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2.
Chem Sci ; 10(7): 2101-2110, 2019 Feb 21.
Artigo em Inglês | MEDLINE | ID: mdl-30842867

RESUMO

We present the in-depth determination of the magnetic properties and electronic structure of the luminescent and volatile dysprosium-based single molecule magnet [Dy2(bpm)(fod)6] (Hfod = 6,6,7,7,8,8,8-heptafluoro-2,2-dimethyl-3,5-octanedione, bpm = 2,2'-bipyrimidine). Ab initio calculations were used to obtain a global picture of the electronic structure and to predict possible single molecule magnet behaviour, confirmed by experiments. The orientation of the susceptibility tensor was determined by means of cantilever torque magnetometry. An experimental determination of the electronic structure of the lanthanide ion was obtained combining Luminescence, Far Infrared and Magnetic Circular Dichroism spectroscopies. Fitting these energies to the full single ion plus crystal field Hamiltonian allowed determination of the eigenstates and crystal field parameters of a lanthanide complex without symmetry idealization. We then discuss the impact of a stepwise symmetry idealization on the modelling of the experimental data. This result is particularly important in view of the misleading outcomes that are often obtained when the symmetry of lanthanide complexes is idealized.

3.
Org Biomol Chem ; 15(13): 2784-2790, 2017 Mar 28.
Artigo em Inglês | MEDLINE | ID: mdl-28272644

RESUMO

We introduce bis-aryl croconamides as a new member in the family of dual hydrogen bonding anion receptors. In this study a series of croconamides are synthesised, and the selectivity for anion binding is investigated (Cl- > Br- > I- in CH2Cl2). The croconamides exhibit different structures in the crystal phase depending on the substituents on the aromatic rings, and furthermore, the crystal structure revealed the presence of tautomers. DFT calculations elucidated the complex structures formed upon addition of anion to the croconamides, confirming the order of association constants towards the halogen anions. The use of croconamides as organocatalysts in a proof-of-concept study is demonstrated in the formation of THP ethers. In addition to this, construction of a Hammet plot further elucidates the mechanism in action on formation of THP ethers.

4.
Metab Eng ; 36: 57-67, 2016 07.
Artigo em Inglês | MEDLINE | ID: mdl-26969254

RESUMO

Biocompatible chemistry is gaining increasing attention because of its potential within biotechnology for expanding the repertoire of biological transformations carried out by enzymes. Here we demonstrate how biocompatible chemistry can be used for synthesizing valuable compounds as well as for linking metabolic pathways to achieve redox balance and rescued growth. By comprehensive rerouting of metabolism, activation of respiration, and finally metal ion catalysis, we successfully managed to convert the homolactic bacterium Lactococcus lactis into a homo-diacetyl producer with high titer (95mM or 8.2g/L) and high yield (87% of the theoretical maximum). Subsequently, the pathway was extended to (S,S)-2,3-butanediol (S-BDO) through efficiently linking two metabolic pathways via chemical catalysis. This resulted in efficient homo-S-BDO production with a titer of 74mM (6.7g/L) S-BDO and a yield of 82%. The diacetyl and S-BDO production rates and yields obtained are the highest ever reported, demonstrating the promising combination of metabolic engineering and biocompatible chemistry as well as the great potential of L. lactis as a new production platform.


Assuntos
Materiais Biocompatíveis/metabolismo , Vias Biossintéticas/fisiologia , Butileno Glicóis/metabolismo , Melhoramento Genético/métodos , Lactococcus lactis/fisiologia , Engenharia Metabólica/métodos , Redes e Vias Metabólicas/fisiologia , Butileno Glicóis/isolamento & purificação , Proteínas Recombinantes/genética , Proteínas Recombinantes/metabolismo
5.
J Am Chem Soc ; 137(40): 13114-20, 2015 Oct 14.
Artigo em Inglês | MEDLINE | ID: mdl-26394012

RESUMO

The electronic structure of a novel lanthanide-based single-ion magnet, {C(NH2)3}5[Er(CO3)4]·11H2O, was comprehensively studied by means of a large number of different spectroscopic techniques, including far-infrared, optical, and magnetic resonance spectroscopies. A thorough analysis, based on crystal field theory, allowed an unambiguous determination of all relevant free ion and crystal field parameters. We show that inclusion of methods sensitive to the nature of the lowest-energy states is essential to arrive at a correct description of the states that are most relevant for the static and dynamic magnetic properties. The spectroscopic investigations also allowed for a full understanding of the magnetic relaxation processes occurring in this system. Thus, the importance of spectroscopic studies for the improvement of single-molecule magnets is underlined.

6.
Org Biomol Chem ; 13(21): 5937-43, 2015 Jun 07.
Artigo em Inglês | MEDLINE | ID: mdl-25925233

RESUMO

Insights to the subtle reactivity patterns of hydroxy-substituted carbazoles allows the precise synthesis of unsymmetrical azatrioxa[8]circulenes by the reaction of N-benzyl-2,7-di-tert-butyl-3,6-dihydroxycarbazole with two different 1,4-benzoquinones in the presence of an oxidant (chloranil) and a Lewis acid (BF3OEt2). The unique synthetic control obtained originates from the selectivity obtained upon reacting N-benzyl-2,7-di-tert-butyl-3,6-dihydroxycarbazole with an electron-rich benzoquinone to give first the C-C bond formation and then subsequently the dibenzofuran formation with high regioselectivity. Herein the first synthesis of unsymmetrical antiaromatic azatrioxa[8]circulenes and the full characterization using NMR spectroscopy, optical spectroscopy, electrochemistry, computational techniques and single crystal X-ray crystallography is reported. The controlled stepwise condensation of N-benzyl-2,7-di-tert-butyl-3,6-dihydroxycarbazole with two different 1,4-benzoquinones gives selectively the unsymmetrical azatrioxa[8]circulenes.

7.
Inorg Chem ; 54(7): 3660-9, 2015 Apr 06.
Artigo em Inglês | MEDLINE | ID: mdl-25756298

RESUMO

Proper assignment of redox loci in coordination complexes with redox-active ligands to either the metal or the ligand is essential for rationalization of their chemical reactivity. However, the high covalency endemic to complexes of late, third-row transition metals complicates such assignments. Herein, we systematically explore the redox behavior of a series of group 9 tris(dithiolene) complexes, [M(mnt)3]3­ (M = Ir, Rh, Co; mnt = maleonitriledithiolate). The Ir species described comprise the first examples of homoleptic Ir dithiolene complexes. The enhanced metal­ligand covalency of the Ir­S interaction leads to remarkable reactivity of [Ir(mnt)3]3­ and stabilization of mononuclear [Ir(mnt)3]2­ complex ions as well as dimerized versions featuring weak, covalent, intermolecular S­S bonds. The dianionic Rh and Co analogues are, in contrast, highly unstable, resulting in the rapid formation of [Rh2(mnt)5]4­ and [Co(mnt)2]22­, respectively. The synthesized complexes were studied by single-crystal X-ray diffraction, X-ray absorption spectroscopy, optical spectroscopy, magnetometry, density functional theory, and spectroscopy-oriented configuration interaction calculations. Spectroscopic and theoretical analyses suggest that the stability of [Ir(mnt)3]2­ may be attributed to dilution of ligand radical character by a high degree of Ir 5d character in the singly occupied molecular orbital.

8.
Chemistry ; 19(50): 17097-102, 2013 Dec 09.
Artigo em Inglês | MEDLINE | ID: mdl-24194455

RESUMO

In this paper we describe a new class of antiaromatic planar cyclooctatetraenes: the diazadioxa[8]circulenes. The synthesis was achieved by means of a new acid-mediated oxidative dimerization of 3,6-dihydroxycarbazoles to yield the diazadioxa[8]circulenes in high yields. The synthetic protocol appears to be general, and is a one-pot transformation in which two C-C bonds and two C-O bonds are formed with the loss of two molecules of water. We also present a detailed characterization of the optical and electrochemical properties of this new class of stable planar cyclooctatetraenes. The properties of the diazadioxa[8]circulenes are compared with the properties of isoelectronic tetraoxa[8]circulenes and azatrioxa[8]circulenes. We discuss the antiaromatic nature of the planar central cyclooctatetraene moiety. The antiaromatic nature of the planar cyclooctatetraenes was studied by using computational methods (NICS calculations), and these calculations reveal that the central eight-membered ring has antiaromatic character.

9.
Chemistry ; 19(12): 3898-904, 2013 Mar 18.
Artigo em Inglês | MEDLINE | ID: mdl-23400907

RESUMO

We describe herein the first synthesis of a new class of anti-aromatic planar cyclooctatetraenes: the azatrioxa[8]circulenes. This was achieved by treating a suitably functionalised 3,6-dihydroxycarbazole with 1,4-benzoquinones or a 1,4-naphthoquinone. We fully characterised the azatrioxa[8]circulenes by using optical, electrochemical and computational techniques as well as by single-crystal X-ray crystallography. The results of a computational study (NICS) suggest that the central planar cyclooctatetraene is anti-aromatic when the molecules are in neutral or oxidised states (2+), and that the corresponding dianions are aromatic. We discuss the aromatic/anti-aromatic nature of the planar cyclooctatetraenes and compare them with the isoelectronic tetraoxa[8]circulenes.

10.
Chemistry ; 18(28): 8716-23, 2012 Jul 09.
Artigo em Inglês | MEDLINE | ID: mdl-22693135

RESUMO

We describe herein the synthesis of a triptycene-based surfactant designed with the ability to solubilise single-walled carbon nanotubes (SWNTs) and C(60) in water through non-covalent interactions. Furthermore, an amphiphilic naphthalene-based surfactant with the same ability to solubilise SWNTs and C(60) has also been prepared. The compounds synthesised were designed with either two ionic or non-ionic tails to ensure a large number of supramolecular interactions with the solvent, thereby promoting strong solubilisation. The surfactants produced stable suspensions in which the SWNTs are dispersed and the surfactant/SWNT complexes formed are stable for more than one year. UV/Vis/NIR absorption spectroscopy, TEM and AFM were employed to probe the solubilisation properties of the dispersion of surfactants and SWNTs in water.


Assuntos
Antracenos/química , Fulerenos/química , Nanotubos de Carbono/química , Estrutura Molecular , Solubilidade , Espectroscopia de Luz Próxima ao Infravermelho , Tensoativos/química , Água/química
12.
Inorg Chem ; 50(13): 5867-9, 2011 Jul 04.
Artigo em Inglês | MEDLINE | ID: mdl-21634364

RESUMO

The corrole-chromium(V)-nitrido moiety is introduced as a uniquely sensitive EPR spin probe. We describe a series of corrole-centered poly(amidoamine) (PAMAM) dendrimers and the selective incorporation of the chromium(V)-nitrido moiety. The chromium-corrole cores are reactive toward both neutral and charged reagents, and the accessibility of the dendrimer cores enables easy manipulation of the spin probe. The spin probe reveals a pronounced solvent dependence of the solution-phase structure of the dendrimers.


Assuntos
Aminas/química , Cromo/química , Dendrímeros/química , Compostos Organometálicos/química , Porfirinas/química , Dendrímeros/síntese química , Estrutura Molecular , Compostos Organometálicos/síntese química , Soluções , Estereoisomerismo
15.
Inorg Chem ; 48(1): 128-37, 2009 Jan 05.
Artigo em Inglês | MEDLINE | ID: mdl-19035636

RESUMO

The electronic structures of the compounds K[(5-Brsalen)(2)(H(2)O)(2)-Mn(2)M(III)(CN)(6)].2H(2)O (M(III) = Co(III), Cr(III), Fe(III)) have been determined by inelastic neutron scattering (INS) and magnetic susceptibility studies, revealing the manganese(III) single-ion anisotropy and exchange interactions that define the low-lying states of the Mn-M(III)-Mn trimeric units. Despite the presence of an antiferromagnetic intertrimer interaction, the experimental evidence supports the classification of both the Cr(III) and Fe(III) compounds as single-molecule magnets. The value of 17(2) cm(-1) established from AC susceptibility measurements for a spin-reversal barrier of K[(5-Brsalen)(2)(H(2)O)(2)-Mn(2)Cr(CN)(6)].2H(2)O may be readily rationalized in terms of the energy level diagram determined directly by INS. AC susceptibility measurements on samples of K[(5-Brsalen)(2)(H(2)O)(2)-Mn(2)Fe(CN)(6)].2H(2)O are contrary to those previously reported, exhibiting but the onset of peaks below temperatures of 1.8 K at oscillating frequencies in the range of 100-800 Hz. INS measurements reveal an anisotropic ferromagnetic manganese(III)-iron(III) exchange interaction, in accordance with theoretical expectations based on the unquenched orbital angular momentum of the [Fe(CN)(6)](3-) anion, giving rise to an M(s) approximately +/-9/2 ground state, isolated by approximately 11.5 cm(-1) from the higher-lying levels. The reported INS and magnetic data should now serve as a benchmark against which theoretical models that aim to inter-relate the electronic and molecular structure of molecular magnets should be tested.

16.
Chem Commun (Camb) ; (20): 2358-60, 2008 May 28.
Artigo em Inglês | MEDLINE | ID: mdl-18473069

RESUMO

The synthesis of a series of chiral PAMAM dendrimers and the formation of chiral dendrimer encapsulated metal nanoparticles are described.


Assuntos
Nanopartículas Metálicas/química , Paládio/química , Poliaminas/síntese química , Ródio/química , Dicroísmo Circular , Dendrímeros , Poliaminas/química , Espectrofotometria Ultravioleta
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