Katsuya Kato, H. Morikawa, M. Katayama
Dec 1, 1993
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Journal
Analytical Sciences
Abstract
Chlorinated auxins, 4-chloroindole-3-acetic acid (4. Cl-IAA) and its methyl ester, were isolated from im mature seeds of Pisum sativum.l-3 4-Cl-IAA is charac terized by exceptionally strong hormonal activities compared to that of IAA, i.e., 10-fold more active foi elongation of the Avena coleoptile, more than 100-fok for root inhibition of Chinese cabbage, and 100-fok hypocotyl swelling and lateral root formation of munl bean. These high biological activities of applied 4-Cl IAA relative to IAA have been ascribed to its resistancE to peroxidase oxidation.4 It has been presumed tha IAA is metabolized to 3-methyleneoxindole and 3 methyloxindole via a reaction with oxygen at the 3position of the indole nucleus in the presence of an enzyme, peroxidase.5 Interference of the chlorine atom at the 4-position from the approach of oxygen to the 3position would result in the resistance of 4-Cl-IAA to peroxidase oxidation. In order to confirm this presumption, the present X-ray analysis of 4-Cl-IAA was undertaken. Crystals suitable for the X-ray analysis were obtained by recrystallization from a solution of ethyl acetate/ hexane (1/2, v/v). The data were collected at 23°C using the w-20 scan technique with a variable scan speed to a maximum 20 value of 55° . The weak reflections (I<10.Oa(I)) were rescanned. The intensities of three representative reflections remained constant throughout the data collection, thus indicating crystal stability. Out of a total of 2457 reflections measured, 2291 were unique. The crystal data and experimental details are listed in Table 1. The structure was solved by direct methods with MITHRIL. The non-H atoms were refined with anisotropic thermal parameters, and the H atoms were refined with the isotropic ones. The H atoms of the CH