Optical yield determination procedure

The fact that twelve molybdate ions are bound to each phosphate unit in molybdophosphate has been exploited as an amplifying factor. The molybdophosphoric acid is extracted from the original solution into a mixture of diethyl ether or chloroform with butanol, in order to eliminate the excess of molybdate reagent it is then re-extracted into an aqueous phase and broken down with alkali. The molybdate ions are reacted with ammonium rhodanide90 or aminochlorobenzenethiol76 to give coloured products with absorption maxima at 470 and 710 nm, respectively. One phosphate ion thus yields twelve molybdate units, the optical absorbance is amplified with respect to that of the heteropoly phosphate complex and its measurement provides a sensitive determination procedure. 

Determination of Optical Yields. Optical yields of the siloxycyclopentenones derived from CPDK were determined by chiral HPLC (Chiracel OC column (J. T. Baker)) with the exception of the triphenylsilane derivative which was determined by optical rotation. 2-Butanol was derivatized to the corresponding diastereomeric urethanes with /Mnethylbenzylisocyanate according to literature procedures (32) the optical yield was then determined by G.C analysis using a Chirasil-L-Val column (Chrompack). The optical purity of the remaining alcohols (with the exception of a-tetralol optical rotation) was determined by chiral G.C. analysis of the underivatized alcohol using a CP-Cyclodextrin-B-2,3,6-M-19 column (Chrompack). Baseline resolution of the enantiomeric alcohols was achieved in all cases and it was observed that the / -isomer was eluted first without exception (confirmed by both optical rotation and G.C. analysis of independently prepared optically pure samples). 

The literature procedures were followed initially to separate cis-and trans-DACH (10) and to resolve the latter. Variations of the published procedure (8) were studied to determine the effect on optical yield of the (— ) -antipode. The best results were obtained when the reaction was run with no special precautions. Purification of the DACH was found to be unnecessary. 

The structure of the osazone was established by synthesis. 1,3-Diacetyl-4-desoxy-D-glycerotetrulose (XLI) was synthesized from acetyl-i/-lactyl chloride prepared from L-(dea lactic acid, through 3-acetyl-l-diazo-l,4-didesoxy-L-glycerotetrulose following the general procedure of Wolfrom, Waisbrot and Brown for the synthesis of ketoses. When this diacetyl derivative was hydrolyzed with dilute ammonia and the hydrolyzate was treated with acetic acid and phenylhydrazine, a phenylosazone (XLII) was isolated which was identical with that obtained from streptobiosamine. Its optical rotation was determined in pyridine solution. The preparation of the phenylosazone from streptobiosamine was well reproducible, with yields of 25-30 % of the theoretical in terms of chromatographed material. 

The reaction in ether resulted in a 25% yield of optically active acid 19 along with 42% of racemic hydrocarbon 15. Since the specific rotation of 19 was very small, the optical purity of the acid was determined by the more accurate NMR procedure. Hence, (S)-( —)-a-methylbenzylamide was prepared the diastereoisomeric excess determined by NMR from the signals corresponding to the cyclopropyl protons was 10%. Reaction in THF afforded a much higher yield of the Grignard reagent (58%) and only 20% of racemic hydrocarbon 15. The optical purity of the acid 19 was 13%. 

In quantitative determinations usually the optical density of the product is measured. Absorbance values, obtained for different dilutions of the antibody or antigen of known concentration, mostly yield sigmoidal calibration dose-response curves. Although this procedure seems rather simple and straightforward, it is not. Enzyme kinetics may be influenced by any of the factors discussed in Chapter 9. Correlation of absorbance with sample dilution beyond the linear... 

Neglecting the photo-degradation processes in laser dyes the partial photochemical quantum yields of stilbene-1 derivatives have been determined by evaluation procedures as given above [93]. In Section 4.3.2 a microprocessor controlled device is described [176], which allows convenient measurement of the data. Even an optical multi-channel analyser can be used [175]. 

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