Two New Spirostanol Glycosides from Cestrum parqui

Two new steroidal glycosides, parquisoside A ( 1 ) and B ( 2 ) were isolated from the aerial parts of Cestrum parqui (family Solanaceae). Their common aglycone is a new steroid of the spirostane series, which we name parquigenin. It has the structure (3β,24S,25S)‐spirost‐5‐ene‐3,24‐diol, i.e. a (24S,25S)‐24‐hydroxydiosgenin. The structures of parquisosides A and B were elucidated as (3β,24S,25S)‐spirost‐5‐ene‐3,24‐diol 3‐O‐{[α‐L ‐rhamnopyranosyl‐(1→2)]‐β‐D ‐glucopyranosyl‐(1→4)‐α‐L ‐rhamnopyranosyl‐(1→4)}‐β‐D ‐glucopyranoside ( 1 ) and (3β,24S,25S)‐spirost‐5‐ene‐3,24‐diol 3‐O‐{[α‐L ‐rhamnopyranosyl)‐(1→4)‐α‐L ‐rhamnopyranosyl‐(1→2)]‐β‐D ‐glucopyranosyl‐(1→4)‐α‐L ‐rhamnopyranosyl‐(1→4)}‐β‐D ‐glucopyranoside ( 2 ), respectively, on the basis of detailed spectroscopic studies and chemical analysis. The crude extract of Cestrum parqui showed inhibition of carrageenin‐induced edema.     

Nickel(II), copper(II), palladium(II) and platinum(II) complexes of bidentate SN ligands derived from S-alkyldithiocarbazates and the X-ray crystal structures of the [Ni(tasbz)2] and [Cu(tasbz)2] · CHCl3 complexes

New complexes of general empirical formula, [M(NS)₂] · nCHCl₃ (M = Ni^II, Cu^II, Pd^II or Pt^II; NS = anionic form of the thiophene-2-aldehyde Schiff bases of S-methyl- and S-benzyldithiocarbazate; n = 0, 1) have been synthesized and characterized by physico-chemical techniques. Magnetic and spectroscopic evidence support a square-planar structure for these complexes. The crystal structures of the [Ni(tasbz)₂] and [Cu(tasbz)₂] · CHCl₃ complexes (tasbz = anionic form of the thiophene-2-aldehyde Schiff base of S-benzyldithiocarbazate) have been determined by X-ray diffraction. Both complexes have a trans-planar structure in which the two Schiff base ligands are coordinated to the metal(II) ion as uninegatively charged bidentate ligands via the thiolate sulfur and the azomethine nitrogen atoms. This revised version was published online in June 2006 with corrections to the Cover Date.     

On-line spectrophotometric determination of scandium after preconcentration on XAD-4 resin impregnated with nalidixic acid

An on-line scandium preconcentration and determination method was developed with spectrophotometer associated with flow injection. Scandium from aqueous sample solution of pH 4.5 was selectively retained in the minicolumn containing XAD-4 resin impregnated with nalidixic acid at a flow rate of 11.8 mL min^?1 as scandium–nalidixic acid complex. The scandium complex was desorbed from the resin by 0.1 mol L^?1 HCl at a flow rate of 3.2 mL min^?1 and mixed with arsenazo-III solution (0.05 % solution in 0.1 mol L^?1 HCl, 3.2 mL min^?1) and taken to the flow through cell of spectrophotometer where its absorbance was measured at 640 nm. The preconcentration factors obtained were 35 and 155; detection limits of 1.4 and 0.32 μg L^?1 and sample throughputs of 40 and 11 were obtained for preconcentration time of 60 and 300 s, respectively. The tolerance limits of many interfering cations like Th(IV), U (VI), rare-earths and anions like tartrate, citrate, oxalate and fluoride were improved. The method was successfully applied to the determination of scandium from mock seawater samples and good recovery was obtained. The method was also validated on certified reference material IAEA-SL-1 (lake sediment) and the result was in good agreement with the reported value.     

Solid phase extraction of Cd(II) and Pb(II) using a magnetic metal-organic framework, and their determination by FAAS

We describe a novel magnetic metal-organic framework (MOF) for the preconcentration of Cd(II) and Pb(II) ions. The MOF was prepared from the Fe₃O₄-pyridine conjugate and the copper(II) complex of trimesic acid. The MOF was characterized by IR spectroscopy, elemental analysis, SEM and XRD. A Box-Behnken design through response surface methodology and experimental design was used to identify the optimal parameters for preconcentration. Extraction time, amount of magnetic MOF and pH value were found to be critical factors for uptake, while type, volume, concentration of eluent, and elution time are critical in the elution step. The ions were then determined by FAAS. The limits of detection are 0.2 and 1.1 μg?L^?1 for Cd(II), and Pb(II) ions, respectively, relative standard deviations are <4.5% (for five replicates at 50 μg?L^?1 of Cd(II) and Pb(II) ions), and the enrichment capacity of the MOF is at around 190 mg?g^?1 for both ions which is higher than the conventional Fe3O4-pyridine material. The magnetic MOF was successfully applied to the rapid extraction of trace quantities of Cd(II) and Pb(II) ions in fish, sediment, and water samples.

Structure and properties of NR/BR blend/clay nanocomposites prepared by the latex method

Rubber blend/clay nanocomposites based on the 50/50 (wt %) natural rubber/butadiene rubber was prepared by the latex method via mixing the latex of 50/50 NR/BR blend with different amounts of the aqueous sodium montmorillonite (Na-MMT) dispersion and co-coagulating the mixture. XRD and TEM were used to characterize structure of the nanocomposites. It was found that fully exfoliated structure could be obtained by this method only when the low loading of layered silicate (up to 5 phr) is used. With increasing the clay content, both non-exfoliated (stacked layers) and exfoliated structures can be observed simultaneously in the nanocomposites. Nanocomposites showed mechanical properties better than the clay-free volcanizate. Moreover, modulus, tensile strength, elongation at break and tear strength increased significantly by increasing the clay amount up to 5 phr and then remained almost constant by further increasing the clay content. Improvement in the mechanical properties by increasing the clay loading up to 5 phr was attributed to the nano-reinforcement effect of Na-MMT. TGA results indicated an improvement in the main decomposition temperature by increasing the clay amount.     

Photoelectrocatalytic degradation of 3-nitrophenol at surface of Ti/TiO2 electrode

The widely utilization of phenol and its derivatives such as 3-nitrophenol (3-NP) has led to the worldwide pollution in the environment. In this study, Ti/TiO₂ photoelectrode was prepared with anodic oxidation of Ti foil electrode and then the photoelectrocatalytic (PEC) degradation of 3-NP was performed via this electrode, comparing with photocatalytic (PC), electrooxidation and direct photolysis by ultraviolet light. A significant photoelectrochemical synergetic effect in 3-NP degradation was observed on the Ti/TiO₂ electrode and rate constant for the PEC process of Ti/TiO₂ electrode was about three times as high as its PC degradation process. 3-NP concentration monitoring was carried out with differential pulse voltammetry. Results showed that PEC degradation has highest effect on concentration decreasing of 3-NP at solution and degraded it about 38 %, while other processes degradation efficiencies were about 4, 7, and 12 % for electrooxidation, direct photolysis and photocatalytic degradation, respectively. Finally, effects of solution pH and applied potential on degradation efficiency were studied and results showed that optimum pH for degradation is equal 4.00 and optimum potential is 1.2 V vs. Ag|AgCl|KCl (3M) reference electrode.     

pTSA-catalyzed condensation of xylenols and aldehydes under solvent-free conditions: One-pot synthesis of 9H-xanthene or bisphenol derivatives

A simple and efficient procedure for the synthesis of 9H-xanthene or bisphenol derivatives has been developed by one-pot condensation of xylenols with aromatic aldehydes in the presence of p-toluenesulfonic acid (pTSA) as a catalyst under solvent-free conditions at 100 °C. It is noteworthy that the condensation reaction of 3,5-xylenol with aldehydes produces 9H-xanthene derivatives, while the reaction with other xylenols leads to the corresponding bisphenol derivatives. Different types of aromatic aldehydes are used in the reaction and in every case the products were obtained in good to excellent yields. The structures of these compounds were established on the basis of IR, ¹H NMR, ¹³C NMR and CHN data.     

Palladium(II) and platinum(II) complexes of Schiff bases derived from 2,6-diacetylpyridine and S-methyldithiocarbazate and the X-ray crystal structure of the [Pd(mdapsme)Cl] complex

Condensation of 2,6-diacetylpyridine (dap) with S-methyldithiocarbazate (smdtc) in a 1:2 molar ratio yields a bicondensed pentadentate Schiff base (H₂dapsme) which reacts with K₂MCl₄ (M = Pd^II, Pt^II) giving stable complexes of empirical formula, [M(dapsme)] · 0.5Me₂CO. These complexes have been characterized by a variety of physico-chemical techniques. Condensation of dap with smdtc in a 1:1 molar ratio also yields the bicondensed Schiff base (H₂dapsme) as the major product, but a mono-condensed one-armed Schiff base (Hmdapsme) is also obtained as a minor product. The latter reacts with K₂PdCl₄ in an EtOH–H₂O mixture yielding a crystalline complex of empirical formula, [Pd(mdapsme)Cl], the crystal structure of which has been determined by X-ray diffraction. The complex has a distorted square-planar structure in which the ligand is coordinated to the palladium(II) ion as a uninegatively charged tridentate chelating agent via the pyridine nitrogen atom, the azomethine nitrogen atom and the thiolate sulfur atom; the oxygen atom of the acetyl group does not participate in coordination.     

Synthesis of 2-arylbenzimidazoles catalyzed by transition metal nitrates

A simple and practical procedure for synthesis of 2-arylbenzimidazoles by a one-pot condensation of o-phenylenediamine with aromatic aldehydes in the presence of a catalytic amount of M(NO₃)₂·6H₂O (M = Mn, Fe, Co, Ni, Cu) in ethanol at room temperature is described. Major advantages of this practical procedure are use of a readily available catalyst, high yields, short reaction times, and simplicity of the reaction and workup.     

Comparison of dispersive liquid–liquid microextraction and hollow fiber liquid–liquid–liquid microextraction for the determination of fentanyl,alfentanil, and sufentanil in water and biological fluids by high-performance liquid chromatography

Dispersive liquid–liquid microextraction (DLLME) and hollow fiber liquid–liquid–liquid microextraction (HF-LLLME) combined with HPLC–DAD have been applied for the determination of three narcotic drugs (alfentanil, fentanyl, and sufentanil) in biological samples (human plasma and urine). Different DLLME parameters influencing the extraction efficiency such as type and volume of the extraction solvent and the disperser solvent, concentration of NaOH, and salt addition were investigated. In the HF-LLLME, the effects of important parameters including organic solvent type, concentration of NaOH as donor solution, concentration of H₂SO₄ as acceptor phase, salt addition, stirring rate, temperature, and extraction time were investigated and optimized. The results showed that both extraction methods exhibited good linearity, precision, enrichment factor, and detection limit. Under optimal condition, the limits of detection ranged from 0.4 to 1.9 μg/L and from 1.1 to 2.3 μg/L for DLLME and HF-LLLME, respectively. For DLLME, the intra- and inter-day precisions were 1.7–6.4% and 14.2–15.9%, respectively; and for HF-LLLME were 0.7–5.2% and 3.3–10.1%, respectively. The enrichment factors were from 275 to 325 and 190 to 237 for DLLME and HF-LLLME, respectively. The applicability of the proposed methods was investigated by analyzing biological samples. For analysis of human plasma and urine samples, HF-LLLME showed higher precision, more effective sample clean-up, higher extraction efficiency, lower organic solvent consumption than DLLME.