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1.
Anal Bioanal Chem ; 412(17): 4195-4207, 2020 Jul.
Artigo em Inglês | MEDLINE | ID: mdl-32377866

RESUMO

To mimic the activity of hyaluronidase in natural environment, the hydrolysis of hyaluronic acid (HA) by hyaluronidase was investigated for the first time in the presence of crowding agents using capillary electrophoresis (CE) as a simple and reliable technique for conducting enzymatic assay. Polyethylene glycol (PEG) 6000 was selected as a model crowder and the hyaluronic acid degradation catalyzed by bovine testes hyaluronidase (BTH) was carried out at different PEG concentrations (0%, 10%, and 17%). After optimization of the CE analytical method and enzymatic assay, the degradation products were monitored at different HA concentrations. At 10% of PEG and 0.3 mg mL-1 of HA, the activity of the enzyme was significantly reduced showing inconvenient interactions of PEG with the hyaluronidase blocking the release of hydrolysis products. A similar reduction of hyaluronidase activity was observed at 1 mg mL-1 of HA due to the presumable formation of the BTH-substrate complex. The experimental curves obtained by CE also evidence that the overall kinetics are governed by the hydrolysis of hexasaccharide intermediates. Finally, the effect of PEG on hyaluronidase activity was evaluated in the presence of natural or synthetic inhibitors. Our results show a significant difference of the inhibitors' affinity toward hyaluronidase in the presence of PEG. Surprisingly, the presence of the crowding agent results in a loss of the inhibition effect of small polycyclic inhibitors, while larger charged inhibitors were less affected. In this work, CE analyses confirm the importance of mimicking the cellular environment for the discovery and development of reliable inhibitors. Graphical abstract.

2.
J Phys Chem B ; 124(5): 727-734, 2020 02 06.
Artigo em Inglês | MEDLINE | ID: mdl-31917571

RESUMO

The cell is an extremely complex environment, notably highly crowded, segmented, and confining. Overall, there is overwhelming and ever-growing evidence that to understand how biochemical reactions proceed in vivo, one cannot separate the biochemical actors from their environment. Effects such as excluded volume, obstructed diffusion, weak nonspecific interactions, and fluctuations all team up to steer biochemical reactions often very far from what is observed in ideal conditions. In this paper, we use Ficoll PM70 and PEG 6000 to build an artificial crowded milieu of controlled composition and density in order to assess how such environments influence the biocatalytic activity of lactate dehydrogenase (LDH). Our measurements show that the normalized apparent affinity and maximum velocity decrease in the same fashion, a behavior reminiscent of uncompetitive inhibition, with PEG resulting in the largest reduction. In line with previous studies on other enzymes of the same family, and in agreement with the known role of a surface loop involved in enzyme isomerization and regulation of access to the active site, we suggest that the crowding matrix interferes with the conformational ensemble of the enzyme. This likely results in both impaired enzyme-complex isomerization and thwarted product release. Molecular dynamics simulations confirm that excluded-volume effects lead to an entropic force that effectively tends to push the loop closed, thereby effectively shifting the conformational ensemble of the enzyme in favor of a more stable complex isoform. Overall, our study substantiates the idea that most biochemical kinetics cannot be fully explained without including the subtle action of the environment where they take place naturally, in particular accounting for important factors such as excluded-volume effects and also weak nonspecific interactions when present, confinement, and fluctuations.

3.
Inorg Chem ; 56(5): 2742-2749, 2017 Mar 06.
Artigo em Inglês | MEDLINE | ID: mdl-28211688

RESUMO

In this Article, we report the self-assembly of lanthanide complexes formed with two new tripodal ligands, L2 and L3, where binding strands are connected to a rigid triptycene anchor. The pyridine moieties are functionalized with methoxy and PEG groups to enhance ligand solubility and to evaluate the effect of these substituents on lanthanide coordination. These ligands were successfully synthesized and characterized, and their coordination properties were examined along the lanthanide series through speciation studies with NMR and ESI-MS. Well-defined tetranuclear complexes are formed with both ligands, but their stabilities with heavier lanthanides are considerably reduced, especially for complexes with L3. This is attributed to a destabilizing effect of pending PEG arms in combination with increased steric hindrance between binding strands upon complexation with smaller cations. The sensitization of lanthanide luminescence in tetranuclear complexes occurs despite one water molecule being coordinated to a metal ion.

4.
Chemistry ; 21(18): 6695-9, 2015 Apr 27.
Artigo em Inglês | MEDLINE | ID: mdl-25765709

RESUMO

Herein, we report on the rational design, preparation and characterization of a novel homo-octanuclear helicate, which results from a spatial extension of the central tetranuclear platform. The 3D supramolecular assembly is obtained by complexing europium(III) with a new hexatopic tripodal ligand. The isolated octanuclear helicate is fully characterized by different methods clearly evidencing the structure predicted with molecular modelling. The ligand preorganization plays a crucial role in a successful self-assembly process and induces the formation of a well-defined triple-stranded helical structure. This prototypal octanuclear edifice accommodating functional lanthanides within a 3D scaffold offers attractive perspectives for further applications.

5.
Dalton Trans ; 41(22): 6777-82, 2012 Jun 14.
Artigo em Inglês | MEDLINE | ID: mdl-22523756

RESUMO

A new tripodal ligand has been designed by coupling pyridyldicarbonyl binding strands with a triazatriangulenium platform (TATA). The complexation reaction with europium provides a C(3)-symmetrical mononuclear compound that is characterized with NMR, ESMS and qualitatively with single-crystal X-ray crystallography. In addition, photophysical studies of this dual emissive system have been performed, since the combination of the TATA fluorophore with trivalent lanthanides is of potential interest for the further development of imaging applications.


Assuntos
Acridinas/química , Corantes/química , Európio/química , Compostos Heterocíclicos de 4 ou mais Anéis/química , Compostos Organometálicos/química , Cristalografia por Raios X , Medições Luminescentes , Modelos Moleculares , Conformação Molecular , Compostos Organometálicos/síntese química , Espectrofotometria
6.
Dalton Trans ; 41(16): 4817-23, 2012 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-22392102

RESUMO

This contribution investigates Ln(III) complexes formed with a small ditopic ligand, L1, and their structural, thermodynamic and photophysical properties. The spectrophotometric and NMR titrations evidence the triangular assemblies [Ln(3)(L1-H)(3)](6+) at stoichiometric conditions and their properties are discussed in relation to L2-containing analogues. In addition, the dinuclear species, [Ln(2)(L1-H)](5+), is observed with an excess of metal.

7.
Chem Commun (Camb) ; 48(9): 1281-3, 2012 Jan 30.
Artigo em Inglês | MEDLINE | ID: mdl-22179299

RESUMO

A new tripodal ligand has been designed by connecting pyridine-based coordination units to a rigid triptycene moiety. Its reaction with europium(III) provides three-dimensional tetranuclear edifices, whose structural and photophysical characteristics as well as host-guest interactions are discussed in this contribution.

8.
J Org Chem ; 76(21): 9081-5, 2011 Nov 04.
Artigo em Inglês | MEDLINE | ID: mdl-21995637

RESUMO

A propeller-shaped boron-nitrogen compound (NB(3)) with three binding sites for fluoride anions was synthesized and investigated by optical absorption, luminescence, and ((1)H, (11)B, (13)C, (19)F) NMR spectroscopy. Binding of fluoride in dichloromethane solution occurs in three clearly identifiable steps and leads to stepwise blocking of the three initially present nitrogen-to-boron charge transfer pathways. As a consequence, the initially bright blue charge transfer emission is red-shifted and decreases in intensity, until it is quenched completely in presence of large fluoride excess. Fluoride binding constants were determined from global fits to optical absorption and luminescence titration data and were found to be K(a1) = 4 × 10(7) M(-1), K(a2) = 2.5 × 10(6) M(-1), and K(a3) = 3.2 × 10(4) M(-1) in room temperature dichloromethane solution. Complexation of fluoride to a given dimesitylboryl site increases the electron density at the central nitrogen atom of NB(3), and this leads to red shifts of the remaining nitrogen-to-boron charge transfer transitions involving yet unfluorinated dimesitylboryl groups.

9.
Acta Crystallogr Sect E Struct Rep Online ; 67(Pt 7): m968-9, 2011 Jul 01.
Artigo em Inglês | MEDLINE | ID: mdl-21836945

RESUMO

In the title compound, [Tb(C(7)H(4)NO(4))(3)]·2.75H(2)O, the Tb(3+) atom is coordinated by three tridentate 6-carb-oxy-pyridine-2-carboxyl-ate ligands and lies on a crystallographic threefold rotation axis. The coordination polyhedron around Tb(III) adopts a distorted tricapped trigonal-prismatic geometry. Disordered water mol-ecules with partial occupancy are also present in the crystal, one of which is associated with each of the carboxyl-ate O atoms of the complex unit.

10.
Inorg Chem ; 50(17): 8588-97, 2011 Sep 05.
Artigo em Inglês | MEDLINE | ID: mdl-21797240

RESUMO

The structure and thermodynamic properties of lanthanide complexes with a new tripodal ligand L2 have been elucidated using different physicochemical methods. At stoichiometric ratios, the tetrahedral three-dimensional complexes with lanthanide cations are formed in acetonitrile with good stabilities. Despite minor structural changes comparing to previously investigated tripodal ligands, the resulting assembly exhibits different features revealed with the crystal structure of [Eu(4)L2(4)](OH)(ClO(4))(11) (orthorhombic, Pbcn). Interestingly, the highly charged edifice contains an inner cage encapsulating a perchlorate anion. Such lanthanide mediated cage-like assemblies are rare, and may be of interest for different sensing applications. Indeed, the anionic guest can be exchanged with different anions. The related host-guest equilibria were investigated with NMR techniques. Various aspects of these reactions are qualitatively discussed.

11.
J Am Chem Soc ; 133(28): 10764-7, 2011 Jul 20.
Artigo em Inglês | MEDLINE | ID: mdl-21688784

RESUMO

The self-assembly of the first pentanuclear helicate was predicted on the structural basis obtained for linear and tetranuclear parent supramolecular compounds. Accordingly, the designed ternary supramolecular system requires appropriate polytopic organic receptors, which were successfully synthesized. Indeed, the formation of pentanuclear complexes was experimentally evidenced with NMR and ESMS spectra that perfectly reflect the expected pattern. The structural features in the europium pentanuclear complex are highlighted with semiempirical molecular modeling. The present work validates the combinatorial approach leading to the thermodynamically driven formation of tower-like pentanuclear edifices.

12.
Chemistry ; 17(24): 6753-64, 2011 Jun 06.
Artigo em Inglês | MEDLINE | ID: mdl-21547967

RESUMO

Self-assembly processes between a tripodal ligand and Ln(III) cations have been investigated by means of supramolecular analytical methods. At an equimolar ratio of components, tetranuclear tetrahedral complexes are readily formed in acetonitrile. The structural analysis of the crystallographic data shows a helical wrapping of binding strands around metallic cations. The properties of this series of highly charged 3D compounds were examined by using NMR spectroscopy and optical methods in solution and in the solid state. In the presence of excess metal, a new trinuclear complex was identified. The X-ray crystal structure elucidated the coordination of metallic cations with two ligands of different conformations. By varying the metal/ligand ratio, a global speciation of this supramolecular system has been evidenced with different spectroscopic methods. In addition, these rather complicated equilibria were successfully characterised with the thermodynamic stability constants. A rational analysis of the self-assembly processes was attempted by using the thermodynamic free energy model and the impact of the ligand structure on the effective concentration is discussed.

13.
Dalton Trans ; 40(16): 4284-90, 2011 Apr 28.
Artigo em Inglês | MEDLINE | ID: mdl-21394331

RESUMO

The self-assembly of a carbonylpyridine-based heptadentate ligand with Ln(III) results in the formation of triangular trinuclear europium complexes, which exhibit interesting luminescent properties in the solid state and in solution. With a view to developing multimodal responsive systems, we report here the preparation and characterisation of analogous complexes with Gd(III). The X-ray crystal structure of Gd(3)L2(3) indeed reveals the isostructurality with the Eu(III) complexes. A combination of (1)H NMRD and variable temperature studies yields the parameters elucidating the exchange of coordinated water and relaxivity properties. Conveniently, the competitive spectrophotometric titrations with EDTA and NTA are used to determine the thermodynamic stability constants of the europium complexes in aqueous media. In addition, the exchange reaction with EDTA is monitored with NMR and fluorimetry. The interactions of the Eu(III) trinuclear complex with some potentially interfering ligands are qualitatively investigated by means of luminescence titrations.


Assuntos
Elementos da Série dos Lantanídeos/química , Ácidos Carboxílicos/química , Cristalografia por Raios X , Ácido Edético/química , Espectroscopia de Ressonância Magnética , Magnetismo , Modelos Moleculares , Conformação Molecular , Termodinâmica
14.
Inorg Chem ; 49(2): 606-15, 2010 Jan 18.
Artigo em Inglês | MEDLINE | ID: mdl-20020694

RESUMO

Two tridentate and one bidentate binding strands have been anchored on a carbon atom to provide a new unsymmetrical tripodal ligand L for Ln(III) coordination. The ligand itself adopts a single conformation in solution stabilized by intramolecular hydrogen bonds evidenced in the solid state. The reaction of L with trivalent lanthanides provides different coordination complexes depending on the metal/ligand ratio. The speciation studies with selected lanthanides were performed in solution by means of NMR, ESMS, and spectrophotometric titrations. Differences in coordination properties along the lanthanide series were evidenced and may be associated with the changes in the ionic size. However, thermodynamic stability constants for the species of the same stoichiometry do not significantly vary. In addition, the structure of the dinuclear complex [Eu(2)L(2)](6+) has been elucidated in the solid state, where the complex crystallizes predominantly as an M-isomer. The crystal structure shows the coordination of two different ligands to each europium cation through tridentate strands, and the europium nine-coordinate sphere is completed with three solvent molecules. Finally, the results of photophysical investigations of [Eu(2)L(2)](6+) are in close agreement with the structural parameters determined by crystallography.

15.
Chemistry ; 15(14): 3355-8, 2009.
Artigo em Inglês | MEDLINE | ID: mdl-19235190

RESUMO

Triangular luminescent box: Self-assembly of a new multidentate receptor with europium cations results in the formation of trinuclear discrete complexes. X-ray crystallography shows that nine-coordinate cations are linked by ligands to provide a triangular complex in the solid state and in solution. Despite the coordinated solvent molecules, this topologically unusual complex exhibits remarkable luminescent properties.


Assuntos
Európio/química , Substâncias Luminescentes/química , Compostos Organometálicos/química , Cátions/química , Cristalografia por Raios X , Substâncias Luminescentes/efeitos da radiação
16.
Chemistry ; 14(10): 2994-3005, 2008.
Artigo em Inglês | MEDLINE | ID: mdl-18293346

RESUMO

The contribution of the solvation energies to the assembly of polynuclear helicates reduces the free energy of intermetallic repulsion, DeltaE(MM), in condensed phase to such an extent that stable D(3)-symmetrical tetranuclear lanthanide-containing triple-stranded helicates [Ln(4)(L4)(3)](12+) are quantitatively produced at millimolar concentrations, despite the twelve positive charge borne by these complexes. A detailed modelling of the formation constants using statistical factors, adapted to self-assembly processes involving intra- and intermolecular connections, provides a set of five microscopic parameters, which can be successfully used for rationalizing the stepwise generation of linear bi-, tri- and tetranuclear analogues. Photophysical studies of [Eu(4)(L4)(3)](12+) confirm the existence of two different binding sites producing differentiated metal-centred emission at low temperature, which transforms into single site luminescence at room temperature because of intramolecular energy funelling processes.

18.
J Phys Chem B ; 111(42): 12195-203, 2007 Oct 25.
Artigo em Inglês | MEDLINE | ID: mdl-17918883

RESUMO

Evaluation of statistical factors in self-assembly processes is not a firmly settled question. As a contribution to solve this problem, a critical re-examination of the symmetry number method and generalization of the direct count method are presented. The two approaches, producing the same results, mutually reinforce their role with respect to other discordant methods whose results cannot be independently checked. The direct count method moreover serves as a rationale for the apparently odd results the symmetry number method sometimes provides. The two methods thus turn out to be complementary to each other. Discussion of some exemplary cases points to the importance and subtlety of the role played by the geometrical features of assemblies involving intramolecular bonds.


Assuntos
Modelos Biológicos , Modelos Químicos , Interpretação Estatística de Dados , Cinética , Modelos Moleculares
19.
Inorg Chem ; 46(22): 9312-22, 2007 Oct 29.
Artigo em Inglês | MEDLINE | ID: mdl-17915861

RESUMO

Statistical mechanics predicts that the design of pure organized heteropolymetallic chains of metal ions bound to linear receptors depends on controlled deviations from the mixing rule DeltaE(MiMj) = 1/2 (DeltaE(MiMi) + DeltaE(MjMj)), whereby DeltaE(MiMj) is the intramolecular intermetallic interaction between neighboring metal i and metal j along the receptor. A thorough investigation of linear polymetallic trivalent lanthanide triple-stranded helicates shows that such deviations are amplified by an increase in the nuclearity of the final complexes and are thus easily evidenced in the tetranuclear heterobimetallic helicates [La(4-y)Lu(y)(L6)3](12+) (y = 0-4). The chemical and physical origins of this unprecedented behavior are discussed together with its practical consequences for programming pure heteropolymetallic 4f-4f complexes.

20.
J Phys Chem B ; 110(15): 7783-92, 2006 Apr 20.
Artigo em Inglês | MEDLINE | ID: mdl-16610874

RESUMO

A graphical method has been developed for the reliable detection of cooperativity in polymetallic complexes involving intra- and intermolecular complexation processes. The method relies on the determination of the partial occupancy r(AL)n, which represents the average number of metals bound per preassembled receptor AL(n) made up of n ligands bound to a linker A. We observe nonlinear, i.e., nonstatistical, Scatchard-like plots (r(AL)n/[M] vs r(AL)n) for metal-binding in double-stranded helicates. The present concept is extended to a virtual, pre-organized receptor L(n), in which no specific linker is involved. Applications to several polymetallic helicates reveal the presence of negatively cooperative processes attributed mainly to intermetallic repulsions, in agreement with recent thermodynamic models.

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