Separation of overlapping spectra from evolving systems using factor analysis. 4. Fluorescence spectra of hematoporphyrin IX

Infrared spectroscopy of aqueous ionic salt solutions at low concentrations

The analysis by infrared spectroscopy of aqueous solutions of the binary inorganic salts NaI and NaCl and the ternary salts CaCl2 and BaCl2 at concentrations from 1000 to 2 mM was carried out to complement a previous study done at higher concentrations on nine binary salts (alkali halides) and one ternary salt (MgCl2) [J.-J. Max and C. Chapados, J. Chem. Phys. 115, 2664 (2001)]. These salts are completely ionized in aqueous solutions, forming monoatomic species that do not absorb IR but that perturb the surrounding water, modifying its spectrum. The factor analysis of the spectra revealed that all these salt solutions were composed of two water types: pure water and salt solvated water. The authors obtained pure salt solvated water spectra for all the salts using an extrapolation technique. The water types obtained are constant for the binary and ternary salts down to 2 mM. For the binary salts, we determine that 5.0 and 4.0 water molecules are solvated to the Na+-Cl- and Na+-I- ion pairs, respectively. These numbers are the same as that obtained at higher concentrations. For the new ternary salts, we find that 6.0 and 8.0 water molecules are solvated to Ca++-(Cl-)2 and Ba++-(Cl-)2 ion pairs, respectively. These numbers are higher than the four water molecules solvated to Mg++-(Cl-)2 ion pairs determined previously, but show a progression that follows their atomic numbers. These results constitute new experimental results on "simple" systems whose molecular organization is still a matter of debate. The IR method that probes the system at the molecular level is a method different than the macroscopic ones that give the activity coefficients. The IR gives direct observation at the molecular level of the strong ion-water interactions that are often neglected and its water structure not considered in macroscopic methods. The present results and their analysis together with those obtained by other methods will facilitate the determination of the organization of these aqueous systems.

Infrared spectroscopy of acetone-hexane liquid mixtures

Acetone and hexane mixtures covering the whole solubility range were studied by Fourier transform infrared attenuated total reflectance spectroscopy. Factor analysis separates the spectra into four principal factor spectra and multiplying factors. Those containing negative factors are abstract, but the spectra are real. A statistical distribution model of the molecules in the solutions rendered the factors real. From these we define the intermediate species that occur in a 1:2 molar ratio of acetone in hexane, present principally in the low acetone concentration regions, and in a 2:1 molar ratio of acetone in hexane, present principally in the higher acetone concentration region. However, except at the concentration range limits where only pure acetone and pure hexane are present, the four species are present over the whole solubility range. The IR spectra of the species indicated very little displacement of the CH stretch bands, HCH deformation bands, and CC stretch bands, although there are some small intensity variations. Most of the modifications are observed on the acetone C=O stretch band. From the gas phase position, a strong bathochromic shift of 19 cm(-1) of the pure liquid is assigned to dipole-dipole interactions. In the 2:1 groupings, the shift that decreases to 15 cm(-1) is due to the diminished dipole-dipole interactions. In the 1:2 groupings, no dipole-dipole interaction can exist, and the bathochromic displacement of 9 cm(-1) is attributed to van der Waals interactions. In the one acetone to two hexanes grouping, no dipole-dipole interaction can exist, and the bathochromic displacement of 9 cm(-1) is attributed to van der Waals interactions. From the statistical distribution of the molecules, we determine that mixtures of hexane and acetone form a random organization with no preferred association or complex.

Infrared spectroscopy of acetone-methanol liquid mixtures: Hydrogen bond network

Acetone and methanol mixtures covering the whole solubility range are studied by Fourier transform infrared attenuated total reflectance spectroscopy. The strong bathochromic shifts observed on methanol OH and acetone CO stretch IR bands are related to hydrogen bonds between these groups. Factor analysis separates the spectra into four acetone and four methanol principal factors. A random molecular model developed for the acetone-water system [Max and Chapados, J. Chem. Phys. 119, 5632 (2003); 120, 6625 (2004)] was modified for the acetone-methanol system. This model, which takes into account H bonds accepted by methanol and acetone, is made up of 12 methanol and 11 acetone species. The 23 species abundances are regrouped according to evolving patterns or spectral similarities to compare them to the eight experimental factors. Methanol acetone mixtures are almost but not exactly random: the methanol oxygen atoms have stronger capacities than acetone to accept H bonds from methanol in the proportion 1.5 to 1. Since oxygen atoms are in excess, all labile hydrogen atoms will form H bonds. As acetone is added to methanol, its OH stretch band blueshifts as the number of accepted H bonds decreases. When methanol gives one H bond and accepts one, an H-bonding network is formed that was coined "chained organization." However, the acetone molecules do not sequester any methanol molecules by breaking or increasing the H-bond methanol network. Similarly, the methanol molecules do not sequester any acetone molecules. Consequently no acetone-methanol complex is formed in the mixtures. Gaussian simulation of the four principal factors in the methanol OH stretch region gave three distinct absorption regimes consisting of the OH stretch bands and their satellites that are identified as MeOH(1), MeOH(2), and MeOH(3) (subscript indicates the number of H, covalent and H bond, which surround the oxygen). These regimes are related to those identified in the water-acetone system as OH(2), OH(3), and OH(4).

Interaction of dicarboxylic metalloporphyrins with liposomes. The effect of pH on membrane binding revisited

The acid-base properties of Zn-hematoporphyrin IX (ZnHP) and Zn-mesoporphyrin IX (ZnMP) and the effect of pH on their binding to liposomes have been studied. The ionization constants for the two carboxylate groups of ZnHP were calculated by principal component analysis and are 5.7 +/- 0.1 and 6.9 +/- 0.05. The neutral species and the mono- and dianionic forms all bind to liposomes, but a strong pH effect on the binding constant was observed for both the investigated compounds. We also observed a decrease in the binding of the two anionic species when the membranes carried a negative charge. These results indicate that the porphyrins partition into the membrane with their carboxylic moieties near the lipid-water interface so that their deprotonation, leading to a charged molecule, does not prevent the insertion of the tetrapyrrole ring into the lipid environment of neutral liposomes.