Minimal Optimized Effective Potentials for Density Functional Theory Studies on Excited-State Proton Dissociation

Recently, a new method [P. Partovi-Azar and D. Sebastiani, J. Chem. Phys. 152, 064101 (2020)] was proposed to increase the efficiency of proton transfer energy calculations in density functional theory by using the T1 state with additional optimized effective potentials instead of calculations at S1. In this work, we focus on proton transfer from six prototypical photoacids to neighboring water molecules and show that the reference proton dissociation curves obtained at S1 states using time-dependent density functional theory can be reproduced with a reasonable accuracy by performing T1 calculations at density functional theory level with only one additional effective potential for the acidic hydrogens. We also find that the extra effective potentials for the acidic hydrogens neither change the nature of the T1 state nor the structural properties of solvent molecules upon transfer from the acids. The presented method is not only beneficial for theoretical studies on excited state proton transfer, but we believe that it would also be useful for studying other excited state photochemical reactions.

Dynamics of diffractive dissociation

We describe a QCD based model which incorporates the main properties of the inclusive particle distributions expected for diffractive processes, including the diffractive dissociation at high energies. We study, in turn, the total cross section, $$\sigma _\mathrm{tot}$$ σ tot , the differential elastic, $$d\sigma _\mathrm{el}/dt$$ d σ el / d t , cross section, the dependence of the single proton dissociation cross section, $$\xi d\sigma ^\mathrm{SD}/d\xi $$ ξ d σ SD / d ξ , on the momentum fraction, $$\xi =1-x_L$$ ξ = 1 - x L , lost by the leading proton, the multiplicity distributions in inelastic (non-diffractive) collisions and in the processes of dissociation. Besides this we calculate the mean transverse momenta of the ‘wee partons’ (secondaries) produced in the case of dissociation (that is in the processes with a large rapidity gap) and compare it with that in inelastic interactions.

Hydration and Proton Transfer Processes in Sulfonated Nata De Coco Membrane with Density Functional Theory

Direct Methanol Fuel Cells (DMFCs) is one of the most promising alternative energy resources to meet human energy needs. DMFCs is fuel cells that use polymer membranes as the electrolytes to transfer the protons from anode to cathode. The characteristics of those two types of membranes in ion exchange capacity (IEC) and degree of swelling (swelling) have shown a very important role of water in the proton transfer. However, the mechanism of interaction between the repeating units of the polymer with water molecules has not been studied in depth. Computational methods can be used to study such interactions as well as the transfer of protons. To examine the transfer of protons in the membrane, studies of computing via electronic structure calculations, geometry optimization, interaction inter/intra molecular, as well as the hydration process and transfer of protons in the sulfonated nata-de-coco membranes (NDCS) has been conducted in this work. All calculations were performed using DFT with B3LYP functional and basis set 6-311G(d). The repeating units of the membranes were optimized (n=1,2,...,5), to obtain the structure with minimum energy. The optimized structure was then interacted with one water molecule in the same position to study the effect of chain length on its interaction strength with water molecules. The thermodynamic and proton dissociation parameters was calculated by adding n water molecules (n=1,2, …,10) to determine the hydration process and the proton transfer on the membranes. The calculations showed that for interactions with water, the polymer structure in NDCS can be represented/modeled by two repeating units. Therefore, the hydration process and transfer of protons in the membranes were studied by adding n water molecules gradually into the two repeating units. The results showed that the proton dissociation process in NDCS membrane started with the addition of two molecules of water. The presence of water molecules promoted the proton dissociation in the -SO3H groups to form SO3- and H3O+ ions, which further formed Zundel ions and Eigen ions. The energy profile of proton transfer showed that the barrier energy was 58.13 kcal/mol for NDCS-5(H2O). Its thermodynamic parameters, the calculation showed that the interaction energy (ΔE), the enthalpy change (ΔH) and the Gibbs free energy (ΔG) to its interaction with n water molecules (n=1,2,…,10) in NDCS are getting more negative. This indicated that the interaction with water molecule is stronger. So, based on these results, it can be concluded that the computational calculations using DFT method at B3LYP functional and 6-311G(d) basis set can be used to describe the process of hydration and proton transfer in the interactions in the polymer electrolyte membrane (NDCS membrane)

Degradation effect on proton dissociation and transfer in perfluorosulfonic acid membranes

In the operation of proton exchange membrane fuel cells (PEMFCs), the ionomer- perfluorosulfonic acid (PSFA) membrane side chains are easily attacked by free radicals, resulting in the membrane degradation. In...

Tuning proton dissociation energy in proton carrier doped 2D covalent organic frameworks for anhydrous proton conduction at elevated temperature

The proton dissociation degrees and dielectric properties of proton carriers doped COFs with neutral, polar, Lewis base and positively charged sites are investigated to get better understanding of structure–conductivity relationship.

Microwave-Assisted Synthesis, Proton Dissociation Processes, and Anticancer Evaluation of Novel D-Ring-Fused Steroidal 5-Amino-1-Arylpyrazoles

Taking into account the pharmacological relevance of heterocycle-fused natural steroids, the objective of the current study was to develop a multistep reaction sequence for the efficient synthesis of novel D-ring-condensed 5-amino-1-arylpyrazoles from dehydroepiandrosterone (DHEA). A condensation reaction of 16-formyl-DHEA with hydroxylamine afforded the corresponding oxime, which was demonstrated to be stable in one of its cyclic isoxazoline forms due to possible ring-chain tautomerism. The subsequent base-induced dehydration to a diastereomeric β-ketonitrile, followed by microwave-assisted heterocyclization with different arylhydrazines led to the desired pyrazoles. The generally good yields of the products depended slightly on the electronic character of the substituent present on the aromatic ring of the reagent. The proton dissociation processes of the DHEA-derived heterocycles were investigated in aqueous solution by UV-visible spectrophotometric titrations to reveal their actual chemical forms at physiological pH. The determined pKa values attributed to the pyrazole NH+ moiety were low (1.8–4.0) and varied by the different substituents of the benzene ring. The antiproliferative effects of the structurally similar compounds were screened in vitro on human cancer cells (namely on HeLa, U2Os, MCF-7, PC-3, and A549), along with a noncancerous cell line (MRC-5). The IC50 values of the most active derivative were determined on all cell lines.