Phosphorescence oxygen probes

Will Y, Hynes J, Ogurtsov VI, Papkovsky DB. Analysis of mitochondrial function using phosphorescent oxygen-sensitive probes. Nat Protoc. 2006 1 2563-2572. 

The fluorescence and phosphorescence of luminescent materials are modulated by the characteristics of the environment to which these materials are exposed. Consequently, luminescent materials can be used as sensors (referred also as transducers or probes) to measure and monitor parameters of importance in medicine, industry and the environment. Temperature, oxygen, carbon dioxide, pH, voltage, and ions are examples of parameters that affect the luminescence of many materials. These transducers need to be excited by light. The manner in which the excited sensor returns to the ground state establishes the transducing characteristics of the luminescent material. It is determined by the concentration or value of the external parameter. A practical and unified approach to characterize the luminescence of all sensors is presented in this chapter. This approach introduces two general mechanisms referred as the radiative and the nonradiative paths. The radiative path, in the general approach, is determined by the molecular nature of the sensor. The nonradiative path is determined by the sensor environment, e.g., value or concentration of the external parameter. The nonradiative decay rate, associated with the nonradiative path, increases... 

Based on steady-state and time-resolved emission studies, Scaiano and coworkers have concluded that silicalite (a pentasil zeolite) provides at least two types of sites for guest molecules [234-236], The triplet states of several arylalkyl ketones and diaryl ketones (benzophenone, xanthone, and benzil) have been used as probes. Phosphorescence from each molecule included in silicalite was observed. With the help of time-resolved diffuse reflectance spectroscopy, it has been possible to show that these triplet decays follow complex kinetics and extend over long periods of time. Experiments with benzophenone and arylalkyl ketones demonstrate that some sites are more easily accessed by the small quencher molecule oxygen. Also, diffuse reflectance studies in Na + -X showed that diphenylmethyl radicals in various sites decay over time periods differing by seven orders of magnitude (t varies between 20/is and 30 min) [237]. 

A similar phenomenon may be observed even when BrNp is free to diffuse into and out of the CD bucket. Turro et al. have modified 4-BrNp with protecting, (n-alkyl)trimethylammonium detergent groups [300], Although cationic phosphorescent probes 5 are quenched efficiently by oxygen and Co(NH3)g+ in aque-... 

Song, B., Wang, G.L., and Yuan, J.L. (2005) A new europium chelate-based phosphorescence probe specific for singlet oxygen. Chemical Communications, 3553—3555. 

The phosphorescence of l-bromo-4-naphthoyl probes (52) with n = 5 was not observable in air-equilibrated water because it was completely quenched by Oj. However, in 5 x 10 M y-CD, the phosphorescence could be observed, even in oxygen-saturated solutions. In particular, for group IV,... 

Cellulose. Cellulose has been used as a solid powdered substrate for the study of photophysical and photochemical studies of several organic probes, mostly dyes. Some of the properties of this substrate, namely the capacity of adsorbing molecules both by entrapment and on the surface of the natural polymer (forming in many cases hydrogen bonds) and also the absence (or extremely reduced) of diffusion of oxygen, make this substrate a particularly attractive one for room temperature luminescence studies [75-83]. We recently published some fluorescence and phosphorescence studies of rhodamine dyes [15,81,82], auramine O [81b], 2,3-naphthalimides [84], oxazine [85], acridine orange [86], and cyanine dyes [16, 87, 88] adsorbed on cellulose. 

Several other diaryl and alkylarylketones also exhibit room temperature phosphorescence in air equilibrated samples when included in silicalite [83c] or forming inclusion complexes with cyclodextrins [83c, 102], depending on the probe and cavity size. Both substrates provide some degree of protection from oxygen quenching, as well as imposed conformational restrictions that decrease the non-radiative mechanisms of deactivation. 

Long-decay luminescent dyes and probes that are effectively quenched by molecular oxygen can be used for its quantitation. Examples of such probes include ruthe-nium(II)-rm(diphenyl phenanthroline) and phosphorescent platinum(II) porphyrins. Their long emission lifetimes facilitate quantitation by lifetime or intensity measurements. Other chemical specie, such as heavy-metal ions and heterocyclic compounds, can be quantified by luminescence quenching, according to Eq. 3. 

The MLCs have several advantages over the phosphorescent probes. In contrast to phosphorescence, the luminescence from MLCs can be measured in the presence of dissolved oxygen. The MLCs are only partially quenched by ambient oxygen, whereas phosphorescence is usually completely quenched. Additionally, there are relatively few phosphorescent probes, but there are numerous MLCs (Chapter 20). 

The use of metalloporphyrin-based materials for the detection of molecular oxygen is well developed. One approach that has been employed extensively involves the well-known phenomenon of quenching of metalloporphyrin phosphorescence by O2. Due to their high phosphorescence quantum yields and short triplet lifetimes, platinum and palladium porphyrins were originally suggested as probes... 

The relationship between segmental and group motion in solid polymers and the rates of diffusion of small molecules suggests that diffusion measurements might be used to detect the transitions associated with the occurrence of this type of motion, and indeed this turns out to be the case. One of the most sensitive measurements of the occurrence of solid-phase transitions is obtained by observing the quenching of phosphorescent probes in solid polymers by the diffusion of oxygen. 

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