A solvatochromic model calibrates nitriles' vibrational frequencies to electrostatic fields
Sayan Bagchi1, Stephen D Fried, Steven G Boxer
1Department of Chemistry, Stanford University, Stanford, California 94305-5080, USA.
Journal of the American Chemical Society
|June 15, 2012
Summary
Infrared spectroscopy can now measure protein electric fields. A new model calibrates nitrile probes, enabling precise electrostatic field mapping in proteins like ribonuclease S.
Area of Science:
- Biophysics
- Spectroscopy
- Protein Science
Background:
- Electrostatic interactions are crucial for protein structure and function.
- Infrared (IR) spectroscopy, using nitrile chemical groups as probes, can detect local electrostatic fields.
- Previous IR studies lacked calibration to total electric fields due to H-bonding and chemical complexities.
Purpose of the Study:
- To develop a solvatochromic model for calibrating vibrational frequencies of aromatic nitrile probes.
- To assess the H-bonding status of nitrile probes within proteins.
- To quantify the average total electrostatic field in proteins using IR spectroscopy.
Main Methods:
- Developed a solvatochromic model correlating IR frequency with (13)C chemical shift.
- Utilized a robust method for isotopic labeling of aromatic nitriles.
- Applied the method to p-CN-Phe labeled ribonuclease S (RNase S) near its active site.
Main Results:
- Successfully calibrated vibrational frequencies of nitrile probes to electrostatic fields.
- Estimated the average total electrostatic field at the p-CN-Phe location in RNase S.
- Quantitative agreement was found between experimental measurements and molecular dynamics simulations.
Conclusions:
- The developed model enables accurate assessment of protein electrostatics using IR probes.
- This approach overcomes limitations of previous IR spectroscopic studies on proteins.
- IR probes show significant potential for detailed studies of electrostatic fields in biological systems.
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