinetic enantio-recognition of chiral viologen guests by planar-chiral porphyrin cage compounds, measured in terms of Delta Delta G double dagger on, is determined by the planar-chirality of the host and influenced by the size, as measured by ion mobility-mass spectrometry, but not the chirality of its substituents. The enantio-kinetic threading of chiral guests by chiral porphyrin hosts is determined by the planar chirality of the host and influenced by the size but not the chirality of the substituent X

Evaluation of a quality improvement intervention to reduce anastomotic leak following right colectomy (EAGLE): pragmatic, batched stepped-wedge, cluster-randomized trial in 64 countries

Background Anastomotic leak affects 8 per cent of patients after right colectomy with a 10-fold increased risk of postoperative death. The EAGLE study aimed to develop and test whether an international, standardized quality improvement intervention could reduce anastomotic leaks. Methods The internationally intended protocol, iteratively co-developed by a multistage Delphi process, comprised an online educational module introducing risk stratification, an intraoperative checklist, and harmonized surgical techniques. Clusters (hospital teams) were randomized to one of three arms with varied sequences of intervention/data collection by a derived stepped-wedge batch design (at least 18 hospital teams per batch). Patients were blinded to the study allocation. Low- and middle-income country enrolment was encouraged. The primary outcome (assessed by intention to treat) was anastomotic leak rate, and subgroup analyses by module completion (at least 80 per cent of surgeons, high engagement; less than 50 per cent, low engagement) were preplanned. Results A total 355 hospital teams registered, with 332 from 64 countries (39.2 per cent low and middle income) included in the final analysis. The online modules were completed by half of the surgeons (2143 of 4411). The primary analysis included 3039 of the 3268 patients recruited (206 patients had no anastomosis and 23 were lost to follow-up), with anastomotic leaks arising before and after the intervention in 10.1 and 9.6 per cent respectively (adjusted OR 0.87, 95 per cent c.i. 0.59 to 1.30; P = 0.498). The proportion of surgeons completing the educational modules was an influence: the leak rate decreased from 12.2 per cent (61 of 500) before intervention to 5.1 per cent (24 of 473) after intervention in high-engagement centres (adjusted OR 0.36, 0.20 to 0.64; P < 0.001), but this was not observed in low-engagement hospitals (8.3 per cent (59 of 714) and 13.8 per cent (61 of 443) respectively; adjusted OR 2.09, 1.31 to 3.31). Conclusion Completion of globally available digital training by engaged teams can alter anastomotic leak rates. Registration number: NCT04270721 (http://www.clinicaltrials.gov)