Circular dichroism effect

However, if the dependence of the angle of rotation a upon the wavelength is measured in the region of the absorption band of the optically active substance under investigation, then superposition of an S-shaped component on the normal ORD curve is observed in this region. Circular dichroism effects are responsible for this anomalous ORD curve. 

Spada GP (2008) Alignment by the convective and vortex flow of achiral self-assembled fibers induces strong circular dichroism effects. Angew Chem Int Ed Engl 47 636-638... 

C-O-C groups rather than connected with the CH2 subunits of the dendritic branches. The VCD results support the explanation of the observed induced circular dichroism effect as a consequence of the chiral arrangement of the inherently achiral benzene rings within the dendritic branches that was induced by the chiral center. 

Cotton effects. Otonecine (125) does not display the spectral properties of an aminoketone. Circular dichroism effects are absent from otonecine and its derivatives, supporting the zwitterionic representation. ... 

Wolffs, M., George, S.J., Tomovic, Z., Meskers, S.C.J., Schenning, A.P.H.J., and Meijer, E.W. (2007) Macroscopic origin of circular dichroism effects by alignment of self-assembled fibers in solution. Angewandte Chemie-International Edition, 46,8203—8205. 

Strictly, ICD encompasses all kinds of circular dichroism effects except for those of inherently chiral chromophores. This is so because most systems (molecules) may be more or less arbitrarily divided into one achiral chromophore in which the ICD is observed and a remaining component that includes the chirality. Thus, the CD exhibited by a chiral molecule may be considered ICD if the chromophoric entity itself is achiral. With this broader definition of ICD, molecules such as carbonyl compounds (in which the carbonyl chromophore is achiral) display an intramolecular ICD in the first allowed n —> 7t transition around 300 nm due to perturbation from a surrounding chiral (e.g. steroid) skeleton. Distinction between this type of molecule and one which is an inherently chiral chromophore could be difficult to make as the boundaries of the chromophore are often diffuse. For example, when a diene is in immediate proximity of a carbonyl, a composite chromophore is obtained, which, if skewed, is inherently chiral. Therefore, it is practical to restrict the definition of ICD to cases in which the achiral part is... 

It is worth mentioning that the extent of induced circular dichroism on NVC units when inserted in copolymers with intrinsically chiral comonomers is of the same order of magnitude as that extrinsically induced by thermotropic cholesteric mesophases on achiral 9-ethylcarbazole when physically trapped within the mesophase . Higher extrinsic circular dichroism effects are by contrast reported when lyotropic cholesteric mesophases, such as those obtained from polyfy-benzylglutamate) in tetrachloroethane, are used as chiral traps of achiral carbazole derivatives and iso-electronic aromatic compounds ... 

Benedetti M, Biscarini P and Brillante A, The effect of pressure on circular dichroism spectra of chiral transition metal complexes Physica B 265 1... 

These y9 -peptides are not expected to adopt a 3i4-helical conformation in an aqueous environment because of the destabihzing effect of cationic charges. The circular dichroism spectrum of a non-labeled analog of 165 does not display the characteristic signature of the 3i4-helix in aqueous solution however it is highly hehcoidal in MeOH. 

The racemization of the phosphine (118) has been followed by optical rotation. The lack of a solvent effect indicates that there is little change in dipole moment in the formation of the planar transition state. Circular dichroism has been used to study the interactions of nucleotides with proteins and DNA with a histone. Faraday effects have been reviewed. Refraction studies on chloro-amino-phosphines, fluoro-amino-phosphines, and some chalcogenides are reported. 

Circular Dichroism. - The absolute configuration of the ot-hydr oxyphosphonat e (49) was established through its negative Cotton effect at 215 nm.144... 

Optical activity in metal complexes may also arise either if one of the ligands bound to the metal in the first co-ordination sphere is itself optically active or if the complex as a whole lacks a centre of inversion and a plane of symmetry. Thus all octahedral cts-complexes of the tris-or bis-chelate type have two isomeric forms related by a mirror plane, the d- and /-forms. These species have circular dichroism spectra of identical intensities but opposite in sign. The bands in the circular dichroism spectrum are, of course, modified if ligand exchange occurs but they are also exceedingly sensitive to the environment beyond the first co-ordination sphere. This effect has been used to obtain association constants for ion-pair formation. There also exists the possibility that, if such compounds display anti-tumour activity, only one of the mirror isomers will be effective. 

The absolute configuration of C-3 of the chromophore 459 of isopyoverdins was determined to be S from the circular dichroism (CD) spectrum (Cotton effect +242 nm, —290 nm, +358 nm) of 460 obtained from isopyoverdin by acidic hydrolysis <2001T1019>. Diorganotin(iv) complexes with 4//-pyrido[l,2-/z pyrimidin-4-ones 461 <1996AOM47>, complexes of 2-methyl- and 2-methyl-8-nitro-9-hydroxy-4//-pyrido[l,2-tf]pyrimidin-4-ones with Ag(i), Cu(ll), Ni(n), Co(n), and Mn(n) ions <2000RJD587>, 2,4-dimethyl-9-hydroxypyrido[l,2-tf]pyrimidinium perchlorate and its complexes with prasedynium, neodymium, samarium, and europium <2000RJD310> were characterized by UV spectroscopy. 

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