Gas-phase conformations of cationized poly(styrene) oligomers.
The gas-phase conformations of poly(styrene) oligomers cationized by Li+, Na+, Cu+, and Ag+ (M+ PSn) were examined using ion mobility experiments and molecular mechanics/ dynamics calculations. M+PSn ions were formed by MALDI and their ion-He collision cross-sections were measured by ion mobility methods. The experimental collision cross-sections of each M+PS n-mer were similar for all four metal cations and increased linearly with n. Molecular modeling of selected M+ PS oligomers cationized by Li+ and Na+ yielded quasi-linear structures with the metal cation sandwiched between two phenyl groups. The relative energies of the structures were approximately 2-3 kcal/mol more stable when the metal cation was sandwiched near the middle of the oligomer chain than when it was near the ends of the oligomer. The cross-sections of these theoretical structures agree well with the experimental values with deviations typically around 1-2%. The calculations also show that the metal cation tends to align the phenyl groups on the same side of the -CH2-CH- backbone. Calculations on neutral poly(styrene), on the other hand, showed structures in which the phenyl groups were more randomly positioned about the oligomer backbone. The conformations and metal-oligomer binding energies of M+PS are also used to help explain CID product distributions and fragmentation mechanisms of cationized PS oligomers. etry
Gidden
Jennifer
J
Department of Chemistry and Biochemistry, University of California, Santa Barbara 93106, USA.
Bowers
Michael T
MT
Jackson
Anthony T
AT
Scrivens
James H
JH
D002412:Cations; D055598:Chemical Phenomena; D002627:Chemistry, Physical; D002942:Circular Dichroism; D005740:Gases / Q000737:chemistry; D008958:Models, Molecular; D008968:Molecular Conformation; D019904:Polymethyl Methacrylate; D011137:Polystyrenes / Q000737:chemistry*; D019032:Spectrometry, Mass, Matrix-Assisted Laser Desorption-Ionization
D002412:Cations; D005740:Gases; D011137:Polystyrenes; D019904:Polymethyl Methacrylate