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Dissociation energies, equilibrium structures, equilibrium dipole moments, harmonic vibrational frequencies, infrared (IR) intensities, and zero-point vibrational energies (ZPVEs) are presented for the hydrogen fluoride monomer and dimer at the coupled cluster with single and double excitations plus perturbative connected triple excitations [CCSD(T)] level of theory with a series of large basis sets. Discussion focuses on the results from the largest basis set, triple zeta plus double polarization and one set of higher angular momentum functions [TZ2P(f,d)]. The structural parameters and dissociation energy agree well with the recent theoretical values reported in a high level ab initio study by Peterson and Dunning [J. Chem. Phys. 102, 2032 (1995)] and with experimental results. Here, the harmonic vibrational frequencies and IR intensities for the dimer are also predicted. The predicted vibrational frequency shifts relative to the monomer for the HF and DF stretching coordinates in the dimer are close to the experimental estimates. © 1995 American Institute of Physics. [ABSTRACT FROM AUTHOR]

1-Methyl-3-(N-(1,8-naphthalimidyl)ethyl)imidazolium (MNEI) has potential as a versatile sensor that can measure the electronegativity of anions based on the fluorescence intensity upon irradiation. To clarify the factors that determine the fluorescence intensity, constrained density functional theory (CDFT) was applied to explore the electron transfer (ET) states of MNEI halide species (MNEI–X; X = F, Cl, Br, I). According to the CDFT potential energy surface, intra-molecular ET (SM1) states on MNEI are responsible for the intensity of absorption and fluorescence spectra. However, inter-molecular ET (SET) states between MNEI and X are certainly responsible for fluorescence quenching. Hence, the energetic difference between the SM1 state and the SET state (ΔEM1_ET) is a crucial factor that determines the fluorescence intensity in the spectra of MNEI–X complexes. ΔEM1_ET decreases as the electronegativity of X decreases (i.e., F ＞ Cl ＞ Br ＞ I). This explains the fluorescence intensity of MNEI–X. [ABSTRACT FROM AUTHOR]

Examines the role of one- and two-electron spin-orbit coupling terms to the parity-violating energy shifts for amino acids and helical alkanes. Use of sum-over-state perturbation theory in the study; Effect of weak neutral-current interaction between an electron and nucleus; Inclusion of one-center terms for amino acid and n-alkane calculations.

Electron transfer (ET) states of 1-methyl-3-(N-(1,8-naphthalimidyl)ethyl)imidazolium iodide are responsible for its photophysics. Investigation of an ET state based on constrained density functional theory (CDFT) revealed that nonradiative decay from the ET excited state is mediated by the interaction of the iodine atom with the 1,8-naphthalimide or the imidazolium group. [ABSTRACT FROM AUTHOR]

We have designed a novel 1,8-naphthalimide derivative with an open space for an anion. Computational calculation has predicted that the space could trap various anion species and photo-induced charge transfer depending on the anion's electrophilic properties. Indeed, the fluorescence behaviour of the 1,8-naphthalimide derivative complexes with each anion is consistent with the computational prediction. [ABSTRACT FROM AUTHOR]

Functional regulation of myoglobin (Mb) is thought to be achieved through the heme environment furnished by nearby amino acid residues, and subtle tuning of the intrinsic heme Fe reactivity. We have performed substitution of strongly electron-withdrawing perfluoromethyt (CF3) group(s) as heme side chain(s) of Mb to obtain large alterations of the heme electronic structure in order to elucidate the relationship between the O2 affinity of Mb and the electronic properties of heme peripheral side chains. We have utilized the equilibrium constant (pKa) of the "acid-alkaline transition" in metmyoglobin in order to quantitatively assess the effects of the CF3 substitutions for the electron density of heme Fe atom (ρFe) of the protein. The pKa value of the protein was found to decrease by ~1 pH unit upon the introduction of one CF3 group, and the decrease in the pKa value with decreasing the PFQ value was confirmed by density functional theory calculations on some model compounds. The O2 affinity of Mb was found to correlate well with the pKa value in such a manner that the P50 value, which is the partial pressure of O2 required to achieve 50% oxygenation, increases by a factor of 2.7 with a decrease of 1 pKa unit. Kinetic studies on the proteins revealed that the decrease in O2 affinity upon the introduction of an electron-withdrawing CF3 group is due to an increase in the O2 dissociation rate. Since the introduction of a CF3 group substitution is thought to prevent further Fe2+-O2 bond polarization and hence formation of a putative Fe3+-O2--like species of the oxy form of the protein [Maxwell, J. C.; Volpe, J. A.; Barlow, C. H.; Caughey, W. S. Biochem. Biophys. Res. Commun. 1974, 58, 166-171], the O2 dissociation is expected to be enhanced by the substitution of electron-withdrawing groups as heme side chains. We also found that, in sharp contrast to the case of the O2 binding to the protein, the CO association and dissociation rates are essentially independent of the ρFe value. As a result, the introduction of electron-withdrawing group(s) enhances the preferential binding of CO to the protein over that of O2. These findings not only resolve the long-standing issue of the mechanism underlying the subtle tuning of the intrinsic heme Fe reactivity, but also provide new insights into the structure-function relationship of the protein. [ABSTRACT FROM AUTHOR]