Carla C. Schmitt

Photophysical studies on the interaction of two water-soluble porphyrins with bovine serum albumin. Effects upon the porphyrin triplet state characteristics

Abstract The interaction of two metal-free water soluble porphyrins (PPh): meso -tetrakis ( p -sulfo-natophenyl)porphyrin (TPPS 4 ) and meso -tetrakis(4- N -methyl-pyridiniumyl)porphyrin (TMPyP), with bovine serum albumin (BSA) was investigated in the pH range from 4.0 to 8.5 using the flash-photolysis technique in comparison with results obtained by optical absorption, fluorescence and resonance light scattering. It was found that in the presence of BSA, TPPS 4 can exist in aqueous solutions as free monomers, aggregates and/or monomers bound to a single BSA molecule and monomers inside the BSA aggregates, while TMPyP does not form aggregates at binding. Binding to BSA transforms the profile of the triplet decay curve from monoexponential to biexponential form with the component lifetimes and relative amplitudes depending on binding characteristics. The triplet lifetime of a bound porphyrin monomer is longer than that of a free one. The aggregation of TPPS 4 observed at [TPPS 4 ]/[BSA] > I reduces the T-T absorption since the lifetimes of the aggregate excited states are very short and/or quantum yield of the aggregate triplet state is very low. The porphyrin binding to BSA reduces the quenching constants of the porphyrin triplet states by molecular oxygen due to obstacles produced by binding. This effect is especially pronounced for the porphyrin molecules located inside BSA aggregates formed around the porphyrin molecules in excess BSA.

Effect of sonication on the particle size of montmorillonite clays

This paper reports on the effect of sonication on SAz-1 and SWy-1 montmorillonite suspensions. Changes in the size of the particles of these materials and modifications of their properties have been investigated. The variation of the particle size has been analyzed by DLS (dynamic light scattering). In all cases the clay particles show a bimodal distribution. Sonication resulted in a decrease of the larger modal diameter, as well as a reduction of its volume percentage. Simultaneously, the proportion of the smallest particles increases. After 60 min of sonication, SAz-1 presented a very broad particle size distribution with a modal diameter of 283 nm. On the other hand, the SWy-1 sonicated for 60 min presents a bimodal distribution of particles at 140 and 454 nm. Changes in the properties of the clay suspensions due to sonication were evaluated spectroscopically from dye-clay interactions, using Methylene Blue. The acidic sites present in the interlamellar region, which are responsible for dye protonation, disappeared after sonication of the clay. The changes in the size of the scattering particles and the lack of acidic sites after sonication suggest that sonication induces delamination of the clay particles.

Dependence of the thioxanthone triplet-triplet absorption spectrum with solvent polarity and aromatic ring substitution

Foram estudadas as absorcoes triplete-triplete (TT) e de transientes de tioxantonas substituidas e nao substituidas em diferentes solventes, com a finalidade de avaliar o efeito do solvente, assim como dos substituintes no anel aromatico. Os espectros determinados alguns microssegundos depois da excitacao mostram absorcoes de tres transientes principais: o estado triplete (600-650 nm), o radical cetila da tioxantona (~450 nm) e uma superposicao de ambos (~300 nm). A quantidade de radicais formados em solventes nao-hidroxilicos e muito menor do que em alcoois. O maximo da absorcao TT mostra uma boa correlacao com o parâmetro ET(30) dos solventes.

A fluorescence study of the interactions between sodium alginate and surfactants.

The interactions between the polysaccharide alginate with charged ionic surfactants (anionic and cationic) in aqueous solution have been investigated using pyrene as a photophysical probe. Static fluorescence determinations have been used to obtain information about the new microenvironments arising by these interactions. Micropolarity studies using the I(1)/I(3) ratio of the vibronic bands and I(E)/I(M) ratio between the excimer and monomer emissions of pyrene shows the formation of hydrophobic domains. The interactions between the natural polyelectrolytes and the oppositely charged surfactants lead to the formation of pre-micelles at surfactant concentrations lower than the CMC of the surfactants. The aggregation process is assumed to be due to electrostatic attraction. On the other side, systems containing an anionic surfactant do not show the same behaviour at low concentrations.

Polymerization kinetics and reactivity of alternative initiators systems for use in light-activated dental resins

OBJECTIVES The purpose of this study was to evaluate the reactivity and polymerization kinetics behavior of a model dental adhesive resin with water-soluble initiator systems. METHODS A monomer blend based on Bis-GMA, TEGDMA and HEMA was used as a model dental adhesive resin, which was polymerized using a thioxanthone type (QTX) as a photoinitiator. Binary and ternary photoinitiator systems were formulated using 1mol% of each initiator. The co-initiators used in this study were ethyl 4-dimethylaminobenzoate (EDAB), diphenyliodonium hexafluorophosphate (DPIHFP), 1,3-diethyl-2-thiobarbituric acid (BARB), p-toluenesulfinic acid and sodium salt hydrate (SULF). Absorption spectra of the initiators were measured using a UV-Vis spectrophotometer, and the photon absorption energy (PAE) was calculated. The binary system camphorquinone (CQ)/amine was used as a reference group (control). Twelve groups were tested in triplicate. Fourier-transform infrared spectroscopy (FTIR) was used to investigate the polymerization reaction during the photoactivation period to obtain the degree of conversion (DC) and maximum polymerization rate (R(p)(max)) profile of the model resin. RESULTS In the analyzed absorption profiles, the absorption spectrum of QTX is almost entirely localized in the UV region, whereas that of CQ is in the visible range. With respect to binary systems, CQ+EDAB exhibited higher DC and R(p)(max) values. In formulations that contained ternary initiator systems, the group CQ+QTX+EDAB was the only one of the investigated experimental groups that exhibited an R(p)(max) value greater than that of CQ+EDAB. The groups QTX+EDAB+DPIHFP and QTX+DPIHFP+SULF exhibited values similar to those of CQ+EDAB with respect to the final DC; however, they also exhibited lower reactivity. SIGNIFICANCE Water-soluble initiator systems should be considered as alternatives to the widely used CQ/amine system in dentin adhesive formulations.

Syntheses and characterization of amphiphilic quaternary ammonium chitosan derivatives.

Amphiphilic chitosan derivatives possess improved physico-chemical properties and could be used as carriers in drug delivery systems. The aim of this study was to investigate the behaviour of an amphiphilic system involving (5-pentyl) trimethylammonium and dodecyl aldehyde-modified chitosan. Amphiphilic chitosan derivatives were synthesized and characterized by (1)HNMR and ATR-FTIR spectroscopy. Self-assembled aggregates formed in aqueous solution have hydrophobic cores that were characterized by fluorescence spectroscopy using pyrene as probe and dynamic light scattering (DLS). The critical aggregation concentration of the aggregates in water varied from 0.004 to 0.037g/L and the average size distribution was in the 230-500nm range. The ζ-potential (+15.5 to +44.8mV) confirmed that the surfaces of the aggregates were positively charged and stable in physiological-like environments. TEM images suggest that the aggregates have a spherical shape, showing good agreement with DLS results. These results suggest that the synthesized copolymers have the capability of being used as carriers for hydrophobic drugs.

Photoreduction of resazurin in the presence of aliphatic amines

Abstract Photophysical and photochemical properties of the dye resazurin were measured. The quantum yields of fluorescence and triplet formation were determined to be 0.10±0.01 and 0.2, respectively. The lifetimes of the singlet and triplet states are 1.2 ns and 30 μs. In the presence of aliphatic amines, resazurin is readily photoreduced to resorufin. This reaction proceeds through the triplet state and is inhibited by the presence of oxygen.

Photochemical synthesis of silver nanoparticles on chitosans/montmorillonite nanocomposite films and antibacterial activity

Silver nanoparticles (AgNPs) were synthetized on chitosans/montmorillonite nanocomposite films by photochemical method. Nanocomposites were prepared using chitosans with different molar masses and deacetylation degrees, as well as modified with diethylaminoethyl (DEAE) and dodecyl groups. AgNPs formation on the films was followed by the appearance of the plasmon band around 440nm as a function of irradiation time. TEM images revealed AgNPs with spherical morphology for all nanocomposites. For nanocomposites using modified chitosans, the AgNPs synthesis occurred quickly (1.5h) while for the others films it was above 11h. The film of modified chitosan with dodecyl and DEAE groups presented smaller and more uniform nanoparticles size along mixture of exfoliated and intercalated structures. This modified chitosan is an amphiphilic compound that can act controlling the size/shape of the AgNPs. The results of antibacterial activity suggested that all nanocomposite-AgNPs films inhibited the growth of Escherichia coli and Bacillus subtilis.

A fluorescence emission study of the formation of induced premicelles in solutions of polyelectrolytes and ionic surfactants

The interactions between PSS-co-BVE copolymers and ionic surfactants (anionic and cationic) in aqueous solution have been investigated using pyrene as a photophysical probe. Static and dynamic fluorescence determinations have been used to obtain information about the microenvironments formed between both species. Micropolarity studies using the I1/I3 ratio of the vibronic bands of pyrene and the behavior of the I(E)/I(M) ratio between the monomer and excimer emissions show the formation of hydrophobic domains. The interactions between the polyelectrolytes and the oppositely charged surfactants lead to the formation of induced premicelles at surfactant concentrations lower than the cmc of the surfactants. This aggregation process is assumed to be due to electrostatic attraction. At the same concentration, the excimer-to-monomer emission ratio shows its first peak. At higher surfactant concentrations, near the cmc, micelles with the same properties as those found in pure aqueous solution are formed. On the other side, systems containing an anionic surfactant do not show this behavior at low concentrations. There is no apparent dependence of the cac on the composition of the polymer, reinforcing the assumption that the electrostatic interactions induce the formation of the premicelles. The values of the cacs follow the same trend as for the cmcs, DTAC>DTAB>CTAC. The polarity of the induced premicelles, as measured by the I1/I3 ratio, also indicates that the microdomains formed by the longer chain surfactants are more hydrophobic than those of the shorter chain surfactants, as also happens with real micelles.

Photo-fenton degradation of poly(Ethyleneglycol)

PEG samples needed 490 min to reduce their —w by 50%, whereas under UV irradiation, only 10 min were necessary. The exponential decay of —w with a concomitant increase in polydispersity and number of average chain scission, characterized a random chain scission mechanism. The degradation products of PEG in both systems showed the presence of lower molecular weight products, including smaller ethyleneglycols and formic acid. The mechanism involves consecutive processes, were the larger ethyleneglycols give rise, successively, to smaller ones. This suggests that the mechanism involves successive scissions of the polymer chain. Irradiated samples decomposed faster than those kept in the dark This study proves that the foto-Fenton method associated with UV-light is a good reactant for PEG photodegradation.