NMR Approach to the Quantification of Nonstatistical ¹³C Distribution in Natural Products:  Vanillin

Abstract

Quantitative (13)C NMR conditions have been established that permit the precise determination of site-specific (13)C/(12)C ratios at low or natural abundance. Spectral acquisition parameters have been optimized in order to obtain minimum intensity distortions over the spectral width and in relation to the major sources of inaccuracy: the relaxation times, the decoupling pulse and power, and nuclear Overhauser effects. A major reduction in experimental time resulting from a study of the relaxation times and variance analysis has been achieved. The influence of (1)H decoupling conditions on peak areas was shown to be critical in that different relative peak areas are obtained according to the decoupling power. The efficiency with which the quantitative (13)C NMR method can determine site-specific (13)C/(12)C ratios in natural products has been tested for 12 independent samples of vanillin from different sources. Discriminatory analysis performed in the space defined by the site-specific carbon isotope ratios allows natural vanillin and that from different synthetic origins to be unambiguously distinguished.

Phenolic compounds from Sidastrum micranthum (A. St.-Hil.) fryxell and evaluation of acacetin and 7,4'-Di-O-methylisoscutellarein as motulator of bacterial drug resistence

“…Thus, their structures were identified as Vanillin 14 and salicylic acid. 15 The structural identifications of the compounds 3-7 were based on spectral analysis and also by comparison with literature data, which allowed their assignments as quercetin (3), 16 acacetin (4), 17 7,4′-Di-O-methylisoscutellarein (5), 18 Genkwanin (6), 17 and tiliroside (7).…”

Nonstatistical 13C Distribution during Carbon Transfer from Glucose to Ethanol during Fermentation Is Determined by the Catabolic Pathway Exploited

“…The NOE has to be eliminated, and the efficiency of the 1 H decoupling sequence must be uniform over the whole range of 1 H chemical shifts (12 ppm). Studies (3,(5)(6)(7) on the optimization of an NMR methodology for accurate and precise measurements of 13 C/ 12 C isotope ratios have shed light on how the decoupling conditions of 1 H in 13 C single-pulse NMR experiments strongly affect the precision of measured peak surface areas. A major breakthrough was achieved with the development of an optimized adiabatic 1 H decoupling sequence (3).…”

Quantitative 19F NMR method validation and application to the quantitative analysis of a fluoro-polyphosphates mixture

“…(General, in order to better control the amount of internal reference, it was dissolved in suitable solvent to get a stock solution with desired concentration). Although some papers [1][2][3][4][5][6][7][9][10][11]] about 1 H, 13 C and 31 P QNMR method has been published and their validities has been proved, but it still cannot be widely used in industrial fields. Apart from lower sensitivity of QNMR method and relative expensive NMR instrument, another important reason is that the people, who are not very familiar with NMR instrument/ experiment, still have suspicion for the validity of QNMR.…”

“…Hence, it is timesaving method. 1 H QNMR, 13 C QNMR, 2 H QNMR and 31 P QNMR methods have been developed and demonstrated as useful methods for the quantitative analysis of silicone rubber [1], blood plasma metabolites [2], algal toxins and other natural products [3], lactide composition [4], analysis of polymer sequence distribution [5], vanillin [6], coals [7], determination of deuterium isotope ratios [8], short-chain inorganic phosphate [9], purity determinations of military nerve agents [10] and agricultural chemicals. Experimental precision, accuracy, specificity, linearity and limits of detection was systematically addressed [11].…”