Luminescent ruthenium(II) bipyridine-calix[4]arene complexes as receptors for lanthanide cations

The synthesis and photophysical properties of novel luminescent ruthenium(II) bipyridyl complexes containing one, two, or six lower rim acid-amide-modified calix[4]arene moieties covalently linked to the bipyridine groups are reported which are designed to coordinate and sense luminescent lanthanide ions. All the Ru-calixarene complexes synthesized in this work are able to coordinate Nd(3+), Eu(3+), and Tb(3+) ions with formation of adducts of variable stoichiometry. The absorbance changes allow the evaluation of association constants whose magnitudes depend on the nature of the complexes as well as on the nature of the lanthanide cation. Lanthanide cation complex formation affects the ruthenium luminescence which is strongly quenched by Nd(3+) ion, moderately quenched by the Eu(3+) ion, and poorly or moderately increased by the Tb(3+) ion. In the case of Nd(3+), the excitation spectra show that (i) the quenching of the Ru luminescence occurs via energy transfer and (ii) the electronic energy of the excited calixarene is not transferred to the Ru(bpy)(3) but to the neodymium cation. In the case of Tb(3+), the adduct's formation leads to an increase of the emission intensities and lifetimes. The reason for this behavior was ascribed to the electric field created around the Ru calix[4]arene complexes by the Tb(3+) ions by comparison with the Gd(3+) ion, which behaves identically and can affect ruthenium luminescence only by its charge. However, especially for compounds 1 and 3, it cannot be excluded that some contribution comes from the decrease of vibrational motions (and nonradiative processes) due to the rigidification of the structure upon Tb(3+) complexation. In the case of Eu(3+), compounds 1, 2, and 4 were quenched by the lanthanide addition but the quenching of the ruthenium luminescence is not accompanied by europium-sensitized emission which suggests that an electron-transfer mechanism is responsible for the quenching. On the contrary, compound 3 exhibits enhanced emission upon addition of Eu(3+) (as nitrate salt); it is suggested that the lack of quenching in the [3.2Eu(3+)] adduct is due to kinetic reasons because the electron-transfer quenching process is thermodynamically allowed.     

Inhibition of Emulsin by D-Gluconhydroximo-1,5-lactone and Related Compounds

At pH 4.5 (citrate buffer), D -gluconhydroximo-lactone ( 2 ), the N-methylurethane 3 and the N-phenylurethane 4 inhibit competitively the hydrolysis of p-nitrophenyl β-D -glucopyranoside by emulsin. The IC₅₀ values of 2, 3 , and 4 were 1.6 × 10^?4, 1.0 × 10^?4, and 5.8 × 10^?6 M , respectively. The K_i values of 2 and 4 were 9.8 × 10^?5 and 2.3 × 10^?6 M , respectively, while D-glucono-1,5-lactone ( 1 ) showed IC₅₀ = 1.1 × 10^?4 M and K_i = 3.7 × 10^?5 M .     

NON-NUCLEAR DAMAGE AND CELL LYSIS ARE INDUCED BY UVA, BUT NOT UVB OR UVC, RADIATION IN THREE STRAINS OF L5178Y CELLS

The potential to induce non-nuclear changes in mammalian cells has been examined for (1) UVA1 radiation (340–400 nm, UVASUN 2000 lamp), (2) UVA + UVB (peak at 313 nm) radiation (FS20 lamp), and (3) UVC (254 nm) radiation (GI5T8 lamp). The effects of irradiation were monitored in vitro using three strains of L5178Y (LY) mouse lymphoma cells that markedly differ in sensitivity to UV radiation. Comparisons were made for the effects of approximately equitoxic fluences that reduced cell survival to 1–15%. Depending on the cell strain, the fluences ranged from 830 to 1600 kJ/m² for the UVASUN lamp, 75 to 390 J/m² for the FS20 lamp and 3.8 to 17.2 J/m² for the G15T8 lamp. At the exposure level used in this study, irradiation with the UVASUN, but not the FS20 or G15T8, lamp induced a variety of non-nuclear changes including damage to cytoplasmic organelles and increased plasma membrane permeability and cell lysis. Cell lysis and membrane permeabilization were induced by the UVA1 emission of the UVASUN lamp, but not by its visible + IR components (>400 nm). The results show that the plasma membrane and other organelles of LY cells are highly sensitive to UVA1 but not to UVB or UVC radiation. Also UVA1, but not UVB or UVC radiation, causes rapid and extensive lysis of LY cells. In conclusion, non-nuclear damage contributes substantially to UVA cytotoxicity in all three strains of LY cells.     

Halogen-Bonding Strapped Porphyrin BODIPY Rotaxanes for Dual Optical and Electrochemical Anion Sensing

Anion receptors employing two distinct sensory mechanisms are rare. Herein, we report the first examples of halogen-bonding porphyrin BODIPY [2]rotaxanes capable of both fluorescent and redox electrochemical sensing of anions. ¹H NMR, UV/visible and electrochemical studies revealed rotaxane axle triazole group coordination to the zinc(II) metalloporphyrin-containing macrocycle component, serves to preorganise the rotaxane binding cavity and dramatically enhances anion binding affinities. Mechanically bonded, integrated-axle BODIPY and macrocycle strapped metalloporphyrin motifs enable the anion recognition event to be sensed by the significant quenching of the BODIPY fluorophore and cathodic perturbations of the metalloporphyrin P/P^+. redox couple.     

Advances in Anion Supramolecular Chemistry: From Recognition to Chemical Applications

Since the start of this millennium, remarkable progress in the binding and sensing of anions has been taking place, driven in part by discoveries in the use of hydrogen bonding, as well as the previously under‐exploited anion–π interactions and halogen bonding. However, anion supramolecular chemistry has developed substantially beyond anion recognition, and now encompasses a diverse range of disciplines. Dramatic advance has been made in the anion‐templated synthesis of macrocycles and interlocked molecular architectures, while the study of transmembrane anion transporters has flourished from almost nothing into a rapidly maturing field of research. The supramolecular chemistry of anions has also found real practical use in a variety of applications such as catalysis, ion extraction, and the use of anions as stimuli for responsive chemical systems.     

Halotriazolium Axle Functionalised [2]Rotaxanes for Anion Recognition: Investigating the Effects of Halogen‐Bond Donor and Preorganisation

The anion‐templated synthesis of three novel halogen‐bonding 5‐halo‐1,2,3‐triazolium axle containing [2]rotaxanes is described, and the effects of altering the nature of the halogen‐bond donor atom together with the degree of inter‐component preorganisation on the anion‐recognition properties of the interlocked host investigated. The ability of the bromotriazolium motif to direct the halide‐anion‐templated assembly of interpenetrated [2]pseudorotaxanes was studied initially; bromide was found to be the most effective template. As a consequence, bromide anion templation was used to synthesise the first bromotriazolium axle containing [2]rotaxane, the anion‐binding properties of which, determined by ¹H NMR spectroscopic titration experiments, revealed enhanced bromide and iodide recognition relative to a hydrogen‐bonding protic triazolium rotaxane analogue. Two halogen‐bonding [2]rotaxanes with bromo‐ and iodotriazolium motifs integrated into shortened axles designed to increase inter‐component preorganisation were also synthesised. Anion ¹H NMR spectroscopic titration experiments demonstrated that these rotaxanes were able to bind halide anions even more strongly, with the iodotriazolium axle integrated rotaxane capable of recognising halides in aqueous solvent media. Importantly, these observations suggest that a halogen‐bonding interlocked host binding domain, in combination with increased inter‐component preorganisation, are requisite design features for a potent anion receptor.     

Detection of myocardial viability by low-dose dobutamine Cine MR imaging

The purpose of this work was to test the diagnostic value of dobutamine stress magnetic resonance imaging (MRI) for predicting recovery of regional myocardial contractility after revascularization. Cardiac wall motion abnormalities are due to either non-viable and/or scarred, or viable, but hibernating, myocardial tissue. Dobutamine stress leads to increased systolic wall thickening only in viable myocardium. Twenty-five patients with akinetic or dyskinetic myocardial regions were examined with a Cine FLASH-2D sequence at rest and during dobutamine stress (10 μg/kg/min). Patients were re-examined at rest 3, and in case of persisting wall motion defects, 6 months after revascularization. Criterion of viability was increasing end-systolic wall thickening during stress and/or at follow-up. Akinetic regions related either to the LAD (n = 19) or to the RCA (n = 6) were judged viable if >=50% of the affected segments improved. MR studies were completed in all subjects without arrhythmia or need for early terminations due to symptoms. Sensitivity, specificity, and positive predictive value for the prediction of myocardial viability were 61%, 90%, and 87% for the segment-related analysis, and 76%, 100%, and 100% for the patient-related analysis based on coronary artery distribution, respectively. Dobutamine stress MRI allows to predict global functional recovery of akinetic myocardial regions after revascularization with a high positive predictive value and high specificity.