Effects of Microsolvation on the Stability of Zwitterionic Valine

Abstract

We present calculations for valine (Val) -(H2O)n (n = 0-5) to examine the effects of microsolvating water on the relative stability of the zwitterionic vs. canonical forms of Val. We calculate the structures, energies and Gibbs free energies of the conformers at B3LYP/6-311++G(d,p), wB97XD/6-311++G(d,p) and MP2/aug-ccpvdz level of theory. We find that five water molecules are needed to stabilize the zwitterionic form of Val. By calculating the barriers of the canonical ↔ zwitterionic pathways of Val -(H2O)5 conformers, we suggest that both forms of Val -(H2O)5 may be observed in low temperature gas phase

An ab initio analysis of the structure of l-tryptophan tautomers in microhydrated environments, in water and in hydrophobic solvents

“…Table 2 summarizes the calculated tautomerization energies with the explicit microsolvation model. The variation of the tautomerization energy with increasing hydration number obtained in our study is consistent with the trends observed by Blom et al for Trp [52], by Kim et al for Val [49], and by Rodziewic et al for Phe [50]. Thus, we predict a decrease of the tautomerization energy for Trp interacting with one (9.95 kcal/mol), two (7.15 kcal/mol) or Table 4 Tautomerization energies, DE T , and free energies, DG T , and solvation energies (in kcal/mol) of the most stable neutral and zwitterionic isomers of Trp in different solvents calculated with the PCM model at the MP2/aug-cc-pVDZ//PCM-B3LYP/6-31+G(d,p) level.…”

“…However, the tautomer preference in partially hydrated environments and/or in more or less hydrophobic media cannot be predicted in a straightforward manner. This question has biological relevance and it has been thoroughly studied in the case of the amino acids such glycine (Gly) [47,48], valine (Val) [49], phenylalanine (Phe) [50], lysine (Lys) [51], and serine (Ser) [51]. The obtained results, however, do not necessarily apply to other amino acids, in particular to those bearing large hydrophobic groups such as Trp, and further research on this topic is required to progress in the understanding of key questions such as passive diffusion across cell membranes or the structure and stability of membrane proteins.…”

Gas phase hydration of amino acids and dipeptides: effects on the relative stability of zwitterionvs.canonical conformers

“…Calculations for the valine (Val)(H 2 O) n (n ¼ 0-5) system by B3LYP/6-311++G(d,p), wB97XD/6-311++G(d,p) and MP2/aug-ccpvdz level of theory revealed that ve water molecules are necessary to stabilize the zwitterionic form of this amino acid. 38 Fig. 4 shows the lowest energy canonical and zwitterionic forms of Val(H 2 O) 5 .…”

Solvent effects on the structures and vibrational features of zwitterionic dipeptides: L-diglycine and L-dialanine

“…Several theoretical and experimental studies were carried out on the behavior of amino acids in hydrated media. It was established that at least three water molecules were necessary to stabilize the zwitterionic character of an amino acid backbone [16][17][18][19], but it is not sufficient. Ghomi's group [10] had also confirmed these results and added that this number of solvent molecules present an adequate hydration network of NH + 3 and COO − terminals, thus avoiding the proton transfer from NH + 3 to COO − .…”