Dissymmetry defined

Online CD detectors are now commercially available for use with HPLC that are inherently more sensitive than corresponding OR detectors and not affected by solvent changes to the same extent and are thus more gradient compatible [121]. Provided Ae and the concentration of an analyte are known with good precision/accuracy, the measurement of CD will allow the determination of enantiomeric purity. In addition, with CD-based detection systems, both chiroptical and ordinary absorbance can be determined simultaneously allowing the measurement of the g-factor (or dissymmetry factor), which is defined as the ratio of the CD to the absorbance (AA/A) [122]. The g-factor is concentration independent and its measurement allows a more reliable determination of enantiomeric purity (without using a CSP) with reference to standards of known enantiomeric composition irrespective of their concentration [123]. A small number of recent literature examples have suggested the potential use of achiral HPLC with online CD detection for the determination of extreme enantiomeric ratios [121, 124-126] however, chiral separation techniques currently provide a more reliable measurement of enantiomeric purity. 

Particles which are too small to show a series of maxima and minima in the angular variation of scattered light are frequently studied by measuring the dissymmetry of scattering (usually defined as the ratio of the light scattered at 45° to that scattered at 135°). The dissymmetry of scattering is a measure of the extent of the particles compared with A. If the molecular or particle size is known, it can be related to the axial ratio of rod-like particles or the coiling of flexible linear macromolecules. 

In circularly polarized luminescence spectroscopy, one normally reports the ratio of Al to the total intensity 7. The results are most often reported in terms of the luminescence dissymmetry ratio, glum, which is defined as the ratio of the differential emission intensity to the average total emission intensity.75... 

Because of the difficulty in measuring absolute emission intensities, in CPL spectroscopy one commonly reports the ratio of AI(X) to the total intensity I(X). This ratio, glum(X), is referred to as the luminescence (or emission) dissymmetry ratio, and is explicitly defined at wavelength, X, as... 

The extra factor of 1/2 in this equation results from the fact that the equivalent expression for the absorption dissymmetry factor (or ratio), gabs > employed in CD spectroscopy is defined in terms of the difference in extinction coefficients, Ae, divided by the average extinction coefficient, e. 

A chiral substance is defined by the International Union of Pure and Applied Chemistry (lUPAC) as one that interacts differently with left and right circularly polarized light. Two types of molecular optical activity are recognized inherent dissymmetry characterized by large rotational strengths and inherently symmetrical, but asymmetrically perturbed, molecules for which rotational strengths are less by a factor of a thousand or so. 

In 1964, Cahn, Ingold, and Prelog (see p. 130) proposed that chemists use the terms chiral and chirality as defined by Kelvin. Based on the Greek word for hand (cheir), chirality means handedness, in reference to that pair of non-supcrimposablc mirror images we constantly-have before us our two hands. There has been wide-spread acceptance of Kelvin s terms, and they have largely displaced the earlier dissymmetric and dissymmetry (and the still earlier—and less accurate— asymmetric and asymmetry ), although one must expect to encounter the older terms in the older chemical literature. 

The flow birefringence of actomyosin is appreciably higher than that of L-myosin (Szent-Gyorg5d and coworkers, 1942 Schramm and Weber, 1942), but has not yet been measured under quantitatively defined conditions greater too are the turbidity due to light scattering (Portzehl et al., 1950) and the angular dissymmetry (Jordan and Oster, 1948 Mommaerts and Parrish, 1951). The turbidity of a 1% solution is about 0.5 cm. X-Ray studies have introduced no new concepts since the discussion by Bailey (1944). 

Vernadsky and Teilhard de Chardin constructed different concepts of the noosphere and biosphere according to their purposes by interpreting the empirical facts in favour of their theoretical demands. This is clearly shown by their interpretation, of molecular dissymmetry. In 1848, L. Pasteur discovered a phenomenon that he later defined as molecular dissymmetry". He discovered that some of the basic organic compounds found in living matter (crystals) are structurally different from those usually found in the inert envirorunent. Although there are two possible isomers of these organismal compounds which could theoretically exist, one finds pure steric compounds in the... 

Fig. 6.8 Glassy liquid crystal Films A-D defined by wt% of (20) in the (19) (20) mixtures at 100, 95, 51, and 38, respectively, all doped with Exalite 428 at 0.2 wt% for photoexcitation at 370 nm dissymmetry factors for a 14-pm-thick films, and b Film A as a function of film thickness. Used with permission [43]...

Fig. 6.14 Molecular structure of a nonafluorene (40) as the emitting layer in the FOLED device shown as the inset in Fig. 6.11 with its circularly polarized electroluminescence spectra and the calculated dissymmetry factor, where ELl and ELr represent the left- and right-handed circularly polarized electroluminescence, respectively, and the dissymmetry factor is as defined for circularly polarized fluorescence in Sect. 6.7.3. Used with permission [51]...

The CPL results were placed on a quantitative basis by calculating the luminescence dissymmetry factor lum as defined by Richardson and Riehl [Ri 77] ... 

Barron, L. D.. Am. Chem. Soc. 1986, 108, 5539 noted that there is a difference between the words dissymmetry and chirality, since dissymmetry is the absence of certain symmetry elements, while chirality is the presence of the attribute of handedness. However, Mislow defined chirality as the "absence of reflection symmetry" and investigated the quantification of chirality Buda, A. B. Auf der Heyde, T. Mislow, K. Angew. Chem. Int. Ed. Engl. 1992, 31, 989. Zabrodsky, H. Peleg, S. Avnir, D. /. Am. Chem. Soc. 1993,115, 8278 treated symmetry as a continuous and quantifiable property rather than as a "yes or no" condition. Zabrodsky, H. Avnir, D. /. Am. Chem. Soc. 1995, 117, 462 gave a quantitative definition of chirality. also the discussion in reference 22, pp. 241-256. 

The dimension is given, as still used even today, in cgs units. A frequency-independent dissymmetry factor g can also be defined with the help of the dipole strength and rotational strength of the electronic... 

We thus define the luminescence dissymmetry ratio, as follows ... 

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