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T Gullion

Publications and source records attributed to T Gullion.

8 recordsLinked to original sources
PubMed2003

Interatomic distance measurement in solid-state NMR between a spin- 1/2 and a spin- 5/2 using a universal REAPDOR curve.

A universal curve for the solid-state NMR REAPDOR experiment on an isolated spin-1/2-spin-5/2 pair is proposed that provides a simple means to measure their interatomic distance. REAPDOR data were obtained at three separate REAPDOR experiments using different values of the rotor spinning frequency. All points were fitted simultaneously to the universal formula without a need for full density matrix calculations. The 13C-17O distance of 2.45 A was measured between the C6 carbon and the 17O label in a tyrosine sample. The error of 8% in the dipolar coupling (Dfit = 278 Hz) is well within the 15% theoretical tolerance of this curve.

Journal Article↗
PubMed2000

Measuring (13)C-(2)D dipolar couplings with a universal REDOR dephasing curve

A (13)C-observe REDOR experiment is described which allows (13)C-(2)D dipolar couplings to be obtained by a universal dipolar dephasing curve. Previous (13)C-observe REDOR experiments on (13)C-(2)D spin pairs generally relied on numerical simulations to obtain the dipolar coupling. The REDOR experiment described in this article is based on a deuterium composite pulse, and the data analysis eliminates the need for numerical simulations and is the same as the traditional REDOR analysis performed on pairs of spin-12 nuclei. Copyright 2000 Academic Press.

Journal Article↗
PubMed2000

13C-14N REAPDOR and 13C-2D theta-REDOR NMR on a blend of tri-p-tolylamine and bisphenol-A-polycarbonate.

Solid-state NMR experiments are performed on amorphous blends of tri-p-tolylamine (TTA) and polycarbonate. Amines that are similar to TTA are blended with polycarbonates and used as photoconducting components in xerography. Because of its simple molecular structure, TTA is a charge-transporting molecule that is used as a model to understand charge transport in photoconducting materials. Charge transfer between amine molecules must depend on the separation and relative orientation between amine molecules. However, little information is known about the structural relationship between the amine molecules and the polymer host, presumably because of the difficulties associated with characterizing amorphous materials. We report the results of 13C-14N rotational-echo, adiabatic-passage, double-resonance (REAPDOR) and 13C-2D theta-rotational-echo, double-resonance (theta-REDOR) magic-angle spinning NMR experiments on a TTA/polycarbonate blend. The experiments provide information about the organization of TTA relative to polycarbonate.

Aniline Compounds↗
PubMed1999

A comparison between REDOR and theta-REDOR for measuring (13)C-(2)D dipolar interactions in solids.

(13)C-observe REDOR and theta-REDOR experiments for recovering the (13)C-(2)D dipolar interaction during MAS NMR are compared. It is found that limited (2)D RF power may severely compromise the performance of the REDOR experiment whereas the theta-REDOR experiment can be designed to work well. Results are presented for an isolated (13)C-(2)D spin pair with a large deuterium quadrupolar coupling constant and for a (13)C coupled to three methyl deuterons undergoing fast methyl group rotation.

Carbon Isotopes↗
PubMed1998

Optimizing the 13C-14N REAPDOR NMR experiment: a theoretical and experimental study.

The optimum 14N pulse lengths in the 13C-14N rotational-echo adiabatic-passage double-resonance (REAPDOR) NMR experiment are determined from calculations and from experiments on samples of glycine and L-alanine. The REAPDOR experiment utilizes the adiabatic passages that 14N spins make between the 14N Zeeman energy levels during the application of a single, short 14N radiofrequency pulse. Use of a short 14N irradiation time of less than one-quarter of a rotor period ensures that the number of 14N spins that undergo more than one passage is minimized. This simplifies calculations describing 13C dipolar dephasing and provides better agreement between calculations and experiments. Recovery of the 13C-14N dipolar couplings and 14N quadrupolar coupling constants and asymmetry parameters is described.

Alanine↗
PubMed1998

Counting spins with a new spin echo double resonance

In traditional spin echo double resonance (SEDOR), the echo amplitude M is decreased when the observed spins S are flipped by pi together with the pi refocusing pulse on the observed spins I; the dependence on tau is then determined. In the new version of SEDOR, the echo amplitude is measured as a function of the S spin flip angle theta at a constant pulse spacing tau. The analysis is simple and powerful for long tau, where the strong collision limit applies. There, the variation of M with theta can be fit, yielding the number n of spins S to which each spin I is coupled. Data from amorphous silicon with 1H and 2D show the described effect. A MAS version of the new method is used on multiply labeled alanine and urea, with results in good agreement with the predictions for n = 2, as expected. By Fourier transforming M with respect to the flip angle theta, a stick spectrum results; the largest numbered non-vanishing stick yields the number n of spins S coupled to each spin I. Simulations are presented for an n = 2 system. The present technique is compared to the multiple-quantum spin-counting method. Copyright 1998 Academic Press.

Journal Article↗