Geometry optimizations are performed at the DFT/B3LYP/6-311+G* level. Four intriguing coupling modes, totally eight stable structures are found in the potential energy surfaces of the water-assisted coupling of imidazole dimer radical cation. In these isomers, the water molecules are embedded between two imidazole moieties, and the oxygen atom is tridentate or quadridentate, respectively. The distinct redshifts of the vibrational frequencies of the O-H...N and N-H...O type H bonds indicate the strong interaction of two imidazole rings of respective isomer. Inspection of the highest occupied molecular orbital predicts the alterations of the geometry structures on oxidation and reduction. The low barrier of the fragment rotation demonstrates that the isomerization processes by experiencing the distinct transition states are easy to fulfill, especially for those with O-H...N and C-H...O H bonds. Both the energy difference of the 0

The electronic effects on the protonated hydrogen-bonded imidazole trimer (Im) 3H1 and the derivatives cationized by alkali metals (Li1, Na1, and K1) are investigated using B3LYP method in conjunction with the 6-3111G* basis set. The prominent characteristics of (Im) 3H1 on reduction are the backflow of the transferred proton to its original fragment and the remoteness of the H atom from the attached side bare N atom. The proton transfer occurs on both reduction and oxidation for the corresponding hydrogen-bonded imidazole trimer. For the derivatives cationized by Li1, (Im) 3Li1, the backflow of the transferred proton occurs on reduction. The electron detachment from respective highest occupied molecular orbital of (Im)3Na1 and (Im)3K1 causes the proton transferring from the fragment attached by the alkali metal cation to the middle one. The order of the adiabatic ionization potentials of (Im) 3M1 is (Im) 3H1.(Im) 3Li1.(Im) 3Na1.(Im) 3K1; the order of (Im) 3M indicates that (Im) 3H is the easicst complex to be ionized. The polarity of (Im) 3M1 (Mdenotes H, Li, Na, and K) increases on both oxidation and reduction. The (Im)3M1 complexes dissociate into (Im) 3 and M1 except (Im) 3H1, which dissociates preferably into (Im) 3 1 and H atom, while the neutral complexes dissociate into (Im) 3 and M. The stabilization energy of (Im) 3Li21, (Im) 3Na21, and (Im) 3K21 indicate that their energies are higher as compared to those of the monomers.

The structural parameters, relative stability, proton transfer energy barriers of four typical and life related isomers and conformers of different charged (n50,61,62) glycine species have been investigated using B3LYP, BHLYP, and CCSDT methods. Results indicate that those neutral and (61)-charged species are stable. For the (12)-charged cases, all four triplet-state glycine species and only the singlet-state zwitterionic one are stable. On the other hand, only the singlet-state zwtterionic glycine (1GlyZW(-2)) and the corresponding neutral form counterpart (1Gly(-2)) are stable for the 2-charged cases. Either of the two stable structures holds a proton lying in the position (2-3?) of being separated from its corresponding parental species. Those unstable divalent glycine species are dissociated into different smaller species spontaneously according to the characters of their different structures and electron spins. The presented fragmentation and deformation mechanisms can effectively predict and satisfactorily explain some experimental phenomena, which had been puzzling the mass spectrometry chemists. Also, the mechanisms should be suitable for any other similar molecule systems. Comparisons of the relative energies of the four (11)-charged glycine species show that doublet-state glycine Ⅲ (2GlyⅢ1) is more stable in energy by 12.1 kcal/mol than the (11)-charged glycine Gly (2Gly1). This is consistent with the energy ordering of their corresponding mono-valence metal ion-bound derivatives. In addition, calculations show that an intramolecular proton transfer of 2Gly(-1) to become its zwitterionic counterpart is preferred due to its least activation energy barrier (5.8 kcal/mol) among four discussed processes.