Your browser doesn't support javascript.
loading
Mostrar: 20 | 50 | 100
Resultados 1 - 20 de 112
Filtrar
Mais filtros










Base de dados
Tipo de estudo
Intervalo de ano de publicação
1.
Artigo em Inglês | MEDLINE | ID: mdl-32512994

RESUMO

The increase in demand and popularity of smart textiles brings new and innovative ideas to develop a diverse range of textile-based devices for our daily life applications. Smart textile-based sensors (TEX sensors) become attractive due to the potential to replace current solid-state sensor devices with flexible and wearable devices. We have developed a smart textile sensor for humidity detection using a metal-organic framework (MOF) as an active thin-film layer. We show for the first time the use of the Langmuir-Blodgett (LB) technique for the deposition of a MIL-96(Al) MOF thin film directly onto the fabrics containing interdigitated textile electrodes for the fabrication of a highly selective humidity sensor. The humidity sensors were made from two different types of textiles, namely, linen and cotton, with the linen-based sensor giving the best response due to better coverage of MOF. The TEX sensor showed a reproducible response after multiple cycles of measurements. After 3 weeks of storage, the sensor showed a moderate decrease in response. Moreover, TEX sensors showed a high level of selectivity for the detection of water vapors in the presence of several volatile organic compounds (VOCs). Interestingly, the selectivity is superior to some of the previously reported MOF-coated solid-state interdigitated electrode devices and textile sensors. The method herein described is generic and can be extended to other textiles and coating materials for the detection of toxic gases and vapors.

2.
Dalton Trans ; 2020 May 15.
Artigo em Inglês | MEDLINE | ID: mdl-32412564

RESUMO

The design of photoactive ligands may provide access to multifunctional molecular nanomagnets. We report here the design and synthesis of a new multitopic chelating ligand, 1,2-bis-(5-(N'-(pyridine-2-yl-methylene)-carbohydrazide)-3-methyl-thien-3-yl)-cyclopentene (H2L), bearing a photoswitchable spacer and demonstrate that it undergoes reversible photoisomerization in solution. In the presence of the base NaH, H2L reacts with LnCl3 salts (Ln = Dy, Tb) to form the supramolecular assemblies H2O@[Ln4L4Cl4(H2O)4] (Ln = Dy, 1; Tb, 2). The single crystal X-ray diffraction data of 1 and 2 reveal that both compounds consist of highly symmetric molecular rings efficiently folded through intramolecular weak interactions in the form of tetrahedra. This arrangement imparts a conformation to the photochromic spacer of the ligand which inhibits its photoswitching activity. Despite the low symmetry of the coordination geometry around the Ln ions, the Dy analog exhibits slow relaxation of the magnetization. The relaxation rate under various conditions has been investigated, allowing us to elucidate the mechanisms involved in this relaxation.

3.
Chembiochem ; 2020 Mar 24.
Artigo em Inglês | MEDLINE | ID: mdl-32212203

RESUMO

Five copper complexes supported by terpyridine ligands were prepared and characterized, viz. [Cu3 Cl4 (naphtpy)2 ][CuCl2 ] (1), [Cu2 Cl2 (naphtpy)2 ](ClO4 )2 (2), [CuCl2 (naphtpy)]2 (MeOH)3 (H2 O) (3), [CuCl2 (Cltpy)] (4) and [Cu(Cltpy)2 ](ClO4 )2 (5); (where naphtpy stands for 4'-((naphthalen-2-yl)methoxy)-2,2':6',2''-terpyridine and Cltpy for 4'-chloro-2,2':6',2''-terpyridine). Their ability to interact with DNA was investigated, and their cytotoxic behaviour was examined with three cells lines, namely human ovarian carcinoma cells (A2780), their derived cisplatin-resistant line (A2780cis), and human cervix adenocarcinoma cells (HeLa). All compounds show good cytotoxic properties (especially after 72 h of incubation). Remarkably, two compounds, 4 and 5, are still almost inactive after 24 h (particularly 4), but are highly active after 72 h, with IC50 values in the low-micromolar to sub-micromolar range. Compounds 1 and 2 induce necrosis, whereas late apoptosis is observed with 3-5, 4 exhibiting a behaviour close to that of cisplatin.

4.
Chem Commun (Camb) ; 2020 Feb 14.
Artigo em Inglês | MEDLINE | ID: mdl-32057059

RESUMO

A new bis-hydroxyphenylpyrazolyl ligand, H4L, allows isolating and structurally characterizing vanadyl and titanyl dinuclear complexes (Bu4N)2[(MO)2(HL)2] (M = V, Ti). The weak dipolar coupling and relatively short quantum coherence of the divanadyl anions are optimal for a 2-qubit molecular architecture proposed to implement electron-mediated nuclear quantum simulations.

5.
ACS Appl Mater Interfaces ; 12(3): 4155-4162, 2020 Jan 22.
Artigo em Inglês | MEDLINE | ID: mdl-31909968

RESUMO

The successful development of modern gas sensing technologies requires high sensitivity and selectivity coupled to cost effectiveness, which implies the necessity to miniaturize devices while reducing the amount of sensing material. The appealing alternative of integrating nanoparticles of a porous metal-organic framework (MOF) onto capacitive sensors based on interdigitated electrode (IDE) chips is presented. We report the deposition of MIL-96(Al) MOF thin films via the Langmuir-Blodgett (LB) method on the IDE chips, which allowed the study of their gas/vapor sensing properties. First, sorption studies of several organic vapors like methanol, toluene, chloroform, etc. were conducted on bulk MOF. The sorption data revealed that MIL-96(Al) presents high affinity toward water and methanol. Later on, ordered LB monolayer films of MIL-96(Al) particles of ∼200 nm were successfully deposited onto IDE chips with homogeneous coverage of the surface in comparison to conventional thin film fabrication techniques such as drop-casting. The sensing tests showed that MOF LB films were selective for water and methanol, and short response/recovery times were achieved. Finally, chemical vapor deposition (CVD) of a porous thin film of Parylene C (thickness ∼250-300 nm) was performed on top of the MOF LB films to fabricate a thin selective layer. The sensing results showed an increase in the water selectivity and sensitivity, while those of methanol showed a huge decrease. These results prove the feasibility of the LB technique for the fabrication of ordered MOF thin films onto IDE chips using very small MOF quantities.

6.
Chemistry ; 26(1): 143-147, 2020 Jan 02.
Artigo em Inglês | MEDLINE | ID: mdl-31692089

RESUMO

Ultrathin films of a robust RhII -based porous metal-organic polyhedra (MOP) have been obtained. Homogeneous and compact monolayer films (ca. 2.5 nm thick) were first formed at the air-water interface, deposited onto different substrates and characterized using spectroscopic methods, scanning transmission electron microscopy and atomic force microscopy. As a proof of concept, the gas separation performance of MOP-supported membranes has also been evaluated. Selective MOP ultrathin films (thickness ca. 60 nm) exhibit remarkable CO2 permeance and CO2 /N2 selectivity, demonstrating the great combined potential of MOP and Langmuir-based techniques in separation technologies.

7.
Dalton Trans ; 48(45): 16844-16847, 2019 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-31681934

RESUMO

A new bis-(ß-diketone) ligand featuring built-up structural asymmetry yields non-symmetric Fe(iii) and Ga(iii) dinuclear, triple-stranded helicates by design. Their structural properties have been studied, both in solid state and in solution, and compared with their corresponding symmetric analogues. The robustness observed shows the potential of this synthetic strategy to develop non-symmetric helicoidal motifs with specific functional groups.

8.
Chemistry ; 25(67): 15228-15232, 2019 Dec 02.
Artigo em Inglês | MEDLINE | ID: mdl-31506989

RESUMO

The combination of two different ß-diketone ligands facilitates the size-controlled assembly of pure heterometallic [LnLn'Ln] linear compounds thanks to two different coordination sites present in the molecular scaffold. [HoCeHo], [ErCeEr], and [YbCeYb] analogues are presented here and are characterized both in the solid state and in solution, demonstrating the selectivity of this unique method to produce heterometallic 4f molecular entities.

9.
Inorg Chem ; 58(15): 9562-9566, 2019 Aug 05.
Artigo em Inglês | MEDLINE | ID: mdl-31283191

RESUMO

The slow magnetic relaxation of CoII ions in the elusive intermediate geometry between the trigonal prism and antiprism has been studied on the new [Co2L3]4+ and [CoZnL3]4+ coordination helicates [L is a bis(pyrazolylpyridine) ligand]. Solution paramagnetic 1H NMR and solid-state magnetization measurements unveil single-molecule-magnet behavior with small axial anisotropy, as predicted previously.

10.
Beilstein J Nanotechnol ; 10: 654-665, 2019.
Artigo em Inglês | MEDLINE | ID: mdl-30931207

RESUMO

This work reports on the fabrication, optimization and characterization of ultrathin films containing submicrometer particles (sMPs) of the hydrophilic and water stable UiO-66-COOH(Zr) metal organic framework (MOF). MOF particles of ≈200 nm have been synthesized and assembled at the air-water interface by the Langmuir-Blodgett technique. The use of different solvents, mixtures of solvents and surfactants has been investigated in order to improve the stability of MOF dispersions and reduce particle aggregation. The compact MOF/surfactant films containing 10 wt % octadecylphoshonic acid (ODP) have been deposited on substrates of different nature by Langmuir-Blodgett (LB) and Langmuir-Schaefer (LS) methods, showing that the presence of even only one MOF/ODP monolayer can increase the water contact angle of highly hydrophilic substrates such as mica or glass up to 120°. These films were characterized by scanning electron microscopy, grazing incidence X-ray diffraction, Fourier transform infrared spectroscopy and atomic force microscopy, revealing the formation of a continuous film where ODP molecules adopt an almost vertical position and cover MOF particles. Moreover, the presence of MOF particles significantly enhances the surface roughness and allows ultrathin, hydrophobic coverage to be obtained. Finally, it has been shown that the crystallinity and the porosity of the MOF remains almost unaltered in MOF/ODP films.

11.
Angew Chem Int Ed Engl ; 57(41): 13509-13513, 2018 Oct 08.
Artigo em Inglês | MEDLINE | ID: mdl-30161280

RESUMO

Single functional molecules are regarded as future components of nanoscale spintronic devices. Supramolecular coordination chemistry provides unlimited resources to implement multiple functions to individual molecules. A novel coordination [Fe2 ] helicate exhibiting spin-crossover is demonstrated to be ideally suited to encapsulate a [Cr(ox)3 ]3- complex anion (ox=oxalate), unveiling for the first-time single ion slow relaxation of the magnetization for this metal. A possibility of tuning the dynamics of this relaxation as well as the performance of the CrIII center as qubit arises from the observation that metastable high spin FeII centers from the host can be generated by irradiation with green light at low temperature.

12.
Inorg Chem ; 57(17): 11019-11026, 2018 Sep 04.
Artigo em Inglês | MEDLINE | ID: mdl-30133264

RESUMO

Spin-crossover (SCO) molecular solids are valued switchable materials for their common abrupt and reversible thermal transitions, large thermal hysteresis, or guest-dependent effects. These properties usually involve crystallographic transitions coupled to the SCO events. These phenomena are of great value for the understanding of solid-state transformations and also for exploiting them. We present here a lattice of the complex [FeL(bbp)](ClO4)2 (1; L and bbp are tris-imine ligands) featuring an unprecedented rich succession of SCO and crystallographic phase transformations. Magnetometry measurements unveil a thermally irreversible sequence of spin conversions that delineate four different thermal pathways. All of these are single-crystal-to-single-crystal processes and can thus be monitored by single crystal X-ray diffraction using one unique specimen. Fresh crystals of 1 contain one molecule of acetone per Fe center (1·ac) that abandons the lattice upon warming at the same time that a SCO from an ordered mixed spin state (1:1 high spin/low spin; HS/LS) to a fully HS state, 1α, occurs. This crystallographic phase, accessed through a template effect by the solvent, converts into another one, 1ß, upon cooling, as triggered by a HS to LS SCO. Warming of 1ß induces a new SCO (LS to ordered HS/LS) coupled to another crystallographic phase transition, 1ß â†’ 1γ. The fully HS state of 1γ can not be reached before decomposition of the compound. Instead, this phase cycles between the HS/LS and the LS states through superimposable pathways, different from that of the prerequired 1ß â†’ 1γ phase change. Analysis of the thermal variation of the free energy, G, through density functional theory methods provides trends in agreement with the observation of these transformations and clarifies the possible metastable nature of the various phases identified. This unique behavior allows the access to four different magnetic responses depending on the thermal history of the sample, within a given range of temperatures near the ambient conditions.

13.
Inorg Chem ; 57(14): 8429-8439, 2018 Jul 16.
Artigo em Inglês | MEDLINE | ID: mdl-29969253

RESUMO

The preparation of heterometallic, lanthanide-only complexes is an extremely difficult synthetic challenge. By a ligand-based strategy, a complete isostructural series of dinuclear heterometallic [LnPr] complexes has been synthesized and structurally characterized. The two different coordination sites featured in this molecular entity allow study of the preferences of the praseodymium ion for a specific position depending on the ionic radii of the accompanying lanthanide partner. The purity of each heterometallic moiety has been evaluated in the solid state and in solution by means of crystallographic and spectrometric methods, respectively, revealing the limits of this strategy for ions with similar sizes. DFT calculations have been carried out to support the experimental results, confirming the nature of the site-selective lanthanide distribution. The predictable selectivity of this system has been exploited to assess the magnetic properties of the [DyPr] and [LuPr] derivatives, showing that the origin of the slow dynamics observed in the former arises from the dysprosium ion.

14.
Inorg Chem ; 57(7): 4009-4022, 2018 Apr 02.
Artigo em Inglês | MEDLINE | ID: mdl-29543468

RESUMO

The development of photoactivatable metal complexes with potential anticancer properties is a topical area of current investigation. Photoactivated chemotherapy using coordination compounds is typically based on photochemical processes occurring at the metal center. In the present study, an innovative approach is applied that takes advantage of the remarkable photochemical properties of diarylethenes. Following a proof-of-concept study with two complexes, namely, C1 and C2, a series of additional platinum(II) complexes from dithienylcyclopentene-based ligands was designed and prepared. Like C1 and C2, these new coordination compounds exhibit two thermally stable, interconvertible photoisomers that display distinct properties. The photochemical behavior of ligands L3-L7 has been analyzed by 1H NMR and UV-vis spectroscopies. Subsequently, the corresponding platinum(II) complexes C3-C7 were synthesized and fully characterized, including by single-crystal X-ray diffraction for some of them. Next, the interaction of each photoisomer (i.e., containing the open or closed ligand) of the metal complexes with DNA was examined thoroughly using various techniques, revealing their distinct DNA-binding modes and affinities, as observed for the earlier compounds C1 and C2. The antiproliferative activity of the two forms of the complexes was then assessed with five cancer cell lines and compared with that of C1 and C2, which supported the use of such diarylethene-based systems for the generation of a new class of potential photochemotherapeutic metallodrugs.


Assuntos
Complexos de Coordenação/farmacologia , DNA Super-Helicoidal/química , Compostos Organoplatínicos/farmacologia , Platina/química , Linhagem Celular Tumoral , Complexos de Coordenação/síntese química , Complexos de Coordenação/química , Complexos de Coordenação/efeitos da radiação , Ciclização , Fluorescência , Humanos , Substâncias Intercalantes/síntese química , Substâncias Intercalantes/química , Substâncias Intercalantes/farmacologia , Substâncias Intercalantes/efeitos da radiação , Isomerismo , Ligantes , Compostos Organoplatínicos/síntese química , Compostos Organoplatínicos/química , Compostos Organoplatínicos/efeitos da radiação
15.
Phys Chem Chem Phys ; 19(43): 29084-29091, 2017 Nov 08.
Artigo em Inglês | MEDLINE | ID: mdl-29057417

RESUMO

A combined study involving DFT calculations, neutron scattering, heat capacity and magnetic measurements at very low temperatures demonstrates the long-range magnetic ordering of Ni(pyrazine)[Pt(CN)4] below 1.9 K, describing its antiferromagnetic spin arrangement. This compound belongs to the family of porous coordination polymers M(pyrazine)[Pt(CN)4] (M = divalent metal), renowned for showing interesting combinations of porosity and magnetic properties. The possibility of including long-range magnetic ordering, one of the most pursued functional properties, opens new perspectives for the multifunctionality of this class of compounds.

16.
Angew Chem Int Ed Engl ; 56(49): 15622-15627, 2017 12 04.
Artigo em Inglês | MEDLINE | ID: mdl-29057559

RESUMO

A bis(pyrazolylpyridyl) ligand, L, containing a central photochromic dithienylethene spacer predictably forms a ferrous [Fe2 L3 ]4+ helicate exhibiting spin crossover (SCO). In solution, the compound [Fe2 L3 ](ClO4 )4 (1) preserves the magnetic properties and is fluorescent. The structure of 1 is photo-switchable following the reversible ring closure/opening of the central dithienylethene via irradiation with UV/visible light. This photoisomerization switches on and off some emission bands of 1 and provides a means of externally manipulating the magnetic properties of the assembly.

17.
Chemistry ; 23(55): 13648-13659, 2017 Oct 04.
Artigo em Inglês | MEDLINE | ID: mdl-28621917

RESUMO

Controlling the charges and spins of molecules lies at the heart of spintronics. A photoswitchable molecule consisting of two independent spins separated by a photoswitchable moiety was designed in the form of new ligand H4 L, which features a dithienylethene photochromic unit and two lateral coordinating moieties, and yields molecules with [MM⋅⋅⋅MM] topology. Compounds [M4 L2 (py)6 ] (M=Cu, 1; Co, 2; Ni, 3; Zn, 4) were prepared and studied by single-crystal X-ray diffraction (SCXRD). Different metal centers can be selectively distributed among the two chemically distinct sites of the ligand, and this enables the preparation of many double-spin systems. Heterometallic [MM'⋅⋅⋅M'M] analogues with formulas [Cu2 Ni2 L2 (py)6 ] (5), [Co2 Ni2 L2 (py)6 ] (6), [Co2 Cu2 L2 (py)6 ] (7), [Cu2 Zn2 L2 (py)6 ] (8), and [Ni2 Zn2 L2 (py)6 ] (9) were prepared and analyzed by SCXRD. Their composition was established unambiguously. All complexes exhibit two weakly interacting [MM'] moieties, some of which embody two-level quantum systems. Compounds 5 and 8 each exhibit a pair of weakly coupled S=1/2 spins that show quantum coherence in pulsed Q-band EPR spectroscopy, as required for quantum computing, with good phase memory times (TM =3.59 and 6.03 µs at 7 K). Reversible photoswitching of all the molecules was confirmed in solution. DFT calculations on 5 indicate that the interaction between the two spins of the molecule can be switched on and off on photocyclization.

18.
Chemistry ; 23(21): 5117-5125, 2017 Apr 11.
Artigo em Inglês | MEDLINE | ID: mdl-28220975

RESUMO

The solid-state and solution configurations of the heterodimetallic complexes (Hpy)[LaEr(HL)3 (NO3 )(py)(H2 O)] (1), (Hpy)[CeEr(HL)3 (NO3 )(py)(H2 O)] (2), (Hpy)[CeGd(HL)3 (NO3 )(py)(H2 O)] (3), (Hpy)[PrSm(HL)3 (NO3 )(py)(H2 O)] (4), and (Hpy)2 [LaYb(HL)3 (NO3 )(H2 O)](NO3 ) (5), in which H3 L is 6-(3-oxo-3-(2-hydroxyphenyl)propionyl)pyridine-2-carboxylic acid and py is pyridine, were analyzed experimentally and by using DFT calculations. Complexes 3, 4, and 5 are described here for the first time, and were analyzed by using single-crystal X-ray diffraction and mass spectrometry. The theoretical study was also extended to the [LaCe] and [LaLu] analogues. The results are consistent with a remarkable selectivity of the metal distribution within the molecule in the solid state, enhanced by the size difference between the different ions. This selectivity was reduced in solution, particularly for ions with the most similar radii. This unique entry into 4f-4f'' heterometallic chemistry establishes for the first time the difference between the selectivity in solution and that in the solid state, as a result of changes to the coordination that follow the dissociation of terminal ligands upon dissolution of the complexes.

19.
Chemistry ; 22(36): 12767-76, 2016 Aug 26.
Artigo em Inglês | MEDLINE | ID: mdl-27483197

RESUMO

Two polymorphs of the spin crossover (SCO) compound [Fe(1,3-bpp)2 ](ClO4 )2 (1 and 2; 1,3-bpp=2-(pyrazol-1-yl)-6-(pyrazol-3-yl)pyridine) were prepared using a novel, stepwise procedure. Crystals of 1 deposit from dry solvents, while 2 is obtained from a solid-state procedure, by sequentially removing lattice H2 O molecules from the solvatomorph [Fe(1,3-bpp)2 ](ClO4 )2 ⋅2 H2 O (2⋅2 H2 O), using single-crystal-to-single-crystal (SCSC) transformations. Hydrate 2⋅2 H2 O is obtained through the same reaction as 1, now with 2.5 % of water added. Compounds 2 and 2⋅2 H2 O are unstable in the atmosphere and absorb or lose one equivalent of water, respectively, to both yield the stable solvatomorph [Fe(1,3-bpp)2 ](ClO4 )2 ⋅H2 O (2⋅H2 O), also following SCSC processes. The four derivatives have been characterised by single-crystal X-ray diffraction (SCXRD). Furthermore, the homogeneity of the various compounds as well as their SCSC interconversions have been confirmed by powder X-ray diffraction (PXRD). Polymorphs 1 and 2 exhibit abrupt SCO behaviour near room temperature with T1/2↑ =279/316 K and T1/2↓ =276/314 K (near 40 K of shift) and different cooperativity.

20.
Chemistry ; 22(25): 8635-45, 2016 Jun 13.
Artigo em Inglês | MEDLINE | ID: mdl-27161198

RESUMO

A new bis(pyrazolylpyridine) ligand (H2 L) has been prepared to form functional [Fe2 (H2 L)3 ](4+) metallohelicates. Changes to the synthesis yield six derivatives, X@[Fe2 (H2 L)3 ]X(PF6 )2 ⋅xCH3 OH (1, x=5.7 and X=Cl; 2, x=4 and X=Br), X@[Fe2 (H2 L)3 ]X(PF6 )2 ⋅yCH3 OH⋅H2 O (1 a, y=3 and X=Cl; 2 a, y=1 and X=Br) and X@[Fe2 (H2 L)3 ](I3 )2 ⋅3 Et2 O (1 b, X=Cl; 2 b, X=Br). Their structure and functional properties are described in detail by single-crystal X-ray diffraction experiments at several temperatures. Helicates 1 a and 2 a are obtained from 1 and 2, respectively, by a single-crystal-to-single-crystal mechanism. The three possible magnetic states, [LS-LS], [LS-HS], and [HS-HS] can be accessed over large temperature ranges as a result of the structural nonequivalence of the Fe(II) centers. The nature of the guest (Cl(-) vs. Br(-) ) shifts the spin crossover (SCO) temperature by roughly 40 K. Also, metastable [LS-HS] or [HS-HS] states are generated through irradiation. All helicates (X@[Fe2 (H2 L)3 ])(3+) persist in solution.

SELEÇÃO DE REFERÊNCIAS
DETALHE DA PESQUISA