Circular dichroism main applications

The circular dichroism (CD) spectrum of a number of polysaccharides is close to that of the corresponding monosaccharides (Morris, 1994). CD information gleaned from monosaccharides and extrapolated to polysaccharides is valid, insofar as mono- and oligosaccharides are representative of the complete polymer structure. CD applications to polysaccharides have been reviewed (Johnson, 1987). With the use of CD and complementary instrumentation, Morris (1976) studied xanthan insensitivity to salt and temperature, and observed that stability was introduced by a folding back of side chains around the main chain. Dentini et al. (1991) outlined the use of CD to measure the average charge density of pectin chains. 

Other IRRAS applications to peptides and proteins. In addition to the pulmonary surfactant system, a variety of other applications employing IRRAS to study peptide and protein conformation and orientation have appeared. The secondary structure conversion of the amyloid (prion)-protein in the normal form into the abnormal form is the main cause of several human and animal diseases, such as Alzheimer s disease [68]. The secondary structure of the first 40 residues of the amyloid protein was detected by circular dichroism (CD) in aqueous solution and with IRRAS at the interface. A stable /1-sheet-enriched state of the amyloid is formed at the air-water interface, in contrast to the initial bulk solution containing high a-helix/random coil and low /l-sheet parts. The change in the pH going from bulk (alkaline pH) to the interface (neutral or slightly acidic pH) can have effects on the conformation at the interface. Another alternative might be the intrinsic hydrophobicity of the air-water interface, which is a hydrophobic-hydrophilic system with air as the hydrophobic part. 

At present, the density functional theory (DFT) prevails in calculations of the structural and spectral parameters of transition metal complexes [18]. For this reason, and thanks to our previous positive experience with simulation and interpretation of the UV-Vis, IR, electronic and vibrational circular dichroism (BCD and VCD) spectra of chiral vanadium complexes [19], we decided to use the DFT methods as the main tool in the present work as weU. We shall present the calculated molecular stractures, vibrational and electronic spectra, as well as the V chemical shifts of the chosen anions of the vanadium(V) tartrato complexes. Where applicable, results are confronted with the available experimental data, with the aim to assess the reliability of the individual methods for future calculations of a similar kind. 

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