Mixtures spectral characteristics

Isobutyryl chloride (25.9 g, 0.24 mol) was added dropwise to triethyl phosphite (43.9 g, 0.26 mol) with stirring under a nitrogen atmosphere, and the temperature was maintained at 30 to 40°C. After the addition was complete, the reaction mixture was allowed to stand overnight at room temperature. The reaction mixture was vacuum distilled to give the pure diethyl isobutyrylphosphonate (43.9 g, 88%) of bp 75 to 83°C/3-4 torr, which exhibited IR spectral characteristics in accord with the assigned structure. 

The structure of HRP-I has been identified as an Fe(IV) porphyrin -ir-cation radical by a variety of spectroscopic methods (71-74). The oxidized forms of HRP present differences in their visible absorption spectra (75-77). These distinct spectral characteristics of HRP have made this a very useful redox protein for studying one-electron transfers in alkaloid reactions. An example is illustrated in Fig. 2 where the one-electron oxidation of vindoline is followed by observing the oxidation of native HRP (curve A) with equimolar H202 to HRP-compound I (curve B). Addition of vindoline to the reaction mixture yields the absorption spectrum of HRP-compound II (curve C) (78). This methodology can yield useful information on the stoichiometry and kinetics of electron transfer from an alkaloid substrate to HRP. Several excellent reviews on the properties, mechanism, and oxidation states of peroxidases have been published (79-81). 

A sample from Slieve Gullion, Ireland (K Na Ca — 43 57 -), described as a sanidine, has exactly the same spectral characteristics as the moonstone (Figure 2d) namely, a mixture of high-K and intermediate. This sample does not have a "moonstone" appearance but is nevertheless clearly a similar mixture of phases... 

The spectral characteristic of 4.3 in solution is indicative of the presence of a mixture of isomers in solution. From the reaction of CH3I with 4.1, under... 

In many cases, underlying factors corresponding to individual compounds in a mixture are unimodal in time, that this, they have one maximum. The aim is to deconvolute the experimentally observed sum into individual components and determine the features of each component. The change in spectral characteristics across the chromatographic peak can be used to provide this information. 

Compound 35 was isolated as amorphous. The H-NMR data for 3 5 and its acetate 35a are summarized in Table 4.4. Compound 35 showed spectral characteristics very similar to compound 27 isolated from Salix sachalinensis. In the chemical investigation of S. sachalinensis, compound 27 was obtained as a mixture of diastereoisomers. On the other hand, comparison of the values of the chemical shift and the coupling constant of H-7" and H-8" with values for acetylated compounds 27a and 35a indicated that compound 35 belongs to the threo series (Table 4.4) (refs. 52,53). 

Acylation of 5-amino-l,2,3,4-thiatriazole with two equivalents of chlorothioformates yields 2,5-disubstituted l,6,6a2 -trithia-3,4-diazapentalenes where a zwitterionic dithioazole ring forms following the opening of the thiatriazole ring and the subsequent loss of nitrogen. As shown in Scheme 21, the second equivalent of the chlorothioformate adds to the imino side chain to form the pentalene. The zwitterionic intermediate, isolated from the reaction mixture, displays mass spectral characteristics consistent with the structure proposed <89M997>. 

Fluorescamine (50) reacts even more readily with a-amino acids [Eq. (8)]. The spectral characteristics are similar to those of MDPF derivatives. The CD spectra of the in situ reaction mixtures (20 different amino acids investigated) show three or four Cotton effects between 400 and 220 nm. As with the MDPF derivatives, the first Cotton effects (396-377 nm) of the chromophores derived from L-amino acids and fluorescamine are positive, and the second Cotton effects are negative. Within the experimental error, the CD curves of the chromophores derived from D-amino acids are mirror... 

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