Encapsulation of a β-carboline in cucurbit[7]uril

Inclusion of a biological photosensitizer and prototype of β-carbolines, norharmane (NHM), into the cavity of cucurbit[7]uril (CB[7]) has been investigated for the first time, by using ¹H NMR and UV–visible spectroscopy, and ab initio calculations. Protonated NHM forms a very stable host–guest complex with CB[7] in aqueous solution, with a binding constant of (9.0 ± 0.5) × 10⁴ M^?1. The encapsulation of NHM into CB[7] has driven the prototropic equilibrium of NHM to protonated NHM (NHMH⁺) at neutral pH. A pH titration for the host–guest complex revealed a moderate shift of the acid–base equilibrium in the ground-state (from 7.2 to 7.9), which may be caused by the low polarity microenvironment of the CB[7] cavity. The CB[7] provides a binding pocket for the hydrophobic molecule, and the polar, carbonyl-lined portals offering an anchoring site for the positive charge of the cationic species NHMH⁺.     

Novel ‘Nano in Nano’ Composites for Sustained Drug Delivery: Biodegradable Nanoparticles Encapsulated into Nanofiber Non‐Wovens

Novel ‘nano in nano’ composites consisting of biodegradable polymer nanoparticles incorporated into polymer nanofibers may efficiently modulate drug delivery. This is shown here using a combination of model compound‐loaded biodegradable nanoparticles encapsulated in electrospun fibers. The dye coumarin 6 is used as model compound for a drug in order to simulate drug release from loaded poly(lactide‐co‐glycolide) nanoparticles. Dye release from the nanoparticles occurs immediately in aqueous solution. Dye‐loaded nanoparticles which are encapsulated by electrospun polymer nanofibers display a significantly retarded release.

     

Quiesent Crystallization Kinetics of Nucleated Metallocene and ZN Isotactic Polypropylenes

Crystallization kinetics and thermodynamic properties of nucleated isotactic polypropylene (PP) are analyzed using Hoffman—Lauritzen crystallization theory to determine the mechanistic effects of the nucleators. Calorimetric data provides quantitative comparisons between nucleating efficiences of the (Millad) and (NJSTAR) nucleator in Metallocene (M) and Ziegler—Natta (ZN) PP. The two types of PP without nucleators showed similar crystallization behavior though the T°_m for ZN-iPP was about 10°C higher than M-iPP. Both nucleators show significant improvement in crystallization rate in both types of PP. In addition, Millad outperforms NJSTAR. The magnitude of the kinetic response is,however, different and both the nucleators appear to function better in ZN than in Metallocene PP. nucleated PP shows predominantly the form. The amount of the form is thermal history dependent and changes with supercooling (T=T°_m–T_c). Similar equilibrium melting temperature (T°_m) in the nucleated and control PPs indicates the lack of any thermodynamic effect of the nucleator. All nucleated PPs show a much lower secondary nucleation rate constant, K_g.This revised version was published online in November 2005 with corrections to the Cover Date.     

Generation of substituted styrenes via Suzuki cross-coupling of aryl halides with 2,4,6-trivinylcyclotriboroxane

The synthesis of functionalized styrene derivatives can be readily achieved utilizing a Suzuki cross-coupling protocol between aryl halides and 2,4,6-trivinylcyclotriboroxane-pyridine complex. The scope and limitations of the procedure were demonstrated by investigation of an array of ortho-substituted aryl halides.     

Synthesis and properties of monodisperse oligofluorene-functionalized truxenes: highly fluorescent star-shaped architectures

This paper describes the strategy toward novel monodisperse, well-defined, star-shaped oligofluorenes with a central truxene core and from monofluorene to quaterfluorene arms. Introduction of solubilizing n-hexyl groups at both fluorene and truxene moieties results in highly soluble, intrinsically two-dimensional nanosized macromolecules T1-T4. The radius for the largest oligomer of ca. 3.9 nm represents one of the largest known star-shaped conjugated systems. Cyclic voltammetry experiments reveal reversible or quasi-reversible oxidation and reduction processes (Eox = +0.74 to 0.80 V, Ered = -2.66 to 2.80 eV vs Fc/Fc+), demonstrating excellent electrochemical stability toward both p- and n-doping, while the band gaps of the oligomers are quite high (EgCV = 3.20-3.40 eV). Close band gaps of 3.05-3.29 eV have been estimated from the electron absorption spectra. These star-shaped macromolecules demonstrate good thermal stability (up to 400-420 degrees C) and improved glass transition temperatures with an increase in length of the oligofluorene arms (from Tg = 63 degrees C for T1 to 116 degrees C for T4) and show very efficient blue photoluminescence (lambdaPL = 398-422 nm) in both solution (PhiPL = 70-86%) and solid state (PhiPL = 43-60%). Spectroelectrochemical experiments reveal that compounds T1-T4 are stable electrochromic systems which change their color reversibly from colorless in the neutral state (approximately 340-400 nm) to colored (from red to purple color; approximately 500-600 nm) in the oxidized state.     

Protic acid (HClO4 supported on silica gel)-mediated synthesis of 2,3-unsaturated-O-glucosides and a chiral furan diol from 2,3-glycals

Perchloric acid supported on silica gel acts as an excellent reagent system in converting glucals into 2,3-unsaturated-O-glucosides in good to excellent yields in short reaction time with good alpha selectivity. Primary, secondary, and allylic alcohols, phenols, and thiols react with 3,4,6-tri-O-acetyl glucal with equal ease. In addition to this, a chiral furan diol is obtained from unprotected D-glucal or D-galactal in good yields.     

Thermo‐Switchable Antibacterial Activity

A copolymer system of 2‐aminoethyl methacrylate and N‐isopropylacrylamide comprises novel properties: changes in conformation and hydrophilicity upon heating influence the antibacterial activity and result in a switchable biocidal effect. The copolymers are characterized via NMR, MALDI‐ToF MS, phase transition behavior, and antibacterial tests with E. coli or B. subtilis. MIC and MBC are determined using standard dilution methods, temperature‐dependence via incubation at different temperatures and cytotoxicity by MTT tests. The copolymers exhibit lower MIC in globule than coil conformation, crosslinking on cotton results in non‐leaching materials with better antibacterial activity above than below the phase‐transition point.

     

Evolution of microstructure and crack pattern in NiO thin films under 200 MeV Au ion irradiation

NiO thin films grown on Si (100) substrate by electron beam evaporation method and sintered at 700 °C were irradiated with 200 MeV Au¹⁵⁺ ions. The fcc structure of the sintered films was retained up to the highest fluence (1×10¹³ ions cm^?2) of irradiation. However the microstructure of the pristine film underwent a considerable modification with increasing ion fluence. 200 MeV Au ion irradiation led to compressive stress generation in NiO medium. The diameter of the stressed region created by 200 MeV Au ions along the ion path was estimated from the variation of stress with ion fluence and found to be ～11.6 nm. The film surface started cracking when irradiated at and above the fluence of 3×10¹² ions cm^?2. Ratio of the fractal dimension of the cracked surface obtained at 200 MeV and 120 MeV (Mallick et al., 2010a) Au ions was compared with the ratio of the radii of ion tracks calculated based on Coulomb explosion and thermal spike models. This comparison indicated applicability of thermal spike model for crack formation.     

Polymers with Upper Critical Solution Temperature in Aqueous Solution

This review focuses on polymers with upper critical solution temperature (UCST) in water or electrolyte solution and provides a detailed survey of the yet few existing examples. A guide for synthetic chemists for the design of novel UCST polymers is presented and possible handles to tune the phase transition temperature, sharpness of transition, hysteresis, and effectiveness of phase separation are discussed. This review tries to answer the question why polymers with UCST remained largely underrepresented in academic as well as applied research and what requirements have to be fulfilled to make these polymers suitable for the development of smart materials with a positive thermoresponse.