31P NMR chemical shifts

TABLE 1 31P NMR chemical shifts (ppm) and line width (in parentheses Hz) of the wild... 

The behaviour of the mutant enzymes where, for example, histidine-152 has been changed to alanine is compared with that of wild type enzymes.60 The 31P NMR chemical shift values and signal width for H152A mutant enzyme have shown the presence of two conformers open and closed forms of the enzyme that interconvert slowly on the NMR time scale. The tightness of the binding of the cofactor to the protein surface and its protonation state have been also discussed for intermediate Schiff bases in different steps of the catalytic cycle (Table 1). 

Fig. 6. The 31P-NMR Chemical shift scale for pyridyl phosphane based systems...

The acceptor number (AN) [10, 11] of solvent A (Lewis acid) is obtained by measuring the 31P-NMR chemical shift (AS, ppm) of triethylphosphine oxide (Et3P=0,... 

TABLE 2. 31P NMR chemical shifts (ppm) of phosphonium and aminophosphonium halides35,37 (also steric compression was shown to give upfield 31P chemical shifts in cycloalkyltriphenylphosphonium salts)... 

FIGURE 1. 31P NMR chemical shifts of four-coordinate (A5phosphonium salts (and betaines)... 

The 31P NMR chemical shifts of compounds 36-38 are also in line with the expected trends previously reported for S P within group 6 metal carbonyl-phosphine complexes. The 31P NMR spectra of compound 38 also exhibit the tungsten (183W) satellites around the resonance of P-2 and the typical 1J P-W coupling constants for y/digated [W(CO)s]-phosphine complexes. 

The minor product, having in each instance the more upfield 31p nmr chemical shift (R=CH3, 6 33P + 59.4, 10% yield) R=CgH5 ... 

To solve this problem, the very high sensitivity of the 31p NMR chemical shift to changes in the hydrophobicity of the environment has proven to be very useful. The sensitivity of the chemica shift to structural changes in the phospholipid molecule several atoms away allowed us to also examine several other mechanistic questions including the hydrolysis and specificity of phospholipas... 

We found the 31p-NMR chemical shift of monomeric dihexanoyl PC increases upon the addition of the nonionic detergent Triton X-100. This phenomenon was used to quantitate the solubilization of this phospholipid by the detergent micelles as a function of detergent concentration using a simple phase separation model ( 5). Similar studies were carried out on dibutyryl PC. At a phospholipid concentration of 7 mM and 56 mM detergent, 85% of the dihexanoyl PC, but only 3% of the dibutyryl PC was incorporated into the micelles. 

All aspects of NMR studies (similar NOE cross-peak patterns, unusual 1H- and 31P-NMR chemical shifts, imino-proton exchange patterns for all sequences (including a d(A pG ) cross-link) suggest strongly that the main structural features should be the same for all six duplexes. Modeling studies, however, provide differing interpretations of these NMR observations. 

Because of the one-step polymerization procedure, hyperbranched polymers often contain not only D and T but also L repeating units. This can be expressed by DB, which is an important structural parameter of hyperbranched polymers. DB is estimated as the sum of the D and T units divided by the sum of all the three structural units, that is, D, T and L [41]. By definition, a linear polymer has no dendritic units and its DB is zero, while a perfect dendrimer has no linear units and its DB is thus unity. Frey has pointed out that DB statistically approaches 0.5 in the case of polymerization of AB2 monomers, provided that all the functional groups possess the same reactivity [42]. The structures of the hb-PYs could be analyzed by spectroscopic methods such as NMR and FTIR. The DB value of the phosphorous-containing polymer hb-F21, for example, was estimated to be 53% from its 31P NMR chemical shifts (Chart 1). 

Chart 1 Structures of dendrtic (D), linear (L) and terminal (T) units in hb-P21 and their 31P NMR chemical shifts... 

P AN (acceptor number) Relative 15F NMR chemical shift Relative 31P NMR chemical shift... 

In 2008, Zheng et al.193 attempted to predict theoretically the 31P NMR chemical shift of adsorbed TMPO and the configuration of the corresponding TMPOH+... 

The Lewis acidity of the carboxylates can be measured from the equilibrium constants determined from the 31P NMR chemical shift of the mixture with triethyl-phosphine oxide ... 

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