Absorption and Dichroism

Nonbnear Absorption and Dichroism Two-Photon Absorption and Circular Dichroism... 

Section 2.1 with those in Section 2.2 for one- and two-photon absorption and dichroism and for magnetic circular dichroism. In the second part of the section, attention will be focused on some vibrational spectroscopies, namely vibrational circular dichroism (VCD), ROA, and coherent anti-Stokes Raman scattering (CARS), which have become increasingly popular in the last few years. 

Materials characterization techniques, ie, atomic and molecular identification and analysis, ate discussed ia articles the tides of which, for the most part, are descriptive of the analytical method. For example, both iaftared (it) and near iaftared analysis (nira) are described ia Infrared and raman SPECTROSCOPY. Nucleai magaetic resoaance (nmr) and electron spia resonance (esr) are discussed ia Magnetic spin resonance. Ultraviolet (uv) and visible (vis), absorption and emission, as well as Raman spectroscopy, circular dichroism (cd), etc are discussed ia Spectroscopy (see also Chemiluminescence Electho-analytical techniques It unoassay Mass specthot thy Microscopy Microwave technology Plasma technology and X-ray technology). 

Although the usual absorption and scattering spectroscopies caimot distinguish enantiomers, certain techniques are sensitive to optical activity in chiral molecules. These include optical rotatory dispersion (ORD), the rotation by the sample of the plane of linearly polari2ed light, used in simple polarimeters and circular dichroism (CD), the differential absorption of circularly polari2ed light. 

A. Electronic Spectroscopy Absorption, Circular Dichroism, and Magnetic Circular Dichroism (MCD) Spectroscopy... 

Stephens, P. J., Devlin, J. F., Chabalowski, C. F., Frisch, M. J, 1994, Ab Initio Calculations of Vibrational Absorption and Circular Dichroism Spectra Using SCF, MP2, and Density Functional Theory Force Fields , J. Phys. 

The photochemical formation and the analysis of the absorption and magnetic circular dichro-ism spectra of the anion radical of zinc phthalocyanine were carried out. A complete assignment of the optical spectrum of the anion radical was proposed.834 Similarly, spectroelectrochemical cells have been used to record absorption and magnetic circular dichroism spectra of zinc phthalocyanines and a band assignment scheme proposed.835... 

The redox potentials of zinc-substituted phthalocyanines are shown to be linearly dependent on the total Hammett substituent constant.837 In 1987, Stillman and co-workers used the absorption and magnetic circular dichroism spectra of the zinc phthalocyanine and its 7r-cation-radical species to assign the observed bands on the basis of theoretical calculations. The neutral and oxidized zinc phthalocyanine complexes with cyanide, imidazole, and pyridine were used with the key factor in these studies the stability of the 7r-cation-radical species.838 The structure of zinc chloro(phthalocyaninato) has been determined and conductivity investigated.839... 

Zsila, F., Z. Bikadi, Z. Keresztes, J. Deli, and M. Simonyi. 2001b. Investigation of the self-organization of lutein diacetate by electronic absorption, circular dichroism spectroscopy, and atomic force microscopy. J. Phys. Chem. B 105 9413-9421. 

UNFOLDED PEPTIDES AND PROTEINS STUDIED WITH INFRARED ABSORPTION AND VIBRATIONAL CIRCULAR DICHROISM SPECTRA... 

Ross WN, Salzberg BM, Cohen LB et al (1977) Changes in absorption, fluorescence, dichroism and birefringence in stained giant axons optical measurement of membrane potential. J Membr Biol 33 141-183... 

While it is tempting to explain regulatory and cosolvent effects on the basis of conformational changes favorable or unfavorable to enzyme activity, it is much more difficult to demonstrate the actual involvement, amount, and structural details of such changes. Experimental evidence consists in most cases of bits and pieces provided by techniques such as absorption and fluorescence spectroscopy, circular dichroism, and magnetic circular dichroism. These tools work in solution (and, when desired, at subzero temperatures) to investigate not simply empty enzymes but enzyme—substrate intermediates. However, even with this information, the conformational basis of enzyme activity remains more postulated than demonstrated at the ball and stick level, and in spite of data about the number and sequence of intermediates, definition of their approximate nature, rate constants, and identification of the types of catalysis involved, full explanation of any particular reaction cannot be given and rests on speculative hypothesis. 

In order to obtain more information about the interactions between AmB and lipids at the molecular level, we chose to use spectroscopic measurements electronic absorption and circular dichroism (19). The particular structure of the AmB molecule, with several conjugated double bonds in the hydrophobic stretch, means that these techniques can be used to study its aggregation state under different conditions. Of the two, circular dichroism spectroscopy is the more sensitive way of detecting the aggregated forms of AmB. 

Deoxvhemerythrin. Henrerythrin appears to retain its triply bridged crae structure in the deoxy form. A low (3.9 A) resoluticm difference electron density map of deoxyHr vs. metHr fi- n X-ray diffraction suggests that the iron atoms move slightly further apart in deoxyHr, but remain five and six coordinate, respectively (29). Confirmation of the iron coordination comes from near-IR absorption and circular dichroism spectra (40,46,47). Based on model high-spin ferrous complexes, the six coordinate iron is expected to give two of the three observed transitions near 10000 cm- while the five-coordinate iron accounts for the d-d transition at ca. 5000 cm-. ... 

Figure 9. Absorption and magnetic circular dichroism spectra of compounds 6(a) and 10(b) in THF-DE at 293 K. Optical path is 2mm. (Reproduced with permission from Ref. 15. Copyright 1985 North-Holland Physics Publishing Company.)...

Optical Spectroscopy General principles and overview, 246, 13 absorption and circular dichroism spectroscopy of nucleic acid duplexes and triplexes, 246, 19 circular dichroism, 246, 34 bioinorganic spectroscopy, 246, 71 magnetic circular dichroism, 246, 110 low-temperature spectroscopy, 246, 131 rapid-scanning ultraviolet/visible spectroscopy applied in stopped-flow studies, 246, 168 transient absorption spectroscopy in the study of processes and dynamics in biology, 246, 201 hole burning spectroscopy and physics of proteins, 246, 226 ultraviolet/visible spectroelectrochemistry of redox proteins, 246, 701 diode array detection in liquid chromatography, 246, 749. 

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... 

---