Resonance energy transfer in the solution phase photophysics of -Re(CO)3 L+ pendants bonded to poly(4-vinylpyridine).

Polymers with general formula ([(vpy) 2vpyRe(CO) 3(tmphen) (+)]) n ([(vpy) 2vpyRe(CO) 3(NO 2-phen) (+)]) m (NO 2-phen = 5-nitro-1,10-phenanthroline; tmphen = 3,4,7,8-tetramethyl-1,10-phenanthroline); vpy = 4-vinylpyridine) were prepared and their morphologies were studied by transmission electron microscopy (TEM). Multiple morphologies of aggregates from these Re I polymers were obtained by using different solvents. Energy transfer between MLCT Re-->tmphen and MLCT Re-->NO 2 -phen excited states inside the polymers was evidenced by steady state and time-resolved spectroscopy. Current Forster resonance energy transfer theory was successfully applied to energy transfer processes in these polymers.

Intercalation of fac-[(4,4'-bpy)ReI(CO)3(dppz)]+, dppz = dipyridyl[3,2-a:2'3'-c]phenazine, in polynucleotides. On the UV-vis photophysics of the Re(I) intercalator and the redox reactions with pulse radiolysis-generated radicals.

The intercalation of fac-[(4,4'-bpy)Re(I)(CO)3(dppz)]+ (dppz = dipyridyl[3,2-a:2'3'-c]phenazine) in polynucleotides, poly[dAdT]2 and poly[dGdC]2, where A = adenine, G = guanine, C = cytosine and T = thymine, is a major cause of changes in the absorption and emission spectra of the complex. A strong complex-poly[dAdT]2 interaction drives the intercalation process, which has a binding constant, Kb approximately 1.8 x 10(5) M(-1). Pulse radiolysis was used for a study of the redox reactions of e(-)(aq), C*H(2)OH and N3* radicals with the intercalated complex. These radicals exhibited more affinity for the intercalated complex than for the bases. Ligand-radical complexes, fac-[(4,4'-bpy*)Re(I)(CO)3(dppz)] and fac-[(4,4'-bpy)Re(I)(CO)3(dppz *)], were produced by e(-)(aq) and C*H(2)OH, respectively. A Re(II) species, fac-[(4,4'-bpy)Re(II)(CO)3(dppz)](2+), was produced by N3* radicals. The rate of annihilation of the ligand-radical species was second order on the concentration of ligand-radical while the disappearance of the Re(II) complex induced the oxidative cleavage of the polynucleotide strand.

On the association and structure of radicals derived from dipyridil[3,2-a:2'3'-c]phenazine. Contrast between the electrochemical, radiolytic, and photochemical reduction processes.

The reduction of dipyridil[3,2-a:2'3'-c]phenazine, dppz, by pulse radiolytically generated e(-)(sol) or by the reaction of the dppz excited states with electron donors produces the radical dppzH(.). The dimer radical, (dppz)(2)H(.), exists in equilibrium with dppz with an association constant, K = 10(3) M(-1). The rate constant for the reaction of dppzH(.) with dppz is k = 4.3 x 10(6) M(-1) s(-1). DFT calculations on the structures of dppzH(.) and the doubly reduced and doubly protonated dppzH(2) rendered a planar structure for the former species and a bent one for the latter.

Contrasting intrastrand photoinduced processes in macromolecules containing pendant -Re(CO)3(1,10-phenanthroline)+: electron versus energy transfer.

The photochemical and photophysical properties of the polymers [(vpy-CH3+)2-vpyRe(CO)3(phen)+]200 (vpy = vinyl pyridine, phen = 1,10-phenanthroline) have been investigated in solution phase and compared to those of a related polymer, [(vpy)2-vpyRe(CO)3(phen)+]200, and monomer, pyRe(CO)3(phen)+. Irradiations at 350 nm induce intrastrand charge separation in the peralkylated polymer, a process that stands in contrast with the energy migration observed with [(vpy)(2)-vpyRe(CO)3(phen)+]200. Electronically excited -vpyRe(CO)3(phen)+ chromophores and charge-separated intermediates react with neutral species, e.g., 2,2',2' '-nitrilotriethanol, and anionic electron donors, e.g., SO3(2-) and I-. The anionic electron donors react more efficiently with the metal-to-ligand charge transfer excited state of these polyelectrolytes than with the excited state of pyRe(CO)3(phen)+.

Properties of gel phase lipid-trehalose bilayers upon rehydration.

When dipalmitoylphosphatidylcholine bilayers dried under vacuum in different concentrations of trehalose are rehydrated in buffer without the sugar they show different physicochemical properties in the gel state in comparison to the normal gel state. Dry DPPC/trehalose mixtures are readily dispersed in buffer below the phase transition showing by electron microscopy a morphology similar to liposomes prepared by dispersing the lipids in buffer above the phase transition temperature. In these conditions, an increase in the peak at 570 nm of merocyanine after the dehydration-rehydration process in the presence of the sugar is observed and the water permeation increases to values comparable to those found in the fluid state as indicated by the activation energy values and the osmotic volume. The trehalose-dried liposomes rehydrated in buffer show a similar osmotic response to hypertonic gradient as DPPC liposomes without sugar near the phase transition temperature. In accordance with this behavior the trehalose-dried liposomes are lysed below the phase transition temperature by lysoderivatives. These modifications of the gel state of hydrated phospholipids by trehalose can only be achieved if a drastic dehydration is performed in the presence of the sugar. After rehydration the changes in the gel state can be detected after dyalizing the rehydrated membranes in media without trehalose during at least 24 h. These results suggest that trehalose is still intercalated between the phospholipids after restoring water to the dried liposomes either at temperatures below or above the phase transition.

Surface changes induced by osmotic stress and its influence on the glycerol permeability in lipid bilayers.

The penetration rate of glycerol across lipid bilayers can be assayed dispersing liposomes filled with a 0.1 M glucose solution in an isotonic or a hypertonic solution of glycerol. The kinetic of glycerol permeation is found to be different in each of those cases. Liposomes dispersed above the phase transition temperature in hypertonic solutions show an increase in the surface polarization as measured by means of merocyanine 540. Under this condition, the permeation of glycerol shows a two-step kinetic which is indicative of a non-fickean diffusion process. In contrast, liposomes dispersed in isotonic solutions of the permeant show a fickean behavior. The changes in polarization of the membrane interface are ascribed to variations in the surface potential due to the osmotic collapse and the glycerol concentration in contact with the outer surface. The permeability of polar molecules can, in consequence, be considered as a function of the surface potential of the liposome which is congruent with previous data in literature reporting that water permeability increases as a function of the zeta potential of liposomes shrunken in hypertonic solutions.

Effect of dolichyl monophosphate on the permeability properties of lipid membranes.

The effect of dolichyl monophosphate on the permeability properties of dimyristoylphosphatidylcholine bilayers to alkaline cations, Ca2+ and glucose has been determined by stop-flow spectrophotometry. The results show that, in contrast to free dolichol effects, the monophosphate derivative increased the permeability following a decreasing order of the permeating particle size. Phase diagrams indicate that dolichyl monophosphate is fully incorporated into the phosphatidylcholine bilayer around 0.75% weight/weight ratio. For these ratios, the permeation of ions is higher in the gel than in the liquid crystalline state.