Chiroptical effects

The molar rotation of the dendrimers 49-51 is proportional to the excess of (R,R)- or (S,S)-threitol units. This means that the chiroptical effects of threitol building blocks of opposite chirality cancel out each other. For the homo dendrimers an average positive molar optical rotation value of 146 for each (i, k)-threitol unit was calculated whereas a value of -185 resulted for each... 

Measurement of circular dichroism can even permit elucidation of relatively small structural changes. CD spectroscopy is also suitable for the solution of specific application-relevant questions. Studies of the sensor properties of chiral dendrimers make use of the fact that complexation of chiral guest molecules induces changes in the CD bands of the host dendrimers. Thus guest-selective chiroptical effects observed in titration experiments with enantiomeric guest molecules give an indication of the potential of the chiral dendrimer to act as an enantioselective sensor [87]. 

The most commonly encountered manifestations of chiroptical phenomena are circular birefringence (also known as optical rotation), optical rotatory dispersion (ORD), and circular dichroism (CD). An explanation as to the nature of circularly and linearly polarized light is provided, and the origins of the various chiroptical effects are discussed. In each instance, a concise summary of the calculations used by workers in the field to report the results of their investigations is provided. 

Since the polymeric serum proteins are inherently optically active, it follows that chiroptical behavior can be observed if the solute interacts with the protein in a stereoselective manner. A variety of studies have been performed in which the induced CD has been used to evaluate critical details of drug-protein interaction, and the early applications of these have been reviewed by Perrin and Hart [67]. When the chiroptical effects are sufficiently intense, the method may even be used to study the competitive binding of two drugs to a given protein system, thus providing data pertaining to the concurrent administration of these agents. 

Terms of higher order in the field amplitudes or in the multipole expansion are indicated by. . . The other two tensors in (1) are the electric polarizability ax and the magnetizability The linear response tensors in (1) are molecular properties, amenable to ab initio computations, and the tensor elements are functions of the frequency m of the applied fields. Because of the time derivatives of the fields involved with the mixed electric-magnetic polarizabilities, chiroptical effects vanish as a> goes to zero (however, f has a nonzero static limit). Away from resonances, the OR parameter is given by [32]... 

After this brief discussion of the physical significance of the OR parameter, the role of TDDFT in the description of chiroptical effects becomes clear. Chiroptical effects, on a molecular level, are related to perturbations of the electric or magnetic dipole moment by time-dependent magnetic and electric fields, respectively. Since equations (1) establish that the perturbations are linear in the applied field amplitudes, the computational protocol will typically first involve a (static, no external fields) DFT computation of the molecule s ground state, followed by a linear response computation to determine />(oj) from the elements of the tensor computed for a specific EM field frequency co. These tensor elements are computed from the first-order perturbations of the dipole moments due to the presence of EM fields of a specified frequency. 

Charge-transfer complexes of dissymmetric olefins with either tetracyano-ethylene or Pt (sodium tetrachloroplatinate) exhibit chiroptical effects related to the chirality of the olefin. TT)e Pt complexes generally obey a Quadrant Rule. Chiral olefins may also be converted into osmate esters, exhibiting Cotton effects in the region of 480 nm the sign obeys a chirality rule (Figure 3) which... 

Peptides with aromatic or disulfide residues, as a rule, give chiroptical effects arising from the induced asymmetry of their aromatic or disulfide chromophores (Strickland, 1974, pp. 113-175). 

With that idea, in 1958, Overberger s group undertook a program of research to study the factors contributing to the formation of preferred conformation of optically active polyamides. The synthesis and optical properties of a series of asymmetric polyamides with different degrees of structural rigidity imposed on the polymer chain, and generally also their models, have been reviewed by these authors in 1969 [49] and also by Pino [2] in 1970. The conformational aspect is treated in this book in detail, by Dr Montaudo and Dr P. Finocchiaro, and chiroptical effects independent of conformation by Dr Vert (XXI). 

M. R. Provorse and C. M. Aikens, Origin of Intense Chiroptical Effects in Undecagold Subnanometer Particles,/ Am. Chem Soc., 2010,132,1302-1310. 

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