Structure and stability of ion pairs A?�K+�H2O with a strong anion

1992 ◽  
Vol 41 (12) ◽  
pp. 2137-2142
Author(s):  
A. M. Kariev ◽  
A. A. Ovchinnikov
1980 ◽  
Vol 77 ◽  
pp. 759-768 ◽  
Author(s):  
R. Stephen Berry
Keyword(s):  

2020 ◽  
Author(s):  
James Sterling ◽  
Wenjuan Jiang ◽  
Wesley M. Botello-Smith ◽  
Yun L. Luo

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.


2018 ◽  
Author(s):  
David Ascough ◽  
Fernanda Duarte ◽  
Robert Paton

The base-catalyzed rearrangement of arylindenols is a rare example of a suprafacial [1,3]-hydrogen atom transfer. The mechanism has been proposed to proceed via sequential [1,5]-sigmatropic shifts, which occur in a selective sense and avoid an achiral intermediate. A computational analysis using quantum chemistry casts serious doubt on these suggestions: these pathways have enormous activation barriers and in constrast to what is observed experimentally, they overwhelmingly favor a racemic product. Instead we propose that a suprafacial [1,3]-prototopic shift occurs in a two-step deprotonation/reprotonation sequence. This mechanism is favored by 15 kcal mol<sup>-1</sup> over that previously proposed. Most importantly, this is also consistent with stereospecificity since reprotonation occurs rapidly on the same p-face. We have used explicitly-solvated molecular dynamics studies to study the persistence and condensed-phase dynamics of the intermediate ion-pair formed in this reaction. Chirality transfer is the result of a particularly resilient contact ion-pair, held together by electrostatic attraction and a critical NH···p interaction which ensures that this species has an appreciable lifetime even in polar solvents such as DMSO and MeOH.


2020 ◽  
Author(s):  
Swati Arora ◽  
Julisa Rozon ◽  
Jennifer Laaser

<div>In this work, we investigate the dynamics of ion motion in “doubly-polymerized” ionic liquids (DPILs) in which both charged species of an ionic liquid are covalently linked to the same polymer chains. Broadband dielectric spectroscopy is used to characterize these materials over a broad frequency and temperature range, and their behavior is compared to that of conventional “singly-polymerized” ionic liquids (SPILs) in which only one of the charged species is attached to the polymer chains. Polymerization of the DPIL decreases the bulk ionic conductivity by four orders of magnitude relative to both SPILs. The timescales for local ionic rearrangement are similarly found to be approximately four orders of magnitude slower in the DPILs than in the SPILs, and the DPILs also have a lower static dielectric constant. These results suggest that copolymerization of the ionic monomers affects ion motion on both the bulk and the local scales, with ion pairs serving to form strong physical crosslinks between the polymer chains. This study provides quantitative insight into the energetics and timescales of ion motion that drive the phenomenon of “ion locking” currently under investigation for new classes of organic electronics.</div>


Author(s):  
Rohan Aggarwal ◽  
Monika Targhotra ◽  
Bhumika Kumar ◽  
P.K Sahoo ◽  
Meenakshi K Chauhan

In the past few years gene delivery system has gained a huge attention owing to its proved efficacy in several diseases especially in those caused by genetic and/oroncological malfunctioning. The effective gene delivery mainly depends on the carrier molecules that can ensure the safe and specific delivery of the nucleic acidmolecules. Viral vectors have been used for a longer period as the gene transfer vehicle. However, these viral vectors have potential immunological disadvantages that made them less preferred. Recently, non-viral vectors such as polyplexes have emerged as a promising alternative for viral vectors. Polyplexes are formed by conjugating a polymer with DNA and in maximum cases the cationic polymers are preferred over others. The structure and stability of the polyplexes depends on various factors. The ability of the polymer to condense the DNA mainly dictates the efficiency of the polyplex mediated transfection. In this review we are going to provide a framework for the synthesis and design of the polyplexes along with the structure and stability of the complexes pertaining to mechanism of action, characterization and therapeutic application, including polyethyleneimine mediated cytotoxicity as well as newer strategies for the generation of better polyplexes.


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