This review will consider solution studies of structure and interactions of DNA and DNA complexes using linear dichroism spectroscopy, with emphasis on the technique of orientation by flow. The theoretical and experimental background to be given may serve, in addition, as a general introduction into the state of the art of linear dichroism spectroscopy, particularly as it is applied to biophysical problems.
The application of linear and circular dichroism (LD and CD) in nucleic acid research is illustrated by recent results aimed at answering specific structural problems in the interaction of DNA with molecules of biological importance. We first consider the circumstances under which ligands, such as DAPI (4',6-diamidino-2-phenylindole), change their preferred binding mode in the minor groove to major groove binding or intercalation. As an extension of this problem we refer to the switch between groove binding and intercalation of structurally similar ligands such as ellipticines and trigonal ruthenium complexes. We also explore the use of LD and CD in the determination of the structure of the complex formed between the polynucleotide poly(dA) and the novel 'peptide nucleic acid', consisting of nucleic acid bases joined by a polyamide homomorphous with the deoxyribose-phosphate backbone of DNA. Finally, the structure and interaction of the recombination enzyme RecA with DNA is discussed, in particular the influence of the presence of intercalators, groove binders or covalent DNA adducts.
Abstract— We determined the polarized and isotropic visible/UV absorption spectra of chlorophyll a (Chi a) and pheophytin a (Pheo a) oriented in the lamellar phase of glycerylmonooctanoate/H2O. Resolution into mutually perpendicular X‐ and Y‐polarized absorption spectra of the pigments was achieved assuming that the transition moments of Chi a and Pheo a are located in the plane of the chromophores. The polarized spectra were deconvoluted into harmonic progressions and the resultant assignment of band positions in the long‐wavelength region was found to correlate well with independent spectral measurements, such as the polarisation of fluorescence. However, the correlation of the experimentally determined transitions with the results of theoretical calculations is not straightforward. The overall conclusions are of fundamental interest in the determination of orientations of the tetrapyrrole macrocycle in lipid lamellae and pigment‐protein structures of photosynthetic membranes.
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