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1.
Soft Matter ; 16(11): 2795-2802, 2020 Mar 21.
Artigo em Inglês | MEDLINE | ID: mdl-32104828

RESUMO

Square planar platinum(ii) complexes are attractive building blocks for multifunctional soft materials due to their unique optoelectronic properties. However, for soft materials derived from synthetically simple discrete metal complexes, achieving a combination of optical properties, thermoresponsiveness and excellent mechanical properties is a major challenge. Here, we report the rapid self-recovery of luminescent metallogels derived from platinum(ii) complexes of perfluoroalkyl and alkyl derivatives of terpyridine ligands. Using single crystal X-ray diffraction studies, we show that the presence of synergistic platinum-platinum (PtPt) metallopolymerization and fluorine-fluorine (FF) interactions are the major driving forces in achieving hierarchical superstructures. The resulting bright red gels showed the presence of highly entangled three-dimensional networks and helical nanofibres with both (P and M) handedness. The gels recover up to 87% of their original storage modulus even after several cycles under oscillatory step-strain rheological measurements showing rapid self-healing. The luminescence properties, along with thermo- and mechanoresponsive gelation, provide the potential to utilize synthetically simple discrete complexes in advanced optical materials.

2.
Beilstein J Org Chem ; 15: 2486-2492, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-31728162

RESUMO

Pyridine[4]arenes have previously been considered as anion binding hosts due to the electron-poor nature of the pyridine ring. Herein, we demonstrate the encapsulation of Me4N+ cations inside a dimeric hydrogen-bonded pyridine[4]arene capsule, which contradicts with earlier assumptions. The complexation of a cationic guest inside the pyridine[4]arene dimer has been detected and studied by multiple gas-phase techniques, ESI-QTOF-MS, IRMPD, and DT-IMMS experiments, as well as DFT calculations. The comparison of classical resorcinarenes with pyridinearenes by MS and NMR experiments reveals clear differences in their host-guest chemistry and implies that cation encapsulation in pyridine[4]arene is an anion-driven process.

3.
Org Biomol Chem ; 17(29): 6980-6984, 2019 Jul 24.
Artigo em Inglês | MEDLINE | ID: mdl-31276147

RESUMO

Pyridinearene macrocycles have previously shown unique host-guest properties in their capsular dimers including endo complexation of neutral molecules and exo complexation of anions. Here, we demonstrate for the first time the formation of hydrogen bonded hexamer of tetraisobutyl-octahydroxypyridinearene in all three states of matter - gas phase, solution and solid-state. Cationic tris(bipyridine)ruthenium(ii) template was found to stabilize the hexamer in gas phase, whereas solvent molecules do this in condensed phases. In solution, the capsular hexamer was found to be the thermodynamically favoured self-assembly product and transition from dimer to hexamer occurred in course of time. The crystal structure of hexamer revealed 24 N-HO direct intermolecular hydrogen bonds between the six pyridinearene macrocycles without any bridging solvent molecules. Hydrogen bond patterns correlate well with DFT computed structures. Thus, all structural chemistry methods (IM-MS, DOSY NMR, DFT, X-ray crystallography) support the same structure of the hexameric capsule that has a diameter of ca. 3 nm and volume of 1160 Å3.

4.
Chem Asian J ; 14(5): 647-654, 2019 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-30644629

RESUMO

The anion-binding properties of three closely related oligoamide foldamers were studied using NMR spectroscopy, isothermal titration calorimetry and mass spectrometry, as well as DFT calculations. The 1 H NMR spectra of the foldamers in [D6 ]acetone solution revealed partial preorganization by intramolecular hydrogen bonding, which creates a suitable cavity for anion binding. The limited size of the cavity, however, enabled efficient binding by the inner amide protons only for the chloride anion resulting in the formation of a thermodynamically stable 1:1 complex. All 1:1 chloride complexes displayed a significant favourable contribution of the entropy term. Most likely, this is due to the release of ordered solvent molecules solvating the free foldamer and the anion to the bulk solution upon complex formation. The introduction of electron-withdrawing substituents in foldamers 2 and 3 had only a slight effect on the thermodynamic constants for chloride binding compared to the parent receptor. Remarkably, the binding of chloride to foldamer 3 not only produced the expected 1:1 complex but also open aggregates with 1:2 (host:anion) stoichiometry.

5.
J Am Chem Soc ; 140(39): 12396-12404, 2018 10 03.
Artigo em Inglês | MEDLINE | ID: mdl-30183281

RESUMO

Phytochrome proteins regulate many photoresponses of plants and microorganisms. Light absorption causes isomerization of the biliverdin chromophore, which triggers a series of structural changes to activate the signaling domains of the protein. However, the structural changes are elusive, and therefore the molecular mechanism of signal transduction remains poorly understood. Here, we apply two-color step-scan infrared spectroscopy to the bacteriophytochrome from Deinococcus radiodurans. We show by recordings in H2O and D2O that the hydrogen bonds to the biliverdin D-ring carbonyl become disordered in the first intermediate (Lumi-R) forming a dynamic microenvironment, then completely detach in the second intermediate (Meta-R), and finally reform in the signaling state (Pfr). The spectra reveal via isotope labeling that the refolding of the conserved "PHY-tongue" region occurs with the last transition between Meta-R and Pfr. Additional changes in the protein backbone are detected already within microseconds in Lumi-R. Aided by molecular dynamics simulations, we find that a strictly conserved salt bridge between an arginine of the PHY tongue and an aspartate of the chromophore binding domains is broken in Lumi-R and the arginine is recruited to the D-ring C═O. This rationalizes how isomerization of the chromophore is linked to the global structural rearrangement in the sensory receptor. Our findings advance the structural understanding of phytochrome photoactivation.


Assuntos
Biliverdina/química , Deinococcus/química , Fitocromo/química , Adenilil Ciclases/química , Adenilil Ciclases/metabolismo , Proteínas de Bactérias/química , Proteínas de Bactérias/metabolismo , Biliverdina/metabolismo , Deinococcus/metabolismo , Ligação de Hidrogênio , Simulação de Dinâmica Molecular , Processos Fotoquímicos , Fitocromo/metabolismo , Conformação Proteica em Folha beta , Espectroscopia de Infravermelho com Transformada de Fourier , Água/química
6.
Dalton Trans ; 46(39): 13582-13589, 2017 Oct 10.
Artigo em Inglês | MEDLINE | ID: mdl-28952629

RESUMO

The synthesis and structural characterization of two benzoquinone-bridged dinuclear rare-earth complexes [BQ(MCl2·THF3)2] (BQ = 2,5-bisoxide-1,4-benzoquinone; M = Y (1), Dy (2)) are described. Of these reported metal complexes, the dysprosium analogue 2 is the first discrete bridged dinuclear lanthanide complex in which both metal centres reside in pentagonal bipyramidal environments. Interestingly, both complexes undergo significant thermal expansion upon heating from 120 K to 293 K as illustrated by single-crystal X-ray and powder diffraction experiments. AC magnetic susceptibility measurements reveal that 2 does not show the slow relation of magnetization in zero dc field. The absent of single-molecule behaviour in 2 arises from the rotation of the principal magnetic axis as compared to the pseudo-C5 axis of the pentagonal bipyramidal environment as suggested by ab initio calculations. The cyclic voltammetry and chemical reduction experiments demonstrated that complexes 1 and 2 can be reduced to radical species containing [BQ3˙-]. This study establishes efficient synthetic strategy to make bridged redox-active multinuclear lanthanide complexes with a pentagonal bipyramidal coordination environment that are potential precursors for single-molecule magnets.

7.
Angew Chem Int Ed Engl ; 56(36): 10942-10946, 2017 08 28.
Artigo em Inglês | MEDLINE | ID: mdl-28665506

RESUMO

The formation of complexes between hexafluorophosphate (PF6- ) and tetraisobutyloctahydroxypyridine[4]arene has been thoroughly studied in the gas phase (ESI-QTOF-MS, IM-MS, DFT calculations), in the solid state (X-ray crystallography), and in chloroform solution (1 H, 19 F, and DOSY NMR spectroscopy). In all states of matter, simultaneous endo complexation of solvent molecules and exo complexation of a PF6- anion within a pyridine[4]arene dimer was observed. While similar ternary complexes are often observed in the solid state, this is a unique example of such behavior in the gas phase.

8.
Chem Sci ; 8(3): 2184-2190, 2017 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-28694954

RESUMO

A novel eight-membered macrocycle of the hemicucurbit[n]uril family, chiral (all-R)-cyclohexanohemicucurbit[8]uril (cycHC[8]) ‡The name cyclohexylhemicucurbituril, previously used for these macrocycles, is changed in accordance with the IUPAC nomenclature for fused cycles, as the cyclohexane substituents are fused with the parent hemicucurbituril. binds anions in a purely protic solvent with remarkable selectivity. The cycHC[8] portals open and close to fully encapsulate anions in a 1 : 1 ratio, resembling a molecular Pac-Man™. Comprehensive gas, solution and solid phase studies prove that the binding is governed by the size, shape and charge distribution of the bound anion. Gas phase studies show an order of SbF6- ≈ PF6- > ReO4- > ClO4- > SCN- > BF4- > HSO4- > CF3SO3- for anion complexation strength. An extensive crystallographic study reveals the preferred orientations of the anions within the octahedral cavity of cycHC[8] and highlights the importance of the size- and shape-matching between the anion and the receptor cavity. The solution studies show the strongest binding of the ideally fitting SbF6- anion, with an association constant of 2.5 × 105 M-1 in pure methanol. The symmetric, receptor cavity-matching charge distribution of the anions results in drastically stronger binding than in the case of anions with asymmetric charge distribution. Isothermal titration calorimetry (ITC) reveals the complexation to be exothermic and enthalpy-driven. The DFT calculations and VT-NMR studies confirmed that the complexation proceeds through a pre-complex formation while the exchange of methanol solvent with the anion is the rate-limiting step. The octameric cycHC[8] offers a unique example of template-controlled design of an electroneutral host for binding large anions in a competitive polar solvent.

9.
Chemistry ; 23(48): 11714-11718, 2017 Aug 25.
Artigo em Inglês | MEDLINE | ID: mdl-28631856

RESUMO

Tripodal N-donor ligands are used to form halogen-bonded assemblies via structurally analogous Ag+ -complexes. Selective formation of discrete tetrameric I6 L4 and dimeric I3 L2 halonium cages, wherein multiple [N⋅⋅⋅I+ ⋅⋅⋅N] halogen bonds are used in concert, can be achieved by using sterically rigidified cationic tris(1-methyl-1-azonia-4-azabicyclo[2.2.2]octane)-mesitylene ligand, L1(PF6 )3 , and flexible ligand 1,3,5-tris(imidazole-1-ylmethyl)-2,4,6-trimethylbenzene, L2, respectively. The iodonium cages, I6 L14 (PF6 )18 and I3 L22 (PF6 )3 , were obtained through the [N⋅⋅⋅Ag+ ⋅⋅⋅N]→ [N⋅⋅⋅I+ ⋅⋅⋅N] cation exchange reaction between the corresponding Ag6 L14 (PF6 )18 and Ag3 L22 (PF6 )3 coordination cages, prepared as intermediates, and I2 . The synthesized metallo- and halonium cages were studied in solution by NMR, in gas phase by ESI-MS and in the solid-state by single crystal X-ray diffraction.

10.
J Org Chem ; 82(10): 5198-5203, 2017 05 19.
Artigo em Inglês | MEDLINE | ID: mdl-28452495

RESUMO

Three water-soluble N-alkyl ammonium resorcinarene chlorides decorated with terminal hydroxyl groups at the lower rims were synthesized and characterized. The receptors were decorated at the upper rim with either terminal hydroxyl, rigid cyclohexyl, or flexible benzyl groups. The binding affinities of these receptors toward three viologen derivatives, two of which possess an acetylmethyl group attached to one of the pyridine nitrogens, in water were investigated via 1H NMR spectroscopy, fluorescence spectroscopy, and isothermal titration calorimetry (ITC). ITC quantification of the binding process gave association constants of up to 103 M-1. Analyses reveal a spontaneous binding process which are all exothermic and are both enthalpy and entropy driven.

11.
Chemistry ; 22(40): 14264-72, 2016 Sep 26.
Artigo em Inglês | MEDLINE | ID: mdl-27514501

RESUMO

Synthesis and ion-pair complexation properties of novel ditopic bis-urea receptors based on dibenzo[21]crown-7 (R(1) ) and dibenzo[24]crown-8 (R(2) ) scaffolds have been studied in the solid state, solution, and gas phase. In a 4:1 CDCl3 /[D6 ]DMSO solution, both receptors clearly show positive heterotropic cooperativity toward halide anions when complexed with Rb(+) or Cs(+) , with the halide affinity increasing in order I(-)

12.
Chem Commun (Camb) ; 52(52): 8115-8, 2016 Jun 21.
Artigo em Inglês | MEDLINE | ID: mdl-27272024

RESUMO

Mono- and tetra-deprotonated 2-methylresorcinarene anions ( and ) as their trans-1,4-diammoniumcyclohexane inclusion complexes are reported. The mono-anion forms a fully closed dimeric capsule [·H2O·MeOH]2(2-) with a cavity volume of 165 Å(3) and as the guest with an extremely high packing coefficient, PC = 84.2%, while the tetra-anion forms a close-packed structure with two structurally isomeric tetra-anions and with a 50 : 50 ratio in the crystal lattice.

13.
Angew Chem Int Ed Engl ; 54(51): 15462-7, 2015 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-26530790

RESUMO

Large, non-symmetrical, inherently chiral bispyridyl ligand L derived from natural ursodeoxycholic bile acid was used for square-planar coordination of tetravalent Pd(II) , yielding the cationic single enantiomer of superchiral coordination complex 1 Pd3 L6 containing 60 well-defined chiral centers in its flower-like structure. Complex 1 can readily be transformed by addition of chloride into a smaller enantiomerically pure cyclic trimer 2 Pd3 L3 Cl6 containing 30 chiral centers. This transformation is reversible and can be restored by the addition of silver cations. Furthermore, a mixture of two constitutional isomers of trimer, 2 and 2', and dimer, 3 and 3', can be obtained directly from L by its coordination to trans- or cis-N-pyridyl-coordinating Pd(II) . These intriguing, water-resistant, stable supramolecular assemblies have been thoroughly described by (1) H DOSY NMR, mass spectrometry, circular dichroism, molecular modelling, and drift tube ion-mobility mass spectrometry.

14.
Angew Chem Int Ed Engl ; 54(49): 14890-3, 2015 Dec 01.
Artigo em Inglês | MEDLINE | ID: mdl-26457686

RESUMO

A highly electron-deficient C3-symmetric tris(bipyridyl) ligand was prepared in four steps and used for the coordination of Fe(OTf)2, thereby resulting in the homochiral assembly of a new family of robust tetrahedral M4L4 cages. This homochiral T-symmetric cage containing a relatively large cavity of 330 Å(3) is capable of encapsulating an anionic guest, as was determined by mass spectrometry, (19)F NMR spectroscopy, and finally shown from its crystal structure. Moreover, crystallization of the cage from CH3CN led to crystals containing both (ΔΔΔΔ and ΛΛΛΛ) enantiomers, while crystallization from CH3 OH resulted in crystals containing only the right-handed (ΔΔΔΔ) cage. The difference in the crystal packing of the two crystal structures is discussed and a feasible explanation for the unique phenomenon among supramolecular cages--spontaneous resolution--is given.

15.
Nanoscale ; 7(40): 17012-9, 2015 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-26415984

RESUMO

The location of the Pd atoms in Pd2Au36(SC2H4Ph)24, is studied both experimentally and theoretically. X-ray photoelectron spectroscopy (XPS) indicates oxidized Pd atoms. Palladium K-edge extended X-ray absorption fine-structure (EXAFS) data clearly show Pd-S bonds, which is supported by far infrared spectroscopy and by comparing theoretical EXAFS spectra in R space and circular dichroism spectra of the staple, surface and core doped structures with experimental spectra.

16.
Inorg Chem ; 54(18): 9154-65, 2015 Sep 21.
Artigo em Inglês | MEDLINE | ID: mdl-26335947

RESUMO

A simple 18-crown-6-based bis-urea receptor R(1) was synthesized in three steps from a commercial starting material. The receptor's behavior toward anions, cations, and ion pairs was studied in solution with (1)H NMR, in solid state with single-crystal X-ray diffraction, and in gas phase with mass spectrometry. In 4:1 CDCl3/dimethyl sulfoxide solution the receptor's binding preference of halide anions is I(-) < Br(-) < Cl(-) following the trend of the hydrogen-bonding acceptor ability of the anions. The receptor shows a remarkable positive cooperativity toward halide anions Cl(-), Br(-), and I(-) when complexed with Na(+), K(+), or Rb(+). The solid-state binding modes of R(1) with alkali and ammonium halides or oxyanions were confirmed by the X-ray structures of R(1) with KF, KCl, KBr, KI, RbCl, NH4Cl, NH4Br, KAcO, K2CO3, and K2SO4. They clearly present two different binding modes, either as separated or contact ion pairs depending on the nature and size of the bound cation and anion. Complexation capability of R(1) in the gas phase was studied with competition experiments with electrospray ionization mass spectrometry showing preference of KCl complexation over NaCl, KBr, or KI supporting the results obtained in solution.

17.
Inorg Chem ; 54(12): 6055-61, 2015 Jun 15.
Artigo em Inglês | MEDLINE | ID: mdl-26039343

RESUMO

A novel modular approach to electron-deficient and electron-rich M6L4 cages is presented. From the same starting compound, via a minor modulation of the synthesis route, two C3-symmetric ligands L1 and L2 with different electronic properties are obtained in good yield. The trifluoro-triethynylbenzene-based ligand L1 is more electron-deficient than the well-known 2,4,6-tri(4-pyridyl)-1,3,5-triazine, while the trimethoxy-triethynylbenzene-based ligand L2 is more electron-rich than the corresponding benzene analogue. Complexation of the ligands with cis-protected square-planar [(dppp)Pt(OTf)2] or [(dppp)Pd(OTf)2] corner-complexes yields two electron-deficient (1a and 1b) and two electron-rich (2a and 2b) M6L4 cages. The single crystal X-ray diffraction study of 1a and 2a confirms the expected octahedral shape with a ca. 2000 Å(3) cavity and ca. 11 Å wide apertures. The crystallographically determined diameters of 1a and 2a are 3.7 and 3.6 nm, respectively. The hydrodynamic diameters obtained from the DOSY NMR in CDCl3:CD3OD (4:1), and diameters calculated from collision cross sections (CCS) acquired by ion-mobility mass spectrometry (IM-MS) were for all four cages similar. In solution, the cage structures have diameters between 3.3 to 3.6 nm, while in the gas phase the corresponding diameters varied between 3.4 to 3.6 nm. In addition to the structural information the relative stabilities of the Pt6L4 and Pd6L4 cages were studied in the gas phase by collision-induced dissociation (CID) experiments, and the photophysical properties of the ligands L1 and L2 and cages 1a, 1b, 2a, and 2b were studied by UV-vis and fluorescence spectroscopy.

18.
Steroids ; 97: 54-61, 2015 May.
Artigo em Inglês | MEDLINE | ID: mdl-25448361

RESUMO

The synthesis and gelation properties of a picolinic acid conjugated bile acid derivative in the presence of metal salts along with the stimuli-responsiveness of the systems are reported. The gels are formed in the presence of Cu(2+) ions in the solvent systems composed of 30-50% of organic solvent (MeOH, acetonitrile, or acetone) in water. The gels respond to various stimuli: they can be formed upon sonication or shaking, and their gel-sol transformation can be triggered by a variety of chemical species. NMR, MS, and SEM techniques are exploited in order to gain a deeper insight on the self-assembled systems.


Assuntos
Amidas/síntese química , Ácidos e Sais Biliares/química , Cobre/química , Géis/síntese química , Amidas/química , Géis/química , Estrutura Molecular , Ácidos Picolínicos/química
19.
Dalton Trans ; 44(1): 254-67, 2015 Jan 07.
Artigo em Inglês | MEDLINE | ID: mdl-25373423

RESUMO

A new fluorescent terpyridyl-diphenylacetylene hybrid fluorophore 4'-[4-{(4-methoxyphenyl)ethynyl}phenyl]-2,2':6',2''-terpyridine, L, was synthesized via Sonogashira cross-coupling of 4'-(4-bromophenyl)-2,2':6',2''-terpyridine and 4-ethynylanisole in the presence of Pd(PPh3)4/CuI as a catalyst. The solid state structure of L shows a trans arrangement of pyridine nitrogen atoms along the interannular bond in the terpyridine domain. Five transition metal complexes of L, {[FeL2](CF3SO3)2 (1), [ZnL2](ClO4)2 (2), [CdL2](ClO4)2 (3), [RuL2](PF6)2 (4), and PtMe3IL (5)}, have also been synthesized and characterized by spectroscopic methods and single crystal X-ray analysis. The X-ray crystal structures of complexes 1-3 show a distorted octahedral MN6 arrangement with tridentate coordination of the two terpyridine ligands, whereas in complex 5 the ligand L binds in a bidentate fashion. The ligand L displays bright blue emission in the solid state and in both non-polar and polar organic media. The fluorescence quantum yield of L is exceptionally high for a monoterpyridine ligand of its kind, which can be rationalized with density functional theory calculations. The electronic structure of L shows that the fluorescence involves intramolecular charge transfer from the diphenylacetylene moiety to the terpyridine group, and it is not affected by the usual non-radiative relaxation processes such as pyridine rotation. The Fe(II), Ru(II) and Pt(IV) complexes of L were found to be non-emissive, whereas both Zn(II) and Cd(II) complexes displayed significant green emission attributed to intra-ligand charge transfer states. These results were supported by the observed red-shift of the emission maxima of complexes 2 and 3 with increasing the solvent polarity.

20.
J Phys Chem Lett ; 5(3): 585-9, 2014 Feb 06.
Artigo em Inglês | MEDLINE | ID: mdl-26276613

RESUMO

Although various complex, bulky ligands have been used to functionalize plasmonic gold nanoparticles, introducing them to small, atomically precise gold clusters is not trivial. Here, we demonstrate a simple one-pot procedure to synthesize fluorescent magic number Au25 clusters carrying controlled amounts of bulky calix[4]arene functionalities. These clusters are obtained from a synthesis feed containing binary mixtures of tetrathiolated calix[4]arene and 1-butanethiol. By systematic variation of the molar ratio of ligands, clusters carrying one to eight calixarene moieties were obtained. Structural characterization reveals unexpected binding of the calix[4]arenes to the Au25 cluster surface with two or four thiolates per moiety.

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