N-heterocyclic germylenes: structural characterisation of some heavy analogues of the ubiquitous N-heterocyclic carbenes

The X-ray crystal structures of three N-heterocyclic germylenes (NHGes) have been elucidated including the previously unknown 1,3-bis(2,6-dimethylphenyl)diazagermol-2-ylidene (1). In addition, the X-ray crystal structures of the previously synthesised 1,3-bis(2,4,6-trimethylphenyl)diazagermol-2-ylidene (2) and 1,3-bis(2,6-diisopropylphenyl)diazagermol-2-ylidene (3) are also reported. The discrete molecular structures of compounds 1 to 3 are comparable, with Ge-N bond lengths in the range 1.835-1.875 Å, while the N-Ge-N bond angles range between 83.6 and 85.2°. Compound 2 was compared to the analogous N-heterocyclic carbene species, 1,3-bis(2,4,6-trimethylphenyl)imidazol-2-ylidene (IMes). The major geometrical difference observed, as expected, was the bond angle around the divalent group 14 atom. The N-Ge-N bond angle was 83.6° for compound 2 versus the N-C-N bond angle of 101.4° for IMes. The Sn equivalent of (1), 1,3-bis(2,6-dimethylphenyl)diazastannol-2-ylidene (4), has also been synthesised and its crystal structure is reported here. In order to test their suitability as ligands, compounds 1 to 3 were reacted with a wide range of transition metal complexes. No NHGes containing metal complexes were observed. In all cases the NHGe either degraded or gave no reaction

Hearing through your eyes: neural basis of audiovisual cross-activation, revealed by transcranial alternating current stimulation

Some people experience auditory sensations when seeing visual flashes or movements. This prevalent synaesthesia-like ‘visual-evoked auditory response’ (vEAR) could result either from over-exuberant cross-activation between brain areas, and/or reduced inhibition of normally-occurring cross-activation. We have used transcranial alternating current stimulation (tACS) to test these theories. We applied tACS at 10Hz (alpha-band frequency) or 40Hz (gamma-band), bilaterally either to temporal or occipital sites, while measuring same/different discrimination of paired auditory (A) versus visual (V) 'Morse code' sequences. At debriefing, participants were classified as vEAR or non-vEAR depending on whether they reported 'hearing' the silent flashes. In non-vEAR participants, temporal 10Hz tACS caused impairment of A performance, which correlated with improved V; conversely under occipital tACS, poorer V performance correlated with improved A. This reciprocal pattern suggests that sensory cortices are normally mutually inhibitory, and that alpha-frequency tACS may bias the balance of competition between them. vEAR participants showed no tACS effects, consistent with reduced inhibition, or enhanced cooperation between modalities. In addition, temporal 40Hz tACS impaired V performance, specifically in individuals who showed a performance advantage for V (relative to A). Gamma-frequency tACS may therefore modulate the ability of these individuals to benefit from recoding flashes into the auditory modality, possibly by disrupting cross-activation of auditory areas by visual stimulation. Our results support both theories, suggesting that vEAR may depend on disinhibition of normally-occurring sensory cross-activation, which may be expressed more strongly in some individuals. Furthermore, endogenous alpha and gamma-frequency oscillations may function respectively to inhibit or promote this cross-activation

Tuneable peptide cross-linked nanogels for enzyme-triggered protein delivery

Many diseases are associated with the dysregulated activity of enzymes, such as matrix metalloproteinases (MMPs). This dysregulation can be leveraged in drug delivery to achieve disease- or site-specific cargo release. Self-assembled polymeric nanoparticles are versatile drug carrier materials due to the accessible diversity of polymer chemistry. However, efficient loading of sensitive cargo, such as proteins, and introducing functional enzyme-responsive behaviour remain challenging. Herein, peptide-crosslinked, temperature-sensitive nanogels for protein delivery were designed to respond to MMP-7, which is overexpressed in many pathologies including cancer and inflammatory diseases. The incorporation of N-cyclopropylacrylamide (NCPAM) into N-isopropylacrylamide (NIPAM)-based copolymers enabled us to tune the polymer lower critical solution temperature from 33 to 44 °C, allowing the encapsulation of protein cargo and nanogel-crosslinking at slightly elevated temperatures. This approach resulted in nanogels that were held together by MMP-sensitive peptides for enzyme-specific protein delivery. We employed a combination of cryogenic transmission electron microscopy (cryo-TEM), dynamic light scattering (DLS), small angle neutron scattering (SANS), and fluorescence correlation spectroscopy (FCS) to precisely decipher the morphology, self-assembly mechanism, enzyme-responsiveness, and model protein loading/release properties of our nanogel platform. Simple variation of the peptide linker sequence and combining multiple different crosslinkers will enable us to adjust our platform to target specific diseases in the future

Preparation and Application of an Inexpensive α‐Formylglycine Building Block Compatible with Fmoc Solid-Phase Peptide Synthesis

α-Formylglycine (fGly) is a rare residue located in the active site of sulfatases and serves as a precursor to pharmaceutically relevant motifs. The installation of fGly motifs into peptides is currently challenging due to degradation under the acidic and nucleophile-rich conditions accompanying resin cleavage during solid-phase peptide synthesis. We report the synthesis of acid- and nucleophile-tolerant α-formylglycine building blocks from vitamin C and use them to prepare callyaerin A, a macrocyclic peptide containing an fGly-derived motif

Insight into ortho-boronoaldehyde conjugation via a FRET-based reporter assay

Ortho-boronoaldehydes react with amine-based nucleophiles with dramatically increased rates and product stabilities, relative to unfunctionalised benzaldehydes, leading to exciting applications across biological and material chemistry. We have developed a novel Förster resonance energy transfer (FRET)-based assay to provide key new insights into the reactivity of these boronoaldehydes, allowing us to track conjugation with unprecedented sensitivity and accuracy under standardised conditions. Our results highlight the key role played by reaction pH, buffer additives, and boronoaldehyde structure in controlling conjugation speed and stability, providing design criteria for further innovations and applications in the field

An Electroactive Oligo-EDOT Platform for Neural Tissue Engineering

The unique electrochemical properties of the conductive polymer poly(3,4-ethylenedioxythiophene):polystyrene sulfonate (PEDOT:PSS) make it an attractive material for use in neural tissue engineering applications. However, inadequate mechanical properties, and difficulties in processing and lack of biodegradability have hindered progress in this field. Here, the functionality of PEDOT:PSS for neural tissue engineering is improved by incorporating 3,4-ethylenedioxythiophene (EDOT) oligomers, synthesized using a novel end-capping strategy, into block co-polymers. By exploiting end-functionalized oligoEDOT constructs as macroinitiators for the polymerization of poly(caprolactone), a block co-polymer is produced that is electroactive, processable, and bio-compatible. By combining these properties, electroactive fibrous mats are produced for neuronal culture via solution electrospinning and melt electrospinning writing. Importantly, it is also shown that neurite length and branching of neural stem cells can be enhanced on the materials under electrical stimulation, demonstrating the promise of these scaffolds for neural tissue engineering

Facet-dependent interactions of islet amyloid polypeptide with gold nanoparticles: implications for fibril formation and peptide-induced lipid membrane disruption

A comprehensive understanding of the mechanisms of interaction between proteins or peptides and nanomaterials is crucial for the development of nanomaterial-based diagnos-tics and therapeutics. In this work, we systematically explored the interactions between citrate-capped gold nanoparticles (AuNPs) and islet amyloid polypeptide (IAPP), a 37-amino acid peptide hormone co-secreted with insulin from the pancreatic islet. We uti-lized diffusion-ordered spectroscopy, isothermal titration calorimetry, localized surface plasmon resonance spectroscopy, gel electrophoresis, atomic force microscopy, transmis-sion electron microscopy (TEM), and molecular dynamics (MD) simulations to systemati-cally elucidate the underlying mechanism of the IAPP−AuNP interactions. Because of the presence of a metal-binding sequence motif in the hydrophilic peptide domain, IAPP strongly interacts with the Au surface in both the monomeric and fibrillar states. Circular dichroism showed that AuNPs triggered the IAPP conformational transition from random coil to ordered structures (α-helix and β-sheet), and TEM imaging suggested the accelera-tion of IAPP fibrillation in the presence of AuNPs. MD simulations revealed that the IAPP−AuNP interactions were initiated by the N-terminal domain (IAPP residues 1−19), which subsequently induced a facet-dependent conformational change in IAPP. On a Au(111) surface, IAPP was unfolded and adsorbed directly onto the Au surface, while for the Au(100) surface, it interacted predominantly with the citrate adlayer and retained some helical conformation. The observed affinity of AuNPs for IAPP was further applied to reduce the level of peptide-induced lipid membrane disruption

Facet-dependent interactions of islet amyloid polypeptide with gold nanoparticles: Implications for fibril formation and peptide-induced lipid membrane disruption

A comprehensive understanding of the mechanisms of interaction between proteins or peptides and nanomaterials is crucial for the development of nanomaterial-based diagnostics and therapeutics. In this work, we systematically explored the interactions between citrate-capped gold nanoparticles (AuNPs) and islet amyloid polypeptide (IAPP), a 37-amino acid peptide hormone co-secreted with insulin from the pancreatic islet. We utilized diffusion-ordered spectroscopy, isothermal titration calorimetry, localized surface plasmon resonance spectroscopy, gel electrophoresis, atomic force microscopy, transmission electron microscopy (TEM), and molecular dynamics (MD) simulations to systematically elucidate the underlying mechanism of the IAPP–AuNP interactions. Because of the presence of a metal-binding sequence motif in the hydrophilic peptide domain, IAPP strongly interacts with the Au surface in both the monomeric and fibrillar states. Circular dichroism showed that AuNPs triggered the IAPP conformational transition from random coil to ordered structures (α-helix and β-sheet), and TEM imaging suggested the acceleration of IAPP fibrillation in the presence of AuNPs. MD simulations revealed that the IAPP–AuNP interactions were initiated by the N-terminal domain (IAPP residues 1–19), which subsequently induced a facet-dependent conformational change in IAPP. On a Au(111) surface, IAPP was unfolded and adsorbed directly onto the Au surface, while for the Au(100) surface, it interacted predominantly with the citrate adlayer and retained some helical conformation. The observed affinity of AuNPs for IAPP was further applied to reduce the level of peptide-induced lipid membrane disruption

Photochemical Methods for Peptide Macrocylization

Photochemical reactions have been the subject of renewed interest over the last two decades, leading to the development of many new diverse and powerful chemical transformations. More recently, these developments have been expanded to enable the photochemical macrocylization of peptides and small proteins. These constructs benefit from increased stability, structural rigidity, and biological potency over their linear counterparts, providing opportunities for improved therapeutic agents. In this review, we provide an overview of both the established and emerging methods for photochemical peptide macrocyclization, highlighting both the limitations and opportunities for further innovation in the field

Nuclear Magnetic Resonance and Metadynamics Simulations Reveal the Atomistic Binding of l -Serine and O-Phospho- l -Serine at Disordered Calcium Phosphate Surfaces of Biocements

Interactions between biomolecules and structurally disordered calcium phosphate (CaP) surfaces are crucial for the regulation of bone mineralization by noncollagenous proteins, the organization of complexes of casein and amorphous calcium phosphate (ACP) in milk, as well as for structure-function relationships of hybrid organic/inorganic interfaces in biomaterials. By a combination of advanced solid-state NMR experiments and metadynamics simulations, we examine the detailed binding of O-phospho-l-serine (Pser) and l-serine (Ser) with ACP in bone-adhesive CaP cements, whose capacity of gluing fractured bone together stems from the close integration of the organic molecules with ACP over a subnanometer scale. The proximity of each carboxy, aliphatic, and amino group of Pser/Ser to the Ca2+ and phosphate species of ACP observed from the metadynamics-derived models agreed well with results from heteronuclear solid-state NMR experiments that are sensitive to the 13C-31P and 15N-31P distances. The inorganic/organic contacts in Pser-doped cements are also contrasted with experimental and modeled data on the Pser binding at nanocrystalline HA particles grown from a Pser-bearing aqueous solution. The molecular adsorption is driven mainly by electrostatic interactions between the negatively charged carboxy/phosphate groups and Ca2+ cations of ACP, along with H bonds to either protonated or nonprotonated inorganic phosphate groups. The Pser and Ser molecules anchor at their phosphate/amino and carboxy/amino moieties, respectively, leading to an extended molecular conformation across the surface, as opposed to an "upright standing"molecule that would result from the binding of one sole functional group