Acide dipicolinique | EPFL Graph Search

L'acide dipicolinique ou acide pyridine-2,6-dicarboxylique est un composé organique qui consiste en un noyau pyridine substitué en 2,6 (de part et d'autre de l'atome d'azote) par deux groupes acide carboxylique. C'est donc un acide dicarboxylique. Son nom dérive de l'acide picolinique (acide pyridine-2-carboxylique). L'acide dipicolinique compose de 5 % à 15 % du poids sec de spores bactériennes. Il est responsable en partie de la résistance à la chaleur des endospores. Synthèse L'acide dipicolinique apparaît pendant la sporulation (formation de spores) de micro-organismes. Il ne se produit que dans le noyau des endospores et pas dans les cellules végétatives. Une autre synthèse peut être effectuée par exemple par l'oxydation des groupes méthyle de la 2,6-lutidine. Propriétés et usages Lorsque l'acide dipicolinique est chauffé, il se décompose au-dessus de par décarboxylation en acide picolinique : : Biochimie L'acide dipicolinique

From Luminescent Lanthanide Complexes to Color Reproduction and Optical Document Security with Invisible Luminescent Inks

Julien Alexandre Andres

The present thesis deals with luminescent compounds based on lanthanide complexes that are suitable for color reproduction and optical document security with invisible luminescent inks. This thesis is divided in two distinct fields: chemistry, which produces luminescent lanthanide complexes, and color science, which was required to characterize luminescent colors and use them for color reproduction and optical document security. Concerning luminescent lanthanide complexes, the investigation is focused on the derivatization of dipicolinic acid. A modification of the carboxylate coordinating moiety of the ligand is first undertaken in order to synthesize phosphorylated ligands, which often show interesting variations of the properties of the complexes among related structures. On another hand, a derivatization of the ligand by grafting a polyoxyethylene side chain with a terminal chromophore at the para position on the pyridine core of dipicolinic acid is carried out. The ability of this chromophore to act as a sensitizer for the distant lanthanide ion coordinated on the dipicolinate moiety is investigated. A series of coumarin fluorophores are tested as sensitizers and the best coumarin is then used to further examine the mechanisms of the sensitization of the lanthanide ion, for example by shortening the polyoxyethylene pendent and thus modifying the distance between the sensitizer and the lanthanide ion. The parent europium and terbium dipicolinate complexes are then used as red emitting and green emitting luminescent dyes in invisible luminescent inks together with a blue luminescent ink. An ink spreading enhanced spectral Neugebauer prediction model is used to predict the spectral radiant emittance of any combination of the luminescent inks. The good prediction accuracy of the model is then related to the photophysical properties of the luminescent inks, which are shown to be unquenched by superposition with the other inks. This trichromic system is finally used to reproduce luminescent color halftone images visible under UV light by relying on a gamut mapping algorithm and on the spectral prediction model. In a final part, a new spectral prediction model for transmittances and reflectances is developed. It is then used for building a backlighting model where the backlight source is a luminescent emission under UV light from printed luminescent inks, and where the backlit colors are obtained by the transmission of the backlight source through color halftones printed with classical cyan, magenta and yellow inks on the other side of the same substrate. Luminescent backlit color images can then be created, which produces a new security feature for optical document security combining recto classical images under normal light, with verso luminescent images and recto luminescent backlit images under UV excitation.

EPFL2012

6-Phosphoryl Picolinic Acids as Europium and Terbium Sensitizers

Julien Alexandre Andres, Anne-Sophie Chauvin

Three 6-phosphoryl picolinic acid (6PPA) derivatives were synthesized and used as europium and terbium sensitizers. Two of the three ligands (6-diethoxyphosphoryl picolinic acid (Hdeppa) and 6-monoethoxyphosphoryl picofinic acid (H(2)meppa)) are water-soluble, once complexed to lanthanide ions, while the third (6-dihydroxyphosphoryl picolinic acid (H(3)dhppa)) forms a precipitate. The stability constants of the phosphoryl-based complexes were found to be higher than the carboxylate analogue (dipicolinic acid, H(2)dpa). The main species are the [LnL(3)] complexes under strict stoichiometric conditions, confirmed by P-31 NMR spectroscopy, mass spectrometry and lifetime analyses. The photophysical measurements reveal that the emission intensity of [Eu(deppa)(3)] is maximal at pH 4.8, whereas for Eu(meppa)(3), the optimum pH is observed at 9.0. The lifetimes are all in the millisecond range and have confirmed the absence of water molecules in the first coordination sphere. The emissions of the terbium are always brighter than the corresponding europium within this phosphoryl series. The quantum yields of the phosphoryl containing complexes are lower than the carboxylate analogue (Ln(dpa)(3)), except for [Tb(deppa)(3)], which exhibits an interesting quantum yield of 40% in aqueous solution.

2011

Energy transfer in coumarin-sensitised lanthanide luminescence: investigation of the nature of the sensitiser and its distance to the lanthanide ion

Julien Alexandre Andres, Anne-Sophie Chauvin

A series of lanthanide complexes Ln(dpxCy)(3) have been synthesised. The ligands are composed of a coordinating dipicolinic acid backbone decorated with a polyoxyethylene arm fitted with a coumarin moiety at its extremity. The nature of the coumarin as well as the length of the linker have been varied. Upon excitation at 320 nm, the coumarin exclusively acts as an antenna while the dipicolinic acid core is not excited. Upon excitation below 300 nm, both parts are excited. With europium as a metal centre, the relaxation of the europium ion (intrinsic quantum yield Phi(Eu)(Eu) and radiative lifetime tau(r)) is constant for all the studied ligands. Therefore, the observed differences in overall quantum yield (Phi(Eu)(L)) in such systems come exclusively from the variation of the terminal coumarin. The overall quantum yields of the studied complexes are low (Phi(Eu)(L) < 2% in aqueous solution). In order to rationalise the mechanism of the energy transfer and to improve the sensitisation efficiency (eta(sens)), the distance between the coumarin sensitiser and the lanthanide centre was explored in solution and compared to the solid state. In the solid state, a dramatic effect was confirmed, with an improvement of 80% in the quantum yield Phi(Eu)(L) for short linkers ((-CH2CH2O-)(n) with n = 1 compared to n = 3). By monitoring the lifetime decay of the excited state of the lanthanide cation with nanosecond vs. microsecond time-resolved spectroscopy at low temperature, the sensitisation of the lanthanide ions by coumarin derivatives was demonstrated to mainly occur through the singlet excited state of the coumarin and not via the usual triplet pathway. No evidence of a different behaviour at room temperature was found by transient triplet-triplet absorption spectroscopy.

Royal Society of Chemistry2013

From Luminescent Lanthanide Complexes to Color Reproduction and Optical Document Security with Invisible Luminescent Inks

Julien Alexandre Andres

EPFL2012

Energy transfer in coumarin-sensitised lanthanide luminescence: investigation of the nature of the sensitiser and its distance to the lanthanide ion

Julien Alexandre Andres, Anne-Sophie Chauvin

Royal Society of Chemistry2013