MNDO Calculations as a valuable tool for structure evaluation of contact ion pairs

1992 ◽  
Vol 44 (4) ◽  
pp. 449-467 ◽  
Author(s):  
Z. Havlas ◽  
S. Nick ◽  
H. Bock
Keyword(s):  
Ion Pairs ◽  
Mndo Calculations ◽  
Structure Evaluation ◽  
Contact Ion Pairs

Ion Pairing and Dielectric Decrement in Glycosaminoglycan Brushes

2020 ◽  
Author(s):  
James Sterling ◽  
Wenjuan Jiang ◽  
Wesley M. Botello-Smith ◽  
Yun L. Luo
Keyword(s):  
Molecular Dynamics ◽  
Ion Pairs ◽  
Mean Field ◽  
Salt Bridge ◽  
Ion Pairing ◽  
Donnan Potential ◽  
Mean Field Models ◽  
Ion Exclusion ◽  
Dynamics Simulations ◽  
Contact Ion Pairs

Molecular dynamics simulations of hyaluronic acid and heparin brushes are presented that show important effects of ion-pairing, water dielectric decrease, and co-ion exclusion. Results show equilibria with electroneutrality attained through screening and pairing of brush anionic charges by cations. Most surprising is the reversal of the Donnan potential that would be expected based on electrostatic Boltzmann partitioning alone. Water dielectric decrement within the brush domain is also associated with Born hydration-driven cation exclusion from the brush. We observe that the primary partition energy attracting cations to attain brush electroneutrality is the ion-pairing or salt-bridge energy associated with cation-sulfate and cation-carboxylate solvent-separated and contact ion pairs. Potassium and sodium pairing to glycosaminoglycan carboxylates and sulfates consistently show similar abundance of contact-pairing and solvent-separated pairing. In these crowded macromolecular brushes, ion-pairing, Born-hydration, and electrostatic potential energies all contribute to attain electroneutrality and should therefore contribute in mean-field models to accurately represent brush electrostatics.

Reversible fluorescent and colorimetric rhodamine based-chemosensor of Cu 2+ contact ion-pairs using a ditopic receptors

2015 ◽  
Vol 123 ◽  
pp. 204-211 ◽  
Author(s):  
Chatthai Kaewtong ◽  
Buncha Pulpoka ◽  
Thawatchai Tuntulani
Keyword(s):  
Ion Pairs ◽  
Ditopic Receptors ◽  
Contact Ion Pairs

scholarly journals Interactions of Na+ Cations with a Highly Charged Fatty Acid Langmuir Monolayer: Molecular Description of the Phase Transition

2019 ◽  
Author(s):  
Adrien Sthoer ◽  
Eric Tyrode
Keyword(s):  
Phase Transition ◽  
Surface Charge ◽  
Surface Potential ◽  
Arachidic Acid ◽  
Ion Pairs ◽  
Theoretical Models ◽  
Langmuir Monolayer ◽  
Vibrational Sum Frequency Spectroscopy ◽  
Ion Size ◽  
Contact Ion Pairs

Vibrational sum frequency spectroscopy has been used to study the molecular properties upon compression of a highly charged arachidic acid Langmuir monolayer, which displays a first order phase transition plateau in the surface pressure - molecular area (p-A) isotherm. By targeting vibrational modes from the carboxylic acid headgroup, alkyl chain, and interfacial water molecules, information regarding the surface charge, surface potential, type of ion pair formed, and conformational order of the monolayer could be extracted. The monolayer in the liquid expanded phase is found to be fully charged until reaching the 2D-phase transition plateau, where partial reprotonation, as well as the formation of COO⎺ Na<sup>+ </sup>contact-ion pairs, start to take place. In the condensed phase after the transition, three headgroup species, mainly hydrated COO⎺, COOH, and COO⎺ Na<sup>+ </sup>contact-ion pairs could be identified and their proportions quantified. Comparison with theoretical models shows that despite the low ionic strengths used (i.e. 10 mM), the predictions from the Gouy Chapman model are only adequate for the lowest surface densities, when the surface charge does not exceed -0.1 C/m<sup>2</sup>. In contrast, a modified Poisson-Boltzmann (MPB) model that accounts for the steric effects associated with the finite ion-size, captures many of the experimental observables, including the partial reprotonation, and surface potential changes upon compression. The agreement highlights the importance of hydronium ion – carboxylate interactions, as well as the layer of sodium ions packed at the steric limit, for explaining the phase transition behavior. The MPB model, however, does not explicitly consider the formation of contact ion pairs with the sodium counterion. The experimental results provide a quantitative molecular insight that could be used to test potential extensions to the theory.

Elektronentransfer und Ionenpaare, 15 [ 1– 3] Radikalanion und Radikal-Kontakt-Ionenpaare von Dimesityl-tetraketon / Electron Transfer and Ion Pairing, 15 [1-3] Radical Anion and Radical Ion Pairs of Dimesityl Tetraketone

1990 ◽  
Vol 45 (8) ◽  
pp. 1197-1204 ◽  
Author(s):  
H. Bock ◽  
P. Hänel ◽  
H.-F. Herrmann
Keyword(s):  
Electron Transfer ◽  
Radical Anion ◽  
Ion Pairs ◽  
Ion Pairing ◽  
Single Electron ◽  
Single Electron Transfer ◽  
Temperature Dependent ◽  
Contact Ion Pairs

The radical anion of dimesityltetraketone (ERed, I = -0.40 V) is easily generated in THF by potassium mirror/[2.2.2]-cryptand reduction. Its contact ion pairs with Na⊕, Cs⊕ and Ba⊕⊕ counter cations, prepared in THF solution by single electron transfer from the respective metals, are characterized by their ESR/ENDOR spectra, which exhibit temperature-dependent metal couplings of aNa⊕ = 0.061 mT (190 K), aCs⊕ = 0.021 mT (190 K), and aBa⊕⊕ = 0.145 mT (295 K).

Molecular Dynamics Simulations of the Conductivity of Aqueous NaCl in the Presence of Sucrose and Electric Fields

2014 ◽  
Vol 937 ◽  
pp. 200-206
Author(s):  
Xiao Gang Li ◽  
Shu Ai Yang ◽  
Ming Jun Tang ◽  
Jing Lei ◽  
Hui Hu ◽  
...  
Keyword(s):  
Molecular Dynamics ◽  
Molecular Dynamics Simulations ◽  
Electric Fields ◽  
Ion Pairs ◽  
Water Molecules ◽  
Flashover Voltage ◽  
Low Humidity ◽  
Natural Contamination ◽  
Dynamics Simulations ◽  
Contact Ion Pairs

Various natural contamination components distributed on the surface of high-voltage insulators play important roles on the flashover hazard. Under the low humidity condition, the flashover voltage could be affected considerably by the sucrose contaminations. Molecular dynamics simulations have been carried out in order to reveal the microscopic mechanisms for the sucrose-involved flashover uptake. It is found that the diffusion of ions decreases significantly and thus the conductivity of aqueous medium is lowered apparently. In the presence of sucrose, the contact ion pairs formed between Na+ and Cl- ions are enhanced because both ions are less coordinated to water molecules. The influence of the external electric fields on the diffusion and conductivity were investigated as well. It is suggested that the sucrose contamination might lead to the uneven electric fields on the insulator surface.

scholarly journals Contact Ion Pairs on a Protonated Azamacrocycle: the Role of the Anion Basicity

2016 ◽  
Vol 27 (4) ◽  
pp. 615-621 ◽  
Author(s):  
Caterina Fraschetti ◽  
Antonello Filippi ◽  
Maria Elisa Crestoni ◽  
Enrico Marcantoni ◽  
Marco Glucini ◽  
...  
Keyword(s):  
Ion Pairs ◽  
Contact Ion Pairs
Sign in / Sign up

Export Citation Format

Share Document