Jean-Louis Habib Jiwan

HPLC-high resolution mass spectrometry in clinical laboratory?

To date, GC-MS and LC-tandem MS techniques emerged quite frequently in laboratory medicine. However, high-resolution mass spectrometric (HRMS) analyzers remain almost ignored, even though in academic environment, they become more largely used. The main objective of this work is to present and illustrate with several applications, current high resolution mass spectrometric systems which could be useful for clinical applications. Among these systems are the Time-of-Flight (TOF) and Orbitrap instruments. Orbitrap has the advantage of higher resolution but suffers from a slower data acquisition, whereas TOF systems display the opposite characteristics. Both systems could provide accurate mass data and possible structural elucidation, very useful in large scale screening, in different medical areas (clinical or environmental toxicology, anti-doping controls, …). Provided there are further improvements in quantification performances, there is no doubt such HRMS instruments will find their place in clinical laboratories.

Photosensing by a fluorescing probe covalently attached to the silica

Starting from aminopropyl silicagel, an anthracene fluorophore has been covalently grafted on the surface of silica, the secondary amino group being left in the linking arm. When one fifth of the initial amino functions are grafted, the silica behaves as a pH probe, the fluorescence of which switches on when the amino groups are protonated. On the contrary, if the silica loading is almost complete, the pH probing is no longer possible. In this case, an excimeric versus monomeric emission can be used in sensing the solvent water content. Copyright (C) 1996 Elsevier Science Ltd

Ion-responsive fluorescent compounds V. Photophysical and complexing properties of coumarin 343 linked to monoaza-15-crown-5

The photophysical and complexing properties of a fluoroionophore consisting of coumarin 343 linked to monoaza-15-crown-5 are reported in acetonitrile and ethanol. The amide link between the coumarin and the crown precludes pH sensitivity of the tertiary amine bridging group. Upon complexation by calcium and magnesium cations, the photophysical properties undergo marked changes, whereas the effects are insignificant or very weak with alkali metal ions. I.R. spectra were recorded in deuterated acetonitrile in order to unravel the participation of the carbonyl groups in the complexation. The stoichiometry of the complexes is 1:1 apart from the case of complexation with calcium in acetonitrile where two complexes can be formed. The stability constants of the complexes were determined in acetonitrile and ethanol.

Organic sulfides photooxidation using sensitizers covalently grafted on silica : towards a more efficient and selective solar photochemistry

A visible light sensitized oxidation of organic sulfides using a derivative of 9,10 dicyanonoanthracene (DCA) covalently grafted on silica (DCAC-Si) is studied. The reaction is more efficient than the corresponding homogeneous reaction and some improvement in the rate of product formation is noticed. These observations are discussed. In the case of di n-butylsulfide, the sulfoxide/(sulfone + disulfide) selectivity is increased. Diphenyl sulfide leads selectively and efficiently to diphenylsulfoxide. Advantages of the process, using reusable sensitizer and solar light are emphasized

Ion-responsive fluorescent compounds: VI. Coumarin 153 linked to rigid crowns for improvement of selectivity

The photophysical and complexing properties of fluoroionophores consisting of the coumarin C153 linked to dibenzo-16-crown-5 (C153-DBC) and tribenzo-19-crown-6 (C153-TBC) are described in acetonitrile and ethanol. The carbonyl group of the coumarin moiety is in direct interaction with a bound cation. The selectivity of these compounds for a given alkali or alkaline earth metal ion was found to be better than that of previously reported crowned coumarins owing to the rigidity of dibenzo- and tribenzocrowns. In acetonitrile, a very high selectivity for Ca2+ versus Mg2+ has been found. In ethanol, C153-DBC is selective for Na+ and C153-TBC is selective for K+, as expected from the relative size of the crown cavity

A halogen anion sensor based on the hydrophobic entrapment of a fluorescent probe in silica sol-gel thin films

A halogen anion (Cl−, Br−, I−) sensor has been designed, based on the entrapment of a fluorescent molecule in a sol-gel silica film deposited on a glass substrate. A key factor is the use of the newly synthesized hydrophobic fluorophore, N-dodecyl-6-methoxyquinolinium, so as to avoid the problem of leaching. This probe allows detection and measurement of chloride concentrations in the physiological range (100 mM) coupled with a response time less than 1 s. The fluorescence quenching data are fitted to a model which assumes two quenching sites.

Photoinduced electron transfer sensitization of anisyl ether cleavage: studies in homogeneous solution and at the surface of one or two solids

The cleavage of p-methoxybenzyl 2-cyclohexylethyl ether photosensitized in the presence of air by 9,10-dicyanoanthracene is found to give anisaldehyde and 2-cyclohexylethanol together with high amounts of an uncleaved ester. The reaction, considerably accelerated by co-sensitization with biphenyl, may be oriented towards the exclusive formation of the cleavage products when replacing oxygen by bromotrichloromethane used as a sacrificial electron acceptor. Anchoring the sensitizer to silica beads allows to perform the reaction under conditions where the sensitizer may be recycled. Working in a reverse way with the anisyl ether grafted on silica and the sensitizer in the solution shows that the silica surface modification is successful when using a redox photosensitizer together with a charge relaying molecule. Finally, working under doubly heterogeneous conditions is found feasible: the sensitizer and the ether to be cleaved are fixed on different silica beads while the charge shuttling molecule is used in the solution to ensure ‘synaptic like’ communication between the two surfaces.

About the use of an amide group as a linker in fluoroionophores: competition between linker and ionophore acting as chelating groups

The photophysical and complexing properties of a series of aza-crown fluoroionophores based on coumarin 343 and on 3- and 6-methoxynaphthoic amides in acetonitrile are reported. The goal of the work was to probe the participation of the amide bridge linking the fluorophore and the ionophore in the metal chelation. The use of 3- and 6-methoxy substituents in the naphthoic amide fluorophores allowed us to maintain the charge transfer character of the system and to probe the participation of the methoxy group as ancillary ligand. The aza-crown unit is no longer complexing when the amide linker is included in a β-dicarbonyl sub-structure. The amide function itself is still able to form complexes, even if weaker, with the cations.

Sol-gel silicate thin films bearing attached pyrene fluorescing probes hidden from oxygen but still accessible to organic electron transfer quenchers

Acid or base catalysts were used to prepare sol–gel thin films of silica (AF and BF respectively) doped with a pyrene fluorescent probe covalently attached to the silica network. The polarity of the matrix was found to change according to the catalyst used. Fluorescence quenching of the excited states of the pyrene monomer by electron donors and acceptors enabled us to evaluate the accessibility of the probing dopant. A model considering the possibility of two different dopant sites is proposed for the understanding of the fluorescence quenching data. A fraction of the fluorophore is freely accessible and may be quenched, while the rest remains unquenched due, for instance, to a too deep entrapment in the silica network. The pyrene dopant was found to be almost insensitive to oxygen quenching. A tentative explanation of this peculiar protection versus oxygen is discussed.

Electron transfer photochemistry initiated from a twisted intramolecular charge transfer state used as an electron donor and as an acceptor

Electron transfer photochemistry starting from a twisted intramolecular charge transfer (TICT) excited state is shown, using N-(α-naphthyl)carbazole (NC) as sensitizer. The NC TICT state has been used as electron donor and acceptor. This dual reactivity is demonstrated by fluorescence quenching measurements, and the rate constants have been correlated with the help of the Marcus equation. Photochemical reactions have also been performed. Photoisomerization of the quadricyclane into norbornadiene is proof of the radical cationic reactivity of the quadricyclane into norbornadiene is proof of the radical cationic reactivity of the TICT, while photodechlorination of pentachlorobenzene is proof of radical anionic reactivity. A triplet sensitized ring closure of norbornadiene was also shown to occur.