Static dielectric constant bulk water

According to the Kirkwood theory of polar dielectrics, simple relations (23) between molecular dipole moment vectors and the mean-square total dipole moment of water clusters can be used to compute the static dielectric constant of water. As the normalized mean-square total dipole moment increases towards unity, theory predicts decreases in the static dielectric constant. Since MD results indicate that the mean-square total dipole moment of interfacial water is greater than that for bulk water (48), the static dielectric... 

Interestingly, it can be shown that the foree eonstant of polarization relaxation of bulk water increases with the statie dieleetrie constant. Therefore, SD beeomes faster as the static dielectric constant increases. 

Dielectric relaxation results are proven to be the most definitive to infer the distinctly different dynamic behavior of the hydration layer compared to bulk water. However, it is also important to understand the contributions that give rise to such an anomalous spectrum in the protein hydration layer, and in this context MD simulation has proven to be useful. The calculated frequency-dependent dielectric properties of an ubiquitin solution showed a significant dielectric increment for the static dielectric constant at low frequencies but a decrement at high frequencies [8]. When the overall dielectric response was decomposed into protein-protein, water-water, and water-protein cross-terms, the most important contribution was found to arise from the self-term of water. The simulations beautifully captured the bimodal shape of the dielectric response function, as often observed in experiments. 

As the environment inside the lipid bilayer is hydrophobic, it has a low static dielectric constant and therefore the electrostatic field across the membrane does not become screened as in bulk water. 

Another approach proposed by Steel and Walker is based on the concept of molecular rulers [39]. These rulers are solvatochromic surfactants composed of an anionic sulfate group attached to a hydrophobic, solvatochromic probe by alkyl spacers of different lengths. The probe is p-nitroanisole, an aromatic solute whose bulk solution excitation wavelength monotonically shifts by more than 20 nm from 293 to 316 nm as the solvent polarity or static dielectric constant varies from 2 for cyclohexane to 78 for water. To measure only the absorbance of... 

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