Circular dichroism solvent effect

In a study of chiral dipeptide [2]rotaxanes it was found that the presence of an intrinsically achiral benzylic amide macrocycle near to the chiral center could induce an asymmetric response in the aromatic ring absorption bands [62], This induced circular dichroism (ICD) effect was stronger in apolar solvents (Fig. 9), where intercomponent interactions are maximized, showing a direct relationship to the tightness with which the macrocycle binds the chiral thread. Computer simulations showed that chirality is transmitted from the amino acid asymmetric center on the thread via the achiral macrocycle to the aromatic rings of the achiral C-terminal stopper. 

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. 

M. F. Ruiz-Lopez and D. Rinaldi, Electrostatic solvent effect on the circular dichroism of the carbonyl n t 7t transition, J. Mol. Struct. Theochem. 10 277 (1983). 

There have been numerous applications of continuum models to equilibria and reactions in solution surveys of these and extensive listings are provided by Cramer and Truhlar.16 Other studies have focused upon the effects of solvents upon solute molecular properties, such as electronic and vibrational spectra,16 dipole moments, nuclear quadrupole and spin-spin coupling constants and circular dichroism.12... 

There are many more solvent effects on spectroscopic quantities, that cannot be even briefly discussed here, and more specialized works on solvent effects should be consulted. These solvent effects include effects on the line shape and particularly line width of the nuclear magnetic resonance signals and their spin-spin coupling constants, solvent effects on electron spin resonance (ESR) spectra, on circular dichroism (CD) and optical rotatory dispersion (ORD), on vibrational line shapes in both the infrared and the UV/visible spectral ranges, among others. 

It should be recalled that the calculation of solvent effects on optical activity presents some unique problems. A chiral solute induces a chiral structure of the surrounding solvent, even when the individual solvent molecules are achiral. This means that the solvent participates in the observed optical effect not only by a modification of the geometric structure and electronic density of the solute, but that part of the observed OR or circular dichroism arises from the chiral solvent shell rather than from the solute molecule as such. This is not accounted for by the PCM, and can be rendered only by an explicit quantum mechanical treatment of at least the first solvent shell, or preferably by molecular dynamics simulations. 

The development of the MPE method opened an avenue to the theoretical analysis of solvent effects on chemical and physico-chemical properties. The method was intensively applied to spectroscopical properties in the 1980s [28] including NMR nuclear quadrupole coupling [29,30], spin-spin coupling constants [31], IR spectra [28,32-34] vibrational polarizabilities [35], as well as UV-V and circular dichroism spectra [36-38],... 

The cholesteric mesophase formed by cholesteryl p-nitrobenzoate at 200 °C has been used as the solvent to effect an asymmetric synthesis lrans-but-2-enyl p-tolyl ether gave the product of an ortho-Claisen rearrangement, 2-(but-1 -en-3 -yl)-4-methylphenol. This material exhibited circular dichroism, although neither the optical yield nor the configuration of the product is yet known.262 Decarboxylation of ethylphenylmalonic acid in cholesteryl benzoate at 160 °C (cholesteric liquid-crystalline phase) also proceeded with asymmetric induction to give (R)-(—)-2-phenylbutyric acid, with 18% optical yield.263 Electric dipole moments are reported for some esters of 5a-cholest-8(14)-en-3j8-ol there is some slight correlation with melting points.264... 

Wamke I, Ay S, Brase S, Furche F (2009) Chiral cooperativity and solvent-induced tautom-erism effects in electronic circular dichroism spectra of [2.2]paracyclophane ketimines. J Phys Chem A 113 6987-6993... 

These data have led to the development of a catalytic mechanism, shown in Scheme 6, that has been further refined by kinetic isotope effect (KIE) experiments. Substrate binds to Cu(II), replacing bound solvent. The metal coordination facilitates the deprotonation of the substrate hydroxyl group. The proton is transferred to Tyr495, which dissociates from copper. The temperature and pH dependence of the visible absorption and circular dichroism spectra indicate that galactose oxidase exists as an equilibrium of the Tyr495-Cu(II) form (TyroN) and the protonated Tyr495 state. 

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