Preparation of a sulfonated fused-silica capillary and its application in capillary electrophoresis and electrochromatography

In the present paper, two new methods, sol-gel and chemical bonding methods, were proposed for preparation of sulfonated fused-silica capillaries. In the sol-gel method, a fused-silica capillary was coated with the sol solution obtained by hydrolysis of 3-mercaptopropyltrimethoxysilane (MPTS) and tetramethoxysilane, and followed by age; while in the chemical bonding method, a capillary was chemically bonded directly with MPTS. Then, both the resulting capillaries were oxidized with an aqueous solution of hydrogen peroxide solution (H2O2) (30%, m/m) to obtain the sulfonated capillaries. The electroosmotic flow (EOF) for the sulfonated capillaries was found to remain almost constant within the studied pH range, and greater than that of the uncoated capillary. However, the coating efficiency of the capillary prepared by chemical bonding method was higher than that by sol-gel method, by comparing their magnitude of the EOF, the degree of disguise of the silanol and reproducibility of preparation procedure. The effects of the electrolyte's concentration and the content of methanol (MeOH) on the EOF were also studied. Especially, the study of the apparent pH (pH*) on the EOF in a water-MeOH system was reported. Finally, capillary electrophoretic separation of seven organic acids was achieved within 6.5 min under optimal condition using the chemically bonded sulfonated capillary. Moreover, separation of four alkaloids on the sulfonated capillary was compared with that on uncoated capillary in different conditions. Ion-exchange mechanism was found to play a key role for separation of these four basic analytes on the sulfonated capillary.     

Cycloarsanes (AsCF3)n (n = 4, 5) – Precursors for the Highly Reactive Diarsene F3CAs=AsCF3

Tetrakis(trifluoromethyl) cyclotetraarsane (F₃CAs)₄ ( 2 ) was used to repeat the UV initiated [4+2]‐cycloaddition reaction of the diarsene F₃CAs=AsCF₃ ( 1 ) with cyclohexa‐1,3‐diene (CHD) and to isolate single crystals of the cycloadduct 4 for a X‐ray diffraction analysis. 4 crystallizes in the space group and contains the diarsene group in its E‐configuration. 2 was also applied for [2+2]‐cycloaddition reactions of 1 with tBuC≡P and MeC≡CNⁱPr₂, but in contrast to positive results with (F₃CP)₄ the products were too labile for isolation. However, 2 was successfully used at room temperature as precursor for coordinating 1 as π‐donor ligand to the Pd(PPh₃)₂ complex fragment yielding η²‐bis(trifluoromethyl)diarsene‐bis(triphenylphosphane)‐palladium(0) 5 , which was characterized by X‐ray diffraction of single crystals and by spectroscopic investigations (NMR, IR, MS). Attempts to prove the existence of the diarsene 1 , generated by different methods, by spectroscopic studies very probably failed due to its extreme reactivity, not allowing the necessary concentrations for detection. Quantum chemical calculations of the stability of 1 with respect to dimerization, the stability of the [2+2]‐cycloadduct with 1‐di(isopropyl)aminopropyne and the energy difference between 4 and the 2,3‐dimethyl‐1,3‐butadiene cycloadduct of 1 were performed to understand the considerable differences between 1 and the related diphosphene F₃CP=PCF₃.     

Matrix effects and selectivity issues in LC-MS-MS

Summary Chlorobenzenes, triazine and phenylurea herbicides were separated by normal micellar electrokinetic chromatography (MEKC) and by micellar electrokinetic chromatography with reversed flow (RF-MEKC) in running buffers containing organic solvents. The relationship between the two techniques is similar to that between reversed-phase and normal-phase HPLC. Using RF-MEKC, the separation of lipophilic compounds is often improved compared to normal MEKC. The migration in MEKC and in RF-MEKC was characterised by lipophilic and polar indices. The experimental values of the lipophilic indices of the compounds tested in the two techniques were close to the indices in reversed-phase HPLC (RP-HPLC). This enables the use of the indices determined in RP-HPLC for predicting the effects of changing composition of the running buffers on migration times in MEKC and in RF-MEKC. Presented at Balaton Symposium '01 on High-Performance Separation Methods, siófok, Hungary, September 2–4, 2001     

Reaction of hexafluoropropylene and its oligomers with acetone oxime

Reactions of perfluoropropylene and its oligomers with acetone oxime in the presence of a base afford perfluoroalkyl and/or perfluoroalkenyl ethers of acetone oxime. When heated to 100 °C, the 3-perfluoro-2-methyl-2-pentenyl ether of acetone oxime (3) is quantitatively converted to 4-hydroxy-3-methyl-5,5-bistrifluoromethyl-4-pentafluoroethyl-1-pyrroline (4), the structure of which was established by X-ray diffraction analysis. A convenient one-stage synthesis of perfluoro-3-isopropyl-4-methyl-3-penten-2-one (7) was proposed.Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 6, pp. 1068–1072, June, 1994.     

Alkylation of cobalt and lutetium tetra(3,5-di-tert-butyl-4-hydroxyphenyl)dodecachlorophthalocyanine complexes initiated with current

Electrochemical properties of tetra(3,5-di-tert-butyl-4-hydroxyphenyl)dodecachlorophthalocyanine complexes of cobalt(II) and lutetium(III) in DMF solutions have been studied. It was suggested that in the presence ofn-butyl bromide, the electrochemically generated monoanionic complexes undergo alkylation at the metal atom. The geometries of the neutral and anionic complexes were calculated by the ZINDO/I semiempirical method. Translated fromIzvestiya Akademii Nauk. Seriya Khimicheskaya, No. 2, pp. 289–293, February, 1998.     

Reaction ofo-aminobenzohydroxamic acid with aldehydes

The reaction of o-aminobenzohydroxamic acid with aliphatic, aromatic, or heterocyclic aldehydes leads to the formation of derivatives of 3-hydroxy-1,2-dihydroquinazolin-4-one. Translated fromIzvestiya Akademii Nauk, Seriya Khimicheskaya, No. 1, pp. 115–117, January, 1997.     

Investigation of the phosphinyl analog of α-ketoglutaric acid

It was shown by³¹P and¹³C NMR spectroscopy that methyl(3-carboxy-3-oxopropyl)phosphinic acid (4-methylhydroxyphosphinyl-2-oxobutyric acid) (1) and the amide (2) of the latter exist in keto forms in non-aqueous solutions. In aqueous solutions an equilibrium between the keto,gem-diol, and enol forms has been observed. The proportions of the diol and enol forms increase as the acidity of the media increases. Silylation of acid 1 with hexamethyldisilazane gives the tris(trimethylsilyl) derivative of enol form (3) (Z- andE-isomers).Translated fromIzyestiya Akadetnii Nauk. Seriya Khimicheskaya, No. 1, pp. 125–128, January, 1994.     

Experimental and theoretical studies of Diels-Alder dimerization of 1,2,3,4,5-pentachlorocyclopentadiene and of Diels-Alder cycloaddition of polychlorinated cyclopentadienes to norbornadiene

Diels-Alder cyclodimerization of 1,2,3,4,5-pentachlorocyclopentadiene (1) affords 2a as the exclusive reaction product. Diels-Alder cycloaddition of 1 to norbornadiene also proceeds stereoselectively to produce a single [4+2] cycloadduct, 4c. The structures of 2a and 4c were established unequivocally via application of single crystal X-ray crystallographic techniques. The origins of the observed diastereofacial selectivity in each of these cycloaddition processes have been investigated by application of semiempirical (AM1 Hamiltonian) and ab initio (Hartree-Fock 3-21G*) calculations. The computational results thereby obtained, which are based upon consideration of the kinetically favored transition state for each of the two cycloaddition reactions studied, are consistent with experiment. These semiempirical and ab initio methods also have been used to investigate the mechanisms of the Diels-Alder reactions that have been used to prepare aldrin and isodrin (7 and 8, respectively). The results thereby obtained suggest that isodrin formation via Diels-Alder cycloaddition of cyclopentadiene to 1,2,3,4,7,7-hexachloronorbornadiene proceeds with kinetic control of product stereochemistry.     

Syntheses, crystal structures and properties of novel zinc(II) complexes obtained by reactions of zinc(II) malonate with flexible multidentate ligands

Complex [Zn₂(bimb)₂(mal)₂(H₂O)₂]·4H₂O (1) (mal=⁻OCOCH₂COO⁻) was obtained by reaction of bidentate ligand 4,4′-bis(imidazole-1-ylmethyl)biphenyl (bimb) with zinc(II) salt of malonate, while the reaction of the same metal salt with 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene (titmb) gives another novel complex [Zn₂(titmb)₂(mal)][mal]·12H₂O (2). The structures of these complexes were determined by X-ray crystallography. The results revealed that 1 is a cyclic dinuclear complex in which the malonate groups act as terminators and prevent further aggregation, while 2 is a 2D honeycomb network in which each independent 2D sheet contains two sub-layers bridged by the malonate groups and complex 2 also contains free malonate as a counteranion connected to the 2D layer by C-H?O hydrogen bonds. The entirely different structure and topology of complexes 1 and 2, on the one hand, indicates that the nature of organic ligands affected the structures of assemblies greatly, and on the other, reveals the versatility of the malonate which can act as a bridging and/or blocking ligand.     

Synthesis and electrochemical properties of Zn3V3O8 as novel anode material

Zn₃V₃O₈ two-dimensional micro sheets are successfully synthesized by combination of solvothermal method and heat treatment. The Zn₃V₃O₈ has better electrochemical performances after calcinations.