“Anticonnectivity”: A Challenge for Structure−Property−Activity Studies

Application of variable anti-connectivity index to active sites. Modelling pK(a) values of aliphatic monocarboxylic acids

A partial distance-weighted variable anti-connectivity topological index was introduced for modelling pK(a) values of 31 aliphatic carboxylic acids and haloalkyl-carboxylic acids. The partial distance-weighted variable anti-connectivity index showed superior modelling capabilities compared with the index calculated from the complete graph, because it is capable of accounting correctly for the intramolecular interactions of unconnected vertices to specific bond strengths (active site), thereby improving the RMS(CV) error by about 30% (0.221 pK(a) units).

A molecular fragments variable connectivity index for studying the toxicity (Vibrio fischeri pT50) of substituted-benzenes

Molecular fragments variable connectivity index (mfVCI) has been proposed as a molecular descriptor, which has been applied to the study of toxicity (Vibrio fischeri pT50) of 138 substituted-benzenes. Molecular fragments are defined as the atoms or functional groups having different characteristics due to different chemical bonding, which are considered as the molecular structure unit for the major influence of toxicity. The molecular fragment is regarded as the vertex of the topological diagram and endue with variable wi as substitute for the topological matrix diagonal. The QSAR model obtained by molecular fragments variable connectivity index shows good descriptive (R2=0.88) and predictive (Q2EXT=0.72) performance. The optimal weights of the molecular fragments have the ability to interpret the mechanism from the compounds' insight structure.