Sensitized photo-oxidation of gadusol species mediated by singlet oxygen.

Gadusols are efficient nature UV sunscreens with antioxidant capacity. The kinetics of the quenching reactions of singlet oxygen O2(1∆g) by gadusol species was evaluated in aqueous solution as well as in the presence of direct charged micelles. Time-resolved phosphorescence detection of O2(1∆g) indicated that gadusolate, the main species under biological pH, is a more efficient quencher than the enol form with a rate constant of ca. 1.3 × 108 L mol-1 s-1. The deactivation proceeds via a collisional mechanism with clear dominance of chemical pathways, according to the rates of gadusol and oxygen consumptions, and typical photooxidation quantum yields of ca. 7%. The relative contributions of the chemical and physical quenching steps were not affected by the presence of anionic or cationic micelles emulating simple pseudo-biological environments. The products of the photo-oxidative quenching support a type II mechanism initiated by the addition of O2(1∆g) to the C-C double bond of gadusolate. These results point to the relevance of considering the role of sacrifice antioxidant along with the UV-screening function for gadusol, particularly in the context of potential biotechnological applications of this natural molecule.

Diketopyrrolopyrrole-fullerene C60 architectures as highly efficient heavy atom-free photosensitizers: synthesis, photophysical properties and photodynamic activity.

Chromophore-fullerene C60 hybrids possess interesting properties that enable them to act as heavy atom-free photosensitizers and reactive oxygen species (ROS) producers. Here, two new diketopyrrolopyrrole-C60 conjugates were efficiently synthesized and characterized. The conjugates show broadband absorption in the visible spectral region, in which diketopyrrolopyrrole dyes act as light-harvesting antenna with very high capacity to populate excited triplet states. Furthermore, the ability of diketopyrrolopyrrole-C60 systems to generate singlet molecular oxygen was explored for the first time in solvents of different polarities. The experimental results show that these architectures exhibit very high production rates of this ROS. In addition, a preliminary study on Staphylococcus aureus cell suspensions indicates that both conjugates exhibit phototoxicity after irradiation with green LED light. Thus, the data obtained provide evidence that these diketopyrrolopyrrole-C60 architectures act as potential heavy atom-free photosensitizers in photodynamic inactivation of microorganisms and other singlet oxygen-mediated applications.

Light-Harvesting Antenna and Proton-Activated Photodynamic Effect of a Novel BODIPY-Fullerene C60 Dyad as Potential Antimicrobial Agent.

A covalently linked BODIPY-fullerene C60 dyad (BDP-C60 ) was synthesized as a two-segment structure, which consists of a visible light-harvesting antenna attached to an energy or electron acceptor moiety. This structure was designed to improve the photodynamic action of fullerene C60 to inactivate bacteria. The absorption spectrum of BDP-C60 was found to be a superposition of the spectra of its constitutional moieties, whereas the fluorescence emission of the BODIPY unit was strongly quenched by the fullerene C60 . Spectroscopic, calculations, and redox studies indicate a competence between photoinduced energy and electron transfer. Protonating the dimethylaminophenyl substituent through addition of an acidic medium led to a substantial increase in the fluorescence emission, triplet excited state formation, and singlet molecular oxygen production. At physiological pH, photosensitized inactivation of Staphylococcus aureus mediated by 1 µM BDP-C60 exhibited a 4.5 log decrease of cell survival (>99.997 %) after 15 min irradiation. A similar result was obtained with Escherichia coli using 30 min irradiation. Moreover, proton-activated photodynamic action of BDP-C60 turned this dyad into a highly effective photosensitizer to eradicate E. coli. Therefore, BDP-C60 is an interesting photosensitizing structure in which the light-harvesting antenna effect of the BODIPY unit combined with the protonation of dimethylaminophenyl group can be used to improve the photoinactivation of bacteria.

A Comparative Study on the Photophysical and Photochemical Properties of Dyes in the Presence of Low Generation Amino-terminated Polyamidoamine Dendrimers.

The photophysical and photochemical properties of the xanthene dyes mercurochrome (MCr) and eosin-Y (Eos); and the phenazine dye safranine-O (SF) are evaluated in the presence of amino-terminated polyamidoamine (PAMAM) dendrimers of low generations. The dendrimers produce a red shift in the UV-vis absorption spectra of the dyes, which increases with concentration and the size of the PAMAM molecule. The Stern-Volmer plots of fluorescence quenching for xanthenic dyes present a downward curvature. It is ascribed to a static mechanism involving a dye-dendrimer binding. A non-linear fitting of the SV plots allows the calculation of the binding constants. For SF, the fluorescence is only slightly quenched by PAMAMs and the SV plots are linear. The binding constants are in the order Kbind (SF) ≪ Kbind (Eos) < Kbind (MCr). The difference must be due to important specific structural effects. A decrease in the triplet lifetime and an increase in the absorption of the semireduced form of the dyes are observed in the presence of dendrimers. While for the two xanthene dyes, the rate constants reach the diffusional limit for G2 and G3, for SF they are one order of magnitude lower. This is explained by a different quenching mechanism of the two types of dyes.

The interaction of the excited states of safranine-O with low generation carboxyl terminated PAMAM dendrimers in an aqueous medium.

The interaction of the singlet and triplet excited states of the synthetic dye safranine-O with carboxyl-terminated poly(amidoamine) (PAMAM) dendrimers was investigated in a buffer solution at pH 8. Low half-generation PAMAM dendrimers (G -0.5; G +0.5: G 1.5) were employed. The UV-vis absorption spectrum of the dye presents only a very small red shift in the presence of dendrimers. Fluorescence quenching was detected and it was interpreted by a static mechanism in terms of the association of the dye with the dendrimer. Laser flash photolysis experiments were carried out and transient absorption spectra of the triplet and radicals were obtained. The triplet state is quenched by the dendrimers with rate constants well below the diffusional limit. The quenching process was characterized as an electron transfer process and the quantum yield of radicals was estimated. It was found that radicals are formed with a high efficiency in the triplet quenching reaction.

Proton-Dependent Switching of a Novel Amino Chlorin Derivative as a Fluorescent Probe and Photosensitizer for Acidic Media.

A novel chlorin derivative (TPCF20 -NMe2 ) has been synthesized as a syn adduct of a pyrrolidine-fused chlorin bearing a C-linked N,N-dimethylaminophenyl residue. The absorption spectrum of TPCF20 -NMe2 is essentially identical to that of TPCF20 in N,N-dimethylformamide, indicating a very weak interaction between the chlorin macrocycle and the amine group in the ground state. However, the fluorescence emission of the chlorin moiety in TPCF20 -NMe2 is effectively quenched by the attached amine unit. Moreover, TPCF20 -NMe2 is unable to attain a triplet excited state or to photosensitize singlet molecular oxygen. Spectroscopic and redox properties indicate that intramolecular photoinduced electron transfer can take place from the N,N-dimethylaminophenyl group to the chlorin macrocycle. Thus, in an acid medium, protonation of the amino group leads to a considerable increase in the fluorescence emission, triplet excited-state formation, and singlet molecular oxygen production. Photodynamic inactivation of Escherichia coli sensitized by TPCF20 -NMe2 is negligible at neutral pH. However, this chlorin becomes highly effective in inactivating E. coli cells under acidic conditions. Therefore, these results indicate that TPCF20 -NMe2 is an interesting molecular structure, in which protonation of the amino group can be used as an off/on molecular switch activating red fluorescence emission and photodynamic activity capable of eradicating bacteria.

Photochemistry and Photophysics of Shinorine Dimethyl Ester.

The photostability and photophysical properties of the dimethyl ester of the mycosporine-like amino acid shinorine have been experimentally evaluated in aqueous solution and in the presence of direct micelles prepared with a cationic or an anionic detergent, respectively. In comparison with shinorine, the ester molecule increases the photostability, the fluorescence quantum yield and the fluorescence lifetime in water as well as in the micellar solutions. The effects are more pronounced in sodium dodecyl sulfate solutions and suggest that the electrostatic attractions with the micellar interface contribute to limit the movement of the molecules and influence the relative rate of their deactivation channels. However, the predominance of the nonradiative decay is maintained together with the UV photoprotective ability of this atypical mycosporine species.

A Comparative Study on the Photophysics and Photochemistry of Xanthene Dyes in the Presence of Polyamidoamine (PAMAM) Dendrimers.

The photophysical and photochemical properties of the xanthene dyes Eosin Y, Erythrosin B, and Rose Bengal are evaluated in the presence of amino-terminated polyamidoamine (PAMAM) dendrimers of relatively high generation (G3-G5) in alkaline aqueous solution. UV/Vis absorption and fluorescence spectra of the dyes show bathochromic shifts, which correlate with the size of the dendrimer. Binding constants (Kbind ) are calculated from absorption data. The resulting high Kbind values indicate strong interactions between both molecules. Triplet-triplet absorption spectra of the dyes are recorded by laser flash photolysis, and a decrease in the triplet lifetimes is observed in the presence of dendrimers. At the same time, an increase in the absorption of the semireduced form of the dyes is observed. Rate constants for triplet quenching (3 kq ) and radical quantum yields (ΦR ) are obtained. The results are explained by a very efficient electron-transfer process from PAMAM to xanthene dyes for all of the dye/dendrimer couples that are evaluated.

Photodynamic inactivation of microorganisms sensitized by cationic BODIPY derivatives potentiated by potassium iodide.

The photodynamic inactivation mediated by 1,3,5,7-tetramethyl-8-[4-(N,N,N-trimethylamino)phenyl]-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene 3 and 8-[4-(3-(N,N,N-trimethylamino)propoxy)phenyl]-4,4-difluoro-4-bora-3a,4a-diaza-s-indacene 4 was investigated on Staphylococcus aureus, Escherichia coli and Candida albicans. In vitro experiments indicated that BODIPYs 3 and 4 were rapidly bound to microbial cells at short incubation periods. Also, fluorescence microscopy images showed green emission of BODIPYs bound to microbial cells. Photosensitized inactivation improved with an increase of the irradiation time. Similar photoinactivation activities were found for both BODIPYs in bacteria. The photoinactivation induced by these BODIPYs was effective for both bacteria. However, the Gram-positive bacterium was inactivated sooner and with a lower concentration of a photosensitizer than the Gram-negative bacterium. After 15 min irradiation, the complete eradication of S. aureus was obtained with 1 µM photosensitizer. A reduction of 4.5 log in the E. coli viability was found when using 5 µM photosensitizer and 30 min irradiation. Also, the last conditions produced a decrease of 4.5 log in C. albicans cells treated with BODIPY 3, while 4 was poorly effective. On the other hand, the effect of the addition of KI on photoinactivation at different irradiation periods and salt concentrations was investigated. A smaller effect was observed in S. aureus because the photosensitizers alone were already very effective. In E. coli, photokilling potentiation was mainly found at longer irradiation periods. Moreover, the photoinactivation of C. albicans mediated by these BODIPYs was increased in the presence of KI. In solution, an increase in the formation of the BODIPY triplet states was observed with the addition of the salt, due to the effect of external heavy atoms. The greater intersystem crossing together with the formation of reactive iodine species induced by BODIPYs may be contributing to enhance the inactivation of microorganisms. Therefore, these BODIPYs represent interesting photosensitizers to inactivate microorganisms. In particular, BODIPY 3 in combination with KI was highly effective as a broad spectrum antimicrobial photosensitizer.

Triplet state quenching of phenosafranine dye by indolic compounds studied by transient absorption spectroscopy.

The interaction of the triplet state of the synthetic dye phenosafranine (3,7-diamino-5-phenylphenazinium chloride) with indolic compounds of biological relevance was investigated in water by means of laser flash photolysis. The rate constants for the triplet quenching were determined. The quenching process may be explained by an electron transfer from the indole to the dye in its triplet state. The rate constants present a typical dependence of an electron transfer process with the one-electron oxidation potential of the indole. Indole-3-acetic acid and its homologous indole propionic and indole butyric acids are the most effective quenchers with rate constants reaching the diffusion limit. Rate constants for indole itself, tryptophan and indole-3 carboxylic acid are one order of magnitude lower. The electron transfer nature of the quenching reaction is further confirmed by the detection of the semi-reduced form of the dye by its transient absorption. The absorption coefficients of the transient species were estimated, and the quantum yield of the charge separation process was determined. The efficiency of formation of radical species is between 60 and 90% of the triplets intercepted.

Comparison of the kinetics of electron transfer in the diffusion limit for the singlet and triplet quenching of eosin Y by quinones.

Electron transfer (ET) rate constants were determined by means of lifetime measurements for the fluorescence quenching and by laser flash photolysis for the triplet quenching of the dye eosin Y by benzoquinones in acetonitrile. The results represent a new aspect of the dependence of the rate constants with the driving force in the diffusion limit region. That is, the rate constants for singlet quenching in the highly negative region of ΔGet do not decrease as predicted by Marcus theory, but rather show a small positive dependence on the driving force. However, it is found that, in the same free energy range, the triplet rate constants are lower than those for the singlet process. They also increase with the exergonicity of the reaction, but the dependence with ΔGet is less marked than that found for the singlet reaction. Even at a Gibbs energy change of -1.0 eV the triplet quenching rate constants do not reach the theoretical diffusion limit. The results are analyzed using the current theories for diffusion-mediated ET reactions.

Spectral characteristics and photosensitization of TiO2 nanoparticles in reverse micelles by perylenes.

We report on the photosensitization of titanium dioxide nanoparticles (TiO2 NPs) synthesized inside AOT (bis(2-ethylhexyl) sulfosuccinate sodium salt) reverse micelles following photoexcitation of perylene derivatives with dicarboxylate anchoring groups. The dyes, 1,7-dibromoperylene-3,4,9,10-tetracarboxy dianhydride (1), 1,7-dipyrrolidinylperylene-3,4,9,10-tetracarboxy dianhydride (2), and 1,7-bis(4-tert-butylphenyloxy)perylene-3,4,9,10-tetracarboxy dianhydride (3), have considerably different driving forces for photoinduced electron injection into the TiO2 conduction band, as estimated by electrochemical measurements and quantum mechanical calculations. Fluorescence anisotropy measurements indicate that dyes 1 and 2 are preferentially solubilized in the micellar structure, creating a relatively large local concentration that favors the attachment of the dye to the TiO2 surface. The binding process was followed by monitoring the hypsochromic shift of the dye absorption spectra over time for 1 and 2. Photoinduced electron transfer from the singlet excited state of 1 and 2 to the TiO2 conduction band (CB) is indicated by emission quenching of the TiO2-bound form of the dyes and confirmed by transient absorption measurements of the radical cation of the dyes and free carriers (injected electrons) in the TiO2 semiconductor. Steady state and transient spectroscopy indicate that dye 3 does not bind to the TiO2 NPs and does not photosensitize the semiconductor. This observation was rationalized as a consequence of the bulky t-butylphenyloxy groups which create a strong steric impediment for deep access of the dye within the micelle structure to reach the semiconductor oxide surface.

Photoinduced reduction of divalent mercury by quinones in the presence of formic acid under anaerobic conditions.

The laser flash photolysis technique (λ(exc)=355 nm) was used to investigate the mechanism of the HgCl(2) reduction mediated by CO(2)(-) radicals generated from quenching of the triplet states of 1,4-naphthoquinone (NQ) by formic acid. Kinetic simulations of the experimental signals support the proposed reaction mechanism. This system is of potential interest in the development of UV-A photoinduced photolytic procedures for the treatment of Hg(II) contaminated waters. The successful replacement of NQ with a commercial fulvic acid, as a model compound of dissolved organic matter, showed that the method is applicable to organic matter-containing waters without the addition of quinones.

Triplet state of 4-methoxybenzyl alcohol chemisorbed on silica nanoparticles.

The knowledge of photochemical kinetics in colloidal systems is important in understanding environmental photochemistry on dispersed solid surfaces. As model materials for the chemically sorbed organic compounds present in natural environments, modified silica nanoparticles (NPs) were obtained here by condensation of the silanol groups of fumed silica nanoparticles with 4-methoxybenzyl alcohol. These particles were characterized by different techniques. To evaluate their toxicity, the inhibition of the natural luminescence emission of the marine bacterium Vibrio fischeri in suspensions of the particles was measured. Laser flash-photolysis experiments (λ(exc) = 266 nm) performed with NP suspensions in acetonitrile-aqueous phosphate buffer mixtures showed the formation of the lowest triplet excited state of the chemisorbed organic groups (λ(max) = 390 nm). DFT calculations of the absorption spectrum of this radical support the assignment. From the calculated triplet energy, a thermodynamically favorable energy transfer from these triplet states to oxygen to yield singlet molecular oxygen is predicted. A value of 0.09 was measured for the quantum yield of singlet molecular oxygen generation by air-saturated suspensions of the nanoparticles in the mixture of solvents acetonitrile-aqueous phosphate buffer. The quantum yield of singlet molecular oxygen generation by the free 4-methoxybenzyl alcohol in the same solvent is 0.31.

Quenching of the triplet state of Safranine-O by aliphatic amines in AOT reverse micelles studied by transient absorption spectroscopy.

The photophysics of Safranine-O (3,6-diamino-2,7-dimethyl-5 phenyl phenazinium chloride) (SfH(+)Cl(-)) was investigated in reverse micelles (RMs) of AOT (sodium bis(2-ethylhexyl)sulfosuccinate) with special emphasis on the triplet state processes. The triplet is formed in its monoprotonated form, independently of the pH of the water used to prepare the RMs. While the intersystem crossing quantum yields in RMs are similar to those in organic solvents, the triplet lifetime is much longer. Since the pH in the water pool of AOT RMs is close to 5 and the triplet state of the dye is subjected to proton quenching, the long lifetime indicates that the dye resides in a region where it cannot be reached by protons during its lifetime. All the measurements indicate that the dye is localized in the interface, sensing a medium of micropolarity similar to EtOH : water (3:1) mixtures. The quenching by aliphatic amines was also investigated. While the quenching by the hydrophobic tributylamine is similar to that in methanol, the hydro-soluble triethanolamine is one order of magnitude more effective in RMs than in homogeneous solution. In the latter case the quenching process is interpreted by a very fast intramicellar quenching, the overall kinetics being controlled by the exchange of amine molecules between RMs. Semireduced dye is formed in the quenching process in RMs in the di-protonated state with a comparable quantum yield to the monoprotonated state formed in homogeneous solvents. The results point to the advantage of the reverse micellar system for the generation of active radicals for the initiation of vinyl polymerization, since a much lower concentration of amine can be employed with similar quantum yields.

Mechanistic insight of the photodynamic effect induced by tri- and tetra-cationic porphyrins on Candida albicans cells.

The photodynamic mechanism of action induced by 5-(4-trifluorophenyl)-10,15,20-tris(4-N,N,N-trimethylammoniumphenyl)porphyrin (TFAP(3+)), 5,10,15,20-tetrakis(4-N,N,N-trimethylammoniumphenyl)porphyrin (TMAP(4+)) and 5,10,15,20-tetrakis(4-N-methylpyridyl)porphyrin (TMPyP(4+)) was investigated on Candida albicans cells. These cationic porphyrins are effective photosensitizers, producing a ~5 log decrease of cell survival when the cultures are incubated with 5 µM photosensitizer and irradiated for 30 min with visible light. Studies under anoxic conditions indicated that oxygen is necessary for the mechanism of action of photodynamic inactivation of this yeast. Furthermore, photoinactivation of C. albicans cells was negligible in the presence of 100 mM azide ion, whereas the photocytotoxicity induced by these porphyrins increased in D(2)O. In contrast, the addition of 100 mM mannitol produced a negligible effect on the cellular phototoxicity. On the other hand, in vitro direct observation of singlet molecular oxygen, O(2)((1)Δ(g)) phosphorescence at 1270 nm was analyzed using C. albicans in D(2)O. A shorter lifetime of O(2)((1)Δ(g)) was found in yeast cellular suspensions. These cationic porphyrins bind strongly to C. albicans cells and the O(2)((1)Δ(g)) generated inside the cells is rapidly quenched by the biomolecules of the cellular microenvironment. Therefore, the results indicate that these cationic porphyrins appear to act as photosensitizers mainly via the intermediacy of O(2)((1)Δ(g)).

UVB photoprotective role of mycosporines in yeast: photostability and antioxidant activity of mycosporine-glutaminol-glucoside.

Several yeast species are able to synthesize and accumulate UV-radiation-absorbing mycosporine metabolites that are of unclear physiological function. In this work we analyzed the relationship between mycosporine-glutaminol glucoside (MGG) production, cell survival after UVB irradiation, and formation of cyclobutane pyrimidine dimers (CPDs). We also assessed the photostability and singlet oxygen quenching activity of MGG. A set of nine isolates of the basidiomycetous yeast Cryptococcus steppossus cultured in both dark and light conditions was used for the studies. Survival of the UVB-irradiated isolates and MGG concentration had a linear relationship when the concentration was over 2.5 mg g(-1). CPD accumulation and MGG accumulation were inversely related. MGG in aqueous solution was photostable with a photodecomposition quantum yield of 1.16 × 10(-5). MGG quenching of singlet oxygen was also observed, and the rate constant for the process in D(2)O was 5.9 × 10(7) M(-1) s(-1). Our results support the idea that MGG plays an important role as a UVB photoprotective metabolite in yeasts by protecting against direct damage on DNA and probably against indirect damage by singlet oxygen quenching.

Photophysics and reductive quenching reactivity of gadusol in solution.

The photostability and photophysics of gadusol in aqueous solution has been studied. The photodecomposition quantum yields (ca. 4 × 10(-2) and 1 × 10(-4) at acidic and neutral pH, respectively) confirm the high photostability of the metabolite, independently of the presence of oxygen, under physiological conditions. The nature of the electronic transition of gadusol has been assigned as π→π* on the basis of the solvatochromic shifts of the UV absorption spectrum and the time-dependent density functional theory calculation of the vertical transition energies. The results from the photoacoustic calorimetry point to the rapid non-radiative decay as the dominant relaxation pathway of the excited species at pH 7, which is consistent with the proposed UV-sunscreening role of the molecule in the early atmosphere. Laser flash photolysis experiments probed that the ground state of the enolate form (gadusolate) undergoes electron transfer reactions with some triplet sensitizers in water or methanol solution. A rate constant of 2 × 10(8) M(-1) s(-1) has been determined for the quenching of rose bengal triplet state in water at pH 7. This reductive quenching reactivity may be considered as one of the underlying mechanisms that support the antioxidant capacity of gadusol in biological environments.

Silicon nanoparticle photophysics and singlet oxygen generation.

The effect of molecular oxygen and water on the blue photoluminescence of silicon nanoparticles synthesized by anodic oxidation of silicon wafers and surface functionalized with 2-methyl 2-propenoic acid methyl ester is investigated. The particles of 3 +/- 1 nm diameter and a surface composition of Si(3)O(6)(C(5)O(2)H(8)) exhibit room-temperature luminescence in the wavelength range 300-600 nm upon excitation with 300-400 nm light. The luminescence shows vibronic resolution and high quantum yields in toluene suspensions, while a vibronically unresolved spectrum and lower emission quantum yields are observed in aqueous suspensions. The luminescence intensity, though not the spectrum features, depends on the presence of dissolved O(2). Strikingly, the luminescence decay time on the order of 1 ns does not depend on the solvent or on the presence of O(2). To determine the mechanisms involved in these processes, time-resolved and steady-state experiments are performed. These include low-temperature luminescence, heavy atom effect, singlet molecular oxygen ((1)O(2)) phosphorescence detection, reaction of specific probes with (1)O(2), and determination of O(2) and N(2) adsorption isotherms at 77 K. The results obtained indicate that physisorbed O(2) is capable of quenching nondiffusively the particle luminescence at room temperature. The most probable mechanism for (1)O(2) generation involves the energy transfer from an exciton singlet state to O(2) to yield an exciton triplet of low energy (<0.98 eV) and (1)O(2). In aqueous solutions, excited silicon nanoparticles are able to reduce methylviologen on its surface.

The use of molecular probes for the characterization of dispersions of functionalized silica nanoparticles.

Butoxylated silica nanoparticles (BSN) were prepared by esterification of the silanol groups of fumed silica nanoparticles with butanol and characterized by 13C and 29Si NMR and thermogravimetry. The molecular probes benzophenone (BP) and safranine-T were used to investigate the BSN suspensions in water:acetonitrile. Laser flash-photolysis experiments at lambda(exc)=266 nm performed with BSN suspended in acetonitrile:aqueous phosphate buffer supported previous results of our group obtained by time-resolved phosphorescence experiments and showed that only free and adsorbed excited triplet states of BP and diphenylketyl radicals contribute to the signals. The UV-vis spectroscopic and photophysical properties of safranine-T are strongly solvent-dependent. Thus, the analysis of the emission spectra and fluorescence lifetimes yielded information on the localization of this probe molecule in suspensions of BSN and of the bare silica nanoparticles. The values of the equilibrium constant for the adsorption of the ground-state safranine-T on the particles were found to be (9.2+/-0.8)x10(4), (7.2+/-0.8)x10(5), and (3.0+/-0.1)x10(4) for the BSN in 1:1 acetonitrile:water, SiO2 in 1:1 acetonitrile:water, and SiO2 in acetonitrile, respectively.