Always more to yield: unanswered questions in chemistry  

In 2008, a team of researchers busily excavated the tiny (only 55m²) coastal Blombos Cave, 300 km east of Cape Town, South Africa, when they discovered something entirely unexpected: a workshop, dating back some 100,000 years, where liquefied ochre-rich mixture was made and stored.

This processing workshop is evidence that humans had some rudimentary knowledge of chemistry even as far back as the stone age.

Since then, chemistry has spawned multiple sub-disciplines, from biochemistry (the study of matter and their interactions and reactions in living organisms) to astrochemistry (the study of matter in the Universe), including their reactions and interactions.

Chemistry abounds in discoveries, but many questions remain. We asked members of the Canadian Journal of Chemistry’s International Advisory Board: What’s the most important unanswered question in your field?

Ross Boyle | Attaining evolutionary efficiency

Year after year, decade after decade, chemists have gradually unlocked the secrets of some of the smallest components of our world.

“The 20th century was the century of the electron, but the 21st century is the century of the photon,” says Professor Ross Boyle. Based at the University of Hull in England, Boyle specialises in porphyrin chemistry, photochemistry/photobiology, and bioconjugation (linking one molecule to another).

Porphyrins are ring-shaped molecules with a superpower—they bind metal ions in multiple combinations, often creating complex structures. You have porphyrins in your body like heme, which binds iron to transport oxygen around your body.

Porphyrins can be found almost everywhere. “Porphyrins make life on Earth possible as central components of photosynthesis, oxygen transport, and cellular respiration,” Boyle explains.

Today, researchers like Boyle are creating and working with synthetic porphyrins to improve human health by harnessing and mimicking porphyrin’s other superpower—their ability to absorb light.

ACS Omega 2021, 6, 25, 16524-16534 (CC BY-NC-ND 4.0)

“Currently, we are developing antimicrobial surface coatings that are powered by visible light,” says Boyle. “Conventional antibiotics are failing at an alarming rate, leading to a rise in hospital-acquired infections. We hope our coatings can ensure surfaces remain sterile without the need for constant deep cleaning.”

For Boyle, the most important unanswered question surrounds our ability to create synthetic porphyrins.

“Can porphyrin-based biomimetic systems be constructed that perform reactions with efficiencies approaching those of nature?” asks Boyle. “Evolution took billions of years to get there. We have only been at it for a few hundred!”

Stefanie Dehnen | A question of clusters

At the Universität Marburg in Germany, Professor Stefanie Dehnen focuses on inorganic cluster chemistry. Inorganic chemistry is the study of compounds that do not contain carbon–hydrogen bonds. Inorganic compounds are widespread. If you like to add salt to your cooking, for example, you’re adding an inorganic compound.

Not quite molecules and not quite bulk matter (solids, liquids, or gasses), inorganic clusters are a special type of compound, containing at least three metal atoms held together by metal–metal bonds and bridging ligands—molecules or ions that bind two or more atoms.

Clusters can have several hundred atoms, creating complex structures. “I love clusters for their uncommon molecular architectures that may represent highly symmetric or astonishingly asymmetric structures,” says Dehnen.

Structures of 12-vertex (left) and 14-vertex (right) endohedral clusters. Chem. Soc. Rev. 2022, 51, 628-649 (CC BY 3.0)

Despite their complexity, clusters are “atomically precise nano-objects.” With a lot of work, they can be reproduced and used reliably for creating chemical reactions with a wide variety of uses. For example, Dehnen and colleagues have developed an inorganic cluster that could be used to make cheap and sustainable white lights.

For Dehnen, two unanswered questions in inorganic cluster chemistry stand out.

First, “… how [do] metal clusters or non-metal-bridged metal clusters form?”. Understanding this formation, Dehnen notes, could be hugely beneficial because it would mean researchers would be “in a position to predict, design, and control the synthesis of clusters much better than we can do this to date, which would save time and resources.”

Second, on Dehnen’s list: What’s really going on with the catalytic activity (the rate of a chemical reaction) of cluster materials?

“There is a lot of evidence for catalytic activity of cluster materials and also for a variety of further useful properties, like supercontinuum generation [when a laser beam travels through a material and then splits into multiple different colours],” Dehnen explains. “However, most of this is only fragmentarily explored or understood, so we need much more knowledge in order to be able to ultimately apply the compounds.”

Stay tuned for chemical queries about nanocrystal synthesis and chemical probes in part II of this series.