Amine−Hydrogen Halide Complexes:  Experimental Electric Dipole Moments and a Theoretical Decomposition of Dipole Moments and Binding Energies

Abstract

The Stark effect has been observed in the rotational spectra of several gas-phase amine-hydrogen halide complexes and the following electric dipole moments have been determined: H(3)(15)N-H(35)Cl (4.05865 +/- 0.00095 D), (CH(3))(3)(15)N-H(35)Cl (7.128 +/- 0.012 D), H(3)(15)N-H(79)Br (4.2577 +/- 0.0022 D), and (CH(3))(3)(15)N-H(79)Br (8.397 +/- 0.014 D). Calculations of the binding energies and electric dipole moments for the full set of complexes R(n)()(CH(3))(3)(-)(n)()N-HX (n = 0-3; X = F, Cl, Br) at the MP2/aug-cc-pVDZ level are also reported. The block localized wave function (BLW) energy decomposition method has been used to partition the binding energies into contributions from electrostatic, exchange, distortion, polarization, and charge-transfer terms. Similarly, the calculated dipole moments have been decomposed into distortion, polarization, and charge-transfer components. The complexes studied range from hydrogen-bonded systems to proton-transferred ion pairs, and the total interaction energies vary from 7 to 17 kcal/mol across the series. The individual energy components show a much wider variation than this, but cancellation of terms accounts for the relatively narrow range of net binding energies. For both the hydrogen-bonded complexes and the proton-transferred ion pairs, the electrostatic and exchange terms have magnitudes that increase with the degree of proton transfer but are of opposite sign, leaving most of the net stabilization to arise from polarization and charge transfer. In all of the systems studied, the polarization terms contribute the most to the induced dipole moment, followed by smaller but still significant contributions from charge transfer. A significant contribution to the induced moment of the ion pairs also arises from distortion of the HX monomer.

Energy decomposition analysis approaches and their evaluation on prototypical protein–drug interaction patterns

“…Investigations using EDA approaches are naturally well suited to evaluations of molecular bonding forces. The EDA studies in literature typically feature systems of relatively small size (up to tens of atoms) for both the variational [1][2][3][4][5][6]8,[11][12][13][14][15][16][17] and perturbation approaches, [18][19][20][21] and for biomolecular systems approaches such as molecular mechanics (MM) are sometimes combined with the QM region. 22,23 Here we discuss a number of these applications in literature.…”

“…The water dimer has been frequently adopted as a theoretical test model for the purpose of evaluating new EDA approaches 1,3,5,6,[11][12][13]24 as this system is exemplary of a typical hydrogen bonding interaction. Other small interacting systems also studied include the benzene dimer system, 8,17,21 the wateralkali metal cation series 1,4,5,11 and the ammonia-hydrogen fluoride 12,15,18 system. EDA calculations of drug-water clusters have also been performed.…”

Analysis of charge transfer effects in molecular complexes based on absolutely localized molecular orbitals

“…It is also not uncommon for MPA to predict charges of the wrong sign even in very simple systems. 67 Of course, construction of the projected virtual orbitals in ALMO methods unavoidably destroys absolute locality of the virtual orbitals ͓Eq. ͑11͔͒.…”

Block-Localized Density Functional Theory (BLDFT), Diabatic Coupling, and Their Use in Valence Bond Theory for Representing Reactive Potential Energy Surfaces

“…Δ E int can be decomposed into the following energy terms, including geometry distortion Δ E R , static electrostatic interaction energy Δ E stat , electronic polarization Δ E pol , and charge transfer energy Δ E CT :32,33,37,38,45,59,60,62–66,77 $$\mathrm{\Delta }{E}_1=\mathrm{\Delta }{E}_R+\mathrm{\Delta }{E}_{\text{stat}}+\mathrm{\Delta }{E}_{\text{pol}}+\mathrm{\Delta }{E}_{\text{CT}}$$ Δ E R represents the energy penalty due to geometry distortion of the individual molecules in the complex, which is a small factor for the ion–dipole complex (Table 2). …”