A new method for the synthesis of imidazolidinone- and benzimidazolone-containing

A novel acid-catalyzed double nucleophilic addition of bisthiols to heterocyclic bisacetals gives sulfur-containing macrocycles in good yield. Crossover experiments revealed that the acid-catalyzed N-acyl iminium cyclization for the imidazolidinones is reversible. The sulfur atom in the bridge was extruded photochemically, giving new [2.2]heterophanes containing the imidazolidinone and benzimidazolone ring systems. The determined crystal structures for representative members in the benzimidazolone series are also reported.     

Multiple internal reflection poly(dimethylsiloxane) systems for optical sensing

Compact poly(dimethylsiloxane)-based (PDMS) multiple internal reflection systems which comprise self-alignment systems, lenses, microfluidic channels and mirrors have been developed for highly sensitive absorbance measurements. With the proper definition of air mirrors at both sides of the sensing region, the optical path of the light from the LED has been meaningfully lengthened without a dramatic increase of the mean flow cell volume. By recursive positioning of such air mirrors, propagating multiple internal reflection (PMIR) systems have been designed, simulated and characterized. Experimental results confirm the ray-tracing predictions and allow the determining that there are some regions of the mean flow cell volume that do not contribute to the increase of the sensitivity. The tailoring of the sensing region, following the optical path, results in a similar limit of detection (110 nM) for fluorescein diluted in phosphate buffer. Finally, a ring configuration, labelled RMIR, has also been developed. With the addition of a third air mirror, the LOD can be decreased to 41 nM with the additional advantage of a substantial decrease of the length of the sensing region. These results confirm the validity of the proposed systems for high sensitivity measurements.     

Numerical calculation of marangoni convection in a rectangular open boat

Numerical calculations of the flow caused by thermocapillary forces at the free surface in NaNO₃ and Si melts in an open boat geometry have been carried out. The results agree well with measured flow velocities in model experiments for crystal growth configurations with NaNO₃ melts. For Si melts a transition to a more complicated multiple eddy flow occurs. The projection-iteration method used for the calculations is much more effective than the finite difference methods applied until now and is especially advantageous for more complicated flow patterns.