Discordant Supramolecular Fibres Reversibly Depolymerised by Temperature and Light

Synthetic stimuli responsive supramolecular polymers attract increasing interest for their ability to mimic the unique properties of natural assemblies. Here we focus on the well-studied benzene-1,3,5-tricarboxamide (BTA) motif, and substitute it with two (S)-3,7-dimethyloctyl groups and an azobenzene photoswitch. We demonstrate the UV (λ=365 nm) induced depolymerisation of the helical hydrogen-bonded polymers in methylcyclohexane (MCH) through circular dichroism and UV-vis spectroscopy in dilute solution (15 μm), and NMR and iPAINT super-resolution microscopy in concentrated solution (300 μm). The superstructure can be regenerated after thermal depolymerization, whilst repeated depolymerisation can be reversed without degradation by irradiating at λ=455 nm. Molecular dynamics simulations show that the most energetically favourable configuration for these polymers in MCH is a left-handed helical network of hydrogen-bonds between the BTA cores surrounded by two right-handed helices of azobenzenes. The responsiveness to two orthogonal triggers across a broad concentration range holds promise for use in, for example, photo-responsive gelation

Effect of H-Bonding on Order Amplification in the Growth of a Supramolecular Polymer in Water

While a great deal of knowledge on the roles of hydrogen bonding and hydrophobicity in proteins has resulted in the creation of rationally designed and functional peptidic structures, the roles of these forces on purely synthetic supramolecular architectures in water have proven difficult to ascertain. Focusing on a 1,3,5-benzenetricarboxamide (BTA)-based supramolecular polymer, we have designed a molecular modeling strategy to dissect the energetic contributions involved in the self-assembly (electrostatic, hydrophobic, etc.) upon growth of both ordered BTA stacks and random BTA aggregates. Utilizing this set of simulations, we have unraveled the cooperative mechanism for polymer growth, where a critical size must be reached in the aggregates before emergence and amplification of order into the experimentally observed fibers. Furthermore, we have found that the formation of ordered fibers is favored over disordered aggregates solely on the basis of electrostatic interactions. Detailed analysis of the simulation data suggests that H-bonding is a major source of this stabilization energy. Experimental and computational comparison with a newly synthesized 1,3,5-benzenetricarboxyester (BTE) derivative, lacking the ability to form the H-bonding network, demonstrated that this BTE variant is also capable of fiber formation, albeit at a reduced persistence length. This work provides unambiguous evidence for the key 1D driving force of hydrogen bonding in enhancing the persistency of monomer stacking and amplifying the level of order into the growing supramolecular polymer in water. Our computational approach provides an important relationship directly linking the structure of the monomer to the structure and properties of the supramolecular polymer

International multicenter evaluation of the DiversiLab bacterial typing system for Escherichia coli and Klebsiella spp.

Successful multidrug-resistant clones are increasing in prevalence globally, which makes the ability to identify these clones urgent. However, adequate, easy-to-perform, and reproducible typing methods are lacking. We investigated whether DiversiLab (DL), an automated repetitive-sequence-based PCR bacterial typing system (bioMérieux), is suitable for comparing isolates analyzed at different geographic centers. A total of 39 Escherichia coli and 39 Klebsiella species isolates previously typed by the coordinating center were analyzed. Pulsed-field gel electrophoresis (PFGE) confirmed the presence of one cluster of 6 isolates, three clusters of 3 isolates, and three clusters of 2 isolates for each set of isolates. DL analysis was performed in 11 centers in six different countries using the same protocol. The DL profiles of 425 E. coli and 422 Klebsiella spp. were obtained. The DL system showed a lower discriminatory power for E. coli than did PFGE. The local DL data showed a low concordance, as indicated by the adjusted Rand and Wallace coefficients (0.132 to 0.740 and 0.070 to 1.0 [E. coli] and 0.091 to 0.864 and 0.056 to 1.0 [Klebsiella spp.], respectively). The central analysis showed a significantly improved concordance (0.473 to 1.0 and 0.290 to 1.0 [E. coli] and 0.513 to 0.965 and 0.425 to 1.0 [Klebsiella spp.], respectively). The misclassifications of profiles for individual isolates were mainly due to inconsistent amplification, which was most likely due to variations in the quality and amounts of the isolated DNA used for amplification. Despite local variations, the DL system has the potential to indicate the occurrence of clonal outbreaks in an international setting, provided there is strict adherence to standardized, reproducible DNA isolation methods and analysis protocols, all supported by a central database for profile comparisons

Grafted ionomer complexes and their effect on protein adsorption on silica and polysulfone surfaces

We have studied the formation and the stability of ionomer complexes from grafted copolymers (GICs) in solution and the influence of GIC coatings on the adsorption of the proteins β-lactoglobulin (β-lac), bovine serum albumin (BSA), and lysozyme (Lsz) on silica and polysulfone. The GICs consist of the grafted copolymer PAA28-co-PAPEO22 {poly(acrylic acid)-co-poly[acrylate methoxy poly(ethylene oxide)]} with negatively charged AA and neutral APEO groups, and the positively charged homopolymers: P2MVPI43 [poly(N-methyl 2-vinyl pyridinium iodide)] and PAH∙HCl160 [poly(allylamine hydrochloride)]. In solution, these aggregates are characterized by means of dynamic and static light scattering. They appear to be assemblies with hydrodynamic radii of 8 nm (GIC-PAPEO22/P2MVPI43) and 22 nm (GIC-PAPEO22/PAH∙HCl160), respectively. The GICs partly disintegrate in solution at salt concentrations above 10 mM NaCl. Adsorption of GICs and proteins has been studied with fixed angle optical reflectometry at salt concentrations ranging from 1 to 50 mM NaCl. Adsorption of GICs results in high density PEO side chains on the surface. Higher densities were obtained for GICs consisting of PAH∙HCl160 (1.6 ÷ 1.9 chains/nm2) than of P2MVPI43 (0.6 ÷ 1.5 chains/nm2). Both GIC coatings strongly suppress adsorption of all proteins on silica (>90%); however, reduction of protein adsorption on polysulfone depends on the composition of the coating and the type of protein. We observed a moderate reduction of β-lac and Lsz adsorption (>60%). Adsorption of BSA on the GIC-PAPEO22/P2MVPI43 coating is moderately reduced, but on the GIC-PAPEO22/PAH∙HCl160 coating it is enhanced

Superior verbal memory outcome after stereotactic laser amygdalohippocampotomy

Objective: To evaluate declarative memory outcomes in medically refractory epilepsy patients who underwent either a highly selective laser ablation of the amygdalohippocampal complex or a conventional open temporal lobe resection. Methods: Post-operative change scores were examined for verbal memory outcome in epilepsy patients who underwent stereotactic laser amygdalohippocampotomy (SLAH: n = 40) or open resection procedures (n = 40) using both reliable change index (RCI) scores and a 1-SD change metric. Results: Using RCI scores, patients undergoing open resection (12/40, 30.0%) were more likely to decline on verbal memory than those undergoing SLAH (2/40 [5.0%], p = 0.0064, Fisher's exact test). Patients with language dominant procedures were much more likely to experience a significant verbal memory decline following open resection (9/19 [47.4%]) compared to laser ablation (2/19 [10.5%], p = 0.0293, Fisher's exact test). 1 SD verbal memory decline frequently occurred in the open resection sample of language dominant temporal lobe patients with mesial temporal sclerosis (8/10 [80.0%]), although it rarely occurred in such patients after SLAH (2/14, 14.3%) (p = 0.0027, Fisher's exact test). Memory improvement occurred significantly more frequently following SLAH than after open resection. Interpretation: These findings suggest that while verbal memory function can decline after laser ablation of the amygdalohippocampal complex, it is better preserved when compared to open temporal lobe resection. Our findings also highlight that the dominant hippocampus is not uniquely responsible for verbal memory. While this is at odds with our simple and common heuristic of the hippocampus in memory, it supports the findings of non-human primate studies showing that memory depends on broader medial and lateral TL regions

Quantifying Exocytosis by Combination of Membrane Capacitance Measurements and Total Internal Reflection Fluorescence Microscopy in Chromaffin Cells

Total internal reflection fluorescence microscopy (TIRF-Microscopy) allows the observation of individual secretory vesicles in real-time during exocytosis. In contrast to electrophysiological methods, such as membrane capacitance recording or carbon fiber amperometry, TIRF-Microscopy also enables the observation of vesicles as they reside close to the plasma membrane prior to fusion. However, TIRF-Microscopy is limited to the visualization of vesicles that are located near the membrane attached to the glass coverslip on which the cell grows. This has raised concerns as to whether exocytosis measured with TIRF-Microscopy is comparable to global secretion of the cell measured with membrane capacitance recording. Here we address this concern by combining TIRF-Microscopy and membrane capacitance recording to quantify exocytosis from adrenal chromaffin cells. We found that secretion measured with TIRF-Microscopy is representative of the overall secretion of the cells, thereby validating for the first time the TIRF method as a measure of secretion. Furthermore, the combination of these two techniques provides a new tool for investigating the molecular mechanism of synaptic transmission with combined electrophysiological and imaging techniques

Multicore liquid perfluorocarbon-loaded multimodal nanoparticles for stable ultrasound and ¹⁹ F MRI applied to in vivo cell tracking

Ultrasound is the most commonly used clinical imaging modality. However, in applications requiring cell-labeling, the large size and short active lifetime of ultrasound contrast agents limit their longitudinal use. Here, 100 nm radius, clinically applicable, polymeric nanoparticles containing a liquid perfluorocarbon, which enhance ultrasound contrast during repeated ultrasound imaging over the course of at least 48 h, are described. The perfluorocarbon enables monitoring the nanoparticles with quantitative 19 F magnetic resonance imaging, making these particles effective multimodal imaging agents. Unlike typical core–shell perfluorocarbon-based ultrasound contrast agents, these nanoparticles have an atypical fractal internal structure. The nonvaporizing highly hydrophobic perfluorocarbon forms multiple cores within the polymeric matrix and is, surprisingly, hydrated with water, as determined from small-angle neutron scattering and nuclear magnetic resonance spectroscopy. Finally, the nanoparticles are used to image therapeutic dendritic cells with ultrasound in vivo, as well as with 19 F MRI and fluorescence imaging, demonstrating their potential for long-term in vivo multimodal imaging. </p

Docking of Secretory Vesicles Is Syntaxin Dependent

Secretory vesicles dock at the plasma membrane before they undergo fusion. Molecular docking mechanisms are poorly defined but believed to be independent of SNARE proteins. Here, we challenged this hypothesis by acute deletion of the target SNARE, syntaxin, in vertebrate neurons and neuroendocrine cells. Deletion resulted in fusion arrest in both systems. No docking defects were observed in synapses, in line with previous observations. However, a drastic reduction in morphologically docked secretory vesicles was observed in chromaffin cells. Syntaxin-deficient chromaffin cells showed a small reduction in total and plasma membrane staining for the docking factor Munc18-1, which appears insufficient to explain the drastic reduction in docking. The sub-membrane cortical actin network was unaffected by syntaxin deletion. These observations expose a docking role for syntaxin in the neuroendocrine system. Additional layers of regulation may have evolved to make syntaxin redundant for docking in highly specialized systems like synaptic active zones