Gadolinium and neodymium citrates: evidence for weak ferromagnetic exchange between gadolinium(III) cations

A new lanthanide citrate motif of general formula [Ln(Hcit)(H2O)2.H2O]n, where Ln = Gd (1) and Nd (2) and Hcit3- = C(OH)(COO-)(CH2COO-)2, has been synthesized hydrothermally from Ln2O3 and citric acid at 100 degrees C and characterized by elemental analysis, IR, TG-DTA, single-crystal X-ray diffraction, and magnetic measurements. The structures can be seen as "ladder chains" along the a axis, with dinuclear Ln2O2 units serving as "steps" and R-COO groups as "uprights", which are connected by H bonds. The magnetic susceptibility between 2 and 300 K and the magnetization at 2 K, as a function of magnetic field between 0 and 5 T, were measured for both compounds. By modeling the magnetic behavior of the Gd compound with a dinuclear Hamiltonian [symbol: see text](S) = gmu(B)(S(A) + S(B))B(o) - J(o)S(A)S(B) (S(A) = S(B) = 7/2), a ferromagnetic exchange interaction J(o) = 0.039 cm(-1) was evaluated between Gd ions situated at d(o) = 4.321 angstroms in dinuclear units bridged by two symmetry-related tridentate carboxylate oxygens. The EPR spectrum of the Gd compound is discussed. The temperature dependence of the susceptibility of the Nd compound is caused by the depopulation of the excited crystal-field levels when the temperature decreases. The magnetic-field dependence of the magnetization of 2 is attributed to the ground-state Kramers' doublet populated at 2 K. The g factor of this ground-state doublet is calculated from the data and compared with values for other compounds reported in the literature.     

The Dakin-West reaction: Past,present and future

The decarboxylation of amino acids in presence of a carboxylic anhydride leading to the corresponding ketones, known as Dakin-West reaction, is about to complete almost one century of discovery. In this review, we firstly present the chronological progress in the mechanistic study of the reaction, with an overview about types of substrates, anhydrides and bases already used in the Dakin-West reaction. And ultimately, the application of the reaction in the synthesis of compounds of pharmaceutical or industrial interest is also discussed.     

An unusual eight‐coordinated copper complex: bis­(4,7‐diphenyl‐1,10‐phenanthroline)dinitratocopper(II)

In the title monomer, [Cu(NO₃)₂(C₂₄H₁₆N₂)₂], the copper(II) cation is eight‐coordinate within an octa­hedral‐like polyhedron. The coordination polyhedron is formed by two chelating diphenyl­phenanthroline groups that define the highly distorted CuN₄ equatorial plane and two weakly bound bidentate (chelating) nitrate groups in the apical or axial positions. The complex crystallizes in the monoclinic space group C2/c; a twofold axis passes through the copper(II) cation and bis­ects the two nitrate ligands. This gives the mol­ecule C₂ point‐group symmetry, rendering only half of the mol­ecule independent.     

High-pressure vapor–liquid equilibria for CO2 + alkanol systems and densities of n-dodecane and n-tridecane

An apparatus based on the static-analytic method was used to measure the vapor–liquid equilibria (VLE) for CO₂ + alkanol systems. Equilibrium measurements for the CO₂ + 1-propanol system were performed from 344 to 426 K. For the case of the CO₂ + 2-propanol system, measurements were made from 334 to 443 K, and for the CO₂ + 1-butanol were obtained from 354 to 430 K. VLE data were correlated with the Peng–Robinson equation of state using the classical and the Wong–Sandler mixing rules. Moreover, compressed liquid densities for the n-dodecane and n-tridecane were obtained via a vibrating tube densitometer at temperatures from 313 to 363 K and pressures up to 25 MPa. The Starling and Han (BWRS), and The five-parameter Modified Toscani-Swarcz (MTS) equations were used to correlate them. The experimental density data were compared with those from literature, and with the calculated values obtained from available equations for these n-alkanes.     

Construction of titanasiloxanes by incorporation of silanols to the metal oxide model [(Ti(eta 5-C5Me5)(mu-O))3(mu3-CR)]: DFT elucidation of the reaction mechanism

A family of novel titanasiloxanes containing the structural unit {[Ti(eta(5)-C(5)Me(5))O](3)} were synthesized by hydron-transfer processes involving reactions with equimolecular amounts of mu(3)-alkylidyne derivatives [{Ti(eta(5)-C(5)Me(5))(mu-O)}(3)(mu(3)-CR)] (R=H (1), Me (2)) and monosilanols, R(3)'Si(OH), silanediols, R(2)'Si(OH)(2), and the silanetriol tBuSi(OH)(3). Treatment of 1 and 2 with triorganosilanols (R'=Ph, iPr) in hexane affords the new metallasiloxane derivatives [{Ti(eta(5)-C(5)Me(5))(mu-O)}(3)(mu-CHR)(OSiR(3)')] (R=H, R'=Ph (3), iPr (4); R=Me, R'=Ph (5), iPr (6)). Analogous reactions with silanediols, (R'=Ph, iPr), give the cyclic titanasiloxanes [{Ti(eta(5)-C(5)Me(5))(mu-O)}(3)(mu-O(2)SiR'(2))(R)] (R=Me, R'=Ph (7), iPr (8); R=Et, R'=Ph (9), iPr (10)). Utilization of tBuSi(OH)(3) with 1 or 2 at room temperature produces the intermediate complexes [{Ti(eta(5)-C(5)Me(5)) (mu-O)}(3)(mu-O(2)Si(OH)tBu)(R)] (R=Me (11), Et(12)). Further heating of solutions of 11 or 12 affords the same compound with an adamantanoid structure, [{Ti(eta(5)-C(5)Me(5))(mu-O)}(3)(mu-O(3)SitBu)] (13) and methane or ethane elimination, respectively. The X-ray crystal structures of 3, 4, 6, 8, 10, 12, and 13 have been determined. To gain an insight into the mechanism of these reactions, DFT calculations have been performed on the incorporation of monosilanols to the model complex [{Ti(eta(5)-C(5)H(5))(mu-O)}(3)(mu(3)-CMe)] (2 H). The proposed mechanism consists of three steps: 1) hydron transfer from the silanol to one of the oxygen atoms of the Ti(3)O(3) ring, forming a titanasiloxane; 2) intramolecular hydron migration to the alkylidyne moiety; and 3) a mu-alkylidene ligand rotation to give the final product.     

On the dynamics of the H+ +D2(v=0,j=0)-->HD+D + reaction: a comparison between theory and experiment

The H+ +D2(v=0,j=0)-->HD+D + reaction has been theoretically investigated by means of a time independent exact quantum mechanical approach, a quantum wave packet calculation within an adiabatic centrifugal sudden approximation, a statistical quantum model, and a quasiclassical trajectory calculation. Besides reaction probabilities as a function of collision energy at different values of the total angular momentum, J, special emphasis has been made at two specific collision energies, 0.1 and 0.524 eV. The occurrence of distinctive dynamical behavior at these two energies is analyzed in some detail. An extensive comparison with previous experimental measurements on the Rydberg H atom with D2 molecules has been carried out at the higher collision energy. In particular, the present theoretical results have been employed to perform simulations of the experimental kinetic energy spectra.     

Immobilized microorganisms in the reduction of ethyl 4-chloro acetoacetate

Microorganisms were used to reduce ethyl 4-chloroacetoacetate (CAAE) to ethyl (S)-4-chloro-3-hydroxybutanoate [(S)-CHBE]. Mucor ramannianus provided 98% conversion with 84% ee. Free cells of Kluyveromyces marxianus led to 95% conversion with 81% ee. After a fractionary factorial design to study the reaction conditions, calcium alginate immobilized cells of K. marxianus furnished the product with 99% conversion with 91% ee.     

Non commuting quantum cosmology with scalar matter

We study noncommutative quantum and classical cosmology with a scalar field by means of deforming the minisuperspace. We analyze the homogeneous and isotropic model and compare our results with the usual commutative case. In particular the classical behaviour of the scalar field can dramatically change due to the presence of noncommutativity.We dedicate this work to Michael P. Ryan on the occasion of his sixtieth birthday. Around 30 years ago, Mike patiently introduced us to Quantum Cosmology. Since that time, we have had rich and friendly discussions and fruitful collaborations.     

Characterization of a Marine Microbial Community Used for Enhanced Sulfate Reduction and Copper Precipitation in a Two-Step Process

Marine microorganisms that are obtained from hydrothermal vent sediments present a great metabolic potential for applications in environmental biotechnology. However, the work done regarding their applications in engineered systems is still scarce. Hence, in this work, the sulfate reduction process carried out by a marine microbial community in an upflow anaerobic sludge blanket (UASB) reactor was investigated for 190 days under sequential batch mode. The effects of 1000 to 5500 mg L^?1 of SO₄ ^?2 and the chemical oxygen demand (COD)/SO₄ ^?2 ratio were studied along with a kinetic characterization with lactate as the electron donor. Also, the feasibility of using the sulfide produced in the UASB for copper precipitation in a second column was studied under continuous mode. The system presented here is an alternative to sulfidogenesis, particularly when it is necessary to avoid toxicity to sulfide and competition with methanogens. The bioreactor performed better with relatively low concentrations of sulfate (up to 1100 mg L^?1) and COD/SO₄ ^?2 ratios between 1.4 and 3.6. Under the continuous regime, the biogenic sulfide was sufficient to precipitate copper at a removal rate of 234 mg L^?1 day^?1. Finally, the identification of the microorganisms in the sludge was carried out; some genera of microorganisms identified were Desulfitobacterium and Clostridium.