Interconversions during

Fig. 13.9 Facsimile of a molecular and kinetic scheme of the one-pot glucose into mannitol bio-chemo cascade, showing the many different species that undergo interconversion during the overall process, involving enzymatic isomerization, homogeneous mutarotation and heterogeneous hydrogenation. For simplicity, the various sugar-borate species have been omitted [23, 24],...

Recent interlaboratory comparisons of HPLC and microbiological methods for vitamin B6 revealed significant variability among laboratories (42,70). The extraction and hydrolysis of the B6 vitamers, especially the pyridoxine-/ -glucoside (PNG) in plant-based foods, were cited as problem areas. Other sources of analytical error included HPLC (mis)identification of the individual B6 vitamers, and vitamer interconversion during extraction and analysis. 

Jemal, M., and Xia, Y. Q. (2000). Bioanalytical method validation design for the simultaneous quantitation of analytes that may undergo interconversion during analysis. J. Pharm. Biomed. Anal. 22 813-827. 

A rapid, sensitive, and enantioselective LC-MS-MS method using deuterium-labeled IS was developed and evaluated for the simultaneous quantitative determination of donepezil enantiomers in human plasma without interconversion during clean-up process and measurement [37]. The use of an avidin column allowed the separation of donepezil enantiomers, which were specifically detected by MS-MS without interference from its metabolites and plasma constituents. Evaluation of this assay method shows that samples can be assayed with acceptable accuracy and precision within the range from 0.0206 to 51.6 ng/ml for both R-donepezil and S-donepezil. This analytical method was applied to the simultaneous quantitation of donepezil enantiomers in human plasma. 

The stability of arsenobetaine in baby foods under different experimental conditions was evaluated. The highest As levels in the analyzed baby foods corresponded to those containing plaice (2D3p,g g-1). Arsenobetaine was the only As compound present. Its levels remained unchanged in baby foods stored for different times or when the samples were freeze-dried, thus conbrming the stability of arsenobetaine and the absence of the formation of other As species by interconversion during storage [98]. 

In the case of spins-1 to the number of pairs of satellite transitions increases and is given by / —. Adiabaticity arguments show that interconversion, during sample spinning, of higher-order coherences with SQC may be achieved with a single FAM pulse... 

In many systems, measurement of the solubility of a metastable form can be directly obtained if there is an energy barrier between the metastable polymorph and the stable polymorph that prevents interconversion during the lifetime of the measurement. If the free energy difference of the polymorphs, which is the driving force of the phase transformation, does not overcome the activation energy barrier, the metastable polymorph may stay unchanged for a sufficiently long period of time to permit a direct determination of solubility to be made. 

Fig. 13. Represraitative elution profile of soyabean trypsin inhibitor undergoing dynamic interconversion during chromatographic separation on a 30x0.4 cm column packed with 10 /im, n-propylphenyl ilica, flow 2 ml/min, linear gradients of 20 and 120 min from IS mM orthophosphoric acid to acetonitrile-lS mM orthophosphoric acid-water (1 1, v/v). Reinjection of component A or component B demonstrated a time-dependent conversion to component C. Reinjection of component C resulted in the emergence of a single peak with the same elution time and peak shape.

Half-sandwich C-N chelates of Ir have been used for the cyclohydroamination of select substrates [270]. While efficient catalysis was observed, the key proposal put forward by the authors was a potential pyrazole-pyrazolato interconversion during the catalytic cycle resulting in bifunctional catalysis with this Ir system [270]. Further elaboration of this catalytic cycle will be discussed in a later section (Section 15.3.8). 

Dalessandro G. and Northcote D.H. 1977. Changes in enzymatic activities of nucleoside diphosphate sugar interconversions during differentiation of cambium to xylem in sycamore and poplar. Biochem J 162 267-279. 

The life record for one maaomolecule (not scaled) is shown in Scheme 28. The number of interconversions during the lifetime of one maaomolecule can be calculated from the total time of growth and the time of one interconversion. The total time of growth is 10 s, and the time of one interconversion is lO s. Iliere are 10 periods of artivity of 10" s each 10 X 10" s = 10 s is the total time when a macromolecule is active out of 10 s 10 rmits are added during 10" s. Thus, there is one monomer molecule every 10" s per chain. 

With the benefit of hindsight, were there any other hints along the way that CP-392,110 was actually present as a mixture of enantiomeric rotational isomers with a relatively high barrier to interconversion During the aldol addition to form CP-392,1 IQ (Scheme 13), we observed peak doubling in the HPLC traces which would be consistent with the diastereomeric aldolates and acylated aldolates 29a and 29b (Scheme 21). As the elimination proceeded, both of these sets of peaks disappeared. The same "doubling was observed by HPLC and NMR for the bisulfite addition complexes 29c. The chiral center present in these... 

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