Palladium-catalyzed cascade allylation/carbopalladation/cross coupling: a novel three-component reaction for the synthesis of 3,3-disubstituted-2,3-dihydrobenzofurans

A novel one-pot palladium-catalyzed cascade between 2-iodophenol, methyl bromomethylacrylate and an arylboronic acid provides an efficient access to heterocycles possessing the 3,3-disubstituted-2,3-dihydrobenzofuran skeleton via allylation/carbopalladation/Suzuki cross-coupling.     

Cross-metathesis assisted by microwave irradiation

Microwave irradiation effectively accelerates cross-coupling metathesis reactions between deactivated olefins. Reactions have been carried out with the phosphine-free Hoveyda-Grubbs catalyst and the "second generation Grubbs' catalyst." While there have been reports that a "microwave effect" is observed in various transformations, the accelerations we observe are due to the efficient and rapid heating and increased pressure in the microwave apparatus.     

Formation of Small Silica Aggregates by Turbulent Aggregation

Aggregation of silica powder in water has been experimentally studied by turbidimetry. Aggregation was carried out in a stirred tank under physicochemical conditions corresponding to attractive interparticle forces. The effects of different primary particle sizes and stirring rates on aggregation dynamics have been studied. The scattering cross sections of silica aggregates were calculated in the framework of the anomalous diffraction approximation of light scattering theory. Aggregation has been studied by using Kusters's and Brakalov's approaches. By comparison between experimental and theoretical turbidity changes with time it has been shown that aggregates are small and slightly porous. The aggregation process is characterized by a weak fractal dimension D(wf) and an aggregate limit size L.D(wf) is found in the range 2.4-2.5. D(wf) (respectively L) is a weakly increasing (respectively decreasing) function of the stirring rate or of the shear rate. Copyright 2001 Academic Press.     

Peculiarities of the chemical properties of vicinally disubstituted veratrole and synthesis of 1-methyl-4,5-dimethoxybenzimidazole derivatives

Various paths for the synthesis of 4-methylamino-3-aminoveratrole (I) from 4-amino-3-nitroveratrole (II) were investigated, and it was found that I can be obtained in a high overall yield of 65% through the tosyl derivative of II. 1-Methyl-4,5-dimethoxybenzimidazolone, 1-methyl-4,5-dimethoxybenzimidazole and its 2-phenyl-, 2-chloro-, and 2-dimethylamino derivatives were synthesized on the basis of I in order to investigate their biological activity. It was established that the chemical properties of vicinally disubstituted veratrole, particularly the increased basicity of II, are determined to a significant degree by steric strains caused by bulky substituents. It is shown that 85% formic acid can be successfully used in place of 98–100% formic acid for the N-formylation of aromatic amines with a mixture of formic acid and acetic anhydride.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 10, pp. 1387–1392, October, 1970.     

Partial purification and some properties of a hemolymph lectin from panstrongylus megistus (Hemiptera,Reduviidae)

Hemagglutinating activity was studied in homogenates of three embryonic stages, and in the hemolymph of most instar larvae and in adult insects of Panstrongylus megistus, an important Chagas' disease vector in Brazil. A hemolymph lectin from the 5th instar larvae of P. megistus was purified through a biospecific adsorption by using formaldehyde-treated erythrocytes. The lectin fraction was desorbed with 0.2M D-galactose in 0.15M NaCl. The lectin fraction activity was inhibited by L-rhamnose, D-lactose, raffinose, D-galactose, and D-fucose. The electrophoretic pattern to native and acidic proteins resolved lectin fraction in two main bands with lectin activity. These bands were considered as multiple molecular forms or isoforms of P. megistus lectin. Under denaturating conditions, isoform 1 showed one band with apparent mol wt (MW) of 64 kDa while isoform 2 was resolved in two bands with MW of 64 and 33 kDa.     

Emission of neutrino pairs by an electron in an ultrastrong magnetic field

The transitions of relativistic electrons in a magnetic field with the emission of an antineutrino-neutrino pair are considered. Probabilities are obtained for electron transitions to the ground state and weakly excited states. It is shown that in the case of an ultrastrong magnetic field (HH_o=m²c³/e=4.41·10¹³ G) such transitions made a considerable contribution to the total probability of the process.Translated from Izvestiya Vysshikh Uchebnykh Zavedenii, Fizika, No. 3, pp. 110–114, March, 1978.In conclusion, the authors express their profound gratitude to A. A. Sokolov for his attention to our work.     

Platinum complexes of oxopurines: cis‐bis(theophyllinato‐N7)bis(triphenylphosphine)platinum(II) and cis‐chloro(theobrominato‐N1)bis(triphenylphosphine)platinum(II) ethanol hemisolvate

The syntheses and structures of two mixed‐ligand complexes of platinum(II) with deprotonated oxopurine bases and tri­phenyl­phosphine are reported, namely the theophyllinate complex cis‐bis(1,2,3,6‐tetra­hydro‐1,3‐di­methyl­purine‐2,6‐dionato‐κN⁷)­bis(tri­phenyl­phosphine‐κP)­platinum(II), [Pt(C₇H₇N₄O₂)₂(C₁₈H₁₅P)₂], (I), and the theobrominate complex cis‐chloro(1,2,3,6‐tetrahydro‐3,7‐dimethylpurine‐2,6‐dionato‐κN¹)­bis(tri­phenyl­phosphine‐κP)­platinum(II) ethanol hemisolvate, [PtCl(C₇H₇N₄O₂)(C₁₈H₁₅P)₂]·0.5C₂H₅OH, (II). In (I), the coordination geometry of Pt is square planar, formed by the two coordinating N atoms of the theophyl­linate anions in a cis arrangement and two P atoms from the tri­phenyl­phosphine groups. In (II), there are two crystallographically independent mol­ecules. They both exhibit a square‐planar coordination geometry around Pt involving one Cl atom, the coordinating N atom of the theobrominate anion and two P atoms from the tri­phenyl­phosphine groups. The two tri­phenyl­phosphine groups are arranged in a cis configuration in both structures. The heterocyclic rings are rotated with respect to the coordination plane of the metal by 82.99 (8) and 88.09 (8)° in complex (I), and by 85.91 (16) and 88.14 (18)° in complex (II). Both structures are stabilized by intramolecular stacking interactions involving the purine rings and the phenyl rings of adjacent tri­phenyl­phosphine moieties.     

Two-stage Off-Gel isoelectric focusing: protein followed by peptide fractionation and application to proteome analysis of human plasma

This paper presents the recently introduced Off-Gel electrophoresis (OGE) technology as a versatile tool to reproducibly fractionate intact proteins and peptides into discrete liquid fractions. The coupling of two stages of OGE, i.e., the separation of intact proteins in a first-stage followed by fractionation of peptides derived from each protein fraction after proteolysis in a second stage, results in an array of 15 x 15 fractions that are directly amenable to additional peptide fractionation like reverse-phase liquid chromatography (RPC). The analysis of all second-stage peptide fractions from only the first-stage protein fraction representing pH 5.0 -5.15 by on-line reverse-phase LC-tandem mass spectrometry resulted in the identification of 53 proteins (337 peptides), of which 10 were on different immunoglobulin (Ig) chains, with an input of only 1.5 mg human blood plasma proteins. Increasing the protein load to approximately 12 mg increased the number of identified proteins in the same protein fraction to 73 proteins (449 peptides), of which 15 were Ig-related. Immunodepletion of six of the most abundant proteins (albumin, transferrin, haptoglobin, IgG, IgA, and alpha-1-antitrypsin) prior to first-stage OGE with an input of 1.5 mg of protein (equivalent to approximately 10 mg nondepleted plasma) resulted in the identification of 81 proteins (660 peptides), of which three were still Ig fragments. The pI-based separation of peptides appears to be nonuniform based on the theoretically determined pI values of identified peptides. This observation specifically accounts for the neutral zone (pI 5-8) and can be accounted for by the physicochemical properties of the peptides given by their amino acid composition. The power of OGE separation of proteins and peptides is discussed with a focus on the use of the knowledge about the pI of proteins and peptides that assist the validation of correct identifications together with the retention time of peptides on RPC.     

Synthesis and characterization of Mo(6) chalcobromides and cyano-substituted compounds built from a novel [(Mo(6)Br(i)(6)Y(i)(2))L(a)(6)](n)()(-) discrete cluster unit (Y(i) = S or Se and L(a) = Br or CN)

The syntheses, crystal structures determined by single-crystal X-ray diffraction, and characterizations of new Mo(6) cluster chalcobromides and cyano-substituted compounds with 24 valence electrons per Mo(6) cluster (VEC = 24), are presented in this work. The structures of Cs(4)Mo(6)Br(12)S(2) and Cs(4)Mo(6)Br(12)Se(2) prepared by solid state routes are based on the novel [(Mo(6)Br(i)(6)Y(i)(2))Br(a)(6)](4)(-) (Y = S, Se) discrete units in which two chalcogen and six bromine ligands randomly occupy the inner positions, while the six apical ones are fully occupied by bromine atoms. The interaction of these two compounds with aqueous KCN solution results in apical ligand exchange giving the two first Mo(6) cyano-chalcohalides: Cs(0.4)K(0.6)(Et(4)N)(11)[(Mo(6)Br(6)S(2))(CN)(6)](3).16H(2)O and Cs(0.4)K(0.6)(Et(4)N)(11)[(Mo(6)Br(6)Se(2))(CN)(6)](3).16H(2)O. Their crystal structures, built from the original [(Mo(6)Br(i)(6)Y(i)(2))(CN)(a)(6)](4)(-) discrete units, will be compared to those of the two solid state precursors and other previously reported Mo(6) cluster compounds. Their redox properties and (77)Se NMR characterizations will be presented. Crystal data: Cs(4)Mo(6)Br(12)S(2), orthorhombic, Pbca (No. 61), a = 11.511(5) A, b = 18.772(5) A, c = 28.381 A (5), Z = 8; Cs(4)Mo(6)Br(12)Se(2), Pbca (No. 61), a = 11.6237(1) A, b = 18.9447(1) A, c = 28.4874(1) A, Z = 8; Cs(0.4)K(0.6)(Et(4)N)(11)[(Mo(6)Br(6)S(2))(CN)(6)](3).16H(2)O, Pm-3m (No. 221), a = 17.1969(4) A, Z = 1; Cs(0.4)K(0.6)(Et(4)N)(11)[(Mo(6)Br(6)Se(2))(CN)(6)](3).16H(2)O, Pm-3m (No. 221), a = 17.235(5) A, Z = 1.     

The solubility of an hydroxyaluminosilicate

Hydroxyaluminosilicates (HAS) are critical secondary mineral phases in the biogeochemical cycle of aluminium. They are formed from the reaction of silicic acid (Si(OH)₄) with an aluminium hydroxide template and act as a geochemical control of the biological availability of Al. There are two main forms of HAS which we have called HAS_A and HAS_B and which of these will predominate will depend upon the Si(OH)₄ to Al ratio in any one environment. In all but the most heavily weathered environments or those undergoing a progressive acidification Si(OH)₄ will be present in significant excess to Al and HAS_B will be the dominant secondary mineral phase. We have tried to determine the solubility of HAS_B(s) so that its contribution to Al solubility control might be compared with other secondary minerals such as Al(OH)_3(gibbsite). In preliminary experiments, the dissolution of HAS_B(s) was found to be non-congruent with almost no Al being released during 18 months ageing. We then demonstrated that HAS_B(s) was significantly less soluble than Al(OH)_3(s) prepared under identical experimental conditions. We have used this information to describe a solubility expression for HAS_B(s) at a predefined quasi-equibrium and to calculate a solubility constant.

K^*Al₂Si₂O₅(OH)₄=[Al₂O⁴⁺][SiO₂]²[OH^-]⁴