Unusual 1,6-diphenyl-1,3,5-hexatriene (DPH) spectrophotometric behavior in water/ethanol and water/DMSO mixtures

Abstract

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...

Nanostructured Polymeric Micelles Carrying Xanthene Dyes for Photodynamic Evaluation

“…). The fluorescence intensity decrease may be related to three competitive processes: (1) decrease in the molar absorptivity; (2) water molecules acting as quencher agents of the PS monomers in electronic excited states; and (3) the formation of nonfluorescent species as PS self‐aggregate at higher water contents .…”

“…This deviation at approximately 70% vol/vol of water in ethanol is justified by the self‐aggregation of the Decyl esters. Our research group had nominated this inflection point as critical water percentage for aggregation, CWPA . This aggregative process can be attributed to the decrease in hydrophilic/hydrophobic balance of PS with the solvent, the higher self‐interaction between the alkyl chains of the PS and entropic effects in water media .…”

“…Our research group had nominated this inflection point as critical water percentage for aggregation, CWPA . This aggregative process can be attributed to the decrease in hydrophilic/hydrophobic balance of PS with the solvent, the higher self‐interaction between the alkyl chains of the PS and entropic effects in water media . Samples of EOSDEC analyzed at this high water condition demonstrated that the aggregated particles were too small to be detected by resonance light scattering .…”

“…Below CWPA, the heating increases the diffusional coefficient of the suppressor (water) leading to higher effectiveness in the quenching . However, above CWPA, the heating favors the monomers formation from self‐aggregate of the Decyl esters, which is caused by entropic factors that increases the fluorescence intensity.…”

Effects of Metal and the Phytyl Chain on Chlorophyll Derivatives: Physicochemical Evaluation for Photodynamic Inactivation of Microorganisms

“…In the self-aggregate states, excited molecules have their energy suppressed by collisions among monomer units that constitutes the own aggregate, the self-quenching process (36,(38)(39)(40)(41)(42)(43). On the other hand, it is well known that water molecules act as an excited state quencher for several chromophores (44,45).…”