2006, 2008; Lambrev et al. 2007),
and for monitoring of the oligomerization state of these complexes (Garab et al. 2002; Büchel 2003) and the effect of single mutations (Morosinotto et al. 2003; Croce et al. 2004; Mozzo et al. 2008). Polymer and salt-induced (psi)-type CD bands Psi-type aggregates are three-dimensional macroaggregates containing a high density of interacting chromophores and see more possessing sizes commensurate with the wavelength of the measuring light and a long-range chiral order of their chromophores. These are of interest because they are contained in many highly organized biological materials. The CD theory of psi-type aggregates (Keller and Bustamante 1986; Kim et al. 1986; Tinoco et al. 1987) is based on the classical theory of coupled oscillators (DeVoe 1965). The theory of H. DeVoe considers that light induces oscillating (transition) dipoles in the polarizable groups of the object, and the induced dipoles interact as static dipoles. In contrast selleck kinase inhibitor to small aggregates, where it is sufficient to consider the short-range dipole–dipole interactions, with r −3 dependence (r is the distance between the dipoles), in psi-type aggregates, the full electrodynamic interaction between the dipoles must be taken into account. At distant points of observation, the oscillating dipole can be regarded as a radiating spherical wave. Thus, the chromophores at large distances can be coupled via radiation
and intermediate coupling mechanisms between the dipoles (with r −1 and r −2 dependencies, respectively). For psi-type aggregates, the radiation Reverse transcriptase and intermediate couplings between the chromophores in the aggregate cannot be neglected, and they play an important role in determining the shape and magnitude of the psi-type CD spectrum. In the suspension of small aggregates, or in large aggregates that possess no long-range order, the relatively weak CD signals, arising from these relatively weak interactions, cancel each other. In contrast, in psi-type aggregates, they can sum up due to the long-range chiral order of
the chromophores, explaining that the magnitude of the psi-type CD spectrum is controlled by the size (and chromophore density) of the particle (Kim et al. 1986; Barzda et al. 1994). The shape of the psi-type CD spectrum is determined mostly by the pitch and the handedness of the aggregate. In small aggregates, the entire aggregate at any instant is at the same phase of the wave upon interaction with the light. In contrast, in large aggregates, which are commensurate with the wavelength, this is not true, and retardation effects can play an important role (Kim et al. 1986). As a result of the long-range chiral order and additional long-distance interactions in psi-type aggregates, these aggregates exhibit unusual CD spectroscopic properties, which have also been identified and studied in granal thylakoid membranes (Fig. 3) and lamellar aggregates of LHCII.