Researchers from North Carolina State University have successfully synthesized bacteriochlorophyll a, a photosynthetic pigment found in bacteria which absorbs infrared light. The work represents the first chemical synthesis of this molecule and could give scientists deeper insights into photosynthetic function and photosynthetic energy.

“There are two ‘worlds’ of photosynthesis: the green plant-based world that all of us are familiar with, and a microbial world that represents a simpler form of photosynthesis where no oxygen is made,” says Jonathan Lindsey, Glaxo Distinguished University Professor of Chemistry at NC State and corresponding author of the research.

“These photosynthetic microbes have been intensively studied as a cornerstone of basic science in the field of photosynthesis,” Lindsey says. “But their light-absorbing pigments have not been targets of chemical synthesis.”

This is due, in part, to the structure of the bacteriochlorophyll a molecule, a large, disc-shaped molecule, or macrocycle, composed of five rings of atoms. Structurally, the outer fifth ring – known as ring E – has always been a challenge for chemists.

Prior approaches to synthesizing the macrocycle have consisted of creating the four inner rings and then attempting to bolt ring E to the outside. But the NC State group took a different approach.

“Ring E, the fifth ring, was always regarded as this final mountain that had to be climbed,” says Duy Chung, who received his Ph.D. from NC State while conducting the research.

“What we did was synthesize both halves of the macrocycle, then use constituents of ring E as the joining site for bringing the two halves together,” Chung says. “When the halves are attached to an atom that will eventually become ring E, a cascade reaction triggers and the molecule self-assembles in the last step.” Chung is the first author of the paper.

The researchers hope that the strategy can be used to synthesize other photosynthetic macrocycles of interest, leading to increased exploration in photosynthesis and energy sciences.

“This self-assembly method may open access to the whole family of molecules,” Lindsey says. “And from there we can make specific derivatives for experimentation.

“It’s always been striking to me that molecular biologists can go in and do all kinds of gene manipulations to create modified organisms and tailor the proteins that hold these pigments, but the pigments themselves could not be created from scratch by methods of chemical synthesis. But that’s what we’ve been able to do here – create a method for synthesizing these macrocycles.”

The work appears in Chemical Science and is supported by the National Science Foundation under grant CHE-2348052. Former NC State Ph.D. students Khiem Chau Nguyen and Yizhou Liu also contributed to the research.

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