Monday, March 31, 2008

Bryan's Extravagant Journal Update

Hi kids! It's all the news fit to print about NMR! You've paid for your whole seat but you'll only use the edge!!!


Chemical Physics Vol: 344, Issue: 3, March 13, 2008, pp. 291-298

Dynamics of [Zn(D2O)6]^2^+ in [Zn(D2O)6][SiF6] crystal as studied by 1D, 2D spectra and spin-lattice relaxation time of ^2H NMR
Araya, T.; Niwa, A.; Mizuno, M.; Endo, K.

Abstract: The dynamics of [Zn(D2O)6]^2^+ in [Zn(D2O)6][SiF6] was investigated by ^2H NMR one-dimensional spectra, two-dimensional exchange spectra and spin-lattice relaxation time (T1). The lineshapes of those spectra and T1 were dominated by the 180^o flip of the water molecules and the reorientation of [Zn(D2O)6]^2^+ about the C3 axis. The variation of lineshape of the one-dimensional spectrum below room temperature can be explained by only the 180^o flip of the water molecules. The spectrum at room temperature showed a typical shape due to the rapid 180^o flip of water molecules. The change in lineshape of the one-dimensional ^2H NMR spectrum is caused by the three-site jump of [Zn(D2O)6]^2^+ about its C3 axis above 333K. Information of the reorientation of [Zn(D2O)6]^2^+ below 333K could not be obtained from the one-dimensional spectrum and T1. In this temperature range, the two-dimensional exchange spectrum was effective for analysis of molecular motion. The effects of multiple motions, the 180^o flip of the water molecules and the reorientation of [Zn(D2O)6]^2^+ about the C3 axis, on the lineshape of the two-dimensional exchange spectrum were studied using spectral simulation.


Chemical Physics Vol: 344, Issue: 3, March 13, 2008, pp. 281-290

Inversion, internal rotation, and nitrogen nuclear quadrupole coupling of p-toluidine as obtained from microwave spectroscopy and ab initio calculations
Hellweg, A.

A highly accurate combined experimental and theoretical investigation has been conducted on p-toluidine (4-methylaniline) in its vibrational and electronic ground state. Rotational transitions have been recorded using pulsed molecular beam Fourier transform microwave (MB-FTMW) spectroscopy in the frequency range 7-20GHz. The rotational spectrum of this molecule is complicated by the inversion of the amino group, the internal rotation of the methyl group, and the ^1^4N nuclear quadrupole hyperfine structure. Second-order Moller-Plesset perturbation theory and coupled-cluster singles-and-doubles with a perturbative correction for connected triples have been used in conjunction with high-level basis sets for the quantum chemical investigation. The torsional fine and quadrupole hyperfine structures of the spectra could be interpreted by means of these theoretical data.


Chemical Physics Vol: 345, Issue: 1, April 3, 2008, pp. 116-118

The relationship between crystal structure and NMR relaxation in molecular solids with tert-butyl groups
Rheingold, A.L.; DiPasquale, A.G.; Beckmann, P.A.

We correlate an X-ray determination of the molecular and crystal structures of 2-tert-butylanthracene and 2-tert-butylanthraquinone reported here with the previously reported dynamical nuclear magnetic resonance determination of the motions of the tert-butyl groups and their resident methyl groups in the solid state [P.A. Beckmann, K.S. Burbank, M.M.W. Lau, J.N. Ree, T.L. Weber, Chem. Phys. 290 (2003) 241]


Chemical Physics Letters Vol: 451, Issue: 4-6, January 21, 2008, pp. 226-232

Solvent effects on zero-point vibrational corrections to optical rotations and nuclear magnetic resonance shielding constants
Kongsted, J.; Ruud, K.

We present zero-point vibrational corrections to nuclear magnetic shielding constants and optical rotations of molecules in gas-phase and solution.


Chemical Physics Letters Vol: 452, Issue: 4-6, February 11, 2008, pp. 233-238

Magic angle spinning (MAS) NMR linewidths in the presence of solid-state dynamics
Thrippleton, M.J.; Cutajar, M.; Wimperis, S.

The failure of magic angle spinning (MAS) to achieve narrow NMR linewidths in the presence of solid-state dynamics is discussed.


Chemical Physics Letters Vol: 454, Issue: 1-3, March 10, 2008, pp. 56-60

Orientational order of solutes in liquid crystals: The effect of distributed electric quadrupoles
Lee, J.S.J.; Sokolovskii, R.O.; Berardi, R.; Zannoni, C.; Burnell, E.E.

The layout of electrical quadrupoles in acetylene, benzene, and 1,3,5-trifluorobenzene molecules.


Chemical Physics Letters Vol: 454, Issue: 1-3, March 10, 2008, pp. 129-132

Density functionals for calculating NMR ^1JCH coupling constants in electron-rich systems
Neto, A.C.; Santos, F.P.d.; Paula, A.S.; Tormena, C.F.; Rittner, R.

Experimental and theoretically calculated ^1JCH values, using several DFT exchange-correlation functionals, were obtained, compared and the results interpreted.


Chem. Commun., 2008, 868 - 870, DOI: 10.1039/b716383e

Measuring nitrogen quadrupolar coupling with 13C detected wide-line 14N NMR under magic-angle spinning
Zhehong Gan

A 13C-detected 14N wide-line NMR experiment is described for measuring nitrogen quadrupolar coupling under magic-angle spinning.


Chem. Commun., 2008, 1621 - 1634, DOI: 10.1039/b711551b

Solid-state NMR studies of weak interactions in supramolecular systems
Michele R. Chierotti and Roberto Gobetto

The field of application of solid-state NMR to the study of supramolecular systems is growing rapidly, with many research groups involved in the development of techniques for the study of crystalline and amorphous phases. This Feature Article aims to provide an overview of the recent contributions of our research group to this field, paying particular attention to the study of the weak interactions such as hydrogen bonds in supramolecular systems through solid-state NMR investigations. The structure and dynamic behaviour of selected host–guest systems will be also discussed. An overview of the characterization of supramolecular systems by means of solid-state NMR is presented: many parameters NMR have been discussed and particular attention has been given to the hydrogen-bond investigation and to the detection of molecular motion in the solid state.


Dalton Trans., 2008, 1195 - 1202, DOI: 10.1039/b717390c

A benzene-core trinuclear GdIII complex: towards the optimization of relaxivity for MRI contrast agent applications at high magnetic field
João Bruno Livramento, Lothar Helm, Angélique Sour, Conlin O'Neil, André E. Merbach and Éva Tóth

A novel ligand, H12L, based on a trimethylbenzene core bearing three methylenediethylenetriamine-N,N,N,N-tetraacetate moieties (–CH2DTTA4-) for Gd3+ chelation has been synthesized, and its trinuclear Gd3+ complex [Gd3L(H2O)6]3- investigated with respect to MRI contrast agent applications. A multiple-field, variable-temperature 17O NMR and proton relaxivity study on [Gd3L(H2O)6]3- yielded the parameters characterizing water exchange and rotational dynamics. On the basis of the 17O chemical shifts, bishydration of Gd3+ could be evidenced. The water exchange rate, kex298 = 9.0 ± 3.0 s-1 is around twice as high as kex298 of the commercial [Gd(DTPA)(H2O)]2- and comparable to those on analogous Gd3+-DTTA chelates. Despite the relatively small size of the complex, the rotational dynamics had to be described with the Lipari–Szabo approach, by separating global and local motions. The difference between the local and global rotational correlation times, lO298 = 170 ± 10 ps and gO298 = 540 ± 100 ps respectively, shows that [Gd3L(H2O)6]3- is not fully rigid; its flexibility originates from the CH2 linker between the benzene core and the poly(amino carboxylate) moiety. As a consequence of the two inner-sphere water molecules per Gd3+, their close to optimal exchange rate and the appropriate size and limited flexibility of the molecule, [Gd3L(H2O)6]3-
has remarkable proton relaxivities when compared with commercial contrast agents, particularly at high magnetic fields (r1 = 21.6, 17.0 and 10.7 mM-1s-1 at 60, 200 and 400 MHz respectively, at 25 °C; r1 is the paramagnetic enhancement of the longitudinal water proton relaxation rate, referred to 1 mM concentration of Gd3+).


Dalton Trans., 2008, 481 - 490, DOI: 10.1039/b712011g

A solid-state NMR investigation of single-source precursors for group 12 metal selenides; M[N(iPr2PSe)2]2 (M = Zn, Cd, Hg)
Bryan A. Demko and Roderick E. Wasylishen

Abstract: The first solid-state NMR investigation of dichalcogenoimidodiphosphinato complexes, M[N(R2PE)2]n, is presented. The single-source precursors for metal-selenide materials, M[N(iPr2PSe)2]2 (M = Zn, Cd, Hg), were studied by solid-state 31P, 77Se, 113Cd, and 199Hg NMR at 4.7, 7.0, and 11.7 T, representing the only 77Se NMR measurements, and in the case of Cd[N(iPr2PSe)2]2113Cd NMR measurements, to have been performed on these complexes. Residual dipolar coupling between 14N and 31P was observed in solid-state 31P NMR spectra at 4.7 and 7.0 T yielding average values of R(31P,14N)eff = 880 Hz, CQ(14N) = 3.0 MHz, 1J(31P,14N)iso = 15 Hz, = 90°, = 26°. The solid-state NMR spectra obtained were used to determine the respective phosphorus, selenium, cadmium, and mercury chemical shift tensors along with the indirect spin–spin coupling constants: 1J(77Se,31P)iso, 1J(111/113Cd,77Se)iso, 1J(199Hg,77Se)iso, and 2J(199Hg,31P)iso. Density functional theory magnetic shielding tensor calculations were performed yielding the orientations of the corresponding chemical shift tensors. For this series of complexes the phosphorus magnetic shielding tensors are essentially identical, the selenium magnetic shielding tensors are also very similar with respect to each other, and the magnetic shielding tensors of the central metals, cadmium and mercury, display near axial symmetry demonstrating an expected deviation from local S4 symmetry.


J. Mater. Chem., 2008, 18, 894 - 904, DOI: 10.1039/b715319h

Preparation and photophysical characterisation of Zn–Al layered double hydroxides intercalated by anionic pyrene derivatives
Sandra Gago, Telma Costa, J. Seixas de Melo, Isabel S. Gonçalves and Martyn Pillinger

Zn–Al hydrotalcite-like compounds intercalated by 1,3,6,8-pyrenetetrasulfonate (PTS), 1-pyrenesulfonate (PS) and 1-pyrenecarboxylate (PC) anions were synthesised by an ion-exchange procedure. The materials were characterised by powder X-ray diffraction at different temperatures, thermogravimetric analysis, FTIR, 13C{1H} CP/MAS NMR and photoluminescence techniques. In the fully hydrated states, the interlayer distances are 13.7 Å for Zn–Al–PTS, 18.9 Å for Zn–Al–PS, and 24.8 Å for Zn–Al–PC. These can be ascribed to a monolayer arrangement for intercalated PTS anions and bilayer arrangements for the 1-pyrenyl derivatives. The samples exhibit different thermal decomposition pathways, and in the case of Zn–Al–PTS the removal of physisorbed and interlayer water leads to a change in the orientation of the organic anion with respect to the hydroxide layers. The structural transformation is fully reversible upon hydration. The photophysical characterisation of the bulk materials was based on the determination of their emission and fluorescence excitation spectra, and the fluorescence lifetimes. From the steady-state (monomer and excimer-like bands) and time-resolved (triple exponential decays) data, evidence for the presence of a structure with similar characteristics to pyrene dimer together with monomer (by comparison with the emission of dilute solutions of PS and PC), pre-associated and (possibly) dynamic excimer species could be presented.


J. Mater. Chem., 2008, 18, 392 - 399, DOI: 10.1039/b714785f

Organosilicas based on purine–pyrimidine base pair assemblies: a solid state NMR point of view
Guilhem Arrachart, Carole Carcel, Joël J. E. Moreau, Geoffrey Hartmeyer, Bruno Alonso, Dominique Massiot, Gaëlle Creff, Jean-Louis Bantignies, Philippe Dieudonne, Michel Wong Chi Man, Gerhard Althoff, Florence Babonneau and Christian Bonhomme

Organosilicas based on adenine (A) and thymine (T) assemblies have been synthesized. A surfactant-free route, based on specific molecular recognition between A and T entities, has been developed. The characterization of the H-bond networks, in both homo- and hetero-assemblies, has been emphasized by using 1H solid state NMR (nuclear magnetic resonance). The latest experimental developments were implemented (i.e. very fast MAS (magic angle spinning) experiments at 750 MHz and 33 kHz), in order to enhance drastically the spectral resolution. Moreover, 1H experiments at 67 kHz in 1.3 mm rotors were performed. Spatial connectivities between protons were established by using 1H–1H DQ (double quantum) MAS experiments, allowing the precise characterization of A/A, T/T and A/T associations.


No comments: