Tuesday, June 19, 2007

Chemical Physics Letters (CPL) update

Simultaneous acquisition and effective separation of intermolecular multiple-quantum signals of different orders
Zhu, Xiaoqin; Chen, Song; Chen, Zhong; Cai, Shuhui; Zhong, Jianhui vol 438, iss 4-6, pp. 308-314.
Abstract: A three-pulse sequence was designed to simultaneously acquire intermolecular multiple-quantum coherence (iMQC) signals of coherence order n=2,1,0,−1,−2. Analytical expressions were derived from modified Bloch equations. Signal of a specific order was obtained by optimal combinations of data from different acquisition steps. This allows a time saving of 5/7 compared to the phase cycling designs targeted for individual coherence orders. The method also results in pure iMQC signal of all the above five orders which are insensitive to radio-frequency flip angle errors, in contrast to some previous methods. Theoretical predictions are supported by the experimental observations and numerically simulated results.

13C and 1H nuclear magnetic shielding and spin–spin coupling constants of 13C-enriched bromomethane in the gas phase 13C and 1H nuclear magnetic shielding and spin–spin coupling constants of 13C-enriched bromomethane in the gas phase
Jackowski, Karol; Kubiszewski, Marek; Wilczek, Marcin vol 440, iss 4-6, pp. 176-179.
Abstract: 13C and 1H NMR spectral parameters are investigated for 13CH3Br in gaseous matrices. It is found that both the 13C and 1H chemical shifts of 13CH3Br are linearly dependent on solvent density. Similar dependence is also detected for one-bond spin–spin coupling, 1J(CH). For the first time the 13C and 1H magnetic shielding constants and 1J(CH) spin–spin coupling are obtained for an isolated 13CH3Br molecule together with the coefficients responsible for solute–solvent molecular interactions in gaseous matrices. The present experimental results confirm the accuracy of some recent ab initio calculations of nuclear magnetic shielding performed for bromomethane.

Analysis of molecular structures by homo- and hetero-nuclear J-coupled NMR in ultra-low field J-coupled NMR in ultra-low field
Appelt, Stephan; Häsing, F. Wolfgang; Kühn, Holger; Sieling, Ulrich; Blümich, Bernhard vol 440, iss 4-6, pp. 308-312.
Abstract: The drawback of nuclear magnetic resonance (NMR) spectroscopy at ultra-low magnetic fields appears to be the lack of access to chemical information in terms of chemical shifts and homo-nuclear J-couplings. Here we report that a chemical group can be identified by the multiplet structure of the NMR spectrum in ultra-low fields if the condition of the strong hetero-nuclear J-coupling is fulfilled. Moreover we found that high-resolution ultra-low field proton-NMR spectra of liquids indeed reveal all hetero- and homo-nuclear J-couplings in terms of pairs of multiplets. This opens the door for the study of molecular structures at ultra-low magnetic fields.

Contribution of 43Ca MAS NMR for probing the structural configuration of calcium in glass 43Ca MAS NMR for probing the structural configuration of calcium in glass
Angeli, Frédéric; Gaillard, Marina; Jollivet, Patrick; Charpentier, Thibault vol 440, iss 4-6, pp. 324-328.
Abstract: The 43Ca MAS NMR spectra obtained for three calcium silicate glasses containing aluminum and/or sodium are analyzed. The 43Ca NMR parameters are shown to be highly sensitive to variations in its chemical environment. The transition from a charge-compensating role of [AlO4]− groups to a network-modifying role near nonbridging oxygen atoms results in an increase of both the isotropic chemical shift and the quadrupolar coupling constant of 43Ca. This effect can be related to the first coordination shell of calcium (through the Ca–O bond distance) which is affected by the chemical environment beyond the first neighbors of calcium.

Evaluation of nanometer-scale droplets in a ternary o/w microemulsion using SAXS and 129Xe NMR 129Xe NMR
Kataoka, Hiroshi; Ueda, Takahiro; Ichimei, Daisuke; Miyakubo, Keisuke; Eguchi, Taro; Takeichi, Nobuhiko; et. al. vol 441, iss 1-3, pp. 109-114.
Abstract: This study revealed a linear correlation between the nanometer-scale oil droplet sizes estimated using small angle X-ray scatterings (SAXS) and the 129Xe NMR chemical shift in an oil-in-water ternary microemulsion system comprising pentaethylene glycol mono-n-dodecyl ether, n-decane, and deuterium oxide. The absolute values of the droplet size estimated using 129Xe NMR show good agreement with those using SAXS. We also found that the results are consistent with a reported relation derived using small angle neutron scattering. The results suggest the validity of 129Xe NMR chemical shifts for investigation of colloidal systems to evaluate their internal structures’ characteristic sizes.

No comments: