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Galvanic coupling can explain how copper kills bacteria

by Bal Heo 06 Jul 2023 0 Comments

Galvanic coupling can explain how copper kills bacteria

 Copper gutters corroded steel nails

Copper gutter patina

 When I was a roofer, I was instructed to use copper nails only when installing copper gutters. Although copper nails can be expensive and hard to find, they are essential for this task.

My boss instructed me to do it, but couldn't explain why. However, during a service call at a multi-million dollar house, I discovered the reason myself. The steel nails holding the copper gutter in place had completely rusted, despite being only five years old. This phenomenon is called galvanic coupling.

When it rains, a potential difference arises between the copper and steel nails that are immersed in the rainwater, creating a battery that causes the movement of electrons between the metals. Copper, having a higher potential, becomes the cathode, while iron, with a lower potential, becomes the anode. As a result, copper's corrosion rate decreases, while iron's corrosion rate increases, causing the iron to corrode faster than the copper. This can result in a premium copper gutter coming loose and falling off.

 Copper kills bacteria

 Interestingly, copper is also effective in killing bacteria. The antimicrobial effect of Antimicrobial Copper is simple, but its mechanism is complex. According to scientific research, copper ion attacks bacteria in various ways to eliminate them. Here's a summary of the ongoing research to explain why copper has excellent antimicrobial properties as a contact material:

  • What is the effect of copper on bacteria? According to scientific research, the copper surface attacks bacteria in two stages. First, direct interaction occurs between the copper surface and the outer cell wall of the bacteria, causing the cell wall to rupture. As a result, essential nutrients and moisture necessary for the survival of the bacteria are released through the holes in the outer cell wall, weakening the entire bacterial cell.
  • How does copper create holes in the bacteria's cell wall? All cells, including bacteria and other single-celled organisms, have a characteristic of stable microcurrents flowing between the outer cell wall and the inside of the cell. This is called "membrane potential," which means a voltage difference inside and outside the cell. According to a plausible theory, when bacteria come into contact with a copper surface, the current flowing through the cell membrane is cut off. This weakens the cell membrane and creates holes.

Another way to create holes in the cell membrane is by local oxidation or rusting. This phenomenon occurs when a single copper molecule or copper ion falls off the copper surface and collides with the basic components of the cell membrane, such as protein or fatty acid. When such "collisions" occur in an oxygen-rich environment, a phenomenon called "oxidative damage" or "rusting" occurs. This is similar to a metal fragment rusting and weakening, creating holes.

  • After creating holes, how does copper ion further damage the bacterial cell? When a hole is created in the outer cell wall, which is the primary defense barrier of a bacterial cell, copper ions flow into the cell without hindrance. This makes it difficult for essential life functions to occur within the cell. Excess copper fills the cell, interfering with biochemical reactions required for maintaining life, which are achieved or accelerated by enzymes. When excess copper attaches to enzymes, their activity stops. As a result, bacteria cannot perform activities such as respiration, digestion, or energy generation.
  • Why does copper's effect appear so quickly and affect a wide range of microorganisms? According to experts, the reason why copper's antimicrobial effect appears quickly and affects a wide range of microorganisms is because it acts simultaneously in various aspects. After creating holes in the cell membrane, copper inhibits all enzymes that interfere with its action, preventing the cell from transferring nutrients, digesting, recovering the destroyed cell membrane, respiration, or division. This is also believed to be why a wide range of microorganisms are affected by copper's antimicrobial properties.

 What is copper ions?

 When copper comes into contact with certain things like water or air, it starts to change. It loses some of its tiny parts called electrons and becomes something new called copper ions.

You can think of copper ions as little pieces of copper that have a special positive charge. They can move around in the air or water. This change happens slowly over time, and we might not notice it happening.

This process is called oxidation, and it's just a natural thing that happens to copper when it meets certain substances.

Oxidation is indeed responsible for the formation of copper patina. Copper patina refers to the greenish or bluish-green coating that develops on the surface of copper over time when it reacts with air or certain chemicals.

When copper is exposed to air, it undergoes a process called oxidation. Oxygen molecules in the air react with the copper atoms on the surface, leading to the formation of copper oxide. Initially, copper oxide appears as a reddish-brown color, known as cuprous oxide (Cu₂O). Over time, this layer can further react with air and moisture, resulting in the formation of a greenish-blue compound called copper carbonate hydroxide (Cu₂CO₃(OH)₂), which is commonly known as patina,

For example, the interaction between copper ions, carbon dioxide (CO₂), and water (H₂O) can result in the formation of copper carbonate hydroxide. This compound contributes to the greenish-blue color characteristic of patina.

This phenomenon is caused by copper ions, which were responsible for killing both the steel nail and bacteria.

bland new statue of liberty before patina reflecting sun

Copper ions also have caused the Statue of Liberty to turn green with patina. The statue weighs 450,000 pounds and is made of copper. When it was brand new and the sun was directly reflecting on it, it shone brightly like a mirror.

I know this because I used to put copper caps on roofs.

copper caps on roofs

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