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The quantum topological electrostatic potential as a probe for functional group transferability
P L A Popelier1, M Devereux, M Rafat
1Department of Chemistry, UMIST, Manchester M60 1QD, England.
Acta Crystallographica. Section A, Foundations of Crystallography
|October 13, 2004
Summary
Electrostatic potential effectively indicates functional group transferability between molecules. Quantum-chemical topology reveals the aldehyde group in retinal is influenced by distant molecular fragments, unlike lysine's amino group.
Area of Science:
- Computational chemistry
- Molecular modeling
- Quantum chemistry
Background:
- The transferability of atoms or functional groups between molecules is crucial in chemistry.
- Electrostatic potential serves as a valuable indicator for assessing this transferability.
- Quantum-chemical topology (QCT) provides a method to analyze electron density and generated potentials.
Purpose of the Study:
- To compare the electrostatic potential and transferability of functional groups in different molecular environments.
- To investigate the influence of molecular structure on the electrostatic potential of terminal groups.
- To elucidate the impact of conjugated versus aliphatic carbon chains on functional group behavior.
Main Methods:
- Geometry optimization of molecules using ab initio calculations at the B3LYP/6-311G+(2d,p)//HF/6-31G(d) level.
- Application of Quantum-chemical Topology (QCT) to define electron density and electrostatic potential.
- Comparison of electrostatic potentials generated by aldehyde groups in retinal and derived molecules.
- Similar analysis performed on the amino group of lysine.
Main Results:
- The amino group in lysine showed minimal influence from molecular parts beyond two carbon atoms.
- The aldehyde group in retinal was significantly influenced by molecular fragments up to six carbon atoms away.
- A notable difference in the extent of molecular influence was observed between the two functional groups.
- This disparity was attributed to the differing saturation of carbon chains (conjugated in retinal, aliphatic in lysine).
Conclusions:
- The electrostatic potential is a reliable metric for functional group transferability.
- Molecular structure, particularly chain saturation, profoundly impacts the electrostatic potential and influence range of functional groups.
- Retinal's conjugated system allows for long-range electronic effects on its aldehyde group, unlike lysine's aliphatic amino group.