What governs magnetic exchange couplings in radical-bridged dinuclear complexes?

Coupling transition metal or lanthanide ions through a radical bridging ligand is a promising route to increase performances in the area of single molecular magnets. A better understanding of the underlying physical mechanisms governing the magnetic exchange couplings is thus of valuable importance to design future compounds. Here, couplings in three series of metal-radical-metal compounds based on transition metal ions are investigated by means of the decomposition/recomposition methods. This work presents the generalisation and first application of the method to systems with an arbitrary number of magnetic centres featuring several unpaired electrons. Thanks to the decomposition into the three main contributions (direct exchange, kinetic exchange, and spin polarisation) as well as a description in terms of electron-electron interactions, we study the influence of the nature of the metal centre and the radical ligand on the couplings. We combine the energetic contributions extracted with orbital and charge population analysis to rationalise the results.

On Entangled Singlet Pure Diradicals.

This work addresses a class of conjugated hydrocarbons that are expected to be singlet diradicals according to the topological Hückel Hamiltonian while possibly satisfying full on-bond electron pairing. These systems possess two degenerate singly occupied molecular orbitals (SOMOs), but aromaticity brought by properly positioned six-membered rings does prevent Jahn-Teller distortions. Density functional theory (DFT) calculations performed on two emblematic examples confirm the strong bond-length alternation in the closed-shell solutions and the clear spatial symmetry in the open-shell spin-unrestricted determinants, the latter solution always being found to have significantly lower energy. Since the SOMOs are here of different symmetry, the wave function is free from ionic valence-bond component, and spin decontamination of the unrestricted DFT solutions and wave function calculations at the CASSCF-plus-second-order-perturbation level confirm the expected pure diradical character of such molecules. In contrast to disjoint diradicals, the SOMOs of present systems have large amplitudes on neighbor atoms, and we propose to name them entangled pure diradicals, further providing some prescription rules for their design. Additional calculations point out the qualitative contrast between these molecules and the related diradicaloids.

Modeling interactions between rubidium atom and magnetometer cell wall molecules.

Magnetometer cell wall coat molecules play an important role in preserving the lifetime of pumped alkali metal atoms for use in magnetometers that are capable of measuring very small magnetic fields. The goal of this study is to help rationalize the design of the cell coat molecules. Rubidium-87 is studied in terms of its interaction with three template cell coat molecules: ethane, ethene, and methyltrichlorosilane (MeTS). Ab initio electronic structure methods are applied to investigate the effect that the coat molecules have on the 2S ground state and 2P excited state of 87Rb. We find that, from the ab initio results, the three template molecules have differing effects, with MeTS having the largest effect on the ground state and ethane or ethene having the largest effect on the non-degenerate excited states.

Revisiting magnetic exchange couplings in heterodinuclear complexes through the decomposition method in KS-DFT.

Providing tools to understand the physical mechanisms governing magnetic properties in transition metal-based compounds is still of great interest. Here, the magnetic exchange coupling in a series of heterodinuclear complexes is investigated by means of the decomposition method. This work presents the first application of the decomposition method to systems where magnetic centres may bear more than one unpaired electron. By decomposing the coupling into three physical contributions (direct exchange, kinetic exchange, and spin polarisation), we provide numerical arguments to confirm or infirm the rationalisation allowed by the conceptual analysis of the magnetic d orbitals. We also take advantage of the recently proposed generalisation of the method [David et al., J. Chem. Theory Comput., 2023, 19, 157] to get more insights into the underlying mechanisms by disentangling the coupling between centres into its electron-electron interactions.

Difficulty of the evaluation of the barrier height of an open-shell transition state between closed shell minima: The case of small C4n rings.

C4n cyclacenes exhibit strong bond-alternation in their equilibrium geometry. In the two equivalent geometries, the system keeps an essentially closed-shell character. The two energy minima are separated by a transition state suppressing the bond-alternation, where the wave function is strongly diradical. This paper discusses the physical factors involved in this energy difference and possible evaluations of the barrier height. The barrier given as the energy difference between the restricted density functional theory (DFT)/B3LYP for the equilibrium and the broken symmetry DFT/B3LYP of the transition state is either negative or small, in contradiction with the most reliable Wave Function Theory calculations. The minimal (two electrons in two molecular orbitals) Complete Active Space self-consistent field (CASSCF) overestimates the barrier, and the subsequent second-order perturbation cancels it. Due to the collective character of the spin-polarization effect, it is necessary to perform a full π CASSCF + second-order perturbation to reach a reasonable value of the barrier, but this type of treatment cannot be applied to large molecules. DFT procedures treating on an equal foot the closed-shell and open-shell geometries have been explored, such as Mixed-Reference Spin-Flip Time-dependent-DFT and a new spin-decontamination proposal, namely, DFT-dressed configuration interaction, but the results still depend on the density functional. M06-2X without or with spin-decontamination gives the best agreement with the accurate wave function results.

Analyzing Magnetically Induced Currents in Molecular Systems Using Current-Density-Functional Theory.

A suite of tools for the analysis of magnetically induced currents is introduced. These are applicable to both the weak-field regime, well described by linear response perturbation theory, and to the strong-field regime, which is inaccessible to such methods. A disc-based quadrature scheme is proposed for the analysis of magnetically induced current susceptibilities, providing quadratures that are consistently defined between different molecular systems and applicable to both planar 2D and general 3D molecular systems in a black-box manner. The applicability of the approach is demonstrated for a range of planar ring systems, the ground and excited states of the benzene molecule, and the ring, bowl, and cage isomers of the C20 molecule in the presence of a weak magnetic field. In the presence of a strong magnetic field, the para- to diamagnetic transition of the BH molecule is studied, demonstrating that magnetically induced currents present a visual interpretation of this phenomenon, providing insight beyond that accessible using linear response methods.

Consistent spin decontamination of broken-symmetry calculations of diradicals.

Broken-symmetry calculations of diradicals exploit the mean-field energies of determinants that are not eigenfunctions of the S2 operator, the mean value of which is close to 1 for the ms = 0 solution. This spin contamination must be corrected. Two different contributions affect ⟨S2⟩, namely, the mixing between neutral and ionic valence bond components, the so-called kinetic exchange, which decreases ⟨S2⟩, and the spin polarization of the supposedly closed shell orbitals, which increases ⟨S2⟩. The popular Yamaguchi formula is valid for the first effect but irrelevant for the second one. From a few constrained broken-symmetry calculations, one may treat separately the two contributions and apply their specific spin decontamination correction. This work proposes a consistent spin-decontaminated procedure for the evaluation of singlet-triplet gaps in diradicals.

Improved evaluation of spin-polarization energy contributions using broken-symmetry calculations.

Spin-polarization effects may play an important role in free radicals and in the magnetic coupling between radical centers. Starting from restricted open-shell calculations, i.e., a closed-shell description of the non-magnetic core electrons, a low-order perturbation expansion identifies the spin-polarization contribution to the energy of mono-radicals and to singlet-triplet energy differences in diradicals. Broken-symmetry (BS) single-determinant calculations introduce only a fraction of spin-polarization effects, and in a biased manner, since BS determinants are not spin eigenfunctions. We propose a simple technique to correctly evaluate spin-polarization energies by taking into account the effect of spin-flip components on one-hole one-particle excited configurations. Spin-decontamination corrections are shown to play a non-negligible role in the BS evaluation of bond energies. The importance of spin decontamination is illustrated in cases for which spin polarization is the leading contribution to the singlet-triplet gap, which characterizes twisted conjugated double bonds and disjoint diradicals.

[Pancreatic insufficiency†: diagnostic insufficiency†?] / Insuffisance pancréatique†: insuffisance diagnostique†?

Exocrine pancreatic insufficiency is characterized by insufficient secretion of pancreatic enzymes with subsequent inability to maintain adequate digestion of food. Maldigestion may lead to malnutrition with associated various morbidities. Exocrine pancreatic insufficiency is also associated with a reduced quality of life and, in some studies, increased mortality. Exocrine pancreatic insufficiency may develop due to numerous causes and is often underdiagnosed and not adequately treated. Particularly in the early stages, diagnosis of exocrine pancreatic insufficiency may be difficult, as steatorrhea may be absent and a specific diagnostic test currently does not exist. Hence, it is crucial to recall the situations at risk for exocrine pancreatic insufficiency in order not to miss its diagnosis. In this article, we will provide a summary of the main causes of exocrine pancreatic insufficiency as well as its diagnosis and management.

L'insuffisance pancréatique exocrine (IPE) est caractérisée par une activité pancréatique enzymatique insuffisante pour maintenir une digestion adéquate des nutriments. Cette maldigestion peut mener à un état de malnutrition avec de nombreuses conséquences en termes de morbidité. L'IPE est également associée à une diminution de la qualité de vie et à une augmentation de la mortalité. Elle peut se retrouver dans de nombreuses circonstances et plusieurs études suggèrent que sa prise en charge est insuffisante. Son diagnostic, surtout précoce, peut s'avérer difficile car les symptômes classiques de stéatorrhée ne sont pas toujours présents et il n'existe actuellement pas de test diagnostique de certitude. Il est donc essentiel de savoir reconnaître les situations à risque. Dans cet article, nous passerons en revue les principales causes, méthodes diagnostiques et possibilités thérapeutiques de l'IPE.

Quantitative assessment of mucosal architecture using computer-based analysis of confocal laser endomicroscopy in inflammatory bowel diseases.

BACKGROUND AND AIMS: Confocal laser endomicroscopy (CLE) might discriminate mucosal lesions between Crohn's disease (CD) and ulcerative colitis (UC). However, the analysis of CLE images requires time-consuming methods, a long training time, and potential impediments, such as significant interobserver variability. Therefore, we developed a computer-based method to analyze mucosal architecture from CLE images and discriminate between healthy subjects and patients with inflammatory bowel disease (IBD) as well as between UC and CD patients. METHODS: We retrospectively screened patients who had undergone CLE either for an evaluation of IBD in remission or for colorectal cancer screening (control subjects) between 2009 and 2016. We assessed 14 morphologic and functional parameters in each CLE recording from 23 CD patients, 27 UC patients, and 9 control patients. Next, we constructed 2 scores, 1 for the IBD diagnosis and 1 for the differential diagnosis between UC and CD. RESULTS: In IBD patients, the mean intercrypt distance, wall thickness, and fluorescein leakage through the colonic mucosa were significantly increased compared with control patients by 155%, 188%, and 297%, respectively (P < .05). In UC patients, the same parameters were significantly increased by 109%, 117%, and 174%, respectively (P < .05), compared with CD patients. IBD diagnosis had 100% (95%CI, 93%; 100%) sensitivity and 100% (95%CI, 66%; 100%) specificity. IBD differential diagnosis provided discrimination of UC from CD patients with 92% (95%CI, 75%; 99%) sensitivity and 91% (95%CI, 72%; 99%) specificity. CONCLUSIONS: Confirming these results using prospective validation cohorts can substantiate that computer-based analysis of CLE images may provide new biomarkers for the diagnosis and characterization of IBD.

How Vine Shoots as Fillers Impact the Biodegradation of PHBV-Based Composites.

Vine shoots are lignocellulosic agricultural residues. In addition to being an interesting source of polyphenols, they can be used as fillers in a poly(3-hydroxybutyrate-3-hydroxyvalerate) (PHBV) matrix to decrease the overall cost and to propose an alternative to non-biodegradable fossil-based materials. The objective of the present work was to investigate how the incorporation of vine shoots fillers and a preliminary polyphenol extraction step could impact the biodegradability of biocomposites. Biocomposites (20 wt %) were produced by microcompounding. The biodegradation of materials was assessed by respirometric tests in soil. The negative impact of polyphenols on the biodegradability of vine shoots was confirmed. This was supported by crystallinity measurements and scanning electron microscopy (SEM) observations, which showed no difference in structure nor morphology between virgin and exhausted vine shoots particles. The incorporation of vine shoots fillers in PHBV slightly accelerated the overall biodegradation kinetics. All the biocomposites produced were considered fully biodegradable according to the French and European standard NF EN 17033, allowing the conclusion that up-cycling vine shoots for the production of lignocellulosic fillers is a promising strategy to provide biodegradable materials in natural conditions. Moreover, in a biorefinery context, polyphenol extraction from vine shoots has the advantage of improving their biodegradability.

[Abecedary of colonic polyps]. / ABC des polypes coliques.

Colonic polyps are very common in the general population. Some polyps present a cancerization risk and their screening and management by endoscopy reduce the risk of colorectal cancer. Other polyps do not need specific follow-up. There are different types of polyps whose classification has been updated over the last ten years. Serrated polyps now intersect hyperplastic polyps, sessile serrated adenomas and traditional serrated adenomas. Current recommendations are to resect and histologically analyze each colonic polyp to define a personalized endoscopic surveillance strategy. Some colonic polyposis syndromes require management in a specialized center.

Les polypes coliques sont très fréquents dans la population générale. Certains sont à risque de cancérisation et leurs dépistage et prise en charge par le biais de l'endoscopie permettent une diminution du risque de cancer colorectal. D'autres ne nécessitent pas de surveillance. La classification des polypes a été remise à jour au cours de ces dix dernières années et, à côté des adénomes conventionnels, on reconnaît à présent les festonnés ou dentelés qui regroupent les polypes hyperplasiques, les adénomes dentelés sessiles et les dentelés traditionnels. Les recommandations actuelles sont de réséquer et d'analyser histologiquement chaque polype colique afin de définir une stratégie de surveillance endoscopique personnalisée. Certains syndromes dits de polypose colique nécessitent une prise en charge en centre spécialisé.

Chemical Tuning of Magnetic Exchange Couplings Using Broken-Symmetry Density Functional Theory.

With broken-symmetry Kohn-Sham density functional theory calculations, it is demonstrated that the ferromagnetic or anti-ferromagnetic character of two prototypical binuclear copper complexes can be modified, both in the sign and in magnitude, by means of chemical substitutions operated on the bridges connecting the two magnetic centers. The level of detail provided by the magnetic exchange decomposition in terms of direct exchange, kinetic exchange, and core polarization puts forward the relative importance of the different bridges. At variance with the principal bridge for which chemical substitutions modify both the direct and the kinetic exchange contributions, modifications of the secondary bridge only affect the magnitude of the anti-ferromagnetic kinetic exchange mechanism, ultimately allowing for a direct control of the magnetic character of the modified compound.

Qualitative Views on the Polyradical Character of Long Acenes.

Spin-symmetry breaking appears in the DFT treatment of polyacenes, beyond a certain length, the critical length depending on the exchange-correlation potential. This phenomenon may be attributed to an instability with respect to HOMO-LUMO mixing, which suggests a diradical character of long acenes. However, the increase of the S2 operator with acene length questions this simple view. It is shown that this increase cannot be attributed to spin polarization of the inner MOs, and that a second symmetry breaking takes place for the pentadecacene, with four unpaired electrons centered at the first and third quarters of the chain. The spin density distributions of broken-symmetry solutions support a qualitative picture in terms of tetra-methylene hexacenes separated by Clar sextets. A strategy is proposed to identify local symmetry breaking in polyradical systems.

[Endoscopic ultrasound - guided biliary and pancreatic drainage: an update]. / Drainage des voies biliaires et du pancréas par échographie endoscopique : actualités.

Endosonography is an effective diagnostic procedure for intraluminal, parietal and extradigestive pathologies with superior resolution compared to other imaging modalities. The evolution of this technique permits targeted biopsies and offers new therapeutic approaches, initially for the drainage of abdominal collections, and now also for the drainage of bile ducts and the pancreas. These procedures offer a wide range of minimal invasive curative or palliative therapeutic options. The safety profile of these procedures is good and equivalent to a percutaneous approach. They provide a greater comfort and are associated with lower overall cost.

L'échographie endoscopique est une méthode reconnue et efficace dans le processus diagnostique des pathologies digestives intraluminales, pariétales et extradigestives, avec une résolution inégalée par rapport aux autres modalités d'imagerie. L'évolution de cette technique a non seulement permis de faire des biopsies ciblées, mais a aussi offert de nouveaux abords thérapeutiques tels que le drainage des collections abdominales puis des voies biliaires et du pancréas. Ces procédures ont l'avantage d'offrir un large panel d'options thérapeutiques grâce à de nombreuses possibilités d'abord, avec un caractère minimalement invasif. Le profil de sécurité de ces interventions est bon, équivalent à un abord percutané, et présente l'avantage d'un confort supérieur pour les patients, à un coût global inférieur.

Scrutinizing "Invisible" astatine: A challenge for modern density functionals.

The main-group 6p elements did not receive much attention in the development of recent density functionals. In many cases it is still difficult to choose among the modern ones a relevant functional for various applications. Here, we illustrate the case of astatine species (At, Z = 85) and we report the first, and quite complete, benchmark study on several properties concerning such species. Insights on geometries, transition energies and thermodynamic properties of a set of 19 astatine species, for which reference experimental or theoretical data has been reported, are obtained with relativistic (two-component) density functional theory calculations. An extensive set of widely used functionals is employed. The hybrid meta-generalized gradient approximation (meta-GGA) PW6B95 functional is overall the best choice. It is worth noting that the range-separated HSE06 functional as well as the old and very popular B3LYP and PBE0 hybrid-GGAs appear to perform quite well too. Moreover, we found that astatine chemistry in solution can accurately be predicted using implicit solvent models, provided that specific parameters are used to build At cavities. © 2016 Wiley Periodicals, Inc.

Consistent Evaluation of Magnetic Exchange Couplings in Multicenter Compounds in KS-DFT: The Recomposition Method.

The use of broken-symmetry calculations in Kohn-Sham density functional theory has offered an affordable route to study magnetic exchange couplings in transition-metal-based compounds. However, computing this property in compounds exhibiting several couplings is still challenging and especially due to the difficulties to overcome the well-known problem of spin contamination. Here, we present a new and general method to compute magnetic exchange couplings in systems featuring several spin sites. To provide a consistent spin decontamination of J values, our strategy exploits the decomposition method of the magnetic exchange coupling proposed by Coulaud et al. and generalizes our previous work on diradical compounds where the overall magnetic exchange coupling is defined as the sum of its three main and properly extracted physical contributions (direct exchange, kinetic exchange, and spin polarization). In this aim, the generalized extraction of all contributions is presented to systems with multiple spin sites bearing one unpaired electron. This is done by proposing a new paradigm to treat the kinetic exchange contribution, which proceeds through monorelaxations of the magnetic orbitals. This method, so-called the recomposition method, is applied to a compound featuring three Cu(II) ions with a linear arrangement and to a recently synthesized complex containing a Cu4O4 cubane unit presenting an unusual magnetic behavior.

Biocomposites from poly(3-hydroxybutyrate-co-3-hydroxyvalerate) and lignocellulosic fillers: Processes stored in data warehouse structured by an ontology.

Due to the rising amount of plastic waste generated each year, multiple questions are emerging about their harmful long-term effects on the environment, the eco-systems and human health. One possible strategy to mitigate these issues is to substitute conventional plastics by materials fully biodegradable in natural conditions, such as poly(3-hydroxybutyrate-co-3-hydroxyvalerate) (PHBV). In order to decrease the overall cost and environmental impact of PHBV-based materials while modulating their technical performance, PHBV can be combined with lignocellulosic fillers. In this article, a total of 88 formulations of PHBV-based biocomposites has been collected, distributed over 5 interdisciplinary projects involving computer scientists, data scientists and biomass processing experts for food and bio-based material production. Available data concern the technical process descriptions, including the description of each step and the different observations measured. These data are stored in a knowledge base that can be queried on the Web.

An Embedded Fragment Method for Molecules in Strong Magnetic Fields.

An extension of the embedded fragment method for calculations on molecular clusters is presented, which includes strong external magnetic fields. The approach is flexible, allowing for calculations at the Hartree-Fock, current-density-functional theory, Møller-Plesset perturbation theory, and coupled-cluster levels using London atomic orbitals. For systems consisting of discrete molecular subunits, calculations using London atomic orbitals can be performed in a computationally tractable manner for systems beyond the reach of conventional calculations, even those accelerated by resolution-of-the-identity or Cholesky decomposition methods. To assess the applicability of the approach, applications to water clusters are presented, showing how strong magnetic fields enhance binding within the clusters. However, our calculations suggest that, contrary to previous suggestions in the literature, this enhanced binding may not be directly attributable to strengthening of hydrogen bonding. Instead, these results suggest that this arises for larger field strengths as a response of the system to the presence of the external field, which induces a charge density build up between the monomer units. The approach is embarrassingly parallel and its computational tractability is demonstrated for clusters of up to 103 water molecules in triple-ζ basis sets, which would correspond to conventional calculations with more than 12 000 basis functions.