Strong Negative Synergism of Ion Pair Extinction Coefficients in Chloroform–Acetone and Methylene Dichloride–Acetone Mixtures

2012 ◽  
Vol 22 (6) ◽  
pp. 320-322 ◽  
Author(s):  
Kirill P. Birin ◽  
Dmitry S. Dunin ◽  
Maxim V. Tolstykh ◽  
Vitalii Yu. Kotov
Keyword(s):  
Ion Pair ◽  
Extinction Coefficients ◽  
Methylene Dichloride

The effect of temperature on the optical spectra and the yields of solvated electrons and ion-pairs in amines

1978 ◽  
Vol 56 (6) ◽  
pp. 839-843 ◽  
Author(s):  
William Arthur Seddon ◽  
John Wallace Fletcher ◽  
Fred Charles Sopchyshyn
Keyword(s):  
Ion Pairs ◽  
Solvent Polarity ◽  
Solute Concentration ◽  
Ion Pair ◽  
Effect Of Temperature ◽  
Gradual Transition ◽  
Solvated Electron ◽  
Solvated Electrons ◽  
Extinction Coefficients ◽  
Yield Formula

Optical absorption spectra for the solvated electron, es−, and ion-pairs, (Na+, es−), have been observed in methylamine (MA), ethylamine (EA), and isopropylamine (IPA), at temperatures ranging from 184 to 338 K. Changes in the (Na+, es−) spectra, relative to es−, are consistent with a gradual transition in the ion-pair structure toward a more 'electron-like' entity with decreasing temperature and increasing solvent polarity. Extinction coefficients, εmax(es−) = 3.3 ± 0.2, 3.2 ± 0.5, and 3.2 ± 0.5 × 104 M−1 cm−1 in MA, EA, and IPA respectively. Corresponding values for the ion-pairs, εmax(Na+, es−) = 2.5 ± 0.2, 2.1 ± 0.2, and 1.9 ± 0.2 × 104 M−1 cm−1.In EA and IPA, the yield [Formula: see text] (molecules/100 eV) shows a marked solute concentration dependence. This is consistent with an empirical scavenging model from which the escaped solvated G(es−)esc and spur G(es−)spur electrons are estimated as G(es−)esc = 0.5 and 0.4, G(es−)spur = 1.8 and 1.4, giving G(es−)total = 2.3 and 1.8 in EA and IPA, respectively. In MA, [Formula: see text] = G(es−)esc = 2.25 ± 0.2, independent of solute concentration.

Flash photolysis of alkali metal anions in tetrahydrofuran and dimethoxyethane

1979 ◽  
Vol 57 (14) ◽  
pp. 1792-1800 ◽  
Author(s):  
W. A. Seddon ◽  
J. W. Fletcher ◽  
F. C. Sopchyshyn ◽  
E. B. Selkirk
Keyword(s):  
Pulse Radiolysis ◽  
Shape Function ◽  
Flash Photolysis ◽  
Ion Pairs ◽  
Ion Pair ◽  
Parent Metal ◽  
Initial Formation ◽  
Extinction Coefficients ◽  
Best Fit ◽  
Good Agreement

Flash photolysis of K−, Rb−, and Cs− in tetrahydrofuran (THF) produces the corresponding ion-pairs (K+, es−), (Rb+, es−), and (Cs+, es−), followed by the regeneration of the parent metal anion, M−. In mixed-metal solutions containing Na and M where M is K, Rb, or Cs, photolysis of Na− also forms the (M+, es−) ion-pair and M−, but with the latter then reforming Na− on an extended time scale. Similar results were obtained in dimethoxyethane (DME) at 213 K, but in this case with the initial formation of a loose ion-pair, (M+, es−)loose.Based on a Gaussian–Lorenztian shape function, the 'best-fit' optical bands for the (M+, es−) and M− species were used to simulate the experimental spectra and deduce the corresponding extinction coefficients in both solvents.The overall mechanism is complex but is in good agreement with previous interpretations deduced by pulse radiolysis.

National primary standard of air kerma, air kerma rate, exposure, exposure rate and energy flux for X-rays and gamma radiation GET 8-2019

2020 ◽  
pp. 8-12
Author(s):  
Alexandr V. Oborin ◽  
Anna Y. Villevalde ◽  
Sergey G. Trofimchuk
Keyword(s):  
Gamma Radiation ◽  
Energy Flux ◽  
Primary Standard ◽  
Average Energy ◽  
Ion Pair ◽  
X Rays ◽  
Exposure Rate ◽  
Ionization Chambers ◽  
Air Kerma ◽  
Air Kerma Rate

The results of development of the national primary standard of air kerma, air kerma rate, exposure, exposure rate and energy flux for X-rays and gamma radiation GET 8-2011 in 2019 are presented according to the recommendations of the ICRU Report No. 90 “Key Data for Ionizing-Radiation Dosimetry: Measurement Standards and Applications”. The following changes are made to the equations for the units determination with the standard: in the field of X-rays, new correction coefficients of the free-air ionization chambers are introduced and the relative standard uncertainty of the average energy to create an ion pair in air is changed; in the field of gamma radiation, the product of the average energy to create an ion pair in air and the electron stopping-power graphite to air ratio for the cavity ionization chambers is changed. More accurate values of the units reproduced by GET 8-2019 are obtained and new metrological characteristics of the standard are stated.

Extractive Spectrophotometric Method for the Determination of Glibenclamide by Ion-Pair Complex in Pure Form and Pharmaceutical Formulation

2019 ◽  
Vol 9 (o3) ◽  
Author(s):  
RUAA MUAYAD MAHMOOD ◽  
HAMSA MUNAM YASSEN ◽  
SAMAR , NAJWA ISSAC ABDULLA AHMED DARWEESH ◽  
NAJWA ISSAC ABDULLA
Keyword(s):  
Spectrophotometric Method ◽  
Molar Absorptivity ◽  
Ion Pair ◽  
Pharmaceutical Formulation ◽  
Ratio Method ◽  
Colored Complex ◽  
Colored Product ◽  
Method Of Continuous Variation ◽  
Job's Method

Simple, rapid and sensitive extractive spectrophotometric method is presented for the determination of glibenclamide (Glb) based on the formation of ion-pair complex between the Glb and anionic dye, methyl orange (MO) at pH 4. The yellow colored complex formed was quantitatively extracted into dichloromethane and measured at 426 nm. The colored product obeyed Beer’s law in the concentration range of (0.5-40) μg.ml-1. The value of molar absorptivity obtained from Beer’s data was found to be 31122 L.mol-1.cm-1, Sandell’s sensitivity value was calculated to be 0.0159 μg.cm-2, while the limits of detection (LOD) and quantification (LOQ) were found to be 0.1086 and 0.3292 μg.ml-1, respectively. The stoichiometry of the complex created between the Glb and MO was 1:1 as determined via Job’s method of continuous variation and mole ratio method. The method was successfully applied for the analysis of pharmaceutical formulation.

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.

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