Calculated Spectroscopy and Atmospheric Photodissociation of Phosphoric Acid

A role for phosphorus redox in emerging and modern biochemistry

Phosphorus is a major biogeochemical element controlling growth in many ecosystems. It has presumably been an important element since the onset of life. In most chemical and biochemical considerations, phosphorus is synonymous with phosphates, a pentavalent oxidation state that includes the phosphate backbone of DNA and RNA, as well as major metabolites such as ATP. However, redox processing of phosphates to phosphites and phosphonates, and to even lower oxidation states provides a work-around to many of the problems of prebiotic chemistry, including phosphorus's low solubility and poor reactivity. In addition, modern phosphorus cycling has increasingly identified reduced P compounds as playing a role, sometimes significant, in biogeochemical processes. This suggests that phosphorus is not redox-insensitive and reduced P compounds should be considered as part of the phosphorus biogeochemical cycle.

Ab initio study of hydrogen bonding in the H3PO2 dimer and H3PO2-DMF complex

The molecular structures and H-bonding interactions in the phosphinic acid dimer and the complex of phosphinic acid with N,N-dimethylformamide (DMF) were investigated by density functional theory calculations at the B3LYP level of theory. In order to better understand these phenomena, the individual molecules were also studied. The results were compared with previously obtained data for similar H-bonded complexes of phosphoric and phosphorous acids with DMF. Various correlations were found between geometric characteristics and parameters derived from Bader's theory and natural bond orbital analysis. Graphical abstract Irina V. Fedorova and Lyubov P. Safonova. Ab initio study of hydrogen bonding in the H₃PO₂ dimer and H₃PO₂-DMF complex. The acids of phosphorus are considered suitable candidates for ionomers due to their efficient proton transport properties. In order to better understand their molecular structures and their H-bond characteristics in real liquids, the most stable configurations of the H₃PO₂ dimer and the H₃PO₂-DMF complex were examined using computational methods in quantum chemistry. It was found that the strength of the H-bonding interactions in these systems depends strongly on the environment.

Ab initio molecular dynamics study of H-bonding and proton transfer in the phosphoric acid-N,N-Dimethylformamide system

Car-Parrinello molecular dynamics simulations of phosphoric acid (H₃PO₄)-N,N-dimethylformamide (DMF) mixtures over the whole composition range have been carried out. It has been found that the neutral molecules are the dominant species in this system. The concentration dependences of the average number of H-bonds per proton acceptor atom in P=O and C=O groups as well as per proton donor atom in DMFH⁺ ions towards phosphate species have been discussed. The H-bonding between components in all investigated mixtures of H₃PO₄ and DMF is possible. A significant fraction of the protonated DMF forms appears at phosphoric acid mole fraction higher than 0.37, indicating a high probability of proton transfer from phosphate species to oxygen atoms in C=O groups. The intermolecular proton transfer between phosphate species themselves is mainly observed when x_H3PO4 > 0.19. Satisfactory agreement with available experimental data for structural characteristics of the investigated system was obtained.

Positively Charged Phosphorus as a Hydrogen Bond Acceptor

Phosphorus (P) is an element that is essential to the life of all organisms, and the atmospheric detection of phosphine suggests the existence of a volatile biogeochemical P cycle. Here, we investigate the ability of P to participate in the formation of OH···P hydrogen bonds. Three bimolecular alcohol-trimethylphosphine complexes have been detected. Initially, the complexes were detected using matrix isolation spectroscopy, which favors complex formation. Subsequently, the fundamental OH-stretching vibration was observed in room-temperature gas-phase spectra. On the basis of our measured OH-stretching frequency red shifts and quantum chemical calculations, we find that P is an acceptor atom similar in strength to O and S and that all three P, O, and S atoms are weaker acceptors than N. The quantum chemical calculations show that both H and P in the OH···P hydrogen bond have partial positive charges, as expected from their electronegativities. However, the electrostatic potentials show a negative potential area on the electron density surface around P that facilitates formation of hydrogen bonds.

Fundamental and overtone vibrational spectroscopy, enthalpy of hydrogen bond formation and equilibrium constant determination of the methanol-dimethylamine complex

We have measured gas phase vibrational spectra of the bimolecular complex formed between methanol (MeOH) and dimethylamine (DMA) up to about 9800 cm(-1). In addition to the strong fundamental OH-stretching transition we have also detected the weak second overtone NH-stretching transition. The spectra of the complex are obtained by spectral subtraction of the monomer spectra from spectra recorded for the mixture. For comparison, we also measured the fundamental OH-stretching transition in the bimolecular complex between MeOH and trimethylamine (TMA). The enthalpies of hydrogen bond formation (ΔH) for the MeOH-DMA and MeOH-TMA complexes have been determined by measurements of the fundamental OH-stretching transition in the temperature range from 298 to 358 K. The enthalpy of formation is found to be -35.8 ± 3.9 and -38.2 ± 3.3 kJ mol(-1) for MeOH-DMA and MeOH-TMA, respectively, in the 298 to 358 K region. The equilibrium constant (Kp) for the formation of the MeOH-DMA complex has been determined from the measured and calculated transition intensities of the OH-stretching fundamental transition and the NH-stretching second overtone transition. The transition intensities were calculated using an anharmonic oscillator local mode model with dipole moment and potential energy curves calculated using explicitly correlated coupled cluster methods. The equilibrium constant for formation of the MeOH-DMA complex was determined to be 0.2 ± 0.1 atm(-1), corresponding to a ΔG value of about 4.0 kJ mol(-1).