Circular dichroism 3, single-crystal

Probing Metalloproteins Electronic absorption spectroscopy of copper proteins, 226, 1 electronic absorption spectroscopy of nonheme iron proteins, 226, 33 cobalt as probe and label of proteins, 226, 52 biochemical and spectroscopic probes of mercury(ii) coordination environments in proteins, 226, 71 low-temperature optical spectroscopy metalloprotein structure and dynamics, 226, 97 nanosecond transient absorption spectroscopy, 226, 119 nanosecond time-resolved absorption and polarization dichroism spectroscopies, 226, 147 real-time spectroscopic techniques for probing conformational dynamics of heme proteins, 226, 177 variable-temperature magnetic circular dichroism, 226, 199 linear dichroism, 226, 232 infrared spectroscopy, 226, 259 Fourier transform infrared spectroscopy, 226, 289 infrared circular dichroism, 226, 306 Raman and resonance Raman spectroscopy, 226, 319 protein structure from ultraviolet resonance Raman spectroscopy, 226, 374 single-crystal micro-Raman spectroscopy, 226, 397 nanosecond time-resolved resonance Raman spectroscopy, 226, 409 techniques for obtaining resonance Raman spectra of metalloproteins, 226, 431 Raman optical activity, 226, 470 surface-enhanced resonance Raman scattering, 226, 482 luminescence... 

Recent investigations 1 2) of the hallucinogenic Mexican mint Salvia divinorum have resulted in the isolation of the phannacologically active diterpene salvinorin (divinorin) A (1) and its desacetyl analog salvinorin B (2). Extensive H and l C NMR studies on these /raz/.s-clerodanes and their derivatives, ) as well as single-crystal X-ray analysis, have led to the fonnulation of the structures of these compounds. The absolute chemistry of the salvinorins was postulated based on the observed negative n jc Cotton effect of the 1-ketone around 295 nm in their circular dichroism (CD) spectra. 1 2)... 

As established by NMR spectroscopy and circular dichroism, the dia-stereomerically pure chloro complexes can be epimerized in the presence of donor solvents to afford mixtures of (R)- and (S)-configurational isomers. The isomer ratio depends on solvent, R, and lanthanide ion. Importantly, selective epimerization allowed enrichment in either antipode with diastereomerically pure complexes obtained in a single recrystallization step. This was a crucial prerequisite for the preparation of molecular structure of [Me2SiCp" ( + )-neomenthylCp ] Lu(/2-Cl)2Li(Et20)2 has been determined by single-crystal X-ray analysis (Fig. 4) [42]. 

As a first step towards the measurement of single molecule effects, Schrader and Korte (1972) reported the measurement of the infrared rotatory dispersion of carvone in liquid crystalline solution. They used a modified commercial spectrometer. They observed a huge effect which is not the result of the carvone itself but of the liquid crystal in which a helical arrangement (cholesteric state) is induced by the chiral solute (Sec. 4.6.4). In this case the liquid crystal acts as a kind of molecular amplifier which allows the absolute configuration of tiny amounts of solutes to be determined reliably. At about the same time Dudley et al., (1972) measured the infrared circular dichroism of (-)-menthol in a liquid crystal. Their equipment consisted of a normal infrared spectrometer supplemented by a Fresnel rhomb made from sodium chloride. 

Three-dimensional Cholesteric liquid crystal Multilayer Single crystal Optical notary pourcf Circular dichroism... 

Although the dimer has asymmetric carbon atoms, the photoproduct from a large single crystal of the monomer does not show any detectable values of optical rotation and circular dichroism. Both enantiomers are formed equivalently from the monomer crystal, for the center of symmetry exists between two molecules arranged in the g-form and the two pairs of double bonds should be equivalent in reactivity, as is illustrated in Figure 5. 

Fig. 2. The axial single crystal circular dichroism spectrum (Ae/10) of 2 A-t+XCofenlslCls NaCl 6 H2O (solid curve) and the absorption and CD spectrum of A-(+)-[Co(en)3l(a04)3 in water (upper and lower broken curves, respectively). The axial crystal CD spectrum characterises electronic transitions of the complex ion to upper states of symmetry, polarized perpendicular to the threefold rotation axis of the complex...

The structure of a given biflavonoid is typically elucidated using intensive ID and 2D NMR (COSY, NOESY).[10, 11] Circular dichroism (CD) is used to determine the absolute configuration in molecules that possess stereocenters. [12] Occasionally, additional spectroscopic techniques are used (MS, IR, UV and single crystal X-ray). 

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