Flavonoids are natural products commonly found in the human diet that show antioxidant, anti-inflammatory and anti-hepatotoxic activities. These nutraceutical properties may relate to the electrochemical activity of flavonoids. To increase the understanding of structure-electrochemical activity relations and the inductive effects that OH substituents have on the redox potential of flavonoids, we carried out square-wave voltammetry experiments and ab initio calculations of eight flavonoids selected following a systematic variation in the number of hydroxyl substituents and their location on the flavan backbone: three flavonols, three anthocyanidins, one anthocyanin and the flavonoid backbone flavone. We compared the effect that the number of -OH groups in the ring B of flavan has on the oxidation potential of the flavonoids considered, finding linear correlations for both flavonols and anthocyanidins ( R 2 = 0.98 ). We analyzed the effects that position and number of -OH substituents have on electron density distributions via ab initio quantum chemical calculations. We present direct correlations between structural features and oxidation potentials that provide a deeper insight into the redox chemistry of these molecules.
We have determined the barrier and exothermicity of the aminoboranylidene (H2NB) to iminoborane (HNBH) isomerization reaction using coupled cluster energies extrapolated to the complete basis set limit, including core-correlation corrections and zero-point vibrational energies based on computed fundamental frequencies. Our best estimates of the reaction energy and reaction barrier are −41.35 kcal/mol and 27.40 kcal/mol, respectively. In addition, coupled cluster structural properties and fundamental vibrational frequencies, including isotopic shifts, are compared against experimental data.
Electronic structures, vibrational analyses, stabilization energies and amorphicity were analyzed for the most stable configurations of the neutral gas phase clusters of calcium carbonate (CaCO 3 ) n (n = 2-7). Minimum-energy structures were generated through simulated annealing using a mix of molecular dynamics/semiempirical optimization and then full optimization at the ab initio level (RHF/6-31G*). HF-level results are calibrated versus MP2/6-31G* results. Though many clusters are symmetric, the structural arrangements are not crystalline and resemble neither calcite nor aragonite. In general, greater symmetry means a lower stabilization energy. The BSSE-and zero point energy-corrected stabilization energies appear to plateau at about -113 kcal/mol when n = 7. Amorphous clusters start appearing when n = 4 and the lowest-energy minima for n C 5 are of C 1 symmetry. No solvent effect is necessary to induce amorphism.
We studied hydrated calcium oxalate and its ions at the restricted Hartree-Fock RHF/6-31G* level of theory. Performing a configurational search seems to improve the fit of the HF/6-31G* level to experimental data. The first solvation shell of calcium oxalate contains 13 water molecules, while the first solvation shell of oxalate ion is formed by 14 water molecules. The first solvation shell of Ca(II) is formed by six water molecules, while the second shell contains five. At 298.15 K, we estimate the asymptotic limits (infinite dilution) of the total standard enthalpies of hydration for Ca(II), oxalate ion and calcium oxalate as -480.78, -302.78 and -312.73 kcal mol(-1), resp. The dissociation of hydrated calcium oxalate is an endothermic process with an asymptotic limit of +470.84 kcal mol(-1).
We consider two measures of the quality of one-electron basis sets for quantum-chemical calculations: The electron–electron coalescence curvature and the correlation energy virial ratio. The former is based on the Kato cusp condition that many-electron wave functions must exhibit discontinuous first derivatives with respect to r12 as the coordinates of any two electrons coalesce. The latter is based on a simple modification of the quantum-mechanical virial theorem that makes use of only the correlation contributions to the kinetic and potential energy expectation values. The two measures are tested using coupled cluster wave functions for helium, neon, argon, calcium, and phosphorus atoms and are found to indicate good correlation with the quality of the basis set. These techniques may provide a foundation for the development of reliable basis set diagnostics for a variety of quantum-chemical applications.
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