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PRINCIPAL PUBLICATION AND AUTHORS
Structure and anisotropic dynamics of stimuli responsive colloidal ellipsoids at the nearest neighbor length scale, A. Pal (a), M. Arif Kamal (a), P. Schurtenberger (a), J. Coll. Interface Sci. 621, 352-359 (2022); https:/doi.org/10.1016/j.jcis.2022.04.063 (a) Division of Physical Chemistry, Department of Chemistry, Lund University (Sweden)
(f) and magnetic field (B) range. As a function of f and B, different self-assembled phases are formed. At high- volume fraction, the system approached a kinetically arrested state. The anisotropic slowdown of long-time diffusion coefficients (Deff(q)) hints towards the formation of an oriented glass. Further, it was found that the concentration corresponding to the kinetic arrest (fg) lies slightly above the isotropic-nematic transition, i.e., within the nematic region. Interestingly, while clear differences are observed for the concentration dependence of collective long-time diffusion along the two principal directions parallel (Deff||(q)) and perpendicular Deff^(q)) to B, the location of the arrest line seems fairly independent of field strength and direction (Figure 45). Although there are reports in the literature pertaining the scaling behaviour of the collective short-time diffusion coefficient with the inverse of the effective structure factor for (an) isotropic systems, this study is the first to report that a similar scaling behaviour also holds good for the collective long-time diffusion coefficient for a stimuli- responsive anisotropic system. Figure 46 demonstrates a representative scenario for a field-induced nematic phase for colloidal ellipsoids.
Until recently, an endeavour to measure the anisotropic dynamics at the nearest-neighbour length scale of stimuli- responsive colloidal particles at high concentrations, where several (field-induced) transitions into liquid crystalline phases are observed, would have been perceived as extremely challenging. This stems not only from a lack of available suitable model systems but also from the limitations inherent in the traditional experimental tools such as DLS or confocal microscopy used for such a task. This study now demonstrates that hematite-based colloids are ideal model systems to characterise the influence of shape and interaction anisotropy on various structural and dynamic properties of systems that have undergone classical or field-driven self-assembly into ordered or amorphous structures. When combined with XPCS, this makes it possible to look at anisotropic collective diffusion on nearest-neighbour length scales and, for example, to investigate local structural relaxation and kinetic arrest in these systems despite their high turbidity and optical absorption. This approach opens up new avenues for exploring the stimuli-responsive dynamics of strongly interacting colloidal systems with a large variety of shapes and chemical compositions.
Quick and dirty how antimicrobial peptides impair bacteria
Time-resolved small-angle X-ray scattering was used to resolve the response of E. coli to membrane- active lactoferricins in real time. Impairment of the barrier function of the bacterial cell membranes occurs within a few seconds, but does not as previously thought kill the cells. Instead, a rapid intracellular accumulation of lactoferricins broadly interferes with the physiological functions of bacteria.
Research on new antibiotics is not keeping pace with the growing number of multi-resistant pathogenic bacteria, whose threat was ranked among the first 10 hazards to global health by the World Health Organization. Antimicrobial-peptides (AMPs) are part of the native immune system and their activity is based on generic, massive interactions with one or more cell components, such as their lipid-membrane envelope. Compared to
conventional antibiotics, tailored to interact via specific key-lock mechanisms, bacteria are consequently much less likely to develop any resistance. Yet, details on the mode-of-action of AMPs at the molecular level in cells are still scarce, but are needed to improve the design of novel and effective drugs.
This work focused on the amidated lactoferricin-derivatives LF11-215 (FWRIRIRR), LF11-324 (PFFWRIRIRR) and O-LF11-215 (octanoyl-FWRIRIRR) that were originally classified as membrane-active AMPs, i.e., whose activities rely on the disruption of the bacterial cell-envelope. A combination of time-resolved (ultra) small-angle X-ray scattering (U)SAXS at beamline ID02 and contrast- variation small-angle neutron scattering (SANS) was used to monitor the kinetics of the AMP activity on live E. coli cells from a few tens of milliseconds up to the equilibrated state at one hour after mixing (end-states). Scattering curves were analysed with an analytical model that provided quantitative insight on effects on the internal bacterial structure on multiple scale-lengths,