Proton transfer and complex formation of angiotensin I ions with gaseous molecules at various temperature

•Proton transfer from angiotensin I ions (z = 2, 3) to gaseous molecules was studied.•Temperature dependence of absolute reaction rate constants was measured.•Remarkable changes were obtained for distribution of product ions and reaction rate constants.•Proton transfer reaction was enhanced and reduced by complex formation.•Conformation changes are induced by complex formation and or by thermal collision with He.

Proton transfer reactions of angiotensin I ions for +2 charge state, [M + 2H]2+, to primary, secondary and aromatic amines were examined in the gas phase. Absolute reaction rate constants for proton transfer were determined from intensities of parent and product ions in the mass spectra. Temperature dependence of the reaction rate constants was measured. Remarkable change was observed for distribution of product ions and reaction rate constants. Proton transfer reaction was enhanced or reduced by complex formation of [M + 2H]2+ with gaseous molecules. The results relate to conformation changes of [M + 2H]2+ with change of temperature, which are induced by complex formation and or by thermal collision with He. Proton transfer reactions of angiotensin I ions for +3 charge state, [M + 3H]3+, were also studied. The reaction rates did not depend on temperature so definitely.

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