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We describe the synthesis and fluorescence spectral characterization of a pH-sensitive metal-ligand complex, [Ru(deabpy)(bpy)2]2., where deabpy is 4,4'-diethylaminomethyl-2,2'-bipyridine. This metal-ligand complex (MLC) was found to display pH-dependent intensities, emission spectra, and decay times, with the changes centered near the physiological useful pH value of 7.5. The apparent pKa values were not found to be dependent on ionic strength. The compound was found to be useful for lifetime-based sensing by phase-modulation fluorometry. Global analysis of the intensity decays over a range of pH values revealed two decay times of 235 and 380 ns, associated with the protonated and unprotonated forms, respectively. Because of its long decay time, optical pH measurements could be accomplished by phase-modulation fluorometry with a conveniently low modulation frequency of 700 kHz. The lifetime data were obtained with either a amplitude-modulated laser or with an amplitude-modulated blue-light-emitting diode. This pH-sensitive complex also displays a modest spectral shift with change in pH, allowing its use as a wavelength-ratiometric MLC probe. One can imagine lifetime sensors for a variety of blood cations and point-of-care assays based on long-lifetime metal-ligand complexes and simple solid-state light sources and detectors.

Throughout this paper, denotes a fixed stopping time that will be considered to be the time of occurrence of some physical event which signals the end of the lifetime of a process. We imagine that processes with lifetime are observable only strictly prior to , so that all meaningful constructions associated with such processes should be based only on their values strictly prior to . Of particular interest is the case in which is the lifetime of a right process X. In this situation, X is supposed to be sent to a dead state after its lifetime, and no further information is generated by it after that time.

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Vanessa Hayes is making her wish finally come true: Christmas in Paris. But when her passport gets delayed, it looks like the Yuletide she longs for won't happen until a stranger suddenly enters her life, and changes it forever. Overwhelmed by responsibility, Judith Guthrie is too busy worrying about her seriously ill brother to have time to celebrate. A trip to France is a kind of happiness she can't imagine. When she accidentally receives Vanessa's passport, Judith can't resist delivering it in person so Vanessa will at least have her holiday dream. She can't anticipate that her small gesture will result in lifelong rewards that all will be thankful for. 2351a5e196