Crystal structures and phase behaviour of acetaldehyde-d4: a study by high-resolution neutron powder diffraction and calorimetry

High-resolution neutron powder diffraction is particularly suited for structure solution and refinement of low-melting point organic crystals of moderate complexity. Here we present the ab initio structure solution and refinement of stable-phase and metastable-phase perdeuterated acetaldehyde (m.p.: 151 K). In the stable phase, the molecule crystallises in the space group P2₁/c (no. 14) with a=3.9069(1) Å, b=5.4224(1) Å, c=12.1868(1) Å, β=94.2970(2)° at 5 K, Z=4. In the metastable phase, the molecule crystallises in the space group Pna2₁ (no. 33) with a=5.1973(1) Å, b=6.9791(1) Å, c=6.9712(1) Å at 5 K, Z=4. The metastable to stable phase transition is characterised by heat capacity measurements.     

Natural radioactivity in Brazilian bottled mineral waters and consequent doses

Instrumental neutron activation analysis (INAA) has been applied tomultielement determination of five medicinal plants which are used to curevarious diseases in Ghana. These are: Sirappac powder-E, Tina-A powder, Aphrodisiacpowder, Blighia powder and Olax powder. Concentrations of fifteen elementsAl, Ba, Br, Ca, Cl, Co, K, Mn, Mg, Na, Rb, Sb, Sc, Se, Ta, V and Zn have beendetermined by short, medium, and long irradiation times with a thermal neutronflux of 5 . 10 11 n . cm –2. s –1 . Of these Co, Sb, and Sc arefound to be present at trace level, Br, Mn, Rb, Ta, V and Zn at the minorlevel and Al, Ca, Cl, K, Mg, and Na are generally at the major level. StandardReference Material NIST SRM-1571(Orchard Leaf) was analysed simultaneouslywith the samples. The precision and accuracy of the method was evaluated usingreal samples and the standard reference material. It was found out that theelemental concentrations measured in the NIST SRM-1571 are within ±10%of the reported values.     

Synthesis and solution properties of poly(vinyl ether)s with long alkyl chain,biphenyl, and cholesteryl pendants

The judicious choice of reaction conditions permitted living cationic polymerization of vinyl ethers with bulky and strongly interacting pendant groups, such as crystalline long alkyl chains and liquid crystalline mesogenic structures, using appropriate combinations of Lewis acids with added bases. Thus, well‐defined random and block copolymers with various pendants were also synthesized. Highly sensitive UCST‐type phase separation in various organic solvents was achieved employing crystallization of octadecyl pendants of homopolymers and random copolymers. This phase separation behavior is unusual for a polymer‐organic solvent system. Furthermore, thermally induced reversible physical gelation was conducted using this thermosensitive behavior. These specific pendants were very effective not only in organic media but also in water, in obtaining hydrogels with relatively low polymer concentrations. © 2008 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 46: 4392–4406, 2008     

High resolution laser spectroscopy of metallic atoms and molecules: Storage of singly and doubly charged ions transferred from externally generated laser plasmas

A radio-frequency (RF) ion trap has been constructed for high resolution laser spectroscopy of metallic ions. Ions in externally generated laser plasma have been directly introduced into the RF ion trap. An Nd:YAG laser is used to vaporize and ionize sample metals placed behind a ring electrode. Both hyperbolic and cylindrical electrodes are successfully used for confinement of the ions. Trapped ions are detected either with a quadrupole mass spectrometer or with a photomultiplier for the measurement of laser-induced fluorescence. Metallic ions such as Ca⁺, Ba⁺, La⁺, Nd⁺, Tm⁺, Lu⁺, and Ta⁺ have been confined for the time range of several to 20 minutes in the presence of He buffer gas, and a doubly charged ion Ba²⁺ for several seconds. Some ions like Nd⁺, Lu⁺, Hf⁺, and Ta⁺ are found to be highly reactive with background gaseous molecules.     

Vibrational analysis of ethylamines: Trans and gauche forms

Starting from force constant values calculated by an ab initio MO method ($\text{4-31G(N}{}^1\text{)}$), and by adjusting the diagonal elements, a practical force constant matrix (F) has been reached which could explain the observed infrared and Raman spectra (in the frequency range lower than 2000 cm^?1) of the gauche form of the ethylamine CH₃CH₂NH₂ molecule and five isotopic species CH₃¹³CH₂NH₂, CH₃CH₂¹⁵NH₂, CH₃CD₂NH₂, CH₃CH₂ND₂, and CD₃CD₂NH₂. The F matrix for the trans form of ethylamine was constructed by transferring ab initio $\text{4-31G(N}{}^1\text{)}$ values and by revising diagonal elements with conversion factors whose values are equal to the corresponding values of gauche form. A nearly complete set of assignments was achieved of the vibrational bands of ethylamines, observed so far in the spectral range 2000–100 cm^?1. In matrix isolation spectroscopy, two bands assignable to the NH₂ wagging vibrations of gauche and trans forms have been found at 775 and 782 cm^?1, respectively, for CH₃CH₂NH₂. They are at 768 and 774 cm^?1, respectively, for CD₃CD₂NH₂. From the intensity changes of these bands observed on changing the nozzle temperature in the matrix formation, the energy difference ΔE (gauche-trans) of these two conformers has been estimated to be 100 ± 10 cm^?1.     

Molecular weight control in polycondensation of hydroxyl diesters with hexamethylenediamine by polymer matrices

Polycondensation reactions of hydroxyl diesters such as dimethyl tartrate (DMT) and diethyl mucate (DEM) with hexamethylenediamine (HMD) were carried out in the presence of poly(vinyl pyridine) (P-VPy) and its copolymers with styrene of different compositions as matrix polymers in order to investigate the difference in interaction forces with monomers or the resulting polyamides owing to hydrogen bonding. It was found that matrix effects of poly(4-vinyl pyridine) (P-4VPy) on the rate enhancement and solution viscosity of the resulting polyamide became more pronounced with decreasing solvent polarity. This result suggests that the matrix effects of P-4VPy on polycondensation are due to hydrogen bonding interactions between hydroxyl diesters and P-4VPy. The addition of P-4VPy increased the molecular weight of the resulting polyamide to a higher extent than poly(2-vinyl pyridine) (P-2VPy), and the molecular weight of the resulting polyamide could be controlled according to the molecular weight of P-4VPy. Copolymer composition of 4-vinyl pyridine–styrene (4VPy/St) copolymers as matrix polymers also affected the molecular weight of the polyamide, which increased with increasing P-4VPy unit contents in the copolymers.     

Phase transition and freezing of ionic disorder in CsNO2 and TINO2 crystals2

The heat capacities of CsNO₂ and TlNO₂ have been measured in the temperature region between 13 and 350 K. The phase transitions of CsNO₂ and TlNO₂ were found at (209.16 ± 0.10)K and (282.4 ± 0.1)K. The enthalpy and entropy of the phase transition were (3.45 ± 0.20) kJ mol^?1 and (17.2 ± 1.0) JK^?1 mol^?1 for the former, and (6.44 ± 0.31) kJ mol^?1 and (23.8 ± 1.1) JK^?1 mol^?1 for the latter. The glass transitions were found around 42 K in CsNO₂ and around 60 K for TlNO₂, respectively. The corresponding dielectric relaxations were observed between 58 and 130 K for CsNO₂ in the frequency range between 10² and 10⁵ Hz and between 80 and 180 K for TlNO₂ in the frequency range between 2 × 10² and 10⁵ Hz. The calorimetric and dielectric relaxation times yielded a straight line in the Arrhenius plot over a wide time scale ranging from 10^?6 to 10⁵ sec. The slope gave the activation enthalpy of 13.8 kJ mol^?1 and 19.5 kJ mol^?1 for CsNO₂ and TlNO₂, respectively. The transition entropy supplemented by a residual entropy R ln 3 for CsNO₂ and R ln 2 for TlNO₂ gave (26.3 ± 1.0) JK^?1 mol^?1 and (29.6 ± 1.1) JK^?1 mol^?1 for the orientational entropy of the NO₂^? ion in the high-temperature phase. Based on the packing and symmetry considerations, these entropies were interpreted by the model which included two different sets of orientations of the NO₂^? ions parallel to [110] and [111] in the CsCl type unit cell. The existence of the different sets of orientation was proved by the doublet (Δv ~ 10 cm^?1) of the Raman spectrum of the bending mode of the NO₂^? ion in the cubic phase of the CsNO₂ crystal. The band narrowed to an ordinary singlet with increasing temperature. This observation was accounted for as the motional narrowing in which the NO₂^? ion felt an averaged field of the two different sets owing to the increased rate of jumping as the temperature increased.     

Simultaneous determination of trimethyl-and triethyllead in urban dust by species-specific isotope dilution/gas chromatography-inductively coupled plasma mass spectrometry

Both (206)Pb-labeled trimethyllead (TML) and triethyllead (TEL) were synthesized from (206)Pb-enriched metallic Pb certified reference material (NIST SRM 983) and iodomethane or iodoethane through a one-process reaction in a closed system using centrifuge tubes, respectively. Organolead compounds in an urban dust reference material (BCR CRM 605) were extracted with an acetic acid/methanol (1:1) solution, which was mechanically shaken for 24 h. After adjusting the pH of the extracted solution to pH 5, the extracted organolead compounds were derivatized by tetrabutylammonium tetrabutylborate (TATB) and measured with GC-ICPMS. The analytical results of TML and TEL for BCR CRM 605 were 8.22 +/- 0.04 microg kg(-1) (mean +/- standard deviation, n = 3) and 1.12 +/- 0.06 microg kg(-1), respectively. The analytical results of TML agreed well with the certified value (7.9 +/- 1.2 microg kg(-1)).