Conformational modeling of a new building block of humic acid: Approaches to the lowest energy conformer

Multiple structural models of humic acid (HA) building blocks have been reported. In this work, the modeling is based on two structural motifs: (i) the Steelink structure and (ii) a new humic acid [TNB] building block, which incorporates more fully the results of experimental data and retro-biosynthetic analyses. Both have significant conformational freedom complicated by their stereochemistry. A molecular modeling approach for the analysis of complex molecules with significant conformational freedom is described as it relates to the newly proposed humic acid building block. A potential energy surface for various conformers of the low-energy stereoisomer has been generated. Included in this discussion is the relationship of the stereochemistry to conformation and secondary structure.