Synthesis, Structure, and Ion Pair Dynamics of β-Diketiminato-Supported Organoscandium Contact Ion Pairs

2005 ◽  
Vol 24 (6) ◽  
pp. 1173-1183 ◽  
Author(s):  
Paul G. Hayes ◽  
Warren E. Piers ◽  
Masood Parvez
Keyword(s):  
Ion Pairs ◽  
Ion Pair ◽  
Contact Ion Pairs

scholarly journals When spectroscopy fails: The measurement of ion pairing

2006 ◽  
Vol 78 (8) ◽  
pp. 1571-1586 ◽  
Author(s):  
Glenn Hefter
Keyword(s):  
Metal Ion ◽  
Chemical Speciation ◽  
Ion Pairs ◽  
Ion Association ◽  
Ion Pair ◽  
Association Constants ◽  
Spectroscopic Techniques ◽  
Association Equilibria ◽  
Solvent Molecules ◽  
Contact Ion Pairs

Spectroscopic techniques such as UV/vis, NMR, and Raman are powerful tools for the investigation of chemical speciation in solution. However, it is not widely recognized that such techniques do not always provide reliable information about ion association equilibria. Specifically, spectroscopic measurements do not in general produce thermodynamically meaningful association constants for non-contact ion pairs, where the ions are separated by one or more solvent molecules. Such systems can only be properly quantified by techniques such as dielectric or ultrasonic relaxation, which can detect all ion-pair types (or equilibria), or by traditional thermodynamic methods, which detect the overall level of association. Various types of quantitative data are presented for metal ion/sulfate systems in aqueous solution that demonstrate the inadequacy of the major spectroscopic techniques for the investigation of systems that involve solvent-separated ion pairs. The implications for ion association equilibria in general are briefly discussed.

scholarly journals Aqueous Contact Ion Pairs of Phosphate Groups with Na+, Ca2+ and Mg2+ – Structural Discrimination by Femtosecond Infrared Spectroscopy and Molecular Dynamics Simulations

2020 ◽  
Vol 234 (7-9) ◽  
pp. 1453-1474 ◽  
Author(s):  
Benjamin P. Fingerhut ◽  
Jakob Schauss ◽  
Achintya Kundu ◽  
Thomas Elsaesser
Keyword(s):  
Ion Pairs ◽  
Model System ◽  
Ion Pair ◽  
Pair Formation ◽  
Phosphate Group ◽  
Phosphate Ion ◽  
2D Ir ◽  
Dna And Rna ◽  
Contact Ion Pairs ◽  
Phosphate Groups

AbstractThe extent of contact and solvent shared ion pairs of phosphate groups with Na+, Ca2+ and Mg2+ ions in aqueous environment and their relevance for the stability of polyanionic DNA and RNA structures is highly debated. Employing the asymmetric phosphate stretching vibration of dimethyl phosphate (DMP), a model system of the sugar-phosphate backbone of DNA and RNA, we present linear infrared, femtosecond infrared pump-probe and absorptive 2D-IR spectra that report on contact ion pair formation via the presence of blue shifted spectral signatures. Compared to the linear infrared spectra, the nonlinear spectra reveal contact ion pairs with increased sensitivity because the spectra accentuate differences in peak frequency, transition dipole moment strength, and excited state lifetime. The experimental results are corroborated by long time scale MD simulations, benchmarked by density functional simulations on phosphate-ion-water clusters. The microscopic interpretation reveals subtle structural differences of ion pairs formed by the phosphate group and the ions Na+, Ca2+ and Mg2+. Intricate properties of the solvation shell around the phosphate group and the ion are essential to explain the experimental observations. The present work addresses a challenging to probe topic with the help of a model system and establishes new experimental data of contact ion pair formation, thereby underlining the potential of nonlinear 2D-IR spectroscopy as an analytical probe of phosphate-ion interactions in complex biological systems.

ESR- und ENDOR-Untersuchungen von p-Benzosemichinon-Diarylthallium-Ionenpaaren / ESR- and ENDO R-Investigations of p-Benzosemiquinone-Diarylthallium Ion Pairs

1984 ◽  
Vol 39 (10) ◽  
pp. 1416-1424 ◽  
Author(s):  
Hartmut B. Stegmann ◽  
Karl B. Ulmschneider ◽  
Paul Schuler ◽  
Thomas Jülich ◽  
Klaus Scheffler
Keyword(s):  
Ion Pairs ◽  
Organometallic Compounds ◽  
Ion Pair ◽  
Coupling Constants ◽  
Paramagnetic Species ◽  
Contact Ion Pair ◽  
Basic Solutions ◽  
G Value ◽  
Contact Ion Pairs ◽  
Doublet Splitting

Diarylthallium hydroxides react very smoothly in organic solvents with hydroquinones to stable paramagnetic complexes. This reaction has been investigated with two ligands and several organometallic compounds in 8 different solvents. In basic solutions clearly two paramagnetic species can be detected by ESR spectroscopy. One component exhibits a large doublet splitting assigned to the thallium counterion and the second radical does not show any metal coupling. The relative concentrations of both radicals depend strongly on the solvent and the temperature. Therefore, a slow equilibrium betw een a contact ion pair and a solvent separated ion pair is assumed. The thermodynamic parameters are determined to ⊿H = 0.8 kcal/mol, ⊿G293 = -0.1 kcal/mol, ⊿S = 3.04 cl/mol. The proton and thallium coupling constants as well as the g-value of the contact ion pair show a rem arkable temperature dependence. The signs of proton splitting constants are determined by ENDOR-TRIPLE investigations. The change of the electronic structure of the radical anion by formation of a contact ion pair is discussed. For interpretation of these results we assumed a fast equilibrium between different conformations of the contact ion pair according to behaviour of comparable aroxyl radicals. Therefore, the systems investigated allow a simultaneous observation of solvent separated and different contact ion pairs.

Ion-ion-solvent interactions in solution. Aqueous solutions of nitrates of cations from Groups 2A and 3A

1982 ◽  
Vol 35 (9) ◽  
pp. 1793 ◽  
Author(s):  
DW James ◽  
RL Frost
Keyword(s):  
Aqueous Solutions ◽  
Ion Pairs ◽  
Ion Pair ◽  
Band Shape ◽  
Nitrate Ion ◽  
Solvent Interactions ◽  
Contact Ion Pair ◽  
Component Band ◽  
Association Equilibria ◽  
Contact Ion Pairs

Association equilibria in aqueous solutions of the salts Be(NO3)2, Ca(NO3)2 Sr(NO3)2, Ba(NO3)2 and Al(NO3)3 have been studied through band shape and component band analysis of the non-degenerate, Raman-active V1 vibrational band of the nitrate ion. Band contributions due to the aquated nitrate ion, solvent-separated ion pair, and contact ion pair were made for all salts. The nature of the contact ion pair was shown to be different in the presence of Be2+ and Al3+ from that seen for the other salts. This difference was associated with a strongly directional perturbation of the nitrate ion. For all salts the solvent-separated ion pair species was present in the lowest concentration solution studied (as low as 0.05 M). At intermediate concentrations the solvent separated ion pair species was the dominant solution species while at the higher concentrations the species with anion and cation in contact becomes appreciable. For solutions of Ca(NO3)2 some evidence for a more extensive ion aggregate was found at the highest concentration (5M). Equilibrium quotients calculated from the spectroscopic components are in reasonable agreement with previous values determined by equilibrium and transport measurements, and it is suggested that these previous determinations detected the presence of solvent-separated ion pairs rather than 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.

Stereospecific 1,3-H Transfer of Indenols Proceeds via Persistent Ion-Pairs Anchored By NH···Pi Interactions

2018 ◽  
Author(s):  
David Ascough ◽  
Fernanda Duarte ◽  
Robert Paton
Keyword(s):  
Computational Analysis ◽  
Ion Pairs ◽  
Ion Pair ◽  
Hydrogen Atom Transfer ◽  
Polar Solvents ◽  
Chirality Transfer ◽  
Activation Barriers ◽  
Sense And Avoid ◽  
Phase Dynamics ◽  
Pi Interactions

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.

scholarly journals Tripodal, Squaramide-Based Ion Pair Receptor for Effective Extraction of Sulfate Salt

Molecules ◽  
2021 ◽  
Vol 26 (9) ◽  
pp. 2751
Author(s):  
Damian Jagleniec ◽  
Marcin Wilczek ◽  
Jan Romański
Keyword(s):  
Ion Pairs ◽  
Binding Mode ◽  
Selective Extraction ◽  
Ion Pair ◽  
Hofmeister Series ◽  
Sulfate Salt ◽  
Lower Affinity ◽  
High Affinity ◽  
Binding Domains ◽  
Hydrated Sulfate

Combining three features—the high affinity of squaramides toward anions, cooperation in ion pair binding and preorganization of the binding domains in the tripodal platform—led to the effective receptor 2. The lack of at least one of these key elements in the structures of reference receptors 3 and 4 caused a lower affinity towards ion pairs. Receptor 2 was found to form an intramolecular network in wet chloroform, which changed into inorganic–organic associates after contact with ions and allowed salts to be extracted from an aqueous to an organic phase. The disparity in the binding mode of 2 with sulfates and with other monovalent anions led to the selective extraction of extremely hydrated sulfate anions in the presence of more lipophilic salts, thus overcoming the Hofmeister series.

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
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