A convenient solid phase synthesis of S-palmitoyl transmembrane peptides

S-Palmitoylated peptides are important tools as models for integral membrane proteins to study peptide-lipid interactions. Herein, we report a convenient solid phase synthesis of S-palmitoyl transmembrane peptides. The highly acid labile S-(4-methoxytrityl) group is preferred over the S-(tert-butylsulfanyl) group for protection of the cysteine side chain since the latter gives rise to quantitative desulfurization during on-resin deprotection. The resulting free thiol function is modified with palmitic acid via a carbodiimide-mediated coupling and the title compounds are obtained in good yields and purity.     

Synthese und Bau von (4-Picolinium)2[LnCl4(H2O)3]Cl (Ln = Eu,Ho)

Preparation and Structure of (4-Picolinium)₂[LnCl₄(H₂O)₃]Cl (Ln = Eu, Ho) The complex water containing chlorides (4-Picolinium)₂[LnCl₄(H₂O)₃]Cl (Ln = Eu, Ho) were prepared for the first time. The crystal structures were determined on single crystals by X-ray methods. The isotypic compounds crystallize with triclinic symmetry, space group P–1, Z = 2. Surprisingly the structures contain the complex anions [LnCl₄(H₂O)₃]^? (Ln = Eu, Ho) where the ligands form a distorted pentagonal bipyramid, which to our knowledge has not been observed in lanthanide compounds till now.     

A zeolite-enzyme combination for biphasic dynamic kinetic resolution of benzylic alcohols

Acid zeolites like H-Beta are efficient heterogeneous catalysts for racemization of benzylic alcohols in water; by combination of the racemization with an enzymatic kinetic resolution in a two-phase system, enantiomerically pure esters were obtained in high yield via a dynamic kinetic resolution.     

An industrially viable catalyst system for palladium-catalyzed telomerizations of 1,3-butadiene with alcohols

The telomerization reaction of 1,3-butadiene with alcohols to give alkyl octadienyl ethers in the presence of palladium-carbene catalysts has been studied in detail. Unprecedented catalyst efficiency with turnover numbers (TON) up to 1,500,000 and turnover frequencies (TOF) up to 100,000 h(-1) have been obtained after optimization for the reaction of methanol in the presence of an excess of in situ generated carbene ligands. High yields (75-97 %) and catalyst productivities (TON 15,000-100,000) are observed for other aliphatic alcohols and phenols. For comparison five carbene-palladium(0) complexes have been synthesized and characterized by X-ray crystallography. Both electronic and steric effects on the stability and reactivity of the catalysts have been discussed on the basis of density functional theory calculations.     

Investigation of swelling and diffusion in polymers by NMR imaging

The kinetics of diffusion in polymers ranges from simple Fickian diffusion to higher order diffusion, such as Case II diffusion^1-2). The conventional method for determining the characteristics of solvents into polymer matrices is by measuring the mass uptake of the polymer as the solvent penetrates the matrix. However, since such measurements perform observations at a macroscopic level, little information has been obtained relating to the nature of the solvent in the polymer matrix and the mechanisms of the processes that control the diffusion. Nuclear magnetic resonance (NMR) imaging (‘MRI’) has been used to observe the penetration of solvents into solid systems in realtime. The method provides a one- or more-dimensional image of the density and the mobility of the solvent in a material or of the network changes of the material itself due to the softening influence of the solvent. The first (imaging of the solvent) can be used for a quantitative measurement of the diffusion whereas the observation of the network gives information about the changing of the network (mobility, de-crystallization…) during the swelling process. For example the diffusion of organic solvents in some polymeric materials (natural rubber, water gels (PNIPAAm), and nematic diblock-copolymers) are investigated.     

Selective Alkene Oxidation with H2O2 and a Heterogenized Mn Catalyst: Epoxidation and a New Entry to Vicinal cis-Diols

Covalent anchoring of 1,4-dimethyl-1,4,7-triazacyclononane on silica gel is the first step in the preparation of a heterogenized Mn catalyst. When H₂O₂ is used as the oxidant, this material can catalyze the vicinal cis-dihydroxylation of disubstituted olefins, as shown schematically here. Both enantiomers of the product are obtained.