Synthesis, photophysical properties, in vivo photosensitizing efficacy, and human serum albumin binding properties of some novel bacteriochlorins.

The synthesis, photophysical characteristics, in vivo photosensitizing efficacy, human serum albumin (HSA) binding properties, and skin phototoxicity of some stable bacteriochlorins were investigated. The novel bacteriochlorins, obtained from chlorophyll-a, have long-wavelength absorptions in the range lambda max = 734-758 nm. Preferential migration of ethyl over methyl substituents among ketobacteriochlorins obtained in the pinacol-pinacolone rearrangements of vic-dihydroxybacteriochlorins was confirmed by NOE studies. The bacteriochlorins show relatively low fluorescence quantum yields. Among all the bacteriochlorins the triplet states were quenched by ground state molecular oxygen in a relatively similar manner, yielding comparable singlet oxygen quantum yields. In preliminary in vivo studies (DBA/2 mice, transplanted with SMT/F tumors), ketobacteriochlorins were found to be more photodynamically active than the related vic-dihydroxy analogues. Replacement of the methyl ester functionalities with di-tert-butylaspartic acids enhanced the in vivo efficacy. Site specific human serum albumin (HSA) binding studies indicated a direct correlation between the ability of the compound to bind to the diazepam binding site (albumin site II) and the in vivo photosensitizing efficacy.

Self-assembled complexes of oligopeptides and metalloporphyrins: measurements of the reorganization and electronic interaction energies for photoinduced electron-transfer reactions.

Cationic porphyrins form ground state electrostatically associated complexes with anionic oligo-electrolytes such as those formed by a series of glutamic acid (E) residues. Temperature dependencies were measured of the rate constants for intra-complex electron transfer to the triplet state of Pd(II)TMPyP4+ from a tyrosine (tyr, Y) or tryptophan (trp, W) moiety connected to a glutamic acid tetramer. In complexes such as YE4, E2YE2, YE4G10E (G, glycine), and WE4 these data were used to estimate the reorganization energy (lambda) and electronic interaction energy (HDA) relevant to the process. For all tyr-peptide complexes, lambda values were found to be large (lambda approximately 1.60 +/- 0.06 eV), reflecting a relatively high medium polarity in the vicinity of tyr residues. It further indicates that the tyr residues in all oligo-peptides are exposed to the aqueous medium in a similar way irrespective of the position of the aromatic moiety in the peptide chain. A significantly lower lambda value (lambda = 1.08 eV) was derived for the tryptophan-containing peptide complex, indicating a relatively higher hydrophobic character of trp compared to tyr. The electronic coupling matrix elements (HDA) derived for tyr-peptide complexes (5.1 meV for YE4, 5.4 meV for YE4G10E and 7.5 meV for E2YE2) were larger than that found for WE4 (1.1 meV). Molecular dynamics calculations were employed to obtain structural features of the porphyrin-peptide complexes. These showed average distances between the center of mass (COM) of the porphyrin ring and the center of mass of the amino acid aromatic ring of 816 +/- 140 pm (YE4), 800 +/- 80 pm (E2YE2), 900 +/- 130 pm (YE4G10E) and 970 +/- 160 pm (WE4). The molecular dynamics calculations were shown to be in good agreement with the experimentally determined electronic interaction energies, strongly suggesting that HDA is primarily responsible for the dependence of the electron-transfer rate constant (KET) on the donor-acceptor separation distance and relative orientation. The higher HDA (7.55 meV) derived for tyr incorporated into the middle of the peptide backbone (E2YE2) was presumed to be associated with a higher degree of orbital overlap due to a more favorable ring-ring orientation. Overlap parameters (beta derived for all peptide-porphyrin complexes were similar (approximately 0.95 +/- 0.06 A-1), being in good agreement with most literature values for similar systems. Finally, the intra-complex electron-transfer ratio (ktrp/ktyr) derived from flash photolysis experiments and the corresponding ratio derived from Marcus' theory combined with experimental data from the temperature-dependence investigations and electrochemical measurements were found to be in excellent agreement. This same consistency was found for the couple E4Y and E2YE2. The empirical expression (Moser and Dutton) governing the intraprotein electron-transfer rate constant in native systems combined with our experimental data (kET, lambda, delta G0) yielded tunneling pathway distances in excellent agreement with those arising from the molecular modeling studies. The exception was for the long peptide YE4G10E, for which the Quenched Molecular Dynamic (QMD) sampling technique was complicated and is probably inadequate.

Effect of temperature and surfactant structure on the microviscosity at the micelle-water interface: isomeric alkylbenzenesulfonates used as their own probe.

We investigated the effect of temperature and surfactant structure on the microviscosity in aqueous micellar solutions formed by isomeric hexadecylbenzenesulfonates (xphiC16, where x=4-6 and indicates the position of the benzene ring [phi] along the alkyl chain) by fluorescence polarization and excimer emission spectroscopy. For a given isomer, the degree of polarization (p) was found to decrease with increasing temperature, with no evidence for changes in micellar structure. etaint/tau ratios, where etaint is the microviscosity of the benzene environment in micelles and tau its natural lifetime, were derived from fluorescence polarization measurements and showed a similar temperature behavior to that observed with the degree of polarization, suggesting that a thermal effect is the determinant factor in the variation of etaint. Interestingly, the microviscosity around the benzene ring was found to depend on the isomer structure in the entire range of temperatures investigated (8-60 degrees C) and is mainly determined by the orientation of the surfactant at the micelle-water interface in which the short alkyl chain is preferentially located at the interface and the long alkyl chain in the micellar core. This micelle conformation was found to prevail in the entire range of temperatures. In contrast to the dependence of p with temperature, excimer to monomer maximum emission ratios (IE/IM) were found to increase with increasing temperature, showing that when IE/IM is high (strong excimer emission), the degree of polarization is low (low microviscosity) and vice versa. Thus, the two independent measurements (IE/IM and p) yield the same information, namely, that the benzene moiety in all xphiC16 aqueous micelles resists both translational and rotational diffusion in a similar manner in the entire range of temperatures investigated (approximately 8-60 degrees C).

Spectroscopic investigations of metalloporphyrin-oligopeptide systems: evidence for peptide aggregation.

Anionic pentapeptides consisting of a string of four glutamic acid residues terminated by either tyrosine (Glu4Tyr) or tryptophan (Glu4Trp) were synthesized, and their aggregation properties in buffered (pH = 7.0) aqueous solutions were investigated using two different approaches. In the first approach, the effects of the concentration of peptide used as its own probe (intrinsic probe) on its fluorescence emission, circular dichroism, surface tension, and solution pH yielded similar critical peptide concentrations of around 175 microM. This particular concentration was taken as evidence for peptide aggregation. In the second approach, peptide aggregation was investigated using cationic metalloporphyrins, tetrakis(N-methyl-4-pyridyl)porphyrin (Pd(II)TMPyP(4+) and Zn(II)TMPyP(4+)), as extrinsic probes. The effect of peptide concentration on porphyrin ground-state absorption confirmed peptide aggregation, but at a lower critical peptide concentration near 125 microM. This difference was attributed to the possible distortion introduced by the association of one (or more) large metalloporphyrin molecule with the peptide aggregates. Evidence for peptide aggregation was also demonstrated from the effect of peptide concentration on Pd(II)TMPyP(4+) triplet-state decay. The fast component (k(f), associated with electron transfer from the target Tyr and Trp residues to the porphyrin triplet state) was found to be independent of peptide concentration, implying no noticeable effect of peptide aggregation on the electron-transfer event. This was attributed to the fact that species formed by excitation of porphyrin associated with ion-pair complexes or bound to peptide aggregates and the diffusion together of the separate T(1) and peptide entities in the bulk phase are kinetically similar. On the other hand, the slower component (k(s)) of the decay, which is associated with the diffuse formation of an encounter complex between the free peptide and T(1) porphyrin (bulk phase), was peptide-dependent and displayed a critical peptide concentration near 125 microM, above which it became practically independent of peptide concentration. This invariance of k(s) was taken as an indication that the free peptide concentration in the bulk phase remains constant above 125 microM, the concentration at which peptide molecules prefer to associate as aggregates.

Aggregation Behavior of Sugar Surfactants in Aqueous Solutions: Effects of Temperature and the Addition of Nonionic Polymers.

The aggregation behavior, critical micelle concentration (cmc) and micelle aggregation number (N), of dodecyl maltoside (DM), octyl glucoside (OG), and Hecameg has been investigated in water and in water plus one of the three water-soluble polymers, polyoxyethylene (POE), polyoxypropylene (POP), and polyvinyl pyrrolidone (PVP), by means of florescence probing and time-resolved fluorescence quenching. The cmc of DM in water increased with temperature and showed a slight increase in the presence of POE. The aggregation number N of DM micelles was nearly independent of concentration (0.25-1 wt %) and temperature (16-60 degreesC). It remained invariant upon addition of 2 wt % POE or PVP but decreased slightly upon addition of the more hydrophobic POP. With increasing temperature, the cmc of OG decreased, went through a shallow minimum at around 35 degreesC, and increased. Addition of POE slightly increased the cmc in the whole temperature range. The aggregation number of OG micelles showed a fairly flat maximum at around 30 degreesC, and was unaffected by the presence of 2 wt % POE or PVP. However, N showed a complex dependence on temperature in the presence of POP, with lower values than in pure water below 15 degreesC, and rapidly increasing quencher-dependent values above this temperature. Hecameg was characterized by N-values nearly independent of temperature and concentration. Intermicellar exchanges of probe and/or quencher were observed with OG and Hecameg, but not with DM. The above results are compared to those for the nonionic ethoxylated surfactants. The effect of various parameters on the micelle aggregation number, the micelle polydispersity, the occurrence of sugar surfactant/nonionic polymer interactions, and the mechanisms responsible for the observed intermicellar exchanges are discussed. Copyright 1998 Academic Press.