Collisions and coalescence in droplet streams for the production of freeze-dried powders.

Streams of mono-disperse micro-droplets with diameters ranging from about 20 μm to 100 μm were produced from diluted aqueous solutions containing carbohydrates and proteins using a pinhole type piezoelectric generator with either a 20 μm or a 50 μm single-orifice diaphragm. Image sequences indicating droplet size, velocity, inter-droplet spacing at various distances from the nozzles as well as collision events and coalescence were recorded using a high-speed camera and analysed quantitatively. The size-dependent gradual deceleration of the droplets is superimposed by small scale random movements, which equally affect both large and small droplets and lead to early contacts and coalescence.

Collisions in fast droplet streams for the production of spherolyophilisates.

Standard spray freeze drying usually leads to highly polydisperse particles, while a fast jet method allows for the preparation of lyophilisates with low polydispersity which is beneficial for a homogeneous drying process. Droplets of a monodisperse stream generated by Rayleigh disintegration of a fast liquid jet exiting from a piezoelectric dispenser are apparently subject to uncontrolled collisions. The process has been visualized by high-speed stroboscopic imaging, laser diffraction spectroscopy and image analysis of the footprint on a target moving at constant velocity across the spray plume.

Molecular recognition of N-acetylneuraminic acid by acyclic pyridinium- and quinolinium-based receptors in aqueous media: recognition through combination of cationic and neutral recognition sites.

Compounds 5b-8b and 10b, and 11b, containing a triethylbenzene scaffold substituted with both neutral and cationic recognition sites, were shown to be effective receptors for N-acetylneuraminic acid (NeuAc), the most common occurring sialic acid, in highly competitive solvents. These compounds were established to be more powerful receptors for NeuAc than the symmetrical pyridinium- and quinolinium-based compounds 9b and 12b in aqueous media. As in natural protein-sialic acid complexes, the combination of neutral/charge-reinforced hydrogen bonds, ion pairs, CH-π, and van der Waals interactions seems to be responsible for the effective binding of this naturally widespread anionic carbohydrate in aqueous media.

Highly effective acyclic carbohydrate receptors consisting of aminopyridine, imidazole, and indole recognition units.

Neutral imidazole/aminopyridine- and indole/aminopyridine-based receptors, 1 and 2, have been established as highly effective and selective carbohydrate receptors. These receptors effectively recognise neutral carbohydrates through multiple interactions, including neutral hydrogen bonds and CH..

Crown ethers as building blocks for carbohydrate receptors.

Acyclic receptors containing neutral hydrogen bonding sites, such as amino-pyridine groups and a crown unit, perform effective recognition of neutral sugar molecules through multiple interactions. Receptor 1 has been shown to be a particularly effective and highly selective receptor for beta-glucopyranoside.

CH-stretching overtone spectra of cis- and trans-1,3-pentadiene.

The room-temperature vapor-phase overtone spectra of cis- and trans-1,3-pentadiene (piperylene) have been recorded in the 5000-17500 cm(-1) region with the use of conventional and intracavity laser photoacoustic spectroscopy. The presence of five nonequivalent olefinic CH bonds and one methyl group in each molecule complicates assignment of the spectra. We have used a harmonically coupled anharmonic oscillator local mode model with one oscillator for each of the nonequivalent CH bonds to calculate the CH-stretching overtone spectra and thus facilitate assignment of the spectra.