Receptor for anionic pyrene derivatives provides the basis for new biomembrane assays

This study describes a new receptor cyclen 1 capable of strong selective binding of pyrene-based anionic dyes under near-physiological conditions. This receptor comprises four naphthylthiourea groups tethered to a cyclen core via an ester linkage. The complexation behavior of cyclen 1 receptor is characterized by a series of (1)H NMR, microcalorimetry, UV-vis, and fluorometry experiments. The relevance of structural features of this receptor to its recognition function is assessed using control compounds that lack some of the groups found in cyclen 1. The specificity of cyclen 1 toward pyrene-based dyes is assessed through experiments using dyes with different molecular organization. The most important finding was the ability of cyclen 1 to bind efficiently to a pH-sensitive dye pyranine, a dye that is commonly used in various biomembrane assays. The high affinity of cyclen 1 to pyranine, its impermeability to the lipid bilayer membrane, fast kinetics of binding, and ability to quench the pyranine's fluorescence were used as a basis for a new membrane leakage assay. This membrane leakage assay is fully compatible with the commonly applied pH-stat transport assay, and therefore it allows for differentiation of the ion transport and nonselective leakage mechanisms within a single set of experiments. The ability of cyclen 1 to quench the fluorescence of pyranine also finds limited applicability to the detection of endovesiculation.     

Cis‐ and trans‐bis(2‐cyano­ethyl­sulfan­yl)(decane‐1,10‐diyldithio)tetra­thia­fulvalene

The isomeric title compounds, 2,7‐bis(2‐cyanoethylsulfanyl)‐3,6‐(decane‐1,10‐diyldithio)tetrathiafulvalene and 2,6‐bis­(2‐cyanoethylsulfanyl)‐3,7‐(decane‐1,10‐diyldithio)­tetra­thiafulvalene, both C₂₂H₂₈N₂S₈, comprise bis­(2‐cyano­ethyl­sulfan­yl)tetra­thia­fulvalene units tethered by a saturated deca­methyl­enedithio linker attached in either a cis or a trans manner. The tetra­thia­fulvalene (TTF) group is planar in the cis isomer, but distorted significantly from planarity and twisted about its long axis in the trans isomer. In both structures, inter­molecular inter­actions are segregated into regions in which TTF units are brought into close contact and regions where the polymethyl­ene chains are brought into close contact. In the cis isomer, TTF units exhibit π–π stacking inter­actions, while in the trans isomer they do not.     

Resonant two-photon two-color photoionization (R2P2CI) spectra of aniline-Ar n clusters: Isomer strutures and solvent shifts

We present resonant two-photon two-color photoionization (R2P2CI) spectra of a series of Aniline-Ar _n complexes (n=1?6). An apparently anomalous blue shifted spectra for An-Ar₃ is explained by a modified spectral shift additivity rule which assigns different shifts to different relative positions of the Ar with respect to aniline. Evidence is presented for the existence of several isomers of clusters withn≧2. It is shown that, by changing the nucleation conditions, it is possible to control the relative populations of the various isomers.     

Multifunctional Tricarbazolo Triazolophane Macrocycles: One‐Pot Preparation,Anion Binding,and Hierarchical Self‐Organization of Multilayers

Programming the synthesis and self‐assembly of molecules is a compelling strategy for the bottom‐up fabrication of ordered materials. To this end, shape‐persistent macrocycles were designed with alternating carbazoles and triazoles to program a one‐pot synthesis and to bind large anions. The macrocycles bind anions that were once considered too weak to be coordinated, such as PF₆^?, with surprisingly high affinities (β₂=10¹¹ M ^?2 in 80:20 chloroform/methanol) and positive cooperativity, α=(4 K₂/K₁)=1200. We also discovered that the macrocycles assemble into ultrathin films of hierarchically ordered tubes on graphite surfaces. The remarkable surface‐templated self‐assembly properties, as was observed by using scanning tunneling microscopy, are attributed to the complementary pairing of alternating triazoles and carbazoles inscribed into both the co‐facial and edge‐sharing seams that exist between shape‐persistent macrocycles. The multilayer assembly is also consistent with the high degree of molecular self‐association observed in solution, with self‐association constants of K=300 000 M ^?1 (chloroform/methanol 80:20). Scanning tunneling microscopy data also showed that surface assemblies readily sequester iodide anions from solution, modulating their assembly. This multifunctional macrocycle provides a foundation for materials composed of hierarchically organized and nanotubular self‐assemblies.     

A two-step sulfurization for efficient solution-phase synthesis of phosphorothioate oligonucleotides

A solution-phase approach for the synthesis of phosphorothioate oligonucleotides that circumvents the use of chromatographic purifications of protected phosphorothioate intermediates was developed. Implementation of a two-step sulfurization protocol in the phosphoramidite method allows efficient isolation of the intermediate phosphorothioates by extractions. The viability of this approach is demonstrated by the synthesis of a hexameric phosphorothioate oligonucleotide fragment.     

Toward Electrochemically Controllable Tristable Three‐Station [2]Catenanes

Encouraged by the prospect of producing an electrochemical, color‐switchable red–green–blue (RGB) dye compound, we have designed, synthesized, and characterized two three‐station [2]catenanes. Both are composed of macrocyclic polyethers containing three π‐electron‐rich stations, which act as recognition sites for a π‐electron‐deficient tetracationic cyclophane. The molecular structures of the two three‐station [2]catenanes were characterized fully by mass spectrometry and ¹H NMR spectroscopy. To anticipate the relative occupancies of the three stations in each [2]catenane by the cyclophane, model compounds with the same constitutions in the vicinity of the stations were synthesized. The relative ground‐state populations of the three stations occupied in both [2]catenanes were estimated from the thermodynamic parameters for 1:1 complexes between all these model compounds and the cyclophane, obtained from isothermal titration calorimetry (ITC). The electrochemical and electromechanical properties of the three‐station [2]catenanes were analyzed by cyclic voltammetry (CV), differential pulse voltammetry (DPV), and spectroelectrochemistry (SEC). The first three‐station [2]catenane was found to behave like a bistable system, whereas the second can be described as a quasi‐tristable system.     

How do invariant transformations affect the calibration and optimization of the Kalman filtering algorithm used in the estimation of continuous-time affine term structure models?

Computational Management Science - In studying affine term structure models (ATSM), researchers have made significant theoretical advances in simplifying the burden of the Kalman filtering...     

Determination of 90Sr in environmental samples using solid phase extraction chromatography

The p-tert-butyl calix[4]arene thiophenol derivative was successfully synthesized with reflux condition and was characterized by FT-IR and ¹H-NMR. This work mainly adopted the method of controlling variables. The results showed that the optimum pH value, temperature and extraction time were respectively 4.5, 25 °C and 90 min. By calculating the data of the enthalpy change and gibbs free energy, indicating that the process of reaction was an exothermic and spontaneous process, and it demonstrated a close agreement with pseudo-second-order kinetic model. It is also found that the coexisting cations on the extraction of uranium had greater influence.

     

Nonlinear Leray–Schauder Alternatives for Decomposable Operators in Dunford–Pettis Spaces and Application to Nonlinear Eigenvalue Problems

We present some new variants of Leray–Schauder type fixed point theorems and eigenvalue results for decomposable single-valued nonlinear weakly compact operators in Dunford-Pettis spaces.