Structure-activity correlations for phenoxyacetic acids and indoleacetic acids used for plant growth regulations

Conference · Wed Jan 01 04:00:00 EST 1975

OSTI ID:7358415

Block, A McB; Clements, R G

Experiments on substituted indole-3-acetic acids and halogenated indoles have led to the suggestion that fractional positive charge development on the -NH group of the indole ring at a fortuitous distance (5.5A) from the carboxylic acid function is requisite for plant auxin activity exhibited by indoleacetic acids. Calculations using self-consistent field (SCF) molecular orbital (MO) theory with complete neglect of differential overlap (CNDO) were carried out on a series of halo-substituted indoleacetic acids and on a series of substituted phenoxyacetic acids. No net positive charge development calculated for the N-H group in the substituted indoleacetic acids gave the observed order of auxin activity. No development of positive charge in the II-p/sub z/ system calculated for N was in any way comparable to the observed auxin activity increase. However, the energies of the lowest unoccupied molecular orbitals (LUMO's) decreased nearly linearly with increasing auxin activity. Twelve substituted phenoxyacetic acids, also treated, showed a correlation between the LUMO energies and the square of the LUMO coefficients at the ortho position and plant auxin activity when the lipophilicity of the molecules in the series was taken into account. While no fractional positive charge development at the suggested distance from the carboxylic acid group in either series emerged from the calculations, there are clear indications of an electron accepting role for auxin activity of both series. (auth)

• Research Organization: Puerto Rico Nuclear Center, Mayaguez
• OSTI ID: 7358415
• Report Number(s): CONF-750136-1
• Country of Publication: United States
• Language: English

Related Subjects

550200* -- Biochemistry
59 BASIC BIOLOGICAL SCIENCES
AUXINS
AZOLES
CARBOXYLIC ACIDS
CHEMICAL ACTIVATION
CHEMICAL REACTION KINETICS
HETEROCYCLIC COMPOUNDS
INDOLES
KINETICS
MOLECULAR STRUCTURE
ORGANIC ACIDS
ORGANIC COMPOUNDS
ORGANIC HALOGEN COMPOUNDS
ORGANIC NITROGEN COMPOUNDS
PLANT GROWTH REGULATORS
PYRROLES
REACTION KINETICS