Chemistry World Podcast: 6PPD Tire Additive Toxicity and Cable-Bacteria MOFs

Overview

The Chemistry World podcast examines two cutting edge chemistry stories, one about the environmental and toxicological challenges of replacing the tire preservative 6PPD and the other about a living organism that biosynthesizes and uses nickel-based metal-organic frameworks (MOFs) as conductive cables on the sea floor. A concluding historical note highlights Christopher Ingold and his impact on reaction mechanisms.

• 6PPD toxicity and the quest for safer tire additives
• Biological MOFs and chemosynthetic electronics on the ocean floor
• Regulatory and toxicology considerations to avoid regrettable substitutions
• Ingold and the development of curly arrows and SN1/SN2 concepts

Overview

In this Chemistry World podcast, host Mariana Kneppers guides listeners through two major chemistry stories and a historical reflection. The first story centers on 6PPD, a tire preservative used for decades to prevent cracking, and the environmental and toxicological concerns surrounding its breakdown product 6PPD quinone. The discussion explains how 6PPD protects rubber by reacting with ozone at the tire surface and the importance of the molecule’s mobility to diffuse through the solid tyre. The byproduct quinone is highly toxic to certain fish species such as coho salmon, presenting a difficult problem for replacement compounds and raising questions about broader ecological impacts. Regulators in the US, Canada, and the EU are moving to regulate this chemical family, which could limit available substitutes and push researchers to take a holistic view of related paraphenylenediamine (PPD) derivatives. The narrative emphasizes the risk of regrettable substitution, where a safer chemical in one respect introduces new hazards elsewhere. After narrowing candidates from about 40 compounds—some PPDS and some from other families—researchers continue to evaluate both performance and toxicology to identify viable replacements without new environmental trade-offs.

MOFs In Nature: Cable Bacteria and Biologically Grown MOFs

The second major segment reports a striking discovery: cable bacteria, long filaments that transport electrons over centimetre scales, synthesize nickel-based metal-organic frameworks (MOFs) that form nanoribbons and act as conductive cables on the seafloor. This first natural example of MOFs biosynthesized by organisms challenges the notion that MOFs are exclusively human-made and aligns them with the broader Nobel Prize recognition for MOFs. The bacteria use these nickel-dithiolene MOFs to shuttle electrons from sediment sulfides up into their cells, enabling chemosynthesis in an energy-poor, sunless environment. The discussion explores how this natural design compares with synthetic MOFs, the potential to emulate such networked, ribbon-like MOFs, and the implications for sustainable electronics, bioelectronics, and materials science. The segment also touches on the idea of learning from nature to develop three-dimensional MOFs and scalable production strategies that could transform electronics design and energy storage.

Reaction Mechanisms and Convergent Design

As the conversation continues, parallels are drawn between biological MOF motifs and synthetic conductive polymers, highlighting convergent evolution in molecular design. The guests discuss how nickel-based complexes traditionally function as cofactors in electron transfer and how these motifs appear repurposed in MOF-based nano ribbons, suggesting new pathways to bio-inspired materials. The potential to create sustainable, biologically grown electronics is presented as a future direction, alongside the challenges of replicating nanoribbon MOFs at scale. A final note considers actin-like structural features and how biological architectures might inspire novel MOF assembly strategies, including scalable routes to produce ribbon-like MOFs for real-world devices.

Historical Spotlight: Christopher Ingold

The episode closes with a concise chemistry history segment on Christopher Ingold, whose work on reaction mechanisms, curly arrows, and the SN1/SN2 framework helped formalize how electrons move in reactions. Ingold’s legacy in reaction mechanism notation and three-dimensional understanding of organic chemistry remains foundational, and his humanitarian efforts during the 1930s are acknowledged as part of his broader legacy. The discussion underscores how foundational ideas in organic chemistry continue to influence modern research and education.

For more stories in the chemical sciences, visit chemistryworld.com.