科研之友
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摘要
system, the heme protein myoglobin, but an examination of theoretical aspects of the approach show that it is expected to have wider applicability to the quantitative measurement of internal electric fields in guest-host systems in general. Within a host molecular system, such as cofactors in proteins, active sites in metal-organic frameworks, and dopants in semiconductor solids, a guest molecule experiences a very specific environment that includes interaction with electrostatic forces. As a supramolecular complex with a defined structure, the host will generate a defined net Coulombic force that undoubtedly influences the properties of its guest, including reactivity. This internal electric field experienced by a guest chromophore in a host matrix can be quantitatively determined at the molecular level using Stark spectroscopy, which is the application of an external electric field during spectral collection. Analysis of Stark spectra is typically performed using a truncated classical approach. However, a potentially more accurate quantum-mechanical approach based on perturbation theory was developed and previously described challenges to its implementation are overcome by the rigorous protocol reported here to achieve convergence for this theoretically infinite-order approach. In addition, a comparison of methods to calculate the required input for the approach (electronic properties, specifically transition energies and transition dipole moment) is made, ranging from semiempirical to time-dependent density functional to ab initio methods, which further reveals the governing aspects of this quantum-mechanical Stark effect analysis. The approach is illustrated with a biological guest-host system, the heme protein myoglobin, but an examination of theoretical aspects of the approach show that it is expected to have wider applicability to the quantitative measurement of internal electric fields in guest-host systems in general.
- 出版日期2016-4-6
