2022, Cölfen, Helmut, Xu, Xufeng

Ultracentrifugation is a commonly used method for separation scientists due to easy and scalable working procedures. Analytical ultracentrifugation (AUC) is in particular a versatile method to precisely characterize sedimentation rates of all types of samples, ranging from colloids to biological entities. By providing accurate sedimentation coefficient distributions for measuring samples, conventional trial-and-error determination of appropriate centrifugation speed and time of separation processes can be avoided. Thus, the application of AUC in particle separation may realize tailor-made separation protocols for different types of particle systems. In this chapter, the basics of AUC will be introduced first. After that, two main experiments for particle separation, including sedimentation velocity and density gradient methods, will be described with recent examples of applications. Finally, the pros and cons of this method will be discussed.

2017-06-16, Cölfen, Helmut

2016, Karabudak, Engin, Cölfen, Helmut

The multiwavelength (MWL) detector is a new type of absorption detector for AUC. The commercial absorption detector of the Beckman Coulter XLA AUC can only handle a single wavelength per scan with the possibility to scan at maximum 3 wavelengths, whereas MWL-AUC can handle all the wavelengths in the UV/Vis region at one time. The result is impressive since now a full spectral dimension is added to each single scan. In this chapter, we are explaining development history, instrumentation, and future perspective of MWL-AUC.

2014, Seto, Jong, Rao, Ashit, Cölfen, Helmut

Biological materials are complex organic–inorganic hybrid materials having characteristic superior functional properties. Most spectacular is the ability for these materials to undergo the processes of growth, development, and regeneration directed by an external stimulus. And in many of these materials, a diversity of structural organizations from the nanometer to the millimeter length scales can be found to create a hierarchically nanostructured bulk material. Complexity is an understatement to describe the structure and function of these biological materials. We attempt to fully understand the superior performances of these biological materials here by drawing attention to the assembly and construction schemes of these nanostructured materials found in nature.

2020-09-30, Brunner, Julian, Cölfen, Helmut

In this book chapter, we briefly summarize progress in nonclassical crystallization and mesocrystal formation. We discuss the classification of mesocrystals by means of recent examples. Building upon this, we comment on the progress of mesocrystal fabrication methods and their usefulness for materials design and further applications.

2017, Rao, Ashit, Cölfen, Helmut

Morphology is a critical aspect determining the physical behavior of crystals especially at small-length scales. Insights into the fundamental aspects of nucleation and particle growth enable tuning of crystals with respect to shape, size, crystallography, and composition. With a brief introduction on recent developments concerning nucleation and crystal growth, this article presents diverse methods for nanoparticle synthesis and highlights the individual roles of additives, solvents, templates, surfactants, and seeds. Each route is exemplified with interesting examples that facilitate a lucid understanding of underlying methods.

2015, Gorbet, Gary E., Pearson, Joseph, Demeler, Aysha K., Cölfen, Helmut, Demeler, Borries

We describe important advances in methodologies for the analysis of multiwavelength data. In contrast to the Beckman-Coulter XL-A/I ultraviolet-visible light detector, multiwavelength detection is able to simultaneously collect sedimentation data for a large wavelength range in a single experiment. The additional dimension increases the data density by orders of magnitude, posing new challenges for data analysis and management. The additional data not only improve the statistics of the measurement but also provide new information for spectral characterization, which complements the hydrodynamic information. New data analysis and management approaches were integrated into the UltraScan software to address these challenges. In this chapter, we describe the enhancements and benefits realized by multiwavelength analysis and compare the results to those obtained from the traditional single-wavelength detector. We illustrate the advances offered by the new instruments by comparing results from mixtures that contain different ratios of protein and DNA samples, representing analytes with distinct spectral and hydrodynamic properties. For the first time, we demonstrate that the spectral dimension not only adds valuable detail, but when spectral properties are known, individual components with distinct spectral properties measured in a mixture by the multiwavelength system can be clearly separated and decomposed into traditional datasets for each of the spectrally distinct components, even when their sedimentation coefficients are virtually identical.

2018, Debus, Christian, Siglreitmeier, Maria, Cölfen, Helmut

The question investigated in this chapter is: Can a material obtain the advantageous material properties of multiple biominerals, when the structural elements in each model biomineral, which are responsible for these properties, are combined into one new bioinspired material? Drawing inspiration from the natural biominerals nacre, chiton teeth, and bacterial magnetosomes, a model material, containing a magnetite-gelatin composite, filling a layered scaffold extracted from natural nacre, can be synthesized. The biopolymer gelatin has a distinct influence on the size and shape of magnetite mineralized at ambient conditions. In the gel state, gelatin can be mineralized to form superpara- and ferrimagnetic gels with tunable particle size. The ferrogel synthesis can also be transferred into demineralized nacre scaffolds, yielding layered hybrid composites. Besides more common analytical methods, SANS is used to investigate the structure of organic and inorganic phases individually, and molecular simulations following the Kawska-Zahn approach are employed to gain insight into the earliest stages of nucleation.

2017, Rao, Ashit, Cölfen, Helmut

With the expanding knowledge on structure–property relations in biogenic minerals, an emerging challenge is to decipher the underlying biochemical and physical mechanisms of material formation. For this purpose, the dependence of spatial properties of minerals including composition, structure, and orientation on dynamic processes such as the transport of mineral precursors as well as the nucleation and growth of particles requires elucidation. The aim of this chapter is to provide an overview of biomineralization processes in light of the nonclassical pathways of nucleation and crystallization. We address the mechanistic emergence of mesocrystallinity among diverse biomineral architectures as well as the associated checkpoints regulating particle nucleation, growth, and assembly.

2015, Pearson, Joseph, Krause, Frank, Haffke, Dirk, Demeler, Borries, Schilling, Kristian, Cölfen, Helmut

We describe important advances in analytical ultracentrifugation (AUC) hardware, which add new information to the hydrodynamic information observed in traditional AUC instruments. In contrast to the Beckman-Coulter XLA UV/visible detector, multiwavelength (MWL) detection is able to collect sedimentation data not just for one wavelength, but for a large wavelength range in a single experiment. The additional dimension increases the data density by orders of magnitude, significantly improving the statistics of the measurement and adding important information to the experiment since an additional dimension of spectral characterization is now available to complement the hydrodynamic information. The new detector avoids tedious repeats of experiments at different wavelengths and opens up new avenues for the solution-based investigation of complex mixtures. In this chapter, we describe the capabilities, characteristics, and applications of the new detector design with biopolymers as the focus of study. We show data from two different MWL detectors and discuss strengths and weaknesses of differences in the hardware and different data acquisition modes. Also, difficulties with fiber optic applications in the UV are discussed. Data quality is compared across platforms.