As with most things in life, "seeing is believing" is also true in soft nanomaterials. Visualization of nanostructures with electron microscopy is limited to dry or frozen samples, whereas, traditional fluorescence microscopy has lower optical resolution and often involves a complex dye labeling procedure. The latest work by Mohit, with contributions from Jiye, Richard and Deborah demonstrates a new and remarkably simple method to fluorescently label peptide nanostructures for their visualization in solution with super-resolution microscopy. We show that by simply mixing a small amount (0.1 mole%) of a commercially available dye (Alexa) with cationic self-assembling peptides gives rise to selective electrostatic association of the dyes with the peptide nanostructure surface, which enables imaging using Stimulated Emission Depletion (STED) based super-resolution microscopy. Importantly, the method gave new insights into the hierarchical organization of peptide nanostructures, and enabled visualization of a metabolic transformation as demonstrated by enzymatic degradation of peptide nanofibers which could be imaged in real-time in situ. The ease and general scope of the method developed and the high resolution (approx. 50 nm) will open doors for potential in vivo imaging for bio-medical applications.
We are interested in developing approaches to produce melanin-like materials with precisely controlled properties by using a bio-inspired approach, but radically simplified so that properties can be optimized specifically for technological applications, thus going beyond biologically available structures.
In this manuscript- by Eileen and Ayala in collaboration with the group of Nurit Ashkenasy at Ben Gurion University of the Negev, Israel, and Tell Tuttle and colleagues at the University of Strathclyde, UK, we demonstrate the use of a self-assembling tripeptide as a precursor for enzymatic formation of nanofibrous melanin-like structures with well-defined, and controllable electronic properties. We demonstrate two-fold conceptual novelty in (i) the ability to control oxidation but retain a well-defined fibrous morphology, that does not have a known equivalent in biology, and (ii) demonstrate unprecedented conductivity that is enhanced by enzymatic oxidation, and is demonstrated to be mediated by proton charge transfer.
Water evaporation is a remarkably powerful process, providing a clean source of energy to power mechanical machines and devices. In a newly published paper in Nature Materials, PhD student Roxy Piotrowska and collaborators within CUNY and at The University of Strathclyde demonstrate the development of shape-shifting crystals that directly convert evaporation energy into powerful motions.
These water-responsive materials are based on supramolecular tripeptide crystals that contain nanoscale pores where water tightly binds, and these pores are interspersed with a molecular network of stiff and flexible regions that powerfully contract when humidity reaches a critical value. This results in the crystals temporarily losing their ordered patterns, until humidity is restored and the crystals regain their original shape. This newly designed process can be repeated over and over, and gives rise to a remarkably efficient method of harvesting evaporation energy to perform mechanical work.
Mohit's latest paper in Nature Chemistry demonstrates the use of amino acids as chemical signals to enable the active editing of a self-assembling semiconducting structure, which results in temporal control over nanostructures and consequent transient electronic conductivity. The work will be of potential use in interfacing electronics with biological system.
Chunqiu's latest paper shows reversible regulation of catalytic activity of supramolecular peptide catalyst achieved by conformational transition from random coil to β-hairpin by changing the pH, which results in the reversible formation of an ordered array of 'active sites' composed of hydrophobic binding pockets and catalytic histidine residues with significant esterase activity. The work provides a step toward formation of self-regulating supramolecular assemblies.
Melanins-the pigments that give color to skin, hair and eyes-have numerous useful qualities, including providing protection from cancer-causing UV radiation and free radicals, but also electronic conductance, adhesiveness and the capacity to store energy. We have developed a new approach for producing materials that not only mimic the properties of melanin, but also provide unprecedented control over expressing specific properties of the biopolymer, as published in Science. Unlike other biopolymers, such as DNA and proteins, where a direct link exists between the polymers ordered structures and their properties, melanin is inherently disordered, so directly relating structure to function is not possible. We found that the key to achieving polymers with controlled disorder is to start from systems that have variable order built in, which could be achieved by using self-assembling tripeptides with varying sequence as substrates for oxidative, biocatalytic polymerization. The discovery could enable the development of cosmetic and biomedical products.