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1. Capacity for increased surface area in the hydrophobic core of β ‐sheet peptide bilayer nanoribbons

   https://doi.org/10.1002/psc.3334  

   Jones, Christopher W.; Morales, Crystal G.; Eltiste, Sharon L.; Yanchik‐Slade, Francine E.; Lee, Naomi R.; Nilsson, Bradley L. (June 2021, Journal of Peptide Science)

   Amphipathic peptides with amino acids arranged in alternating patterns of hydrophobic and hydrophilic residues efficiently self‐assemble intoβ‐sheet bilayer nanoribbons. Hydrophobic side chain functionality is effectively buried in the interior of the putative bilayer of these nanoribbons. This study investigates consequences on self‐assembly of increasing the surface area of aromatic side chain groups that reside in the hydrophobic core of nanoribbons derived from Ac‐(XKXE)₂‐NH₂peptides (X = hydrophobic residue). A series of Ac‐(XKXE)₂‐NH₂peptides incorporating aromatic amino acids of increasing molecular volume and steric profile (X = phenylalanine [Phe], homophenylalanine [Hph], tryptophan [Trp], 1‐naphthylalanine [1‐Nal], 2‐naphthylalanine [2‐Nal], or biphenylalanine [Bip]) were assessed to determine substitution effects on self‐assembly propensity and on morphology of the resulting nanoribbon structures. Additional studies were conducted to determine the effects of incorporating amino acids of differing steric profile in the hydrophobic core (Ac‐X₁KFEFKFE‐NH₂and Ac‐(X_1,5KFE)‐NH₂peptides, X = Trp or Bip). Spectroscopic analysis by circular dichroism (CD) and Fourier transform infrared (FT‐IR) spectroscopy indicatedβ‐sheet formation for all variants. Self‐assembly rate increased with peptide hydrophobicity; increased molecular volume of the hydrophobic side chain groups did not appear to induce kinetic penalties on self‐assembly rates. Transmission electron microscopy (TEM) imaging indicated variation in fibril morphology as a function of amino acid in the X positions. This study confirms that hydrophobicity of amphipathic Ac‐(XKXE)₂‐NH₂peptides correlates to self‐assembly propensity and that the hydrophobic core of the resulting nanoribbon bilayers has a significant capacity to accommodate sterically demanding functional groups. These findings provide insight that may be used to guide the exploitation of self‐assembled amphipathic peptides as functional biomaterials. 

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2. Mechanism of hierarchical plasmonic biomaterials engineered through peptide‐directed self‐assembly

   https://doi.org/10.1002/agt2.677  

   Amer, Lubna; Retout, Maurice; Jin, Zhicheng; Kakanar, Sumathi; Jokerst, Jesse_V (October 2024, Aggregate)

   Abstract Hierarchical plasmonic biomaterials constructed from small nanoparticles (NPs) that combine into larger micron‐sized structures exhibit unique properties that can be harnessed for various applications. Using diffusion‐limited aggregation (DLA) and defined peptide sequences, we developed fractal silver biomaterials with a Brownian tree structure. This method avoids complex redox chemistry and allows precise control of interparticle distance and material morphology through peptide design and concentration. Our systematic investigation revealed how peptide charge, length, and sequence impact biomaterial morphology, confirming that peptides act as bridging motifs between particles and induce coalescence. Characterization through spectroscopy and microscopy demonstrated that arginine‐based peptides are optimal for fractal assembly based on both quantitative and qualitative measurements. Additionally, our study of diffusion behavior confirmed the effect of particle size, temperature, and medium viscosity on nanoparticle mobility. This work also provides insights into the facet distribution in silver NPs and their assembly mechanisms, offering potential advancements in the design of materials for medical, environmental, and electronic applications. 

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3. Influence of central sidechain on self-assembly of glycine-x-glycine peptides

   https://doi.org/10.1039/d2sm01082h  

   Thursch, Lavenia J.; Lima, Thamires A.; O’Neill, Nichole; Ferreira, Fabio F.; Schweitzer-Stenner, Reinhard; Alvarez, Nicolas J. (January 2023, Soft Matter)

   Low molecular weight gelators (LMWGs) are the subject of intense research for a range of biomedical and engineering applications. Peptides are a special class of LMWG, which offer infinite sequence possibilities and, therefore, engineered properties. This work examines the propensity of the GxG peptide family, where x denotes a guest residue, to self-assemble into fibril networks via changes in pH and ethanol concentration. These triggers for gelation are motivated by recent work on GHG and GAG, which unexpectedly self-assemble into centimeter long fibril networks with unique rheological properties. The propensity of GxG peptides to self-assemble, and the physical and chemical properties of the self-assembled structures are characterized by microscopy, spectroscopy, rheology, and X-ray diffraction. Interestingly, we show that the number, length, size, and morphology of the crystalline self-assembled aggregates depend significantly on the x-residue chemistry and the solution conditions, i.e. pH, temperature, peptide concentration, etc. The different x-residues allow us to probe the importance of different peptide interactions, e.g. π–π stacking, hydrogen bonding, and hydrophobicity, on the formation of fibrils. We conclude that fibril formation requires π–π stacking interactions in pure water, while hydrogen bonding can form fibrils in the presence of ethanol–water solutions. These results validate and support theoretical arguments on the propensity for self-assembly and leads to a better understanding of the relationship between peptide chemistry and fibril self-assembly. Overall, GxG peptides constitute a unique family of peptides, whose characterization will aid in advancing our understanding of self-assembly driving forces for fibril formation in peptide systems. 

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4. Mapping the Morphological Landscape of Oligomeric Di‐block Peptide–Polymer Amphiphiles**

   https://doi.org/10.1002/anie.202115547  

   Allen, Benjamin P.; Wright, Zoe M.; Taylor, Hailey F.; Oweida, Thomas J.; Kader‐Pinky, Sabila; Patteson, Emily F.; Bucci, Kara M.; Cox, Caleb A.; Senthilvel, Abishec Sundar; Yingling, Yaroslava G.; et al (January 2022, Angewandte Chemie International Edition)

   Abstract Peptide–polymer amphiphiles (PPAs) are tunable hybrid materials that achieve complex assembly landscapes by combining the sequence‐dependent properties of peptides with the structural diversity of polymers. Despite their promise as biomimetic materials, determining how polymer and peptide properties simultaneously affect PPA self‐assembly remains challenging. We herein present a systematic study of PPA structure–assembly relationships. PPAs containing oligo(ethyl acrylate) and random‐coil peptides were used to determine the role of oligomer molecular weight, dispersity, peptide length, and charge density on self‐assembly. We observed that PPAs predominantly formed spheres rather than anisotropic particles. Oligomer molecular weight and peptide hydrophilicity dictated morphology, while dispersity and peptide charge affected particle size. These key benchmarks will facilitate the rational design of PPAs that expand the scope of biomimetic functionality within assembled soft materials. 

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5. Factors Affecting Secondary and Supramolecular Structures of Self‐Assembling Peptide Nanocarriers

   https://doi.org/10.1002/mabi.202100347  

   Pitz, Megan E.; Nukovic, Alexandra M.; Elpers, Margaret A.; Alexander‐Bryant, Angela A. (November 2021, Macromolecular Bioscience)

   Abstract Self‐assembling peptides are a popular vector for therapeutic cargo delivery due to their versatility, tunability, and biocompatibility. Accurately predicting secondary and supramolecular structures of self‐assembling peptides is essential for de novo peptide design. However, computational modeling of such assemblies is not yet able to accurately predict structure formation for many peptide sequences. This review identifies patterns in literature between secondary and supramolecular structures, primary sequences, and applications to provide a guide for informed peptide design. An overview of peptide structures, their applications as nanocarriers, and analytical methods for characterizing secondary and supramolecular structure is examined. A top‐down approach is then used to identify trends between peptide sequence and assembly structure from the current literature, including an analysis of the drivers at work, such as local and nonlocal sequence effects and solution conditions. 

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