Philippe Giamarchi

A novel cationic lipophosphoramide with diunsaturated lipid chains: synthesis, physicochemical properties, and transfection activities.

Cationic lipophosphoramidates constitute a class of cationic lipids we have previously reported to be efficient for gene transfection. Here, we synthesized and studied a novel lipophosphoramidate derivative characterized by an arsonium headgroup linked, via a phosphoramidate linker, to an unconventional lipidic moiety consisting of two diunsaturated linoleic chains. Physicochemical studies allowed us to comparatively evaluate the specific fluidity and fusogenicity properties of the liposomes formed. Although corresponding lipoplexes exhibited significant but relatively modest in vitro transfection efficiencies, they showed a remarkably efficient and reproducible ability to transfect mouse lung, with in vivo transfection levels higher than those observed with a monounsaturated analogue previously described. Thus, these results demonstrate that this diunsaturated cationic lipophosphoramidate constitutes an efficient and versatile nonviral vector for gene transfection. They also invite further evaluations of the transfection activity, especially in vivo, of gene delivery systems incorporating the lipid reported herein and/or other lipids bearing polyunsaturated chains.

Determination of iron in seawater by electrothermal atomic absorption spectrometry and atomic fluorescence spectrometry: A comparative study

Two methods available for direct determination of total Fe in seawater at low concentration level have been examined: electrothermal atomization atomic absorption spectrometry (ETAAS) and electrothermal atomization laser excited atomic fluorescence spectrometry (ETA-LEAFS). In a first part, we have optimized experimental conditions of ETAAS (electrothermal program, matrix chemical modification) for the determination of Fe in seawater by minimizing the chemical interference effects and the magnitude of the simultaneous background absorption signal. By using the best experimental conditions, a detection limit of 80 ng L(-1) (20 microL, 3sigma) for total Fe concentration was obtained by ETAAS. Using similar experimental conditions (electrothermal program, chemical modification), we have optimized experimental conditions for the determination of Fe by LEAFS. The selected experimental conditions for ETA-LEAFS: excitation wavelength (296.69 nm), noise attenuation and adequate background correction led to a detection limit (3sigma) of 3 ng L(-1) (i.e. 54 pM) for total Fe concentration with the use a 20 microL seawater sample. For the two methods, concentration values obtained for the analysis of Fe in a NASS-5 (0.2 microg L(-1)) seawater sample were in good agreement with the certified values.

Improvements in the determination of nanomolar concentrations of aluminium in seawater by electrothermal atomic absorption spectrometry

Abstract The optimization in two steps of seven adjustable parameters through experimental designs associated to an optimal and individualized processing of atomization data allowed to reach a detection limit of 30 ng l −1 for the quantification of Al in seawater. This detection limit is approximately eightfold lower than that reported previously. Moreover, near the detection limit, the presence of systematic errors, i.e. mathematical miscorrection and weak spectral interferences, which are usually neglected, must be corrected either by using a suitable blank or by estimating such errors. A procedure of highlighting and estimating the mathematical miscorrection and significant Mg and Ca atomic interferences for Al determination at 309.271 nm using a commercial Zeeman apparatus in absence of an Al-free blank is described. Moreover, how to obtain a convenient Al-free blank of seawater is also shown.

Polyethylene glycol aggregates in water formed through hydrophobic helical structures

The present study was aimed at elucidating the mechanism of aggregation in water of hydroxyl-terminated polyethylene glycol (PEG) of low molecular weight (600 g/mol). The results from fluorescence spectroscopy at different temperatures were consistent with surface tension measurements, suggesting aggregate formation. Indeed, the process of aggregation is accompanied by an increase in the fluorescence emission of a hydrophobic probe. So, PEG aggregates in the form of internal hydrated helices covered with CH(2) groups are shown to yield hydrophobic regions. These regions created upon PEG aggregation in water and at a temperature close to 35°C result from a balance between H bonding and entropic effects. By providing the first experimental evidence for hydrophobic mediation of aggregation with OH-terminated oxy-ethylene chains of low molecular weight, this study highlights their surfactant-like behaviour.

Molecular and atomic ultra trace analysis by laser induced fluorescence with OPO system and ICCD camera.

This paper presents a synthesis of some analytical potentialities of an equipment designed for both laser induced molecular and atomic fluorescence in the field of ultra-trace analysis (ng l(-1)). Excitation of fluorescence was performed with a pulsed Nd:Yag laser coupled to an optical parametric oscillator (OPO). Fluorescence spectra were recorded with a spectrograph and an intensified charge-coupled device (ICCD). The high energy and the tunability of the excitation combined with the sensitivity of the ICCD and the time-resolution provide better limit of detection (LOD) and selectivity. By molecular fluorescence, some major organic contaminants in the environment were studied, i.e. polycyclic aromatic hydrocarbons (PAHs) (benzo[a]pyrene and hydroxypyrene) and a pesticide (carbaryl). The LODs achieved by direct analysis were far below the restricted European values for tap water. Analysis was performed in water containing humic acids using time resolution to avoid the matrix fluorescence. By electro thermal atomisation-laser excited atomic fluorescence (ETA-LEAF), we detected traces of aluminium and lead in seawater. Some general considerations about the signal to noise ratio optimisation are reported. LODs reached the femtogram level.

Electrothermic factors optimization in electrothermal atomic absorption spectrometry via an optimal experimental design matrix

Abstract A new approach is proposed to optimize some instrumental electrothermic parameters, i.e. injected volume, calcination duration, calcination and atomization temperatures, gas flow, in electrothermal atomic absorption spectrometry. It is based on the monitoring of the detection limit estimation variation by using an unconventional experimental design well adapted to a particular experimental domain. This method was tested on Cd, Mn and Cu in sea water. By comparison with the default operating conditions, the limits of detection were improved in some cases and always obtained on carrying out less experiments than usual.

Direct determination of aluminum content in seawater by electrothermal atomization-laser excited atomic fluorescence

Abstract The development of an analytical method for the direct determination of ultra trace content of aluminum in seawater by electrothermal atomization-laser excited atomic fluorescence (ETA-LEAF) using a pulsed Nd:Yag laser associated with an optical parametric oscillator (OPO) and an intensified CCD (ICCD) camera is described. The good temporal reproducibility of the device and the fairly long lifetime of the selected Al radiation allowed optimization of the temporal parameters in the nanosecond range. After optimizing thermal and optical parameters, this potentiality allowed to reach a 100 fg detection limit (5 ng l−1). The method was developed within a multidisciplinary program involving chemical and physical applications, thereby demonstrating the versatility of the apparatus.

Multicomponent Determination of a Polyaromatic Hydrocarbon Mixture by Direct Fluorescence Measurements

This study deals with an analysis of a mixture of five polyaromatic hydrocarbons (PAHs) with the aim of avoiding any preliminary treatment of the sample such as extraction or concentration, which are time-consuming procedures. To reach this goal we studied a direct multicomponent determination of the PAHs in mixture by applying principal-component analysis and principal-component regression techniques, which are briefly explained in this work. After a calibration procedure we were able to analyze each PAH of the mixture by a simple and direct fluorescence measurement. Moreover, the quantitative results obtained were assessed on some test samples. The results obtained and the further developments of this study will be also discussed.

Physicochemical properties of cationic lipophosphoramidates with an arsonium head group and various lipid chains: A structure–activity approach

We studied the physicochemical properties of some cationic lipophosphoramidates used as gene vectors in an attempt to better understand the link between the nature of the hydrophobic chain and both physico-chemical properties and transfection efficiency. These compounds have an arsonium head group and various chain lengths and unsaturation numbers. The synthesis of cationic phospholipids with oleic (Guenin et al., 2000 [1]; Floch et al., 2000 [2]) or linoleic (Fraix et al., 2011 [3]; Le Gall et al., 2010 [4]) chains has already been reported by our group and their efficiency as gene carriers has been demonstrated. Four new compounds were synthesized which incorporated either C14:0, C18:0, C20:4 or C20:5 chains. The membrane fluidity was studied by fluorescence anisotropy measurements. The fusion of liposomes and lipoplexes with membrane models was studied by Förster Resonant Energy Transfer. Finally, DNA condensation was studied and the lipoplexes were tested in vitro to quantify their transfection efficiency. From the results obtained on these cationic lipophosphoramidates series, we show that aliphatic chain length and unsaturation number have an important influence on liposomes physicochemical properties and transfection efficiency. However there is no direct link between fluidity and fusion efficiency or between fluidity and DNA condensation. Nevertheless, it seems that for best transfection efficiency the compounds need to combine the properties of fluidity, fusion efficiency and DNA condensation efficiency. This was the case for the C18:1 and C18:2 compounds.

Fluorescence study of lipid-based DNA carriers properties: influence of cationic lipid chemical structure.

We report here a study on the physicochemical properties of cationic phospholipids liposomes used for lipoplex formulation and DNA transfer. The original cationic phospholipids synthesized in our laboratory are first presented with the liposome formulation process. The second part deals with the liposomes fusogenic properties studied by fluorescence resonant energy transfer (FRET). The nature of the cationic polar head and the formulation with or without a neutral colipid have a great influence on the FRET signal. The third part reports the study of the viscosity of the liposome by fluorescence anisotropy measurements. It has been observed that the vectors having a saturated lipid chain exhibit a more pronounced anisotropy than those having unsaturated lipid chains. Finally, liposomes formed by a mixture of phospholipids and DC-Chol (a rigid lipid) leads to increase the anisotropy denoting a more rigid liposome.