PubMed Health⌕ Search
Home/Archive/PubMed

PubMed · 9500905

An efficient broadband decoupling sequence for liquid crystals.

Y Yu·B M Fung
View original source ↗Export metadata ↓

Abstract

A new and efficient broadband decoupling sequence is presented. It is based on the phase cycling of two pulses with small phase angles. The pulse width is 180 degrees +/- 30 degrees, and the phase angle is +/-10 degrees-12 degrees. The sequence contains 16 elements, and is called SPARC-16 as an abbreviation for small phase angle rapid cycling. The application of this sequence to a liquid crystalline compound, 4-n-pentyl-4'-cyanobiphenyl (5CB), is reported. The signal-to-noise ratios and the linewidths of the 13C peaks of 5CB with SPARC-16 decoupling and with other decoupling methods are compared. The results show that the broadband decoupling efficiency of SPARC-16 is considerably better than those of other methods.

Explore related subjects

CrystallizationNuclear Magnetic Resonance, BiomolecularOsteonectinProtein ConformationSolutionsComparative StudyJournal ArticleResearch Support, U.S. Gov't, Non-P.H.S.

Keep this discovery

Explore connections, maps & timelines

BibTeXRIS

Y Yu, B M Fung. 1998. An efficient broadband decoupling sequence for liquid crystals.. https://doi.org/10.1006/jmre.1997.1322

Cite the original work for its findings. Save a collection to share your selection of sources.

KEEP EXPLORING

Related citations

PubMed2001

Approaches to determining membrane protein structures to high resolution: do selections of subpopulations occur?

Three different methods are currently used for the study of high-resolution structures of membrane proteins: X-ray crystallography, electron crystallography, and nuclear magnetic resonance (NMR) spectroscopy. Thus far, all methods combined have yielded a rather modest number of crystal structures that have been solved at the atomic level. It is hypothesized here that different methods may select different populations of proteins on the basis of various properties. Thus, protein stability may be a significant factor in the formation of three-dimensional (3D) crystals from detergent solutions, since exposure of hydrophobic protein zones to water may cause structural perturbation or denaturation in conformationally labile proteins. This is different in the formation of two-dimensional (2D) crystals where a protein remains protected in its native membrane environment. A biological selection mechanism may therefore be operative in that highly ordered lattices may form only if strong protein-protein interactions are relevant in vivo, thereby limiting the number of proteins that are amenable to electron crystallography. Keeping a protein in a bilayer environment throughout 3D crystallization maintains the lateral pressure existing in native membranes. This can be accomplished by using lipidic cubic phases. Alternatively, the hydrophobic interface of a membrane protein may be spared from contact with water by crystallization from organic solvents where the polar caps are protected in reverse micelles by using appropriate detergents. Some of the criteria that are useful in optimizing the various approaches are given. While the usefulness of complementary methods seems obvious, the results presented may be particularly critical in recognizing key problems in other structural approaches.

Crystallization↗
PubMed2000

Highly crystalline faujasitic zeolites from flyash.

The process for the synthesis of flyash-based zeolites (FAZs) are presented, which basically includes alkaline treatment of flyash by a fusion method, followed by hydrothermal crystallization. Zeolite-Y has been identified, and conditions have been optimized for their synthesis by the fusion method. Optimal conditions for synthesis of Zeolite-Y are a NaOH/flyash ratio of 1.2:1, fusion temperature between 500 degrees C and 600 degrees C, crystallization time of 8-10 h and crystallization temperature between 100 degrees C and 110 degrees C. The cation exchange capacity (CEC) of FAZ-Y ranges between 400 and 450 meq/100 g. The surface area of FAZs (500-600 m(2)/g) compare well with the commercial zeolites procured from Mobil Oil. Morphological characterization of FAZ using scanning electron microscopy (SEM) reveals cubic structure, and XRD data reveal unit cells to be cubic system.

Crystallization↗
PubMed2000

Discriminating between homodimeric and monomeric proteins in the crystalline state.

Scores calculated from intermolecular contacts of proteins in the crystalline state are used to differentiate monomeric and homodimeric proteins, by classification into two categories separated by a cut-off score value. The generalized classification error is estimated by using bootstrap re-sampling on a nonredundant set of 172 water-soluble proteins whose prevalent quaternary state in solution is known to be either monomeric or homodimeric. A statistical potential, based on atom-pair frequencies across interfaces observed with homodimers, is found to yield an error rate of 12.5%. This indicates a small but significant improvement over the measure of solvent accessible surface area buried in the contact interface, which achieves an error rate of 15.4%. A further modification of the latter parameter relating the two most extensive contacts of the crystal results in an even lower error rate of 11.1%.

Crystallization↗