Analytische Chemie
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Molecular self-assembly primarily occurs in solution. To better understand this process, techniques capable of probing the solvated state are consequently required. Smallangle scattering (SAS) has a proven ability to detect and characterize solutions, but it is rarely applied to more complex assembly shapes. Here, small-angle X-ray and neutron scattering are applied to observe toroidal assemblies in solution. Combined analysis confirms that the toroids have a core–shell structure, with a p-conjugated core and an alkyl shell into which solvent penetrates. The dimensions determined by SAS agree well with those obtained by (dried-state) atomic force microscopy. Increasing the number of naphthalene units in the molecular building block yields greater rigidity, as evidenced by a larger toroid and a reduction in solvent penetration into the shell. The detailed structural analysis demonstrates the applicability of SAS to monitor complex solution-based selfassembly.
The communication of experimental results is common to scientific investigation. The method of presentation varies widely across investigation technique, and may stymie fundamental scientific goals such as sharing of results and replication of experiments. Even within a limited community, such as small-angle scattering, the choice of how to organize stored information is fragmented, with the result that often, the data are deposited in ad hoc form.
To increase access to data produced from publicly-funded research, funding agencies are now requiring that proposals describe how data will be made available. With the increases in data volume due to higher-efficiency collection, increased experimental complexity, and larger and faster detectors, the plethora of ad hoc formats is a burden to the scientific community. Reliance on a few, well-considered standards facilitates automated processes for analysis and correlation of scientific data. Furthermore, it leads to development of common tools for data visualization and analysis, and data catalogues for access, reference, and data mining.
The Worldwide Protein Data Bank is such an example where, by the provision of a standardized data format, scientific data and metadata from a vast range of methods has become available for research on the structures of proteins. Guidelines for structural modelling of smallangle scattering data from biomolecules in solution were adopted by the IUCr Commission on Small-Angle Scattering in 2012.
NXcanSAS is a standard to store reduced small-angle scattering data of any dimension. It is sufficiently general that it may be used for any form of reduced SAS data in different scientific applications. The hierarchical structure of the canSAS (http://www.cansas.org) standard has been designed within the NeXus (http://www.nexusformat.org) data format. This presentation will describe the NXcanSAS standard, underlying concepts, and will give some examples.
Ever since increasing a reaction’s yield while shortening the reaction time is the main objective in synthesis optimization. Microwave reactors meet these demands. In literature however their usage is under discussion due to claims of the existence of non-thermal effects resulting from the microwave radiation. Especially for nano-material syntheses it is of crucial importance to be aware of influences on the reaction pathway. Therefore, we compare ultra-small silver nanoparticles with mean radii of 3 nm, synthesized via conventional and microwave heating. We employed a versatile one-pot polyol synthesis of poly(acrylic acid) (PAA) stabilized silver nanoparticles, which display superior catalytic properties. No microwave specific effects in terms of particle size distribution characteristics, as derived by small-angle X-ray scattering (SAXS) and dynamic light scattering (DLS), are revealed. Due to the microwave reactor’s characteristics of a closed system, syntheses can be carried out at temperatures beyond the solvent’s boiling point. Particle formation was accelerated by a factor of 30 by increasing the reaction temperature from 200 °C to 250 °C. The particle growth process follows a cluster coalescence mechanism. A post-synthetic incubation step at 250 °C induces a further growth of the particles while the size distribution broadens. Thus, utilization of microwave reactors enables an enormous decrease of the reaction time as well as the opportunity of tuning the particles’ size. Possibly, decomposition of the stabilizing ligand at elevated temperatures results in reduced yields. A temperature of 250 °C and a corresponding reaction time of 30 s represent a compromise between short reaction times and high yields.
The formation and alignment of gel fibres in alkanes (solvents) was investigated. The gel fibres consist of small amphiphilic molecules containing a C60 molecule and a small ligand chain. Under the right conditions, these self-assemble in core-shell micelles, which themselves pack into micron-sized fibre-like structures. These can be aligned using a strong magnetic field, as investigated using SANS with a 17T superconducting magnet at a range of field strengths.
This poster deals with improvements and characteriztion of small-angle scattering limitations, by looking at the trifecta of Data collection and uncertainty propagation, data analysis methodologies, and real-world tests. It is found that - with appropriate care and instrumentation - accuracies of 1% on mean nanomaterial sizes, and 10% on the size distribution width as well as the volume fraction can be achieved.