The quantum mechanics of photosynthesis

Thankfully, Jared Sagoff included a description of photosynthesis (I’ve long since forgotten the mechanics of the process) in his May 21, 2012 article, Scientists uncover a photosynthetic puzzle, on the US Dept. of Energy’s Argonne National Laboratory website. From Sagoff’s article, here’s the photosynthesis  description along with a description of the quantum effect the scientists observed,

While different species of plants, algae and bacteria have evolved a variety of different mechanisms to harvest light energy, they all share a feature known as a photosynthetic reaction center. Pigments and proteins found in the reaction center help organisms perform the initial stage of energy conversion.

These pigment molecules, or chromophores, are responsible for absorbing the energy carried by incoming light. After a photon hits the cell, it excites one of the electrons inside the chromophore. As they observed the initial step of the process, Argonne scientists saw something no one had observed before: a single photon appeared to excite different chromophores simultaneously.

Here’s a gorgeous image of a leaf provided with the article,

I was aware that scientists are working at hard at duplicating photosynthesis but until reading this upcoming excerpt from Sagoff’s article, I had not appreciated the dimensions of the problem,

The result of the study could significantly influence efforts by chemists and nanoscientists to create artificial materials and devices that can imitate natural photosynthetic systems. Researchers still have a long way to go before they will be able to create devices that match the light harvesting efficiency of a plant.

One reason for this shortcoming, Tiede [Argonne biochemist David Tiede] explained, is that artificial photosynthesis experiments have not been able to replicate the molecular matrix that contains the chromophores. “The level that we are at with artificial photosynthesis is that we can make the pigments and stick them together, but we cannot duplicate any of the external environment,” he said.  “The next step is to build in this framework, and then these kinds of quantum effects may become more apparent.”

Because the moment when the quantum effect occurs is so short-lived – less than a trillionth of a second – scientists will have a hard time ascertaining biological and physical rationales for their existence in the first place. [emphasis mine] “It makes us wonder if they are really just there by accident, or if they are telling us something subtle and unique about these materials,” Tiede said. “Whatever the case, we’re getting at the fundamentals of the first step of energy conversion in photosynthesis.”

Thanks to Nanowerk for the May 24, 2012 news item which drew this article to my attention.

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  1. Pingback: Integrated artificial photosynthesis nanosystem, a first for Lawrence Berkeley National Laboratory « FrogHeart

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