Crosslinking photosensitized by a ruthenium chelate as a tool for labeling and topographical studies of G-protein-coupled receptors

The purpose was to apply oxidative crosslinking reactions to the study of recognition and signaling mechanisms associated to G-protein-coupled receptors. Using a ruthenium chelate, Ru(bipy)(3)(2+), as photosensitizer and visible light irradiation, in the presence of ammonium persulfate, we performed fast and efficient covalent labeling of the B(2) bradykinin receptor by agonist or antagonist ligands possessing a radio-iodinated phenol moiety. The chemical and topographical specificities of these crosslinking experiments were investigated. The strategy could also be applied to the covalent labeling of the B(1) bradykinin receptor, the AT(1) angiotensin II receptor, the V(1a) vasopressin receptor and the oxytocin receptor. Interestingly, we demonstrated the possibility to covalently label the AT(1) and B(2) receptors with functionalized ligands. The potential applications of metal-chelate chemistry to receptor structural and signaling studies through intramolecular or intermolecular crosslinking are presented.     

Theoretical analysis of the influence of the adosorption process on the voltammetric curves in the case of a second order adsorption step followed by a first order charge transfer reaction: Part II. Comparison between linear potential sweep voltammetry and steady state cyclic voltammetry

The voltammetric curves for a 2-step sequential reaction involving a 2nd order adsorption process (such as the catalytic mechanism met in the anodic oxidation of hydrogen) are investigated theoretically by computer calculations. Steady state cyclic voltammetry (s.s.c.v.) is particularly treated by repeating forward and backward sweeps as many times as necessary to reach the steady state. For both l.p.s.v. and s.s.c.v., the usual characteristic features are considered, i.e. E_M, θ_M, i_M as a function of sweep rate υ, especially in the range of υ, where the computed data fit the results derived from analytical solution (quasi-reversible charge transfer, and irreversible charge transfer). In s.s.c.v., indications are given to obtain the kinetic parameters (k₁, k₂, α) from experimental plots.     

Enhanced emission efficiency and excited state lifetime due to restricted intramolecular motion in silole aggregates

The aggregation-induced emission (AIE) properties of 1,1,2,3,4,5-hexaphenylsilole (HPS) and poly{11-[(1,2,3,4,5-pentaphenylsilolyl)oxy]-1-phenyl-1-undecyne} (PS9PA) were studied by time-resolved fluorescence technique. The enhanced fluorescence and long fluorescent lifetime were obtained for the sample in an aggregate state as compared to the sample in solution. The time-decay of fluorescence of HPS and PS9PA in high viscosity solvents and low-temperature glasses has also been measured in detail to further investigate the possible mechanism for AIE. Enhanced light emission and long fluorescence lifetime were detected for both HPS and PS9PA in the solution-thickening and -cooling experiments. These results provided direct evidence that the enhanced photoluminescence (PL) efficiency is due to restricted intramolecular motion, which ascribes AIE to the deactivation of nonradiative decay caused by restricted torsional motions of the molecules in the solid state or aggregate form.     

Steric Effects on Reaction Rates. Part VIII. The Significance of Front Strain Release in Solvolysis of Bridgehead Derivatives

The steric requirements of leaving groups for 14 bridgehead derivatives have been examined using MM2 calculations. The strain varies almost monotonously throughout the series upon variation of the leaving group from H to C1, OH, CH₃, CH₃CH₂O, (CH₃)₃CO, (CH₃)₃C and no significant trends for differential F-strain effects are detected expect for the perhydrophenalene derivative 13 . The experimental rates of solvolysis of bridgehead derivatives correlate well with the calculated steric energy differences between substrate R-X and the corresponding carbenium ion R⊕. However, the strain calculations using the more recent force-fields ( MM2 ) disagree, in part, with those reported in the literature: chloride and p-toluenesulfonate leaving groups correlate with identical slopes, and the perhydrotriquinacene derivative 10 shows no anomalous behavior. The calculations suggest that F-strain and C,C-hyperconjugation should not play any dominant role in bridgehead solvolysis.     

Designing Efficient and Ultralong Pure Organic Room‐Temperature Phosphorescent Materials by Structural Isomerism

Pure organic materials with ultralong room‐temperature phosphorescence (RTP) are attractive alternatives to inorganic phosphors. However, they generally show inefficient intersystem crossing (ISC) owing to weak spin–orbit coupling (SOC). A design principle based on the realization of small energy gap between the lowest singlet and triplet states (ΔE_ST) and pure ππ* configuration of the lowest triplet state (T₁) via structural isomerism was used to obtain efficient and ultralong RTP materials. The meta isomer of carbazole‐substituted methyl benzoate exhibits an ultralong lifetime of 795.0 ms with a quantum yield of 2.1 %. Study of the structure–property relationship shows that the varied steric and conjugation effects imposed by ester substituent at different positions are responsible for the small ΔE_ST and pure ππ* configuration of T₁.     

A λ-Lemma for Partially Hyperbolic Tori and the Obstruction Property

Using a scheme given by Marco, we prove that partially hyperbolic tori along resonant surfaces of near-integrable Hamiltonian systems possess the obstruction property in Arnold's terminology. The proof is based on a specific lambda lemma for these tori.     

Absorption and fluorescence properties of acridinones,thioacridinones, aminoacridines and related crown ethers

We report a study on the absorptive and emissive properties of 9‐acridinones, 9‐thioacridinones and 9‐aminoacridines including six crown ether derivatives. The effect of solvents and of the addition of cations (Na⁺, K⁺, Ca2⁺ and Mg2⁺) on these properties has been studied. The absorption of the crown ether derivative of 9‐thioacridinone is sensitive to solvents while the fluorescence of crown ethers derived from 9‐aminoacridines shows some specificity towards cations. Empirical modeling was used to discuss the emission characteristics of these compounds.     

Spontaneous and Fast Molecular Motion at Room Temperature in the Solid State

The development of molecular machines requires new building blocks which are easy to characterize and visualize to realize a complexity comparable to their natural counterparts such as biological enzymes. Furthermore, with the desire to build functional nanobots capable of navigating living organisms, it is necessary that the building blocks show mobility even in the solid state. Herein we report a system which is emissive in the amorphous state but is non‐fluorescent in the crystalline state due to the formation of extensive π‐π interactions. This dual nature could be exploited for easy visualization of its solid‐state molecular rearrangement. The emission of the amorphous film was quenched as the molecules spontaneously formed π‐π interactions even in the solid state. Scratching the non‐emissive film destroyed the interactions and restored the emission of the film. The emission quickly disappeared with an average lifetime of 20 s as the compound reformed the π‐network even at room temperature.