SOLVENT EFFECTS ON TRIPLET-STATE BACTERIOCHLOROPHYLL a AS DETECTED BY TRANSIENT RAMAN SPECTROSCOPY AND THE ENVIRONMENT OF BACTERIOCHLOROPHYLL a IN THE LIGHT-HARVESTING COMPLEX OF Rhodobacter sphaeroides R26

The frequency of BChl that was bound to the light-harvesting complex (LHC) of Rhodobacter sphaeroides R26 was found to be 1598 cm^-1, a result which suggests that a pair of BChl molecules form a dimer in the LHC in the T₁ state.     

Photostability of bacteriochlorophyll a and derivatives: potential sensitizers for photodynamic tumor therapy

The photostabilities of bacteriochlorophyll a and several of its derivatives, which are of interest as potential sensitizers in photodynamic tumor therapy, were investigated. The pigments were irradiated with light >630 nm in organic solvents (acetone, tetrahydrofuran, pyridine, methanol, ethanol, n-propanol, 2-propanol and toluene) and in aqueous detergent solutions (cetyl-trimethyl-ammonium bromide [CTAB], lauryldimethyl-aminoxide [LDAO] or sodium dodecyl-sulfate [SDS] and Triton X-100 [TX100]). Their stabilities in these different solvents were determined in the presence and absence of an external sensitizer (pyromethyl-pheophorbide a), oxygen, sodium ascorbate and inert gas (Ar) or vacuum. The photodegradation products of bacteriochlorophyll a in acetone solution were isolated, purified by HPLC and analyzed by their absorption spectra and mass spectroscopy. Besides the well-known dehydrogenation products, such as [3-acetyl]-chlorophyll a, which were obtained as by-products, the major products had low absorption in the visible-near infrared spectral range. The spectral signature of the major component of these products was characteristic of linear open-chain tetrapyrroles, but they lacked the characteristic protonation-deprotonation behavior and reactivity of bilins with Zn(++).     

Effects of Nonpolar and Polar Solvents on the Qx and QY Energies of Bacteriochlorophyll a and Bacteriopheophytin a

The effects of nonpolar and polar solvents on the Q_x and Q_y energies of bacteriochlorophyll (BChl) a and bacteriopheophytin (BPhe) a were examined by electronic absorption spectroscopy. All of the four different energies exhibited a linear dependence on R(n) = (n² - l)/(n²+ 2), where n is the refractive index of the solvent, in both nonpolar and polar solvents. The energy of each state of both pigments could be expressed as v = -dR(n) + e (in cm^-1) where coefficient d was related to the dispersive interaction between the solute and the solvent molecules. A theory developed by Nagae showed that coefficient d originates from the quantum-mechanical fluctuation of the multipole moments of the solute, in terms of which the following characteristics of the observed d values were explained: (1) In all of the four cases of the Q_x, and Q_y energies of both BChl a and BPhe a, the d values for the polar solvents were smaller than those for the non-polar solvents. (2) In both nonpolar and polar solvents, the d value of BChl a was larger than that of BPhe a in the Q_y energy, whereas the d value of BPhe a was larger than that of BChl a in the Q_x energy. (3) The d value of the Q_x energy was larger than that of the Q_y, energy for either case of BChl a or BPhe a.