1. Introduction Methods Conclusions Acknowledgement The geometries, energies, and harmonic vibrational frequencies of complexes studied were calculated using the B3LYP functional (Gaussian 03) with the 6-31+G(d,p) basis set for ligands, and the Stuttgart-Dresden basis set incorporating a quasi-relativisitic effective core potential for metals. The electronic energies are zero point corrected without scaling. COUPLING A TUNABLE OPO LASER TO AN FT- ICR MASS SPECTROMETER FOR INFRARED PHOTODISSOCIATION STUDIES J. Szczepanski, E. Cagmat, W. Mino, W. Pearson, D. Powell, J.R. Eyler, N. Polfer Department of Chemistry, University of Florida, Gainesville, FL 32611-7200, USA Computational Experimental The infrared tunable OPO laser has been coupled to an FT-ICR mass spectrometer to collect resonantly enhanced multiple-photon dissociation (IR-MPD) spectra of selected ions. The IR-MPD spectra for D-Glucuronic Acid-Rb +, Tryptophan-Ba 2+ and O-methyl-β-D-glucoside-Rb + cations have been recorded. The IR-MPD spectrum observed for the D-Glucuronic Acid-Rb+ complex fits best to the predicted IR spectra of a mixture of lowest energy  - and  -conformers (bands A and D), to the  -conformer only (band shoulder B) and to the  -conformer only (band C in the MPD spectrum). Thus, in the MPD spectrum we found spectral signatures for both the  - and  - conformers. The IR-MPD spectrum of Tryptophan-Ba 2+ complexes was consistent with that predicted for the zwitterion (Z-1) structure, while formation of the charge solvated form (C-1) is not supported by the recorded IR-MPD spectrum. The strongest band in the MPD spectrum is assigned to the N-H stretch vibration on the ring. The IR-MPD spectrum recorded in both O-H and C-H stretch ranges for O-methyl-  -glucoside-Rb + fits best to that predicted for a mixture of four (A-D) lowest energy conformers. OPO Laser ICR Cell 4.7 T Magnet Power Meter Uniblitz Beam Reflecting Shutter Wavemeter IR Idler Beam NIR Signal Beam ESI CO 2 Laser IR, 2 nd Step Excitation FT-ICR: 4.7 Tesla (Apex II by Bruker) OPO Laser: CW multimode laser with a single mode locked (by LINOS). Tunable wavelength range, 2.32 - 4.76 mm (4300 – 2100 cm -1 ) covers the OH, NH, CH, OHN(or O) stretching fundamental modes. Power output, ~ 60 mW for each of two idler beams. Laser tuning by varying the lithium niobate crystal temperature and/or tilting a intracavity etalon. CO 2 Laser: CW, 10.6 μm output up to 15W, used with OPO as a second pump, in cases of weak mode intensities. Infrared multiple-photon dissociation (IR-MPD) spectroscopy has been applied to probe the structures of various biologically relevant ligands tagged by metal cations (shown at right). Complexes were generated via electrospray ionization (ESI) and transferred into a Fourier transform – ion cyclotron resonance (FT-ICR) mass spectrometer. After isolation, the ions were irradiated with a wavelength-tunable IR OPO laser. The dissociation yield of the parent ion induced by resonant multiple-photon absorption was monitored at each wavelength step to yield the IR spectrum. An IR-MPD spectrum contains information related to the structure of an ion. A detailed structural assignment is achieved by comparing the IR- MPD spectrum to predicted vibrational spectra of lowest energy conformers. We have applied IR-MPD spectroscopy to carbohydrate isomers, including glucuronic acid and glucoside anomers. Whereas mass spectrometry alone cannot distinguish between  - and  -anomers of these saccharides, it is shown here that the differences in the O-H stretch region of these Rb + -adducted isomers are pronounced, thus allowing a clear distinction. Moreover, IR-MPD spectroscopy is shown to successfully distinguish between zwitterionic and non-zwitterionic forms of Ba 2+ -chelated tryptophan. Fig. A2. IR spectra (O-H stretch modes) for the  - and  -GlcARb + complexes Integral Intensities (km/mol) Fragment Yield Wavenumbers (cm -1 )  -3 (2.82 kcal/mol)  -2 (1.52 kcal/mol)  -1 (0.0 kcal/mol) MPD (exp)  -3 (2.83 kcal/mol)  -2 (1.87 kcal/mol)  -1 (0.0 kcal/mol) MPD (exp) Fig. A3. Predicted  - and  -GlcARb + IR spectra overlapped with observed IR-MPD spectrum  -1  -1 MPD Wavenumbers (cm -1 ) Intensity (a. u.) A C B D A (  +  ) B  C  D (  +  ) MPD band Assignment Results  -1 (0.00 kcal/mol)  -2 (1.52 kcal/mol)  -3 (2.82 kcal/mol)  -1 (0.00 kcal/mol)  -2 (1.87 kcal/mol)  -3 (2.83 kcal/mol) Fig. A1. Lowest energy isomers for the  - and  -GlcARb + complexes A. D-Glucuronic Acid-Rb + B. Tryptophan-Ba 2+ C. O-methyl-β-D-glucoside-Rb + Fig. B1. Lowest energy isomers for the Tryptophan-Ba 2+ complexes Fig. B2. Predicted and observed IR spectra for the Tryptophan-Ba 2+ complexes Z-1 (0.0 kcal/mol) Z-2 (0.4 kcal/mol)Z-3 (6.7 kcal/mol) C1 (8.0 kcal/mol) Fragment Yield Integral Intensities (km/mol) Wavenumbers (cm -1 ) C1 (8.0 kcal/mol) Z-2 (0.4 kcal/mol) Z-3 (6.7 kcal/mol) Z-1 (0.0 kcal/mol) MPD (exp) 1 2 3 4 1 3 2 4 1. (N-H)ring 2. (N-H)as 3. (N-H)s+(N-H)out-ph 4. (N-H)s+(N-H)in-ph 1. O-H 2. (N-H)ring 3. (N-H)as 4. (N-H)s Fig. C1. Four stable conformers of O-methyl-β-D-glucoside-Rb+ complexes A. (0.0 kcal/mol) B. (1.79 kcal/mol) D. (6.49 kcal/mol) C. (5.19 kcal/mol) Fig. C2. IR-MPD spectrum (in red) compared to the predicted spectra of four conformers of O-methyl-β-D-glucoside-Rb + complexes The authors thank the National High Magnetic Field Laboratory's User Collaboration Program for the purchase of the OPO laser, the National Science Foundation (under Grants CHE-0718007 and INT- 0730072) for partial graduate student support and Prof. Brad Bendiak of the University of Colorado Health Sciences Center for providing some of the O-methylated monosaccharide samples. A. (0.0 kcal/mol) B. (1.79 kcal/mol) C. (5.19 kcal/mol) D. (6.49 kcal/mol)