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1.
Chem Commun (Camb) ; 56(65): 9300-9303, 2020 Aug 21.
Artigo em Inglês | MEDLINE | ID: mdl-32666980

RESUMO

Two mixed-metal hydride clusters, corresponding to x = 3 and 4, were structurally characterized from a set of atomically precise heptanuclear clusters, CuxAg7-x(H){S2P(OiPr)2}6 (x = 1-6). An interstitial hydride lying at the center of a tricapped tetrahedral cage was located and refined anisotropically by using X-ray data, and its presence acertained by multinuclear NMR spectroscopy and DFT calculations.

2.
Steroids ; 115: 18-25, 2016 11.
Artigo em Inglês | MEDLINE | ID: mdl-27477887

RESUMO

We have previously reported that testosterone (Tes) is able to interact with magnesium chloride dissolved in methanol. In this study, we have applied 1H and 13C NMR spectroscopies to a series of Tes solutions containing Mg2+ at various concentrations. High-resolution 13C NMR spectra of Tes/Mg2+ revealed well-resolved 13C signals, and the intensities of those arising from C3, C5, C16, and C17 decreased linearly with increasing Mg2+ concentration. The magnitude of the chelation affinity could be deduced from the slopes of the 13C intensity variations; typically, the greater the slope the higher the chelation affinity. The results revealed Tes/Mg2+ chelation to be mediated by the oxygen atom attached to C3 in ring A, and the hydroxyl group attached to C17 in ring D. With regard to the chelation specificity, we showed that Tes chelates Mg2+, but not Ca2+ or Zn2+. We also explored the cation-induced signal shift effects of Tes in the presence of Mg2+, Ca2+, or Zn2+. We demonstrate that high-resolution 13C NMR spectroscopy provides a better probe than 1H NMR for the detection of cation chelation and cation-induced signal shift effects for steroid compounds such as Tes.


Assuntos
Magnésio/química , Espectroscopia de Ressonância Magnética/métodos , Testosterona/química , Isótopos de Carbono/química , Oxigênio/química
3.
Analyst ; 137(3): 571-4, 2012 Feb 07.
Artigo em Inglês | MEDLINE | ID: mdl-22158630

RESUMO

We synthesized a simple fluorescent receptor 3 bearing two boronic acid groups as recognition sites. The recognition behaviour of receptor 3 towards various anions was evaluated in THF/H(2)O (1:1, v/v) solution. Receptor 3 showed high selectivity for iodide among a series of anions. Fluorescence spectroscopy and computational calculations revealed that the electrostatic interaction played a crucial role in its high selectivity for iodide.


Assuntos
Iodetos/metabolismo , Receptores de Superfície Celular/metabolismo , Água/química , Modelos Moleculares , Soluções , Espectrometria de Fluorescência , Eletricidade Estática
4.
Inorg Chem ; 50(17): 8410-7, 2011 Sep 05.
Artigo em Inglês | MEDLINE | ID: mdl-21806033

RESUMO

The hydrido copper(I) and silver(I) clusters incorporating 1,1-dicyanoethylene-2,2-dithiolate (i-MNT) ligands are presented in this paper. Reactions of M(I) (M = Cu, Ag) salts, [Bu(4)N](2)[S(2)CC(CN)(2)], with the anion sources ([Bu(4)N][BH(4)] for H(-), [Bu(4)N][BD(4)] for D(-)) in an 8:6:1 molar ratio in THF produce octanuclear penta-anionic Cu(I)/Ag(I) clusters, [Bu(4)N](5)[M(8)(X){S(2)CC(CN)(2)}(6)] (M = Cu, X = H, 1(H); X = D, 1(D); M = Ag, X = H, 2(H); X = D, 2(D)). They can also be produced from the stoichiometric reaction of M(8)(i-MNT)(6)(4-) with the ammonium borohydride. All four compounds have been fully characterized spectroscopically ((1)H and (13)C NMR, IR, UV-vis) and by elemental analyses. The deuteride-encapsulated Cu(8)/Ag(8) clusters of 1(D) and 2(D) are also characterized by (2)H NMR. X-ray crystal structures of 1(H) and 2(H) reveal a hydride-centered tetracapped tetrahedral Cu(8)/Ag(8) core, which is inscribed within an S(12) icosahedron formed by six i-MNT ligands, each in a tetrametallic-tetraconnective (µ(2), µ(2)) bonding mode. The encapsulated hydride in 2(H) is unequivocally characterized by both (1)H and (109)Ag NMR spectroscopies, and the results strongly suggest that the hydride is coupled to eight magnetically equivalent silver nuclei on the NMR time scale. Therefore, a fast interchange between the vertex and capping silver atoms in solution gives a plausible explanation for the perceived structural differences between the Ag(8) geometry deduced from the X-ray structure and the NMR spectra.

5.
Inorg Chem ; 49(2): 468-75, 2010 Jan 18.
Artigo em Inglês | MEDLINE | ID: mdl-20025253

RESUMO

The first stable structure of silver(I) cluster cations [Ag(8)(mu(4)-H){Se(2)P(OR)(2)}(6)](+) [R = (i)Pr, 1; Et, 2] containing Ag(I)-hydride bridges (Ag-mu-H-Ag) in T symmetry was reported. The clusters having an interstitial hydride were composed of an octanuclear silver core in tetracapped tetrahedral geometry, which was inscribed within a Se(12) icosahedron represented by six dialkyl diselenophosphate ligands in a tetrametallic-tetraconnective (mu(2), mu(2)) bonding mode. The presence of hydride was unequivocally corroborated by both (1)H and (109)Ag NMR spectroscopies of which a nonet in the (1)H NMR spectrum for the hydride resonance coupled with a doublet peak observed in the (109)Ag NMR spectrum clearly suggests that eight silver nuclei are equivalent in the NMR time scale and a fast exchange of the positions between the vertex and capping silver atoms in solution must occur. The hypothesis was also supported by a density functional theory (DFT) investigation on a simplified model [Ag(8)(H)(Se(2)PH(2))(6)](+), which confirmed that the Ag(8)H cubic core of T(h) symmetry may not be formed as it is energetically highly unfavorable (0.67 eV less stable than the T structure).

6.
Dalton Trans ; (5): 985-90, 2005 Mar 07.
Artigo em Inglês | MEDLINE | ID: mdl-15726154

RESUMO

The reaction of Kpmf (pmf = anion of N,N[prime or minute]-bis(pyrimidyl-2-yl)formamidine, Hpmf) with CuSCN afforded the complexes K[Cu4(pmF)3(SCN)2], 1, and Cu(4)(pmf)4, 2. Reaction of 1 with [(n-Bu)4N]PF6 in THF gave the complex [(n-Bu)4N][Cu4(pmf)3(SCN)2], 3. Their structures were characterized by X-ray crystallography. Complexes 1 and 3 are the first linear tetranuclear complexes containing only Cu(I) atoms, while complex 2 is cyclic. The four Cu(I) atoms of complexes 1 and 3 are helically bridged by three tetradentate pmf- ligands. The [Cu4(pmf)3(SCN)2]- anions of 1 show weak interactions with adjacent [K(THF)5]+ cations through the sulfur atoms, forming infinite chains which are subjected to a series of intermolecular pi-pi interactions. In complex 2, the pmf- ligands are coordinated to the copper atoms in bidentate fashion through the two central amine nitrogen atoms, leaving the pyrimidine nitrogen atoms uncoordinated. Unexpected fluxional behaviors were observed for complexes 1 and 3 in solution. By the DNMR analysis, the free energy of activation (DeltaGc(not equal)) for the exchange is 12.8 kcal mol(-1) at 278 K (T(c)), and the rate constant of exchange (K(c)) is 470 s(-1) for 1. The DeltaGc(not equal) and Kc are 12.6 kcal mol(-1) at 273 K and 433 s(-1), respectively, for 3.


Assuntos
Amidinas/química , Amidinas/metabolismo , Ânions/química , Cobre/química , Pirimidinas/química , Amidinas/síntese química , Cristalografia por Raios X , Ligantes , Espectroscopia de Ressonância Magnética , Estrutura Molecular
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