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The main concern pertaining to the safety of Gadolinium(III)-based contrast agents (GBCAs) is the toxicity caused by the unchelated ion, which may be inadvertently present in the solution due most commonly to excess unreacted starting material or dissociation of the complexes. Detecting the aqueous free ion during the synthesis and preparation of GBCA solutions is therefore instrumental in ensuring the safety of the agents. This paper reports the development of a sensitive fluorogenic sensor for aqueous unchelated Gadolinium(III) (Gd(III)). Our design utilizes single-stranded oligodeoxynucleotides with a specific sequence of 44 bases as the targeting moiety. The fluorescence-based assay may be run at ambient pH with very small amounts of samples in 384-well plates. The sensor is able to detect nanomolar concentration of Gd(III), and is relatively unresponsive toward a range of biologically relevant ions and the chelated Gd(III). Although some cross-reactivity with other trivalent lanthanide ions, such as Europium(III) and Terbium(III), is observed, these are not commonly found in biological systems and contrast agents. This convenient and rapid method may be useful in ascertaining a high purity of GBCA solutions. Graphical abstract Fluorescent aptamer-based assay for detecting unchelated Ln(III) ions in aqueous solution.

We have previously identified and reported several potent piperidine-derived amide inhibitors of the human soluble epoxide hydrolase (sEH) enzyme. The inhibition of this enzyme leads to elevated levels of epoxyeicosatrienoic acids (EETs), which are known to possess anti-inflammatory, vasodilatory, and anti-fibrotic effects. Herein, we report the synthesis of 9 analogs of the lead sEH inhibitor and the follow-up structure-activity relationship and liver microsome stability studies. Our findings show that isosteric modifications that lead to significant alterations in the steric and electronic properties at a specific position in the molecule can reduce the efficacy by up to 75-fold. On the other hand, substituting hydrogen with deuterium produces a notable increase (∼30%) in the molecules' half-lives in both rat and human microsomes, while maintaining sEH inhibition potency. These data highlight the utility of isosteric replacement for improving bioavailability, and the newly-synthesized inhibitor structures may thus, serve as a starting point for preclinical development. Our docking study reveals that in the catalytic pocket of sEH, these analogs are in proximity of the key amino acids involved in hydrolysis of EETs.

A method for determining the presence of unchelated trivalent gadolinium ion (Gd3+) in aqueous solution is demonstrated. Gd3+ is often present in samples of gadolinium-based contrast agents as a result of incomplete reactions between the ligand and the ion, or as a dissociation product. Since the ion is toxic, its detection is of critical importance. Herein, the design and usage of an aptamer-based sensor (Gd-sensor) for Gd3+ are described. The sensor produces a fluorescence change in response to increasing concentrations of the ion, and has a limit of detection in the nanomolar range (~100 nM with a signal-to-noise ratio of 3). The assay may be run in an aqueous buffer at ambient pH (~7 - 7.4) in a 384-well microplate. The sensor is relatively unreactive toward other physiologically relevant metal ions such as sodium, potassium, and calcium ions, although it is not specific for Gd3+ over other trivalent lanthanides such as europium(III) and terbium(III). Nevertheless, the lanthanides are not commonly found in contrast agents or the biological systems, and the sensor may therefore be used to selectively determine unchelated Gd3+ in aqueous conditions.

Oligonucleotide-based receptors or aptamers can interact with small molecules, but the ability to achieve high-affinity and specificity of these interactions depends strongly on functional groups or epitopes displayed by the binding targets. Some classes of targets are particularly challenging: for example, monosaccharides have scarce functionalities and no aptamers have been reported to recognize, let alone distinguish from each other, glucose and other hexoses. Here we report aptamers that differentiate low-epitope targets such as glucose, fructose or galactose by forming ternary complexes with high-epitope organic receptors for monosaccharides. In a follow-up example, we expand this method to isolate high-affinity oligonucleotides against aromatic amino acids complexed in situ with a nonspecific organometallic receptor. The method is general and enables broad clinical use of aptamers for the detection of small molecules in mix-and-measure assays, as demonstrated by monitoring postprandial waves of phenylalanine in human subjects.

We here present an optical method for monitoring the activity of the inducible aldo-keto reductases AKR1C2 and AKR1C3 in living human cells. The induction of these enzymes is regulated by the antioxidant response element (ARE), as demonstrated in recent literature, which in turn is dependent on the transcription factor Nrf2. The activation of ARE leads to the transcription of a coalition of cytoprotective enzymes and thus represents an important target for the development of new therapies in the area of neurodegenerative diseases and cancer. Through the use of Coumberone, a metabolic fluorogenic probe, and isoform-selective inhibitors, the upregulation of cellular stress markers AKR1C2 and AKR1C3 can be quantitatively measured in the presence of ARE activator compounds, via either a fluorimetric assay or fluorescence microscopy imaging of intact cells. The method has both high sensitivity and broad dynamic range, as demonstrated by induction studies in three cell lines with dramatically different metabolic capabilities (transfected monkey kidney COS-1 cells, human neuroblastoma IMR-32 cells, and human liver HepG2 cells). We applied the new method to examine a number of neurotrophic natural products (spirotenuipesine A, spirotenuipesine B, scabronine G-methylester, and panaxytriol), and discovered that panaxytriol, an active component of red ginseng extracts, is a potent ARE inducer. The upregulation of AKR1C enzymes, induced by chemically homogeneous panaxytriol, was partially dependent on PKC and PI3K kinases as demonstrated by the application of selective inhibitors. This cellular mechanism may account for panaxytriol's neurotrophic, neuroprotective, and anticancer properties. The protective effects of ARE inducers against tumorgenesis and neurodegeneration fuel the growing interest in this area of research and the method described here will greatly enable these endeavors.

Fluorogenic probes for redox metabolism are shown to exhibit two-photon absorption using femtosecond pulses from a Ti/sapphire laser. The probes consist of a coumarin or naphthalene core and a ketone−alcohol functional group. The probe design is based on the changes in fluorescence properties and two-photon cross section values when the ketone derivative is reduced to the corresponding alcohol. The resulting contrast ratio of the fluorescence differs significantly from that obtained by one-photon excitation. This phenomenon was demonstrated with all three switches examined herein and represents an attractive approach to modulation of emission properties of molecular switches. The practical applicability of the two-photon-excitation redox switch was demonstrated in an enzyme-catalyzed transformation. The nonfluorescent probe 1 is efficiently converted by AKR1C3, a human 3α-hydroxysteroid dehydrogenase, to the fluorescent derivative 2. Using two-photon excitation (775 nm), we achieved a large contrast ratio...

[reaction: see text] A luminogenic probe for peptide dephosphorylation has been developed. It consists of a serine-/tyrosine-containing peptide modified on the N-terminus with a tryptophan residue and a DTPA chelate capable of binding Tb(3+). We propose a mechanistic model for the luminescence enhancement based on the interconversion of monomeric and dimeric lanthanide species, which is affected by the phosphorylation state of the serine or tyrosine residue. The optical switch reports effectively on phosphatase-catalyzed dephosphorylation in vitro.

The dynamic properties of two-photon pumped blue lasing (similar to 470 nm) in the solution of an organic chromophore [2-acetyl-6-(dimethylamino)naphthalene], excited by similar to 160-fs laser pul ...

This study reports the development of a Nd(III)-based near-IR luminescent probe for monitoring aldo-ketoreductase (AKR) enzyme activity. We have adapted a coumarin-based reporter substrate for the AKR1C2 to a near-IR emitting format by tethering the former to a macrocyclic Nd(III) moiety via an alkyl linker. Enzymatic reduction of the ketone functionality on the coumarin alters the energy transfer efficiency from the fluorophore to the emitting lanthanide species, resulting in emission at ∼1060 nm from the alcohol product. The efficiency of sensitization is not significantly affected by extending the alkyl tether from two to three carbons, and even a six-carbon linker still supports viable sensitized luminescence. In addition, the suitability of these complexes to act as enzyme substrates improves with longer linker length. We have thus developed long wavelength luminogenic reporter substrates for a redox enzyme and also a general platform for transposing molecular fluorescence into the more desirable nea...

Fluorescent and luminescent reporters that signal molecular events of interest by modulating the ratio of peaks in their emission profile have advantages over reporters that simply modulate their emission intensity, since ratiometric measurement is concentration-independent and allows them to be effective in complex contexts, such as living cells or sensor microarrays. We herein describe a general platform for the design of ratiometric probes based on a heterometallic Tb(3+)/Eu(3+) bis-lanthanide ensemble, consisting of a mixture, or "cocktail", of otherwise identical heterometalated chelates. The chelate contains an organic photon antenna that sensitizes the Tb(3+)/Eu(3+) luminescence. The contributions of the two metals to the composite luminescence spectrum can be tuned to the same relative scale by adjusting the stoichiometry of the cocktail, allowing subtle changes in their ratio to be accurately measured. Importantly, the ratio responds to chemical and environmental changes experienced by the photon antenna, making the system an ideal platform for the design of chemical and enzymatic probes. As proofs of concept, we describe a ratiometric probe for esterase activity and a polarity-responsive ratiometric sensor.