Isolation and identification of new vasodilative substances in diesel exhaust particles
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Background, aim, and scope
We recently developed a new isolation method for diesel exhaust particles (DEP), involving successive extraction with H2O, sodium bicarbonate, and sodium hydroxide, in which the sodium hydroxide extract was found to consist of phenolic components. Analysis of the extract revealed that vasodilative-active nitrophenols are in DEP in significantly higher concentrations than those estimated by an earlier method involving a combination of solvent extraction and repeated chromatography. These findings indicated that our new procedure offers a simple, efficient, and reliable method for the isolation and identification of bioactive substances in DEP. This encouraged us to extend our work toward investigating new vasodilatory substances in the sodium bicarbonate extract.
Materials and methods
DEP were collected from the exhaust of a 4JB1-type engine (ISUZU Automobile Co., Tokyo, Japan). GC-MS analysis was performed with a GCMS-QP2010 instrument (Shimadzu, Kyoto, Japan).
DEP dissolved in 1-butanol was successively extracted with water, sodium bicarbonate, and then aqueous sodium hydroxide. The sodium bicarbonate extract was neutralized and the resulting mixture of acidic components was subjected to reverse-phase (RP) column chromatography followed by RP-HPLC with fractions assayed for vasodilative activity. This led to the identification of terephthalic acid, p-hydroxybenzoic acid, isophthalic acid, phthalic acid, 3-hydroxy-4-nitrobenzoic acid, 4-hydroxy-3-nitrophenol, and 1,4,5-naphthalene tricarboxylic acid as components of DEP.
The sodium bicarbonate extract was rich in aromatic carboxylic acid components. Repeated reverse-phase chromatography resulted in the successful isolation of several acidic substances including the new vasodilative materials, 4-hydroxy-3-nitrobenzoic acid, and 3-hydroxy-4-nitrobenzoic acid.
Our new fractionation method for DEP has made possible the isolation of new vasodilative compounds from the sodium bicarbonate extract.
KeywordsAcidic components Diesel exhaust particles Fractionation 3-Hydroxy-4-nitrobenzoic acid 4-Hydroxy-3-nitrobenzoic acid Separation method Vasodilatory compounds
This study was supported in part by a grant from the Japan Society for the Promotion of Science (Basic Research C-17510052). KS gratefully acknowledges Dr. Nagara Tamaki (Hokkaido University) and Dr. Raymond Jeremy Hugh Davies (Emeritus professor, Queens University Belfast) for their constructive comments and suggestions.
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