Protein energetics have been classically studied by the excitation of a chromophore bound to the protein. The inherent chromophores include UV-active amino acids embedded within the primary structure of the peptide or chemically-bonded optically-active metal or organic prosthetic groups. These techniques have been used to successfully study regions of a protein and the respective quenching mechanisms of the excited inherent chromophores.
Impedance or dielectric spectroscopy is an ultra-low energy technique based on the capacitive response of a sample. A real capacitor exhibits both the capability to effectively store charge (dispersive) and dissipate energy (absorptive) from an external time-varying electric field. A well designed dielectric spectrometer will simultaneously measure both the dispersive and absorption responses of the sample versus incident frequency. Dielectric spectroscopy has been used in the last decade to study organic solvents, solid-state materials and devices, corrosion, thin-films, and coatings.
The primary structure of all peptide chains exhibit a permanent dipole moment based on the positive charge of the amine group and the negative charge of the carboxylic group of every amino acid in the chain and those electric dipoles based on the polar R groups laterally from the primary chain. The secondary and tertiary folding will further enhance or diminish the local dipoles into a net permanent dipole moment, or a series of local permanent dipole moments. Every protein possesses a permanent dipole moment which could in principle be directly studied by dielectric spectroscopy.
It is our proposal to build a custom dielectric spectrometers with enough sensitivity, down to 2 fA, or better, and a spectral range, 10 uHz to 32 MHz, to directly observe and characterize the intramolecular dipole moments of peptides and proteins. This technique will study the protein itself, and not only be limited to only the UV- or optically-active chromophores. The characterization of such dipole moments will allow for the empirical deduction of the hydrophobic and hydrophilic interactions and local internal environments of the proteins’ secondary and tertiary structures. The empirical data gathered from these interactions and environments will allow for further qualitative and quantitative characterization of structural motifs such as a-helices, b-sheets, and hairpin bends, as well as, enzymatic, antibiotic, and hormonal active sites.
The beforementioned empirical data will eventually lead to permanent molar polarization and structural motif catalogs of spectral responses that will be invaluable in biophysics, biochemistry, proteomics, micro- and molecular cell biology, immunology, endocrinology, pharmacology, bioengineering, and nanotechnology.