Internal rotation and halogen bonds in CF3I···NH3 and CF3I···N(CH3)3 probed by broadband rotational spectroscopy

The rotational spectra of CF(3)I···NH(3) and CF(3)I···N(CH(3))(3) are measured between 6.7 and 18 GHz using a chirped-pulse Fourier transform microwave spectrometer. Transitions in each spectrum are assigned to A and E species associated with ground and excited internal rotor states respectively. Rotational constants, B(0), centrifugal distortion constants, D(J), D(Jm), D(JKm), nuclear quadrupole coupling constants of the (14)N and (127)I atoms, χ(aa)(N) and χ(aa)(I), are determined for each complex. D(JK) is additionally determined for CF(3)I···NH(3). Results are presented for both (14)N and (15)N-substituted isotopologues. All data are consistent with C(3v) symmetric top structures for both complexes. The nuclear quadrupole coupling constants of iodine are determined to be -2230.030(83) MHz and -2241.61(17) MHz in CF(3)I···(14)NH(3) and CF(3)I···(14)N(CH(3))(3) respectively. The data are interpreted through a model that accounts for the internal dynamics of the complexes in order to determine the length of the halogen bond between the iodine and nitrogen atoms, r(N···I). Values of r(N···I) are thus determined to lie in the ranges 3.054 ? > r(N···I) > 3.034 ? and 2.790 ? > r(N···I) > 2.769 ? for CF(3)I···NH(3) and CF(3)I···N(CH(3))(3) respectively.     

Behavior of polyethylene in a variable temperature density gradient column

Polymer morphology (phase size and phase density) of slow cooled and quenched polyethylene (HDPE, LDPE, and LLDPE) has been characterized over a range of temperatures. The characterization methodology includes variable-temperature density gradient column (VT-DGC), small-angle x-ray scattering (SAXS), wide-angle x-ray diffraction (WAXD) and differential scanning calorimetry (DSC). Using a novel technique, a VT-DGC was prepared and cycled over a range of service temperatures (20-60 °C) for 5 cycles to investigate the changes of slow cooled and quenched HDPE, LDPE and LLDPE. A significant change in bulk density was present in each sample between the first cycle and subsequent cycles. Morphological analysis was performed using both the two-phase and three-phase models. The two-phase model showed that, for a particular sample, the thickness of the crystalline and amorphous phases varied very little within the experimental temperature range. Using the three-phase model, differences in the interfacial layer thickness were measured and observed to be significant compared to the amorphous and crystalline phase changes. The amorphous and crystalline densities of all samples varied less than 2%. Overall, significant difference in crystalline density was observed between HDPE, LDPE and LLDPE due to molecular structure.     

The Pt(111)/electrolyte interface under oxygen reduction reaction conditions: an electrochemical impedance spectroscopy study

The Pt(111)/electrolyte interface has been characterized during the oxygen reduction reaction (ORR) in 0.1 M HClO(4) using electrochemical impedance spectroscopy. The surface was studied within the potential region where adsorption of OH* and O* species occur without significant place exchange between the adsorbate and Pt surface atoms (0.45-1.15 V vs RHE). An equivalent electric circuit is proposed to model the Pt(111)/electrolyte interface under ORR conditions within the selected potential window. This equivalent circuit reflects three processes with different time constants, which occur simultaneously during the ORR at Pt(111). Density functional theory (DFT) calculations were used to correlate and interpret the results of the measurements. The calculations indicate that the coadsorption of ClO(4)* and Cl* with OH* is unlikely. Our analysis suggests that the two-dimensional (2D) structures formed in O(2)-free solution are also formed under ORR conditions.     

Laser heating of solid matter by light-pressure-driven shocks at ultrarelativistic intensities

The heating of solid targets irradiated by 5 x 10(20) W cm(-2), 0.8 ps, 1.05 microm wavelength laser light is studied by x-ray spectroscopy of the K-shell emission from thin layers of Ni, Mo, and V. A surface layer is heated to approximately 5 keV with an axial temperature gradient of 0.6 microm scale length. Images of Ni Ly(alpha) show the hot region has 100 G bar light pressure compresses the preformed plasma and drives a shock into the solid, heating a thin layer.     

Decreased Water Mobility Contributes To Increased α-Synuclein Aggregation**

The solvation shell is essential for the folding and function of proteins, but how it contributes to protein misfolding and aggregation has still to be elucidated. We show that the mobility of solvation shell H₂O molecules influences the aggregation rate of the amyloid protein α-synuclein (αSyn), a protein associated with Parkinson's disease. When the mobility of H₂O within the solvation shell is reduced by the presence of NaCl, αSyn aggregation rate increases. Conversely, in the presence CsI the mobility of the solvation shell is increased and αSyn aggregation is reduced. Changing the solvent from H₂O to D₂O leads to increased aggregation rates, indicating a solvent driven effect. We show the increased aggregation rate is not directly due to a change in the structural conformations of αSyn, it is also influenced by a reduction in both the H₂O mobility and αSyn mobility. We propose that reduced mobility of αSyn contributes to increased aggregation by promoting intermolecular interactions.     

ChemInform Abstract: Three Lowest-Lying Electronic States of NH2.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.     

ChemInform Abstract: Synthesis and Crystal Structure of Rb3PbCl5.

ChemInform is a weekly Abstracting Service, delivering concise information at a glance that was extracted from about 100 leading journals. To access a ChemInform Abstract of an article which was published elsewhere, please select a “Full Text” option. The original article is trackable via the “References” option.