The diazo route to diazonamide A: studies on the tyrosine-derived fragment

Various approaches to the tyrosine-derived fragment of the marine secondary metabolite diazonamide A are described. Initial efforts were focused on the originally proposed structure of the natural product, and a feasibility study established that a model 4-aryltryptamine could be readily prepared. Protected 4-bromotryptamine underwent Pd0-catalyzed coupling with the boronic acid derived from 2-bromophenyl allyl ether by Claisen rearrangement, O-methylation and lithiation-boration. The resulting biaryl was elaborated into an alpha-diazo-beta-ketoester, dirhodium(II)-catalyzed reaction of which with N-Z-valinamide gave the desired tryptamine-oxazole following cyclodehydration of the intermediate ketoamide. A potential precursor to the benzofuran ring of the original structure of diazonamide A was prepared in eight steps from N-Z-tyrosine tert-butyl ester. Iodination, O-protection and Stille coupling gave the cinnamyl alcohol 25, converted via the bromide into the allyl aryl ether 27. Subsequent Claisen rearrangement and oxidative cleavage of the alkene gave the lactol 29, converted into the desired benzofuranone 31. The revision in the structure of diazonamide A to 2 resulted in the targeting of an alternative tyrosine-derived model benzofuranone 41 synthesized in four steps from N-Z-tyrosine methyl ester 36 by a route involving Claisen rearrangement of cinnamyl ether 37. Poor yields in this sequence prompted an investigation into the intramolecular Heck reaction as a route to benzofuranone 50. Coupling of 3-iodotyrosine 44 with 2-phenylbutenoic acid 48 gave ester 49 that readily underwent intramolecular Heck reaction to give benzofuranone 50, albeit with poor stereocontrol.     

Settling of paraffin crystals in cooled middle distillate fuels

The mechanism of action of additives that control the sedimentation of paraffin crystals after their crystallization in model diesel oil has been studied by means of a new experimental approach. The chemical analysis of the crystals and detailed measurements of the sedimentation phenomenon give new insights into this complex process. Thus, the wax antisettling additives used for preventing wax crystal sedimentation adsorb at the surfaces of wax particles and provide them with enhanced colloidal stability. The settling rate is not related to the size of the crystals or the viscosity of the liquid medium, but to the ability of the additives to prevent the aggregation of wax crystals. The reported methodology makes it possible to investigate the fundamental mechanisms, but also to evaluate structure-activity relationships of the various additives used in the petroleum industry.     

Synthesis and photochemistry of binary and mixed ligand complexes of copper(II) containing 5-arylazo-8-hydroxyquinoline derivatives and alkyl xanthates

Summary Mixed ligand complexes of the type K[Cu(x-HQA)Rxan] [x-HQA = 5-arylazo-8-hydroxyquinoline derivatives; Rxan = methyl or ethylxanthate] have been prepared and characterised by elemental analysis, spectral measurements and conductivity. Upon irradiation, solutions of these complexes photoeliminate dinitrogen and a mechanism for this reaction is proposed. The photosensitivity of the oxine ligand was found to be responsible for the observed photolysis of the complexes.     

Microrobotics and MEMS-based fabrication techniques for scaffold-based tissue engineering

Scaffold based tissue engineering strategies use cells, biomolecules and a scaffold to promote the repair and regeneration of tissues. Although scaffold-based tissue engineering approaches are being actively developed, most are still experimental, and it is not yet clear what defines an ideal scaffold/cell construct. Solid free form fabrication (SFF) techniques can precisely control matrix architecture (size, shape, interconnectivity, branching, geometry and orientation). The SFF methods enable the fabrication of scaffolds with various designs and material compositions, thus providing a control of mechanical properties, biological effects and degradation kinetics. This paper reviews the application of micro-robotics and MEMS-based fabrication techniques for scaffold design and fabrication. It also presents a novel robotic technique to fabricate scaffold/cell constructs for tissue engineering by the assembly of microscopic building blocks.     

Sorption of uranium by non-living water hyacinth roots

Summary Many studies have shown that water hyacinth (Eichhornia crassipes) roots can be used to accumulate high concentrations of organic as well as inorganic pollutants. They are currently used to remediate aquatic environments and aqueous solutions. In the present study, sorption of uranium from aqueous solutions by using dried roots of water hyacinth has been investigated. The sorption of uranium was examined as a function of initial concentration, pH, weight of roots and contact time. Five different concentrations 20, 40, 60, 80, and 100 μg ^. ml^-1 were used. Sorption proves to be very rapid and depend on pH, weight of roots and concentration of uranium. Maximum sorption capacity of water hyacinth roots was 64,000 U⁶⁺ μg/g. The sorption of uranium by water hyacinth roots follows a Langmuir isotherm.     

Chemiluminescence determination of some fluoroquinolone derivatives in pharmaceutical formulations and biological fluids using [Ru(bipy)(3)(2+)]-Ce(IV) system

A new chemiluminescence (CL) method using flow injection has been described for the rapid and sensitive determination of three fluoroquinolone derivatives, namely ofloxacin, norfloxacin and ciprofloxacin hydrochloride. The method is based on the CL reaction of the studied fluoroquinolones with tris(2,2'-bipyridyl)ruthenium(II) [Ru(bipy)(3)(2+)] and Ce(IV) in sulfuric acid medium. Under the optimum conditions, the CL intensity is proportional to the concentration of the drugs in solution over the range 0.05-7.0 mug ml(-1) for norfloxacin, 0.05-6.0 mug ml(-1) for ciprofloxacin hydrochloride and 0.003-0.7 mug ml(-1) for ofloxacin. The limits of detection (s/n=3) were 3.1x10(-8) M norfloxacin, 2.6x10(-8) M ciprofloxacin hydrochloride and 5.5x10(-9) M ofloxacin. The method was applied successfully to the determination of these compounds in dosage forms and biological fluids.     

Separation of Carrier Free Manganese-54 and Iron-59 Using Reversed Phase Partition Chromatography

Carrier free radioactive ⁵⁴Mn and ⁵⁹Fe enjoy favoured position in industrial, agricultural and medical applications [1]. The main methods used for their isolation from suitable irradiated targets are mainly based on solvent extraction [2] or ion exchange [3].