Closer to Absolute Zero

Absolute zero is the lowest possible temperature, occurring when no heat energy remains in a substance.

It is the point at which molecules do not move (relative to the rest of the body) more than they are required to by a quantum mechanical effect called zero-point energy. By international agreement, absolute zero is defined as precisely 0 K on the Kelvin scale, which is a thermodynamic (absolute) temperature scale, and -273.15 C on the Celsius scale and -459.67 F on the Fahrenheit scale.

Recently, researchers report cooling large organic molecules to less than 0.1 K using a technique that should also work with proteins and other biomolecules.

They have previously cooled single atoms and molecules with two or three atoms to just a few thousandths of a degree above absolute zero, but it has proved hard to push larger molecules below about 10 degrees Kelvin.

Cooling large molecules is difficult because they can move and wriggle in many different ways, each of which must be brought under control.

Bernhard Roth of the Heinrich-Heine University in Düsseldorf, Germany and his colleagues chilled a dye called Alexa Fluor 350 (AF), a molecule with 42 atoms, using a technique called sympathetic cooling, and in a matter of minutes, the AF ions got to 95 mK.

Achieving temperatures this low will allow scientists to study molecular structures and chemical processes with unprecedented precision and perhaps explore novel issues of fundamental physics.

The applications of this technique are possible to any molecule that can be charged, Roth says. "In the future, we'd like to cool even heavier molecules, such as proteins or polymers." The cold molecules can stay in the trap for hours or even days at a time, allowing researchers to study the progress of certain internal processes, such as some very slow electronic transitions.