Quantum secrets of water molecules discovered in the lab through spectroscopy

Water is essential for life, but there’s still so much we don’t understand about it. One of the biggest mysteries lies in how water molecules connect through hydrogen bonds.

These tiny interactions are responsible for water’s unique properties, yet they’ve been hard to study directly — until now.

Enter Dr. Sylvie Roke, head of the Laboratory for Fundamental BioPhotonics. She and her team have developed a new method to observe how water molecules behave when they form hydrogen bond networks.

Correlated vibrational spectroscopy

Working at the Swiss Federal Institute of Technology Lausanne (EPFL), Dr. Roke’s team has introduced a technique called correlated vibrational spectroscopy (CVS).

This method allows scientists to distinguish between water molecules that are interacting through hydrogen bonds and those that aren’t — a feat that wasn’t possible with previous technologies.

Hydrogen bonds and water molecules

So, what’s a hydrogen bond anyway?

Think of water molecules as tiny magnets, each with a positive and negative side. They stick together because the positive side of one is attracted to the negative side of another.

This attraction is the hydrogen bond, and it’s what gives water its special characteristics, like surface tension and its ability to dissolve many substances.

Before CVS, scientists had a hard time telling which water molecules were bonded and which weren’t.

Traditional spectroscopy methods measured the vibrations of all the molecules together, making it a bit like trying to hear a single voice in a noisy crowd.

Studying water molecules with CVS

Dr. Roke explains, “Current spectroscopy methods measure the scattering of laser light caused by the vibrations of all molecules in a system, so you have to guess or assume that what you are seeing is due to the molecular interaction you’re interested in.”

With CVS, however, each type of molecule shows up with its own unique signature, allowing researchers to focus on the ones that are actually interacting.

Changing the angle

How did they pull this off? The team used ultra-short laser pulses — lasting just a quadrillionth of a second — to illuminate the water.

These pulses cause tiny movements in the water molecules, which then emit visible light. By analyzing this light, scientists can see how the molecules are arranged and how they’re moving.

One clever twist was changing the angle of their detector.

“Typical experiments place the spectrographic detector at a 90-degree angle to the incoming laser beam,” says Dr. Roke.

“But we realized that we could probe interacting molecules simply by changing the detector position, and recording spectra using certain combinations of polarized light. In this way, we can create separate spectra for non-interacting and interacting molecules.”

Experimenting with pH levels

The team didn’t stop there. They also experimented with changing the pH of the water by adding hydroxide ions (making it more basic) or protons (making it more acidic). This allowed them to see how these changes affect hydrogen bonding.

“Hydroxide ions and protons participate in H-bonding, so changing the pH of water changes its reactivity,” explains PhD student Mischa Flór, the paper’s first author.

“With CVS, we can now quantify exactly how much extra charge hydroxide ions donate to H-bond networks — 8% — and how much charge protons accept from it — 4% — precise measurements that could never have been done experimentally before.”

Why does this matter?

What’s the significance of all this? Understanding hydrogen bonds at this level could have wide-ranging implications.

From biology to chemistry, many processes depend on these interactions. For instance, the structure of DNA and the behavior of proteins are influenced by hydrogen bonding.

But the excitement doesn’t end with water.

“The ability to quantify directly H-bonding strength is a powerful method that can be used to clarify molecular-level details of any solution, for example containing electrolytes, sugars, amino acids, DNA, or proteins,” says Dr. Roke.

“As CVS is not limited to water, it can also deliver a wealth of information on other liquids, systems, and processes.”

Water molecules, CVS, and the future

The team is already applying CVS to other materials. This could open up new avenues in material science, nanotechnology, and even medicine.

By better understanding molecular interactions, scientists could design more effective drugs or develop new materials with special properties.

Ever wonder why ice is slippery or how plants pull water from their roots to their leaves? It all comes back to hydrogen bonds. Techniques like CVS help us get a clearer picture of these everyday wonders.

All things considered, what Dr. Roke and her team have achieved is pretty incredible. They’ve found a new way to look at the tiny hydrogen bonds that make water — and so many other things — work the way they do.

Unlocking the secrets of water’s hydrogen bonds is a step toward understanding the very fabric of life.

With their CVS technique, we might soon unlock more of nature’s secrets, leading to breakthroughs in science and technology that could touch our everyday lives.

The full study was published in the journal Science.

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