Influence of Melanin Characteristics on Drug Binding Properties.

Melanins are biopolymers encompassing a high degree of chemical heterogeneity. Binding of small-molecule drugs to ocular melanin significantly affects the ocular pharmacokinetics, and could serve as a strategy for prolonged drug retention in the eye. The influence of the structural and physical characteristics of melanins originating from different sources on their drug binding properties has not yet been methodically investigated. We performed physical characterization of Sepia officinalis, synthetic and porcine melanin. The particle size distribution was analyzed by laser diffractometry. A dynamic vapor sorption method, requiring small amounts of the material, was developed to analyze the differences in the specific surface area of the melanins. The extent of melanin binding at equilibrium was determined for a set of 34 small-molecule drugs and compared across different melanin types. Despite systematic shifts in the extent of binding within a twofold range, binding data were highly correlated across the melanins. These moderate differences in binding could not be directly explained by the substantial differences in particle size and were more in line with the relatively similar specific surface area of these different melanin materials. Overall, these results suggest that the specific surface area reflects the actual accessibility of a small molecule in the melanin structure and could serve as a surrogate to explain the binding differences observed for the respective melanin materials.

Time domain NMR as a new process monitoring method for characterization of pharmaceutical hydrates.

Hydrates are of great pharmaceutical relevance and even though they have been characterized thoroughly by various analytical techniques, there is barely literature available on molecular mobility of the hydrate water studied by NMR relaxation in the time domain. The aim of this work was to examine the possibility of differentiating hydration states of drugs by 1H time domain NMR (TD-NMR) regarding spin-spin and spin-lattice relaxation times (T2 and T1) using benchtop equipment. Caffeine and theophylline were selected as model compounds and binary mixtures of hydrate to anhydrate were analyzed for each drug using a spin echo and inversion recovery pulse sequence. It was possible to extract a signal that was specific for the water in the hydrates so that differentiation from anhydrous solid forms was enabled. Excellent calibrations were obtained for quantitative analysis of hydrate/anhydrate mixtures and predicted water contents were in good agreement with water amounts determined in desiccator sorption experiments. TD-NMR was therefore found to be a suitable new technique to characterize pharmaceutical hydrates in a non-invasive and hence sample-sparing manner. Quantification of the hydrate content in pharmaceutical mixtures appears highly attractive for product development and process monitoring. TD-NMR provides here a valuable and complementary technique to established process analytics, such as for example Raman spectroscopy.

The influence of the modality of telecooperation on performance and workload.

Current industrial processes often involve the collaboration of people at distant and remote locations. The technological media for such a tele-cooperation reach from simple email or text-based chatting systems to highly-sophisticated systems for an interactive video-conferencing. But with limited bandwidth the communication between persons at distant locations is often restricted to single modalities. Although this may still be suitable for some tasks, it may result into serious shortcomings and decreased performance with complex tasks like cooperative assembly or maintenance. This is because restricted communication reduces the availability of a common ground, i.e. sharing a common understanding of knowledge, opinions, and goals. The study presented in this paper examines the effect of different communication media on performance of a collaborative assembly task. The results show that tele-cooperation leads to additional verbal communication (AM(direct)=71.1s; AM(video)=145.6s; AM(audio)=204.7s) and, thus, longer times to complete the task (AM (direct)=45.95 min; AM (video)= 50.2 min; am AM(audio)=56.16 min). The percentage of relative speech duration also increases significantly. Workload measurement with NASA-TLX did not show any significant differences between cooperation modes. The results allow estimating the effect of reduced communication modalities on time to complete an assembly task. This facilitates a quantification of temporal requirements in time-critical maintenance and repair tasks.

Structure elucidation of polyheptazine imide by electron diffraction--a templated 2D carbon nitride network.

Structure elucidation of a condensed carbon(IV) nitride with a stoichiometry close to C3N4 by electron diffraction reveals a two-dimensional planar heptazine-based network containing isolated melamine molecules in the trigonal voids.

Single nanocrystals of platinum prepared by partial dissolution of Au-Pt nanoalloys.

Small metal nanoparticles that are also highly crystalline have the potential for showing enhanced catalytic activity. We describe the preparation of single nanocrystals of platinum that are 2 to 3 nanometers in diameter. These particles were generated and immobilized on spherical polyelectrolyte brushes consisting of a polystyrene core (diameter of approximately 100 nanometers) onto which long chains of a cationic polyelectrolyte were affixed. In a first step, a nanoalloy of gold and platinum (a solid solution) was generated within the layer of cationic polyelectrolyte chains. In a second step, the gold was slowly and selectively dissolved by cyanide ions in the presence of oxygen. Cryogenic transmission electron microscopy, wide-angle x-ray scattering, and high-resolution transmission electron microscopy showed that the resulting platinum nanoparticles are faceted single crystals that remain embedded in the polyelectrolyte-chain layer. The composite systems of the core particles and the platinum single nanocrystals exhibit an excellent colloidal stability, as well as high catalytic activity in hydrogenation reactions in the aqueous phase.