Proton Dynamics in the Strong Chelate Hydrogen Bond of Crystalline Picolinic Acid N-Oxide. A New Computational Approach and Infrared, Raman and INS Study

Abstract

Infrared, Raman and INS spectra of picolinic acid N-oxide (PANO) were recorded and examined for the location of the hydronic modes, particularly O-H stretching and COH bending. PANO is representative of strong chelate hydrogen bonds (H-bonds) with its short O...O distance (2.425 A). H-bonding is possibly well-characterized by diffraction, NMR and NQR data and calculated potential energy functions. The analysis of the spectra is assisted by DFT frequency calculations both in the gas phase and in the solid state. The Car-Parrinello quantum mechanical solid-state method is also used for the proton dynamics simulation; it shows the hydron to be located about 99% of time in the energy minimum near the carboxylic oxygen; jumps to the N-O acceptor are rare. The infrared spectrum excels by an extended absorption (Zundel's continuum) interrupted by numerous Evans transmissions. The model proton potential functions on which the theories of continuum formation are based do not correspond to the experimental and computed characteristics of the hydrogen bond in PANO, therefore a novel approach has been developed; it is based on crystal dynamics driven hydronium potential fluctuation. The envelope of one hundred 0 --> 1 OH stretching transitions generated by molecular dynamics simulation exhibits a maximum at 1400 cm-1 and a minor hump at approximately 1600 cm-1. These positions square well with ones predicted for the COH bending and OH stretching frequencies derived from various one- and two-dimensional model potentials. The coincidences with experimental features have to be considered with caution because the CPMD transition envelope is based solely on the OH stretching coordinate while the observed infrared bands correspond to heavily mixed modes as was previously shown by the normal coordinate analysis of the IR spectrum of argon matrix isolated PANO, the present CPMD frequency calculation and the empirical analysis of spectra. The experimental infrared spectra show some unusual characteristics such as large temperature effects on the intensity of some bands, thus presenting a challenge for theoretical band shape treatments. Our calculations clearly show that the present system is characterized by an asymmetric single well potential with no large amplitudes in the hydronium motion, which extends the existence of Zundel-type spectra beyond the established set of hydrogen bonds with large hydronic vibrational amplitudes.

Vibrational Dynamics of the Double Hydrogen Bonds in Nucleic Acid Base Pairs

“…Further, the Troullier-Martins (TM) pseudopotential [73] with a wavefunction cutoff of 70 Ry is adopted to describe the interaction between the core and valence electrons in the quantum region. Note that BLYP, together with the plane wave base set, has been reported to yield good results for the simulation of a hydrogen-bonded system, such as liquid water [74], liquid HF [75] and strong HB in crystalline picolinic acid N-oxide [40].…”

“…In other words, a quantitative result would not be expected from this approach. An alternative approach is the on-the-fly calculation of NH stretching snapshot potentials in a frozen environment for some representative configurations along the trajectory [37][38][39][40]. To accomplish this goal, geometry snapshots in the time interval 1.0-9.0 ps are sampled at typical long, short and intermediate base-pair separations for the computation of potential curves.…”

“…Finally, a different N-oxide in the crystalline phase with a rather strong HB was studied in Ref. [40].…”

Solving the vibrational Schrödinger equation on an arbitrary multidimensional potential energy surface by the finite element method

“…Furthermore, harmonic frequency calculations at B3LYP/6-311++G(3df, 3pd), B3LYP/6-31+G(d, p) and B3LYP/6-31G(d, p) levels yield O-H stretching frequencies ν OH of 2977 cm −1 [25], 2965 cm −1 [84], and 2991 cm −1 [85] respectively. In the experimental infrared spectrum of PANO isolated in an Ar matrix, however, Szczepaniak et al [85] found no intense absorption band within 1200 cm [86]. Here, we present a 2D analysis using the potential surfaces for PANO calculated by Stare and Balint-Kurti [25] and by Stare and Mavri [84].…”

Theoretical and spectroscopic studies of vibrational spectra of hydrogen bonds in molecular crystal of β-oxalic acid

“…The theory presented by Yaremko et al takes into account FermiDavydov resonance and interaction of the H-bond vibrations with the lattice phonons but this theory applied to adipic acid crystal reproduces only the main features of the experimental spectra. Crystal field effects and thermal fluctuations were recently incorporated in simulations of spectra of hydrogen-bonded systems using the Car-Parinello method [37][38][39] but this approach is computationally expensive and limited to quantization of few degrees of freedom. Our quantum-mechanical model considers major vibrational interactions in hydrogen-bonded systems, treats the broadening as a phenomenological process, and allows for quantitative reproduction of experimental spectra of hydrogenbonded systems and their deuterated analogs [32,40,41].…”