Structural analysis of bioinspired nano materials with synchrotron far IR spectroscopy

Abstract

Bioinspired fibres and hierarchical nano-materials are based on the self-assembly of organic building blocks such as polypeptides. Confirming the core structure of such materials is often challenging as they lack the long-range order required by crystallographic methods. Far-IR spectroscopy characterizes the vibrational modes of large molecular units. These vibrational modes are very sensitive to angle strain and second order interactions such as hydrogen bonding. As such, far-IR spectra hold information about the secondary structure and interactions of large biomolecules. Here we analyze the far-IR vibrational spectra of fibrous nano-materials based on three isomeric unnatural tripeptides, Ac-β(3)Leu-β(3)Ile-β(3)Ala, Ac-β(3)Ile-β(3)Ala-β(3)Leu, and Ac-β(3)Ala-β(3)Leu-β(3)Ile. These peptides have well described self-assembly characteristics, forming one-dimensional nanorods that impose tight conformational constraints on the constituent molecules. The synchrotron far-IR spectroscopic results were interpreted by using density functional theory (DFT) modelling based vibrational analysis. The sensitivity of the spectra to peptide conformation was assessed by comparing the experimental spectra with DFT predictions. In high dielectric implicit solvent, intramolecular hydrogen-bonding is inhibited and thus the energy minimized peptide structure remains close to the 14-helix folding characteristic of substituted β(3)-peptides, giving good agreement between the experimental and predicted vibration spectra. In contrast, energy minimization in vacuum alters the peptide conformation leading to intramolecular hydrogen bonds, and hence the predicted vibration spectra do not agree with the experimental data. Therefore, our results demonstrate the ability of far-IR spectroscopy to identify correct structural predictions and thus open the way for using far-IR spectroscopy for the characterization and structural analysis of bioinspired nano-materials and potentially their interactions with surfaces, ionic environments and other biomolecules. Far-IR structural analysis is particularly powerful in case of one- and two-dimensional materials such as fibres, hydrogels and thin layers where standard crystallographic analysis is not available.

Coordination crosslinking of helical substituted oligoamide nanorods with Cu(II)

“…[1,3,6,7,10,11] The 14-helix structure is unique among substituted oligoamides (including natural peptides) due to its pitch of ≈3 residues, which aligns every 4 th residue such that it creates three 'faces' of the helix. [3][4][5][17][18][19] This symmetry yields an ideal building block for the design of complex nanostructures. [20][21][22] One dimensional assembly of the 14-helices can be achieved by the acylation of the N-terminus of the oligoamides, yielding a head-to-tail 3-point hydrogen-bonding motif that copies the intramolecular 14-helix hydrogen bonding pattern to the termini.…”

“…[20][21][22] One dimensional assembly of the 14-helices can be achieved by the acylation of the N-terminus of the oligoamides, yielding a head-to-tail 3-point hydrogen-bonding motif that copies the intramolecular 14-helix hydrogen bonding pattern to the termini. [1,[17][18][19][23][24][25] The resulting nanorods are stable in a range of solvents and may also assemble into a wide variety of superstructures, such as fibrils, rope-like bundles, dendritic, and mesh-like structures. [17][18][19][23][24][25] These superstructures form through a variety of interactions including hydrophobic attractions, van der Waals interactions, and supramolecular H-bonding interactions, the strength and propensity of which are strongly dependent on the oligoamide primary structure (i.e.…”

“…[1,[17][18][19][23][24][25] The resulting nanorods are stable in a range of solvents and may also assemble into a wide variety of superstructures, such as fibrils, rope-like bundles, dendritic, and mesh-like structures. [17][18][19][23][24][25] These superstructures form through a variety of interactions including hydrophobic attractions, van der Waals interactions, and supramolecular H-bonding interactions, the strength and propensity of which are strongly dependent on the oligoamide primary structure (i.e. side chains and cross section geometry), as well as the chemical and physical properties of the solvents used.…”

“…side chains and cross section geometry), as well as the chemical and physical properties of the solvents used. [17][18][19][23][24][25] The diversity of superstructures available from oligoamides coupled with the high level of control achievable via molecule design and assembly conditions makes substituted oligoamides remarkably robust candidates for the design of spontaneously assembling nano-materials. [1,9,[17][18][19][23][24][25] In particular, the stability of the 14-helix raises the possibility of using metal coordination to crosslink the supramolecular nanorod assemblies without interfering with the primary supramolecular assembly motif; yielding a hitherto unprecedented metallosupramolecular framework (MSF) structure.…”

Mesoscale design of heterogeneous material systems in multi-material additive manufacturing

“…Abundant in nature, as exemplified by bones, bamboos, and mollusk shells, [1][2][3][4][5][6][7][8][9][10][11] mesoscale heterogeneous material systems are more efficient and adaptive to thermal and mechanical environments than their statistically homogeneous counterparts. The mesostructures in natural materials are designed through the evolutionary processes on a large time-scale, where multiple design goals, such as weight reduction, mechanical performance (e.g., contact resistance, damage localization, and bending resistance), growth and health, etc., are taken into account.…”