D spectroscopy

Bioinorganic applications of m.c.d. spectroscopy copper, rare earth ions, cobalt and non-heme iron systems. D. M. Dooley and J. H. Dawson, Coord. Chem. Rev., 1984, 60,1 (176). 

Circular dichroism (c.d.) spectroscopy measures the difference in absorption between left- and right-circularly polarized light by an asymmetric molecule. The spectrum results from the interaction between neighboring groups, and is thus extremely sensitive to the conformation of a molecule. Because the method may be applied to molecules in solution, it has become popular for monitoring the structure of biological molecules as a function of solvent conditions. 

Extensive studies have been performed on the (1- 6)-)8-D-glucan (pustulan) and the (l- 4)-a-D-glucan (amylose). These are linear polysaccharides that may exist as helical polymers in aqueous solution, as demonstrated by c.d. spectroscopy. Characteristic of the helical structure of these glucans is a negative band at 182 nm, a crossover at 177 nm, and a more intensely positive band at shorter wavelengths (see Figs. 8 and 9). 

Amide derivatives have proved especially useful sugars for study by c.d. spectroscopy. The amide substituent is the same as the chromophore found in proteins, so that its optical properties have been extensively studied both experimentally and theoretically. 2-Acetamido sugars are found in many glycoproteins. The structure of 2-acetamido-2-deoxy-a-D-glucopyranose is given as an example in formula 7. 

C.d. spectroscopy is now being applied to more complicated polysaccharides. The 3-deoxy-D-man o-2-octulopyranosylonic acids found in Escherichia coli LP1092 have been definitely assigned the a-D configuration. The negative nir c.d. band exhibited by this polysaccharide correlates with the negative c.d. of methyl 3-deoxy-a-D-wianno-2-octulopyranosidonic acid rather than the positive c.d. band exhibited by methyl 3-deoxy-)3-D-/ a/ino-2-octulopyranosidonic acid. 

The complex oligosaccharides comprising the Y and T antennae of three glycoproteins have been studied by c.d. spectroscopy. Five antennae were studied in all, because two of the proteins have two closely related forms. The c.d. for the three fundamental oligosaccharides are given in Fig. 36. These are asparagine-linked glycopeptides, and the intense, conservative c.d. band that results from the interaction between the two amides has already been discussed in Section III,2. Fig. 36 shows that the c.d. spectra... 

Many of these instrumental techniques have a two-dimensional (2-D) counterpart, which have their own advantages and disadvantages. Rather than treat 2-D spectroscopy as a separate issue, we will include it where appropriate, interleaving it with the corresponding 1-D method. 2-D spectroscopy should perhaps be viewed as an interpretational aid for 1-D spectroscopy, rather than an end itself. 

The second purpose of the work is to describe the use of three-dimensional (3-D) spectroscopy in which the TL intensity is measured as a function of both temperature and wavelength. 

Barjat H, Morris GA, Smart S, Swanson AG, Williams SCR, High-resolution diffusion-ordered 2-D spectroscopy (HR-DOSY)—A new tool for the analysis of complex mixtures, /. Magn. Reson. B, 108 170-172, 1995. 

Conformational analysis of BS I by c.d. spectroscopy indicated that the protein contained 30-40% of /3 structure in its native conformation.623 The c.d. spectrum was relatively insensitive to alteration in pH, removal of bound metal, and addition of methyl a-D-galactopyranoside. However, addition of dodecyl sodium sulfate or 2,2,2-trifluoroethanol resulted in the formation of some a-helical structure, and was accompanied by the loss of polysaccharide-precipitating capacity. Urea (8 M) irreversibly denatured the lectin. 

Adams D.M., Long G.J., Williams A.D. Spectroscopy at very high pressures. An infrared study of spin-state equihbrium in some iron (II) complexes. Inorg. Chem. 1982 21 1049-53. 

WEL/MCL] Weltner, W., McLeod, D., Spectroscopy of titanium, zirconium and hafnium oxides in neon and argon matrices at 4 and 20 K, J. Phys. Chem., 69, (1965), 3488-3500. Cited on page 127. 

The detection of the endocyclic, enolacetal double bond (in conjugation with the carboxyl function) obtained during these alkaline, )8-elim-ination processes proved to be easy by such physical methods as those already described (for example, u.v. or o.r.d.-c.d. spectroscopy). 

Coggins BE, Zhou P (2008) High resolution 4-D spectroscopy with sparse concentric shell sampling and PFT-CLEAN. J Biomol NMR 42 225-239... 

A comparative study on the secondary structure of hen egg white, turtle Testudo grorea) egg white, and fruit fly Ceratitis capitata) egg lysozymes has been carried out using c.d. spectroscopy. Differences in the near-u.v. spectra of these enzymes agreed with the different contents of L-tryptophan residues. The far-u.v. c.d. spectra showed the existence of a high content of unordered structure in the insect lysozyme in comparison with the high participation of a-helical conformation in the hen egg white enzyme. Differences in the dichroic behaviour between both enzymes were also remarkable under denaturing conditions. 

Miscellaneous Glycoproteins. Bovine lutrophin, bovine thyrotrophin, and human chorionic gonadotrophin preparations with carbodi-imide-mediated covalently cross-linked sub-units have been isolated in high yield and characterized by c.d. spectroscopy, radioligand receptor assays, and hormone-specific bioassays. The c.d. spectra of the native and cross-linked hormones did not differ much, suggesting that there is little conformational change on cross-linking. 

D. Spectroscopy of unsymmetric dimers and donor-acceptor pairs... 

The conformational changes induced by 0-acetylation of the poly-hydroxyalkylpyrazoloC3, i)-b]quinoxalines ( 8) have been studied by %-n.m.r. and c.d. spectroscopy they are considered to be due to... 

Data about chain alignment and reorientation must usually be obtained by modelling or simulation of the lineshape, and usually, data from several different experiments are required to yield an unambiguous conclusion. An exception involves the more recent multi-dimensional experiments, described in section 8.5 [53, 59], that are designed to yield the appropriate data graphically or with simple calculation. Even with 2-D spectroscopy, if multiple motions are present or if diffusion is also present, there remains a requirement to model the data. 

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