Optical rotatory dispersion , solvent effects

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. 

Palytoxin is a white, amorphous, hydroscopic solid that has not yet been crystallized. It is insoluble in nonpolar solvents such as chlorophorm, ether, and acetone sparingly soluble in methanol and ethanol and soluble in pyridine, dimethyl sulfoxide, and water. The partition coefficient for the distribution of palytoxin between 1-butanol and water is 0.21 at 25°C based on comparison of the absorbance at 263 nm for the two layers. In aqueous solutions, palytoxin foams on agitation, like a steroidal saponin, probably because of its amphipathic nature. The toxin shows no definite melting point and is resistant to heat but chars at 300°C. It is an optically active compound, having a specific rotation of -i-26° 2° in water. The optical rotatory dispersion curve of palytoxin exhibits a positive Cotton effect with [a]25o being -i-700° and [a]2,j being +600° (Moore and Scheuer 1971 Tan and Lau 2000). 

More recently, Doty and co-workers (Doty, 1959) have found that a large number of globular proteins are directly soluble in the solvent 2-chloroethanol. While the apparently unique solubilizing power of this substance is probably attributable to the HCl present in the unstable solvent, some very significant measurements of the optical rotatory dispersions of proteins in a pure weakly protic nonaqueous solvent were made as a result of this discovery. In all cases studied, proteins exhibited larger, often substantially larger, values of —ho in 2-chloroethanol than in HjO (Table VII). These effects are reversible with change of solvent. 

Since Werner s pioneering work on optical activity in complex inorganic compounds there have been many important developments in the field. One of the more interesting of these is known as the Pfeiffer effect which is a change in the optical rotation of a solution of an optically active substance e,g, ammonium d-a-bromo-camphor-T-sulfonate) upon the addition of solutions of racemic mixtures of certain coordination compounds (e,g, D,L-[Zn o-phen)z](NOz)2, where o-phen = ortho-phenan-throline). Not all combinations of complexes, optically active environments and solvents show the effect, however, and this work attempts to apply optical rotatory dispersion techniques to the problem, as well as to determine whether solvents other than water may be used without quenching the effect. Further, the question of whether systems containing metal ions, ligands, and optically active environments other than those already used will show the effect has been studied also,... 

In this work the authors have attempted to expand the scope of the Pfeiffer effect to other systems and solvents and to determine unambiguously the source of the effect. To this end they applied optical rotatory dispersion techniques as a tool in their study. 

ABA is a C, organic acid with one asymmetric carbon atom at C-1 (Fig. 1). The naturally occurring form is 5-( + )-ABA the side chain of ABA is by definition 2-cis,4-trans [2]. The optical rotatory dispersion (ORD) spectrum of ABA exhibits an intense Cotton effect. This property was initially exploited to identify and measure ABA in purified extracts of a number of plants [11]. ABA in organic solvents can be photo-isomerized by ultraviolet radiation to give a mixture of approximately 50% ABA and 50% 2-trans,4 trans-ABA (f-ABA) (Fig. 1). The latter compound is biologically inactive. 

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