How the formation process influences the structure of BChl c aggregates

The change of absorption spectra has been measured during the drying proces s of (3(1) R)bacteriochlorophyll (BChl) c from diethyl ether, dichlorometha ne (CH2Cl2) and carbon tetrachloride (CCl4) solutions. Absorption maxima of the Q(y)(0-0) transition of BChl c appear at 659 nm in diethyl ether, 680 nm in CH2Cl2 and 710 nm in CCl4. All these peaks are red-shifted to about 7 40 nm with formation of solid high aggregates when the solutions are comple tely dried. Fourier transform infrared spectra of the three solid aggregate s are almost identical. However, magnetic circular dichroism and circular d ichroism spectra are different and can be explained in terms of variations in stacking size of the aggregates and molecular arrangement of BChl c. Sma ll-angle X-ray diffraction has been observed only for the aggregates treate d with CH2Cl2, and the same sample gave rise to highly resolved cross polar ization/magic angle spinning C-13 nuclear magnetic resonance spectrum. The results suggest that molecular ordering of the solid-state BChl c aggregate s is highly dependent on the formation process which is largely determined by the solvent used.