Transferred Echo Double Resonance Research Articles

Two-dimensional transferred-echo double resonance study of molecular motion in a fluorinated polycarbonate

A two-dimensional version of the transferred-echo double resonance (TEDOR) experiment is introduced to measure strong heteronuclear magnetic dipolar interactions between rare spins. A quantitative description of this 2D-TEDOR experiment is given for an I– S pair of spins undergoing relative motion. 2D-TEDOR calculations are consistent with data for a calibration model: the directly bound 13 C– 31 P pair in [3- 13 C] glyphosate, HO 3 31P 13CH 2NHCH 2COOH. Analysis shows that the indirect spin–spin interaction and the dipole–dipole interaction have opposite signs in this system. The 2D-TEDOR experiment is then used to measure heteronuclear 13 C– 19 F interactions in a fluorinated polycarbonate in which an aromatic proton is replaced by a fluorine on every fourth ring. Results from the 2D-TEDOR experiment show that the aromatic ring flips that occur in ordinary polycarbonate are blocked for a fluorinated ring.

Double TEDOR for the Direct Detection of Stable-Isotope Triads

Abstract An extension of transferred-echo double-resonance (TEDOR) NMR is presented for the detection of three coupled spin- 1 2 nuclei: I1–S–I2, where I1and I2are a homonuclear pair with an isotropic chemical-shift difference. By performing two coherence transfers (in combination with a DANTE preparation sequence), it is possible to monitor coherence transferred sequentially from I1to S to I2(or the reverse). Initial experiments demonstrating the feasibility of this approach were performed on both mixed and recrystallized13C- and15N-labeled alanines, and the results are found to be in good agreement with predictions based on a density matrix formalism. This technique has also been applied to characterize the covalent cross-linking of the bacterial cell wall of a triple-labeledBacillus subtilisby demonstrating the connectivity of13C–15N–13C triads. These triads occur only in the cross-link bond.

27Al/31P solid-state n.m.r. structural investigations of AlPO4-5 molecular sieve

27 Al/ 31 P solid-state n.m.r. connectivity experiments were used to investigate the structure of the molecular sieve AIPO 4 -5 hydrated with D 2 O. Hydration with D 2 O resulted in an increased efficiency of coherence transfer from octahedral 27 Al to 31 P compared with hydration with H 2 O. The experiments prove directly that both the tetrahedral aluminum and the octahedral aluminum formed upon hydration are connected to phosphorus in the framework. The two-dimensional 27 Al → 31 P transferred-echo double-resonance and cross-polarization experiments show a downfield offset of the octahedral 27 Al correlation from the tetrahedral 27 Al correlation, consistent with the growth of a downfield shoulder on the 31 P resonance as water is incorporated into the lattice.

Structural investigations of SAPO-37 molecular sieve by coherence-transfer and dipolar-dephasing solid-state nuclear magnetic resonance experiments

In this work, dipolar-based coherence-transfer and dipolar-dephasing solid-state nuclear magnetic resonance (NMR) experiments were performed to investigate the structure of the silicoaluminophosphate molecular sieve SAPO-37. The 27Al→ 29Si transferred-echo double-resonance (TEDOR) experiment directly proves, for the first time, that silicon substitutes for phosphorus atoms in the framework via the SM2 mechanism. The 27Al ( 31P) and 27Al ( 29Si) dipolar-dephasing difference experiments and the two-dimensional 27Al→ 31P TEDOR experiment indicate the presence of three types of aluminum environments: tetrahedral Al surrounded by symmetrical [4P] or [4Si] environments which give rise to a sharp resonance, tetrahedral Al surrounded by asymmetrical [3P, Si], [2P, 2Si] or [P, 3Si] environments which give rise to a broad resonance, and also extra-framework amorphous octahedral Al.

Spin density description of rotational-echo double-resonance, transferred-echo double-resonance and two-dimensional transferred-echo double-resonance solid state nuclear magnetic resonance

The spin density matrix formalism has been applied to rotational-echo double-resonance (REDOR), transferred-echo double-resonance (TEDOR) and two-dimensional (2D) TEDOR experiments in order to obtain an expression for the signal intensities. TEDOR spectra of 15N-labeled glycine were measured with different dipolar evolution times. 2D-TEDOR spectra were measured of doubly labeled glycine-2- 13C, 15N and of 15N-labeled glycine. Both the TEDOR and the 2D-TEDOR spectra were readily obtained although the 2D-TEDOR experiment on 15N-labeled glycine used a lot of machine time. Even though the 15N-1- 13C dipolar coupling is relatively small (200 Hz), the 1-C resonance can still be observed.

Measurement of Heteronuclear Dipolar Coupling by Transferred-Echo Double-Resonance NMR

A magic-angle spinning experiment called transferred-echo double resonance (TEDOR) has been introduced recently to measure the I-S dipolar coupling of heteronuclear I-S pairs of spin- 1 2 nuclei while eliminating unwanted background signals from uncoupled I and S spins via a coherence-transfer process. In this paper, a quantitative description of the TEDOR experiment is given in terms of the evolution of the density matrix for a pair of heteronuclear spins. The resulting equations provide a theoretical basis for evaluating the selectivity and sensitivity of TEDOR and suggest strategies for determining dipolar coupling constants directly from TEDOR data. Experimental examples illustrating these aspects of TEDOR are provided by studies performed on a range of 13C- 15N dipolar couplings found in double-labeled asparagine, alanine, glycine, and the linear peptide antibiotic, gramicidin.

Dipolar dephasing between quadrupolar and spin- [formula omitted] nuclei. REDOR and TEDOR NMR experiments on VPI-5

In this work we examine the use of dipolar-dephasing magic-angle spinning NMR to study mixed pairs of quadrupolar and spin- 1 2 nuclei in solids. Dipolar connectivities are examined in both directions between the 27Al ( I=5/2) spins in the very large pore aluminophosphate VPI-5, which is considered representative of a range of inorganic framework materials. Rotational-echo double-resonance (REDOR) and transferred-echo double-resonance (TEDOR) experiments are demonstrated, as well as a two-dimensional extension of the TEDOR experiment. These experiments restore the heteronuclear dipolar coupling under MAS conditions via a train of radiofrequency pulses, thereby providing information about connectivities and distances between coupled nuclei in these inorganic solids.

Determination of an 8-.ANG. interatomic distance in a helical peptide by solid-state NMR spectroscopy

The combination of transferred-echo double resonance (TEDOR) with rotational-echo double resonance (REDOR) has been used to measure an 8-A fluorine-carbon internuclear distance in a nine-residue fragment of the peptide antibiotic emerimicin. The fragment is 19 FCH 2 CO-Phe-MeA-MeA-[1- 13 C]MeA-[ 15 N]Val-Gly-Leu-MeA-MeA-OBzl (MeA=α-methylalanine or aminoisobutyric acid). The TEDOR part of this magic-angle-spinning, solid-state NMR experiment selects the 13 C label by its dipolar coupling to 15 N and suppresses the natural-abundance carbon background