Blackbody infrared radiative dissociation of small peptides and nucleic acids

Dissociation energies for noncovalently bound molecules are obtained using blackbody infrared radiative dissociation (BIRD). Dissociation energies obtained using BIRD can provide insight both mechanisms of dissociation and structures for a variety of biomolecules.;Gas-phase dissociation energies for several complementary and non-complementary nucleotide dimers were determined. For the guanosine-cytosine pair, the measured dissociation energy was significantly higher than that measured for any other of the dimers. This higher dissociation energy can be attributed to the existence of Watson-Crick pairing between the nucleobases. The unique ability of guanine-cytosine dimer among the other nucleotide dimers to form Watson-Crick hydrogen bonds is also known to occur in nonaqueous solution.;Dissociation experiments were also carried out on several trimolecular complexes or "trimers" consisting of two basic molecules and one acidic molecule. For the trimers composed of basic molecules that are strong proton acceptors; the measured dissociation energy was ∼0.2 eV higher than those trimers containing bases that were weak proton acceptors. The differences in the measured dissociation energies were attributed to the occurrence of salt-bridge structures.;Computational chemistry techniques were used to investigate the factors involved in the stability of ions with salt-bridge structures. A zwitterion is formed in an amino acid when a proton is transferred from the carboxylic acid to the amino group. The energy required to perform this transfer is largely provided from intramolecular electrostatic interactions or from interactions with a nearby charge. Glycine itself is not a zwitterion in the gas-phase, but in the presence of a divalent metal ion (except Be2+) the zwitterion form is stabilized. Computational studies on protonated bradykinin and arginine dialer indicate that intramolecular hydrogen bonding can increase the stability of the salt-bridge containing peptide ions relative to their charge-solvated forms.;In addition to probing ion structure, mass spectrometry can also be used to determine the composition of protein mixtures. Using capillary electrophoresis, protein components can be resolved into separated zones within a short time frame (<10 min). Detection of hemoglobin from a sample of 10 red blood cells is demonstrated, indicating that low sample quantities (<1 x 10-15 moles) can be analyzed.