New example of a non-heme mononuclear iron(IV) oxo complex. Spectroscopic data and oxidation activity

The green complex S=1 [(TPEN)FeO]2+ [TPEN=N,N,N',N'-tetrakis(2-pyridylmethyl)ethane-1,2-diamine] has been obtained by treating the [(TPEN)Fe]2+ precursor with meta-chloroperoxybenzoic acid (m-CPBA). This high-valent complex belongs to the emerging family of synthetic models of Fe(IV)=O intermediates invoked during the catalytic cycle of biological systems. This complex exhibits spectroscopic characteristics that are similar to those of other models reported recently with a similar amine/pyridine environment. Thanks to its relative stability, vibrational data in solution have been obtained by Fourier transform infrared. A comparison of the Fe=O and Fe=(18)O wavenumbers reveals that the Fe-oxo vibration is not a pure one. The ability of the green complex to oxidize small organic molecules has been studied. Mixtures of oxygenated products derived from two- or four-electron oxidations are obtained. The reactivity of this [FeO]2+ complex is then not straightforward, and different mechanisms may be involved.     

Shape recognition of alkylammonium ions by 1,3-bridged calix[5]arene crown-6 ethers: endo- vs exo-cavity complexation

A series of tri-O-substituted 1,3-bridged calix[5]arene crown-6 ethers bearing alkyl, arylalkyl, alkoxyalkyl, and alkoxycarbonylmethyl residues at the lower rim and either (t)()Bu or H substituents at the upper rim have been synthesized. (1)H NMR studies have shown that p-tert-butylcalix[5]crowns, irrespective of the size and nature of their lower rim pendant groups, adopt preorganized conelike conformations, whereas p-H-calix[5]crowns with bulky substituents preferentially exist in solution as partial cone conformers (C(1) symmetry). Calix[5]crown derivatives behave as mono- or ditopic receptors for isomeric butylammonium ions, forming endo-cavity (inside the calixarene cup) and/or exo-cavity (at the crown ether moiety) 1:1 complexes according to the shape of the guest. These two binding modes can be clearly distinguished and monitored by (1)H NMR titration experiments.     

Molecularly imprinted solid-phase extraction of (-)-ephedrine from Chinese Ephedra

Method of molecularly imprinted solid phase extraction (MISPE) of (-)-ephedrine from Chinese Ephedra has been developed in the research. The molecularly imprinted polymer (MIP) with good selectivity and affinity for (-)-ephedrine was synthesized with (-)-ephedrine as the template, methacrylic acid as the functional monomer. The washing and elution conditions in MISPE were selected and optimized for efficient analyte extraction and sample clean-up. A clean analytical HPLC base line of ephedra extract was obtained after MISPE, which indicated that the sample pre-treatment was efficient. Good recovery and precision were obtained in the assessment for the MISPE-HPLC procedure, which demonstrated it is a reliable method and can be used for the determination of (-)-ephedrine in herbal ephedra.     

Designed nanostructured pt film for electrocatalytic activities by underpotential deposition combined chemical replacement techniques

Multiple-deposited Pt overlayer modified Pt nanoparticle (MD-Pt overlayer/PtNPs) films were deliberately constructed on glassy carbon electrodes through alternately multiple underpotential deposition (UPD) of Ag followed redox replacement reaction by Pt (II) cations. The linear and regular growth of the films characterized by cyclic voltammetry was observed. Atomic force spectroscopy (AFM) provides the surface morphology of the nanostructured Pt films. Rotating disk electrode (RDE) voltammetry and rotating ring-disk electrode (RRDE) voltammetry demonstrate that the MD-Pt overlayer/PtNPs films can catalyze an almost four-electron reduction of O(2) to H(2)O in air-saturated 0.1 M H(2)SO(4). Thus-prepared Pt films behave as novel nanostructured electrocatalysts for dioxygen reduction and hydrogen evolution reaction (HER) with enhanced electrocatalytic activities, in terms of both reduction peak potential and peak current, when compared to that of the bulk polycrystalline Pt electrode. Additionally, it is noted that after multiple replacement cycles, the electrocatalytic activities improved remarkably, although the increased amount of Pt is very low in comparison to that of pre-modified PtNPs due to the intrinsic feature of the UPD-redox replacement technique. In other words, the electrocatalytic activities could be improved markedly without using very much Pt by the technique of tailoring the catalytic surface. These features may provide an interesting way to produce Pt catalysts with a reliable catalytic performance as well as a reduction in cost.     

One-carbon homologation of carboxylic acids via BtCH(2)TMS: a safe alternative to the Arndt--Eistert reaction

Carboxylic acids are converted into the corresponding homologated acids or esters, using easily available 1-(trimethylsilylmethyl)benzotriazole (1) as a one-carbon synthon. The effectiveness of the reaction has been investigated on six aryl and seven alkyl carboxylic acids.     

Synthesis and metal-ion binding properties of monoazathiacrown ethers

Synthetic procedures for monoazathiacrown ethers were explored, and monoazatrithia-12-crown-4, monoazatetrathia-15-crown-5, and monoazapentathia-18-crown-6 were obtained in moderate yields by the reaction of bis(2-chloroethyl)amine with the appropriate dithiols in the presence of lithium hydroxide in THF. To evaluate metal-ion binding properties of the monoazathiacrown ethers by solvent extraction, lipophilic dodecyl and dodecanoyl groups were incorporated onto the monoazathiacrown ethers. The solvent extraction experiments suggested that monoazathiacrown ethers have Ag(+) and Hg(2+) selectivities and that the relative selectivity between Ag(+) and Hg(2+) depends on their nitrogen atom properties and numbers of sulfur atoms reflecting the respective affinities of nitrogen and sulfur atoms to Hg(2+) and Ag(+). An interesting ability to bind Mg(2+) was observed in the case of N-dodecyl monoazatrithia-12-crown-4.     

Structural features of aliphatic N-nitrosamines of 7-azabicyclo[2.2.1]heptanes that facilitate N-NO bond cleavage

N-Nitrosamines can be considered as potential nitric oxide (NO)/nitrosonium ion (NO(+)) donors. However, the relation of the structures of N-nitrosamines, in particular of aliphatic N-nitrosamines, to the characteristics of release of NO or NO(+) remains unclear. Here we show that aliphatic N-nitrosoamines of 7-azabicyclo[2.2.1]heptanes can undergo heterolytic N-NO bond cleavage. On the basis of the observation of reduced rotational barriers of the N-NO bonds in solution and nitrogen-pyramidal structures of the N-nitroso group in the solid state, we postulate that N-NO bond cleavage of N-nitrosamines is enhanced by a reduction of the resonance in the N-NO group. Computational studies suggest that these structural features of the N-nitrosamines of 7-azabicyclo[2.2.1]heptane are derived from angle strain imposed on the CNC angles.     

Enantioselective crystallization of D,L-amino acids induced by spontaneous asymmetric resolution of D,L-asparagine

Racemic D,L-asparagine induced spontaneous asymmetric resolution of co-existing D,L-phenylalanine or D,L-tryptophan by recrystallization from a homogeneous aqueous solution, and the enantiomeric excess of phenylalanine or tryptophan in the resulting crystals correlated linearly with that of asparagine crystallized with phenylalanine or tryptophan.     

Proposal of sampling process for collecting human sweat and determination of caffeine concentration in it by using GC/MS

Caffeine concentration in human sweat was estimated by measuring separately the amounts of water and caffeine. After washing a finger with tap water for 15 s and waiting 2 min for drying, 70 microL aqueous ethanol solution in a small vial (0.6 mL) was used to sample for several minutes. Then 3 microL of the aliquot was used for GC/MS analysis of caffeine. As a first-order relationship between the sweat amount secreted on the left and right hands was obtained (correlation factor 0.848), the amount of sweat secretion during sampling on one hand was estimated by the value obtained on the other hand. This new indirect evaluation was used for the estimation of the amount of sweat secreted during sampling. Typical variations of caffeine concentration in sweat were demonstrated. Thirty minutes after the intake of caffeine, it was secreted in sweat, and the secretion had continued for more than 4 h.