Circular dichroism signal

Figure 15. Circular dichroism of the C=0 C li peak (BE = 292.7 eV) in fenchone at three different photon energies, indicated, (a) Photoelectron spectrum of the carbonyl peak of the (1S,4R) enantiomer, recorded with right (solid line) and left (broken line) circularly polarized radiation at the magic angle, 54.7° to the beam direction, (b) The circular dichroism signal for fenchone for (1R,4A)-fenchone (x) and the (lS,41 )-fenchone (+) plotted as the raw difference / p — /rep of the 54.7° spectra, for example, as in the row above, (c) The asymmetry factor, F, obtained by normalizing the raw difference. In the lower rows, error bars are included, but are often comparable to size of plotting symbol (l/ ,4S)-fenchone (x), (lS,4R)-fenchone (+). Data are taken from Ref. [38],...

As chiral molecules, CD hosts are one of the best chiral selectors [23]. They can also induce circular dichroism signal in an achiral guest. As shown by Zhang and Nau [24] for the complexes of p-CDwith bicyclic azaalkanes 290 or 291, this effect may allow one to determine the orientation of the latter molecule in the CD cavity. An interesting example of the influence of 11 on the guest conformation was reported by Brett and coworkers [25]. They have shown that p-amino-/ -nitrobiphenyl 292, which is planar in the solid state, becomes nonplanar in the solid state complex with 3-CD. 

A two-state transition is usually identified by all spectroscopic probes changing simultaneously as the equilibrium changes. The far ultraviolet circular dichroism signals, which are a measure of secondary structure, should change in parallel with the near ultraviolet, which are a measure of tertiary structure. Fluorescence and near ultraviolet absorbance spectra also probe tertiary structure and should change in parallel with each other and the circular dichroism spectra. Ideally, there should be isosbestic or isodichroic points where spectra converge. 

An interesting phenomenon whereby achiral compounds occupy chiral cavities has been reported. Steroidal host compounds give rise to the attachment of definite chiral conformations of achiral compounds within cavities, making it possible to observe solid-state circular dichroism spectra. Gdaniec and Polonski reported this type of property for the inclusion compounds of DCA and CA with various aromatic ketones [40a] and benzil [40c], Furthermore, it is possible for the selected conformers to maintain their chiral state temporarily in solution. That is, soon after the inclusion compounds are dissolved, the chirality may be retained for some time. /V-Nitrosopiperidines were found to display this type of dynamic chiral recognition in DCA and CA inclusion compounds [40b], In this case, one can observe the decay of the circular dichroism signal after dissolution of these inclusion compounds in methanol. 

Global denaturation of unlabeled RNase H by guanidinium chloride was monitored by following the circular dichroism signal at 222 nm (25°C, lOOmM sodium acetate pH 5.5) from 0 M to 5 M guanidine. The fraction folded, Ff, was calculated as described (Dabora Marqusee, 1994). 

The ratio of the circular dichroism signal and the corresponding absorption is called dissymmetry factor g ... 

A sum rule derived by Thole et al. [151], and also by Altarelli,[152] states that (approximately) the integral of the circular dichroism signal from two spin-orbit partners of a core edge is related to the orbital moment ... 

Binaphthyl consists of two linked naphthalene molecules. The dihedral angle between the two naphthyl planes is around 70 , and can be stabilized by bulky substituents on the naphthyl units, as indicated below for the case of 2,2 -di-biphenylphosphine-1, 1 -binaphthyl. A circular dichroism signal is detected in... 

Inducement of F-DNA Circular Dichroism Signals for Duplex Deoxyribonucleotide Homopolymers by Polycationic Strings. Arch. Biochem. Biophys., Vol. 364, No. 1, pp. 129-131, ISSN 0003-9861. 

A stilbene-cored poly(glutamate) dendrimer in benzene underwent intermolecular photochemical [2 + 2] cycloaddition. The bisignate circular dichroism signal of the resulting cycloadduct indicated the formation of chiral aggregates with through-space electronic interactions between the two stilbene cores. 

Irradiation of stilbene-cored poly(glutamate)dendrimer (254), (255), and (256) afforded the corresponding [2 + 2] cycloadducts in benzene and a bisignate circular dichroism signal was observed, indicating the chiral aggregation of the stilbene core (Scheme 56). ... 

A circular dichroism signal may be observed also for achiral molecules immersed in chiral environments (for example, dissolved in a chiral solvent or complexed by chiral receptors) [6]. This effect is known as induced circular dichroism (ICD) and is generally very weak [7]. ICD spectroscopy is frequently used in supramolecular chemistry to smdy the complexation of an achiral guest by a chiral host [8]. An example of this kind is represented by the association of optically inactive organic chromophores with cyclodextrins, that are macrocyclic receptors possessing a chiral cavity [9, 10]. 

In UV-visible spectrophotometers the detector is usually a photomultiplier tube. The circular dichroism signal is generally quite weak As is small compared with... 

C- and N-terminal ends were blocked respectively with methyl ester and acetyl groups to avoid end effects. Circular dichroism signals and also NMR (Nuclear Overhauser Effect, NOE) spectra were recorded at 5"" and 26°C. At 5" C dichroic signals of peptides 1, 3, and 4 differed from that of peptide 2 (Fig. 10.1). This difference disappears quite entirely at 26°C (Howard et al, 1975). Both CD and NOE data indicate that a small but significant fraction of these peptides are in a chain reversal conformation. These observations were found in agreement with the relative probabilities of bend occurrence in these four peptides as determined by Lewis and co-workers (1971), which were 20/1/40 and 40, respectively, for the four peptides. 

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