RESUMEN
The stereoselective hetero Diels-Alder reaction between ethyl glyoxylate and cyclohexadiene catalyzed by [Cu(ii)t-Bu-(box)](OTf)2 was investigated. The reaction was performed step-by-step and the geometry of the Cu(ii) complexes formed in the course of the catalysis was analysed by EPR spectroscopy, advanced pulsed EPR methods (ENDOR, and HYSCORE) and DFT calculations. Our results show that one triflate counterion is directly coordinated to Cu(ii) during the catalytic process (axial position). This leads to penta-coordinated Cu(ii) complexes. Solvent molecules are able to alter the geometry of the Cu(ii) complexes although their coordination is weak. These findings provide an explanation for the solvent and counterion effects observed in many catalytic reactions.
RESUMEN
Dhat syndrome as a clinical entity has been rarely described in females. Ethnographic studies suggest that as in males, whitish vaginal discharge in females is also associated with depressive and somatic symptoms and many women with symptoms of whitish discharge attribute their depressive and somatic symptoms to the whitish discharge. In this report, we describe two female patients who presented with psychiatric manifestations also with somatic symptoms and attributed their somatic complaints to whitish vaginal discharge. In this background, we discuss whether this entity requires nosological attention and what criteria can be used to define the same.
RESUMEN
Cu(I)-NO complexes, one of the essential intermediates in the NO decomposition reaction, were formed over copper exchanged and autoreduced Cu-ZSM-5, Cu-MCM-58, Cu-ZSM-12, and Cu-L zeolites, and studied by electron spin resonance spectroscopy at X-, Q-, and W-band frequencies. The spin Hamiltonian parameters of the NO adsorption complexes formed over pretreated materials firmly confirm the formation of Cu(I)-NO moieties. Two different Cu(I)-NO species A and B that are formed on account of different numbers of framework oxygen atoms coordinating to the Cu(I) cation are observed for Cu-ZSM-5, Cu-MCM-58, and Cu-ZSM-12 zeolites, while formation of a single Cu(I)-NO species B is observed in Cu-L zeolite. On the basis of the isotropic copper hyperfine couplings and the different channel topologies of the studied zeolite frameworks, we assign species A and B to Cu(I)-NO complexes formed at M5(7)-type and I2-type Cu(I) cation sites with either three or two oxygen co-ligands, respectively, supporting the results of previous quantum chemical studies on the Cu-ZSM-5 reference system. Whereas accessible five- or six-membered rings are clearly a prerequisite for M5(7)-type Cu(I) adsorption sites, the formation of I2-type sites in the unidimensional Cu-MCM-48, Cu-ZSM-12, and Cu-L zeolites suggests that not just channel intersection but also other structural motifs with exposed AlO4 tetrahedra can constitute such I2-type sites provided that sufficiently large channels can freely accommodate the Cu(I)-NO species.
RESUMEN
The Cu(I)-NO adsorption complexes were formed over copper exchanged and autoreduced high siliceous Cu-ZSM-5 and Cu-MCM-22 zeolites and studied by EPR spectroscopy at X-, Q-, and W-band frequencies. The spin Hamiltonian parameters of the Cu(I)-NO species are indicative of a nitrogen-centered radical complex with a bent geometry and a significant contribution of the Cu(I) 4s atomic orbital to the wave function of the unpaired electron. Two different Cu(I)-NO species were found in both zeolites. It has been confirmed by comparing the experimental data with the results of previous theoretical studies that the presence of two different species is due to the formation of Cu(I)-NO adsorption complexes from two different Cu(I) sites in the zeolite matrix with different numbers of oxygen coligands. The structure of the two sites in the Cu-ZSM-5 and Cu-MCM-22 zeolites must be similar as the spin Hamiltonian parameters are found to be almost independent of the zeolite matrix, where the Cu(I)-NO complex is formed. The EPR signal intensity of the Cu(I)-NO species was studied as a function of the NO loading, and the formation of diamagnetic Cu(I)-(NO)(2) species with rising NO pressure at the expense of paramagnetic Cu(I)-NO monomers could be demonstrated for both systems at low temperatures.
Asunto(s)
Cobre/química , Óxido Nítrico/química , Zeolitas/química , Adsorción , Espectroscopía de Resonancia por Spin del Electrón/métodos , Presión , Sensibilidad y Especificidad , Propiedades de SuperficieRESUMEN
The local environments of Cu(I)-NO adsorption complexes formed in zeolites Cu-L and Cu-ZSM-5 were studied by electron spin resonance (ESR), pulsed electron nuclear double resonance (ENDOR), and hyperfine sublevel correlation spectroscopy (HYSCORE). Cu(I)-NO complexes have attracted special interest because they are important intermediates in the catalytic decomposition of nitric oxide over copper exchanged zeolites. Recently, detailed structures of the complexes in Cu-ZSM-5 zeolites, O2-Al-O2-Cu(I)-NO, have been proposed on the basis of quantum chemical calculations (Pietrzyk, et al. J. Phys. Chem. B 2003, 107, 6105. Dedecek, et al. Phys. Chem. Chem. Phys. 2002, 4, 5406). 27Al pulsed ENDOR and HYSCORE experiments allowed the hyperfine coupling parameters of an aluminum nuclei found in the vicinity of the Cu(I)-NO complex formed in zeolite Cu-L to be estimated. The data indicate that the aluminum atom is located in the third coordination sphere of the adsorbed NO molecule in agreement with the suggested geometry of the adsorption sites. Broad distributions of aluminum nuclear quadrupole and hyperfine coupling parameters and short electron spin relaxation times of the Cu(I)-NO species prevented the determination of the 27Al hyperfine couplings for zeolite Cu-ZSM-5.
RESUMEN
Cu(I)-NO adsorption complexes were formed over Cu-ZSM-5 zeolites prepared by (i) solid-state ion exchange of NH(4)-ZSM-5 with CuCl and (ii) liquid-state ion exchange of ZSM-5 with Cu(CH(3)COO)(2). Electron spin resonance spectroscopy revealed the formation of two different Cu(I)-NO species A and B in both systems, whose spin Hamiltonian parameters are comparable with those already reported for the Cu(I)-NO species formed over 66% Cu(II) liquid-state ion-exchanged Cu-ZSM-5 materials. The population of the species A and B differs for the two systems studied. Formation of species B is more favored in the solid-state ion-exchanged Cu-ZSM-5 when compared to the liquid-state exchanged zeolite. The X-, Q- and W-band electron spin resonance spectra recorded at 6 and 77 K reveal the presence of a rigid geometry of the adsorption complexes at 6 K and a dynamic complex structure at higher temperatures such as 77 K. This is indicated by the change in the spin Hamiltonian parameters of the formed Cu(I)-NO species in both the liquid- and solid-state ion-exchanged Cu-ZSM-5 zeolites from 6 to 77 K. Possible models for the motional effects found at elevated temperatures are discussed. The temperature dependence of the electron spin phase memory time measured by two-pulse electron spin-echo experiments indicates, likewise, the onset of a motional process of the adsorbed NO molecules at temperatures above 10 K. The studies support previous assignments where the NO complexes are formed at two different Cu(I) cationic sites in the ZSM-5 framework and highlight that multifrequency electron spin resonance experiments at low temperatures are essential for reliable determination of the spin Hamiltonian parameters of the formed adsorption complexes for further comparison with Cu(I)-NO complex structures predicted by quantum chemical calculations.
RESUMEN
The present study aims to evaluate the topical anti-inflammatory activity of "Pinda thailam", a herbal gel formulation containing aqueous extract of roots of Rubia cordifolia (Rubiaceae) and Hemidesmus indicus (Asclepiadaceae) which are known for their anti-inflammatory activity using the technique of carrageenin induced paw oedema in albino rats. The herbal gel formulation showed significant anti-inflammatory activity comparable to the reference standard Diclofenac sodium gel.