Thermodynamical and quantum-chemical characterization and chemometrical selection of representative congeners of trans-chloroazoxybenzene

Abstract

Polychlorinated trans-azoxybenzenes (PCt-AOBs) consist a group of 399 theoretically possible congeners, which are toxicologically and environmentally relevant compounds. Some of PCt-AOBs have been identified as by-side impurity in technical grade 3,4-dichloroaniline (3,4-DCA), and also in derived of this chemical pesticides such as Diuron, Linuron or Propanil. In this study 31 quantum-chemical descriptors were in silico generated and used to characterize all 399 PCt-AOBs. Further, the basic thermodynamic and quantum-chemical property data matrix of PCt-AOBs made was interpreted with an aid of the Principal Component Analysis (PCA). The PCA of these data matrix created a three-dimensional model that explained 77.31% (63.79% + 8.87% + 4.65%) of the total variance. Polarizability, molecular weight, logarithm of the n-octanol/water partition coefficient, molecular refraction, valence molecular index, kappa index, molecular connectivity index, thermal capacity and entropy were the best positively correlated descriptors, which all are connected with molecular shape and size of the molecules. They all are explained by the first principal component (PC1), while energy of the highest occupied molecular orbital, Gibbs free energy in gas phase, standard heat of formation, the total particle energy and thermal energy were negatively correlated. The PC2 depended on polarizability vector Z and energy of the lowest unoccupied molecular orbital, while the PC3 was negatively impacted by the most positive partial charge on atoms. The congeners of trans-PCAOBs substituted with chlorine at positions 2′ (ortho position) are non-planar. 119 Congeners of trans-chloroazoxybenzene (Ct-AOB) could be classified amongst stereoisomers (analogues) to highly toxic and environmentally persistent 2,3,7,8-tetrachlorodibenzo-p-dioxin (2,3,7,8-TCDD). Data obtained after PCA were further used to create Fractional Factorial Design of PCt-AOBs and eight congeners, i.e., 2′,3′-DiCt−AOB (no. 11), 2,2′,5-TrCt−AOB (no. 32), 3′,4′-DiCt−AOB (no. 24), 2,4,5-TrCt−AOB (no. 58), 2,2′,3,4′,5,5′-HeCt−AOB (no. 271), 2,2′,3′,4′,5,5′,6′-HpCt−AOB (no. 360), 2,3,3′,4,4′,5′,6-HpCt−AOB (no. 364) and 2,2′,3,3′,4′,5′,6′-HpCt−AOB (no. 337), which probably are the best describers of the whole group, could be assigned.

Keywords:

• Polychlorinated azoxybenzenes
• trans-azoxybenzenes
• dioxin-like compounds
• environmental pollution
• multidimensional analysis
• POPs
• quantum-chemical properties.

Acknowledgments

Computations were carried out using computers in TASK-Academic Computer Center in Gdańsk, and supported also from grant no. DS/8250-0092-6.