Kinetic anomalies of mixed crystal growth and their effect on the crystal isomorphic composition

Growth rate anomalies in aqueous solution growth of NaClO₃ and KClO₃ were first revealed by V. V. Sipyagin in 1967 and attributed to “kinetic anomalies”. These phenomena were confirmed in a series of other studies and for a variety of substances. Therefore, some universality of these anomalies was supposed that should be due to structural transformations in the liquid solutions. In this paper, we present for the first time results on growth rate oscillations found in mixed crystal growth and their impact on the isomorphic composition of solid solutions. Thick (100) Na(Cl,Br)O₃ layers were grown at fixed supercooling conditions onto NaClO₃ seeds in a microcrystallization cell equipped with an optical microscope. In the temperature range of 33 – 41 °C, four kinetic anomalies were found in solutions of a chlorate: bromate molar ratio of 20: 1 at supercoolings of 2.0 K and 3.0 K. Lattice parameter measurements of the grown Na(Cl,Br)O₃ layers revealed a linear dependence of lattice constant vs. growth rate. By measuring Vegard's law (lattice parameter vs. solid solution composition) we were able to determine the oscillations in mixed crystal composition that accompany the kinetic anomalies in solid solution systems. (© 2009 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

Rate constants of the thermal cis‐trans isomerization of azobenzene dyes in solvents,acetone/water mixtures,and in microheterogeneous surfactant solutions

Rate constants k_iso of the thermal cis‐trans isomerization of four 4,4’‐nitro‐aminoazobenzenes with different amino groups have been determined in homogeneous aprotic solvents and polyglykol oligomers, primarily by means of conventional flash photolysis. The rate constants have been correlated with polarity (according to λ_max from UV/Vis absorption spectra of the trans isomers) and bulk viscosity of the solvents. Qualitative conclusions about the influence of varying concentrations of water with respect to polarity and hydrogen bonding on k_iso‐ and λ_max‐values in acetone/water mixtures were derived. Based on these results the data from microheterogeneous solutions have been interpreted. In microheterogeneous water/surfactant solutions k_iso‐values of selected azo dyes were strongly dependent on the concentrations of SDS, Triton^®X‐100, C₁₂EO₈ in water, and varied with the composition of bicontinuous microemulsions of Igepal^® CA‐520/ heptane/water. The large spread of isomerization rate constants is in part due to varying microviscosity. Replacement of H₂O by D₂O in aqueous surfactant solutions produced surprisingly large kinetic solvent isotope effects. © 1999 John Wiley & Sons, Inc. Int J Chem Kinet 31: 337–350, 1999     

From fluoral to heterocycles: a survey of polyfluorinated iminiums chemistry

Hemiaminals of fluorinated aldehydes are very useful reagents. They are able, under Lewis acid activation, to generate iminium species which can react with various nucleophiles and provide diverse fluorinated compounds. By this methodology, β-fluoroalkylated enones, which are very interesting building blocks, have been easily obtained. Fluorinated homoallylamines have been also synthesized and used as starting material to prepare α-fluoroalkylated nitrogen heterocycles. Many other synthetic applications of these fluorinated iminium ions provide new bioactive compounds.     

Fully Borylated Methane and Ethane by Ruthenium‐Mediated Cleavage and Coupling of CO

Many transition‐metal complexes and some metal‐free compounds are able to bind carbon monoxide, a molecule which has the strongest chemical bond in nature. However, very few of them have been shown to induce the cleavage of its C?O bond and even fewer are those that are able to transform CO into organic reagents with potential in organic synthesis. This work shows that bis(pinacolato)diboron, B₂pin₂, reacts with ruthenium carbonyl to give metallic complexes containing borylmethylidyne (CBpin) and diborylethyne (pinBC≡CBpin) ligands and also metal‐free perborylated C₁ and C₂ products, such as C(Bpin)₄ and C₂(Bpin)₆, respectively, which have great potential as building blocks for Suzuki–Miyaura cross‐coupling and other reactions. The use of ¹³CO‐enriched ruthenium carbonyl has demonstrated that the boron‐bound carbon atoms of all of these reaction products arise from CO ligands.     

Examples of algebraic groups of type <Emphasis Type="Italic">G</Emphasis> <Subscript>2</Subscript> having the same maximal tori

Answering a question of A. Rapinchuk, we construct examples of non-isomorphic semisimple algebraic groups H₁ and H₂ of type G₂ having coherently equivalent systems of maximal k-tori.     

Reduction of structure for torsors over semilocal rings

Let G be a reductive affine group scheme defined over a semilocal ring k. Assume that either G is semisimple or k is normal and noetherian. We show that G has a finite k-subgroup S such that the natural map H ¹(R, S) → H ¹(R, G) is surjective for every semilocal ring R containing k. In other words, G-torsors over Spec(R) admit reduction of structure to S. We also show that the natural map H ¹(X, S) → H ¹(X, G) is surjective in several other contexts, under suitable assumptions on the base ring k, the scheme X/k and the group scheme G/k. These results have already been used to study loop algebras and essential dimension of connected algebraic groups in prime characteristic. Additional applications are presented at the end of this paper. V. Chernousov was partially supported by the Canada Research Chairs Program and an NSERC research grant. Z. Reichstein was partially supported by NSERC Discovery and Accelerator Supplement grants.     

On the Brauer group of the product of a torus and a semisimple algebraic group

Let T be a torus (not assumed to be split) over a field F, and denote by nH _et ² (X,{ie375-1}) the subgroup of elements of the exponent dividing n in the cohomological Brauer group of a scheme X over the field F. We provide conditions on X and n for which the pull-back homomorphism nH _et ² (T,{ie375-2}) → _n H _et ² (X × _F T, {ie375-3}) is an isomorphism. We apply this to compute the Brauer group of some reductive groups and of non-singular affine quadrics. Apart from this, we investigate the p-torsion of the Azumaya algebra defined Brauer group of a regular affine scheme over a field F of characteristic p > 0.     

Application of thermal analysis to the study of lipidic prodrug incorporation into nanocarriers

Anti HIV molecules as numerous drugs cannot efficiently penetrate into the brain. Prodrug synthesis and encapsulation into pegylated nanocarriers have been proposed as an approach for brain delivery. Pegylated polymeric nanoparticles and liposomes were chosen to incorporate glycerolipidic prodrugs of didanosine. Differential scanning calorimetry experiments were performed on mixtures of prodrugs and lipids or polymer in order to study their interaction. The optimal incorporation ratios were determined for each prodrug and compared for both types of nanocarriers. All these results would be used to prepare optimised formulations of didanosine prodrugs loaded into pegylated nanocarriers for brain drug delivery.     

Essential Oil from Melaleuca leucadendra: Antimicrobial,Antikinetoplastid, Antiproliferative and Cytotoxic Assessment

Essential oils (EOs) are known for their use in cosmetics, food industries, and traditional medicine. This study presents the chemical composition and therapeutic properties against kinetoplastid and eukaryotic cells of the EO from Melaleuca leucadendra (L.) L. (Myrtaceae). Forty-five compounds were identified in the oil by GC-MS, containing a major component the 1,8-cineole (61%). The EO inhibits the growth of Leishmania amazonensis and Trypanosoma brucei at IC₅₀ values <10 μg/mL. However, 1,8 cineole was not the main compound responsible for the activity. Against malignant (22Rv1, MCF-7, EFO-21, including resistant sublines MCF-7/Rap and MCF-7/4OHTAMO) and non-malignant (MCF-10A, J774A.1 and peritoneal macrophage) cells, IC₅₀ values from 55 to 98 μg/mL and from 94 to 144 μg/mL were obtained, respectively. However, no activity was observed on Staphylococcus aureus, Enterococcus faecalis, Escherichia coli, Pseudomonas aeruginosa, Aspergillus niger, Candida parapsilosis, Microsporum canis, or Trypanosoma cruzi. The EO was able to control the lesion size and parasite burden in the model of cutaneous leishmaniasis in BALB/c mice caused by L. amazonensis compared to untreated animals (p < 0.05) and similar with those treated with Glucantime^® (p > 0.05). This work constitutes the first evidence of antiproliferative potentialities of EO from M. leucadendra growing in Cuba and could promote further preclinical investigations to confirm the medical value of this plant, in particular for leishmaniasis treatment.