Terry Gullion

New, compensated Carr-Purcell sequences

Abstract New, compensated Carr-Purcell pulse sequences are reported, all based on x and y phase alternation of the π pulses. The sequences compensate cumulative pulse errors for all three components of magnetization. Applications include the measurement of homonuclear dipole coupling in the presence of chemical shifts and the measurement of heteronuclear dipole coupling in magic-angle spinning experiments (REDOR). The performance of the new pulse sequences is compared experimentally to previously reported schemes.

A simple magic angle spinning NMR experiment for the dephasing of rotational echoes of dipolar coupled homonuclear spin pairs

Abstract A simple NMR experiment for the dephasing of the rotational echo amplitudes of homonuclear dipolar coupled spin pairs in solids rotating at the magic angles is described. The dephasing is generated by π pulses applied synchronously with the sample rotation. One π pulse per rotor cycle is sufficient to cause an echo decay when the homonuclear dipole interaction is present. The dephasing effect of the π pulses is described using Floquet theory. Experimental results obtained on a doubly 13C-labeled alanine are presented and compared with numerical calculations. Effects arising from finite pulse lengths are also demonstrated and discussed.

Determination of CN internuclear distances by rotational-echo double-resonance NMR of solids

Abstract Rotational-echo, double-resonance (REDOR) 15 N 13 C NMR has been performed on an alanine cocrystallized from five-component alanines, isotopically enriched in 13 C, 15 N, or 12 C. REDOR 15 N 13 C NMR involves the dephasing of carbon magnetization by 15 N 180° pulses synchronized with magic-angle spinning. The CN dipolar coupling determines the extent of dephasing. The results of these experiments on alanine show that it is practical to use REDOR to measure the CN dipolar coupling of 5 μmol of a 13 C 15 N-labeled pair having an Internuclear separation of the order of 4.5 A.

Lignin biosynthesis in transgenic Norway spruce plants harboring an antisense construct for cinnamoyl CoA reductase (CCR)

An attractive objective in tree breeding is to reduce the content of lignin or alter its composition, in order to facilitate delignification in pulping. This has been achieved in transgenic angiosperm tree species. In this study we show for the first time that changes in lignin content and composition can be achieved in a conifer by taking a transgenic approach. Lignin content and composition have been altered in five-year-old transgenic plants of Norway spruce (Picea abies [L.] Karst) expressing the Norway spruce gene encoding cinnamoyl CoA reductase (CCR) in antisense orientation. The asCCR plants had a normal phenotype but smaller stem widths compared to the transformed control plants. The transcript abundance of the sense CCR gene was reduced up to 35% relative to the transformed control. The corresponding reduction in lignin content was up to 8%, which is at the lower limit of the 90–99% confidence intervals reported for natural variation. The contribution of H-lignin to the non-condensed fraction of lignin, as judged by thioacidolysis, was reduced up to 34%. The H-lignin content was strongly correlated with the total lignin content. Furthermore, the kappa number of small-scale Kraft pulps from one of the most down-regulated lines was reduced 3.5%. The transcript abundances of the various lignin biosynthetic genes were down-regulated indicating co-regulation of the biosynthetic pathway.

θ-REDOR: an MAS NMR method to simplify multiple coupled heteronuclear spin systems

Abstract The measurement of heteronuclear dipolar couplings with rotational-echo, double-resonance NMR (REDOR) is straightforward for isolated S–I spin pairs. However, measuring the n dipolar couplings for an S spin coupled simultaneously to n I spins is not easy because of additional complications arising from the orientational dependencies between the n dipolar tensors. We present an important modification of REDOR, called θ -REDOR, that is useful for systems with multiple dipolar couplings. This new experiment recovers the n dipolar couplings while eliminating the complicating orientational dependence between the dipolar tensors of the REDOR experiment. A REDOR transform of data obtained by θ -REDOR provides the n dipolar frequencies.

Measurement of like-spin dipole couplings

Abstract The application of modified Carr-Purcell-type pulse sequences to the measurement of like-spin dipole couplings in solids is reported here. The Meiboom-Gill sequence is shown experimentally to be very sensitive to nutation angle errors. Previously reported modifications of the sequence are significantly more tolerant of pulse errors. Experimental results are reported for two different d4-benzenes.

Extended dipolar modulation and magic-angle spinning

The direct detection of weak 13C15N heteronuclear dipolar couplings in magicangle spinning (MAS) NMR experiments is often difficult. A conventional MAS 13C NMR spectrum has spinning sidebands arising from both dipolar and chemical-shift interactions. Two-dimensional NMR experiments which separate dipolar couplings from the chemical-shift anisotropy simplify considerably their determination. Munowitz and Griffin introduced single-sided ( I ) and double-sided (2) two dimensional magic-angle spinning NMR experiments that have proved invaluable in the study of strong r3C‘H dipolar interactions. Unfortunately, when these techniques are applied to the substantially weaker 13C“N coupling, there are usually not enough dipolar sidebands to characterize effectively the dipolar sideband spectrum, even at low spinning speeds. A variation of the Munowitz and Griffin double-sided experiment, called odd p this yields more dipolar sidebands. The extra sidebands often contain enough information to allow a good determination of weak 13C“N dipolar coupling. Typically, however, the experiment must be done at low spinning speeds of the order of 500 Hz with the consequence that an overwhelming number of rotational sidebands can appear in the chemical-shift dimension. This is undesirable since the dipolar-modulated magnetization is actually measured by summing over sidebands in the chemical-shift dimension. The characterization of weak 13C15N couplings at slow spinning speeds in a complicated carbon spectrum can be simplified by the use of double-cross polarization (4) (DCP) as a selective filter; however, DCP is technically difficult to execute and generally does not give equal selection to spins with different spatial orientations (3). This Communication presents preliminary results on new experiments designed to measure weak heteronuclear dipolar couplings without the problems associated with ODRSE. Weak couplings can be measured at higher spinning speeds; very weak couplings can be measured at lower spinning speeds. Our experiments are extensions of rotational echo double resonance (5) (REDOR) which, in turn, was derived from spin-echo double resonance (6, 7) (SEDOR) . Extension of the dipolar evolution time in rotating solids is the principal feature of the experiments; accordingly, this class of experiments is called extended dipolar modulation (XDM) . XDM is a REDOR experiment and is specified by the number

1H MAS NMR Study of Cysteine-Coated Gold Nanoparticles

(1)H MAS NMR experiments were performed on gold nanoparticles coated with l-cysteine. The experiments show that l-cysteine molecules are zwitterions and support a structural model of cysteine forming two layers. The inner layer is composed of cysteine molecules chemisorbed to the gold surface via the sulfur atom. The outer layer interacts with the chemisorbed layer. The (1)H NMR suggests that the cysteine in the outer layer exhibits large amplitude motion about specific carbon-carbon bonds.

A simple, inexpensive, and precise magic angle spinning speed controller

Certain magic-angle spinning heteronuclear dipolar recoupling experiments using rotor-synchronized pulse trains require very precise control of the sample-spinning rate. An inexpensive spinning speed controller for use in magic-angle solid-state NMR experiments is described which can control the spinning rate to within +/- 0.2 Hz. The apparatus is based on a simple micro-controller and is self-contained. Experimental results are presented that show the importance of good spinning speed control.

Measurement of 13C15N coupling by dipolar-rotational spin-echo NMR

Abstract A sign reversal of the 13Cz.sbnd; 15N heteronuclear dipolar interaction after the first of two rotor periods in a dipolar-rotational spin-echo experiment produces a 13C 15N dipolar-modulation period equal to twice that of the rotor. This doubling results in twice as many sidebands in the dipolar powder pattern as in conventional experiments. Some of the sidebands have negative intensities. The increases in the number of sidebands and in the dynamic range of sideband intensities aid in the measurement of weak 13C 15N dipolar couplings in solids.