Synthesis and Binding of Mannose-Specific Synthetic Carbohydrate Receptors

Synthetic carbohydrate receptors (SCRs) that selectively recognize cell-surface glycans could be used for detection, drug delivery, or as therapeutics. Here we report the synthesis of seven new C_2h symmetric tetrapodal SCRs. The structures of these SCRs possess a conserved biaryl core, and they vary in the four heterocyclic binding groups that are linked to the biaryl core via secondary amines. Supramolecular association between these SCRs and five biologically relevant C¹-O-octyloxy glycans, α/β-glucoside ( α/β-Glc ), α/β-mannoside ( α/β-Man ), and β-galactoside ( β-Gal ), was studied by mass spectrometry, ¹H NMR titrations, and molecular modeling. These studies revealed that selectivity can be achieved in these tetrapodal SCRs by varying the heterocyclic binding group. We found that SCR017 (3-pyrrole), SCR021 (3-pyridine), and SCR022 (2-phenol) bind only to β-Glc. SCR019 (3-indole) binds only to β-Man. SCR020 (2-pyridine) binds β-Man and α-Man with a preference to the latter. SCR018 (2-indole) binds α-Man and β-Gal with a preference to the former. The glycan guests bound within their SCR hosts in one of three supramolecular geometries: center-parallel, center-perpendicular, and off-center. Many host–guest combinations formed higher stoichiometry complexes, 2:1 glycan⋅SCR or 1:2 glycan⋅SCR , where the former are driven by positive allosteric cooperativity induced by glycan–glycan contacts.     

Two-particle azimuthal correlations at high transverse momentum in Pb−Au at 158 AGeV/c

The study of two-particle azimuthal correlations at high transverse momentum has become an important tool to investigate the interaction of hard partons with the medium formed in high-energy nucleus-nucleus collisions. At SPS energies, pioneering studies by the CERES Collaboration [1] indicated a significant modification of the away-side structure in central collisions. Here we present new results emerging from the analysis of the year 2000 data set recorded with the CERES Time-Projection Chamber, which provides excellent tracking efficiency and significantly improved momentum determination.     

Determination of the attenuation factor in fluorene-based molecular wires

Fluorene-based bridges exhibit a molecular wire-like behaviour in C(60)-wire-exTTF systems with a very low attenuation factor (beta = 0.09 A(-1)).     

Accelerating Diffusion‐Ordered NMR Spectroscopy by Joint Sparse Sampling of Diffusion and Time Dimensions

Diffusion‐ordered multidimensional NMR spectroscopy is a valuable technique for the analysis of complex chemical mixtures. However, this method is very time‐consuming because of the costly sampling of a multidimensional signal. Various sparse sampling techniques have been proposed to accelerate such measurements, but they have always been limited to frequency dimensions of NMR spectra. It is now revealed how sparse sampling can be extended to diffusion dimensions.     

Heteroaromatic Belts through Fold‐in Synthesis: Mechanistic Insights into a Macrocycle‐Templated Friedel–Crafts Alkylation

Direct alkylation of 9,9′,9′′‐triethyl[2.2.2](2,7)carbazolophane with dimethoxymethane or paraformaldehyde affords a belt‐like heteroaromatic structure, which forms as a kinetic product in acid‐catalyzed condensations. In a competing, thermodynamically favored process, polymeric structures are formed by a largely regioselective condensation of stereochemically rigid “semi‐belts”. The relationship between these reactivity routes is rationalized in terms of strain release and differential reversibility of consecutive condensation steps.     

Synthesis,characterization and photoluminescence of 8-oxyquinolinato organoboron complexes derived from pyrazole

A one-pot protocol was developed for the synthesis of a series of luminescent heteroleptic diaryldiborinic complexes containing the central aryl ring bonded to two boron atoms substituted with pyrazole and complexed with 8-hydroxyquinoline. The luminescent properties of these compounds were measured. In dilute solutions they exhibited an emission at ca. 513 nm with quantum yields of 22–27% which are typical for borinic 8-hydroxyquinoline complexes. The only exception was the complex containing the bithiophene scaffold, for which no fluorescence was observed. The obtained pyrazole-based complexes show improved solubility and thermal stability with respect to their phenyl analogues. The experimental UV–vis absorption and emission data are supported by theoretical calculations of the frontier molecular orbitals, revealing the aromatic linker to quinolinato ligand excitation mechanism.     

Spectroscopy and Photophysics of Monomethyl-Substituted Derivatives of 5-Deazaalloxazine and 10-Ethyl-5-Deaza-Isoalloxazine

Steady-state and time-resolved spectra were used to describe the singlet and triplet states of 8-methyl-5-deazaalloxazine (8-Me-5-DAll), 9-methyl-5-deazaalloxazine (9-Me-5-DAll) and 10-ethyl-5-deaza-isoalloxazine (10-Et-5-DIAll). Solvatochromic properties were described using different polarity scales, including Δf and the four-parameter scale proposed by Catalán. The results indicate that the Catalán scale shows a strong influence of solvent acidity (hydrogen-bond donating ability) on the emission properties of 8-Me-5-DAll and 9-Me-5-DAll. These results indicate the importance of intermolecular solute-solvent hydrogen-bonding interactions in the excited state of these compounds. Contrary to deazaalloxazines, solvent acidity affects the absorption spectra of 10-Et-5-DIAll. Fluorescence lifetimes and quantum yields and also transient absorption spectra were determined for all of the compounds studied. Electronic structure and S ₀ -S _i , S ₀ -T _i , T ₁ -T _i transitions energies and oscillator strengths were calculated using the TD-DFT methods. Theoretical calculations were compared to experimental data.     

Thermal Stability and Flammability of Polypropylene-Silsesquioxane Nanocomposites

This article presents a study of the thermal stability of polypropylene-based nanocomposites filled with tetrasilanolphenyl silsesquioxane (phPOSS). Nanofillers were introduced into a polypropylene matrix in three different amounts: 2, 5, and 10 wt.%. Investigations were carried out by means of thermogravimetric analyses conducted in inert and oxidizing atmospheres, Fourier transform-infrared spectroscopy, scanning electron microscopy, and flammability UL-94 test. The addition of phPOSS into the polymeric matrix increased thermal stability in comparison to neat iPP and introduced significant changes in the flammability of iPP/phPOSS nanocomposites.