Design of dipicolinic acid ligands for the two-photon sensitized luminescence of europium complexes with optimized cross-sections

The multistep synthesis of an extensive series of push-pull donor-pi-conjugated dipicolinic acid ligands is described. The charge transfer character of the ligand can be tuned by changing the donor group (CH 2R, OR, SR, or NR 2) or the nature of the conjugated backbone (phenyl, phenylethynyl, naphtylethynyl, bis(phenylethynyl), or chalcone). The photophysical properties of related D 3 symmetric europium complexes (absorption and luminescence) were measured. Experiments using two-photon sensitized luminescence of a Eu (III) complex reveal large two-photon absorption (TPA) cross-section values (775 GM at 740 nm) in dichloromethane. Furthermore, some structure-property relationships can be derived from this systematic study, allowing an optimization of TPA properties of lanthanide complexes.     

A platinum supramolecular square as an effective G-quadruplex binder and telomerase inhibitor

In this contribution, we report that a self-assembled platinum molecular square [Pt(en)(4,4'-dipyridyl)]4 can act as an efficient G-quadruplex binder and telomerase inhibitor. Molecular modeling studies show that the square arrangement of the four bipyridyl ligands, the highly electropositive nature of the overall complex, as well as hydrogen bonding interactions between the ethylenediamine ligands and phosphates of the DNA backbone all contribute to the observed strong binding affinity to the G-quadruplex. Through thermal denaturation studies with duplex and quadruplex FRET probes and enzymatic assays, we demonstrate that this platinum square strongly binds to G-quadruplexes and can act as an inhibitor of telomerase. This study thus shows the potential of supramolecular self-assembly to readily generate scaffolds of unique geometries for effective targeting of G-quadruplexes and for the ultimate development of selective antitumor therapies.     

Direct access to terpyridine-containing polyazamacrocycles as photosensitizing ligands for Eu(III) luminescence in aqueous media

[reaction: see text] The synthesis of new 18-membered hexaazamacrocycles containing a functionalized 2,2':6',2' '-terpyridine moiety as part of the cyclic backbone and three acetate pendant arms is described. The reported synthetic procedure is based on the use of an efficient metal template ion effect which controls the macrocyclization step. This procedure is compatible with some functional groups present in the macrocyclic structure. The photophysical properties of the Eu(III) complexes derived from these ligands were examined in aqueous solutions. Their luminescence lifetimes (tau approximately 1 ms) and quantum yields (13% < Phi < 18%) on one hand, their high kinetic inertness on the other hand, and the presence of additional functionality allowing their covalent conjugation to biomolecules seriously nominate these complexes as very promising candidates for luminescent labeling of biological materials.     

Quantification of the adsorption of methyl viologen on pyrex glass using a renewable perfluorosulfonated ionomer carbon paste electrode

Square wave voltammograms of methyl viologen (MV²⁺) were recorded at a renewable Nafion-loaded carbon paste electrode immersed in 20 mL of phosphate buffer solution (pH 7.4) contained in a beaker-type electrochemical cell (Pyrex glass; contact area = 33 cm²). From the calibration plot obtained in the concentration range 0.01–2.4 μM, it could be concluded that the maximum surface excess of MV²⁺ adsorbed on Pyrex glass (0.24 nmol cm⁻²) was reached at concentrations above 1.4 μM. The adsorption isotherm presented a sigmoidal shape characteristic of attractive interaction. From this plot, it was evaluated that the maximum depletion of MV²⁺ in solution (28%) did not occur at the lowest concentrations, but in nearly micromolar solutions. This result emphasizes the unavoidable and random errors which are involved when MV²⁺ solutions are purposely diluted in Pyrex glassware. The MV²⁺ adsorption proceeds to a less extent on Duran borosilicate glass and/or in acid or alkaline medium.     

Impact of the structure of phospholipid dispersions on the stability of fluorocarbon/phospholipid emulsions for biomedical uses

The preparation of injectable fluorocarbon emulsions includes the dispersion of the phospholipids in the aqueous phase, then the admixing of the fluorocarbon to produce a crude premix; emulsification is then achieved using a high pressure mechanical procedure, followed by final heat-sterilization. In this work we report that, depending on the procedure used and energy applied, the dispersions of phospholipids consist of poorly organized unclosed “pre-liposomes”, multilamellar vesicles (MLV), or small unilamellar vesicles (SUV). This has a significant impact on the stability of the final fluorocarbon emulsions (90% (w/v) concentration), those prepared from “pre-liposomes” being more stable than those prepared from MLV or SUV. The first emulsion is shown to contain less fluorocarbon-free phospholipid vesicles than the other two. These free vesicles have previously been reported to have a detrimental effect on the stability of concentrated fluorocarbon emulsions.     

Analysis of Scutellaria lateriflora and its adulterants Teucrium canadense and Teucrium chamaedrys by LC-UV/MS,TLC, and digital photomicroscopy

Methods using liquid chromatography with UV detection (LC-UV), thin-layer chromatography (TLC), and digital photomicroscopy were developed to distinguish between the different species of Scutellaria lateriflora L. and its adulterants Teucrium canadense L. and T. chamaedrys L. Chemically, the 70% ethanol extract of S. lateriflora is characterized by the presence of flavonoids--predominantly baicalin, lateriflorin, dihydrobaicalin, and baicalein. The major compounds of the 70% ethanol extract of T. canadense are phenylpropanoids, with verbascoside as the most prominent, and a variable amount of teucrioside. Teucrioside is the major compound in T. chamaedrys, but it is not present in S. lateriflora. The presence of phenylpropane glycosides can therefore be used to distinguish between the S. lateriflora L. and the two Teucrium species by LC-UV and TLC. The abundant strap-shaped trichomes on the stem, as well as bristle-like trichomes on the leaf, are typically seen microscopically for T. canadense, whereas the waxy cuticle with numerous glandular scales is found in T. chamaedrys. These cell structures were used to determine the adulteration of S. lateriflora crude herb with either of the two Teucrium species.     

Addition of Carbon Nucleophiles to Tricarbonylchromium Complexes of 1,2-Dihydrocyclobutabenzene,Indane, 1,2,3,4-Tetrahydronaphtbalene and ortho-Xylene

3-Substituted 1,2-dihydrocyclobutabenzenes (bicyclo[4. 2. 0]octa-1,3,5-triene) are readily accessible from [Cr(CO)₃(1,2-dihydrocyclobutabenzene)] ( 1 ) via a two-step sequence which involves addition of a nucleophile and oxidation of the intermediate anionic cyclohexadienyl complex. Nucleophiles used include LiCMe₂CN (A), LiCH₂CN (B), LiC(Me)(OR)CN (C), (D), (E), LiCMe₂CO₂Me (F), and LiCH₂CO₂(t-Bu) (G). [Cr(CO)₃(Indane)] ( 2 ) also reacts highly regioselectively to give α-substitution, whereas [Cr(CO)₃(tetrahydronaphthalene)] ( 3 ) and [Cr(CO)₃(o-xylene)] ( 4 ) give mixtures of products. In several cases, the mixtures of the intermediate anionic cyclohexadienyl complexes can be equilibrated to give, after oxidation, β-substituted derivatives of 1,2,3,4-tetrahydronaphthalene and ortho-xylene selectively. EHMO calculations were carried out, and they rationalize the observed α-regioselectivity of nucleophilic addition under kinetic control, The X-ray structures of 1 and 4 are reported and in both compounds the Cr(CO)₃ group adopts in the solid state a staggered syn-conformation with respect to the substituted aromatic C-atonis.     

Fe(II)-induced reduction of labelled endoperoxides. NMR degradation studies on G3 factor and its methyl ether

The behavior of G3 factor and of its methylated or fluorinated analogues G3Me and G3F, was studied under Fe(II) conditions. Degradation products were isolated and characterized in each case. The use of labelled compounds allowed us to propose mechanisms in which a tertiary radical is involved. This radical rearranges by 5-exo-trig cyclization, or disproportionates in the case of G3Me. A correlation between antiplasmodial activity and stability of this radical is proposed.     

Ring opening of the cyclobutane in a thymine dimer radical anion

The reactions of hydrated electrons (e(aq) (-)) with thymine dimer 2 and thymidine have been investigated by radiolytic methods coupled with product studies, and addressed computationally by means of BB1K-HMDFT calculations. Pulse radiolysis revealed that one-electron reduction of the thymine dimer 2 affords the radical anion of thymidine (5) with t(1/2)<35 ns. Indeed, the theoretical study suggests that radical anion 3, in which the spin density and charge distribution are located in both thymine rings, undergoes a fast partially ionic splitting of the cyclobutane with a half-life of a few ps. This model fits with the in vivo observation of thymine dimer repair in DNA by photolyase. gamma-Radiolysis of thymine dimer 2 demonstrates that the one-electron reduction and the subsequent cleavage of the cyclobutane ring does not proceed by means of a radical chain mechanism, that is, in this model reaction the T(-)* is unable to transfer an electron to the thymine dimer 2.