A MALDI‐TOF MS study of lanthanide(III)‐cored poly(phenylenevinylene) dendrimers

An extensive study by matrix‐assisted laser desorption/ionization time‐of‐flight (MALDI‐TOF) mass spectrometry (MS) of some first‐generation and second‐generation lanthanide(III)‐cored poly(phenylenevinylene) dendrimers is described. The complexes were obtained by self‐assembly of suitably functionalized carboxylate dendrons around the lanthanide ion (La³⁺, Er³⁺). Fourier transform infrared (FT‐IR) spectroscopy gave reasonable evidence for the proposed structures. However, MS was used to ascertain unequivocally the complex formation. The most reliable results were found in the negative reflector mode, using 2‐[(2E)‐3‐(4‐tert‐butylphenyl)‐2‐methylprop‐2‐enylidene]malononitrile (DCTB) as matrix. Well‐defined and highly resolved base peaks corresponding to negative ions of [Gn₄La]^? and [Gn₄Er]^? were found in all cases, with an excellent match between the theoretical and observed isotope distributions. However, the 3 : 1 stoichiometry used in the synthesis guarantees an empirical formula Gn₃Ln for the complexes. Copyright © 2008 John Wiley & Sons, Ltd.     

Uniform magnetic properties for an ultrahigh-density lattice of noninteracting co nanostructures

We report on the magnetic properties of two-dimensional Co nanoparticles arranged in macroscopically phase-coherent superlattices created by self-assembly on Au(788). Our particles have a density of 26 Tera/in2 (1 Tera=10(12)), are monodomain, and have uniaxial out-of-plane anisotropy. The distribution of the magnetic anisotropy energies has a half width at half maximum of 17%, a factor of 2 more narrow than the best results reported for superlattices of three-dimensional nanoparticles. Our data show the absence of magnetic interactions between the particles. Co/Au(788) thus constitutes an ideal model system to explore the ultimate density limit of magnetic recording.     

Evaluation of distribution and bioavailability of Cr,Mn, Fe,Cu, Zn and Pb in the waters of the upper course of the Lerma River

Distribution and bioavailability of Cr, Mn, Fe, Cu, Zn, and Pb in the waters of the upper course of the Lerma River (UCLR), Mexico, were evaluated by means total reflection x‐ray fluorescence spectrometry. The surface water samples were collected from eight sites distributed along the flow direction of the river. Four sampling campaigns were carried out in each site during a one‐year period. The water samples were analyzed in triplicate, using a TXRF Spectrometer ‘TX‐2000 Ital Structures’ with a Si(Li) detector and a resolution of 140 eV (FWHM) at Mn Kα. A Mo tube (40 kV, 30 mA) with 17.4 KeV excitation energy was used for a counting time of 500 s. Results show that the concentration ranges of heavy metals in the water are the following: Cr, from < 5 to 56 µg/l; Mn, from 9 to 788 µg/l; Fe, from 98 to 8474 µg/l; Cu, from 10 to 225 µg/l; Zn, from 23 to 189 µg/l and Pb, from < 3 to 30 µg/l. There are significant statistical differences in the concentration of heavy metals between the different sampling sites and between the different sampling campaigns. The Pearson correlation results indicate a strong correlation between some heavy metals in the water, this significant correlation (p < 0.05) indicating a natural or/and a shared contamination source for these metals. Metal concentration in the water mostly did not exceed the guide values given by Mexican regulation for agricultural use. Only Cu, Mn and Fe in total water phase exceeded the maximum permissible limits for irrigation proposes at some sites. Copyright © 2007 John Wiley & Sons, Ltd.     

New complexes of zirconium(IV) and hafnium(IV) with heteroscorpionate ligands and the hydrolysis of such complexes to give a zirconium cluster

A series of zirconium and hafnium heteroscorpionate complexes have been prepared by the reaction of MCl4 (M = Zr, Hf) with the compounds [[Li(bdmpza)(H2O)](4)] [bdmpza = bis(3,5-dimethylpyrazol-1-yl)acetate], [[Li(bdmpzdta)(H2O)](4)] [bdmpzdta = bis(3,5-dimethylpyrazol-1-yl)dithioacetate], and (Hbdmpze) [bdmpze = 2,2-bis(3,5-dimethylpyrazol-1-yl)ethoxide] (the latter with the prior addition of Bu(n)Li). Under the appropriate experimental conditions, mononuclear complexes, namely, [MCl3(kappa3-bdmpzx)] [x = a, M = Zr (1), Hf (2); x = dta, M = Zr (3), Hf (4); x = e, M = Zr (5), Hf (6)], and dinuclear complexes, namely, [[MCl2(mu-OH)(kappa3-bdmpzx)]2] [x = a, M = Zr (7), Hf (8); x = dta, M = Zr (9); x = e, M = Zr (10)], were isolated. A family of alkoxide-containing complexes of the general formula [ZrCl2(kappa3-bdmpzx)(OR)] [x = a, R = Me (11), Et (12), iPr (13), tBu (14); x = dta, R = Me (15), Et (16), iPr (17), tBu (18); x = e, R = Me (19), Et (20), (i)Pr (21), (t)Bu (22)] was also prepared. Complexes 11-14 underwent an interesting hydrolysis process to give the cluster complex [Zr6(mu3-OH)8(OH)8(kappa2-bdmpza)8] (23). The structures of these complexes have been determined by spectroscopic methods, and the X-ray crystal structures of 7, 8, and 23 were also established.     

Major and trace elements in sediments of the upper course of Lerma river

Summary The Lerma is one of the most important rivers of Mexico, where it drains highly populated and industrialized regions. The concentration of six major and trace elements: titanium, manganese, iron, zinc, copper and lead in the surface sediments of the upper course of Lerma river was investigated, in order to identify its distribution along the river and to recognize the principal sites of pollution. The surface sediment samples were collected at 8 sites distributed following the stream flow direction of the river. Major and trace elements concentrations were determined by energy dispersive X-ray spectrometry. The results show that the metal concentrations in the sediments decrease in the sequence: Fe > Ti > Mn > Zn > Cu > Pb. Concentration of Fe, Mn and Ti were significantly higher than the other metals in site 8,200 meters downstream the Alzate Dam. The high concentrations and spatial variations of Zn, Cu and Pb in the middle sites of the upper course of the Lerma River indicate that the river pollution is probably associated with urban and industrial discharges.     

Treatment and labeling of silica sand for obtaining a prospective solid 99mTc radiotracer

Journal of Radioanalytical and Nuclear Chemistry - Pretreated silica sand labeling using varying concentrations of tin(II) fluoride and chloride as reducing agents and different times labeling was...     

Synthesis of N-Alkylpyrazoles by Phase Transfer Catalysis Without Solvent Without Solvent

The alkylation of pyrazole is performed by phase transfer catalysis without solvent. High yields of N-alkylpyrazoles are obtained and the principal problems in the alkylation are suitably solved.     

The Raman spectra and cross-sections of H2O, D2O, and HDO in the OH/OD stretching regions

We report the OH and OD stretching regions of the vapor phase Raman spectra of H₂O, and of a D₂O/HDO mixture, at room temperature. Also, the corresponding spectrum of H₂O at ∼2000 K in a methane/air flame is reported. These spectra are interpreted in terms of transition moments of the molecular polarizability, based on high-level ab initio calculations of the polarizability surface, and on variational wavefunctions considering the rotational-vibrational coupling in full. As a byproduct of this analysis several tables have been compiled including scattering strengths and assignments for individual rotational transitions of the three species. From these tables the Raman spectra in the OH/OD stretching regions can be simulated over the range of temperatures up to 2000 K for H₂O, and up to 300 K for D₂O and HDO.     

Alkylation of Imidazole by Solid-Liquid Phase Transfer Catalysis in the Absence of Solvent

Phase Transfer Catalysis in the absence of solvent is described as a useful and general method for the selective N-alkylation of imidazole. In all cases high yields are obtained while quaternization is avoided.