Triazene proton affinities: A comparison between density functional,Hartree–Fock,and post-Hartree–Fock methods

The consistency of three density functional computational implementations (DMol, DGauss, and deMon) are compared with high-level Hartree–Fock and Møller–Plesset (MP) calculations for triazene (HN?NNH₂) and formyl triazene (HN?NNHCOH). Proton affinities on all electronegative sites are investigated as well as the geometries of the neutral and protonated species. Density functional calculations employing the nonlocal gradient corrections show agreement with MP calculations for both proton affinities and geometries of neutral and protonated triazenes. Local spin density approximation DMol calculations using numerical basis sets must employ an extended basis to agree with other density functional codes using analytic Gaussian basis sets. The lowest energy conformation of triazene was found to be nonplanar; however, the degree of nonplanarity, as well as some bond lengths, is dependent on the basis set, electron correlation treatment, and methods used for the calculation. © 1994 by John Wiley & Sons, Inc.

1 This article is a U.S. Government work and, as such, is in the public domain in the United States of America.

     

Electron transmission study of the formaldehyde electron affinity

We have employed electron transmission spectroscopy to detect sharp variations in the total scattering cross section of electron from formaldehyde resulting from temporary negative ion formation. A progression of peaks is observed which we identify with vibrational levels of the H₂CO^?(²B₁) ground state. The adiabatic electron affinity of H₂CO is found to be ?0.65 ± 0.05 eV.     

Bisimidazoacridones: Effect of Molecular Environment on Conformation and Photophysical Properties

Bisimidazoacridones (BIA) are highly selective antineoplastic and antiviral agents. Ultraviolet-visible spectroscopy and steady-state and time-resolved fluorescence spectroscopy studies were carried out to probe the behavior of BIA in aqueous and nonaqueous (organic solvents, colloid micelles) solutions. Three ranges of fluorescence lifetimes were revealed: approximately 0.2-0.5 ns (presumably reflecting the chromophore-chromophore interaction), approximately 1-5 ns (interpreted as linker-perturbed chromophore decay) and approximately 6-12 ns (nonperturbed chromophore decay). The pre-exponential and steady-state contributions of these components to the decay signal as well as the data on steady-state fluorescence intensities, wavelength maxima and bandwidths showed that the BIA conformations in solution were sensitive to the environment and influenced strongly by their propensity to minimize hydrophobic interactions. In water, the molecules tend to adopt condensed conformations that bring the two imidazoacridone moieties into close proximity (resulting in intramolecular fluorescence energy transfer), while in nonaqueous systems the conformations become more relaxed. The transfer from a polar to more lipophilic environment of macromolecules is suggested to be the main driving force for binding of BIA to biomacromolecules, such as nucleic acids.     

A study of the negative ion states of selected cyclodienes by electron transmission spectroscopy

Electron transmission spectroscopy is employed to locate sharp variations in the total cross sections for electrons scattered from several cyclic compounds containing two carboncarbon bonds. For each molecule, structure is observed which we associate with the temporary occupation of the two low-lying, normally unfilled, π^* orbitals by impacting electrons. Electron affinities are reported for 1,5-cyclooctadiene, 1,4-and1,3-cyclohexadiene, norbornadiene and also cyclohexene, propene, and cis-butene.