Synthesis of hindered tertiary amines by a mild reductive amination procedure

An efficient metal-free procedure for the synthesis of tertiary amines by the reductive amination of carbonyl compounds is reported, which allows a convergent access to sterically hindered amines of the general formulas NR(R′)₂ and NRR′R″. The mild and operationally simple protocol uses the Hantzsch ester for transfer hydrogenation and catalytic amounts of thiourea for imine activation.     

On-line electrochemistry/liquid chromatography/mass spectrometry for the simulation of pesticide metabolism

On-line electrochemistry/liquid chromatography/mass spectrometry (EC/LC/MS) was employed to mimic the oxidative metabolism of the fungicide boscalid. High-resolution mass spectrometry and MS/MS experiments were used to identify its electrochemical oxidation products. Furthermore, the introduction of a second electrochemical cell with reductive conditions provided important additional information on the oxidation products. With this equipment, hydroxylation, dehydrogenation, formation of a covalent ammonia adduct, and dimerization were detected after initial one-electron oxidation of boscalid to a radical cation. On-line reaction with glutathione yielded different isomeric covalent glutathione adducts. The results of the electrochemical oxidation are in good accordance with previously reported in vivo experiments, showing that EC/LC/MS is a useful tool for studying biotransformation reactions of various groups of xenobiotics.     

The foam/emulsion analogy in structure and drainage

The often quoted analogy between foams and emulsions is experimentally tested by studying properties after settling and under forced drainage of oil-in-water emulsions of drop size similar as for bubbles generally used in foam experiments. Observations with regard to structure, water fraction and drainage wave properties confirm the expected similarity in the low flow rate range. However, while for foams a convective circulation on the scale of the container sets in for values of water fraction exceeding about 0.2, no such convection is found in emulsions. Here instabilities are only encountered at water fractions of about 0.4, close to the void fraction of random packings of spheres. These take on the form of descending pulses of increased water fraction and lead to the transition from a frozen to a locally agitated structure.Received: 12 December 2003, Published online: 24 August 2004PACS: 82.70.-y Disperse systems; complex fluids - 47.20.-k Hydrodynamic stability - 47.55.Dz Drops and bubbles     

White-light nanosource with directional emission

We report the first observation of white-light emission from femtosecond laser-induced plasma in a water droplet. Such emission is not observed with water in a cell. The microdroplet acts as a lens, focusing the incident light to nanosized regions within itself and directing the emission from these regions primarily back toward the laser source. This focusing increases the intensity so that multiphoton ionization generates plasma and causes it to reach the critical density during the initial part of the pulse, enabling the rest of the pulse to heat the plasma enough to emit in the visible.