Synthesis, X-ray characterization and theoretical study of all-cis1,4:2,3:5,8:6,7-tetraepoxynaphthalenes: On the importance of the through-space α-effect

This manuscript reports the synthesis, X-ray characterization and DFT study of a series of all-cis1,4:2,3:5,8:6,7-tetraepoxynaphthalenes (decahydro-2,6:3,5-diepoxynaphtho[2,3-b:6,7-b′]bis(oxirene) derivatives) obtained by the tandem [4 + 2] cycloaddition between dimethyl acetylenedicarboxylate (DMAD) and three difurans as bis-dienes (the IMDAF reaction). The “pincer”-type adduct formation is controlled by using kinetic conditions. For this work, we were only interested in the synthesis of “pincer”-type adducts to study the formation self-assembled dimers that are governed by quite short C-H⋯O H-bonds. The existence of the “through-space” alpha-effect in the “pincer”-type adducts increases their ability to establish bifurcated C-H⋯O2H-bonds in the solid state. That is, the close distance between the O-bridge atoms provokes an interesting through space lone pair⋯lone pair (LP⋯LP) interaction that increases the H-bond acceptor ability of the O-atoms. It has been analyzed using DFT calculations, molecular electrostatic potential (MEP) surfaces, quantum theory of atoms-in-molecules (QTAIM) and noncovalent interaction plot (NCIplot) index computational tools. This is the second study of the literature where “alpha-effect” hydrogen bonds (AEHBs) are described and studied. The novelty of the present work resides in the exhaustive epoxidation of the double bonds in the resulting “pincer”-type adducts that increases the number of possible H-bond acceptors in the target vicinal tetra-epoxynaphthalenes. The X-ray analyses of the three synthesized tetra-epoxides reveal that the AEHBs are predominant in the solid phase. © The Royal Society of Chemistry 2021

DABCO‐Directed Self‐Assembly of Bisporphyrins (DABCO=1,4‐Diazabicyclo[2.2.2]octane)

[eng] Three isomeric zinc bisporphyrins have been prepared by covalently linking together two aminoporphyrins with an isophthalic acid derivative. The porphyrins differ in the substitution pattern on the meso phenyl groups, that is, ortho, meta, or para. Titrations carried out by UV‐visible and 1H NMR spectroscopy have been used to map out the stabilities and the stoichiometries of the complexes formed with 1,4‐diazabicyclo[2.2.2]octane (DABCO) in chloroform. The ortho‐ and meta‐substituted bisporphyrins form 1:1 intramolecular sandwich complexes. The para‐substituted bisporphyrin cannot adopt the cofacial conformation required for this type of complex and forms a higher order 2:2 intermolecular assembly, which is stable over a wide range of DABCO concentrations

On the importance of halogen bonding interactions in two X-ray structures containing all four (F, Cl, Br, I) halogen atoms

This manuscript reports the synthesis and X-ray characterization of two octahydro-1H-4,6-epoxycyclopenta[c]pyridin-1-one derivatives that contain the four most abundant halogen atoms (Ha) in the structure with the aim of studying the formation of Ha···Ha halogen bonding interactions. The anisotropy of electron density at the heavier halogen atoms provokes the formation of multiple Ha···Ha contacts in the solid state. That is, the heavier Ha-atoms exhibit a region of positive electrostatic potential (σ-hole) along the C–Ha bond and a belt of negative electrostatic potential (σ-lumps) around the atoms. The halogen bonding assemblies in both compounds were analyzed using density functional theory (DFT) calculations, molecular electrostatic potential (MEP) surfaces, the quantum theory of “atom-in-molecules” (QTAIM), the noncovalent interaction plot (NCIplot), and the electron localization function (ELF). © 2021 by the authors. Licensee MDPI, Basel, Switzerland

Novel Chalcogen Bond Donors Derived from [3+2] Cycloaddition Reaction between 2-Pyridylselenyl Reagents and Isocyanates: Synthesis, Structures and Theoretical Studies

A novel [3+2] cycloaddition reaction between 2-pyridylselenyl halides or trifluoroacetates and isocyanates is described herein. This new convenient methodology allows the synthesis of novel 3-oxo-1,2,4-selenodiazolium scaffolds, which are inaccessible by the known methods. The coupling proceeds efficiently for a broad scope of substrates under mild conditions and allows preparation of cationic 3-oxo-1,2,4-selenodiazolium salts in high yields. The mechanism was analyzed using DFT calculations, evidencing the concerted nature of the novel cycloaddition reaction. The new Se-containing heterocycles were demonstrated to be structurally easily tunable donors of the chalcogen bonding (ChB). Noncovalent interactions in the solid state were studied using DFT calculations, molecular electrostatic potential surfaces and the quantum theory of atoms-in-molecules

On the nature of recurrent Au⋯π motifs in tris(2,2′-bipyridine)M(ii) (M = Fe, Co and Ni) dicyanoaurate(i) salts: X-ray analysis and theoretical rationalization

This manuscript reports the synthesis, X-ray characterization and DFT study of three new [M(bipy)3]2[Au(CN)2]3(X) (M = Fe, Co, and Ni; bipy = 2,2′-bipyridine; X = anion) ionic compounds. These salts are composed of [M(bipy)3]2+ dications and [Au(CN)2]- anions in a 2 : 3 ratio. The positive charge is compensated by X = Cl- anions in compounds 1 (M = Fe) and 2 (M = Co) and X = OH- in 3 (M = Ni). The three tridentate bipyridine ligands define the coordination of the M2+ cation, resulting in a nearly octahedral coordination sphere. The linear dicyanoaurate(i) anions are completely surrounded by a cradle of aromatic rings with Au-ring centroid distances below the sum of van der Waals radii, evidencing the existence of a specific Au⋯π attraction. This interaction has been analyzed in terms of the role of the Au-atom (Lewis acid or Lewis base) using DFT calculations combined with the quantum theory of atoms in molecules (QTAIM), noncovalent interaction plot index (NCIplot) and natural bond orbital (NBO) computational tools. The NBO suggests that the Au⋯π interaction is an example of a coinage bond in spite of the anionic nature of the acceptor and the cationic nature of the donor. This journal is © The Royal Society of Chemistry

Towards Anion Recognition and Precipitation with Water-Soluble 1,2,4-Selenodiazolium Salts: Combined Structural and Theoretical Study

The synthesis and structural characterization of a series of supramolecular complexes of bicyclic cationic pyridine-fused 1,2,4-selenodiazoles with various anions is reported. The binding of trifluoroacetate, tetrachloroaurate, tetraphenylborate, perrhenate, and pertechnetate anions in the solid state is regarded. All the anions interact with selenodiazolium cations exclusively via a pair of “chelating” Se· · · O and H· · · O non-covalent interactions, which make them an attractive, novel, non-classical supramolecular recognition unit or a synthon. Trifluoroacetate salts were conveniently generated via novel oxidation reaction of 2,2′-dipyridyl diselenide with bis(trifluoroacetoxy)iodo)benzene in the presence of corresponding nitriles. Isolation and structural characterization of transient 2-pyridylselenyl trifluoroacetate was achieved. X-ray analysis has demonstrated that the latter forms dimers in the solid state featuring very short and strong Se· · · O and Se· · · N ChB con-tacts. 1,2,4-Selenodiazolium trifluoroacetates or halides show good solubility in water. In contrast, (AuCl4 )−, (ReO4 )−, or (TcO4 )− derivatives immediately precipitate from aqueous solutions. Structural features of these supramolecular complexes in the solid state are discussed. The nature and energies of the non-covalent interactions in novel assembles were studied by the theoretical methods. To the best of our knowledge, this is the first study that regards perrhenate and pertechnetate as acceptors in ChB interactions. The results presented here will be useful for further developments in anion recognition and precipitation involving cationic 1,2,4-selenodiazoles. © 2022 by the authors. Licensee MDPI, Basel, Switzerland

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)