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Achiral chromophore inducibility

Photochemically Triggered Induced Circular Dichroism in Liposomes When an optically inactive chromophore is subject to the effect of optically active environment, optical activity may be induced at the absorption wavelength of the optically inactive chromophore. This phenomenon of induced circular dichroism(ICD) is often observed in polypeptides bearing various achiral chromophores on the side chain( ). The strong chiral environment caused by the peptide helix structure is responsible for this. Distance from, and orientation to, the chiral field decide the degree of ICD appearing on the achiral chromophore. [Pg.216]

For the optical activity of achiral chromophores with a dissymmetric environment, two types of theoretical treatments have been proposed coupled oscillator treatment and one-electron treatment. The charge distribution of the magnetic dipole transition correlates Coulombically with an electric dipole induced in the substituents, and the colinear component of the induced dipole provides, with the zero-th order magnetic moment, a non-vanishing rotational strength. [Pg.12]

The chromophores that are prevalent in the molecular structures of natural products are the aromatic ring and the carbonyl functional group. Symmetry elements associated with these functional groups means that they are achiral chromophores, so chirality has to be induced by their structural... [Pg.245]

The Induoibility of A. The (2 are functions purely of the achiral chromophore A. It is impossible to estimate these empirically by other techniques, so that the only approach would seem to be through simple model calculations. These are beyond the scope of this paper, so that the inducibility will be discussed in a general way, with a particular emphasis on its role in establishing CD/stereochemical correlations. [Pg.84]

C(5) The relative intensities of the CV of d-d transitions of A2, E symmetry is determined largely by the inducibilities, and thus the nature of the achiral chromophore. [Pg.85]

A and A" is the same achiral chromophore and B-j and Bj have the same configurational relationship to A in the composite complex as in their respective substituent complexes, the circular dichroism of AB-jBj... is simply the summation of the CD s of A B., A"Bj, etc. The purpose of this effort is to exhibit an achiral 1 chromophore upon which exchange of chiral ligands induces negligible perturbation in the configurational relationship of the chelating ligands, and thus to allow the utility of the predicted additivity to be demonstrated experimentally. [Pg.273]

When eda transitions occur in two non-identical achiral chromophores, as with the degenerate case, a linear motion of charge at a distance (in another chromo-phore) has a circular (magnetic) component locally. Thus if the two transitions couple, an induced CD signal (4) is found. The main differences between the non-degenerate and degenerate cases are that for the non-degenerate case ... [Pg.114]

The equation describing the octant rule dependence of the dynamic coupling induced CD of an transition is derived as follows (4, 7). One first divides the molecule into an achiral chromophore A composed of the C=0 bond and the two carbon atoms to which it is joined (Figure II). The rest of the molecule is divided into chromophores, C,. which are subunits of the molecule that do not exchange electrons with the rest of the molecule. For a molecule where (apart... [Pg.115]

Optical activity opposite to the parent copolymers was observed. Asymmetric induction ascribed to the rigidity of the polymer chain was proposed as an explanation, as for copolymers of (-)menthylvinylether and arylvinylether [14 bis] in which the optical anomalies were attributed to some asymmetric conformations of the initially achiral units induced by the adjacent chiral ones giving rise to new Cotton effects at the absorption band of the aromatic chromophores. [Pg.24]

Induced circular dichroism (ICD) is the CD observed in an optically inactive (achiral) chromophore due to its interaction with an optically active (chiral) moiety. Early applications exploited ICD just as evidence for such an interaction. For example, the ICD in the absorption band of an achiral drug may be used to prove its binding to a (chiral) protein or nucleic acid. More recent use of ICD includes the structural information that theoretical analysis of the inducing mechanism can provide. ICD has been an important complement to linear dichroism (LD) for the assessment of binding geometries in drug-nucleic acid systems. [Pg.869]

The CD induced in an achiral chromophore upon interaction with a chiral substrate can be ascribed to one or several mechanisms, each corresponding to a more or less idealized situation the chromophore molecule may be perturbed, by mainly steric interactions, to adopt a chiral (equilibrium) conformation or it may gain optical activity through electric and/or magnetic interactions with surrounding chromo-phores. [Pg.869]

The analysis of the CD spectrum induced on the achiral chromophore can provide insights on its orientation relatively to the chiral molecule. For example, a rule of thumb exists for cyclodextrin inclusion complexes the CD induced on a certain electronic transition of the guest chromophore is positive if the corresponding transition dipole moment is parallel to the main axis of cyclodextrin, while it is negative if the transition dipole moment is oriented perpendicularly [22]. [Pg.145]

Molecules in this section fall into two general categories those that are inherently achiral, and those that, in their most stable thermodynamic state, are racemic mixtures. All have at least one chromophore. The analytical approach is the same for both. They are made to form derivatives by reaction with a chiral host. In the case of racemates the derivatives are diastereomers and methods for their analytical applications have been referenced in earlier sections. Regardless of the distinction between racemic and non-racemic substances, the induced CD effects are uniformly smaller than the effects inherent to chiral molecules by one to two orders of magnitude. [Pg.266]

The power of circular dichroism (CD) spectroscopy is unfortunately limited to the study of chiral molecules having accessible chromophores, and cannot be applied to the study of achiral compounds. However, a great many compounds of interest are not intrinsically dissymmetric, so the induction of chirality into such species is a fundamental requirement for the performance of CD studies. In the present work, investigations into the CD induced in achiral molecules by the action of chiral agents is reviewed. [Pg.308]

On the lowest level the carbonyl chromophore is viewed as the prototype of an inherently symmetric, but chirally perturbed chromophore This means that in a chiral ketone the particular carbonyl chromophore retains (largely) its (achiral) symmetry and optical activity will be induced by the chiral environment (i.e. the chiral arrangement of other groups in the whole molecule). In terms of perturbation theory this can be expressed by the statement that in zeroth order the chromophore is achiral and chirality is induced by perturbations in first (or higher) order. On the other hand, if, for a given electronic excitation, optical activity exists in zeroth order (without perturbation by the chiral field of the remaining groups of the molecule not directly involved in the electronic transition) the chromophore is termed inherently chiral ... [Pg.71]

Proteins that have tightly bound cofactors, such as heme proteins, photosynthetic reaction centers and antenna proteins, flavoproteins, and pyridoxal phosphate- and NAD-dependent enzymes, provide a variety of chromophores which have absorption bands in the visible and UV region. The CD bands associated with the chromophoric groups are frequently quite intense, despite the fact that the isolated chromophores are achiral in many cases, and therefore have no CD, or are separated from the nearest chiral center by several bonds about which relatively free rotation can occur, and therefore have only weak CD. The extrinsic or induced CD observed in the visible and near-UV spectra of the proteins can provide useful information about the conformation and/or environment of the bound chromophore, which usually plays a critical role in the function of the protein. [Pg.44]

In addition, it was also reported that circular dichroism and circular birefiingence can be induced in thin films of achiral polymer liquid crystals containing 7 to 15 mol % azobenzene chromophores by irradiation with circularly polarized light The polymer can be illustrated as follows ... [Pg.270]


See other pages where Achiral chromophore inducibility is mentioned: [Pg.291]    [Pg.253]    [Pg.116]    [Pg.261]    [Pg.869]    [Pg.9]    [Pg.259]    [Pg.384]    [Pg.620]    [Pg.900]    [Pg.48]    [Pg.48]    [Pg.51]    [Pg.61]    [Pg.81]    [Pg.112]    [Pg.271]    [Pg.649]    [Pg.651]    [Pg.655]    [Pg.658]    [Pg.37]    [Pg.99]    [Pg.63]    [Pg.318]    [Pg.651]    [Pg.655]    [Pg.658]    [Pg.870]    [Pg.106]    [Pg.1144]    [Pg.463]    [Pg.1163]   
See also in sourсe #XX -- [ Pg.84 ]




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