Role of isomerization barriers in the pKa control of the retinal Schiff base: a density functional study

Article Abstract:

The barriers to the rotation of all conventional single and double bonds were computed in a model Schiff base which is structurally very close to the retinal Schiff base chromophore in bacteriorhodopsin. The computed values for the torsional barriers can be utilized to estimate the corresponding values in the retinal Schiff base structure. The torsional barriers were obtained as the energy differences between the all-trans and 90-degree-rotated conformers, respectively, for optimized structures in both neutral and protonated species.

Isomerization, Density functionals, Density functional theory

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Electronic effects on the ground rotational barrier of polyene Schiff bases: a molecular orbital study

Article Abstract:

Several quantum mechanical methods were used to examine the electronic effects of a double bond rotation in protonated and neutral polyene Schiff bases. The performance of these methods is compared to one another to determine their efficiency. In the protonated case, the theoretical and experimental vibrational spectra were also compared to verify the methods. Results showed that the unrestricted natural orbital complete active space and UB3LYP frequencies were close to the experimental values.

Polyenes, Vibrational spectra

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Influence of the methyl groups on the structure, charge distribution and proton affinity of the retinal Schiff base

Article Abstract:

The Schiff base model was used to examine the potential impact of methyl substitutions on carbon atoms in the context of proton affinity (PA), charge distribution and structure. All the samples observed did not exhibit marked structural changes upon the application of large basis sets. It was also shown that methyl substitutions tend to create a direct effect on PA level by determining the overall shape of the chromophore.

Analysis, Methyl groups, Methyl compounds

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