First Hyperpolarizability of Collagen Using the Point Dipole Approximation.

Area of Science:

• Computational Chemistry
• Biophysics
• Materials Science

Background:

• Predicting nonlinear optical properties of proteins is crucial for applications.
• Accurate calculation of molecular hyperpolarizability remains a challenge.
• Localized properties offer a promising approach for complex biomolecules.

Purpose of the Study:

• To present a novel method for predicting total protein hyperpolarizability from localized contributions.
• To apply this model to rat-tail collagen as a proof-of-concept.
• To investigate the atomic and bond contributions to the net molecular hyperpolarizability.

Main Methods:

• Utilized the quadratic Applequist point-dipole approach and LoProp transformation.
• Employed molecular fractionation with conjugate caps for atomic and bond analysis.
• Incorporated Thole's exponential damping modification to the dyadic tensor.

Main Results:

• Achieved qualitative agreement with experimental data for rat-tail collagen.
• Optimized the model by decomposing LoProp properties into atomic positions.
• Thole's damping with the original parameter best reproduced experimental βHRS signal intensity and depolarization ratios.

Conclusions:

• The developed model successfully predicts protein hyperpolarizability from localized properties.
• This approach provides insights into atomic and bond contributions to nonlinear optical responses.
• The methodology has potential for general protein property optimization in various fields.