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1.
Chem Asian J ; 14(5): 627-633, 2019 Mar 01.
Artigo em Inglês | MEDLINE | ID: mdl-30614206

RESUMO

Two dinuclear DyIII complexes, [Dy2 (hmb)2 (OTf)2 (H2 O)4 ]⋅HOTf⋅2 THF (A⋅HOTf⋅2 THF) and [Dy2 (hmi)3 (H2 O)2 ]⋅2 HOTf (B⋅2 HOTf), have been synthesized by the reaction of Dy(OTf)3 and the Schiff-base ligands H2 hmb (N'-(2-hydroxy-3-methoxybenzylidene)benzohydrazide) or H2 hmi ((2-hydroxy-3-methoxyphenyl)methylene isonicotinohydrazine). Disarmed glycosyl trichloroacetimidates can be activated by complex A in the synthesis of 1,2-trans-glycosides with primary and secondary acceptors. This method offers an efficient route to selectively deacetylated monosaccharides and disaccharides in high yields and a green catalyst that can be easily recycled and reused.

2.
Inorg Chem ; 57(20): 12448-12451, 2018 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-30260216

RESUMO

The effect of the directions of the anisotropy axes on the energy barriers of single-molecule magnets (SMMs) was investigated. By introducing nitrophenolate (NP)-type coligands with different substitutions, the energy barrier was significantly changed. The structural and magnetic properties of three novel SMMs based on trinuclear {Dy3O5} phenoxo- and methoxyl-bridged triangular motifs were explored. All complexes share the formula [Dy3(Hhmb)4(µ3-OMe)2(OMe)(NP)][Dy3(Hhmb)4(µ3-OMe)2(NP)]·solvent·3Cl, where Hhmb = (2-hydroxy-3-methoxyphenyl)methylene(benzoicotino)hydrazine, secondary ligand NP = 2-nitrophenol (2-NP, complex 1), 2,4-dinitrophenol (2,4-DNP, complex 2), and 2,4,6-trinitrophenol (2,4,6-TNP, complex 3), and solvent = 2MeOH·2Et2O (1) and 4MeOH (2 and 3). Magnetic measurements for 1 and 2 revealed observable slow magnetic relaxation behavior with anisotropic energy barriers of 12.18 and 4.96 K, respectively, for SMMs and only the tail of the peaks in the out-of-phase susceptibility, χ″, was observed in complex 3. Comparing a series of NP coligands, we could easily study the correlation between the directions of the anisotropic axes and magnetic properties for this trinuclear SMM system.

3.
Dalton Trans ; 47(37): 12847-12851, 2018 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-30141810

RESUMO

Two new hexadecanuclear lanthanide complexes employing the 1,5-bis(salicylidene)carbohydrazide (H2bsc) ligand are reported herein. These polynuclear aggregates crystallize in the R3[combining macron] space group, which is unprecedented in a family of lanthanide complexes with such high nuclearity. Magnetic susceptibility measurements reveal weak intramolecular interactions between the magnetic centres, and in the case of compound 2 (DyIII), single-molecule magnet properties are observed.

4.
Dalton Trans ; 45(42): 16769-16773, 2016 Nov 14.
Artigo em Inglês | MEDLINE | ID: mdl-27722351

RESUMO

A Dy6 complex composed of two Dy3 triangular units, [Dy6(µ3-OH)(CO3)3(bsc)3(MeOH)14(H2O)](Cl)5·(H2O)·(MeOH)2 (1), was isolated and found to exhibit slow relaxation of the magnetisation under zero applied dc field, resulting in a high energetic barrier to relaxation.

5.
Inorg Chem ; 55(12): 6095-9, 2016 Jun 20.
Artigo em Inglês | MEDLINE | ID: mdl-27281290

RESUMO

Inspired by the ferromagnetic coupling in the cubane model CaMn(IV)3O4 of the oxygen-evolving complex of photosystem II, 3d-4f mixed-metal DyMn3O4 clusters were prepared for investigation of the magnetic properties. For comparison, YMn(IV)3O4 and YMn(IV)2Mn(III)O4 clusters were investigated as well and showed ferromagnetic interactions, like the calcium analogue. DyMn(IV)3O4 displays single-molecule-magnet properties, while the one-electron-reduced species (DyMn(IV)2Mn(III)O4) does not, despite the presence of a Mn(III) center with higher spin and single-ion anisotropy.


Assuntos
Manganês/química , Espectroscopia de Ressonância de Spin Eletrônica , Oxirredução
6.
Dalton Trans ; 44(46): 19758-62, 2015 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-26510972

RESUMO

Using the Schiff-base ligand 1,5-bis(2-hydroxy-3-methoxybenzylidene)carbonohydrazide (H2hmc), dinuclear and nonanuclear compounds, [Dy2(Hhmc)2(NO3)4]·THF·MeCN (1) and [Dy9(µ3-O)4(µ-OH)6(hmc)4(NO3)4(DMF)4](OH)·H2O·THF·DMF (2) are generated through the addition of different bases, respectively. Single-crystal X-ray diffraction analysis revealed a unique Dy9 core structure of complex 2, and the magnetic properties of both compounds are fully studied.

7.
Langmuir ; 31(23): 6538-45, 2015 Jun 16.
Artigo em Inglês | MEDLINE | ID: mdl-26030343

RESUMO

Palladium octahedra, truncated octahedra, cuboctahedra, truncated cubes, and nanocubes with sizes of tens of nanometers have been synthesized in an aqueous mixture of H2PdCl4 solution, cetyltrimethylammonium chloride (CTAC) surfactant, KBr solution, dilute KI solution, and ascorbic acid solution at 35 °C for 30 min. By tuning the amount of dilute KBr solution introduced, particle shape control can be achieved. Adjusting the volumes of the Pd precursor and KBr solutions added, smaller and larger Pd nanocrystals were obtained with excellent shape control. Extensive structural and optical characterization of these nanocrystals has been performed. Two absorption bands in the ultraviolet region can be discerned for these Pd nanocrystals. Concave Pd cubes can also be prepared. Pd cubes were found to grow at a faster rate than that for the formation of octahedra. The concentrations of KBr and KI in the solution are so low that spectral shifts were not detected upon their addition to the solution. The Pd nanocrystals can readily be used for various applications after simple removal of surfactant.

8.
Inorg Chem ; 54(1): 59-64, 2015 Jan 05.
Artigo em Inglês | MEDLINE | ID: mdl-25521310

RESUMO

We report the syntheses and electrochemical properties of nine new clusters ([LLnMn(IV)3O4(OAc)3(DMF)n](+) (Ln = La(3+), Ce(3+), Nd(3+), Eu(3+), Gd(3+), Tb(3+), Dy(3+), Yb(3+), and Lu(3+), n = 2 or 3)) supported by a ligand (L(3-)) based on a 1,3,5-triarylbenzene motif appended with alkoxide and pyridine donors. All complexes were obtained by metal substitution of Ca(2+) with lanthanides upon treatment of previously reported LMn3CaO4(OAc)3(THF) with Ln(OTf)3. Structural characterization confirmed that the clusters contain the [LnMn3O4] cubane motif. The effect of the redox-inactive centers on the electronic properties of the Mn3O4 cores was investigated by cyclic voltammetry. A linear correlation between the redox potential of the cluster and the ionic radii or pKa of the lanthanide metal ion was observed. Chemical reduction of the LMn(IV)3GdO4(OAc)3(DMF)2 cluster with decamethylferrocene, resulted in the formation of LGdMn(IV)2Mn(III)O4(OAc)3(DMF)2, a rare example of mixed-valence [MMn3O4] cubane. The lanthanide-coordinated ligands can be substituted with other donors, including water, the biological substrate.


Assuntos
Derivados de Benzeno/química , Elementos da Série dos Lantanídeos/química , Compostos Organometálicos/química , Oxigênio/química , Complexo de Proteína do Fotossistema II/química , Cálcio/química , Técnicas Eletroquímicas , Evolução Molecular , Compostos Ferrosos/química , Manganês/química , Compostos Organometálicos/síntese química , Oxirredução , Piridinas/química , Água/química
9.
J Am Chem Soc ; 136(41): 14373-6, 2014 Oct 15.
Artigo em Inglês | MEDLINE | ID: mdl-25241826

RESUMO

Synthetic model compounds have been targeted to benchmark and better understand the electronic structure, geometry, spectroscopy, and reactivity of the oxygen-evolving complex (OEC) of photosystem II, a low-symmetry Mn4CaOn cluster. Herein, low-symmetry Mn(IV)3GdO4 and Mn(IV)3CaO4 cubanes are synthesized in a rational, stepwise fashion through desymmetrization by ligand substitution, causing significant cubane distortions. As a result of increased electron richness and desymmetrization, a specific µ3-oxo moiety of the Mn3CaO4 unit becomes more basic allowing for selective protonation. Coordination of a fifth metal ion, Ag(+), to the same site gives a Mn3CaAgO4 cluster that models the topology of the OEC by displaying both a cubane motif and a "dangler" transition metal. The present synthetic strategy provides a rational roadmap for accessing more accurate models of the biological catalyst.


Assuntos
Cálcio/química , Manganês/química , Oxigênio/química , Complexo de Proteína do Fotossistema II/química , Cálcio/metabolismo , Elétrons , Ligantes , Manganês/metabolismo , Modelos Moleculares , Estrutura Molecular , Oxigênio/metabolismo , Complexo de Proteína do Fotossistema II/metabolismo
10.
Chemistry ; 20(18): 5327-37, 2014 Apr 25.
Artigo em Inglês | MEDLINE | ID: mdl-24664616

RESUMO

The reaction of (µ-Cl)2Ni2(NHC)2 (NHC = 1,3-bis(2,6-diisopropylphenyl)-1,3-dihydro-2H-imidazol-2-ylidene (IPr) or 1,3-bis(2,6-diisopropylphenyl)imidazolidin-2-ylidene (SIPr)) with either one equivalent of sodium cyclopentadienyl (NaCp) or lithium indenyl (LiInd) results in the formation of diamagnetic NHC supported Ni(I) dimers of the form (µ-Cp)(µ-Cl)Ni2(NHC)2 (NHC = IPr (1 a) or SIPr (1 b); Cp = C5H5) or (µ-Ind)(µ-Cl)Ni2(NHC)2 (NHC = IPr (2 a) or SIPr (2 b); Ind = C7H9), which contain bridging Cp and indenyl ligands. The corresponding reaction between two equivalents of NaCp or LiInd and (µ-Cl)2Ni2(NHC)2 (NHC = IPr or SIPr) generates unusual 17 valence electron Ni(I) monomers of the form (η(5)-Cp)Ni(NHC) (NHC = IPr (3 a) or SIPr (3 b)) or (η(5)-Ind)Ni(NHC) (NHC = IPr (4 a) or SIPr (4 b)), which have nonlinear geometries. A combination of DFT calculations and NBO analysis suggests that the Ni(I) monomers are more strongly stabilized by the Cp ligand than by the indenyl ligand, which is consistent with experimental results. These calculations also show that the monomers have a lone unpaired-single-electron in their valence shell, which is the reason for the nonlinear structures. At room temperature the Cp bridged dimer (µ-Cp)(µ-Cl)Ni2(NHC)2 undergoes homolytic cleavage of the Ni-Ni bond and is in equilibrium with (η(5)-Cp)Ni(NHC) and (µ-Cl)2Ni2(NHC)2. There is no evidence that this equilibrium occurs for (µ-Ind)(µ-Cl)Ni2(NHC)2. DFT calculations suggest that a thermally accessible triplet state facilitates the homolytic dissociation of the Cp bridged dimers, whereas for bridging indenyl species this excited triplet state is significantly higher in energy. In stoichiometric reactions, the Ni(I) monomers (η(5)-Cp)Ni(NHC) or (η(5)-Ind)Ni(NHC) undergo both oxidative and reductive processes with mild reagents. Furthermore, they are rare examples of active Ni(I) precatalysts for the Suzuki-Miyaura reaction. Complexes 1 a, 2 b, 3 a, 4 a and 4 b have been characterized by X-ray crystallography.

11.
Nanoscale ; 6(8): 4316-24, 2014 Apr 21.
Artigo em Inglês | MEDLINE | ID: mdl-24622737

RESUMO

We fabricated Au-Cu2O core-shell octahedra, cuboctahedra, and nanocubes having sizes of 90-220 nm using 50 nm octahedral cores. The smaller particle sizes minimize the strong light scattering features from the Cu2O shells and enable the surface plasmon resonance (SPR) absorption band of the gold cores to be clearly identified. Beyond a lower shell thickness limit, the SPR band positions of the gold cores are independent of the shell thickness, but are strongly dependent on the exposed particle surfaces. The plasmonic band red-shifts from Au-Cu2O octahedra to cuboctahedra and nanocubes, and differs by as much as 26 nm between the octahedra and the nanocubes. The same facet-dependent optical effects were observed using larger octahedral gold cores and cubic gold cores. In contrast, simulation spectra show progressively red-shifted SPR band positions with increasing shell thickness. The Cu2O shells are also found to exhibit facet-dependent optical behavior. These nanocrystals can respond to changes in the solvent environment such as solvents with different refractive indices, indicating that the plasmonic field of the gold cores can extend beyond the particle surfaces despite the presence of thick shells. Plane-selective spectral responses to low concentrations of surfactants were also recorded.


Assuntos
Cobre/química , Ouro/química , Nanoconchas/química , Ressonância de Plasmônio de Superfície , Óptica e Fotônica/instrumentação , Óptica e Fotônica/métodos
12.
J Opt Soc Am A Opt Image Sci Vis ; 31(1): 16-20, 2014 Jan 01.
Artigo em Inglês | MEDLINE | ID: mdl-24561934

RESUMO

Effective methods for speckle reduction are essential in improving the image quality of laser imaging applications. Accordingly, the present study proposes a novel technique for reducing the speckle contrast in laser imaging applications by means of the magneto-optic Kerr effect induced by a rotating magneto-optical (MO) disk. The performance of the proposed method is evaluated experimentally using a laboratory-built prototype model. The experimental results show that the rotating MO disk can reduce the speckle contrast of the captured image by 60% of the previous value. As a result, the proposed method yields an effective improvement in image quality. Overall, the proposed method provides a promising solution for improving the performance of a wide range of laser imaging applications.

13.
PLoS One ; 8(8): e71565, 2013.
Artigo em Inglês | MEDLINE | ID: mdl-23936517

RESUMO

Multipartite viruses contain more than one distinctive genome component, and the origin of multipartite viruses has been suggested to evolve from a non-segmented wild-type virus. To explore whether recombination also plays a role in the evolution of the genomes of multipartite viruses, we developed a systematic approach that employs motif-finding tools to detect conserved motifs from divergent genomic regions and applies statistical approaches to select high-confidence motifs. The information that this approach provides helps us understand the evolution of viruses. In this study, we compared our motif-based strategy with current alignment-based recombination-detecting methods and applied our methods to the analysis of multipartite single-stranded plant DNA viruses, including bipartite begomoviruses, Banana bunchy top virus (BBTV) (consisting of 6 genome components) and Faba bean necrotic yellows virus (FBNYV) (consisting of 8 genome components). Our analysis revealed that recombination occurred between genome components in some begomoviruses, BBTV and FBNYV. Our data also show that several unusual recombination events have contributed to the evolution of BBTV genome components. We believe that similar approaches can be applied to resolve the evolutionary history of other viruses.


Assuntos
Vírus de DNA/genética , DNA de Cadeia Simples/genética , Evolução Molecular , Genômica/métodos , Motivos de Nucleotídeos/genética , Plantas/virologia , Recombinação Genética/genética
14.
Dalton Trans ; 42(37): 13397-403, 2013 Oct 07.
Artigo em Inglês | MEDLINE | ID: mdl-23887476

RESUMO

Three dinuclear [Ln2H2OL(1)2(acac)2]·solvent (1, Ln = Gd, solvent = 2CH2Cl2; 2, Ln = Tb, no solvent; 3, Ln = Er, solvent = (C2H5)2O), and two tetranuclear lanthanide clusters [Ln4(µ3-OH)2L(2)2(acac)6]·2(solvent) (4, Ln = Tb, solvent = CH3OH; 5, Ln = Dy, solvent = CH3CN) were characterized in terms of structure, fluorescence and magnetism. The dinuclear lanthanide complexes were constructed by a rigid salen-type ligand H2L(1) = N,N'-bis(salicylidene)-o-phenylenediamine and ß-diketonate (acac = acetylacetonate) ligands, while the tetranuclear clusters were formed from the flexible ligand H2L(2) = N,N'-bis(salicylidene)-1,2-ethanediamine. Crystal structure analysis indicates that the rigid ligand favors the double-decker sandwich structure (Ln2L(1)2), in which the two lanthanide ions have different coordination numbers and geometry, while the more flexible ligand (H2L(2)) leads to planar tetranuclear clusters. The relationship between their respective magnetic anisotropy and ligand-field geometries and their fluorescence properties was investigated. The Dy and Tb-containing clusters exhibit typical visible fluorescence properties, and single-molecule magnet behavior is seen in complex 5.


Assuntos
Etilenodiaminas/química , Fluorescência , Hidroxibutiratos/química , Elementos da Série dos Lantanídeos/química , Compostos Organometálicos/química , Pentanonas/química , Ligantes , Fenômenos Magnéticos , Modelos Moleculares , Estrutura Molecular , Compostos Organometálicos/síntese química
15.
Dalton Trans ; 41(40): 12349-52, 2012 Oct 28.
Artigo em Inglês | MEDLINE | ID: mdl-22968654

RESUMO

An unusual dinuclear Yb(2) complex isolated using a mixed ligand strategy leads to field-induced SMM behaviour. Low magnetic axiality and a large tunnelling gap lead to significant quantum tunnelling of the magnetisation, which was reduced under an applied static optimum field of 1600 Oe.

16.
Dalton Trans ; 41(44): 13649-55, 2012 Nov 28.
Artigo em Inglês | MEDLINE | ID: mdl-22898676

RESUMO

A mononuclear as well as dinuclear Dy(III) complexes of general formula [Dy(hmb)(NO(3))(2)(DMF)(2)] (1) and [Dy(2)(hmt)(NO(3))(4)(DMF)(4)]·DMF (2), where Hhmb: (N'-(2-hydroxy-3-methoxybenzylidene)benzohydrazide and H(2)hmt: (N(1),N(4))-N'(1),N'(4)-bis(2-hydroxy-3-methoxybenzylidene)terephthalohydrazide were obtained using a synthetic strategy involving a polytopic Schiff base ligand. Single-crystal X-ray analysis reveals the Dy(III) ion is in a distorted pentagonal interpenetrating tetrahedral arrangement. The two symmetrical Dy(III) ions in complex 2 exhibit the same geometry and are well-isolated in the molecule by an hmt(2-) ligand. The direct current (dc) and alternating current (ac) magnetic measurements of the compounds were investigated. Complex 1 did not exhibit any ac signal whereas a frequency dependant signal was observed for 2 under zero dc field. When an optimum dc field was applied, clear frequency dependant signals were obtained for both complexes indicative of Single-Ion Magnet behaviour with relaxation barriers of U(eff) = 34 and 42 K for 1 and 2, respectively.

17.
Langmuir ; 28(30): 11258-64, 2012 Jul 31.
Artigo em Inglês | MEDLINE | ID: mdl-22809109

RESUMO

In this work, palladium tripod nanocrystals have been synthesized by mixing an aqueous solution of cetyltrimethylammonium bromide (CTAB) surfactant, Na(2)PdCl(4), copper acetate, and ascorbic acid at 30 °C for 3 h. Addition of a small amount of copper ion source is critical to the formation of these tripods with a pod length reaching 100 nm. The incorporation of Cu atoms into the Pd tripods has been verified. The entire Pd tripod is single-crystalline with their branches growing along the [111] and [200] directions. Formation of side branches can be observed in some tripods. Triangular nanoplates are initially formed and evolved into the tripod structure in 20-30 min of reaction. Further growth leads to elongation of the pods. The large Pd tripods can serve as active and recyclable catalysts for a broad range of Sonogashira coupling reactions in water using a variety of aromatic halides containing electron-donating and -withdrawing substituents.

18.
J Am Chem Soc ; 134(12): 5598-609, 2012 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-22428955

RESUMO

Ammonia-borane (NH(3)BH(3), AB) has garnered interest as a hydrogen storage material due to its high weight percent hydrogen content and ease of H(2) release relative to metal hydrides. As a consequence of dehydrogenation, B-N-containing oligomeric/polymeric materials are formed. The ability to control this process and dictate the identity of the generated polymer opens up the possibility of the targeted synthesis of new materials. While precious metals have been used in this regard, the ability to construct such materials using earth-abundant metals such as Fe presents a more economical approach. Four Fe complexes containing amido and phosphine supporting ligands were synthesized, and their reactivity with AB was examined. Three-coordinate Fe(PCy(3))[N(SiMe(3))(2)](2) (1) and four-coordinate Fe(DEPE)[N(SiMe(3))(2)](2) (2) yield a mixture of (NH(2)BH(2))(n) and (NHBH)(n) products with up to 1.7 equiv of H(2) released per AB but cannot be recycled (DEPE = 1,2-bis(diethylphosphino)ethane). In contrast, Fe supported by a bidentate P-N ligand (4) can be used in a second cycle to afford a similar product mixture. Intriguingly, the symmetric analogue of 4 (Fe(N-N)(P-P), 3), only generates (NH(2)BH(2))(n) and does so in minutes at room temperature. This marked difference in reactivity may be the result of the chemistry of Fe(II) vs Fe(0).

19.
J Am Chem Soc ; 133(49): 19993-20000, 2011 Dec 14.
Artigo em Inglês | MEDLINE | ID: mdl-22091631

RESUMO

By using octahedral gold nanocrystals with sizes of approximately 50 nm as the structure-directing cores for the overgrowth of Pd shells, Au-Pd core-shell heterostructures with systematic shape evolution can be directly synthesized. Core-shell octahedra, truncated octahedra, cuboctahedra, truncated cubes, and concave cubes were produced by progressively decreasing the amount of the gold nanocrystal solution introduced into the reaction mixture containing cetyltrimethylammonium bromide (CTAB), H(2)PdCl(4), and ascorbic acid. The core-shell structure and composition of these nanocrystals has been confirmed. Only the concave cubes are bounded by a variety of high-index facets. This may be a manifestation of the release of lattice strain with their thick shells at the corners. Formation of the [CTA](2)[PdBr(4)] complex species has been identified spectroscopically. Time-dependent UV-vis absorption spectra showed faster Pd source consumption rates in the growth of truncated cubes and concave cubes, while a much slower reduction rate was observed in the generation of octahedra. The concave cubes and octahedra were used as catalysts for a Suzuki coupling reaction. They can all serve as effective and recyclable catalysts, but the concave cubes gave higher product yields with a shorter reaction time attributed to their high-index surface facets. The concave cubes can also catalyze a wide range of Suzuki coupling reactions using aryl iodides and arylboronic acids with electron-donating and -withdrawing substituents.

20.
J Am Chem Soc ; 133(48): 19286-9, 2011 Dec 07.
Artigo em Inglês | MEDLINE | ID: mdl-22032273

RESUMO

A dysprosium(III) sandwich complex, [Dy(III)(COT″)(2)Li(THF)(DME)], was synthesized using 1,4-bis(trimethylsilyl)cyclooctatetraenyl dianion (COT″). The complex behaves as a single-ion magnet and demonstrates unusual multiple relaxation modes. The observed relaxation pathways strongly depend on the applied static dc fields.

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