Effect of ionic additives on the elution of sodium aryl sulfonates in supercritical fluid chromatography

Addition of a small amount of polar solvent (i.e., modifier) to CO2 in packed column supercritical fluid chromatography (SFC) has shown major improvements in both polar analyte solubility and interaction of the polar analyte with the stationary phase. Recently, the addition of an ionic component (i.e., additive) to the primary modifier by one of us has been shown to extend even further the application of SFC to polar analytes. In this work, the effect of various ionic additives on the elution of ionic compounds, such as sodium 4-dodecylbenzene sulfonate and sodium 4-octylbenene sulfonate, has been studied. The additives were lithium acetate, ammonium acetate, tetramethylammonium acetate, tetrabutylammonium acetate, and ammonium chloride dissolved in methanol. Three stationary phases with different degrees of deactivation were considered: conventional cyanopropyl, deltabond cyanopropyl, and bare silica. The effect of additive concentration and additive functionality on analyte retention was investigated. Sodium 4-dodecylbenzene sulfonate was successfully eluted using all the additives with good peak shape under isocratic/isobaric/isothermal conditions. Different additives, however, yielded different retention times and in some cases different peak shapes.     

Some lessons from the development of metal hydride chemistry in the light of hydrogen storage problems

The main trends of the chemistry of hydrides of transition metals and their alloys are briefly reviewed. “Sensational” hydrogen capacity data and the potential of some metal materials (metals, alloys, and quasi-crystals) and carbon nanomaterials in reversible hydrogen storage applications are critically analyzed. The significance of research in this field for hydrogen energy applications is underlined.     

Heterogeneous-catalytic fischer reaction

The catalytic synthesis of 7-azaindole and its 2-methyl derivative has been accomplished for the first time by cyclization of acetaldehyde and acetone 2-pyridylhydrazones in the presence of -Al₂O₃ and fluorinated aluminum oxide. The temperature dependence of the yields of reaction products — azaindoles and 2-aminopyridine — was studied. The cyclization of acetaldehyde 2-pyridylhydrazone proceeds under more severe conditions. The maximum yield of 7-azaindole is 15% at 450° on fluorinated aluminum oxide. The yield of 2-methyl-7-azaindole reaches 50% at 315°. Fluorinated aluminum oxide displays higher catalytic activity.See [1] for communication III.Translated from Khimiya Geterotsiklicheskikh Soedinenii, No. 5, pp. 656–658, May, 1972.     

Electron screening in low energy scattering of muonic hydrogen on hydrogen atoms

Electron screening corrections to the cross sections for low energy scattering of muonic hydrogen on hydrogen atoms are calculated. It is shown that the presence of the electron influences considerably the elastic cross sections at collision energies below 1 eV. This influence is relatively small for the spin-flip and isotopic exchange processes.     

Separation and determination of arsenic(V) and arsenic(III) in sea-water by solvent extraction and atomic-absorption spectrophotometry by the hydride-generation technique

Arsenic(V) and arsenic(III) in sea-water have been separated by complexing the arsenic(III) with ammonium pyrrolidinedithiocarbamate (APDC) in the range 4.0-4.5 and extracting the complex with chloroform. The organic phase is then wet-ashed with a 1:1 mixture of concentrated nitric acid and perchloric acid to get rid of all organics, and the arsenic(III) is determined by hydride generation and atomic-absorption spectrophotometry. Total arsenic is determined by first reducing arsenic(V) to arsenic(III) with potassium iodide and then applying the method used for arsenic(III). The arsenic(V) content is determined by difference. The low detection limit of 0.031 ng ml and the high sensitivity and precision make the method suitable for analysis of open ocean waters.     

Complete synthesis of serratamolide

Summary 1. A method for the separation and quantitative determination of - and -DNP derivatives of , -DABA, ornithine, and lysine has been proposed.2. A quantitative evaluation of the N N migration in four peptides of , -DABA has been carried out.3. The degree of migration in inactive polymyxin M and the DNP-peptides from a partial hydrolyzate of the inactivated antibiotic has been determined.4. The amino acid composition of the DNP peptide B1 from a partial hydrolyzate of active DNP-polymyxin M has been established.5. The quantitative aspect of the conversion of and diketopiperazines has been studied.Khimiya Prirodnykh Soedinenii, Vol. 2, No. 4, pp. 277–284, 1966     

Nitration of pentaerythritol by HNO3-H2SO4-H2O system

Conclusions It was shown experimentally that the nitrating agent in the O-nitration of pentaerythritol by HNO₃-H₂SO₄-H₂O nitrating mixtures is not the nitronium cation but evidently the free unionized nitric acid molecule.Translated from Izvestiya Akademii Nauk SSSR, Seriya Khimicheskaya, No. 1, pp. 134–140, January, 1970.     

EPR study of the mechanism of interaction of NO and NO2 molecules with zeolite surfaces

The adsorption of the paramagnetic molecules of NO and NO₂ by zeolites in the alkali and alkaline earth cationic forms has been studied by EPR and reflectance spectroscopic methods. The change in the EPR spectra of adsorbed nitric oxide with increase in the degree of covering of the surface of the alkali cationic form of the zeolites, and also the nature of the change in the spectra when oxygen is adsorbed on zeolites on which NO has previously been adsorbed, indicate the existence of two types of adsorption center. At low degrees of covering of the surface, on the order of 10¹⁸ g^–1, as can be judged from the EPR spectra, the adsorbed NO molecule is strongly polarized and the unpaired electron is almost completely localized on the oxygen atom. At high degrees of covering, for an appreciable proportion of the NO molecules, the bond with the surface is weaker. In this case, the EPR spectra show a hyperfine structure (HFS) with a constant which changes with change in the cation in the order Li⁺ Na⁺ K⁺. The replacement of the singly charged Na⁺ by the doubly charged Ca²⁺ produces a marked change in the adsorption properties of the zeolite. The adsorption of NO on CaA leads not only to polarization of the adsorbed molecule but also to transfer of the electron from the nitrogen atom to the atoms of the adsorbent; this is recorded in the EPR spectrum in the form of an F-center. On further adsorption, the NO molecules are adsorbed both on the nitrogen atom and on the oxygen atom of the first molecule; thus, NO₂ and N₂O are formed.     

Sterically controlled reductive oligomerisations of CO by activated magnesium(i) compounds: deltate vs. ethenediolate formation

An extremely bulky, symmetrical three-coordinate magnesium(i) complex, [{(^TCHPNacnac)Mg}₂] (^TCHPNacnac = [{(TCHP)NCMe}₂CH]⁻, TCHP = 2,4,6-tricyclohexylphenyl) has been prepared and shown to have an extremely long Mg–Mg bond (3.021(1) Å) for such a complex. It was shown not to react with either DMAP (4-dimethylaminopyridine) or CO. Three unsymmetrical 1 : 1 DMAP adducts of less bulky Mg–Mg bonded species have been prepared, viz. [(^ArNacnac)Mg–Mg(DMAP)(^ArNacnac)] (^ArNacnac = [(ArNCMe)₂CH]⁻ Ar = 2,6-xylyl (Xyl), mesityl (Mes) or 2,6-diethylphenyl (Dep)), and their reactivity toward CO explored. Like the previously reported bulkier complex, [(^DipNacnac)Mg–Mg(DMAP)(^DipNacnac)] (Dip = 2,6-diisopropylphenyl), [(^DepNacnac)Mg–Mg(DMAP)(^DepNacnac)] reductively trimerises CO to give a rare example of a deltate complex, [{(^DepNacnac)Mg(μ-C₃O₃)Mg(DMAP)(^DepNacnac)}₂]. In contrast, the two smaller adduct complexes react with only two CO molecules, ultimately giving unusual ethenediolate complexes [{(^ArNacnac)Mg{μ-OC(H) C(DMAP^−H)O}Mg(^ArNacnac)}₂] (Ar = Xyl or Mes). DFT calculations show the latter reactions to proceed via reductive dimerizations of CO, and subsequent intramolecular C–H activation of Mg-ligated DMAP by “zig–zag” [C₂O₂]²⁻ fragments of reaction intermediates. Calculations also suggest that magnesium deltate complexes are kinetic products in these reactions, while the magnesium ethenediolates are thermodynamic products. This study shows that subtle changes to the bulk of the reacting 1 : 1 DMAP–magnesium(i) adduct complexes can lead to fine steric control over the products arising from their CO reductive oligomerisations. Furthermore, it is found that the more activated nature of the adduct complexes, relative to their symmetrical, three-coordinate counterparts, [{(^ArNacnac)Mg}₂], likely derives more from the polarisation of the Mg–Mg bonds of the former, than the elongated nature of those bonds.

Subtle changes to the bulk of 1 : 1 adducts of DMAP with magnesium(i) complexes leads to steric control over the products arising from their reductive oligomerisations of carbon monoxide.      

High-throughput cytochrome P450 inhibition screening via cassette probe-dosing strategy. IV. Validation of a direct injection on-line guard cartridge extraction/tandem mass spectrometry method for simultaneous CYP3A4, 2D6 and 2E1 inhibition assessment

A highly efficient direct injection on-line guard cartridge extraction/tandem mass spectrometry (DI-GCE/MS/MS) method has been validated for high-throughput evaluation of cytochrome P450 (CYP) 3A4, 2D6 and 2E1 inhibition potential via cassette dosing of midazolam, dextromethorphan and chlorzoxazone using human hepatic microsomes and 96-well microtiter plates. Microsomal incubations were terminated with formic acid, centrifuged, and the resulting supernatants were injected for analysis by DI-GCE/MS/MS. Due to the novel use of an extremely short C(18) guard cartridge (4 mm in length), this method exhibits several advantages such as no sample preparation, excellent on-line extraction, short run time (2.5 min), and minimized source contamination and performance deterioration. The DI-GCE/MS/MS method demonstrates acceptable accuracy and precision for the simultaneous quantification of 1'-hydroxymidazolam, dextrorphan and 6-hydroxychlorzoxazone in microsomal incubations. The inhibition potential of CYP3A4, 2D6 and 2E1 has been evaluated using their known selective inhibitors. The IC(50) values measured by the cassette dosing approach (high-throughput) are consistent with those observed by an individual dosing regimen (conventional) and are all in good agreement with the literature values. The results suggest that the cassette probe-dosing strategy may provide an in vitro approach to minimize cost while maximizing throughput of CYP inhibition evaluation of new chemical entities in support of drug discovery and development.