Self-Immolative Activation of β-Galactosidase-Responsive Probes for In Vivo MR Imaging in Mouse Models

Our lab has developed a new series of self-immolative MR agents for the rapid detection of enzyme activity in mouse models expressing β-galactosidase (β-gal). We investigated two molecular architectures to create agents that detect β-gal activity by modulating the coordination of water to Gd^III. The first is an intermolecular approach, wherein we designed several structural isomers to maximize coordination of endogenous carbonate ions. The second involves an intramolecular mechanism for q modulation. We incorporated a pendant coordinating carboxylate ligand with a 2, 4, 6, or 8 carbon linker to saturate ligand coordination to the Gd^III ion. This renders the agent ineffective. We show that one agent in particular (6-C pendant carboxylate) is an extremely effective MR reporter for the detection of enzyme activity in a mouse model expressing β-gal.     

Kinetics and mechanism of a macrocyclic chromium(III) complex oxidation to chromium(IV) by hexacyanoferrate(III) in strongly alkaline media

Oxidation of the macrocyclic Cr(III) complex cis-[Cr(cycb)(OH)₂]⁺, where cycb=rac-5,5,7,12,12,14-hexamethyl-1,4,8,11-tetraazacyclotetradecane, by an excess of the hexacyanoferrate(III) in basic solution, slowly produces Cr(V) species. These species, detected using e.p.r. spectroscopy, are stable under ambient conditions for many hours, and the hyperfine structure of the e.p.r. spectrum is consistent with the interaction of the d-electron with four equivalent nitrogen nuclei. Electro-spray ionization mass spectrometry suggests a concomitant oxidation of the macrocyclic ligand, in which double bonds and double bonded oxygen atoms have been introduced. By comparison basic chromate(III) solutions are oxidized rapidly to chromate(VI) by hexacyanoferrate(III) without any detectable generation of stable Cr(V) intermediates.Kinetics of oxidation of the macrocyclic Cr(III) complex in alkaline solution has been studied under excess of the reductant. Rate determining formation of Cr(IV) by a second order process involving the Cr(III) and the Fe(III) reactants is seen. This reaction also involves a characteristic higher order than linear dependence on the hydroxide concentration. Reaction mechanisms for the processes, including oxidation of the coordinated macrocyclic ligand – under excess of the oxidant- are proposed.     

Investigation of the quantitative properties of the quadrupole orthogonal acceleration time-of-flight mass spectrometer with electrospray ionisation using 3,4-methylenedioxymethamphetamine

This paper describes the investigation of the potential of a quadrupole orthogonal acceleration time-of-flight mass spectrometer (Q-TOF) equipped with an atmospheric pressure ionisation interface for quantitative measurements of small molecules separated by reversed phase liquid chromatography. To this end, the detection limits and linear dynamic range in particular were studied in an LC/MS/MS experiment using 3,4-methylenedioxymethamphetamine standards and 3,4-methylenedioxyethylamphetamine for internal standardisation. In a second phase, the experiment was repeated with real biological extracts (whole blood, serum, and vitreous humour). A calibration for 3,4-methylenedioxymethamphetamine and its metabolite 3,4-methylenedioxyamphetamine was prepared in each of these matrices again using 3,4-methylenedioxyethylamphetamine as internal standard. The resulting quantitative data were compared with those obtained by liquid chromatography with fluorescence detection for the same extracts. The Q-TOF results revealed excellent sensitivity and a linear dynamic range of nearly four decades (2-10 000 pg on-column, r(2) = 0.9998, 1/x weighting). Furthermore, all the calibration curves prepared in biological material were superimposable, LC/MS/MS and LC-fluorescence, and the quantitative results for actual samples compared very favourably. It was concluded that the Q-TOF achieves a linear dynamic range for quantitative LC/MS/MS work exceeding that of fluorescence detection and at much better absolute sensitivity. Copyright 1999 John Wiley & Sons, Ltd.     

Exploring Redox States,Doping and Ordering of Electroactive Star‐Shaped Oligo(aniline)s

We have prepared a simple star‐shaped oligo(aniline) ( TDPB ) and characterised it in detail by MALDI‐TOF MS, UV/Vis/NIR spectroscopy, time‐dependent DFT, cyclic voltammetry and EPR spectroscopy. TDPB is part of an underdeveloped class of π‐conjugated molecules with great potential for organic electronics, display and sensor applications. It is redox active and reacts with acids to form radical cations. Acid‐doped TDPB shows behaviour similar to discotic liquid crystals, with X‐ray scattering investigations revealing columnar self‐assembled arrays. The combination of unpaired electrons and supramolecular stacking suggests that star‐shaped oligo(aniline)s like TDPB have the potential to form conducting nanowires and organic magnetic materials.     

Determination of melatonin and monoamines in rat pineal using reversed-phase ion-interaction chromatography with fluorescence detection

A method is reported for the ion-interaction, reversed-phase separation of 24 compounds (chiefly monoamines) arising from the metabolism of tyrosine and tryptophan. These compounds were separated as two groups. The first group comprised 3,4-dihydroxyphenylethylene glycol, tyrosine, 3-methoxy-4-hydroxyphenyl glycol, 5-hydroxytryptophan, norepinephrine, 3,4-dihydroxyphenylacetic acid, epinephrine, 5-hydroxyindole-3-acetic acid, homovanillic acid, 5-hydroxytryptophol, dopamine, tryptophan. N-acetylserotonin, N-acetyltryptophan, 5-methoxytryptophan and serotonin. The mobile phase consisted of a 6.8:93.2 (v/v) mixture of acetonitrile and an aqueous solution containing 0.16 M ammonium phosphate, 0.06 M citric acid, 0.15 mM disodium EDTA, 10 mM dibutylamine and 6 mM sodium 1-octanesulphonate at pH 4.50. The second group of compounds comprised 6-hydroxymelatonin, 5-methoxyindole-3-acetic acid, indole-3-acetic acid, 5-methoxytryptamine, tryptamine, 5-methoxytryptophol, melatonin and tryptophol. The mobile phase consisted of a 16:84 (v/v) mixture of acetonitrile and an aqueous solution containing 0.05 M ammonium phosphate, 0.05 M citric acid, 0.15 mM disodium EDTA, 25 mM dibutylamine and 5 mM sodium 1-octanesulphonate at pH 5.30. Detection was by fluorescence measurement (lambda ex = 280 nm, lambda em = 340 nm). The proposed method exhibited linear calibration over the biochemically significant concentration range, with detection limits in the 10-200 pg range. Excellent precision for peak areas and retention times was observed, even over a period of 24 h. The applicability of amperometric detection (at 0.72V) is also demonstrated. The method is applied to the determination of monoamines in individual rat pineals. Low nanogram levels of tyrosine, norepinephrine, 5-hydroxyindole-3-acetic acid, tryptophan, serotonin and 6-hydroxymelatonin, and picogram levels of 5-hydroxytryptophan, 5-hydroxytryptophol, 5-methoxyindole-3-acetic acid, indole 3-acetic acid, 5-methoxytryptophol and melatonin were indicated in most of the samples.