The aggregation of sodium dehydrocholate in water

 We used a battery of different methods to study the association in aqueous sodium dehydrocholate (NaDHC) solutions. This salt associates by a stepwise mechanism. Below (9.6 ± 4.2) × 10⁻⁴ mol dm⁻³ there is a molecular solution with some strongly insoluble dehydrocholic acid produced by hydrolysis. Between (9.6 ± 4.2) × 10⁻⁴ and (5.2 ± 2.2) × 10⁻³ mol dm⁻³, an aggregate similar to acid soap (NaDHC.HDHC) appears and its amount and the aggregate's size increase with concentration. At =(2.20 ± 0.85) × 10⁻² mol dm⁻³ the aggregates formed have properties usually associated with true micelles, such as solubilisation of water-insoluble dyes. These aggregates increase in size with concentration and change their shape at 8 × 10⁻² mol dm⁻³, giving nonsymmetrical aggregates. The changes in the solution physicochemical properties at these concentrations may be misinterpreted and this explains the different values of the critical micelle concentration reported in the literature for substances with similar structure, such as bile salts. Received: 14 May 2001 Accepted: 10 August 2001     

Synthesis of statistical glycidyl methacrylate‐n‐vinyl pyrrolidone copolymers and their reaction with naproxen

Free‐radical copolymerization of glycidyl methacrylate (GMA) with N‐vinylpyrrolidone (VPD) was carried out at 50 °C using 3.0 mol · L^?1 of N,N′‐dimethylformamide solution and 9.0 · 10^?3 mol · L^?1 of 2,2′‐azobisisobutyronitrile as an initiator. The modification reaction of GMA‐VPD copolymers with a model bioactive carboxylic acid, 6‐methoxy‐α‐methyl‐2‐naphthaleneacetic acid (naproxen), was studied in the homogeneous phase using basic catalysts. The influence of the type of catalyst and the GMA content was evaluated. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 1192–1199, 2002     

Macrocycle synthesis strategy based on step-wise “adding and reacting” three components enables screening of large combinatorial libraries

Macrocycles provide an attractive modality for drug development, but generating ligands for new targets is hampered by the limited availability of large macrocycle libraries. We have established a solution-phase macrocycle synthesis strategy in which three building blocks are coupled sequentially in efficient alkylation reactions that eliminate the need for product purification. We demonstrate the power of the approach by combinatorially reacting 15 bromoacetamide-activated tripeptides, 42 amines, and 6 bis-electrophile cyclization linkers to generate a 3780-compound library with minimal effort. Screening against thrombin yielded a potent and selective inhibitor (K_i = 4.2 ± 0.8 nM) that efficiently blocked blood coagulation in human plasma. Structure–activity relationship and X-ray crystallography analysis revealed that two of the three building blocks acted synergistically and underscored the importance of combinatorial screening in macrocycle development. The three-component library synthesis approach is general and offers a promising avenue to generate macrocycle ligands to other targets.

Combination of three efficient chemical reactions allows for solution-phase synthesis of 3780 macrocycles and identification of potent thrombin inhibitor.     

Synthesis of variolin B

The total synthesis of variolin B from 4-methoxy-7-azaindole is described. The preparation of the protected amino derivative 10 and a coupling reaction of the iodo derivative 12 with 2-acetylamino-4-trimethylstannylpyrimidine are the key steps of the sequence. The use of N-tosyldichloromethanimine for the cyclisation step afforded a good entry to the 9-aminopyrido[3′,2′:4,5]pyrrolo[1,2-c]pyrimidine system. Variolin B was obtained from the triply protected tetracyclic compound 13 in two steps.     

Compatibility tests of low vapour pressure perfluoropolyether oils with UF6

An extensive study has been carried out in order to evaluate the possible use of the perfluoropolyether fluids, obtained from HFP photooxidation and specially purified and selected, as lubricants or vacuum working fluids, in presence of UF₆.Some physicochemical properties are reported and the results of the tests experienced on perfluoropolyether cuts put into contact with UF₆, in different conditions for long aging time at high temperature in presence of some typical engineering materials.The results, shown in this work, allowed a verification of the long term compatibility of the perfluoropolyether special fractions against UF₆ at temperatures up to 130°C.These results still offer a contribution in order to solve some technological problems on UF₆ processing.     

Synthesis of 6,19-sulfamidate bridged pregnanes

Conformationally restrained substituted pregnane-20-one derivatives were obtained by an intramolecular nitrene addition onto a C-5/C-6 double bond involving a tethered C-19 sulfamoyl moiety. The resulting aziridine underwent regioselective nucleophilic ring opening at C-5 at room temperature with cyanide, fluoride, and acetate. In the isolated case of acetate, a reversal of regioselectivity was observed at higher temperatures, a result attributed to a rearrangement process involving aziridine ring opening at the C-5 position and subsequent migration of the acetyl moiety to C-6.     

Study of the alkylation of chlorosilanes. Part I. Synthesis of tetra(1H, 1H, 2H, 2H-polyfluoroalkyl)silanes

The synthesis and structural characterization of tetra(1H, 1H, 2H, 2H-polyfluoroalkyl)silaneswith the same or different chain lengths C_nF_2n+1 linked to Si (1n6) is reported.

When the synthesis was effected from chlorosilanes and fluorinated organomagnesiumor organolithium reagents, the trialkylsilanes were obtained. The last fluorinated chainwas introduced either via a fluoroalkyllithium reagent or by hydrosilylation of thetrialkylsilanes.

Some properties and characterization by ¹H, ¹⁹F and ²⁹Si NMR spectroscopy of the1H, 1H, 2H, 2H-polyfluoroalkylsilanes are described.     

Influence of optical constants in carbon-based dispersions for enhanced solar evaporation

Journal of Thermal Analysis and Calorimetry - Carbon-based nano- and microfluid dispersions show promise as effective media for solar-assisted desalination. They act as strong solar absorbers in...