Search

The structures formed by the adsorption of carboxyalkylphosphonic acids on metal oxides are investigated by (super 1)H fast magic-angle-spinning (MAS) NMR experiments. (super 1)H solid-state NMR techniques will be highly useful for identifying specific non-covalent interactions between organic adsorbates and functionalilzed surfaces.

A study of the time scale and geometry exocyclic CH (sub)2 OH group motion in relation to the main glucose ring is presented. Results indicate that the glucose ring and exocyclic CH (sub)2 OH-group mobility are correlated.

The application of rotor-synchronized two-dimensional carbon-13 magic angle spinning exchange nuclear magnetic resonance measurements successfully characterized the electronic properties of tropolone molecules. These molecules were found to take diffusional lattice jumps and hydrogen shift/molecular pi-flips to maintain their crystal arrangement. Translational self-diffusion mechanisms monitored the occurrence of the two molecular reorientation processes which could be observed from the cross-peak patterns of the solid tropolone spectra at 40 degrees celsius.

Analysis of bullvalene using rotor-synchronized carbon-13 magic angle spinning nuclear magnetic resonance spectroscopy provided molecular data regarding the dynamic behavior of the compound under solid-state conditions. The results identified the symmetric threefold jumps and Cope rearrangement processes which concomitantly occurred with molecular reorientation. Deuterium measurements were conducted to reassess and compare the calculated peak intensities and spectral classification of the compound.

The kinetics of phase transformation from the liquid crystalline mesophase to the crystalline phase has been studied in a model dipole-functionalized hexabenzocoronene derivative by x-ray diffraction, solid state NMR recoupling techniques, and dielectric spectroscopy. These probes revealed long-lived metastability and an intermediate state involving a change in the unit cell prior to crystallization. The barrier properties were dominant and amount to 1 and 2.5 eV, respectively, for the unit cell transformation and crystallization processes. These effects should be considered in the design of discotic liquid crystals for electronic applications. [ABSTRACT FROM AUTHOR]

X-ray scattering, calorimetry and site-specific solid-state NMR techniques are employed to study the role of alkyl chain substitution on the phase formation and core dynamics in a series of diphenylamine functionalized perylenemonoimides (PMIs). The kinetics of phase transformation from the isotropic to the ordered phase proceeds via a nucleation and growth mechanism, and the rates are dominated by the nucleation barrier.

The self-assembled structure of a fluorous biphasic bexa(3,4-substituted-phenyl)benzene (HPB) is analyzed with polarized optical microscopy, differential scanning calorimetry, X-ray scattering and [super 19]F magic-angle spinning NMR and it is shown to be kinetically trapped with mixed fluorocarbon and hydrocarbon side chains. The addition of the parent biphasic diphenylacetylene has unlocked the frustrated conformation in the HPB, which has resulted in the formation of a thermodynamically favorable bilayer structure.

The synthesis and structural and retrostructural analyses of a library containing 10 triphenylenes functionalized with self-assembled benzyl ether and phenyl propyl ether dendrons are described. The self-assembly process of the dendronized triphenylene donor is programmed by a new supramolecular 'polymer effect' generated by donor-acceptor interactions.

Ring-expansion metathesis polymerization (REMP) mediated by cyclic Ru catalysts is analyzed focusing on the polymer products obtained under varied reaction conditions and catalyst architectures. Polymerization conducted with catalysts bearing six-carbon tethers has exhibited rapid polymer molecular weight growth that disclosed a maximum value at 70% monomer conversion, whereas five-carbon-tethered catalysts led to molecular weight growth resembling a step-growth mechanism with increase occurring only after 95% monomer conversion.

Describes a general treatment of nuclear magnetic resonance spectra under magic-angle spinning (MAS) conditions that is applicable to homogeneously and inhomogeneously broadened lines. Details of the method based on a combination of Floquet theory and perturbation theory; Sideband pattern; Spin evolution under MAS for a general Hamiltonian.

Theory and applications of a new 2D-NMR technique for characterizing the molecular structure and order of partially oriented solids are described. After deriving a general expression for the signal intensities in two dimensions in cases of perfect order, the influence of disorder on the spectra is discussed. It is demonstrated that an expansion of the orientational distribution function in terms of Wigner rotation matrices allows spectra from residues with an arbitrary degree of order and arbitrary chemical shielding tensor orientation to be fully characterized. The technique is illustrated by obtaining the orientational distribution function for the crystalline and amorphous regions in semicrystalline polyethylene terephthalate, showing that the molecular orientation is quite different in the two phases. [ABSTRACT FROM AUTHOR]

A new rotor-synchronized carbon-13 three-dimensional magic angle spinning NMR experiment for the extraction of orientational distribution functions from partially ordered solid materials is presented. Problems with overlap of two-dimensional spinning sideband patterns inherent in earlier methods are overcome by extension to three dimensions, allowing the degree of order for each resolvable carbon site to be measured. The new technique is demonstrated on a frozen smectic liquid-crystalline side group polymer which shows an order gradient from the aligned mesogen to the disordered polymer main chain. [ABSTRACT FROM AUTHOR]

Studies the dynamic heterogeneities and cooperativity in a lattice model glass. Quantification of fluctuations within the heterogeneous distribution of reorientation rates in terns of a rate memory parameter; Minimum value of the rate memory parameter; Apparent dependence of the rate memory parameter on cooperativity.