The interaction energies are calculated in the point-dipole approximation assuming a common linewidth for all transitions

of ∼80 cm−1. Screening by the protein is taken into account by a dielectric constant that was used a global free-fit parameter. The initial calculated dipole strength of 68.9 D 2 is thus reduced by a factor 2.4 leading to an effective dipole strength of 28.7 D 2, a value that is lower than that proposed by Pearlstein (1992). This value is close to a physically relevant value of the reduced dipole strength in the range of 25–40 D 2. In order to simulate the spectra, a minimum of free parameters was used to fit the essential features of the spectra. The authors proposed that the model can be improved by inclusion of vibrations, lifetime broadening of the highest energy Protein Tyrosine Kinase inhibitor INCB024360 concentration exciton states, and by allowing for different dipole strengths for the individual BChl a molecules and a variation of the dielectric constant over the protein. Simulations based on the same exciton model were performed by the following research groups: Vulto et al. (1998a, 1999), Wendling et al. (2000, 2002), and Iseri and Gülen (1999). Table 7 Exciton energies

of Prosthecochloris aestuarii in the monomer Exciton A B C D E 1 827.1–824.4 825.6 825.7 825.0 823.8 2 816.3 815.2 814.5 814.1 813.7 3 813.0 813.5 812.2 812.8 811.5 4 807.8 806.7 805.8 805.9 804.7 5 804.8 802.7 800.8 801.5 801.0 6 801.3 800.2 796.4 799.6 PJ34 HCl 797.8 7 793.6 791.5 793.0 791.5 789.4 Where A is from Johnson and Small (1991), B is from Louwe et al. (1997b), C is from Vulto et al. (1999), D is from Iseri and Gülen (1999), E is from Wendling et al. (2002) Nature of the lowest energy band The assignment of the bands in the absorption spectrum, especially of the band, the lowest in energy at 825 nm, has proven to be difficult. The number of excitonic states and their respective energies have been the subject of intense debate. Johnson and Small (1991) concluded that lower and higher spectral energy features flanking the hole-burning line can only be explained when excitonic interactions between the BChls are taken into account. Furthermore,

the results of spectral hole burning show the presence of eight states. Two of those eight identified exciton states, which have perpendicular symmetry, contribute to this lowest exciton band at 825 nm. Models excluding the interactions between the subunits of the trimer are not successful in describing this experimental data (Johnson and Small 1991). Therefore, Johnson and Small (1991) have developed a model in which this interaction is included leading to a maximum of 14 delocalized states (21 states in total, of which 14 are degenerate). This implies that the 825-nm band comprises of three, slightly shifted, bands of the subunits, of which two are degenerate. For the space group C 3, the states having E symmetry are degenerate while the states with A symmetry are not (Atkins 1995).