Large molecular aggregates with sizes ranging from subnanometers to microns are ubiquitous. As atmospheric aerosols they influence our climate, in interstellar space they are discussed as reactive sites, and in medicine small particles are considered as promising candidates to achieve a targeted drug delivery. The present contribution is focused on the characterization of the physical-chemical properties of these particles and on their targeted generation. One of the greatest challenges is to understand the properties of these aggregates on a molecular level. The latter point is discussed in detail focussing on the vibrational dynamics of these particles.

A new apparatus for the in situ characterization of the rapid expansion of supercritical solutions ͑RESS͒ by Fourier transform infrared spectroscopy is presented. The infrared characterization is complemented by particle sizing with a scanning mobility particle sizer, by three-wavelengths-extinction measurements, and by scanning electron microscopy. Several examples show that a wide range of information about particle properties can be obtained with this setup. One new aspect is the possibility to expand into the vacuum which also allows us to investigate the conditions in the collision-free region before the Mach disk. These investigations elucidate that in the free jet region the solvent CO 2 condenses to particles with mean radii Ͼ50 nm for pre-expansion pressures between 100-400 bar and temperatures between 298-398 K.

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The cultivation under adverse growth conditions is a commonly used strategy to trigger carotenoid accumulation in microalgae. In order to characterize important factors affecting the biotechnological productivity of a microalgal species systematic and accurate analysis of cellular properties and the physiological response to abiotic stress is required. Therefore, we have investigated the influence of various stress types on a broad spectrum of cellular properties in a dynamic manner. Cellular properties were monitored in stained samples for cell vitality and neutral lipid fluorescence together with intrinsic parameters. The results revealed that nitrogen limitation and oversaturating light induced distinct adaptational responses in the cells. In the presence of nitrogen stress, the homogeneous population distribution splitted into two heterogeneous sub-populations for the cell vitality and neutral lipid fluorescence. Furthermore, we have demonstrated that flow cytometry is able to rapidly detect changes in the cell population upon exposure to abiotic stress. On the basis of