Acetone relaxational effects

Relaxation Effects on the Barrier, NBO, and Steric Energetics in Acetone (cm ) ... 

Recent work by Zhang and LeBoeuf (in review) examined the effects of the presence of three solvents—water, acetone, and benzene—on the molecular mobility and structural relaxation of a humic acid through DSC analysis combined with molecular dynamics. Again, antiplasticization behavior was observed in two of the three systems (i.e., HA-water and HA-acetone) where solvents present in relatively low concentrations exhibited potential to form hydrogen bonds with the humic acid. Antiplasticization and plasticization behaviors were further interpreted from the perspective of hydrogen bonding analysis and free volume theory. 

Further examination of the excited states reveals a strong dependence of their energy upon solvent polarity that resembles the experimental trends. Single-point calculations on the relaxed structures of the ground and excited states in the simulated solvents hexane (e = 2.023), CCI4 (e = 2.229), benzene (e = 2.274), ether (e = 4.197), chloroform (e = 4.806), methylene chloride (e = 8.930), pyridine (e = 12.40), acetone (e — 20.56), ethanol (e = 24.55), nitrobenzene (e = 43.82), acetonitrile (e = 35.94) and dimethyl sulfoxide (e = 46.45) were performed in order to judge the solvent effects on the relative stabilities of the different states for 9b-d. 

Careful choice of solvent and dilution is particularly important for some samples. In general, the spectra of the sulfones show a marked solvent dependence. The line width is especially sensitive to the nature of the solvent. For example, the line widths for 5 mol dm solutions of sulfolane in acetone and water are 16 and 60 Hz, respectively. A shift difference of 6.5 ppm is observed between 5moldm solutions of sulfolane in water and dioxane. Table 50 shows how the chemical shift (quoted relative to that for neat sulfolane) and line width vary with concentration of sulfolane in acetone. No nuclear Overhauser effect is observed for sulfolane, which suggests that sulfur-hydrogen dipolar interactions are not significant as a relaxation mechanism. 

The effect of temperature on relaxation rate of selected signals from aspen MWL in DMSO has been reported and is shown in Table 5.6 [399], As indicated from the Tj values, heating the sample from 30° to 70° doubles the required relaxation delay, if valid quantification is desired over the entire spectral range. This viscosity effect is much more noticeable in DMSO than in acetone or chloroform. 

Apart from acetone-dried G. candidum IFO 4597, intact whole cells of various strains of G. candidum have been found to be useful for asymmetric reduc-tions(75 78, 101, 120 167 171) For example, methyl 2-acetylbenzoate was reduced by G. candidum ATCC 34614, IFO 5767 or IFO 4597 as well as by other microorganisms such as Mucor javanicus, Mucor heimalis, Endomyces magnusii, Endomyces reessii and bakers yeast to afford phthalide derivatives (Fig. 15-26) which have various pharmacological profiles such as relaxant, antiproliferative or antiplatelet effects, etc.[171). 

The pressure effects on spin relaxation dynamics for these iron(II) complexes have been examined using laser flash photolysis techniques. For Fe(pyim) the two spin states are in equilibrium with a K = 0.56 in 298 K acetone with a partial molar volume difference AV = +8.1 cm mol [34]. Photoexcitation (2ex = 532 nm) leads to transient bleaching of the low spin isomer s MLCT bands followed by first order relaxation to the original spectrum with a 45-ns lifetime. Transient bleaching and subsequent return of the MLCT absorption was attributed to formation of the HS isomer and subsequent spin relaxation. The pressure dependence of the relaxation lifetimes was used to determine the activation volumes of the spin relaxation rates for a variety of FeL in different solvents. It was found that AV j fell into a remarkably narrow range of values (-5.5 + 1 cm mol ) and it was concluded that the spin crossover for these species follows a common mechanism via a transition state located midway between the high and low spin states [33]. 

The radiative and nonradiative (fc ) rate constants estimated using the emission lifetimes (Tobs) and the intrinsic emission quantum yields ( Ln) are summarized in Table 6.1. The radiative rate constant for Eu(hfa)3(fBu-xantpo) in acetone was estimated to be 5.4 x 10 s This value is much similar to that for Eu(hfa)3(fBu-xantpo) in acetone-t/e (5.5 x 10 s ). The nonradiative rate constant for Eu(hfa)3(fBu-xantpo) in acetone-t/s (2.7 x 10 s ) is smaller than that for Eu(hfa)3(fBu-xantpo) in acetone (3.0 x 10 s ). The relatively smaller kai for Eu(hfa)3(fBu-xantpo) in acetone-t/s is attributed to the suppression of vibrational relaxation surroundings of the Eu(Ill) complex. The nonradiative transitions of lanthanide complexes are affected by the high-vibrational frequency of C-H and O-H bonds of solvent. The author consider that introduction of deuterated solvent is effective for enhancement of emission quantum yield of octa-coordinated Eu(lll) complexes. 

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