Fluorescent sensors carboxylates

The design of fluorescent sensors is of major importance because of the high demand in analytical chemistry, clinical biochemistry, medicine, the environment, etc. Numerous chemical and biochemical analytes can be detected by fluorescence methods cations (H+, Li+, Na+, K+, Ca2+, Mg2+, Zn2+, Pb2+, Al3+, Cd2+, etc.), anions (halide ions, citrates, carboxylates, phosphates, ATP, etc.), neutral molecules (sugars, e.g. glucose, etc.) and gases (O2, CO2, NO, etc.). There is already a wide choice of fluorescent molecular sensors for particular applications and many of them are commercially available. However, there is still a need for sensors with improved selectivity and minimum perturbation of the microenvironment to be probed. Moreover, there is the potential for progress in the development of fluorescent sensors for biochemical analytes (amino acids, coenzymes, carbohydrates, nucleosides, nucleotides, etc.). 

A fluorescein derivative (166) immobilized on a PVC membrane showed fluorescence enhancement in the presence of carboxylic acids and fluorescence quenching in the presence of phenols. This property was applied for development of a fluorescence sensor for... 

Unfortunately, no lead sensors have been developed to date that meet all of these criteria. The system that has been used most extensively to quantitate lead levels in vivo is the fluorescent sensor Indo-1 (Fig. 24) (443 45). Although originally developed as a calcium dye (446) log iCfc[Ca(II)] = 6.6, Indo-1 (2-[4-[bis(carboxymethyl)amino]-3-[2-[2-[bis(carboxymethyl)amino]-5-methyl-phenoxy]ethoxy]phenyl]-lH-indole-6-carboxylic acid) binds lead quite tightly (log ffo[Pb(II)] = 10.5 and exhibits a very different fluorescence emission spectrum when bound to lead than when free in solution or bound to calcium (Fig. 24). As a result, Indo-1 can be used to determine whether lead is present in cells, even in the presence of excess calcium, provided that the fluorescence spectrum is deconvoluted to account for calcium interference and all of the possible equilibria are taken into consideration (443, 445). The main drawback of the Indo-1 detection system is that the dye is almost completely quenched when bound to lead (Fig. 24, spectrum b), making it difficult to quantitate the amount of free lead present. 

Qing GY, He YB, Wang F et al (2007) Enantioselective fluorescent sensors for chiral carboxylates based on calix[4]arenes bearing an L-tryptophan unit. Eur J Qrg Chem 11 1768-1778... 

Zhang X, Chi L, Ji S et al (2009) Rational design of d-PeT phenylethynylated-carbazole monoboronic acid fluorescent sensors for the selective detection of a-hydroxyl carboxylic acids and monosaccharides. J Am Chem Soc 131 17452-17463... 

Zinc carboxylate interactions have been exploited as part of a fluorescent molecular sensor for uronic acids. The sensors feature two interactions coordination of the carboxylate to the zinc and a boronic acid diol interaction.389 Photoluminescent coordination polymers from hydrothermal syntheses containing Zn40 or Zn4(OH)2 cores with isophthalate or fumarate and 4,4 -bipyridine form two- and three-dimensional structures. Single X-ray diffraction of both dicarboxylates identified the network structure.373... 

Center for Healthcare Technologies at Lawrence Livermore National Laboratory in Livermore, potentially capable to measure pH at or near the stroke site29. The probe is the distal end of a 125 pm fibre tapered up to a diameter of 50 pm. A fluorescent pH-indicator, seminaphthorhodamine-1-carboxylate, is embedded inside a silica sol-gel matrix which is fixed to the fibre tip. Excitation of the dye takes place at 533 nm and the emission in correspondence of the acid (580 nm) and basic (640 nm) bands are separately detected. The use of this ratiometric technique obviates worrying about source fluctuations, which have the same effects on the two detected signals. The pH sensor developed was first characterised in the laboratory, where it showed fast response time (of the order of tens of seconds) and an accuracy of 0.05 pH units, well below the limit of detection necessary for this clinical application (0.1 pH units). The pH sensor was also tested in vivo on rats, by placing the pH sensor in the brain of a Spraque-Dawley rat at a depth of approximately 5 mm30. 

The sensor reported by Shirai(69) used a natural carboxylic polyether antibiotic (Aem = 481 nm) for the detection of magnesium and calcium. Detection limits of I0 5 and KT4 M, respectively, were reported but, interference from other metals was difficult to overcome. Ishibashi(69) used a bulkier hexadecyl-acridine orange dye (Xem = 525 nm) plasticized in a PVC membrane for the fluorescent detection of ammonium ions. Signal interference due to superfluous ions and poor detection limits of KT5 M restricted the use of the probe. 

A new PET-based chemosensor for uronic and sialic acids utilizing the cooperative action of boronic acid and metal chelate was reported by Shinkai and co-workers. This group synthesized a novel fluorescent chemosensor molecule bearing both an o-aminomethylphenylboronic acid group for diol binding to a saccharide and a l,10-phenanthroline-Zn(II)chelate moiety for the carboxylate binding, which enables this sensor to discriminate between neutral monosaccharides and acidic compounds [110],... 

The feasibility of the screening scheme of fluorescent RNP sensors (Fig. 10.4) was demonstrated by utilizing libraries of fluorescent RNP receptors constructed from the 29 different ATP-binding RNP, which obtained from RRE30N RNAs (Fig. 10.2a) and Rev peptides modified with various fluorophores, 7-methoxycoumarin-3-carboxylic acid (7mC-Rev), 4-fluoro-7-nitrobenz-2-oxa-1,3-diazole (NBD-Rev), and Cy5 mono NHS ester (Cy5-Rev) at the N-terminal. Complex formation of the 29 different RNA subunits and Pyr-Rev, 7mC-Rev, NBD-Rev, or Cy5-Rev afforded four independent fluorescent RNP libraries. 

Amine not only affects the fundamental optical gaps but also produces a significant enhancement of absorbance and fluorescence, as indicated by an enhancement in the oscillator strengths of the amine-capped SiQDs relative to the H-SiQDs. In small clusters, the Si-N bonds most likely act, at least, in two different ways (a) to reduce the optical gap and (b) to enhance the light absorption and emission. Amine is hydrophilic and the produced amine-capped surfaces are expected to be useful for solution phase sequential reactions with various aldehydes and carboxylic acids. Therefore, H2N-SiQDs may play an important role in fabricating hybrid devices and sensors. 

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