TY - JOUR
T1 - Binding energies of water to lithiated valine
T2 - Formation of solution-phase structure in vacuo
AU - Lemoff, Andrew S.
AU - Williams, Evan R.
N1 - Funding Information:
The authors thank Professor Fred W. McLafferty for his outstanding and innovative contributions in all areas of mass spectrometry, including instrumentation, methods development, theory, both ion and neutral chemistry, applications, and beyond. His pioneering achievements in relating gas-phase ion and neutral chemistry to solution-phase chemistry have provided inspiration for this current work. The authors also gratefully acknowledge financial support provided by the National Science Foundation (grant CHE-0098109). This work was also partially supported by the National Computational Science Alliance under CHE010013N and utilizing the NCSA SGI/CRAY Orgin2000. ASL gratefully acknowledges training support from NIH T32GM08295.
PY - 2004/7
Y1 - 2004/7
N2 - Dissociation kinetics for loss of a water molecule from hydrated ions of lithiated valine, alanine ethyl ester and betaine are determined using blackbody infrared radiative dissociation at temperatures between -60 and 110°C. From master equation modeling of these data, values of the threshold dissociation energy are obtained for clusters containing one through three water molecules. By comparing the values for valine with its two isomers, one a model for the nonzwitterion structure, the other a model for the zwitterion structure, information about the structure of valine in these hydrated clusters is inferred. Structures, relative energies, and water binding energies for these ions are also calculated at the B3LYP/6-31++G* level of theory. With one water molecule, both experiment and theory indicate that valine is not a zwitterion and that the lithium ion coordinates with the amino nitrogen and the carbonyl oxygen (NO coordinated) and the water molecule interacts directly with the lithium ion. With two water molecules, the zwitterion and nonzwitterion structures are nearly isoenergetic, but the experiment clearly indicates a NO-coordinated nonzwitterion structure. With three water molecules, both the experimental data and theory indicate that the lithium ion binds to the carboxylate group of valine, i.e., valine is zwitterionic with three water molecules. The agreement between the experimentally determined and calculated binding energies is good for all the clusters, with deviations of ≤ 0.12 eV.
AB - Dissociation kinetics for loss of a water molecule from hydrated ions of lithiated valine, alanine ethyl ester and betaine are determined using blackbody infrared radiative dissociation at temperatures between -60 and 110°C. From master equation modeling of these data, values of the threshold dissociation energy are obtained for clusters containing one through three water molecules. By comparing the values for valine with its two isomers, one a model for the nonzwitterion structure, the other a model for the zwitterion structure, information about the structure of valine in these hydrated clusters is inferred. Structures, relative energies, and water binding energies for these ions are also calculated at the B3LYP/6-31++G* level of theory. With one water molecule, both experiment and theory indicate that valine is not a zwitterion and that the lithium ion coordinates with the amino nitrogen and the carbonyl oxygen (NO coordinated) and the water molecule interacts directly with the lithium ion. With two water molecules, the zwitterion and nonzwitterion structures are nearly isoenergetic, but the experiment clearly indicates a NO-coordinated nonzwitterion structure. With three water molecules, both the experimental data and theory indicate that the lithium ion binds to the carboxylate group of valine, i.e., valine is zwitterionic with three water molecules. The agreement between the experimentally determined and calculated binding energies is good for all the clusters, with deviations of ≤ 0.12 eV.
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U2 - 10.1016/j.jasms.2004.04.001
DO - 10.1016/j.jasms.2004.04.001
M3 - Article
C2 - 15234361
AN - SCOPUS:3242659268
SN - 1044-0305
VL - 15
SP - 1014
EP - 1024
JO - Journal of the American Society for Mass Spectrometry
JF - Journal of the American Society for Mass Spectrometry
IS - 7
ER -