Quantum Biology
Biological systems operate at the edge of quantum chaos. One of the most intriguing discoveries in recent years is that protein nanowires—such as extracellular cytochromes—can conduct electricity with surprising efficiency. These "biological wires" display high conductivity that persists even at low temperatures, challenging standard theories of electron transport.
To understand this, we developed a novel computational approach. By utilizing the Liouville quantum master equation, we derived a formula that accurately describes electron transport in the intermediate regime—where neither pure quantum tunneling (Landauer-Büttiker) nor classical hopping (Marcus theory) provides a complete picture[.
The Three Mechanisms of Transport
Our analysis reveals that total conductance is composed of three distinct terms:
- Elastic Tunneling GLB: The classic quantum mechanical tunneling, which dominates at very short distances but decays exponentially.
- Thermal Excitation GT: A temperature-dependent term describing electrons thermally excited into the molecule.
- Mixed Transport GM: A newly identified mechanism where electrons tunnel into the molecule and then exit via thermal processes.
Our simulations show that these proteins resemble insulated cables. They possess a highly conductive inner core formed by stacked heme groups (porphyrin rings), shielded by an insulating protein shell. This explains why they can transport electrons over micrometers without significant loss.
Implications for Bioelectronics
This computational technique allows us to pinpoint areas of high conductivity and insulation in any protein structure. As protein nanowires exhibit significant potential for energy production and sensing, this method accelerates the design of future nano-bioelectronic devices.
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