Serine–Ca²⁺versus serine–Cu²⁺complexes — A theoretical perspective

Abstract

The association of Ca 2+ and Cu 2+ to serine was investigated by means of B3LYP DFT calculations. The [serine-M] 2+ (M = Ca, Cu) potential energy surfaces include, as does the neutral serine, a large number of conformers, in which a drastic reorganization of the electron density of the serine moiety is observed. This leads to significant changes in the number and strength of the intramolecular hydrogen bonds existing in the neutral serine tautomers. In some cases, a proton is transferred from the carboxylic OH group to the amino group and accordingly, some of the more stable [serine-M] 2+ complexes can be viewed as the result of the interaction of the zwiterionic form of serine with the doubly charged metal ion. Whereas the interaction between Ca 2+ and serine is essentially electrostatic, that between Cu 2+ and serine has a non-negligible covalent character, reflected in larger electron densities at the bond critical points between the metal and the base, in the negative values of the electron density between the two interacting systems, and in much larger Cu 2+ than Ca 2+ binding energies. More importantly, the interaction with Cu 2+ is followed by a partial oxidation of the base, which is not observed when the metal ion is Ca 2+ . The main consequence is that in Cu 2+ complexes a significant acidity enhancement of the serine moiety takes place, which strongly favors the deprotonation of the [serine-Cu] 2+ complexes. This is not the case for Ca 2+ complexes. Thus, [serine-Ca] 2+ complexes, like those formed by urea, thiourea, selenourea, or glycine, should be detected in the gas phase. Conversely, the complexes with Cu 2+ should deprotonate spontaneously and therefore only [(serine-H)-Cu] + monocations should be experimentally accessible. Résumé :On étudié l'association des cations Ca 2+ et Cu 2+ avec la serine en utilisant la théorie de la fonctionnelle de la densité, B3LYP. Pour l'ion [sérine-M] 2+ (M = Ca, Cu), comme c'est le cas pour la sérine neutre, les surfaces d'énergie potentielle comportent un grand nombre de conformères dans lesquels on peut observer une réorganisation drastique de la densité électronique de la sérine. Ces changements conduisent à des changements significatifs dans le nombre et la force des liaisons hydrogènes intramoléculaires par rapport à celles qui existent dans les tautomères neutres de la sérine. Dans quelques cas, il se produit un transfert de proton du groupe OH de l'acide carboxylique vers le groupe amino et, en conséquence, un certain nombre des complexes les plus stables de l'ion [sérine-M] 2+ peuvent être considérés comme étant le résultat de l'interaction de la forme zwitterionique de la sérine avec l'ion métallique doublement chargé. Alors que l'interaction entre la Ca 2+ et la sérine est essentiellement électrostatique, celle entre le Cu 2+ et la sérine comporte un caractère covalent non négligeable qui est le reflet de densités électroniques plus grandes aux points critiques de liaison entre les deux systèmes en interaction ainsi que des énergies de liaisons beaucoup ...

Complexation of Ca2+ with selenocysteine and effects on its intrinsic acidity

“…Also, in agreement with the behavior reported for serine, 25 the global minimum of the [Sec-Ca] 2+ PES is a CS structure, what is at variance with glycine, 46 where the global minimum of the PES is a SB structure. The interconversion between local minima of the [Sec-Ca] 2+ PES is reported in Figure 4.…”

Infrared spectra of charge‐solvated versus salt‐bridge conformations of glycine‐, serine‐, and cysteine‐Ca2+complexes

“…This situation changes significantly when glycine is replaced by serine or cysteine. For both aminoacids, the “conventional” CS structure in which the doubly charged metal ion interacts simultaneously with the carbonyl and the amino groups is again higher in energy than the SB‐type structure [72]. However, in these two cases the global minimum of the potential energy surface is another CS‐type structure ( c ), in which the metal dication appears tricoordinated by association not only with the carbonyl and the amino group, but also with the enol or enethiol group [72].…”

Theoretical Investigation of the Chiral Transition of α‐Alanine Cu2+ Complex in Water Solution

“…Du et al [15] reported that there is about 1 g/ml copper in human plasma, and the formation of Cu 2 + and amino acid complexes could promote the transport of copper to serum protein and participate in the metabolic and biochemical processes in human body. Researchers [16][17][18][19][20] have prepared a lot of research on the important role of amino acid metal complexes such as intramolecular proton migration of Cu 2 + with amino acid complexes has been studied. The result showed that the conformation of amphoteric alanine with the coordination of metal ions was the most stable.…”

“…Therefore, the racemability of optically pure chiral amino acid metal complexes is very important for the health of life. The chiral transition of α-Ala Cu 2 + complex is also chiral while previous work [16][17][18][19][20] has only studied the proton transport reaction of the amino acid copper complex. Li et al [21] studied the chiral transition mechanism of the gas phase α-Ala ⋅ Cu 2 + complex, and the results showed that the racemization energy barrier of isolated α-Ala ⋅ Cu 2 + was about 120.0 kJ mol À 1 .…”

“…In this work, we calculate the chiral transition of α-Ala Cu 2 + complex in water-liquid environment, based on previous works. [7][8][9][10][11][12][13][14][16][17][18][19][20][21]…”