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A density matrix description of 14N overtone nuclear magnetic resonance in static and spinning solids (1999)

Marinelli, Laura ; Wi, Sungsool ; Frydman, Lucio

College Park, Md. : American Institute of Physics (AIP)

The Journal of Chemical Physics 110 (1999), S. 3100-3112

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ISSN: 1089-7690

Source: AIP Digital Archive

Topics: Physics , Chemistry and Pharmacology

Notes: Overtone NMR is an experiment introduced by LeGros, Bloom, Tycko, and Opella, capable of providing 14N powder spectra devoid of first-order quadrupole broadenings by irradiation and observation of the nuclear spins at twice their Larmor frequency. This technique constitutes one of the most promising alternatives for the acquisition of high resolution solid 14N NMR spectra from random powders, particularly if it can be combined with strategies capable of removing the substantial second-order quadrupole broadenings remaining in the overtone line shapes. In order to facilitate the search for these averaging manipulations, we present here a theoretical description of the overtone experiment based on the time-domain propagation of density matrices. It is shown that by combining perturbation methods with appropriate rotating-frame transformations and diagonalizations, overtone spin-1 phenomena can be described using a single set of fictitious spin-1/2 operators. By contrast to conventional spin-1/2 irradiation and detection processes, however, overtone manipulations involve an unusual angular dependence on the azimuthal angle defining rotations about the main Zeeman magnetic field. This behavior introduces unexpected complications toward the narrowing of overtone resonances by conventional sample spinning techniques. Nevertheless, it can still be shown that the removal of all spin-1 anisotropies by certain forms of dynamic-angle spinning overtone NMR remains feasible. © 1999 American Institute of Physics.

Type of Medium: Electronic Resource

URL: http://dx.doi.org/10.1063/1.477906

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Predictions of protein secondary structures using factor analysis on Fourier transform infrared spectra: Effect of Fourier self-deconvolution of the amide I and amide II bands (1998)

Wi, Sungsool ; Pancoska, Petr ; Keiderling, Timothy A.

New York, NY [u.a.] : Wiley-Blackwell

Biospectroscopy 4 (1998), S. 93-106

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ISSN: 1075-4261

Keywords: protein secondary structure ; FTIR spectroscopy ; Fourier self-deconvolution ; factor analysis ; Chemistry ; Analytical Chemistry and Spectroscopy

Source: Wiley InterScience Backfile Collection 1832-2000

Topics: Biology , Physics

Notes: Fourier self-deconvolution (FSD) was performed on protein amide I and II Fourier transform infrared (FTIR) spectra to test if the resultant increased band shape variation would lead to improvements in protein secondary structure prediction with our factor analysis based restricted multiple regression (RMR) methods. FTIR spectra of 23 proteins dissolved in H2O were measured and normalized to a constant amide I peak absorbance. The deconvolved spectra were renormalized by area so that the deconvolved spectra sets had the same area as before. Principal component analysis of the deconvolved spectra sets was carried out, which was followed by a selective multiple linear regression (RMR) analysis of the principal component loadings with regard to the fractional components (FC) of secondary structure. As compared to analyses based on the original spectra set, helix and sheet predictions were not noticeably improved by FSD; but, if a very large number of component spectra (16) were retained in the pool to select which loadings to be used in the RMR optimization, better predictions of turn and “other” resulted. The prediction quality varied depending on the deconvolution parameters used. © 1998 John Wiley & Sons, Inc. Biospectroscopy 4: 93-106, 1998

Additional Material: 5 Ill.

Type of Medium: Electronic Resource

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