Self-assembly of cyclic peptide monolayers by hydrophobic supramolecular hinges.

Supramolecular polymerisation of two-dimensional (2D) materials requires monomers with non-covalent binding motifs that can control the directionality of both dimensions of growth. A tug of war between these propagation forces can bias polymerisation in either direction, ultimately determining the structure and properties of the final 2D ensemble. Deconvolution of the assembly dynamics of 2D supramolecular systems has been widely overlooked, making monomer design largely empirical. It is thus key to define new design principles for suitable monomers that allow the control of the direction and the dynamics of two-dimensional self-assembled architectures. Here, we investigate the sequential assembly mechanism of new monolayer architectures of cyclic peptide nanotubes by computational simulations and synthesised peptide sequences with selected mutations. Rationally designed cyclic peptide scaffolds are shown to undergo hierarchical self-assembly and afford monolayers of supramolecular nanotubes. The particular geometry, the rigidity and the planar conformation of cyclic peptides of alternating chirality allow the orthogonal orientation of hydrophobic domains that define lateral supramolecular contacts, and ultimately direct the propagation of the monolayers of peptide nanotubes. A flexible 'tryptophan hinge' at the hydrophobic interface was found to allow lateral dynamic interactions between cyclic peptides and thus maintain the stability of the tubular monolayer structure. These results unfold the potential of cyclic peptide scaffolds for the rational design of supramolecular polymerisation processes and hierarchical self-assembly across the different dimensions of space.

Next-generation MRI scanner designed for ultra-high-resolution human brain imaging at 7 Tesla.

To increase granularity in human neuroimaging science, we designed and built a next-generation 7 Tesla magnetic resonance imaging scanner to reach ultra-high resolution by implementing several advances in hardware. To improve spatial encoding and increase the image signal-to-noise ratio, we developed a head-only asymmetric gradient coil (200 mT m-1, 900 T m-1s-1) with an additional third layer of windings. We integrated a 128-channel receiver system with 64- and 96-channel receiver coil arrays to boost signal in the cerebral cortex while reducing g-factor noise to enable higher accelerations. A 16-channel transmit system reduced power deposition and improved image uniformity. The scanner routinely performs functional imaging studies at 0.35-0.45 mm isotropic spatial resolution to reveal cortical layer functional activity, achieves high angular resolution in diffusion imaging and reduces acquisition time for both functional and structural imaging.

Bottom-up supramolecular assembly in two dimensions.

The self-assembly of molecules in two dimensions (2D) is gathering attention from all disciplines across the chemical sciences. Attracted by the interesting properties of two-dimensional inorganic analogues, monomers of different chemical natures are being explored for the assembly of dynamic 2D systems. Although many important discoveries have been already achieved, great challenges are still to be addressed in this field. Hierarchical multicomponent assembly, directional non-covalent growth and internal structural control are a just a few of the examples that will be discussed in this perspective about the exciting present and the bright future of two-dimensional supramolecular assemblies.

A bacterial endosymbiont of the fungus Rhizopus microsporus drives phagocyte evasion and opportunistic virulence.

Opportunistic infections by environmental fungi are a growing clinical problem, driven by an increasing population of people with immunocompromising conditions. Spores of the Mucorales order are ubiquitous in the environment but can also cause acute invasive infections in humans through germination and evasion of the mammalian host immune system. How they achieve this and the evolutionary drivers underlying the acquisition of virulence mechanisms are poorly understood. Here, we show that a clinical isolate of Rhizopus microsporus contains a Ralstonia pickettii bacterial endosymbiont required for virulence in both zebrafish and mice and that this endosymbiosis enables the secretion of factors that potently suppress growth of the soil amoeba Dictyostelium discoideum, as well as their ability to engulf and kill other microbes. As amoebas are natural environmental predators of both bacteria and fungi, we propose that this tri-kingdom interaction contributes to establishing endosymbiosis and the acquisition of anti-phagocyte activity. Importantly, we show that this activity also protects fungal spores from phagocytosis and clearance by human macrophages, and endosymbiont removal renders the fungal spores avirulent in vivo. Together, these findings describe a new role for a bacterial endosymbiont in Rhizopus microsporus pathogenesis in animals and suggest a mechanism of virulence acquisition through environmental interactions with amoebas.

Cyclization and Self-Assembly of Cyclic Peptides.

Cyclic peptides are a fascinating class of molecules that can be programmed to fold or self-assemble into diverse mono- and multidimensional structures with potential applications in biomedicine, nanoelectronics, or catalysis. Herein we describe on-resin procedures to carry out head-to-tail peptide cyclization based on orthogonal protected linear structures. We also present essential characterization tools for obtaining dynamic and structural information, including the visualization cyclic peptide assembly into nanotubes (AFM, TEM) as well as the use of fluorescence microscopy.

Supramolecular fibrillation of peptide amphiphiles induces environmental responses in aqueous droplets.

One-dimensional (1D) supramolecular polymers are commonly found in natural and synthetic systems to prompt functional responses that capitalise on hierarchical molecular ordering. Despite amphiphilic self-assembly being significantly studied in the context of aqueous encapsulation and autopoiesis, very little is currently known about the physico-chemical consequences and functional role of 1D supramolecular polymerisation confined in aqueous compartments. Here, we describe the different phenomena that resulted from the chemically triggered supramolecular fibrillation of synthetic peptide amphiphiles inside water microdroplets. The confined connection of suitable dormant precursors triggered a physically autocatalysed chemical reaction that resulted in functional environmental responses such as molecular uptake, fusion and chemical exchange. These results demonstrate the potential of minimalistic 1D supramolecular polymerisation to modulate the behaviour of individual aqueous entities with their environment and within communities.

Sequence Decoding of 1D to 2D Self-Assembling Cyclic Peptides.

The inherent ability of peptides to self-assemble with directional and rationally predictable interactions has fostered a plethora of synthetic two-dimensional (2D) supramolecular biomaterials. However, the design of peptides with hierarchical assembly in different dimensions across mesoscopic lengths remains a challenging task. We here describe the structural exploration of a d/l-alternating cyclic octapeptide capable of assembling one-dimensional (1D) nanotubes in water, which subsequently pack laterally to form giant 2D nanosheets up to 500 µm long with a constant 3.2 nm thickness. Specific amino acid mutations allowed the mapping of structure-assembly relationships that determine 2D self-assembly. Nine peptide modifications were studied, revealing key features in the peptide sequence that nanosheets tolerated, while a total of three peptide variants included modifications that compromised their 2D arrangement. These lessons will serve as guide and inspiration for new 2D supramolecular peptide designs.

1D to 2D Self Assembly of Cyclic Peptides.

Despite recent developments in two-dimensional self-assembly, most supramolecular 2D materials are assembled by tedious methodologies, with complex surface chemistry and small sizes. We here report d/l-alternating cyclic peptides that undergo one-dimensional self-assembly into amphiphilic nanotubes, which subsequently arrange as tubular bilayers to form giant nanosheets in the mesoscale. Reversible transitions between the assembled, dispersed, and aggregated states of these nanosheets can be triggered by external stimuli. The characteristic flexibility, defined chemical topology, and length scale of these nanosheets set a clear distinction between this new supramolecular architecture and previously reported 2D nanostructures. The sequential 1D-to-2D self-assembly of peptides described here provides a conceptually new approach to achieve two-dimensional materials with hierarchical organization. These giant nanosheets represent one of the largest 2D supramolecular materials ever made, with potential application as long-range molecular transporters, responsive surfaces, and (bio)sensors.

Self-assembled micro-fibres by oxime connection of linear peptide amphiphiles.

Linear peptide amphiphiles are excellent biocompatible scaffolds for the hierarchical self-assembly of one-dimensional nano-structures in aqueous media. However, their structural exploration and screening of self-assembling properties are often limited by time-consuming synthesis and purification steps. We here describe the application of an oxime bond as a powerful synthetic tool towards the conjugation of peptide heads bearing a hydroxylamine group with hydrophobic aldehyde tails. This methodology allowed the quick preparation of a small library of oxime-connected peptide amphiphiles, whose supramolecular screening revealed nano-to-micro-fibrillation with dependency on their chemical structure. These results demonstrate the simplicity and the synthetic potential of the oxime conjugation for the preparation of peptide amphiphiles with improved self-assembling capabilities.

Correction: Engineering microbial physiology with synthetic polymers: cationic polymers induce biofilm formation in Vibrio cholerae and downregulate the expression of virulence genes.

[This corrects the article DOI: 10.1039/C7SC00615B.].

Architectural Effects of Star-Shaped "Structurally Nanoengineered Antimicrobial Peptide Polymers" (SNAPPs) on Their Biological Activity.

In this work, the effect of two key structural parameters, number of arms and arm length, of star-shaped "structurally nanoengineered antimicrobial peptide polymers" (SNAPPs) on their antimicrobial activity and biocompatibility, is investigated. A library of star-shaped SNAPPs is prepared, containing varying arm numbers and arm lengths. Antimicrobial assays are then performed to assess the capacity of the SNAPPs to disrupt the membrane, inhibit the growth, and kill pathogenic bacteria. A major finding of the study is that increasing arm number and length of SNAPPs enhanced antimicrobial activity, which can be respectively attributed to the higher local concentrations of polypeptide arms and increased α-helical content. SNAPP architecture is shown to affect the bacteria membrane state and therefore mechanism of killing. Two more potent structures with up to twice the antimicrobial activity of the previously reported SNAPP are discovered in this process. Toxicities of the SNAPPs also increase with arm number and arm length, however therapeutic index calculations identified a 16-arm SNAPP and an easier to prepare 4-arm SNAPP as the best therapeutic agents. The biocompatibility of the SNAPP with the best biological activity is also evaluated in vivo, showing no markers of systemic damage in mice.

Structural Determinants of the Stability of Enzyme-Responsive Polyion Complex Nanoparticles Targeting Pseudomonas aeruginosa's Elastase.

Here, we report how the stability of polyion complex (PIC) particles containing Pseudomonas aeruginosa's elastase (LasB) degradable peptides and antimicrobial poly(ethylene imine) is significantly improved by careful design of the peptide component. Three LasB-degradable peptides are reported herein, all of them carrying the LasB-degradable sequence -GLA- and for which the number of anionic amino acids and cysteine units per peptide were systematically varied. Our results suggest that while net charge and potential to cross-link via disulfide bond formation do not have a predictable effect on the ability of LasB to degrade these peptides, a significant effect of these two parameters on particle preparation and stability is observed. A range of techniques has been used to characterize these new materials and demonstrates that increasing the charge and cross-linking potential of the peptides results in PIC particles with better stability in physiological conditions and upon storage. These results highlight the importance of molecular design for the preparation of PIC particles and should underpin the future development of these materials for responsive drug delivery.

Engineering microbial physiology with synthetic polymers: cationic polymers induce biofilm formation in Vibrio cholerae and downregulate the expression of virulence genes.

Here we report the first application of non-bactericidal synthetic polymers to modulate the physiology of a bacterial pathogen. Poly(N-[3-(dimethylamino)propyl] methacrylamide) (P1) and poly(N-(3-aminopropyl)methacrylamide) (P2), cationic polymers that bind to the surface of V. cholerae, the infectious agent causing cholera disease, can sequester the pathogen into clusters. Upon clustering, V. cholerae transitions to a sessile lifestyle, characterised by increased biofilm production and the repression of key virulence factors such as the cholera toxin (CTX). Moreover, clustering the pathogen results in the minimisation of adherence and toxicity to intestinal epithelial cells. Our results suggest that the reduction in toxicity is associated with the reduction to the number of free bacteria, but also the downregulation of toxin production. Finally we demonstrate that these polymers can reduce colonisation of zebrafish larvae upon ingestion of water contaminated with V. cholerae. Overall, our results suggest that the physiology of this pathogen can be modulated without the need to genetically manipulate the microorganism and that this modulation is an off-target effect that results from the intrinsic ability of the pathogen to sense and adapt to its environment. We believe these findings pave the way towards a better understanding of the interactions between pathogenic bacteria and polymeric materials and will underpin the development of novel antimicrobial polymers.

Polymyxin B containing polyion complex (PIC) nanoparticles: Improving the antimicrobial activity by tailoring the degree of polymerisation of the inert component.

Here, we describe the preparation and characterisation of polyion complex (PIC) nanoparticles containing last resort antimicrobial polymyxin B (Pol-B). PIC nanoparticles were prepared with poly(styrene sulphonate) (PSS) as an inert component, across a range of degrees of polymerisation to evaluate the effect that multivalency of this electrolyte has on the stability and antimicrobial activity of these nanoparticles. Our results demonstrate that while nanoparticles prepared with longer polyelectrolytes are more stable under simulated physiological conditions, those prepared with shorter polyelectrolytes have a higher antimicrobial activity. Tailoring the degree of polymerisation and the ratio of the components we have been able to identify a formulation that shows a sustained inhibitory effect on the growth of P. aeruginosa and can reduce the number of viable colonies of this pathogen over 10,000 times more effectively than our previously reported formulation.

Preparation and antimicrobial evaluation of polyion complex (PIC) nanoparticles loaded with polymyxin B.

Here, we describe novel polyion complex (PIC) particles for the delivery of Polymyxin B (Pol-B), an antimicrobial peptide currently used in the clinic as a last resort antibiotic against multidrug-resistant gram-negative bacteria. A range of conditions for the controlled assembly of Pol-B with poly(styrene sulphonate) (PSS) has been identified which let us prepare stable colloidal PIC particles. This way, PIC particles containing different Pol-B:PSS ratios have been prepared and their stability under simulated physiological conditions (i.e. pH, osmotic pressure and temperature) characterised. Furthermore, preliminary evaluation of the antimicrobial activity of these Pol-B containing PIC particles has been performed, by monitoring their effect on the growth of Pseudomonas aeruginosa, an opportunistic gram-negative bacterium.

Polyion complex (PIC) particles: Preparation and biomedical applications.

Oppositely charged polyions can self-assemble in solution to form colloidal polyion complex (PIC) particles. Such nanomaterials can be loaded with charged therapeutics such as DNA, drugs or probes for application as novel nanomedicines and chemical sensors to detect disease markers. A comprehensive discussion of the factors affecting PIC particle self-assembly and their response to physical and chemical stimuli in solution is described herein. Finally, a collection of key examples of polyionic nanoparticles for biomedical applications is discussed to illustrate their behaviour and demonstrate the potential of PIC nanoparticles in medicine.

Enzyme-responsive polyion complex (PIC) nanoparticles for the targeted delivery of antimicrobial polymers.

Here we present new enzyme-responsive polyion complex (PIC) nanoparticles prepared from antimicrobial poly(ethylene imine) and an anionic enzyme-responsive peptide targeting Pseudomonas aeruginosa's elastase. The synthetic conditions used to prepare these nanomaterials allowed us to optimise particle size and charge, and their stability under physiological conditions. We demonstrate that these enzyme responsive PIC nanoparticles are selectively degraded in the presence of P. aeruginosa elastase without being affected by other endogenous elastases. This enzyme-responsive PIC particle can exert an elastase-specific antimicrobial effect against P. aeruginosa without affecting non-pathogenic strains of these bacteria. These targeted enzyme-responsive PIC nanoparticles constitute a novel platform for the delivery of antimicrobial peptides and polymers, and can be a powerful tool in the current race against antimicrobial resistance.

Fundamentals, achievements and challenges in the electrochemical sensing of pathogens.

Electrochemical sensors are powerful tools widely used in industrial, environmental and medical applications. The versatility of electrochemical methods allows for the investigation of chemical composition in real time and in situ. Electrochemical detection of specific biological molecules is a powerful means for detecting disease-related markers. In the last 10 years, highly-sensitive and specific methods have been developed to detect waterborne and foodborne pathogens. In this review, we classify the different electrochemical techniques used for the qualitative and quantitative detection of pathogens. The robustness of electrochemical methods allows for accurate detection even in heterogeneous and impure samples. We present a fundamental description of the three major electrochemical sensing methods used in the detection of pathogens and the advantages and disadvantages of each of these methods. In each section, we highlight recent breakthroughs, including the utilisation of microfluidics, immunomagnetic separation and multiplexing for the detection of multiple pathogens in a single device. We also include recent studies describing new strategies for the design of future immunosensing systems and protocols. The high sensitivity and selectivity, together with the portability and the cost-effectiveness of the instrumentation, enhances the demand for further development in the electrochemical detection of microbes.

Synthesis and binding affinity of new 1,4-disubstituted triazoles as potential dopamine D(3) receptor ligands.

A series of new 1,4-disubstituted triazoles was prepared from appropriate arylacetylenes and aminoalkylazides using click chemistry methodology. These compounds were evaluated as potential ligands on several subtypes of dopamine receptors in in vitro competition assays, showing high affinity for dopamine D3 receptors, lower affinity for D2 and D4, and no affinity for the D1 receptors. Compound 18 displayed the highest affinity at the D3 receptor with a Ki value of 2.7 nM, selectivity over D2 (70-fold) and D4 (200-fold), and behaviour as a competitive antagonist in the low nanomolar range.