Preparation of 3-azetidinols with non-bulky 1-alkyl substituents

Cyclization of either the tetrahydropyranyl or trimethylsilyl ether of 1-(alkylamino)-3-chloro-2-propanols 1 followed by cleavage of the azetidinyl ether provides a general method for the preparation of 1-alkyl-3-azetidinols. Unhindered amines provide a more facile preparation of derivatives of 1 , or its ethers, than do hindered amines, while hindered derivatives of 1 undergo more facile ring closure.     

Synthesis and characterization of novel anionic siloxane polymers as pseudostationary phases for electrokinetic chromatography

Four novel siloxane polymeric pseudostationary phases with three different ionic head groups have been synthesized and characterized for electrokinetic chromatography. Siloxane polymers are of interest in this application because of the wide range of chemistries that can be developed based on these backbones, including much of the chromatographic stationary phase chemistry developed in the last thirty years. All four of the siloxanes studied were synthesized by modification of a single methylhydrosiloxane polymer with highly acidic anionic functionalities. One of the siloxanes had both ionic groups and alkane chains attached to the siloxane backbone. The electrophoretic mobilities varied from being somewhat less than sodium dodecyl sulfate (SDS) to being much greater than SDS. The siloxanes substituted with ionic groups at all of the silicon sites showed significant nonequilibrium band broadening, severely limiting the efficiencies of these polymers. Substitution of 20% of the silicon sites with an alkyl group improved the efficiency of the separations and the peak symmetry. The chemical selectivities of the siloxane polymers are very different from SDS, but are similar to each other.     

Driving high quantum yield NIR emission through proquinoidal linkage motifs in conjugated supermolecular arrays

High quantum yield NIR fluorophores are rare. Factors that drive low emission quantum yields at long wavelength include the facts that radiative rate constants increase proportional to the cube of the emission energy, while nonradiative rate constants increase in an approximately exponentially with decreasing S₀–S₁ energy gaps (in accordance with the energy gap law). This work demonstrates how the proquinoidal BTD building blocks can be utilized to minimize the extent of excited-state structural relaxation relative to the ground-state conformation in highly conjugated porphyrin oligomers, and shows that 4-ethynylbenzo[c][1,2,5]thiadiazole (E-BTD) units that terminate meso-to-meso ethyne-bridged (porphinato)zinc (PZn_n) arrays, and 4,7-diethynylbenzo[c][1,2,5]thiadiazole (E-BTD-E) spacers that are integrated into the backbone of these compositions, elucidate new classes of impressive NIR fluorophores. We report the syntheses, electronic structural properties, and emissive characteristics of neoteric PZn-(BTD-PZn)_n, PZn₂-(BTD-PZn₂)_n, and BTD-PZn_n-BTD fluorophores. Absolute fluorescence quantum yield (ϕ_f) measurements, acquired using a calibrated integrating-sphere-based measurement system, demonstrate that these supermolecules display extraordinary ϕ_f values that range from 10–25% in THF solvent, and between 28–36% in toluene solvent over the 700–900 nm window of the NIR. These studies underscore how the regulation of proquinoidal conjugation motifs can be exploited to drive excited-state dynamical properties important for high quantum yield long-wavelength fluorescence emission.

Incorporation of proquinoidal BTD building blocks into conjugated porphyrin oligomers minimizes the extent of excited-state structural relaxation relative to the ground-state conformation, elucidating new classes of impressive NIR fluorophores.     

New Cu(II) complexes with polydentate chelating Schiff base ligands: Synthesis, structures, characterisations and biochemical activity studies

We have reported herein the synthesis of three new Cu(II) complexes of tri- and tetradentate Schiff base ligands containing N₃ or N₄ donor set along with terminal NNN⁻ or SCN⁻ ligands: [L¹Cu(NCS)]ClO₄ (1), [L²Cu(NCS)₂] (2) and [L³Cu(NNN)]ClO₄ (3) [L¹ = NC₅H₄C(CH₃)=N(CH₂)₃N=C(CH₃)C₅H₄N, L²= Me₂N–(CH₂)₃–N=C(CH₃)C₅H₄N and L³ = NC₅H₄CH=N–(CH₂)₄–N=CHC₅H₄N]. The complexes have been systematically characterised by elemental, spectroscopic and electrochemical techniques. Antimicrobial activities of the Schiff base ligands and their metal complexes have been studied using the disc diffusion method on the strains of Candida tropicalis and Bacillus megaterium. Structures of all the complexes have been unequivocally established from single crystal X-ray diffraction analyses that show the monomeric units containing a five-coordinated copper center in highly distorted square pyramidal geometry with thiocyanate or azide anion coordinated as terminal ligand. The complexes 1 and 3 crystallise in monoclinic (P2₁/c) and 2 in triclinic (P-1) space group, respectively.     

Effects of ammonium nitrate on sensitivity for determinations of copper,iron, and manganese in sea water by atomic absorption spectrometry with pyrolytically coated graphite tubes

Ammonium nitrate, used as a matrix modifier in sea-water analysis to eliminate the interference of sodium chloride, degrades the pyrolytic coating on graphite-furnace tubes. The initially increased sensitivities for copper, manganese and iron are maintained for up to 15 atomizations; there is then a rapid decline to a constant lower sensitivity. The characteristics depend strongly on the particular lot of furnace tubes. To decrease the NaCl interference without using matrix modifier, estuarine samples must be diluted (1 + 1) with pure water. Blanks and standards are prepared and diluted with Gulf Stream water containing low amounts of trace metals to match the estuarine matrix.     

Characterisation and cryomagnetic study of a hydrothermally synthesised hydrogen bonded L–M–L type co-ordination polymer

A ligand–metal–ligand type co-ordination polymer [Ni (C₆H₁₂N₄)(NCS)₂(H₂O)₂] _n has been synthesised under controlled hydrothermal conditions. Here 1,3,5,7-tetraazatricyclo[3.3.1]decane [or hexamethylenetetramine (hmt)] has been used as a μ-(N,N′) bidentate spacer molecule. The prepared polymeric complex has been characterised by elemental and spectral analyses. The structure has been confirmed by a single crystal X-ray diffraction study. Magneto-structural correlation has been drawn from cryomagnetic susceptibility measurements (2–300 K) which unequivocally reflects very weak magnetic spin interactions among the long distant octahedral Ni(II) metal centres mediated by hmt and weak hydrogen bonding interactions between the adjacent zigzag one-dimensional polymeric chains carrying into a two-dimensional infinite polymeric framework.     

A new column system for isothermal gas chromatographic analysis of light gases (H2, O2, N2, CO,CH4, CO2, C2H4, C2H6 and C2H2) employing a column switch technique

Summary A new column system for the isothermal analysis of H₂, O₂, N₂, CO, CH₄, CO₂, C₂H₄, C₂H₆ and C₂H₂ is described. Higher hydrocarbons and water are backflushed from the system. The use of 13X molecular sieve in a relatively deactivated state shortens the elution times of the light components and improves peak shapes. Both factors enable quantitative analyses to be carried out satisfactorily at lower concentrations than would otherwise be possible. Analysis of all compounds listed can be carried out in eleven minutes. Sparingly activated 13X molecular sieve columns have proved to be very stable and rarely require reactivation.The method of column switching employed avoids the use of mechanical valves in the sample path and is suitable for automatic operation.

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Neue Trennsäulenkombination für die GC-Analyse von Gasen (H₂, O₂, N₂, CO, CH₄, CO₂, C₂H₄, C₂H₆, C₂H₂) unter Anwendung einer nichtmechanischen Säulenschalttechnik

Zusammenfassung Eine neue Trennsäulenkombination zur isothermen Trennung von H₂, O₂, N₂, CO, CH₄, CO₂, C₂H₄, C₂H₆ und C₂H₂ wird beschrieben. Höhere Kohlenwasserstoffe und Wasser werden rückgespült. Durch Anwendung eines auf relativ niedriger Aktivitätsstufe betriebenen Molekularsiebs 13X wird die Elutionszeit der flüchtigen Komponenten verkürzt und deren Peakform verbessert. Beides erlaubt befriedigende quantitative Analysen im Bereich kleinerer Konzentrationen, als dies mit anderen Systemen möglich ist. Die Analyse eines Gemisches aller oben angeführten Komponenten ist innerhalb von 11 Minuten möglich. Mäßig aktivierte Trennsäulen mit Molekularsieb 13X erwiesen sich als sehr stabil, sie erfordern nur selten eine Reaktivierung. Die hier verwendete Säulenschalttechnik vermeidet die Anwendung mechanischer Umschaltsysteme im Probenweg und ist für eine automatische isotheme Arbeitsweise besonders geeignet.

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Une nouvelle combinaison de colonnes pour l'analyse à température constante, par chromatographie en phase gazeuse, de gaz légers (H₂, O₂, N₂, CO, CH₄, CO₂, C₂H₄, C₂H₆ et C₂H₂) employant un système de commutation de colonnes

Résumé On décrit une nouvelle combinaison de colonnes pour l'analyse à température constante des mélanges de H₂, O₂, N₂, CO, CH₄, CO₂, C₂H₄, C₂H₆ et C₂H₂. Les hydrocarbures à plus grand nombre de carbones et l'eau sont éliminés du système par contrebalayage. L'emploi de tamis moléculaire 13X dans un état de désactivation relativement élevé permet de réduire les temps d'élution des composants légers et de rendre la forme des pics plus favorable. Ces deux facteurs permettent d'effectuer des analyses quantitatives à des concentrations plus basses que celles possibles normalement. L'analyse de tous les composants cités peut être faite en 11 minutes. Les colonnes de Tamis moléculaire 13X à degré d'activation modéré sont très stables et leur réactivation n'est nécessaire qu'après une longue période d'emploi. La méthode de commutation employée pour les colonnes évite l'utilisation de vannes mécaniques sur le parcours de l'échantillon; elle est convenable pour le fonctionnement automatique.

     

Reactions of [HOs3(CO)8{µ3-Ph2PCH(R)P(Ph)C6H4}] (R = H,Me) with Bu3SnH: synthesis and structure of bimetallic Os-Sn clusters

Reactions of unsaturated [HOs₃(CO)₈{µ₃-Ph₂PCH(R)P(Ph)C₆H₄}] (R?=?H, Me) with Bu₃SnH are examined. [HOs₃(CO)₈{µ₃-Ph₂PCH(R)P(Ph)C₆H₄}] reacts with Bu₃SnH at room temperature to afford [H₂Os₃(CO)₈(SnBu₃){µ₃-Ph₂PCH(R)P(Ph)C₆H₄}] (1) via oxidative addition of the Sn?H bond to the parent cluster. Heating 1 in refluxing toluene leads to the formation of [H₂Os₃(CO)₇(SnBu₃){µ₃-Ph₂PCH(R)P(Ph)C₆H₄}] (2) through decarbonylation. Cluster 2 exists in two isomeric forms in solution which has been probed by VT NMR spectroscopy. The new Os-Sn bimetallic clusters have been characterized by a combination of analytical and spectroscopic data together with single-crystal X-ray diffraction analysis.

Graphic abstract

     

Use of mobile phase 18-crown-6 to improve peak resolution between mono- and divalent metal and amine cations in ion chromatography

It is difficult to quantify NH4+ by ion chromatography in the presence of high concentrations of Na+ due to peak overlap. The Dionex IonPac CS15 column, which contains phosphonate, carboxylate, and 18-crown-6 functional groups, was originally developed to overcome this problem. We have found that the addition of 18-crown-6 to the eluent promotes improved peak resolution between Na+ and NH4+ even at concentrations as high as 60,000 to 1 using this column. Its use also improves the separation of alkali and alkaline earth metal and amine cations. Mobile phase 18-crown-6 increased the retention times of CH3NH3+, NH4+, and K+, and decreased the retention time of Sr2+. The retention times of Li+, Na+, Mg2+, Ca2+, (CH3)2NH2+, and (CH3)3NH+ were not affected. This method makes possible the direct analysis of ammonia from nitrogenase, the enzyme responsible for biological nitrogen fixation. The resolution of the NH4+ peak from the Na+ and Mg2+ peaks improved from zero resolution to values of 6.19 and 5.65, respectively. This technique considerably reduces the analysis time of NH4+ in the presence of high concentrations of Mg2+ and Na+ over traditional indophenol measurements.