Residual splittings

Not only can molecules constituting the oriented phase be thus studied. Solutes present in this mesophase will also be oriented through operation of anisotropic intermolecular forces. An example is that of deuterium-labeled D gramicidin. When dissolved in a nematic mesophase, it displays a series of deuterium doublets. Their residual splittings 6v are almost temperature-independent. This points to a rigid structure for the peptide, an helix that reorients about the director of the liquid crystalline phase (18). 

Thus the 23Na residual splittings have given information about interaction of various sodium salts with a zwitterionic surfactant. They allow conclusions to be made on the predominant localization of the sodium ions with NaSCN, they penetrate in-between the polar groups of the surfactant they don t with Na2C03 (19). The residual splitting also depends on the hexagonal or lamellar type of the mesophase (19). 

Likewise, 7Li (I 3/2, as for the 23Na nucleus) nmr monitors interaction of lithium cations with model membranes. Competition with divalent cations shows up as a reduction in the lithium residual splitting (20). 

Furthermore, we find linear relations between the observed residual splitting and the amount C of suspended clay ... 

The analysis of the data is straightforward, and parallels that given for D20 molecules oriented in other nematic mesophase. The residual splitting D is given by... 

Similar observations were made for a sodium clay, with Increasing amounts of the divalent calcium or magnesium Ions (32). In the presence of calcium Ions, one can even witness a change In the sign of the deuterium quadrupolar residual splitting. A similar observation was reported recently with heavy water molecules present In and oriented by an uniaxial mesophase (33). 

The switch in sign of the deuterium residual splitting shows that, as there is more divalent ions, the preferred mode of reorientation goes from the 0-D axis to the 0-M axis as the electrostatic bond to the metallic cation is made stronger, water molecules tend to reorient predominantly about it — a not unexpected conclusion. 

This is the classic off-resonance decoupling experiment. If the residual splitting is measured as the proton decoupling frequency is varied, then it is possible to find the chemical shifts of the protons attached to each carbon. This approach has been replaced by two-dimensional C-H correlation. 

In an off-resonance C- H decoupling experiment the residual splitting, Jr, is related to the original splitting, Jo, by Ernst s (190) equation ... 

All the foregoing experiments depend upon having a means of setting the proton offset frequency with sufficient precision, say +10 Hz or better. On certain low-cost spectrometers this may not be possible. It is then convenient to use (197) equation (14) to relate the residual splitting to yB2/2n. 

FIG. 30. C spectra of F2 PN(Me)PF2. (a) With proton noise decoupling, (b) With CW proton irradiation to high frequency of A-methyl signals. The relationships of the residual splittings (1-5) < (3-7) and (2-6) < (4-8) show that V(CNP)/ J(PNCH) and VlCNPFt/VlFPNCH) are both positive. From ref. 465. 

Wideband alternating phase low-power technique for zero residual splitting Windowless isotropic-mbdng sequence Zero-field-in-high-field zero-quantum spectra Zero quantum... 

Inactivation of alcohol dehydrogenase from yeast with 14C-labeled [3-(3-bromoacetylpyridinio)-propyl]-adenosine pyrophosphate followed by oxidation showed the presence of 1-carboxymethyl histidine66. After inactivation of the enzyme with labeled [3-(4-bromoacetylpyridinio)-propyl]-adenosine pyrophosphate followed by oxidation, S-carboxymethyl cysteine was identified in the protein. In the case of glyceraldehyde-3-phosphate dehydrogenase, treatment with either coenzyme analogue leads to the modification of the cysteine residue. Treatment with [14C]nicotinamide-5-bromo-4-methylimidazole dinucleotide did not reveal any modified amino-acid-residues. The labeled nicotinamide residue split off during the recovery of the inactivated enzyme. Attempts to synthesize an inactivator labeled with a 14C-acetyl residue did not give satisfactory yields. If the enzyme-coenzyme derivative was treated with tritiated sodium boron hydride, tritium could be introduced (Fig. 22). Studies with... 

WALTZ Wideband, alternating-phase, low-power technique for zero-residual splitting (broadband decoupling sequence) 9.2... 

Table 3.9 shows the generic ANOVA table for individual model parameters and with residual split into bias and pure error components. Table 3.10 gives the actual numbers. 

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