Defined chemical transformation in Lignin, enabling to access shell-core-functionalized Lignin-colloids for selective ion binding.

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Objective of the research proposal is to investigate a defined two-step chemical reaction to selectively activate important aromatic core structures in the complex structural network of lignin. The reaction will be utilized to access shell-stabilized and core-functionalized lignin colloids, that should be investigated on their capabilities to specifically bind heavy metal ions from complex ion mixtures.Lignins are constituting a renewable resource that offers enormous potential for sustainable material solutions, as raw lignin is an inexpensive “waste” product from paper pulp production. The use of lignin provides various opportunities. However, modern material applications often require chemical derivatization of lignin, where limitations result from the inhomogeneous structure and strong batch-to-batch variations.In contrast to rather unselective reactions that are often used for lignin derivatization, the project is investigating the possibilities of a discrete two-step reaction for the selective manipulation of both, the 4-hydroxy-3-methoxybenzene-(G)-type and p-Hydroxyphenyl-(H)-type structural elements of lignin. The G- and H-type aromatics will be oxidized by 2-iodoxybenzoic acid (IBX) in a metal-free manner to yield ortho-quinones. These react as Michael acceptors with various thiols and can be converted rapidly and cleanly to thiol-catechols.The chemistry provides the possibility of introducing functional thiols, such as Cys-containing di- and tripeptides but also thiol-end functional polymers, such as mPEG-SH, Cys-peptide-PEG conjugates or PNIPAm-SH. Exploiting the diffusion limitations in the lignin network, shell-core lignins will be accessed. The functional lignin core should be adapted to the needs of specific binding of heavy metal ions and the colloidal stability will be adjusted independently of the lignin core via the shell.The IBX activation of lignin with subsequent quinone/thiol-Michael addition not only preserves the phenolic OH-groups that are important for ion binding. Moreover, thiol-catechols are generated as derivatives of the potent 1,2-dihydroxybenzene chelate ligand, which can be functionalized or fine-tuned via the thiol substituents.The project investigates the potential of a precise chemical activation of lignin for the synthesis of lignin-colloids and their use to gain basic understanding of the ion-specific complexation of heavy metal ions from more complex ion mixtures. The investigation utilizes systematic substance libraries of shell-core lignins, to study metal-ion binding, illuminating effects of the polymer shell, the lignin core and the functionalities implemented there including peptide-based binding domains for specific heavy metal ions.