Association constants and distribution functions for ion pairs in binary solvent mixtures: Application to a cyanine dye system

Abstract

The computations of the association constants K(ass) were performed at the microscopic level for the ion pair Cy(+)I(-) composed of the complex cyanine dye cation Cy(+) coupled to the negative iodine counterion. The wide array of K(ass) values is arranged by a variation of the composition of the binary solvent mixtures toluene/dimethylsulfoxide with the accompanying change of the solvent polarity. The potentials of mean force (PMFs) are calculated for a set of interionic separations R in the Cy(+)I(-) by a methodology which combines the quantum-chemical techniques for the treatment of the electronic structure of the Cy(+)I(-) system with the recent dielectric continuum approach which accounts for the solvation effects. For a given solute/solvent system the probability function P(R), which describes the distribution of interionic separations, is constructed in terms of the PMFs and implemented for the evaluation of the K(ass).

Counterion-Mediated Crossing of the Cyanine Limit in Crystals and Fluid Solution: Bond Length Alternation and Spectral Broadening Unveiled by Quantum Chemistry

“…A closer inspection of MD trajectories in DCM, starting from an ion pair structure, confirms the existence of such a stable conformer, which, however, has small residence times, especially at room temperature (Figure S9). Moreover, it was shown earlier that the interaction potentials of cyanine ion pairs become strongly destabilized with increasing solvent polarity , and significantly flatter; in fact, from MP2 calculations (which describe electrostatic interactions well), the dissociation energy is in the range of the thermal energy under ambient conditions so that effective dissociation in the more polar DCM environment can be safely assumed. For these reasons, the following (TD)­DFT calculations in DCM were made only for cyanine cation 1 ⊕ .…”

RM1 Semiempirical Model: Chemistry, Pharmaceutical Research, Molecular Biology and Materials Science

“…Energetic properties of organic compounds can be calculated in both forms: isolated, and in solvent medium. The solvent effects on the RM1 energetic properties of organic compounds 77,100,101,[105][106][107][108]122,123,[125][126][127]133,134 have been calculated, for example, by using the COSMO polarizable continuum model. 135 Another important aspect of RM1 is the easiness to perform the calculations.…”

“…A conclusion of this investigation was that the use of energy theoretical values provides a valuable criterion to characterize thermal hazards. 117 E n e r g e t i c p r o p e r t i e s o f o r g a n i c compounds 98,100,[107][108][109]112,113,116,[118][119][120][121][122] are very important to find the most favorable structure. As previously noted, RM1 semiempirical method was employed to evaluate conformer possibilities of organic compounds, such as: arylazo phosphate dimer; 87 (1R,2R,6S)-3-methyl-6-(1-methylethenyl)cyclohex-3-ene-1,2-diol; 86 isomeric carbocations 9,9-dimethyl-10-R-and 9-R-9,10-dimethylphenanthrenyl, as well as of 3-R-2,3-diphenylbutan-2-yl and 1-R-2-methyl-1,2-diphenylpropan-1-yl cations; 80 2,5-dihydropyridazine-4-carboxylate and 1,4-dihydropyridazine-3,5-dicarboxylate derivatives; 73 aurones synthesized by intramolecular cyclization of monobrominated (+)-usninic acid; 72 substituted cryptophane derivatives; 69 nitrogencontaining derivatives of (18α,19β)-19-hydroxy-2,3-secooleanane-2,3,28-trioic acid 28,19-lactone; 68 aryl and alkyl chlorophosphates; 67 spirocyclic nitroxides of 2,5-dihydroimidazole compounds; 66 lyoniresinol stereoisomers; 95 and 4-and 5-mono-and 4,5-disubstituted 3,3-diphenyl-3H-pyrazoles.…”

Thermodynamic stability of finely dispersed Na+Cl−(H2O) n aerosol particles in water vapor

“…The existence of the barrier makes the two states of an ion pair relatively stable. By analogy with corresponding states in a liquid bulk solution [20][21][22][23][24][25], it is reasonable to refer to these states as a Contact Ion Pair (CIP) and a Solvent Sepa rated Ion Pair (SSIP). In contrast to a bulk liquid phase, the formation of ion pairs in a gaseous medium is accompanied by strong variations in the number of molecules in a hydration shell, which result in the appearance of much higher free energy barriers sepa rating the CIP and SSIP states.…”