Translational cooling and storage of protonated proteins in an ion trap at subkelvin temperatures

Gas-phase multiply charged proteins have been sympathetically cooled to translational temperatures below 1 K by Coulomb interaction with laser-cooled barium ions in a linear ion trap. In one case, an ensemble of 53 cytochrome c molecules (mass similar or equal to 12 390 amu, charge +17e) was cooled by similar or equal to 160 laser-cooled barium ions to less than 0.75 K. Storage times of more than 20 min have been observed and could easily be extended to more than an hour. The technique is applicable to a wide variety of complex molecules.