Nanotubes dipeptide

The first dipeptide nanotube system was L-Val-L-Ala (VA), which forms crystals with narrow hydrophobic channels (diameter about 5 A) lined by peptide side chains.This structure is conceptually different from those of the cyclic peptides in that the pores are generated from self-assembly of small molecules, which are hydrogen bonded, head-to-tail, into helices (Fig. 3a). The extremely robust three-dimensional hydrogen-bonding scaffold was since observed for a series of other hydro-phobic dipeptides.Pore size can be regulated from 3.3 A (L-Ile-L-Val) to 5.2 A (L-Ala-L-Val) by adjusting the bulk of the hydrophobic side chains. Furthermore, L-Ala-L-Val has pores that can adapt their shapes and sizes to absorb large solvent molecules like 2-butanol. 

The crystal structure for AI contains somewhat disordered co-crystallized water molecules in a 1 1 ratio with dipeptide molecules (7 ). This corresponds to a maximum 8% water content within the crystal pores, although it may be noted that solvent content can vary depending upon recrystallization conditions. An AI sample was found to lose 2% of its weight after 5 days of exposure to 1.33 X 10 Pa (10" Torr), corresponding to 25% or more of the water residing within the pores, depending on the initial occupancy. Solvents within the dipeptide nanotubes can be removed (75,79), necessarily changing the hydrophobic interactions between solvent and peptide molecules. Crystal... 

Gorbitz, C. H. (2001). Nanotube formation by hydrophobic dipeptides. Chemistry 7, 5153-5159. 

Gorbitz, C.H. Nanotubes from hydrophobic dipeptides Pore size regulation through side chain substitution, New J. Chem. 27(12) (2003) 1789-1793. 

Crystal structures of dipeptides are often divided into distinct hydrophilic and hydrophobic layers, the former containing two -NH3 -. OOC head-to-tail hydrogen-bonded chains. The essential third amino FI atom is accepted by a functional group in one of the side chains or in a cocrystallized solvent molecule. In solvent-free crystals of dipeptides with two hydrophobic residues, neither alternative is available, which raises an inherent packing problem How can three acceptors still be positioned around each amino group A series of crystal structures revealed a number of ways to solve this problem, one of them being the surprising formation of nanotubes. 

Dipeptides with L-Leu and L-Phe residues also form nanotubes, but these structures are completely different from those in the VA class. In a sense, the basic construction of the VA class was wrapped inside-out. giving a... 

Peptide-based self-assembly is capable of synthesizing nanomaterials with various microstructures from tubes to spheres. Dipeptides, probably the simplest building blocks with a versatility in controlling microstructures, can form tubular, spherical, fibrous, or bundle, and array structures by modifying motifs on the dipeptides and/or altering synthesis conditions (Figure 6.4a). For example, the Alzheimer s p-amyloid peptide with diphenylalanine motif forms multiwaUed nanotubes when the peptide is... 

Figure 6 A (a) Schematic of the formation of tubular (single or multiwalled), spherical, or fihrillar structures via dipeptide self-assembly, (b) Proposed model for the formation of aligned peptide nanotube arrays. Scanning electron micrograph of (i) the vertically aligned peptide nanotubes, (ii) the nanotube arrays, and (iii) an individual nanotube obtained. Reprint with permission from Ref. [7].

Similar studies on cyclodextrins (CDs) instead of dipeptides have also been reported and these gave rise to a novel supramolecular approach for the facile surface functionalization of the fluorescent organic nanotubes... 

Figure 19 Schematic representation of peptide nanotube formation from dipeptides and diketopiperazines.

Zhang and coworkers also reported that linear surfactantlike oligopeptides self-assembled simultaneously into nanotubes and vesicles. °° Such peptide nanotubes can be used for intracellular delivery applications. Cationic dipeptides... 

Instead of dipeptides, bisureas can also self-assemble in nonpolar solvents to form extremely long nanotnbes through a strongly cooperative process (Figure 21a). These nanotnbes are in dynamic exchange with the monomer and with simple hydrogen bonded filaments. Nanotube formation depends on the solvent used, with only small solvent molecnles that can be accommodated... 

Figure 3. Absorbance spectra from the dipeptide alanyl isoleucine a) as received, b) after dehydration under vacuum c) after attempted rehydration. Water normally resides within the pores of the hydrophobic nanotube-forming crystalline dipeptide. Removal of water results in small shifts in the spectral lines, but attempted rehydration does not restore the original spectrum, as it...

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