An investigation of paint from a mural in the church of Sainte Madeleine, Manas, France.

The pigment in brown paint samples taken from a church in the Drôme region of France has been shown to be almost pure 6-bromoindigo and 6,6'-dibromoindigo. The composition of the pigment was established by comparison with 6-bromoindigo and 6,6'-dibromoindigo standards using atmospheric pressure photoionization combined with liquid chromatography and tandem mass spectrometry. The brown paint samples were taken from a frieze of ca 20 brown images having symmetric tree-like forms composed of five overlapping filled circles representing foliage. The tree-like images, simple rather than artistic, had a metallic luster. The molar ratio of 6-bromoindigo and 6,6'-dibromoindigo in the brown paint pigment (98:2) is remarkably similar to that of shellfish purple from the Mediterranean Murex brandaris (96.5:3.5) thus, it is possible that the origin of the indigoid compounds in the brown paint pigment is the eastern coast of the Mediterranean Sea. As the production of Tyrian purple ended with the fall of Byzantium in 1453, purple pigment had to have been produced prior to this time. We have conjectured about the circumstances that may account for the use of 'purple' in this manner in the Drôme region and how the pigment was transported there from the eastern coast of the Mediterranean Sea during the time of the Crusades.

Primary photoprocesses in a fluoroquinolone antibiotic sarafloxacin.

The photophysical properties of the fluoroquinolone antibiotic sarafloxacin (SFX) were investigated in aqueous media. SFX in water, at pH 7.4, shows intense absorption with peaks at 272, 322 and 335 nm, (epsilon=36800 and 17000 dm3 mol(-1) cm(-1), respectively). Both the absorption and emission properties of SFX are pH-dependent; pKa values for the protonation equilibria of both the ground (5.8 and 9.1) and excited singlet states (5.7 and 9.0) of SFX were determined spectroscopically. SFX fluoresces weakly, the quantum yield for fluorescence emission being maximum (0.07) at pH 8. Laser flash photolysis and pulse radiolysis studies have been carried out in order to characterize the transient species of SFX in aqueous solution. Triplet-triplet absorption has a maximum at 610 nm with a molar absorption coefficient of 17,000+/-1000 dm3 mol(-1) cm(-1). The quantum yield of triplet formation has been determined to be 0.35+/-0.05. In the presence of oxygen, the triplet reacts to form excited singlet oxygen with quantum yield of 0.10. The initial triplet (3A*) was found to react with phosphate buffer to form triplet 3B* with lower energy and longer lifetime and having an absorption band centered at 700 nm. SFX triplet was also found to oxidize tryptophan to its radical with concomitant formation of the anion radical of SFX. Hence the photosensitivity of SFX could be initiated by the oxygen radicals and/or by SFX radicals acting as haptens.

Formation of secondary triplet species after excitation of fluoroquinolones in the presence of relatively strong bases.

Laser flash photolysis of 7-(piperazin-1-yl) fluoroquinolones leads to the formation of a triplet excited state (3A*) at the end of the pulse (lambdamax 520, 610, and 620 nm for enoxacin, ciprofloxacin, and norfloxacin, respectively). Phosphate and bicarbonate buffers react with 3A* to form a secondary triplet (3B*, reaction rates (0.8-9.9) x 108 M-1 s-1), whose T-T absorption is red-shifted (lambdamax 670 nm for enoxacin, 700 nm for ciprofloxacin and norfloxacin). The formation of a secondary triplet is not a common process and disagrees with previous work suggesting that electron transfer occurs between phosphate buffer and the primary triplet excited state with the formation of the anion radical of the fluoroquinolone (FQ.-). We have shown that the FQ.- transient absorption spectrum is quite distinct from that of 3B*. The photophysical characteristics of 3B* have been determined by energy transfer to naproxen, and it has been found that its energy is lower than that of 3A*.

Primary photophysical properties of moxifloxacin--a fluoroquinolone antibiotic.

The photophysical properties of the fluoroquinolone antibiotic moxifloxacin (MOX) were investigated in aqueous media. MOX in water, at pH 7.4, shows two intense absorption bands at 287 and 338 nm (epsilon = 44,000 and 17,000 dm(3) mol(-1) cm(-1), respectively). The absorption and emission properties of MOX are pH-dependent, pK(a) values for the protonation equilibria of both the ground (6.1 and 9.6) and excited singlet states (6.8 and 9.1) of MOX were determined spectroscopically. MOX fluoresces weakly, the quantum yield for fluorescence emission being maximum (0.07) at pH 8. Phosphorescence from the excited triplet state in frozen ethanol solution has a quantum yield of 0.046. Laser flash photolysis and pulse radiolysis studies have been carried out to characterize the transient species of MOX in aqueous solution. On laser excitation, MOX undergoes monophotonic photoionization with a quantum yield of 0.14. This leads to the formation of a long-lived cation radical whose absorption is maximum at 470 nm (epsilon(470) = 3400 dm(3) mol(-1) cm(-1)). The photoionization process releases hydrated electron which rapidly reacts (k = 2.8 x 10(10) dm(3) mol(-1) s(-1)) with ground state MOX, yielding a long-lived anion radical with maximum absorption at 390 nm (epsilon(390) = 2400 dm(3) mol(-1) cm(-1)). The cation radical of MOX is able to oxidize protein components tryptophan and tyrosine. The bimolecular rate constants for these reactions are 2.3 x 10(8) dm(3) mol(-1) s(-1) and 1.3 x 10(8) dm(3) mol(-1) s(-1), respectively. Singlet oxygen sensitized by the MOX triplet state was also detected only in oxygen-saturated D(2)O solutions, with a quantum yield of 0.075.

Interfacial interactions in polymer-layered silicate nanocomposites.

Interactions between sodium montmorillonite (Na-MMT) and a variety of probes, some of which are intended to model components of a polyurethane system, have been studied. Particular attention was given to the effect of preadsorbed water on the adsorption behavior of the probes. Flow microcalorimetry (FMC), diffuse reflectance Fourier transform infrared spectroscopy (DRIFTS), and wide-angle X-ray scattering (WAXS) were used to monitor the adsorption process. The probe set included alcohols, amines, ethers, poly(propylene glycol) monobutyl ethers (PPG), and 4-ethylphenyl isocyanate (4-EPI). FMC revealed that the preadsorbed water molecules on undried Na-MMT hindered the adsorption of alcohol and ether probes, but had little effect on the adsorption of amines. Drying of Na-MMT to less than 0.3% w/w H2O led to an increase in heat of adsorption and generally greater retention of the probes. PPG showed strong interaction with Na-MMT due to multipoint adsorption. With dried Na-MMT, WAXS revealed that PPG of molecular weight (MW) 1000 was partly intercalated into the gallery while lower molecular weight PPG (MW 340) did not intercalate the Na-MMT. DRIFTS spectra of 4-EPI adsorbed on undried Na-MMT revealed urea linkages, indicating formation of N,N'-bis(4-ethylphenyl) urea. In contrast, with dried Na-MMT the 4-EPI formed a urethane linkage with hydroxyl groups present at the edges of the silicate platelets.

Photocatalytic coatings for environmental applications.

A series of nano- and micronparticle-grade anatase and rutile titanium dioxide pigments have been prepared with various densities of surface treatments, particle size and surface area. Their photocatalytic activites have been determined in a series of paint films by FTIR, chalking, color, gloss change and weight loss after artifical weathering. The pigments have also been examined by rapid assessment methodologies using photodielectric microwave spectroscopy, 2-propanol oxidation and hydroxyl analysis. The microwave response under light and dark cycles provides an extended timescale probe of charge-carrier dynamics in the pigments. Pigment particle size, surface area and properties clearly play an important role in dispersion and any polymer-pigment interactions. Photooxidation studies on several types of paint films show a clear demarcation between nanoparticle- and pigmentary-grade titanium dioxide, with the former being more active because of their greater degree of catalytic surface activity. The photosensitivity of titanium dioxide is considered to arise from localized sites on the crystal surface (i.e. acidic OH), and occupation of these sites by surface treatments inhibits photoreduction of the pigment by ultraviolet radiation; hence, the destructive oxidation of the binder is inhibited. Coatings containing 2-5% by weight alumina or alumina and silica are satisfactory for general-purpose paints. If greater resistance to weathering is desired, the pigments are coated more heavily to about 7-10% weight. The coating can consist of a combination of several materials, e.g. alumina, silica, zirconia, aluminum phosphates of other metals. For example, the presence of hydrous alumina particles lowers van der Waals forces between pigments particles by several orders of magnitude, decreasing particle-particle attractions. Hydrous aluminum oxide phases appear to improve dispersibility more effectively than most of the other hydroxides and oxides. Coated nanoparticles are shown to exhibit effective light stabilization in various water- and oil-based paint media in comparison with conventional organic stabilizers. Hindered piperidine stabilizers are shown to provide no additional benefits in this regard, often exhibiting strong antagonism. The use of photocatalytic titania nanoparticles in the development of self-cleaning paints and microbiological surfaces is also demonstrated in this study. In the former case, surface erosion is shown to be controlled by varying the ratio of admixture of durable pigmentary-grade rutile (heavily coated) and a catalytic-grade anatase nanoparticle. For environmental applications in the development of coatings for destroying atmospheric pollutants such as nitrogen oxide gases (NO(X)), stable substrates are developed with photocatalytic nanoparticle-grade anatase. In this study, porosity of the coatings through calcium carbonate doping is shown to be crucial in the control of the effective destruction of atmospheric NO(X) gases. For the development of microbiological substrates for the destruction of harmful bacteria, effective nanoparticle anatase titania is shown to be important, with hydrated high surface area particles giving the greatest activity.