Infrared spectral study of species formed on malachite surface by adsorption from aqueous salicylaldoxime solution

The adsorption of salicylaldoxime from aqueous solution by malachite has been studied and the nature of the adsorbed species has been determined by infrared spectroscopy. At low surface coverage, a basic salt is observed whereas the bis-salicylaldoximato-copper II complex is formed when tridimensional condensation of the adsorbate occurs on the surface. At this stage the surface becomes hydrophobic allowing the mineral to be floated. The kinetics of the adsorption process is first order with respect to the salicylaldoxime concentration. The mechanism of this process is discussed in the light of the spectroscopic results.     

Direct synthesis of 4-arylpiperidines via palladium/copper(I)-cocatalyzed Negishi coupling of a 4-piperidylzinc iodide with aromatic halides and triflates

A general procedure for the synthesis of 4-arylpiperidines via the coupling of 4-(N-BOC-piperidyl)zinc iodide with aryl halides and triflates is presented. The reaction requires cocatalysis with both Cl(2)Pd(dppf) and a copper(I) species. An improved, safer procedure for the activation of zinc dust is also presented.     

A Quantitative Spectrometric Assay for the Determination of Solution Concentration of para-sulphonato-calix[n]arenes and Their Derivatives

A spectrometric assay for the determination of concentration of para-sulphonato-calix[n]arenes and their derivatives has been developed using dimethylmethylene blue (DMMB) as a probe. Interaction with para-sulphonato-calix[n]arenes leads to a metachromatic shift in the spectrum of DMMB with appearance of a peak at 536 nm and diminution of the spectral intensity of the peaks at 594 and 649 nm. The method shows good linearity in the concentration range 0–6 μg/ml for para-sulphonato-calix[n]arenes. in final form: 27 December 2004     

Convenient Synthesis of Alkenyl‐, Alkynyl‐, and Allenyl‐Substituted Imidazo[1,2‐a]pyridines via Palladium‐Catalyzed Cross‐Coupling Reactions

A systematic study on the Stille and Sonogashira cross‐coupling of iodinated imidazo[1,2‐a]pyridines was performed, permitting the preparation of various vinyl‐, ethynyl‐, and allenyl‐substituted derivatives. These methods are particularly valuable, given their experimental simplicity and high degree of flexibility with regard to functional groups that can be introduced in positions 3, 6, or 8 of the imidazo[1,2‐a]pyridine core. Effects concerning different substitution positions and the nature of the 2‐substituent under various reaction conditions are reported in detail for the above types of unsaturated groups introduced.     

Enantioseparation of new nucleoside analogs, related to d4T and acyclovir, by chiral capillary electrophoresis using highly sulfated beta-cyclodextrins

Baseline separation of some new acyclic nucleosides which are potential antiviral agents was achieved using cyclodextrin capillary zone electrophoresis (CD-CZE). A method for the enantiomeric resolution of these compounds and determination of their enantiomeric purity was developed using anionic CDs (highly sulfated-CD or highly S-CD) as chiral selectors and capillaries, which were dynamically coated with polyethylene oxide (PEO). Operational parameters including (i) the nature and concentration of the chiral selectors, (ii) organic modifiers, (iii) temperature, and (iv) applied voltage were investigated. The use of charged CDs provides (i) a supplementary driving force for the compounds in a running buffer and (ii) enantiomeric resolution by inclusion of compounds in the CD cavity. The highly S-CD was found to be the most effective complexing agent and allowed good enantiomeric resolution. The complete resolution of five nucleoside analogs was obtained using 25 mM phosphate buffer, pH 2.5, containing either highly S-alpha-CD, S-beta-CD or S-gamma-CD at 30 degrees C with an applied field of 0.30 kV/cm. The apparent association constants of the inclusion complexes were calculated. The enantiomer migration order for the molecules investigated was determined and the detection limit of enantiomeric impurities was found to vary between 0.34 to 3.56 ng.mL(-1) for the first enantiomer.     

Aqueous peptides as experimental models for hydration water dynamics near protein surfaces

We report quasi-elastic neutron scattering experiments to contrast the water dynamics as a function of temperature for hydrophilic and amphiphilic peptides under the same level of confinement, as models for understanding hydration dynamics near chemically heterogeneous protein surfaces. We find that the hydrophilic peptide shows only a single non-Arrhenius translational process with no evidence of spatial heterogeneity unlike the amphiphilic peptide solution that exhibits two translational relaxations with an Arrhenius and non-Arrhenius dependence on temperature. Together these results provide experimental proof that heterogeneous dynamical signatures near protein surfaces arise in part from chemical heterogeneity (energy disorder) as opposed to mere topological roughness of the protein surface.     

Rhodium and palladium complexes of a pyridyl-centred polyphenylene derivative

2-(2'-Pyridyl)-3,4,5,6-tetraphenylpyridine 2 (HL), a ligand with both N,N-bidentate and N,N,C-terdentate coordination potential, was prepared in excellent yield by the Diels-Alder [2+4] cycloaddition of 2-cyanopyridine and tetraphenylcyclopentadien-1-one. Monometallic Pd(II) and Rh(III) complexes were formed which exhibit both types of ligand coordination (trans-[RhCl2(L)(NCMe)] 3, cis-[RhCl(L)(NCMe)2]PF6, cis-[RhCl2(HL)2]PF6 6, [RhCl(L)(HL)]PF6 7, [Rh(L)2]PF6 8, [Pd(OAc)(L)] 9 and [Pd(eta3-methallyl)(HL)]PF6) 10. The molecular structures of the ligand and six complexes, including the chloro-bridged dimer [RhCl(L)(micro-Cl)]2 5, were obtained by single crystal X-ray diffraction.     

Synthesis of a naturally occurring nucleopeptide fragment via a phosphotriester approach

The phosphorylating agent 2-chlorophenyl-O,O-bis[1-benzotriazolyl]phosphate has been used for the introduction of a phosphodiester bond between the hydroxyl group of the tyrosine containing dipeptide (H-Ala-Tyr-NH₂) and the 5′-OH of the RNA dimer UpU.     

Crystal structure and absolute configuration of the indole alkaloid arborescidine C

The structure and absolute configuration (3R, 17R) of the indole alkaloid arborescidine C were determined by x-ray diffraction. The six-membered ring assumes a half-chair conformation and the seven-membered ring has a twist-like conformation. The crystal packing is characterized by intermolecular hydrogen-bonding between the hydroxyl group and nitrogen atom N4 which leads to the formation of infinite chains of molecules along the a-axis of the crystal. The absolute configurations of two related indole alkaloids, arborescidine B and arborescidine D are inferred from the experimentally determined configuration of arborescidin C molecule. A comparison of the present structure with that of a related indole alkaloid akagerine showed significant conformational and configurational differences. Crystal data: C₁₆H₁₉N₂OBr, orthorhombic, P2₁2₁2, a = 10.3376(8), b = 15.461(4), c = 9.2094(9)Å, V = 1471.9(6)ų, Z = 4, D _calc = 1.510 g cm^–3, = 1.54178Å.     

Ultrahigh-water-content supramolecular hydrogels exhibiting multistimuli responsiveness

Hydrogels are three-dimensional networked materials that are similar to soft biological tissues and have highly variable mechanical properties, making them increasingly important in a variety of biomedical and industrial applications. Herein we report the preparation of extremely high water content hydrogels (up to 99.7% water by weight) driven by strong host-guest complexation with cucurbit[8]uril (CB[8]). Cellulosic derivatives and commodity polymers such as poly(vinyl alcohol) were modified with strongly binding guests for CB[8] ternary complex formation (K(eq) = 10(12) M(-2)). When these polymers were mixed in the presence of CB[8], whereby the overall solid content was 90% cellulosic, a lightly colored, transparent hydrogel was formed instantaneously. The supramolecular nature of these hydrogels affords them with highly tunable mechanical properties, and the dynamics of the CB[8] ternary complex cross-links allows for rapid self-healing of the materials after damage caused by deformation. Moreover, these hydrogels display responsivity to a multitude of external stimuli, including temperature, chemical potential, and competing guests. These materials are easily processed, and the simplicity of their preparation, their availability from inexpensive renewable resources, and the tunability of their properties are distinguishing features for many important water-based applications.