Through-Space Charge and Dipolar Effects in Substituted Ethanes and 1,1,1-Trifluoroethanes

Quantified electrostatic preorganization in enzymes using the geometry of the electron charge density

Electrostatic preorganization is thought to be a principle factor responsible for the impressive catalytic capabilities of enzymes. The full protein structure is believed to facilitate catalysis by exerting a highly specific electrostatic field on the active site. Computationally determining the extent of electrostatic preorganization is a challenging process. We propose using the topology and geometry of the electron charge density in the enzyme's active site to asses the effects of electrostatic preorganization. In support of this approach we study the convergence of features of the charge density as the size of the active site model increases in Histone Deacetylase 8. The magnitude of charge density at critical points and most Bader atomic charges are found to converge quickly as more of the protein is included in the simulation. The exact position of critical points however, is found to converge more slowly and be strongly influenced by the protein residues that are further away from the active site. We conjecture that the positions of critical points are affected through perturbations to the wavefunctions in the active site caused by dipole moments from amino acid residues throughout the protein. We further hypothesize that electrostatic preorganization, from the point of view of charge density, can not be easily understood through the charges on atoms or the nature of the bonding interactions, but through the relative positions of critical points that are known to correlate with reactivity and reaction barriers.

Binding Thermodynamics as a Tool To Investigate the Mechanisms of Drug−Receptor Interactions: Thermodynamics of Cytoplasmic Steroid/Nuclear Receptors in Comparison with Membrane Receptors

Drug-receptor binding thermodynamics has proved to be a valid tool for pharmacological and pharmaceutical characterization of molecular mechanisms of receptor-recognition phenomena. The large number of membrane receptors so far studied has led to the discovery of enthalpy-entropy compensation effects in drug-receptor binding and discrimination between agonists and antagonists by thermodynamic methods. Since a single thermodynamic study on cytoplasmic receptors was known, this paper reports on binding thermodynamics of estradiol, ORG2058, and R1881 bound to estrogen, progesterone, and androgen steroid/nuclear receptors, respectively, as determined by variable-temperature binding constant measurements. The binding at 25 degrees C appears enthalpy/entropy-driven (-53.0 </= DeltaG degrees </= -48.6, -34.5 </= DeltaH degrees </= -19.9 kJ/mol, 0.057 </= DeltaS degrees </= 0.111, and -2.4 </= DeltaC(p) degrees </= -1.7 kJ mol(-1) K(-1)) and is interpreted in terms of hydrophobic and hydrogen-bonded specific interactions. Results obtained for cytoplasmic receptors are extensively compared with those known for typical membrane receptors, in particular the adenosine A(1) receptor, to investigate the thermodynamic bases of drug-receptor binding from the most general point of view.