Using LR-HSQMBC to observe long-range H–N correlations

The recently reported LR-HSQMBC experiment has been optimized for ¹H–¹⁵N long-range heteronuclear couplings. Several previously unreported four-bond correlations, consistent with the predicted by DFT calculations (0.2–0.3 Hz ⁴J_NH couplings), have been observed for strychnine using 2 Hz optimization of the LR-HSQMBC experiment. This experiment offers an advantage over accordion-optimized experiments such as IMPEACH and CIGAR for the observation of long-range ¹H–¹⁵N correlations in that the experiment is refocused and employs a CLIP pulse sequence element to bring the long-range correlations into phase, allowing broadband X-decoupling to be employed during acquisition.     

Convenient syntheses of ring-B-nor analogues of Ambrox® and amberketal via a novel ring contraction reaction

Manool is converted into ring-B-nor analogues of commercially important perfumery compounds via a novel ring-B-nor intermediate methylene ketone 9. Compound 9 is synthesised via the formation of an exocyclic bromonium ion and the concomitant ring contraction of the B-ring of a diterpene skeleton derived from manool. Oxidation and base treatment of the ring-contracted product result in dehydrohalogenation and decarboxylation to afford methylene ketone compound 9, which is then converted to ring-B-nor analogues of Ambrox® and amberketal.     

Reduction of water wettability of nanofibrillated cellulose by adsorption of cationic surfactants

Adsorption isotherms of single and double chain cationic surfactants with different chain length (cetyltrimethyl-, didodecyl- and dihexadecyl ammonium bromide) onto cellulose nanofibrils were determined. Nanofibrillated cellulose, also known as microfibrillated cellulose (MFC), with varying contents of carboxyl groups (different surface charge) was prepared by TEMPO-mediated oxidation followed by mechanical fibrillation. The fibril charge was characterized by potentiometric and conductometric titration. Surfactant adsorption was verified by Fourier Transform Infrared Spectroscopy (FTIR) and X-ray Photoelectron Spectroscopy (XPS). Wetting and adhesion of water onto fibril films was determined by contact angle measurements. Small aggregates (admicelles) of surfactant were shown to form on the nanofibril surfaces, well below critical micelle concentrations. The results demonstrate the possibility of using cationic surfactants to systematically control the degree of water wettability of cellulose nanofibrils.     

Thermodynamic evaluation and optimization of the Li,Na, K,Mg, Ca,Sr // F,Cl reciprocal system

A complete critical evaluation of all available phase diagram and thermodynamic data has been performed for all condensed phases of the (LiF + LiCl + NaF + NaCl + KF + KCl + MgF₂ + MgCl₂ + CaF₂ + CaCl₂ + SrF₂ + SrCl₂) system, and optimized model parameters have been found. The (LiCl + NaCl + KCl + MgCl₂ + CaCl₂ + SrCl₂), (LiF + NaF + KF + MgF₂ + CaF₂ + SrF₂), and (LiF + LiCl + NaF + NaCl + KF + KCl + MgF₂ + MgCl₂ + CaF₂ + CaCl₂) subsystems have been critically evaluated previously. The model parameters for the common-ion binary, common-anion ternary, and reciprocal ternary subsystems (i.e. systems with two cations and two anions) can be used to predict thermodynamic properties and phase equilibria for the multicomponent reciprocal system. The Modified Quasichemical Model in the Quadruplet Approximation was used for the molten salt phase. This model takes into account both first-nearest-neighbor (cation–anion) and second-nearest-neighbor (cation–cation and anion–anion) short-range ordering, and the coupling between them. Finally, the CaFCl–SrFCl solid solution was modeled using the Compound Energy Formalism.     

Thermodynamic evaluation and optimization of the (NaCl + KCl + MgCl2 + CaCl2 + ZnCl2) system

A complete critical evaluation of all available phase diagram and thermodynamic data has been performed for all condensed phases and relevant gaseous species of the (NaCl + KCl + MgCl₂ + CaCl₂ + ZnCl₂) system, and optimized model parameters have been found. The (NaCl + KCl + MgCl₂ + CaCl₂) subsystem has been critically evaluated in a previous article. The model parameters obtained for the binary and ternary subsystems can be used to predict thermodynamic properties and phase equilibria for the multicomponent system. The Modified Quasichemical Model for short-range ordering was used for the molten salt phase.     

Rapid determination of 226Ra in drinking water samples using dispersive liquid-liquid microextraction coupled with liquid scintillation counting

A new radioanalytical method was developed for rapid determination of ²²⁶Ra in drinking water samples. The method is based on extraction and preconcentration of ²²⁶Ra from a water sample to an organic solvent using a dispersive liquid-liquid microextraction (DLLME) technique followed by radiometric measurement using liquid scintillation counting. In DLLME for ²²⁶Ra, a mixture of an organic extractant (toluene doped with dibenzo-21-crown-7 and 2-theonyltrifluoroacetone) and a disperser solvent (acetonitrile) is rapidly injected into the water sample resulting in the formation of an emulsion. Within the emulsion, ²²⁶Ra reacts with dibenzo-21-crown-7 and 2-theonyltrifluoroacetone and partitions into the fine droplets of toluene. The water/toluene phases were separated by addition of acetonitrile as a de-emulsifier solvent. The toluene phase containing ²²⁶Ra was then measured by liquid scintillation counting. Several parameters were studied to optimize the extraction efficiency of ²²⁶Ra, including water immiscible organic solvent, disperser and de-emulsifier solvent type and their volume, chelating ligands for ²²⁶Ra and their concentrations, inorganic salt additive and its concentration, and equilibrium pH. With the optimized DLLME conditions, the accuracy (expressed as relative bias, B _r ) and method repeatability (expressed as relative precision, S _B ) were determined by spiking ²²⁶Ra at the maximum acceptable concentration level (0.5 Bq L⁻¹) according to the Guidelines for Canadian Drinking Water Quality. Accuracy and repeatability were found to be less than −5% (B _r ) and less than 6% (S _B ), respectively, for both tap water and bottled natural spring water samples. The minimum detectable activity and sample turnaround time for determination of ²²⁶Ra was 33 mBq L⁻¹ and less than 3 h, respectively. The DLLME technique is selective for extraction of ²²⁶Ra from its decay progenies.     

Rapid determination of 237Np and Pu isotopes in water by inductively-coupled plasma mass spectrometry and alpha spectrometry

A new method that allows rapid preconcentration and separation of plutonium and neptunium in water samples was developed for the measurement of ²³⁷Np and Pu isotopes by inductively-coupled plasma mass spectrometry (ICP-MS) and alpha spectrometry. ²³⁸U can interfere with ²³⁹Pu measurement by ICP-MS as ²³⁸UH⁺ mass overlap and ²³⁷Np via peak tailing. The method provide enhanced removal of uranium by separating Pu and Np initially on TEVA Resin, then moving Pu to DGA resin for additional removal of uranium. The decontamination factor for uranium from Pu is almost 100,000 and the decontamination factor for U from Np is greater than 10,000. This method uses stacked extraction chromatography cartridges and vacuum box technology to facilitate rapid separations. Preconcentration is performed using a streamlined calcium phosphate precipitation method. Purified solutions are split between ICP-MS and alpha spectrometry so that long and short-lived Pu isotopes can be measured successfully. The method allows for simultaneous extraction of 20 samples (including QC samples) in 4?C6 h, and can also be used for emergency response. ²³⁹Pu, ²⁴²Pu and ²³⁷Np were measured by ICP-MS, while ²³⁶Pu, ²³⁸Pu, and ²³⁹Pu were measured by alpha spectrometry.     

Synthesis of the stereogenic triad of the halicyclamine A core

We describe herein our progress toward the synthesis of halicyclamine A, which possesses very interesting biological activities and has never been synthesized. For this purpose, we proposed a stereoselective Diels-Alder reaction as a key step for the establishment of the stereogenic triad of the bis(piperidinyl) core of this molecule. A series of NMR studies was then conducted to establish the correct stereochemical assignment subsequent to the Diels-Alder reaction.     

Cyclic (ALN)n Compounds as Precursors to Aluminum Nitride: Synthesis and Structure of [(CH3)2AlNH2]3 and the Planar Species [(t-C4H9)2AlNH2]3

Abstract

The crystal and molecular structures of the title compounds, [(CH₃)₂AlNH₂]₃ 1 and [(t-C₄H₉)₂AlNH₂]₃ 2, have been determined in connection with their investigation as possible precursors to aluminum nitride. Both compounds have an (AlN)₃ ring-structure with distorted tetrahedral geometries for the ring Al and N atoms. The distortion from tetrahedral geometry is most pronounced for the N atoms where the endocyclic Al-N-Al bond angles average 125.3 for 1 and 134.2 for 2. The (AlN)₃ ring in 1 is in a skew-boat conformation with no unusual intra- or intermolecular contacts. Compound 2 on the other hand exhibits an unprecedented planar (AlN)₃ ring as required by a crystallographic three-fold symmetry axis. The effects of the Al and N substituents on the (AlN)₃ ring size and conformation, as well as on the endocyclic Al-N-Al bond angles, are discussed in the context of the structural results obtained for these and other (AlN)_n ring compounds.     

THE PREPARATION OF TRIALKYL PHOSPHITES DIRECTLY FROM THE ELEMENT

Abstract

The reaction between finely divided white phosphorus and several alkoxide ions in the presence of tetrachloromethane and excess of alcohol has been investigated under a variety of conditions. High yields of trialkylphosphite are obtained when two equivalents of alkoxide are used. With one equivalent of alkoxide, dialkylphosphonate is formed in comparable yield. Maximum yields of triester are obtained within 1–3 h at room temperature. Prolonged treatment results in the conversion of trialkylphosphite to phosphate by reaction with tetrachloromethane. Phenolate ions are unreactive under the same experimental conditions. The mechanism of the reaction is discussed.