Elucidating Tertiary Structures of Affibody in Vacuo Using Genetic Code Expansion and FRIPS Mass Spectrometry.

Radical-directed protein fragmentation techniques, particularly free radical-initiated peptide sequencing (FRIPS) mass spectrometry (MS), offer significant potential for elucidating protein structures in the gas phase. This study presents a novel approach to protein structural analysis in vacuo, combining FRIPS MS with genetic code expansion (GCE) technology. By incorporating unnatural amino acids (UAAs) at specific sites within an Affibody protein, we effectively introduced a radical precursor at six distinct positions.

Infrared Ion Spectroscopic Characterization of the Gaseous [Co(15-crown-5)(HO)] Complex.

We report fingerprint infrared multiple-photon dissociation spectra of the gaseous monohydrated coordination complex of cobalt(II) and the macrocycle 1,4,7,10,13-pentaoxacyclopentadecane (or 15-crown-5), [Co(15-crown-5)(HO)]. The metal-ligand complexes are generated using electrospray ionization, and their IR action spectra are recorded in a quadrupole ion trap mass spectrometer using the free-electron laser FELIX. The electronic structure and chelation motif are derived from spectral comparison with computed vibrational spectra obtained at the density functional theory level.

Facial meridional coordination in gaseous Ni(II)-hexacyclen complexes revealed with infrared ion spectroscopy.

We report fingerprint infrared multiple-photon dissociation (IRMPD) spectra of the isolated gaseous hexa-coordinated complex of the macrocycle hexa-aza-18-crown-6 (hexacyclen, 1,4,7,10,13,16-hexaazacyclooctadecane, 18-azacrown-6) with Ni. The metal-ligand complexes are generated using electrospray ionization (ESI) and IR action spectra are recorded in a Fourier transform ion cyclotron resonance mass spectrometer (FTICR) MS coupled to the infrared free-electron laser FELIX. We investigate geometric structure of the complexes and in particular the chelation motif, by comparison with computed vibrational spectra, obtained using density functional theory (DFT) at the B3LYP/6-31++G(d,p) level.

Vibrational Spectra of the Ruthenium-Tris-Bipyridine Dication and Its Reduced Form in Vacuo.

Experimental IR spectra in the 500-1850 cm fingerprint frequency range are presented for the isolated, gaseous redox pair ions [Ru(bpy)], and [Ru(bpy)], where bpy = 2,2'-bipyridine. Spectra are obtained using the FELIX free-electron laser and a quadrupole ion trap mass spectrometer. The 2+ complex is generated by electrospray ionization and the charge-reduced radical cation is produced by gas-phase one-electron reduction in an ion-ion reaction with the fluoranthene radical anion.

Protoisomerization of Indigo and Isoindigo Dyes Confirmed by Gas-Phase Infrared Ion Spectroscopy.

Gas-phase infrared multiple-photon dissociation (IRMPD) spectra are recorded for the protonated dye molecules indigo and isoindigo by using a quadrupole ion trap (QIT) mass spectrometer coupled to the free electron laser for infrared experiments (FELIX). From their fingerprint IR spectra (600-1800 cm) and comparison with quantum-chemical calculations at the density functional level of theory (B3LYP/6-31++G(d,p)), we derive their structures. We focus particularly on the question of whether -to- isomerization occurs upon protonation and transfer to the gas phase.

Gas-Phase Infrared Ion Spectroscopy Characterization of Cu(II/I)Cyclam and Cu(II/I)2,2'-Bipyridine Redox Pairs.

We report the fingerprint IR spectra of mass-isolated gaseous coordination complexes of 2,2'-bipyridine (bpy) and 1,4,8,11-tetra-azacyclotetradecane (cyclam) with a copper ion in its I and II oxidation states. Experiments are carried out in a quadrupole ion trap (QIT) mass spectrometer coupled to the FELIX infrared free-electron laser. Dications are prepared using electrospray ionization (ESI), while monocations are generated by charge reduction of the dication using electron transfer-reduction (ETR) in the QIT.

Preparation of Labile Ni(cyclam) Cations in the Gas Phase Using Electron-Transfer Reduction through Ion-Ion Recombination in an Ion Trap and Structural Characterization with Vibrational Spectroscopy.

Gas-phase ion chemistry methods that capture and characterize the degree of activation of small molecules in the active sites of homogeneous catalysts form a powerful new tool to unravel how ligand environments affect reactivity. A key roadblock in this development, however, is the ability to generate the fragile metal oxidation states that are essential for catalytic activity. Here we demonstrate the preparation of the key Ni(I) center in the widely used cyclam scaffold using ion-ion recombination as a gas-phase alternative to electrochemical reduction.

Gas-phase vibrational spectroscopy of triphenylamine: the effect of charge on structure and spectra.

The effect of ionization by oxidation and protonation on the structure and IR spectrum of isolated, gas-phase triphenylamine (TPA) has been investigated by infrared multiple photon dissociation (IRMPD) spectroscopy in the fingerprint range from 600 cm to 1800 cm using an infrared free electron laser. IR spectra calculated using density functional theory (DFT) convincingly reproduce the experimental data. Spectral and structural differences are identified among neutral TPA, TPA˙ and protonated TPA and qualitatively related to effects of resonance delocalization.