Variable-temperature, solid-state NMR studies of bonded liquid crystal stationary phases for HPLC

1995 ◽  
Vol 41 (5-6) ◽  
pp. 301-310 ◽  
Author(s):  
J. J. Pesek ◽  
M. T. Matyska ◽  
E. J. Williamser ◽  
R. Tam
Keyword(s):  
Liquid Crystal ◽  
Solid State ◽  
Solid State Nmr ◽  
Variable Temperature ◽  
Stationary Phases ◽  
Nmr Studies ◽  
Liquid Crystal Stationary Phases

Solution and Solid State NMR Studies of the Structure and Dynamics of C60 and C70

1990 ◽  
Vol 206 ◽  
Author(s):  
R. D. Johnson ◽  
C. S. Yannoni ◽  
J. Salem ◽  
G. Meijer ◽  
D. S. Bethune
Keyword(s):  
Solid State ◽  
Solid State Nmr ◽  
Variable Temperature ◽  
Chemical Shift Anisotropy ◽  
Resonance Assignments ◽  
Powder Pattern ◽  
High Symmetry ◽  
Nmr Studies ◽  
Structure And Dynamics ◽  
C Nmr

ABSTRACTWe have investigated the structure and dynamics of C60 and C70 with 13C NMR spectroscopy. In solution, high-resolution spectra reveal that C60 has a single resonance at 143 ppm, indicating a strained, aromatic system with high symmetry. This is strong evidence for a C60 “soccer ball” geometry. A 2D NMR INADEQUATE experiment on 13C-enriched C70 reveals the bonding connectivity to be a linear string, in firm support of the proposed “rugby ball” structure with D5h symmetry, and furnishes resonance assignments. Solid state NMR spectra of C60 at ambient temperatures yield a narrow resonance, indicative of rapid molecular reorientation. Variable temperature T1 measurements show that the rotational correlation time is ∼ 10−9s at 230 K. At 77 K, this time increases to more than 1 ms, and the 13C NMR spectrum of C60 is a powder pattern due to chemical shift anisotropy (tensor components 220, 186, 40 ppm). At intermediate temperatures a narrow peak is superimposed on the powder pattern, suggesting a distribution of barriers to molecular motion in the sample, or the presence of an additional phase in the solid state. A Carr-Purcell dipolar experiment on C60 in the solid state allows the first precise determination of the C60 bond lengths: 1.45 and 1.40Å.

Solid-State NMR of Elastomers

1990 ◽  
Vol 63 (3) ◽  
pp. 407-425 ◽  
Author(s):  
Robert A. Kinsey
Keyword(s):  
Solid State ◽  
Solid State Nmr ◽  
Variable Temperature ◽  
Heterogeneous Systems ◽  
Nmr Studies ◽  
High Magnetic Field Strength ◽  
Relaxation Measurements ◽  
Physical Insight ◽  
Elastomer Composites

Abstract The versatility of solid state NMR for the characterization of elastomers and elastomer composites has been demonstrated. NMR can be used as an analytical tool for identifying the elastomer(s) present (including the sequence distribution and tacticity), measuring crosslink levels, and monitoring chemical modifications. In addition, with relaxation measurements, NMR provides direct physical insight into the dynamics, and hence the spatial interactions of elastomeric systems. The interfacial regions of heterogeneous systems such as IPNs, filled elastomers, and block copolymers can be probed. A variety of NMR parameters can be correlated with physical properties. Future studies will extend the use of variable temperature and high magnetic field strength measurements, as well as utilize the growing number of two-dimensional experiments. The use of solid state H-l NMR should increase as instrumentation progresses, complementing the heteronuclear work. Solid H-l NMR offers significant sensitivity increases over C-13 NMR, but with decreased resolution. N-15 NMR studies have been recently performed at natural abundance with rigid polymers, and will likely be useful for characterizing elastomers.

Characterization of some mesogenic alkyl 1-thioglycosides

2002 ◽  
Vol 80 (8) ◽  
pp. 1162-1165 ◽  
Author(s):  
B Henrissat ◽  
G K Hamer ◽  
M G Taylor ◽  
R H Marchessault
Keyword(s):  
Phase Transition ◽  
Liquid Crystal ◽  
Solid State ◽  
Solid State Nmr ◽  
Liquid Crystalline ◽  
Liquid Crystal Phase ◽  
X Ray Diffraction ◽  
X Ray ◽  
Liquid Crystalline Phases

A series of dodecyl 1-thio-β-D-glycosides has been synthesized and characterized (DSC, NMR, CP MAS, X-ray diffraction) as possible new marking materials with liquid-crystalline properties. These compounds undergo solid to liquid crystal phase transitions at various temperatures, which depend on the nature of the carbohydrate part of the structure. Their liquid-crystalline phases show extreme shear thinning behaviour.Key words: liquid crystal, powder X-ray diffraction, phase transition, thioglycoside, solid-state NMR, marking material

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