PubMed · 14844039
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L P A BARLETTA, D GRINFELD. 1951-04-06. [Fluorescein test in plastic surgery].. https://pubmed.ncbi.nlm.nih.gov/14844039/
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Tryptophan is known to be a major target of oxidative stress and to take part in electron transfer. In proteins, its fluorescence is extinguished after treatment with oxidative agents, like peroxynitrite (ONOO(-)/ONOOH) - the product of the reaction of NO* and superoxide anion (O*(2)(-)) radicals. The main reactions of N-blocked tryptophan derivatives (melatonin or N-acetyl-L-tryptophan) exposed to peroxynitrite at physiological pH are oxidation to formylkynuramine or formylkynurenine, respectively, and nitrosation, which leads to substituted 1-nitrosoindoles. Here we show that peroxynitrite-induced nitrosation is specific to N-blocked L-tryptophan derivatives and is not obtained with free L-tryptophan. Such a nitrosation can be evaluated by using 4,5-diaminofluorescein (DAF-2), which is converted to the fluorescent triazolofluorescein by NO* donors and nitrosating agents. N-acetyl-L-tryptophan was shown to be twice as efficient as melatonin in transferring NO from peroxynitrite to DAF-2. DAF-2 responses were then used to assess the ability of a series of L-tryptophan-containing peptides to give transient N-nitrosoindoles upon treatment with peroxynitrite. Many peptides proved not to be susceptible to nitrosation under these conditions. However, the N-terminally blocked peptide of endothelin-1 (Ac-Asp-Ile-Ile-Trp) reacted in a very similar fashion to melatonin; this shows that tryptophan residue nitrosation could occur when it was exposed to peroxynitrite.
A highly sensitive and selective fluorogenic probe for fluoride ion, fluorescein di-tert-butyldimethylsilyl ether (FTBS), was designed and synthesized. FTBS was a colorless, non-fluorescent compound and was synthesized via the one-step reaction of fluorescein with tert-butyldimethylsilyl chloride. Upon incubation with fluoride ion in DMF-water solution (7 : 3, V/V), the Si-O bond of FTBS was cleaved, causing a large increase in fluorescence intensity and thereby allowing a selective detection of fluoride ion. The fluorescence increase is linearly with fluoride concentration in the range 0.1-2.0 mumol L(-1) with a detection limit of 0.041 mumol L(-1) (3sigma). The excellent selective signaling behavior of the proposed probe was found to originate from the high affinity of silicon toward fluoride ion. The method has been successfully applied to the fluoride determination in multi-trace elements injection and toothpaste samples, and the results are agreed well with those obtained by the fluoride-ion selective electrode method.
We present an experimental study of temperature gradient focusing (TGF) exploiting an inherent Joule heating phenomenon. A simple variable-width PDMS device delivers rapid and repeatable focusing of model analytes using significantly lower power than conventional TGF techniques. High electric potential applied to the device induces a temperature gradient within the microchannel due to the channel's variable width, and the temperature-dependent mobility of the analytes causes focusing at a specific location. The PDMS device also shows simultaneous separation and concentration capability of a mixture of two sample analytes in less than 10 min. An experiment combining Joule heating with external heating/cooling further supports the hypothesis that temperature is indeed the dominant factor in achieving focusing with this technique.