O espectro de absorção de DPH, em concentração fixa, não varia com o teor de água em solvente orgânico. Tem-se a banda de monômeros igual àquela em etanol puro. A absorção não muda até o limite de 54 e 46% de água em etanol e DMSO, respectivamente, para [DPH] = 5,0 × 10 -6 mol L -1 a 30 °C. Entretanto, em misturas com água muito abaixo desses conteúdos críticos, observou-se um decaimento intenso de fluorescência enquanto a absorção manteve-se constante. Propõe-se que moléculas de água atuam como supressores dos estados excitados e a constante de supressão de Stern-Volmer através de intensidade relativas, resultou em 7,4 × 10 -2 (água/etanol) e 2,6 × 10 -2 L mol -1 (água/DMSO). Os tempos de vida do DPH na ausência e presença do supressor forneceram constantes de 7,1 × 10 -2 L mol -1 em água/etanol, indicando supressão dinâmica. Em investigações de ambientes com esta sonda, este processo deve ser considerado tendo em vista o risco de erros de interpretação.The absorption spectra of DPH at fixed concentration do not change with water content in organic solvents. It exhibits monomer bands, such as those obtained in ethanol. The absorption did not change for solutions up to 54 and 46% of water in ethanol and DMSO, respectively, for [DPH] = 5.0 × 10 -6 mol L -1 at 30 °C. However, at the same experimental conditions, a gradual sharp decay of the DPH fluorescence is observed. It is proposed that water molecules below these water concentration limits act as quenchers of the excited states of DPH. Stern-Volmer quenching constants by intensities measurements are 7.4 × 10 -2 (water/ethanol) and 2.6 × 10 -2 L mol -1 (water/DMSO). DPH lifetime measurements in the absence and presence of water resulted in 7.1 × 10 -2 L mol -1 in water/ethanol, which pointed out that the process is a dynamic quenching by water molecules. For experiments using DPH as probe, this process can affect data, leading to misunderstanding interpretation.Keywords: diphenylhexatriene, DPH, DPH fluorescence, dynamic quenching, lifetime 3,, which is used as a fluorescence probe, has a rod-like structure that absorbs and emits light with a high quantum efficiency, although it is not a large conjugative p-electron system. Introduction 1,2The spectrophotometric properties of DPH are very sensitive to the experimental conditions, which allows using this compound and its derivatives as environmental probes in colloidal systems to determine the critical micellar concentration of surfactants 3 and in biological cell membranes. 4,5 The measurement of the fluorescence anisotropy of DPH is extensively used for membranes, particularly in studies of microviscosities, 6 due to the non-polar characteristic, the low water solubility, and the suitable geometric design, which maintains the molecule aligned parallel to the phospholipids chains of the membranes. 7 Although the DPH molecule remains inserted in the membrane layer, it stays in contact with water molecules. 2,5The majority of DPH spectrophotometric studies on electronic transitions are performed in organic solven...

The alkaline hydrolysis of a series of homologous reactants constituted by two reactive centers bridged by a methylene spacers chain, the 1,n-bis(2-azidepyridinium)alkanes (n = 3, 4, 5, 6, and 8), is investigated. The reaction under pseudo-first-order condition was followed by ultraviolet-visible spectrophotometry. The presence of clear isosbestic point suggests the absence of stable intermediates. However, the intermediates 1-(2-azidepyridinium), n-(2-pyridone)alkanes (monocationic compounds), were isolated and characterized as well the reaction end products 1,n-(2-pyridone)alkanes (noncharged compounds). The kinetic analysis fitted to a two-step consecutive reaction, where the k 1 /k 2 values demonstrate the larger reactivity of the first step over the second one, especially for shorter bridged reactants. The OH − reaction order is one for each step. Although Debye-Hückel law was obeyed, the experimental point at ionic strength zero is much higher than the extrapolated one. In addition, the k 1 values substantially decrease as KCl is added especially for shorter homologous whereas the effect on k 2 is almost negligible. Simple charge density effects as a function of the spacer's length do not explain the observations. On the other hand, from the pronounced anion selectivity inhibition effects on k 1 for the shorter derivatives, the existence of an equilibrium involving a conformer, a "sandwich-type" complex with the OH − between the two pyridinium rings, with an "open-stretched" conformer is proposed. For short-bridged reactants, the complex conformer

This work describes the behavior of 1,6-diphenyl-1,3,5-hexatriene (DPH) in ethanol/water mixtures. The dependence of DPH photophysical properties (absorption and fluorescence emission) on the water percentage in ethanol indicates that DPH undergoes self-aggregation processes in solvent conditions above a critical water content. Evidence such as an additional absorption band, Beer's law deviation, kinetic behavior, and other experimental results obtained from temperature variation and surfactant addition demonstrated the presence of several types of DPH aggregates. Resonance light scattering measurements proved that the aggregate grew in water-rich media by a self-catalyzed process.

Benzoporphyrin monoacid derivatives, here named B3A and B3B, are promising new drugs for photodynamic therapy. Although both isomers show interesting characteristics as photosensitizing compounds, they have some distinct physicochemical properties such as the tendency to self‐aggregate in water‐rich media. Because pH drives the presence of each species, the pKa of these compounds assumes strategic importance. However, traditional micro‐titration methods and UV–Vis absorption techniques fail to give reliable pKa values due to the characteristics of this highly complex system, such as the precipitation of hydrophobic species, close pKa values, and high absorption band superposition. In the present work, chemometric tools are employed to evaluate pKa, and the kinetic tendency of monomers to undergo self‐aggregation is investigated. In solvent mixtures at low water percentage in ethanol, both B3A and B3B are stabilized in a monomeric state. However, in mixtures with a high water content, self‐aggregation takes place, mainly under a mild pH acid condition (3 < pH < 6), in which the prevalent protolytic species of both isomers is the neutral charged form, compounds with carboxylic and porphyrin free‐base groups. It is demonstrated that both isomers can undergo aggregation following a self‐catalytic mechanism, which is 2000 times slower to B3A than B3B. For B3A, the aggregation is manifested by a decrease in the monomer band with the aggregation band probably superposed to that of the monomer. For B3B, together with the decrease in the monomer band, a new band related to self‐aggregates is observed. Copyright © 2010 John Wiley & Sons, Ltd.

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RESUMOUm dos grandes problemas da atualidade é o descarte inadequado de resíduos da indústria têxtil, em especial os corantes. Eles afetam características dos efluentes e, consequentemente, a vida existente. Por esse motivo, é preciso estudar métodos de remoção desse corante a fim de diminuir os impactos ambientais. Nesse trabalho utilizouse o algodão hidrofílico como adsorvente de corantes e o mesmo foi estudado in natura e com tratamento químico em HCl e NaOH. A avaliação da adsorção foi realizada em soluções de azul de metileno (AM), monitorada por espectrofotometria, e com auxílio de isotermas de adsorção. Os resultados indicaram que o tratamento com NaOH é o mais eficaz para a adsorção de AM, e que o equilíbrio de adsorção é alcançado antes de 4 horas.

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