Double cross-polarization

Dipolar recoupling may also be accomplished using continuous rf irradiation as demonstrated in the heteronuclear and homonuclear case by the CP at MAS conditions (or for low-y heteronuclear spins called double-cross-polarization, DCP [103]) and HORROR (homonuclear rotary resonance) [26] experiments, respectively. These experiments may easily be described by transforming the description into the interaction frame of the rf irradiation using (14a) exploiting... 

Double-cross-polarization 15N MAS NMR has been employed109 to study the transport and metabolism of D- and L-alanine by aerococcus viridans. 

Knicker, H. (2000). Double cross polarization magic angle spinning 15N 13C NMR spectroscopic studies for characterization of immobilized nitrogen in soils. Proceedings, 10th IHSS International Conference (Toulouse), France, pp. 1105-1108. 

Knicker, H. (2000b). Solid-state 2-D double cross polarization magic angle spinning 1SN 13C NMR spectroscopy on degraded algal residues. Org. Geochem. 31,337-340. 

Cross-polarization/magic-angle spinning and double cross-polarization... 

Double Cross Polarization and Dipolar Rotational Spin-Echo 226... 

The carbon bonding network around phosphorus centres can be determined in solids by the use of the double cross polarization l C n.m.r. technique as illustrated for the phosphine oxide (29).l Nine of the nineteen possible phosphine sulphides of the pentaphosphine (30) have been prepared (by progressive reaction of (30) with sulphur) and their structures have been investigated by 2D 3lp n.m.r. spectroscopy.20... 

Chemical Bond Labeling and Double Cross-Polarization NMR... 

Double-cross polarization (7) combines the directness and specificity of chemical bond analysis for double-labeled materials mentioned above with the convenience of observing Intact biological systems (8). Double-cross polarization is a serial extension of cross polarization to three-spin systems ( H, and N). The experiment involves first a transfer of... 

In this paper we will Illustrate the application of double-cross polarization techniques in experiments in which both specific and non-specific double labels are employed. 

Double-cross polarization nmr spectra were obtained using consecutive matched spin-lock transfers (J), first from H to and then from to The pulse sequence employed... 

The carbon rf Is phase modulated to prevent an accumulation of carbon polarization thereby helping to ensure simple kinetics describing the to transfer (2 ). A direct difference experiment between single- and double-cross polarization procedures (Figure 2) results In the accumulation of a signal arising exclusively from those nitrogens directly bonded to Data collection for difference spectra typically require 12-24 hours. 

Double-Cross Polarization. In the absence of a 5jj 13q drain (Figure 2, rf off resonance), the N magnetization,... 

Figure 2. Double cross-polarization pulse sequence. The y-axis shows radiofrequency field amplitude and K-axis time. A N direct difference signal can be accumulated by shifting the C radiofrequency off resonance for one scan and on resonance for the next. The second NMR signal is subtracted from the first. The time, T, during which the H is off is called the N hold time when the "C radiofrequency is off resonance, and is called the drain time when the C is on resonance. Data acquisition occurs with the H radiofrequency field turned back on for dipolar decoupling. Pulse sequence 1, hold Crf 60 kHz off resonance 2, W - C drain Crf on resonance 3, direct difference 1 minus 2.

Figure 4. Determination of the C-N matched spin-lock cross-polarization transfer time constant for two solid double-labeled amino acids using double cross polarization. T > is the time constant for the transfer from N to an aliphatic C, and T. is for the transfer from N to an amide C. The enrichment for both materials was 90 atom %. Key , NHi CH,COOH (t - 0.9) where Ti, = 10.93 ms and O, NH, COCH,CH(NHi)COOH (t = 0.9) where Ta = 3.64 ms.

In the double-label dilution experiment described here, the specificity of a particular metabolic pathway was examined by monitoring the fate of an existing labeled chemical bond In a molecule entering that pathway. Naturally, the complementary experiment can also be performed in which the formation of a labeled chemical bond from two separate specific labels Is observed directly using double-cross polarization nmr. 

We have Illustrated the use of double cross polarization nmr to follow the formation or metabolism of particular chemical bonds of proteins in Intact biological tissue. Neither the use of radioisotopes, nor the use of other means of detecting stable Isotopes, has comparable directness and specificity. 

Progress has been made recently in identifying bonds between catecholamine aromatic and aliphatic carbon to protein nitrogen in insect cuticle by solid-state H- C- % double-cross polarization (DCPMAS) NMR. (65) and rotational-echo, double resonance (REDOR) C and N NMR (M,67, Christensen et.al., unpublished data). Tobacco hornworm pupal exuviae were labeled by injec-combination of [ring- N2)histidine and either (ring-... 

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