Complexing and self-complexing of peptide-cavitands

Resorc[4]arene based peptide-cavitands with four identical chiral amino acids at their upper rim were synthesized and investigated for the complexation of small guest molecules. Competition experiments show, that the tetra amino acid cavitands complex small organic guests in chloroform in the order ethyl acetate <dichloromethane < acetonitrile < ethanol < acetamide < acetic acid. The peptide-cavitands containing aspartic and glutamic acid derivatives enclose parts of their attached amino acids in the cavity, so that these peptide-cavitands are host and guest at the same time. The starting material for the cavitands, the resorc[4]arenetetraamine 3, is made by a new synthetic route using the Delépine-reaction.     

Influence of the morphology and impurities of Ni(OH)2 on the synthesis of neutral Ni(II)–amino acid complexes

Synthesis of neutral complexes of Ni²⁺ with amino acids has often been reported on a qualitative basis, with a lack of information on the parameters involved in the dissolution of the nickel-containing solid precursor. This paper reports on a systematic study of the reactivity of Ni(OH)₂ toward glycine in aqueous solution. The crystallinity and size of hydroxide particles are found to be key parameters in the rapid glycine-promoted dissolution of the hydroxide and synthesis of [Ni(glycinate)₂(H₂O)₂]. These parameters derive from the nature of the salt used to prepare the hydroxide. Ni(II) chloride leads to the most reactive solid precursor, because of the presence of defects in the Ni(OH)₂ sheets arrangements, assigned to the substitution of Cl⁻ ions to OH⁻ ions at the edges of the particles. The reaction between this hydroxide and glycine at 80 °C is quantitative after 7 min and similar rates of dissolution are obtained with other amino acids, alanine or histidine, the reaction with serine being slower. When the hydroxide contains nitrate or carbonate ions, a glycinato complex with composition similar to [Ni(glycinate)₂(H₂O)₂], but with a different crystal structure, is also formed. Spectroscopic results may suggest a structure involving bridging ligands.     

Preparation of monodisperse PMMA microspheres using 2-vinyl-4,4′-dimethylazlactone as a particle Stabilizer

Polymeric microspheres of methyl methacrylate (PMMA) have been prepared via emulsion polymerization using potassium persulfate as initiator. The polymeric spheres were also prepared with varied concentration of an additional component, 2-vinyl-4,4′-dimethylazlactone (VDMA), which greatly affected the properties of the spheres. NMR analysis indicates the presence of VDMA in the polymer particles, and FT-IR analysis shows hydrolysis of VDMA in the polymer which produced N-acryloylmethylalanine, (NAMA). The VDMA hydrolysis thus led to carboxyl functionality which served to stabilize the microspheres during the emulsion polymerization showing a significant effect on particle size, distribution, and morphology, but little effect on molecular weight or thermal properties of the polymer. Also the effect of varying the concentration of initiator (potassium persulfate, KPS) was investigated, and had little effect on particle size or distribution or molecular weight of the polymer particles.     

Complex formation of uranium(VI) with the amino acids l-glycine and l-cysteine: A fluorescence emission and UV–Vis absorption study

The complexation of uranium(VI) with the amino acids l-glycine and l-cysteine has been investigated by time-resolved laser-induced fluorescence spectroscopy (TRLFS) and UV–Vis spectroscopy at a low pH range. The identified 1:1 and 1:2 uranyl-l-glycine complexes fluoresce and have similar absorbance properties. In contrast to the glycine system, uranyl forms two different non-fluorescent 1:1 complexes with l-cysteine, showing individual absorbance properties under the given experimental conditions. The corresponding complex formation constants were calculated using the spectroscopic data.     

Ex-Chiral Pool Enaminones in the Synthesis of Functionalised Heterocycles

Summary. Various chiral enaminones and hydrazones, derived from chiral pool starting materials, such as L-aspartic acid, L-3-phenylalanine, (+)-camphor, and D-aldoses were employed as key-intermediates in the synthesis of functionalised heterocycles, such as aminomethylidene substituted tetramic acids, heteroaryl substituted phenethylamines and terpenes, and C-nucleosides.     

Reduction of pentafluorophenyl esters to the corresponding primary alcohols using sodium borohydride

Primary alcohols and chiral N-protected 2-amino alcohols can be obtained in high yields from the reaction of pentafluorophenyl esters of the corresponding carboxylic acids with sodium borohydride in THF under mild conditions. This reductive method is rapid and compatible with various functional groups as well as with the most common N-protective groups Z, Boc and Fmoc.     

Concise and stereocontrolled syntheses of phosphonate C-glycoside analogues of β-d-ManNAc and β-d-GlcNAc 1-O-phosphates

Diethyl C-(2-deoxy-2-acetamido-β-d-mannopyranosyl)methylphosphonate and dimethyl C-(2-deoxy-2-acetamido-β-d-glucopyranosyl)methylphosphonate were stereoselectively prepared from N-acetyl d-glucosamine. Routes to such compounds starting from d-GlcNAc have been problematic, but we have found short and efficient implementations of this highly desirable transformation.     

Hydrolytically stable chemically bonded silica supports with metal complexating ligands: Synthesis,characterization and use in high-performance ligand-exchange chromatography (HPLEC)

Summary A silica of 14 nm pore size was reacted according to two procedures with the following silanes: -aminopropyltriethoxysilane (1), N-aminoethyl-N-aminopropyltrimethoxysilane (2), N-aminoethyl-N-aminoethyl-N-aminopropyltrimethoxysilane (3), N-(3-triethoxysilanepropyl)-N, N-diacetic dimethylester (4), N-(3-trisodiumsilanolatepropyl)-N, N-diacetic acid disodium salt (5) and N-(3-trisodiumsilanolatepropyl)-ethylenediamine-N, N, N-triacetic acid trisodium salt (6). The reaction of silanes 1–4 with the silica was carried out under anhydrous conditions (procedure A). Silanes 1–6 were subjected to surface modification under essentially hydrous conditions applying a two-step procedure (procedure B). Procedure B is much simpler to perform and allows binding of high and definite amounts of silane onto the surface. Complexation of all bonded phases with Cu²⁺ was examined by measuring the sorption isotherms at constant pH. The pH-dependence of Cu²⁺ uptake at constant Cu²⁺ concentration was evaluated. Tests on the chemical and chromatographic stability of the packings showed that only the silicas with bonded iminodiacetate and ethylenediaminetriacetate groups remain hydrolytically stable. Retention of aliphatic and -amino acids on these two packings was found to be mainly controlled by the pH and the ionic strength of the eluent.Presented at the 14th International Symposium on Chromatography London, September, 1982     

Comparison of metallic electrodes for constant-potential amperometric detection of carbohydrates,amino acids and related compounds in flow systems

Constant-potential amperometric detection of carbohydrates, amino acids, and other aliphatic organic compounds is possible by means of their oxidation in alkaline solution at a variety of metal/metal oxide electrodes including Pt, Au, Cu, Ni, Ag and Co. The experimental conditions required for optimum detection and the analytical performance obtainable vary widely for different electrode materials and analytes. In this work, the cyclic voltammetric behavior exhibited by selected analytes (glucose, glycine, lactic acid, ethylamine and ethanol) at each of these electrodes was used to determine the optimum potentials suitable for flow detection so that the capabilities of the different metal electrodes could be evaluated and systematically compared. In general, the Cu electrode was found to provide superior detection capabilities in terms of its range of response, detection limits and especially stability. Despite the fact that Pt and Au are typically used only with a pulsed applied potential, both can provide long-lived constant-potential detection of carbohydrates and other analytes at low concentrations if the potentials ere carefully chosen and the electrodes are allowed to undergo an initial stabilization period.     

Synthesis of a series of vicinal diamines with potential biological activity

A broad range of vicinal diamines based on styrene oxide are synthesisedvia mixtures of regioisomeric amino alcohols. The ring opening of the intermediate aziridinium ions by primary amines proceeds with high regioselectivity, leading to the target diamines as single regioisomers for all reaction series. The compounds are of potential biological interest as ligands for cisplatin analogues. Anticancer activity tests of both groups of compounds are in progress.