Towards a mechanism for macromolecular lignin replication

For almost fifty years, the primary structures of lignins have been generally thought to be random. There are, however, a few well-documented peculiarities among the physicochemical properties of lignins that are not consistent with this view. Indeed, the development of a viable working hypothesis about macromolecular lignin replication is long overdue. The fundamental issue pertains to how particular sequences of inter-unit linkages can be reproduced during lignin biosynthesis. The matter can be approached by considering the consequences of specific interactions between complementary substructures in macromolecular lignin domains. Valuable insight has been forthcoming from quantum mechanical ab initio molecular orbital calculations that take dynamical electron correlation into account. It has thus been estimated that the nonbonded orbital interactions between aromatic rings in lignins can be equivalent in strength to two or more hydrogen bonds. Such powerful forces will inevitably have a profound impact on macromolecular lignin configuration. We are now much closer to understanding the effects of these interactions in quite explicit terms.