Andrée Kirsch-De Mesmaeker

Development of a quantitative LC-MS/MS method for the analysis of common propellant powder stabilizers in gunshot residue.

Abstract:  In traditional scanning electron microscopy/energy dispersive X‐ray analysis of gunshot residue (GSR), one has to cope more and more frequently with limitations of this technique due to the use of lead‐free ammunition or ammunition lacking heavy metals. New methods for the analysis of the organic components of common propellant powder stabilizers were developed based on liquid chromatography coupled to tandem mass spectrometry (LC‐MS/MS). A multiple reactions monitoring scanning method was created for the screening of akardite II, ethylcentralite, diphenylamine, methylcentralite, N‐nitrosodiphenylamine, 2‐nitrodiphenylamine, and 4‐nitrodiphenylamine, present in standards mixtures. Five out of seven of these target compounds can be selectively identified and distinguished from the two others with a high accuracy. Samples from the hands of a shooter were collected by swabbing and underwent solid phase extraction prior to analysis. Detection limits ranging from 5 to 115 μg injected were achieved. Results from several firing trials show that the LC‐MS/MS method is suitable for the detection of stabilizers in samples collected following the firing of 9 mm Para ammunitions.

Mesoscale DNA Structural Changes on Binding and Photoreaction with Ru[(TAP)2PHEHAT]2+

We used scanning force microscopy (SFM) to study the binding and excited state reactions of the intercalating photoreagent Ru[(TAP)(2)PHEHAT](2+) (TAP = 1,4,5,8-tetraazaphenanthrene; PHEHAT = 1,10-phenanthrolino[5,6-b]1,4,5,8,9,12-hexaazatriphenylene) with DNA. In the ground state, this ruthenium complex combines a strong intercalative binding mode via the PHEHAT ligand, with TAP-mediated hydrogen bonding capabilities. After visible irradiation, SFM imaging of the photoproducts revealed both the structural implications of photocleavages and photoadduct formation. It is found that the rate of photocleaving is strongly increased when the complex can interact with DNA via hydrogen bonding. We demonstrated that the photoadduct increases DNA rigidity, and that the photo-biadduct can crosslink two separate DNA segments in supercoiled DNA. These mechanical and topological effects might have important implications in future therapeutic applications of this type of compounds.

Stereoselective interactions and photo-electron transfers between mononucleotides or DNA and the stereoisomers of a HAT-bridged dinuclear RuII complex (HAT = 1,4,5,8,9,12-hexaazatriphenylene)

The dinuclear complex [{Ru(phen)2}2(μ-HAT)]4+ (phen = 1,10-phenanthroline, HAT = 1,4,5,8,9,12-hexaazatriphenylene), can exist in three different stereoisomeric forms: the meso (ΔΛ) and rac diastereoisomers, the latter of which has two enantiomeric forms, namely ΔΔ and ΛΛ. Each of the stereoisomers was studied in the presence of the mononucleotides guanosine 59-monophosphate (GMP) and adenosine 59-monophosphate (AMP), and deoxyguanosine (dG) at pH = 7 and 9. Absorption studies revealed the formation of ion pairs or aggregates between the complexes and the mononucleotides (GMP and AMP) and dG. The equilibrium constants for the formation of these species were higher for the meso form than for the ΔΔ and ΛΛ enantiomers. Laser flash photolysis indicated the existence of a stereoselective photo-induced electron-transfer between the guanine of GMP and the stereoisomers. Luminescence data with the purine mononucleotides also indicated the existence of an equilibrium between the free excited complex and a luminescent ion pair or an emitting aggregate between the complex and the mononucleotide. The luminescence of these species depended on the pH and on the identity of the stereoisomer. The investigated spectroscopic behaviour of the complex stereoisomers in the presence of denatured CT-DNA was also isomer-dependent, in agreement with the conclusions drawn from the data with the mononucleotides. The results of this work clearly indicate stereoselectivity of the interaction with the purine mononucleotides and denatured CT-DNA in the ground and excited state of the complex, in favour of the meso form in both cases.

STM imaging of a heptanuclear ruthenium(II) dendrimer, mono-add layer on graphite

Scanning tunneling microscopy (STM) and molecular mechanics calculations were used to investigate the long-range packing and the structure of an heptanuclear ruthenium (II) dendritic species, as a PF6- salt. STM imaging was carried out on a mono-add layer of the ruthenium dendrimer formed by physisorption from a 1,2,4-trichlorobenzene solution at the liquid-graphite interface. The packing of the molecules on the surface was visualised by the formation of ordered patterns and a distance of 27 +/- 2 A was measured between two adjacent lamellae. The comparison of this dimension with the molecular-modelling data indicates that the lamellae were formed by rows of dendrimer molecules in which the counterions (PF6-) were strongly associated with the Ru atoms. The images acquired with higher spatial resolution revealed the presence of repeating units within the lamellae. The comparison of the STM images with the modelling results allowed the attribution of the repeating units observed in the imaged pattern to the STM signature of single dendrimer molecules.

Comparison of the NMR Enantiodifferentiation of a Chiral Ruthenium(II) Complex of C2 Symmetry Using the TRISPHAT Anion and a Lanthanide Shift Reagent

The tris[tetrachlorobenzenediolato]phosphate(V) anion (TRISPHAT) is known to be an efficient NMR chiral shift agent for various chiral cationic species. Here we compare the efficiency of TRISPHAT and of a chiral lanthanide shift reagent for the determination of the enantiomeric purity of the chiral building block [Ru(phen)2py2]2+ which possesses C2 symmetry. We also discuss our results in terms of the geometry of interaction between the Ru(II) complex and the TRISPHAT anion.

A Ru(II)-TAP complex, photoreagent for tryptophan-containing peptides: structure of the covalent photoadduct.

We report the first structure determination of a covalent photoadduct between a Ru(II)-tap complex and a tryptophan-containing peptide (AlaTrpAla) by mass spectrometry and NMR spectroscopy. Ru(II)-tap complexes could thus be exploited as photodamaging agents of Trp-containing polypeptides or proteins.

Revisited photophysics and photochemistry of a Ru-TAP complex using chloride ions and a calix[6]crypturea

The effects of the nonprotonated and protonated calix[6]crypturea 1/1(•)H(+) on the PF6(-) and Cl(-) salts of a luminescent Ru-TAP complex (TAP = 1,4,5,8-tetraazaphenanthrene) were investigated. Thus, the phototriggered basic properties of this complex were examined with 1(•)H(+) in acetonitrile (MeCN) and butyronitrile (BuCN). The Ru excited complex was shown to be able to extract a proton from the protonated calixarene, accompanied by a luminescence quenching in both solvents. However, in BuCN, the Cl(-) salt of the complex exhibited a surprising behavior in the presence of 1/1(•)H(+). Although an emission decrease was observed with the protonated calixarene, an emission increase was evidenced in the presence of nonprotonated 1. As the Cl(-) ions were shown to inhibit the luminescence of the complex in BuCN, this luminescence increase by nonprotonated 1 was attributed to the protection effect of 1 by encapsulation of the Cl(-) anions into the tris-urea binding site. The study of the luminescence lifetimes of the Ru-TAP complex in BuCN as a function of temperature for the PF6(-) and Cl(-) salts in the absence and presence of 1 led to the following conclusions. In BuCN, in contrast to MeCN, in addition to ion pairing, because of the poor solvation of the ions, the luminescent metal-to-ligand charge transfer ((3)MLCT) state could reach two metal-centered ((3)MC) states, one of which is in equilibrium with the (3)MLCT state during the emission lifetime. The reaction of Cl(-) with this latter (3)MC state would be responsible for the luminescence quenching, in agreement with the formation of photosubstitution products.

Synthesis and Electrochemical and Photophysical Properties of Calixarene-Based Ruthenium(II) Complexes as Potential Multivalent Photoreagents

The grafting of photoreactive and photooxidizing Ru(II)(TAP) (TAP = 1,4,5,8-tetraazaphenanthrene) complexes on calix[4 or 6]arene molecular platforms is reported. Thus, either [Ru(TAP)2(phen)](2+) (phen = 1,10-phenanthroline) or [Ru(TAP)2(pytz)](2+) [pytz = 2-(1,2,3-triazol-4-yl)pyridine] complexes are anchored to the calixarenes. The data in electrochemistry, combined with those in emission under steady state and pulsed illumination and the determination of the associated photophysical rate constants, indicate the presence of intramolecular luminescence quenching by the phenol moieties of calixarene. From transient absorption studies under pulsed laser irradiation, it is concluded that the quenching originates from a par proton-coupled electron transfer (PCET) process. Such an intramolecular quenching is absent when the phenol groups of the calixarene platform are derivatized by azido arms.

Probing the interaction between DNA and cell transfection polymers with luminescent RuIIcomplexes

The luminescence properties of RuII complexes [Ru(TAP)2(phen)]Cl2 (1), [Ru(TAP)2(TPAC)]Cl2 (2) and [Ru(phen)2(TPAC)]Cl2 (3) (TAP = 1,4,5,8-tetraazaphenanthrene and TPAC = tetrapyrido-acridine) were used for probing the interactions of cell transfection (co)polymers, such as poly[2-dimethylaminoethyl-methacrylate] (PDMAEMA) and poly[2-dimethylaminoethyl-methacrylate]-b-poly[(ethylene glycol-α-methylether-ω-methacrylate] (P(DMAEMA-b-MAPEG)), with different polynucleotides (poly[(dA–dT)]2 and poly[(dG–dC)]2) and nucleic acids (calf thymus DNA and pBR322 plasmid DNA). It turned out that 1 was not a useful probe because its affinity constant for DNA was too weak. Moreover, 3 was also excluded because DNA–Ru complex aggregates complicated the interpretation of the data. 2 was the only candidate that could be used as a luminescent probe of “DNA–polymer” self-assemblies that would penetrate cell membranes. Different (co)polymer/polynucleotide ratios were tested with complex 2 by luminescence measurements. The results showed that 2 is an interesting probe, which is very sensitive to changes in the polynucleotide double helix structure that are induced by interactions with the synthetic (co)polymer. Moreover, complex 2 has a mode of action of emission that is different from that of the classically used ethidium bromide, i.e. an increase in emission when certain “polymer/DNA” ratios are reached during the titration of DNA with the polymer.

In vitro inhibition of gene transcription by novel photo-activated polyazaaromatic ruthenium(II) complexes

Under visible irradiation, [Ru(TAP)2(phen)]2+(Cl-)2, [Ru(TAP)2(POQ-Nmet)]2+(Cl-)2 and [Ru(bpy)2(phen)]2+(Cl-)2 were able to dramatically reduce the in vitro transcription of a plasmid DNA template by a bacteriophage RNA polymerase. This photoactivity is related to two different mechanisms of reactivity towards DNA exhibited by these complexes under illumination.