Solution Structure of Biomolecules

Biomolecules are mostly chiral, therefore chiroptical methods are the first choice among the spectroscopic methods applied to biomolecular structural studies. Characterization of peptides, nucleotides, proteins and nucleic acids by their ECD spectra became a generally used procedure and was repeatedly reviewed [1]. 

The n-n (210-230 nm) and tc-tc (185-200 nm) transitions of amide groups yield information about the secondary structure of oligopeptides, polypeptides and proteins. Three types of interactions between these two transitions are responsible for the observed ECD exciton interactions between degenerate n-n transitions within different peptide groups, mixing of n-n and n-n transitions within differ- 

In DNA, the UV active chromophores are the bases of adenine (A), guanine (G), cytosine (C), and thymine (T). Their strong ti-ti and weak n-n transitions themselves situated in the 190-300 nm region are not inherently optically active. However, since bases are attached to optically active deoxyribose, the sugar component can induce the CD in the base chromophores. ECD of DNA brought very valuable information about different forms of single strands, double helixes, the dependence of the structure on physico-chemical conditions, as reviewed by Johnson 

Recently, we have also used VCD and a combination of VCD and ECD to study the non-covalent interactions between two groups of important biomolecules, i.e. biopolymers - polypeptide and DNA - and cationic and anionic porphyrins [34-36]. 

The sensitivity of VCD to structural variations of the polypeptide-porphyrin complexes is demonstrated in Fig. 8.7. The secondary structure of the peptidic part of the poly-L-glutamic acid-cationic porphyrin TATP complex can be changed by pH variation. At acidic pH ( 5), its a-helical structure is demonstrated by the 

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