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1.
J Org Chem ; 2020 Sep 10.
Artigo em Inglês | MEDLINE | ID: mdl-32907321

RESUMO

A straightforward approach to the synthesis of two different series of cationic [5]helicenes has been achieved including, in dioxa series, the possibility to introduce aromatic functional groups at the periphery of the helical structure. While photophysical study highlights that the introduction of aryl substituents at position 23 of the helical moieties has a negligible impact on the optical properties, styryl substituents allow a welcoming extension of the conjugation pathways. Finally, a red shift of the optical properties was evidenced upon introduction of nitrogen atoms in the helicene scaffold, leading to particularly good fluorescence efficiencies in the red domain for a helicenic dye. Detailed information on racemization kinetics was collected for the most stable species upon direct high-performance liquid chromatography (HPLC) resolution or, when configurational lability was too high, through VT-HPLC analysis on the chiral stationary phase (ΔG‡ values ranging from 85.0 to 137.1 kJ·mol-1 and above).

2.
J Am Chem Soc ; 2020 Sep 14.
Artigo em Inglês | MEDLINE | ID: mdl-32869987

RESUMO

Two complementary regiodivergent [(P,N)Ni]-catalyzed hydroalkylations of branched dienes are reported. When amides are employed as unstabilized C(sp3) nucleophiles, a highly regioselective 1,4-addition process is favored. The addition products are obtained in high yield and with excellent stereocontrol of the internal olefin. With use of a chiral ligand and imides as carbon nucleophiles, a 3,4-addition protocol was developed, enabling construction of two contiguous tertiary stereocenters in a single step with moderate to high levels of diastereocontrol and excellent enantiocontrol. Both methods operate under mild reaction conditions, display a broad scope, and show excellent functional group tolerance. The synthetic potential of the 3,4-hydroalkylation reaction was established via a series of postcatalytic modifications.

3.
Int J Pharm ; 589: 119783, 2020 Aug 19.
Artigo em Inglês | MEDLINE | ID: mdl-32827674

RESUMO

Osteoarthritis (OA), the most common form of arthritis, is characterized by chronic inflammation, degeneration of articular cartilage and whole joints. Local delivery by intra-articular (IA) injection of small molecules is an established treatment to relieve pain and improve joint motion, requiring month-lasting release of therapeutic drug doses. We incorporated anti-inflammatory drug celecoxib in poly (D, L-lactic acid) microparticles using two spray-drying approaches - either as a solid drug solution or embedded as milled nano drug. Differential scanning calorimetry, X-ray powder diffraction, electron microscopy and in vitro drug release allowed comparison of the microparticles. Both types resulted in spherical particles ranging from 20 to 40 µm mean size, with high drug loadings (10% to 50% w/w) and entrapment efficiencies > 80%. However, after 90 days, in vitro celecoxib release from nano drug embedded microparticles presented a significantly slower release in comparison to drug in solution microparticles, attributed to the presence of stabilized amorphous drug. No cytotoxicity was observed in human articular synoviocytes and PGE2 release was fully suppressed at low doses of both microparticulate systems. This study provides techniques to release high drug loads over months in a tunable manner, providing valuable options for the IA management of osteoarthritis.

4.
Org Biomol Chem ; 18(2): 250-254, 2020 01 02.
Artigo em Inglês | MEDLINE | ID: mdl-31808765

RESUMO

Double hydrothiolation of bis enol ether macrocycles was achieved under photo-mediated conditions. The thiol-ene reactions afford a fully regioselective anti-Markovnikov post-functionalization. Thanks to the use of ethanedithiol as reagent, moderate to excellent diastereoselectivity was accomplished leading to macrocycles containing four defined stereocenters in only three steps from 1,4-dioxane, tetrahydrofuran (THF) or tetrahydropyran (THP).

5.
Org Biomol Chem ; 17(28): 6905-6910, 2019 07 17.
Artigo em Inglês | MEDLINE | ID: mdl-31270519

RESUMO

The stereoselective synthesis of chiral macrocycles bearing two aliphatic amide functional groups is reported. After the amidation mediated by TBD, a guanidine derivative, the olefin transposition step is performed with a slight excess of t-BuOK. The products are afforded in moderate to good combined yields (up to 59%) and with an excellent syn diastereoselectivity (dr > 49 : 1). Introducing enantiopure α-branched substituents was possible and it resulted in mixtures of diastereomers, which could be tested as phase-transfer catalysts using the formation of a phenylalanine analog as a test reaction (up to 43% ee). A clear matched-mismatched situation was observed in the two diastereomeric series.

6.
Org Lett ; 21(3): 687-691, 2019 02 01.
Artigo em Inglês | MEDLINE | ID: mdl-30657690

RESUMO

Selective formation of oxonium ylides from morpholines and α-diazo-ß-ketoesters was achieved. This was applied to the high-concentration (0.5 M) dirhodium-catalyzed (0.1 mol %) [3 + 6 + 3 + 6] synthesis of 18-membered ring diaza macrocycles (46%-72%). Late-stage functionalization of these derivatives is demonstrated. Mechanistic evidence for a novel (undesired) diazo decomposition pathway is also reported.

7.
J Am Chem Soc ; 140(40): 12870-12876, 2018 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-30216056

RESUMO

The spin-crossover compound [Fe( n-Bu-im)3(tren)](PF6)2 shows an unusual long relaxation time of 20 h after light-induced excited spin state trapping when irradiating at 80 K. This is more than 40 times longer than when irradiating at 10 K. Optical absorption spectroscopy, magnetometry, and X-ray diffraction using synchrotron radiation were used to characterize and explain the different relaxation behaviors of this compound after irradiation below and above 70 K. Rearrangement of the butyl chains of the ligands occurring during the relaxation after irradiation above 70 K is thought to be responsible for the unusually long relaxation time at this temperature.

8.
Angew Chem Int Ed Engl ; 57(46): 15172-15176, 2018 Nov 12.
Artigo em Inglês | MEDLINE | ID: mdl-30265427

RESUMO

To date, the piling up of successive photons of low energies (near infrared; NIR) using a single lanthanide center and linear optics to ultimately produce upconverted visible emission was restricted to low-phonon solid materials and nanoparticles. Now we show that the tight helical wrapping of three terdentate N-donor ligands around a single nine-coordinate trivalent erbium cation provides favorable conditions for a mononuclear molecular complex to exhibit unprecedented related upconverted emission. Low power NIR laser excitations into the metal-centered transitions Er(4 I11/2 ←4 I15/2 ) at 801 nm or Er(4 I13/2 ←4 I15/2 ) at 966 nm result in upconverted blue-green emissions, where two or three photons respectively are successively absorbed by a molecular lanthanide complex possessing high-energy vibrations.

9.
Chemistry ; 24(63): 16873-16888, 2018 Nov 13.
Artigo em Inglês | MEDLINE | ID: mdl-30171722

RESUMO

Chelate coordination of non-symmetrical didentate pyrazine-benzimidazole (L1) or pyridine-benzimidazole (L2) N-donor ligands around divalent iron in acetonitrile produces stable homoleptic triple-helical spin crossover [Fe(Lk)3 ]2+ complexes existing as mixtures of meridional (C1 -symmetry) and facial (C3 -symmetry) isomers in slow exchange on the NMR timescale. The speciation deviates from the expected statistical ratio mer/fac=3:1, a trend assigned to the thermodynamic trans-influence, combined with solvation effects. Consequently, the observed spin state FeII low-spin ↔FeII high-spin equilibria occurring in [Fe(Lk)3 ]2+ refer to mixtures of complexes in solution, an issue usually not considered in this field, but which limits rational structure-properties correlations. Taking advantage of the selective and quantitative formation of isostructural facial isomers in non-constrained related spin crossover d-f helicates (HHH)-[LnFe(Lk)3 ]5+ (Ln is a trivalent lanthanide, Lk=L5, L6), we propose a novel strategy for assigning pertinent thermodynamic driving forces to each spin crossover triple-helical isomer. The different enthalpic contributions to the spin state equilibrium found in mer-[Fe(Lk)3 ]2+ and fac-[Fe(Lk)3 ]2+ reflect the Fe-N bond strengths dictated by the trans-influence, whereas a concomitant solvent-based entropic contribution reinforces the latter effect and results in systematic shifts of the spin crossover transitions toward higher temperature in the facial isomers.

10.
Chemistry ; 24(50): 13158-13169, 2018 Sep 06.
Artigo em Inglês | MEDLINE | ID: mdl-30016559

RESUMO

Intrigued by the unexpected room-temperature dual visible/near-infrared (NIR) luminescence observed for fast-relaxing erbium complexes embedded in triple-stranded helicates, in this contribution, we explore a series of six tridentate N-donor receptors L4-L9 with variable aromaticities and alkyl substituents to extricate the stereoelectronic features responsible for such scarce optical signatures. Detailed solid-state (X-ray diffraction, differential scanning calorimetry, optical spectroscopy) and solution (speciations and thermodynamic stabilities, spectrophotometry, NMR and optical spectroscopy) studies of mononuclear unsaturated [Er(Lk)2 ]3+ and saturated triple-helical [Er(Lk)3 ]3+ model complexes reveal that the stereoelectronic changes induced by the organic ligands affect inter- and intramolecular interactions to such an extent that 1) melting temperatures in solids, 2) the affinity for trivalent erbium in solution, and 3) optical properties in luminescent complexes can be rationally varied and controlled. With this toolkit in hand, mononuclear erbium complexes with low stabilities displaying only NIR emission can be transformed into molecular-based dual Er-centered visible/NIR emitters operating at room temperature in both solid and solution states.

11.
Phys Chem Chem Phys ; 20(18): 12493-12502, 2018 May 09.
Artigo em Inglês | MEDLINE | ID: mdl-29707721

RESUMO

The thermal spin transition of [Fe(pz)Pt(CN)4], pz = pyrazine, nanoparticles is compared with the one of the microcrystalline powder by magnetic susceptibility measurements, absorption spectroscopy and X-ray powder diffraction (XRPD) using synchrotron radiation. The thermal transition shows less cooperativity when decreasing the size due to the reduction of cluster formation. Surprisingly, the dispersion of the nanoparticles on a surface entails important effects on the spin crossover properties of the system. These effects are simulated and explained within the framework of the mechanoelastic model.

12.
Chem Sci ; 9(2): 325-335, 2018 Jan 14.
Artigo em Inglês | MEDLINE | ID: mdl-29629101

RESUMO

Metal-containing (bio)organic polymers are materials of continuously increasing importance for applications in energy storage and conversion, drug delivery, shape-memory items, supported catalysts, organic conductors and smart photonic devices. The embodiment of luminescent components provides a revolution in lighting and signaling with the ever-increasing development of polymeric light-emitting devices. Despite the unique properties expected from the introduction of optically and magnetically active lanthanides into organic polymers, the deficient control of the metal loading currently limits their design to empirical and poorly reproducible materials. We show here that the synthetic efforts required for producing soluble multi-site host systems Lk are largely overcome by the virtue of reversible thermodynamics for mastering the metal loading with the help of only two parameters: (1) the affinity of the luminescent lanthanide container for a single binding site and (2) the cooperative effect which modulates the successive fixation of metallic units to adjacent sites. When unsymmetrical perfluorobenzene-trifluoroacetylacetonate co-ligands (pbta-) are selected for balancing the charge of the trivalent lanthanide cations, Ln3+, in six-coordinate [Ln(pbta)3] containers, the explored anti-cooperative complexation processes induce nearest-neighbor intermetallic interactions twice as large as thermal energy at room temperature (RT = 2.5 kJ mol-1). These values have no precedent when using standard symmetrical containers and they pave the way for programming metal alternation in luminescent lanthanidopolymers.

13.
Dalton Trans ; 46(28): 8992-9009, 2017 Jul 18.
Artigo em Inglês | MEDLINE | ID: mdl-28653065

RESUMO

Compared to divalent ruthenium coordination complexes, which are widely exploited as parts of multi-component photonic devices, optically active trivalent chromium complexes are under-represented in multi-metallic supramolecular architectures performing energy conversion mainly because of the tricky preparation of stable heteroleptic CrIII building blocks. We herein propose some improvements with the synthesis of a novel family of kinetically inert heteroleptic bis-terdentate mononuclear complexes, which can be incorporated into dinuclear rod-like dyads as a proof-of-concept. The mechanism and magnitude of intermetallic CrCr communication have been unraveled by a combination of magnetic, photophysical and thermodynamic investigations. Alternated aromatic/alkyne connectors provided by Sonogashira coupling reactions emerge as the most efficient wires for long-distance communication between two chromium centres bridged by Janus-type back-to-back bis-terdentate receptors.

14.
Chemistry ; 23(36): 8678-8684, 2017 Jun 27.
Artigo em Inglês | MEDLINE | ID: mdl-28406541

RESUMO

In the context of Tröger base chemistry, regio- and stereoselective Csp3 -H azidation reactions are reported. Azide functional groups are introduced at either one or the two benzylic positions selectively. Mild conditions and good yields are afforded by the combination of TMSN3 and iodosobenzene PhIO. The process occurs with high enantiospecificity (es 96-99 %) and-interestingly and importantly-via bridgehead iminium intermediates as shown by mechanistic and in-silico studies. Finally, mono- and bistriazole derivatives were prepared in high yields and enantiospecificity by using copper-catalyzed alkyne azide cycloaddition (CuAAC) reactions; some of the products were used as anion-binding organocatalysts for the tritylation of amines and alcohols.

15.
Chemistry ; 23(29): 7104-7112, 2017 May 23.
Artigo em Inglês | MEDLINE | ID: mdl-28317198

RESUMO

The synthesis is reported of a series of homo- and hetero-dinuclear octahedral complexes of the ligand 1, 1,2-bis(1-methyl-benzimidazol-2-yl) ethanol, where the two metal centres are linked by hydrogen bonds between coordinated alcohols and coordinated alkoxides. Homonuclear divalent MII MII , mixed-valent MII MIII and heteronuclear MII M'III species are prepared. The complexes have been characterised by X-ray crystallography and show unusually short O⋅⋅⋅O distances for the hydrogen bonds. Magnetic measurements show the hydrogen-bond bridges can lead to ferromagnetic or antiferromagnetic coupling. The electrochemistry of the dinuclear species is significantly different from the mononuclear systems: the latter show irreversible waves in cyclic voltammograms as a result of the need to couple proton and electron transfer. The dinuclear species, in contrast, show reversible waves, which are attributed to rapid intramolecular proton transfer facilitated by the hydrogen-bonded structure.

16.
J Colloid Interface Sci ; 477: 166-75, 2016 Sep 01.
Artigo em Inglês | MEDLINE | ID: mdl-27267039

RESUMO

Organic molecules imprinting can be used for introducing specific properties and functionalities such as chirality to mesoporous materials. Particularly organic self-assemblies can work as a scaffold for templating inorganic materials such as silica. During recent years chiral imprinting of anionic surfactant for fabrication of twisted rod-like silica structures assisted by co-structuring directing agent were thoroughly investigated. The organic self-assemblies of anionic surfactants can also be used for introducing other shapes in rod-like silica structures. Here we report the formation of amphiphilic N-miristoyl-l-alanine self-assemblies in aqueous solution upon stirring and at presence of l-arginine. These anionic surfactant self-assemblies form fibers that grow by increasing the stirring duration. The fibers were studied using transmission electron microscopy, infra-red spectroscopy and vibrational circular dichroism. Addition of silica precursor 1,2-bis(triethoxysilyl)ethylene and co-structuring directing agent N-trimethoxysilylpropyl-N,N,N-trimethylammonium chloride at different stages of fibers' growth leads to formation of different silica structures. By controlling stirring duration, we obtained twisted tubular silica structures as a result of fibers encapsulation. We decorated these structures with gold nanoparticles by different methods and measured their optical activity.

17.
Inorg Chem ; 55(20): 9964-9972, 2016 Oct 17.
Artigo em Inglês | MEDLINE | ID: mdl-27203270

RESUMO

Considered at the beginning of the 21th century as being incompatible with the presence of closely bound high-energy oscillators, lanthanide-centered superexcitation, which is the raising of an already excited electron to an even higher level by excited-state energy absorption, is therefore a very active topic strictly limited to the statistical doping of low-phonon bulk solids and nanoparticles. We show here that molecular lanthanide-containing coordination complexes may be judiciously tuned to overcome these limitations and to induce near-infrared (NIR)-to-visible (VIS)-light upconversion via the successive absorption of two low-energy photons using linear-optical responses. Whereas single-ion-centered excited-state absorption mechanisms remain difficult to implement in lanthanide complexes, the skillful design of intramolecular intermetallic energy-transfer processes operating in multimetallic architectures is at the origin of the recent programming of erbium-centered molecular upconversion.

18.
Chemistry ; 22(24): 8113-23, 2016 06 06.
Artigo em Inglês | MEDLINE | ID: mdl-27142083

RESUMO

The basic concept of allosteric cooperativity used in biology, chemistry and physics states that any change in the intermolecular host-guest interactions operating in multisite receptors can be assigned to intersite interactions. Using lanthanide metals as guests and linear multi-tridentate linear oligomers of variable lengths and geometries as hosts, this work shows that the quantitative modeling of metal loadings requires the consideration of a novel phenomenon originating from solvation processes. It stepwise modulates the intrinsic affinity of each isolated site in multisite receptors, and this without resorting to allosteric cooperativity. An easy-to-handle additive model predicts a negative power law dependence of the intrinsic affinity on the length of the linear metallopolymer. Applied to lanthanidopolymers, the latter common analysis overestimates cooperativity factors by more than two orders of magnitude.

19.
Phys Chem Chem Phys ; 18(21): 14479-94, 2016 05 25.
Artigo em Inglês | MEDLINE | ID: mdl-27173940

RESUMO

Chemical programming of the temperature domains of existence of liquid crystals is greatly desired by both academic workers and industrial partners. This contribution proposes to combine empirical approaches, which rely on systematic chemical substitutions of mesogenic molecules followed by thermal characterizations, with a rational thermodynamic assessment of the effects induced by chemical perturbations. Taking into account the similarities which exist between temperature-dependent cohesive Gibbs free energy densities (CFEDs) and pressure-temperature phase diagrams modeled with the Clapeyron equation, chemical perturbations are considered as pressure increments along phase boundaries, which control the thermotropic liquid crystalline properties. Taking the familiar calamitic amphiphilic cyanobiphenyl-type mesogens as models, the consequences of (i) methyl substitution of the aromatic polar heads and (ii) connections of bulky silyl groups at the termini of the apolar flexible alkyl chain on the melting and clearing temperatures are quantitatively analyzed. Particular efforts were focused on the translation of the thermodynamic rationalization into a predictive tool accessible to synthetic chemists mainly interested in designing liquid crystals with specific technological applications.

20.
Chemistry ; 22(4): 1385-91, 2016 Jan 22.
Artigo em Inglês | MEDLINE | ID: mdl-26663074

RESUMO

This work illustrates how enthalpy and entropy changes responsible for successive phase transitions of cyanobiphenyl-based liquid crystals can be combined to give cohesive free energy densities. These new parameters are able to rationalize and quantify the demixing of the melting and clearing processes that occur in thermotropic liquid crystals. Minor structural variations at the molecular level can be understood as pressure increments that alter either the melting or clearing temperatures in a predictable way. This assessment of microsegregation operating in amphiphilic molecules paves the way for the chemical programming of the domain of existence of liquid-crystalline phases.

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