Structural stabilities of metalated histidines in gas phase and existence of gaseous zwitterionic histidine conformers

Infrared and Raman spectra of Histidine: an ab initio DFT calculations of Histidine molecule and its different protonated forms

“…The intense peaks in both IR (in solid as well as in solution) and Raman spectra at 1503, 1495 and 1482 cm -1 are easily assigned as NH in-plane bending modes as suggested by earlier workers [7][8][9][10][11]. The band around 1414 cm -1 is, however, assigned to the ring C-N stretching mode instead of a CO 2 -related mode as suggested by Mesu et al [13].…”

“…According to reference [11] histidine has five different pH-dependent ionic forms. In some of these ionic forms, the two nitrogen atoms of the Imidazole ring are not similar.…”

“…Since all amino acids exist as zwitterions in solid form as well as in aqueous solution, it is very important to know which zwitterionic tautomer of Histidine will be the most stable. Regarding the zwitterionic conformers of histidine, Weixin et al have already explored seven tautomers in the gas phase [11]. Simultaneously, Rai et al have also studied the effect of medium on structure of Histidine molecule explicitly combined with two water molecules [12].…”

“…Ashikawa et al [7] have shown that C-C stretching in the imidazole ring has different frequencies for the two neutral tautomers of imidazole ring. Several other authors [8][9][10] have tried to identify Histidine tautomer frequency marker using the [11] have extensively explored the zwitterionic conformers of Histidine molecule at DFT level and found seven tautomers of zwitterions in gas phase. Furthermore, it is a very common feature that zwitterions are more stable as compared to their canonical form in aqueous solution and in solid form.…”

Conformational search for zwitterionic leucine and hydrated conformers of both the canonical and zwitterionic leucine using the DFT-CPCM model

“…in arginine [11,12]. The limitation of this approach is illustrated in lysine which is the second most basic of the amino acids but does not show such a structure [13], while histidine with a lower basicity has this characteristic [14]. On the other hand, the predominance of the zwitterionic structures of the amino acids in solution indicates that hydration is more effective in conversion from neutral to zwitterionic form.…”