Zur physikalisch‐chemischen Charakterisierung von 5‐Amino‐1‐aryl‐1H‐tetrazolen: Kinetik der Verteilung im Zweiphasensystem Octan‐1‐ol/Wasser

The kinetics of distribution of 27 5‐amino‐1‐aryl‐1H‐tetrazoles in the two‐phase system octan‐1‐ol/water were investigated UV/Vis‐spectrophotometrically at various temperatures. Studies on relationships between the obtained firstorder rate constants (logk₁, logk₂) and the hydrophobicity of the tetrazoles described by their partition coefficients (logP) show a nearly constant rate of transport from the aqueous to the organic phase (k₁) above logP = 1,5 while the reverse rate (k₂) strongly depends on hydrophobicity. In the whole logP range investigated the kinetic behaviour can be described by bilinear relationships between logk and logP corresponding to known kinetic models for distribution processes in two‐layer systems.     

Zur physikalisch‐chemischen Charakterisierung von 5‐Amino‐1‐aryl‐1H‐tetrazolen: Elektronische Molekülparameter aus der thermischen Isomerisierung zu 5‐Arylamino‐1H‐tetrazolen

The known thermal isomerization of 5‐amino‐1‐aryl‐1H‐tetrazoles ( A ) into corresponding 5‐arylamino‐1H‐tetrazoles ( HB ) was used to derive physicochemical parameters characterizing the electronic substituent effect on isomerism and dissociation equilibria. For a series of 26 tetrazoles A as starting materials the equilibrium constants (pK_i) of isomerization in boiling ethylene glycol at 197 °C and the dissociation constants (pK_a) of the NH‐acidic tetrazoles HB were determined by potentiometric titration of rapidly cooled equilibrium mixtures in water and ethanol/water with KOH at 25 °C. The pK values are closely correlated with Hammett′s electronic substituent constants σ and can be used as electronic molecule parameters in QSAR or QSPR (QSAR = quantitative structure‐activity relationship; QSPR = quantitative structure‐property relationship) studies.     

Beziehungen zwischen algistatischer Aktivität und physikalisch‐chemischen Eigenschaften von 5‐Amino‐1‐aryl‐1H‐tetrazolen

A series of 20 5‐amino‐1‐aryl‐1H‐tetrazoles was synthesized by diazotation of corresponding 1‐amino‐3‐aryl‐guanidines and tested for growth‐inhibiting activity against autotrophic Chlorella vulgaris cultures. In the used tests the different algae growth was quantified by photometric measurements at 680 nm. From obtained dosage‐effectivity relationships the reciprocal values of isoeffective concentrations c ₅₀ were derived and defined as activity parameters A in QSAR (quantitative structure‐activity relationship) studies. It could be shown that the algistatitic activity (log A) of the tested heterocycles strongly depends on hydrophobicity described by their octan‐1‐ol/water partition coefficients (log P). The calculated linear relationships between log A and log P can be significantly improved by separate treatment of meta‐/para‐ and ortho‐substituted compounds or using an indicator variable to describe the lower activity of ortho‐substituted 5‐ami‐no‐1‐aryl‐1H‐tetrazoles in common regression equations. The results are discussed and compared with analogous QSAR found for earlier tested series of N‐heterocycles and compounds with urea structure.     

Zur physikalisch-chemischen Charakterisierung von 5-Amino-1-aryl-1H-tetrazolen: Substituenteneffekte bei der Verteilung zwischen Octan-1-ol und Wasser

The octanol/water partition coefficients of 27 5-amino-1-aryl-1H-tetrazoles with known biological activity were determined by the shaked-flask method and photometric analysis of both initial and equilibrium concentrations in the aqueous layer. The obtained logP data of meta- and para-substituted derivatives are closely correlated with π constants derived from partition data of substituted benzamides. In contrast to this, a less significant relationship is found with pure hydrophobic π values of monosubstituted benzenes due to electronic interactions between the fixed aminotetrazolyl function and the variable substituents on the benzene ring. The electronic influence of the aminotetrazolyl function on the hydrogen bonding ring substituents and the deviating distribution behaviour of ortho-substituted 5-amino-1-aryl-1H-tetrazoles can be expressed by indicator variables in the calculated regression equations.