کد مقاله | کد نشریه | سال انتشار | مقاله انگلیسی | نسخه تمام متن |
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1193801 | 1492320 | 2010 | 8 صفحه PDF | دانلود رایگان |

Infrared multiple-photon dissociation (IR-MPD) spectra in the N–H and O–H stretching region (3000–3700 cm−1) are reported for gas-phase monomeric M2+Trp and dimeric M2+Trp2 complexes (where M = Mg, Ca, Sr, and Ba). The spectra are obtained by irradiating the complexes in the Penning trap of a Fourier transform ion cyclotron resonance (FT-ICR) mass spectrometer, using a tunable continuous-wave (cw) optical parametric oscillator (OPO) laser in combination with a fixed wavelength CO2 laser (10.6 μm). These spectra are compared with previously recorded mid-IR-MPD spectra, using the free electron laser FELIX, and are interpreted based on harmonic frequency calculations performed with density-functional theory (DFT). The experimental spectra show that a simple assignment of bands can be made to distinguish zwitterionic (ZW) from charge solvation (CS) complexes. In particular, the carboxylic acid O–H stretch at ∼3550 cm−1 identifies the presence of a CS structure, whereas the NH3+ antisymmetric stretching mode in the 3150–3375 cm−1 range is diagnostic of a ZW structure. For the monomeric Ba2+Trp complex, exclusively the ZW structure is observed. Conversely, for the dimeric complexes of M2+Trp2 (M = Sr and Ba) merely CS/CS geometries are confirmed. Surprisingly, for smaller alkaline earth metal dications (M = Mg and Ca), the IR-MPD spectra are consistent with the presence of mixed CS/ZW dimers. This is contrary to most previous trends for alkali metals, where larger cations typically favor ZW stabilization.
Diagnostic vibrations for alkaline earth-tryptophan dimers, M2+Trp2, confirm mixed CS/ZW (charge solvation/Zwitterion) complexes for Mg and Ca, as opposed to CS/CS for Sr and Ba.Figure optionsDownload high-quality image (102 K)Download as PowerPoint slideResearch highlights▶ IR-MPD spectra of alkaline earth-tryptophan dimers, M2+Trp2, in the gas phase. ▶ Diagnostic vibrations confirm charge solvation (CS) or zwitterionic (ZW) structures. ▶ Smaller cations (Mg, Ca) adopt mixed CS/ZW configuration. ▶ Larger cations (Sr,Ba) adopt CS/CS configuration.
Journal: International Journal of Mass Spectrometry - Volume 297, Issues 1–3, 1 November 2010, Pages 131–138