Experimental evidence of chiral crown ether complexation with aromatic amino acids

The complexation of L ‐ and D ‐enantiomers of phenylglycine, phenylalanine, and tryptophan with D ‐mannonaphto‐crown‐6‐ether in methanol solution was studied by NMR and isothermal titration calorimetry (ITC) at 298.15 K. The total heat effects attributed to the binding phenomena were measured in the range of 1.8 to 7.7 mJ, and the complexation was found stereo‐specific. The binding topologies were estimated basing on ¹H 2D‐ROESY experiments. The analysis of Job plots obtained from ¹H NMR‐monitored titrations proved the coexistence of 1:1 and 1:2 (crown ether:amino acids) complexes, which thermodynamic parameters, K_s, ΔG, ΔH°, and TΔS were determined with the aid of ITC. The 1:1 complexes were found enthalpically stabilized, generally by electrostatic interactions between the charged NH group of amino acid and crown ether macrocyclic moiety, while the binding of the second amino acid molecule was driven entropically due to solvatophobic effect. Strong enthalpy–entropy compensation points towards the uniform binding mode of all complexes studied. The mode of complex formation was found solvent dependent. For phenylalanine guest studied in various solvent systems, in contrast to the aqueous media, the noticeable chiral recognition is observed in methanol solution, and the complex stoichiometry (1:2 ether:Phe) differs from the 2:1 one, determined previously for the same host‐guest system in water (J. Thermal. Anal. Cal. 2006; 83: 575–578). Copyright © 2007 John Wiley & Sons, Ltd.     

Abnormal adsorption behavior of dimethyl disulfide on gold surfaces

Adsorption of dimethyl disulfide (DMDS) on gold colloidal nanoparticle surfaces has been examined to check its binding mechanism. Differently from previous results, DMDS molecules adsorbed on the gold surface at high concentration showed the S–S stretching band at 500 cm⁻¹ in surface-enhanced Raman scattering (SERS) spectra, which indicates the presence of intact adsorption of DMDS molecules. However, it was found that the S–S bond of disulfides was easily cleaved on the gold surface at low concentration. These behaviors were not observed for diethyl disulfide (DEDS) or diphenyl disulfide (DPDS). Our results indicate that DMDS molecules with the shortest alkyl chains on the gold surface can be inserted into self-assembled monolayers (SAMs) without the S–S bond cleavage during self-assembly due to insufficient lateral van der Waals interaction and the low adsorption activity of disulfides, whereas DEDS with longer alkyl chains or DPDS with the weak disulfide bond dissociation energy would not. These unusual DMDS adsorption behaviors were examined by scanning tunneling microscopy (STM) and X-ray photoelectron spectroscopy (XPS). We also compared the bonding dissociation energy of the S–S bonds of various disulfides by means of a density functional theory (DFT) calculation.     

Cucurbit[7]uril: A High‐Affinity Host for Encapsulation of Amino Saccharides and Supramolecular Stabilization of Their α‐Anomers in Water

Cucurbit[7]uril (CB[7]), an uncharged and water‐soluble macrocyclic host, binds protonated amino saccharides (D ‐glucosamine, D ‐galactosamine, D ‐mannosamine and 6‐amino‐6‐deoxy‐D ‐glucose) with excellent affinity (K_a=10³ to 10⁴ M ^?1). The host–guest complexation was confirmed by NMR spectroscopy, isothermal titration calorimetry (ITC), and MALDI‐TOF mass spectral analyses. NMR analyses revealed that the amino saccharides, except D ‐mannosamine, are bound as α‐anomers within the CB[7] cavity. ITC analyses reveal that CB[7] has excellent affinity for binding amino saccharides in water. The maximum affinity was observed for D ‐galactosamine hydrochloride (K_a=1.6×10⁴ M ^?1). Such a strong affinity for any saccharide in water using a synthetic receptor is unprecedented, as is the supramolecular stabilization of an α‐anomer by the host.     

Palladium‐Catalyzed Stereoselective Intramolecular Oxidative Amidation of Alkenes in the Synthesis of 1,3‐ and 1,4‐Amino Alcohols and 1,3‐Diamines

An efficient and practical Pd‐catalyzed intramolecular oxidative allylic amidation provides facile access to derivatives of 1,3‐ and 1,4‐amino alcohols and 1,3‐diamines. The method operates under mild reaction conditions (RT) with molecular oxygen (1 atm) as the sole reoxidant of Pd. Excellent diastereoselectivities were attained with substrates bearing a secondary stereogenic center     

Combining [Arene–Ru] with Azocarboxamide to Generate a Complex with Cytotoxic Properties

Azocarboxamide (azcH) has been combined for the first time with [Ru–Cym] to generate metal complexes with N,N‐ and N,O‐coordination mode, [(Cym)Ru(azc)Cl] and [(Cym)Ru(azcH)Cl]⁺[PF₆]^?. Geometric and electronic structures of the complexes are reported along with their in vitro activities against different tumour cell lines and preliminary results on solution chemistry. Compound [(Cym)Ru(azc)Cl] exhibited remarkable cytotoxic properties. It was cell‐type specific and had comparable IC₅₀ values towards both cancer cells and their drug‐resistant subline. A tenfold increase in the sensitivity towards [(Cym)Ru(azc)Cl] was noted for the tumour cells with depleted intracellular glutathione (GSH) level, suggesting the essential role of GSH in cell response to this compound.     

Biodegradable polymer blends and composites: An overview

Biodegradable polymers belong to a family of polymer materials that found applications ranged from medical applications including tissue engineering, wound management, drugs delivery, and orthopedic devices, to packaging and films applications. For broadening their potential applications, biodegradable polymers are modified utilizing several methods such as blending and composites forming, which lead to new materials with unique properties including high performance, low cost, and good processability. This paper reviews the recent information about the morphology of blends consisting of both biodegradable and non-biodegradable polymers and associated mechanical, rheological, and thermal properties of these systems as well as their degradation behavior. In addition, the mechanical performance of composites based on biodegradable polymers is described.     

Anisotropic Electrical,Magnetic, and Thermal Properties of In3Ni2 Intermetallic Catalyst

We present the anisotropic electrical and thermal transport coefficients (electrical resistivity, magnetoresistance, thermoelectric power, thermal conductivity), the magnetic properties, the specific heat and the electronic density of states of a monocrystalline In₃Ni₂ intermetallic compound, representing a precious-metal-free (and noble-metal-free) intermetallic catalyst for the selective hydrogenation of α,β-unsaturated aldehydes. The investigated physical parameters were determined along three orthogonal crystal-symmetry directions of the trigonal structure, the twofold axis, the 3 axis and within the mirror plane. All the investigated tensorial and vectorial quantities show the same anisotropy, with the quantities being isotropic for the twofold direction and in the mirror plane, whereas there is small, though still significant anisotropy to the 3 direction. The In₃Ni₂ crystal conducts the electricity and heat somewhat less efficiently along the 3 direction than along the twofold direction and in the mirror plane, but the differences are not large, of about 20 %. In₃Ni₂ is a diamagnetic intermetallic compound, with a presumably simple Fermi surface and electrons as the majority charge carriers.