Two-dimensional PES plot of the Zwitterionic form of leucine at the B3LYP/6-311++G(d,p) level, scanned along its two dihedral angles, τ 1 and τ 2 (in degree). The atom labelling of leucine and the two C–C bonds associated with these two dihedral angles are shown at the bottom. The energy unit is in hartree. Several low energy minima are indicated, together with the corresponding conformations.
Three most stable structures of the deprotonated (top), Zwitterionic (middle), and protonated (bottom) forms of leucine obtained at the B3LYP/6-311++G(d,p) level with the PCM of water.
Comparison of the experimental VA spectra of leucine under three representative pH conditions with the simulated VA spectra of the most stable conformer of the deprotonated, Zwitterionic, and protonated forms of leucine at 298 K.
Comparison of the VA spectra of the two most stable conformers of the Zwitterionic and neutral forms of leucine and the experimental VA spectrum under near neutral condition.
RDFs obtained from the MD simulations of the Zwitterionic form of leucine in water. The atom labelling of leucine used in the graphs is presented at the bottom. HW and OW refer to the hydrogen and oxygen atom of water molecules, respectively.
Optimized geometries of the most stable conformers of the Zwitterionic leucine-(water)4,5 clusters at the B3LYP/6-311++G(d,p) level with the PCM of water. The important hydrogen bonding lengths (in Å) are also indicated.
Comparison of the optimization step numbers of ZW1_4w at the B3LYP/6-311++G(d,p) level with the PCM of water (left) and in the gas phase (right).
Comparison of the VA (a) and VCD (b) spectra of ZW1_4w and ZW1_5w in the gas phase and with the PCM of water with the corresponding experimental data under near neutral condition.
The relative zero-point energy corrected total energies and Gibbs free energies of the three most stable conformers of the Zwitterionic, deprotonated, and protonated forms of leucine at the B3LYP/6-311++G (d,p) level with the PCM of water, together with their percentage Boltzmann population factors at 298 K.
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