Formation of long, multicenter pi-[TCNE](2)(2-) dimers in solution: solvation and stability assessed through molecular dynamics simulations

Purely organic radical ions dimerize in solution at low temperature, forming long, multicenter bonds, despite the metastability of the isolated dimers. Here, we present the first computational study of these pi-dimers in solution, with explicit consideration of solvent molecules and finite temperature effects. By means of force-field and ab initio molecular dynamics and free energy simulations, the structure and stability of pi-[TCNE](2)(2-) (TCNE = tetracyanoethylene) dimers in dichloromethane have been evaluated. Although the dimers dissociate at room temperature, they are stable at 175 K and their structure is similar to the one in the solid state, with a cofacial arrangement of the radicals at an inter-planar separation of approximately 3.0 angstrom. The pi-[TCNE](2)(2-) dimers form dissociated ion pairs with the NBu4+ counterions, and their first solvation shell comprises approximately 20 CH2Cl2 molecules. Among them, the eight molecules distributed along the equatorial plane of the dimer play a key role in stabilizing the dimer through bridging C-H center dot center dot center dot N contacts. The calculated free energy of dimerization of TCNE center dot- in solution at 175 K is -5.5 kcal mol(-1). These results provide the first quantitative model describing the pairing of radical ions in solution, and demonstrate the key role of solvation forces on the dimerization process

Titanium oxo-clusters derivatized from the Ti10O12(cat)8(py)8 complex: structural investigation and spectroscopic studies of light absorption

A series of deep-red colored nano-sized titanium oxo-clusters bearing catecholato ligands is reported. These architectures are produced via post-synthetic modification of the Ti10O12(cat)8(py)8 (cat = catecholato, py = pyridine) complex through quantitative substitution of labile pyridine ligands by three substituted pyridines (pico, 4-Phpy and pyrald). The crystal structure analysis reveals a common Ti10O12(cat)8 backbone for the three isolated molecular architectures. Partial charge analysis indicates two types of titanium atoms within these complexes with one resembling titanium(IV) found in TiO2. These complexes strongly absorb visible light in solution (λmax = 411 nm, ε = 10 800 for Ti10O12(cat)8(py)8 in CHCl3) and in the solid-state. The band gaps estimated from the reflectance spectra are between 1.85 eV and 1.97 eV. The present work also details the HOMO and LUMO representations obtained via DFT calculation for Ti10O12(cat)8(py)8 and a virtual Ti10O12(cat)8 complex as well as the DOS (density of states) plots calculated for those structures. This computational study highlights an impact of the pyridine ligand on the DOS plots

Identification of Zr(IV)-based architectures generated from ligands incorporating the 2,2′-biphenolato unit

The structural identification in solution of the Zr(IV) complexes involving two 2,2-biphenol-based proligands is reported. The proligand L1H2 contains one 2,2-biphenol unit whereas L2H4 incorporates two 2,2-biphenol units linked by a para-phenylene bridge. Diffusion Ordered Spectroscopy (DOSY) combined with electrospray mass spectrometry analysis and density functional theory (DFT) allowed for determining the molecular structures of such Zr(IV)-based architectures. It is proposed that [Zr(OPri)4(HOPri)] in the presence of L1H2 generates an octahedral complex formulated as [ZrL13H2]. Concerning the self-assembled architecture incorporating the L2 ligand, the analytical data highlight the formation of an unprecedented neutral Zr(IV) triple-stranded helicate ([Zr2L23H4]). Insight into the geometry of these complexes is obtained via DFT calculations. Remarkably, the helicate structure characterized in solution strongly contrasts with the triple-stranded structure of the complex that crystallizes

Delayed Graft Function in Kidney Transplants: Time Evolution, Role of Acute Rejection, Risk Factors, and Impact on Patient and Graft Outcome

Background. Although numerous risk factors for delayed graft function (DGF) have been identified, the role of ischemia-reperfusion injury and acute rejection episodes (ARE) occurring during the DGF period is ill-defined and DGF impact on patient and graft outcome remains controversial. Methods. From 1983 to 2014, 1784 kidney-only transplantations from deceased donors were studied. Classical risk factors for DGF along with two novel ones, recipient’s perioperative saline loading and residual diuresis, were analyzed by logistic regression and receiver operating characteristic (ROC) curves. Results. Along with other risk factors, absence of perioperative saline loading increases acute rejection incidence (OR = 1.9 [1.2–2.9]). Moreover, we observed two novel risk factors for DGF: patient’s residual diuresis ≤500 mL/d (OR = 2.3 [1.6–3.5]) and absence of perioperative saline loading (OR = 3.3 [2.0–5.4]). Area under the curve of the ROC curve (0.77 [0.74–0.81]) shows an excellent discriminant power of our model, irrespective of rejection. DGF does not influence patient survival (P=0.54). However, graft survival is decreased only when rejection was associated with DGF (P<0.001).  Conclusions. Perioperative saline loading efficiently prevents ischemia-reperfusion injury, which is the predominant factor inducing DGF. DGF per se has no influence on patient and graft outcome. Its incidence is currently close to 5% in our centre

Monomeric Ti(IV)-based complexes incorporating luminescent nitrogen ligands: synthesis, structural characterization, emission spectroscopy and cytotoxic activities

This manuscript describes the synthesis of a series of neutral titanium(IV) monomeric complexes constructed around a TiO4N2 core. The two nitrogen atoms that compose the coordination sphere of the metallic center belong to 2,2′-bipyrimidine ligands homo-disubstituted in the 4 and 4′ positions by methyl (2a), phenylvinyl (2b), naphthylvinyl (2c) or anthrylvinyl (2d) groups. The crystal structures of these complexes named [Ti(1)2(2a)], [Ti(1)2(2b)], [Ti(1)2(2c)] and [Ti(1)2(2d)] (where 1 is a 2,2′-biphenolato ligand substituted in the 6 and 6′ positions by phenyl groups) are reported. The hydrolytic stability of the four complexes is evaluated by monitoring the evolution of the free 2a–d signals by 1H NMR spectroscopy. For the conditions tested (6 mM, DMSO-d6/D2O: 8/1), a rather good stability with t1/2 ranging from 180 to 300 min is determined for the complexes. In the presence of an acid (DCl), the hydrolysis of [Ti(1)2(2a)] is faster than without an acid. The cytotoxic activity against gastric cancer cells of the titanium-based compounds and the free disubstituted 2,2′-bipyrimidine ligands is tested, showing IC50 ranging from 6.2 ± 1.2 μM to 274 ± 56 μM. The fluorescence studies of the ligands 2a–d, and the complexes [Ti(1)2(2a–d)] reveal an important fluorescence loss of the ligands 2c and 2d upon coordination with the Ti(1)2 fragment. Frontier orbitals obtained by DFT calculations permit us to explain this fluorescence quenching.Other supports : Centre National pour la Recherche Scientifique (CNRS, France), ARC, Ligue contre le Cancer, European action COST CM1105 (C. G.

Mimicking the chemistry of natural eumelanin synthesis: the ke sequence in polypeptides and in proteins allows for a specific control of nanosized functional polydopamine formation

The oxidation of dopamine and of other catecholamines leads to the formation of conformal films on the surface of all known materials and to the formation of a precipitate in solution. In some cases, it has been shown that the addition of additives in the dopamine solution, like certain surfactants or polymers, polyelectrolytes, and certain proteins, allows to get polydopamine nanoparticles of controlled size and the concomitant decrease, in an additive/dopamine dependent manner, in film formation on the surface of the reaction beaker. However, the mechanism behind this controlled oxidation and self-assembly of catecholamines is not known. In this article, it is shown that a specific diad of amino acids in proteins, namely KE, allows for specific control in the oxidation-self-assembly of dopamine to obtain polydopamine@protein core–shell nanoparticles which are biocompatible. The interactions between dopamine and the adjacent KE amino acids potentially responsible for the size control of polydopamine aggregates was investigated by molecular dynamics simulations. The obtained core– shell nanoparticles display the biological activity of the protein used to control the self- assembly of PDA. The photon to heat conversion ability of PDA is conserved in the PDA@protein particles

Sémantiques anciennes et médiévales du nom propre

Nous avons cherché à éclairer le statut ambigu du nom propre dans la logique ancienne et médiévale. Celui-ci apparaît à la fois comme un modèle d intelligibilité pour comprendre la capacité référentielle des noms et des propositions dans lesquelles ils entrent et un cas-limite pour une sémantique issue du Peri Hermeneias et de l interprétation néoplatonicienne des Catégories formatée pour les termes prédicables. Notre enquête comprend donc l analyse des noms d individus chez Aristote (Catégories, Métaphysique, Réfutations Sophistiques et Peri Hermeneias) et Porphyre (Partie I), sa réception chez Boèce (Partie II), et l étude de l émergence de la catégorie nom propre dans la grammaire grecque et latine à partir de son invention stoïcienne (Partie III). Elle s attache ensuite à suivre la résurgence de cette problématique au moment où s esquissent les conditions d émergence d une philosophie du langage ordinaire, dans la grammaire spéculative et chez Abélard (Partie IV), puis la systématisation des notions alors mises en œuvres dans les sommes de logique du premier terminisme (Partie V). On constate la nécessité d appliquer aux noms propres la définition grammaticale du propre du nom (signifier la substance et la qualité), et la sémantique triadique issue de Boèce (mot / concept-qualité signifié(e) / chose), qui assure à la fois l explication de son imposition et sa capacité à entrer dans une proposition à titre de terme, en même temps que l impossible isomorphisme sémantique entre tous les noms du fait de la valeur d universalité et de prédication attachée au signifié intermédiaire (concept / qualité) fondée en sous-main sur une métaphysique de la forme commune.We have tried an understanding of the ambiguous status of proper name in ancient and medieval logic. Proper name is both a paradigm for the referential power of words and propositions and a borderline case for a semantics founded in the Peri Hermeneias and the neoplatonic interpretation of the Categories , and so shaped for predicable terms. Our research included the analysis of individual names in Aristotle (Catégories, Metaphysics, Sophistical Refutations, Peri Hermeneias) and Porphyry (Part I), its reception in Boethius (Part II), and the study of the birth of proper name as part of speech, in Greek and Latin authors, from its invention in Ancient Stoicism (Part III). We then follow the transformation of this problematics when the conditions for the appearance of a philosophy of ordinary language tend to be satisfied, in speculative grammar and Abailard (Part IV), and study the systematic ordering of the notions then created in logic soms of the first terminism (Part V). We observe the necessity for applying to proper name the grammatical definition of the proper of name (signifying the substance and the quality) and the triadic semantics of Boethius (words / concepts-quality signified / things), which garanties both the explanation of its imposition and its ability to enter a proposition as its term, and the impossibility of a semantic isomorphism of names because of the universal and predicative value of the in-between significate founded (though not explicitly) to a metaphysics of common form.PARIS-EPHE-Sciences religieuses (751052336) / SudocSudocFranceF