Proton Transfer vs Complex Formation Channels in Ionized Formic Acid Dimer: A Direct Ab Initio Molecular Dynamics Study

2020 ◽  
Vol 124 (16) ◽  
pp. 3048-3054 ◽  
Author(s):  
Hiroto Tachikawa
Keyword(s):  
Molecular Dynamics ◽  
Complex Formation ◽  
Proton Transfer ◽  
Formic Acid ◽  
Ab Initio ◽  
Ab Initio Molecular Dynamics

AN AB INITIO MOLECULAR DYNAMICS STUDY ON THE SOLVATION OF FORMATE ION AND FORMIC ACID IN WATER

2012 ◽  
Vol 11 (05) ◽  
pp. 1019-1032 ◽  
Author(s):  
QIUBO CHEN ◽  
ZHIFENG LIU ◽  
CHEE HOW WONG
Keyword(s):  
Molecular Dynamics ◽  
Formic Acid ◽  
Ab Initio ◽  
Thermal Dissociation ◽  
Ab Initio Molecular Dynamics ◽  
Water Molecules ◽  
Hydrogen Bond Interaction ◽  
Acidic Dissociation ◽  
Partial Dissociation ◽  
Dynamics Simulations

Formate ion and formic acid are linked in water by the equilibrium for the acidic dissociation of formic acid, which as the simplest carboxylic acid is an important model system. In this study, the microscopic details of the solvation around a formate ion and around a formic acid molecule in aqueous solution are explored by ab initio molecular dynamics simulations, at 300, 500, 700, and 900 K. The formate ion exerts a strong influence on the surrounding solvent molecules by hydrogen bonding, which restricts the access of other water molecules. With rising temperature, the hydrogen bonds are disrupted, and the space around formic acid becomes more accessible. Solvation of the formic acid is marked by its partial dissociation to produce a proton, and the hydrogen bond interaction around a formic acid is not as strong as that around a formate ion. The acidic dissociation becomes less favorable as temperature rises, which indicates a lesser catalytic role for the water molecules in the thermal dissociation of formic acid.

scholarly journals Proton Transfer from a Photoacid to Water: First Principles Simulations and Fast Fluorescence Spectroscopy

2021 ◽  
Author(s):  
Alice R. Walker ◽  
Boning Wu ◽  
Jan Meisner ◽  
Michael D. Fayer ◽  
Todd J. Martinez
Keyword(s):  
Molecular Dynamics ◽  
Excited State ◽  
Fluorescence Spectroscopy ◽  
Proton Transfer ◽  
Ab Initio ◽  
Time Constant ◽  
Emission Wavelength ◽  
Ab Initio Molecular Dynamics ◽  
Long Distance ◽  
Hydrogen Bonded

Proton transfer reactions are ubiquitous in chemistry, especially in aqueous solutions. We investigate photo-induced proton transfer between the photoacid 8-hydroxypyrene-1,3,6- trisulfonate (HPTS) and water using fast fluorescence spectroscopy and ab initio molecular dynamics simulations. Photo-excitation causes rapid proton release from the HPTS hydroxyl. Previous experiments on HPTS/water described the progress from photoexcitation to proton diffusion using kinetic equations with two time constants. The shortest time constant has been interpreted as protonated and photoexcited HPTS evolving into an “associated” state, where the proton is “shared” between the HPTS hydroxyl and an originally hydrogen bonded water. The longer time constant has been interpreted as indicating evolution to a “solvent separated” state where the shared proton undergoes long distance diffusion. In this work, we refine the previous experimental results using very pure HPTS. We then use excited state ab initio molecular dynamics to elucidate the detailed molecular mechanism of aqueous excited state proton transfer in HPTS. We find that the initial excitation results in rapid rearrangement of water, forming a strong hydrogen bonded network (a “water wire”) around HPTS. HPTS then deprotonates in ≤3 ps, resulting in a proton that migrates back and forth along the wire before localizing on a single water molecule. We find a near linear relationship between emission wavelength and proton-HPTS distance over the simulated time scale, suggesting that emission wavelength can be used as a ruler for proton distance. Our simulations reveal that the “associated” state corresponds to a water wire with a mobile proton and that the diffusion of the proton away from this water wire (to a generalized “solvent-separated” state) corresponds to the longest experimental time constant.

Effect of anion reorientation on proton mobility in the solid acids family CsHyXO4 (X = S, P, Se, y = 1, 2) from ab initio molecular dynamics simulations

2020 ◽  
Vol 22 (19) ◽  
pp. 10738-10752 ◽  
Author(s):  
Christian Dreßler ◽  
Daniel Sebastiani
Keyword(s):  
Molecular Dynamics ◽  
High Temperature ◽  
Proton Transfer ◽  
Ab Initio ◽  
Solid Acids ◽  
Ab Initio Molecular Dynamics ◽  
Proton Mobility ◽  
Transfer Rates ◽  
High Proton ◽  
Dynamics Simulations

The high temperature phases of the solid acids CsHSeO4, CsHSO4 and CsH2PO4 show extraordinary high proton conductivities, which are enabled by the interplay of high proton transfer rates and frequent anion reorientation.

Direct ab initio molecular dynamics study of the two photodissociation channels of formic acid

2005 ◽  
Vol 308 (3) ◽  
pp. 325-334 ◽  
Author(s):  
Yuzuru Kurosaki ◽  
Keiichi Yokoyama ◽  
Yoshiaki Teranishi
Keyword(s):  
Molecular Dynamics ◽  
Formic Acid ◽  
Ab Initio ◽  
Ab Initio Molecular Dynamics

scholarly journals Ab initio molecular dynamics studies of formic acid dimer colliding with liquid water

2018 ◽  
Vol 20 (36) ◽  
pp. 23717-23725 ◽  
Author(s):  
Vesa Hänninen ◽  
Garold Murdachaew ◽  
Gilbert M. Nathanson ◽  
R. Benny Gerber ◽  
Lauri Halonen
Keyword(s):  
Molecular Dynamics ◽  
Density Functional Theory ◽  
Formic Acid ◽  
Ab Initio ◽  
Molecular Dynamics Simulations ◽  
Liquid Water ◽  
Density Functional ◽  
Ab Initio Molecular Dynamics ◽  
Functional Theory ◽  
Dynamics Simulations

Ab initio molecular dynamics simulations of formic acid (FA) dimer colliding with liquid water at 300 K have been performed using density functional theory.

Solid-state proton conduction: An ab initio molecular dynamics investigation of ammonium perchlorate doped with neutral ammonia

2004 ◽  
Vol 76 (1) ◽  
pp. 49-61 ◽  
Author(s):  
L. Rosso ◽  
M. E. Tuckerman
Keyword(s):  
Molecular Dynamics ◽  
Proton Transfer ◽  
Ab Initio ◽  
Ammonium Perchlorate ◽  
Direct Evidence ◽  
Orthorhombic Phase ◽  
Ab Initio Molecular Dynamics ◽  
Cubic Phase ◽  
Diffusion Constants ◽  
Lower Frequency Region

The charge-transport mechanism in solid ammonium perchlorate crystal exposed to an ammonia-rich environment is studied using ab initio molecular dynamics. Ammonium perchlorate is an ionic crystal composed of NH4+ and ClO4- ; units that possesses an orthorhombic phase at T < 513 K and a cubic phase at T > 513 K. Exposure to an ammonia-rich atmosphere allows ammonia molecules to be absorbed into the crystal at interstitial sites. It has been proposed that these neutral ammonias can form short-lived N2H7+ complexes with the NH4+ ions allowing proton transfer between them, thereby enhancing the conductivity considerably. To date, however, there has been no direct evidence of this proposed mechanism. In this paper, ab initio molecular dynamics techniques are employed to explore this mechanism. By comparing computed infrared spectra of the pure and ammonia-doped crystals, we observe a significant broadening of the NH stretch peak into a lower frequency region, indicating through an experimentally verifiable observable, the formation of hydrogen bonds between NH3 and NH4+ units. This suggestion is confirmed by direct observation of N2H7+ complexes from the trajectory. Comparison of the diffusion constants of NH4+ in the pure and doped crystals yields a ratio that is comparable to the experimentally measured conductivity ratio and clearly shows an enhanced positive charge mobility. Finally, compelling evidence suggesting the possibility of an ammonia umbrella inversion following proton transfer from NH4+ and NH3 is obtained.

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