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While the terminally protected tripeptide Boc-Phe-Gly-m-ABA-OMe I (m-ABA, meta-amino benzoic acid) is an excellent gelator of aromatic organic solvents, another similar tripeptide Boc-Leu-Gly-m-ABA-OMe II, where the Phe residue of peptide I is replaced by Leu, cannot form gels with the same solvents. The morphology of the gels of peptide I, characterised by the field-emission scanning electron microscopy and high-resolution transmission electron microscopy, reveals the formation of nanofibrous networks which are known to encapsulate solvent molecules to form gels. The wide-angle X-ray scattering studies of the gels suggest the β-sheet-mediated self-assembly of peptide I in the formation of a nanofibrous network, where π-stacking interactions of Phe play an important role in the self-assembly and gel formation. The dried gel of peptide I observed between crossed polarisers after binding with a physiological dye, Congo red, shows a bluish-green birefringence, a characteristic of amyloid fibrils. [ABSTRACT FROM AUTHOR]

Single crystal X-ray diffraction studies show that the β-turn structure of tetrapeptide I, Boc-Gly-Phe-Aib-Leu-OMe (Aib: α-amino isobutyric acid) self-assembles to a supramolecular helix through intermolecular hydrogen bonding along the crystallographic a axis. By contrast the β-turn structure of an isomeric tetrapeptide II, Boc-Gly-Leu-Aib-Phe-OMe self-assembles to a supramolecular β-sheet-like structure via a two-dimensional (a, b axis) intermolecular hydrogen bonding network and π-π interactions. FT-IR studies of the peptides revealed that both of them form intermolecularly hydrogen bonded supramolecular structures in the solid state. Field emission scanning electron micrographs (FE-SEM) of the dried fibrous materials of the peptides show different morphologies, non-twisted filaments in case of peptide I and non-twisted filaments and ribbon-like structures in case of peptide II. [ABSTRACT FROM AUTHOR]

Abstract: Single crystal X-ray diffraction studies reveal that the incorporation of meta-amino benzoic acid in the middle of a helix forming hexapeptide sequence such as in peptide I Boc-Ile(1)-Aib(2)-Val(3)-m-ABA(4)-Ile(5)-Aib(6)-Leu(7)-OMe (Aib: α-amino isobutyric acid; m-ABA: meta-amino benzoic acid) breaks the helix propagation to produce a turn-linker-turn (T-L-T) foldamer in the solid state. In the crystalline state two conformational isomers of peptide I self-assemble in antiparallel fashion through intermolecular hydrogen bonds and aromatic π–π interactions to form a molecular duplex. The duplexes are further interconnected through intermolecular hydrogen bonds to form a layer of peptides. The layers are stacked one on top of the other through van der Waals interactions to form hydrophilic channels filled with solvent methanol. [Copyright &y& Elsevier]

Three tripeptides Boc-Phe-Aib-Val-OMe (1), Boc-Leu-Aib-p-NA-NO2 (2) and Boc-Pro-Aib-m-NA-NO2 (3) (Aib: α-aminoisobutyric acid; p- and m-NA: para- and meta-nitroaniline) have been designed by incorporating aromatic rings to study the self-assembly and fibril formation. Single crystal X-ray diffraction studies show that all the peptides adopt turn-like structures that are self-assembled through intermolecular hydrogen bonds and van der Waals interactions to create layers of β-sheets. Solvent dependent NMR titration and CD studies show that the turn structures of the peptides also exist in the solution phase. The field emission scanning electron microscopic (FE-SEM) images of the peptides in the solid state reveal fibrillar structures of flat morphology that are formed through β-sheet mediated self-assembly of the preorganized turn building blocks. [ABSTRACT FROM AUTHOR]

Abstract: Single crystal X-ray diffraction studies and solvent dependent NMR titration reveal that the designed peptides I and II, Boc-Xx(1)-Aib(2)-Yy(3)-NH(CH2)2NH-Yy(3)-Aib(2)-Xx(1)-Boc, where Xx and Yy are Ile and Leu in peptide I and Leu and Val in peptide II, respectively, fold into a turn-linker-turn (T-L-T) conformation both in the solid state and in solution. In the crystalline state the T-L-T foldamers of peptide I and II self-assemble to form a three-dimensional framework of channels. The insides of the channels are hydrophilic and found to contain solvent CHCl3 hydrogen bonded to exposed Clocated at the turn regions. [Copyright &y& Elsevier]

A set of three peptides 1-3 of general formula PhCO-Gly-Xx-OCH2Ph, where Xx is Gly in peptide 1, Ala in 2 and Aib (α-animo isobutyric acid) in 3 has been chosen to study the selfassembly and the morphology of the solid biomaterials. FT-IR and single crystal X-ray diffraction studies reveal that the peptides 1-3 self-assemble to form supramolecular β-sheet structures through intermolecular hydrogen bonds and aromatic π-π interactions. Field emission scanning electron micrographs (FE-SEM) of the dried materials of the peptides 1-3 show the formation of flat ribbon like structures which are formed through β-sheet mediated selfassembly. [ABSTRACT FROM AUTHOR]

The pseudopeptide Gly-m-ABA (m-ABA = m-amino benzoic acid) has been chosen to study the formation of supramolecular structures through self-assembly. Single crystal X-ray diffraction studies reveal that the pseudopeptide Boc-Gly-m-ABA-OMe (1), where both N- and C-terminus are protected, self-assembles to a supramolecular helical structure, whereas the pseudopeptide Boc-Gly-m-ABA-OH (2) with free -CO2H at the C-terminus produces molecular staircase through self-assembly. Again the terminally unprotected pseudopeptide +NH3-Gly-m-ABA-CO2- (3) aggregates to a water mediated supramolecular β-sheet structure stabilized by intermolecular hydrogen bonds and p-p interactions. The study reveals that the terminally modified Gly-m-ABA generates various kinds of self-assembling building blocks that can fabricate different types of supramolecular architectures such as helix, β-sheet and staircase. [ABSTRACT FROM AUTHOR]