Ellipticity, molar

Fig. 2.48 CD analysis of oligoureas 177 and 178. CD spectra were recorded in MeOH at room temperature at a concentration of 0.2 mM. Molar ellipticity [0] in deg cm drnol . The mean-residue ellipticities measured at 204 nm for 177 and 178 are 26600 and 41300 deg cm dmol, respectively...

The characteristic of the molecule is sometimes expressed as the molar ellipticity in deg d/-moP dm . This is related to the difference in extinction coefficients by... 

Binding of berberine caused changes in the circular dichroic spectrum of all B-DNAs with an increase of molar ellipticity of the 270 nm band the molar ellipticity value at saturation depended strongly on the base composition of DNA being larger for the AT-rich DNA than the GC-rich DNA. However, the generation of berberine-associated extrinsic circular dichro-ism bands was not dependent on the base composition or sequence of base pairs. 

Fig. 11 Variation of extrinsic molar ellipticity at 440 nm of berberine-DNA complexes against GC content of DNA. a Berberine-B-DNA complexes and b berberine-protonated DNA complexes. Reprinted from [188] with permission from Elsevier...

The molar ellipticity of these dendrimers was found to increase proportional to the number of chiral end groups. This is to be expected, in the absence of interactions between the terminal tryptophane moieties. No higher-generation dendrimers of this type have been reported. Other amino-acid-containing chiral dendrimers have been described by Meijer et al. who attached various amino acid derivatives to the periphery of poly(propylene imine) dendrimers (see Sect. 3) and more recently by Liskamp et al. (modification of polyamide dendra) [22] and Ritter et al. (synthesis of grafted polymerizable dendrimers containing L-aspartic acid components) [23]. 

Figure 5.30 Temperature dependence of molar ellipticity at 218 nm for liposomes prepared from L-DMPC, L-DPPC (39), and L-POPC (40). Reprinted with permission from Ref. 134. Copyright 1997 by the American Chemical Society.

Figure 5.32 Circular dichroism spectra of tubules made from mixtures of opposite enantiomers of DCg.gPC in 80 20 methanol-water. Spectra shown correspond to mixtures of (a) 100 0, (b) 75 25, (c) 50 50, (d) 25 75, and (e) 0 100 L-/D-DC89PC. Inset shows dependence of peak molar ellipticity on enantiomeric excess along with linear fit of data. Reprinted with permission from Ref. 125. Copyright 1998 by the American Chemical Society.

The circular dichroism spectra (Figure 1) was obtained on a 0.0155 mg/ml solution in methanol with a Cary Model 61 Circular Dichroism Spectrophotometer. The following molar ellipticity values were obtained ... 

The molar ellipticities are calculated for leucovorin free acid and have been corrected for water content. These values may be quite different from those of folinic acid. Although a single value is reported for each solvent, both spectra contain more than one absorption band. Whether the extraneous absorptions are due to impurities or are actually due to leucovorin s absorption behavior is not known at this time. 

Optical activity also manifests itself in small differences in the molar extinction coefficients el and er of an enantiomer toward the right and left circularly polarized light. The small differences in e are expressed by the term molecular ellipticity [9 J = 3300(el — r). As a result of the differences in molar extinction coefficients, a circularly polarized beam in one direction is absorbed more than the other. Molecular ellipticity is dependent on temperature, solvent, and wavelength. The wavelength dependence of ellipticity is called circular dichroism (CD). CD spectroscopy is a powerful method for studying the three-dimensional structures of optically active chiral compounds, for example, for studying their absolute configurations or preferred conformations.57... 

Figure 4.20. Variation of the molar ellipticity [0] and torsion constant a of pUC8 dimer with superhelix density. All samples were prepared from the same stock solution as described in the text. Solution conditions were 10 mM NaCl, 10 mM Tris, 1 mM EDTA, and pH 8, and the DNA concentrations were between 40 and 50 g/ml. , Five days after preparation +, 15 days after preparation , 2 months after preparation , samples prepared from the same initial stock solution 4 months after the other samples and measured within 5 days. Top [0] versus superhelix density a. Only the a = -0.015 sample changed significantly over the first few weeks. Bottom a versus superhelix density. Torsion constants are averages for 70- and 120-ns time spans. For the FPA measurements only, ethidium was added to a concentration of 1 dye per 300 base pairs. With the exception of a - - 0.025, the samples denoted by did not change significantly over a period of 2 months, and it is the final values that are plotted. The final measurement for the a= -0.025 sample is denoted by . The error bars are less than or equal to the size of the symbols in the figure. Complete data for o= —0.048 and o= —0.031 are given in Figure 4.10, which demonstrates the ability of FPA measurements to distinguish between samples whose torsion constants differ by only 10%.

Fig. 45 Molar ellipticity at 315 nm for 4 pM dodecamer 71 and 100 equiv of (-)-a-pinene in varying compositions of water in acetonitrile...

Here, the molar ellipticities are calculated per residue, which is the usual practice in peptide and protein work, and kn is the number of missing residues. For a peptide without blocking groups, the number of amides is one less than the number of residues, r=n — 1, and kr=kn — 1. If one terminus is blocked to form an additional amide, e.g. N-acylation or C-carboxyamidation, r and n are equal and so are kr and kn. If both termini are converted into amides, r=n +1 and kr=kn +1. 

The contribution of the poly(Pro)II conformation to the ensemble of unordered peptides has been considered.1158 The temperature dependence of [0]222 for the peptide Ac-YEAAAKEAPAKEAAAKA-NH2 in 8 M guanidinium chloride and of poly(Lys) in water and in ethylene glycol/water (2 1) mixtures 156 was fitted to a two-state equation for a poly(Pro)II-unordered equilibrium with a temperature-independent AH and temperature-independent molar ellipticities for the two components. The peptide with a Pro at the central position is an unordered peptide, the spectrum of which has pronounced poly(Pro)II-like features at low temperatures. This fit yielded [0]222=- -9580 deg-cm2dmol 1 for the poly (Pro)II component and —5560 deg-cm2-dmol 1 for the unordered component. These values provide a method for roughly estimating the poly(Pro)II content, /Pn, of an unordered peptide from [0]222 ... 

A mixture consisting of aniline ( 0.2 g) and (lS)-(+) camphorsulfonic acid (3.48 g) was dissolved in 10 ml of water and then treated with five separate portions of 0.1 g of ammonium peroxydisulfate dissolved in 1 ml water. Each successive portion was added when the solution turned from blue to green while the reaction mixture was maintained at 20°C. After the additions were completed the mixture was centrifuged and the product washed with water. The circular dichroism spectrum of the product suspensed in water indicated a molar ellipticity of about 90 x 103 deg-cm2/dmol. Transmission electron micrographs showed that the product had a nanofibrous structure with fiber diameters from 30 to 70 nm and had a length of several hundred nanometers. 

Transmission electron micrographs showed that the precipitate was in the form of particles, although some nanofibrous structures were observed. The circular dichroism indicated a molar ellipticity of 5 x 103 deg-cm2/dmol. 

The Kronig-Kramers relation is of fundamental importance for optics and for physics in general13). Here, these equations do not seem practical because of the integration of the wavelength from 0 to oo. However, these are very useful for calculating the molar ellipticity magnitude from the observed ORD curve 14). 

Fig. 30. CD spectra (molar ellipticity [0]) at room temperature showing the effect of adriamycin on poly(dG-m5dC) poly(dG-m5dC) conformation 851...

The magnitude of the CD has commonly been calibrated at 290 nm using ( + )-camphor-10-sulfonic acid as a standard. Because of its hygroscopic nature, the water content has led to some confusion. Tsujimura et al. have recommended to use a molar ellipticity of +7.78 x 103 for the compound in an aqueous solution 280). The concentration can be calibrated by the ORD of the same sample, which gave a molar rotation of +4.28 x 103 at 305 nm and of —5.44 x 103 at 270 nm. 

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