Soft Nanotube Hydrogels Functioning As Artificial Chaperones

Self-assembly of rationally designed asymmetric amphiphilic monomers in water produced nanotube hydrogels in the presence of chemically denatured proteins (green fluorescent protein, carbonic anhydrase, and citrate synthase) at room temperature, which were able to encapsulate the proteins in the one-dimensional channel of the nanotube consisting of a monolayer membrane. Decreasing the concentrations of the denaturants induced refolding of part of the encapsulated proteins in the nanotube channel. Changing the pH dramatically reduced electrostatic attraction between the inner surface mainly covered with amino groups of the nanotube channel and the encapsulated proteins. As a result, the refolded proteins were smoothly released into the bulk solution without specific additive agents. This recovery procedure also transformed the encapsulated proteins from an intermediately refolding state to a completely refolded state. Thus, the nanotube hydrogels assisted the refolding of the denatured proteins and acted as artificial chaperones. Introduction of hydrophobic sites such as a benzyloxycarbony group and a <i>tert</i>-butoxycarbonyl group onto the inner surface of the nanotube channels remarkably enhanced the encapsulation and refolding efficiencies based on the hydrophobic interactions between the groups and the surface-exposed hydrophobic amino acid residues of the intermediates in the refolding process. Refolding was strongly dependent on the inner diameters of the nanotube channels. Supramolecular nanotechnology allowed us to not only precisely control the diameters of the nanotube channels but also functionalize their surfaces, enabling us to fine-tune the biocompatibility. Hence, these nanotube hydrogel systems should be widely applicable to various target proteins of different molecular weights, charges, and conformations

Soft Nanotubes Derivatized with Short PEG Chains for Thermally Controllable Extraction and Separation of Peptides

By means of a two-step self-assembly process involving three components, including short poly­(ethylene glycol) (PEG) chains, we produced two different types of molecular monolayer nanotubes: nanotubes densely functionalized with PEG chains on the outer surface and nanotubes densely functionalized with PEG chains in the nanochannel. Turbidity measurements and fluorescence spectroscopy with an environmentally responsive probe suggested that the PEG chains underwent dehydration when the nanotubes were heated above 44–57 °C and rehydration when they were cooled back to 25 °C. Dehydration of the exterior or interior PEG chains rendered them hydrophobic and thus able to effectively extract hydrophobic amino acids from the bulk solution. Rehydration of the PEG chains restored their hydrophilicity, thus allowing the extracted amino acids to be squeezed out into the bulk solutions. The nanotubes with exterior PEG chains exhibited selectivity for all of the hydrophobic amino acids, whereas the interior PEG chains were selective for hydrophobic amino acids with an aliphatic side chain over hydrophobic amino acids with an aromatic side chain. The higher selectivity of the latter system is attributable that the extraction and back-extraction processes involve encapsulation and transportation of the amino acids in the nanotube channel. As the result, the latter system was useful for separation of peptides that differed by only a single amino acid, whereas the former system showed no such separation ability

Control of Self-assembled Morphology and Molecular Packing of Asymmetric Glycolipids by Association/Dissociation with Poly(thiopheneboronic acid)

The molecular packing and self-assembled morphologies of asymmetric bolaamphiphiles, <i>N</i>-(2-aminoethyl)-<i>N′</i>-(β-d-glucopyranosyl)­alkanediamide [<b>1­(</b><i><b>n</b></i><b>)</b>, <i>n</i> = 12, 14, 16, 17, 18, and 20], were precisely controlled by association/dissociation with poly­(thiopheneboronic acid) (PTB). Differential scanning calorimetry, X-ray diffraction, and infrared spectroscopy revealed that the starting film of <b>1­(</b><i><b>n</b></i><b>)</b> associated with 1 equiv of the boronic acid moiety of PTB, (Film-<b>1­(</b><i><b>n</b></i><b>)</b>PTB), had antiparallel molecular packing of <b>1­(</b><i><b>n</b></i><b>)</b> moiety within the monolayer membranes. However, the molecular packing of the starting film that contained 0.5 equiv of the boronic acid moiety of PTB (Film-2eq<b>1­(</b><i><b>n</b></i><b>)</b>PTB) was parallel. The dispersion of Film-<b>1­(</b><i><b>n</b></i><b>)</b>PTB in water gave only nanotapes, whereas that of Film-2eq<b>1­(</b><i><b>n</b></i><b>)</b>PTB in water selectively formed nanotubes, through a dissociation reaction of PTB based on the hydrolysis of the boronate esters in the complexes. The nanotapes and nanotubes memorized the antiparallel and parallel molecular packing of the starting films, respectively. Changes in the length of the oligomethylene spacer of <b>1­(</b><i><b>n</b></i><b>)</b> never affected the molecular packing or self-assembled morphologies. However, the inner diameters of the nanotubes increased irregularly in the range of 67.9–79.6 nm as the length of the oligomethylene spacer of <b>1­(</b><i><b>n</b></i><b>)</b> increased from <i>n</i> = 12 to <i>n</i> = 18

Preparation and Formation Process of Zn(II)-Coordinated Nanovesicles

Mixing a glycylglycine lipid and zinc acetate has been reported to form novel supramolecular Zn­(II)-coordinated nanovesicles in ethanol. In this study, we investigate in detail the formation of nanovesicles by using three lipids at different temperatures and discuss their formation process. The original lipids show extremely low solubilities and appear as plate structures in ethanol. Within a small window of lipid solubility, the formation of lipid–Zn­(II) complexes occurs mainly on the solid surfaces of plate structures. Controlling of the lipid solubility by temperature affects the kinetics of complex formation and the subsequent transformation of the complexes into nanovesicles and nanotubes. An improved method of two-step control of temperature is developed for preparing all the three kinds of nanovesicles. We provide new insights into the formation process of nanovesicles based on several control experiments. A tetrahedral lipid–cobalt­(II) complex similarly produces nanovesicles, whereas an octahedral complex gives sheet structures. Mixing of zinc acetate with a β-alanyl-β-alanine lipid can only give sheet structures, which lack a polyglycine II hydrogen-bond network and induce no morphological changes. We conclude that the formation of the lipid–Zn­(II) complexes on solid plate structures, tetrahedral geometry, and polyglycine II hydrogen-bond network in the complexes shall work cooperatively for the formation of Zn­(II)-coordinated nanovesicles

Spontaneous Nematic Alignment of a Lipid Nanotube in Aqueous Solutions

The dispersibility and liquid crystal formation of a self-assembled lipid nanotube (LNT) was investigated in a variety of aqueous solutions. As the lipid component, we chose a bipolar lipid with glucose and tetraglycine headgroups, which self-assembled into an LNT with a small outer diameter of 16 to 17 nm and a high axial ratio of more than 310. The LNT gave a stable colloidal dispersion in its dilute solutions and showed spontaneous liquid crystal (LC) alignment at relatively low concentrations and in a pH region including neutral pH. The LNT samples with shorter length distributions were prepared by sonication, and the relationship between the LNT axial ratio and the minimum LC formation concentration was examined. The robustness of the LNT made the liquid crystal stable in mixed solvents of water/ethanol, water/acetone, and water/tetrahydrofuran (1:1 by volume) and at a temperature of up to 90 °C in water. The observed colloidal behavior of the LNT was compared to those of similar 1D nanostructures such as a phospholipid tubule

Molecular-Level Understanding of the Encapsulation and Dissolution of Poorly Water-Soluble Ibuprofen by Functionalized Organic Nanotubes Using Solid-State NMR Spectroscopy

A comprehensive study of the encapsulation and dissolution of the poorly water-soluble drug ibuprofen (IBU) using two types of organic nanotubes (ONT-1 and ONT-2) was conducted. ONT-1 and ONT-2 had similar inner and outer diameters, but these surfaces were functionalized with different groups. IBU was encapsulated by each ONT via solvent evaporation. The amount of IBU in the ONTs was 9.1 and 29.2 wt % for ONT-1 and ONT-2, respectively. Dissolution of IBU from ONT-1 was very rapid, while from ONT-2 it was slower after the initial burst release. One-dimensional (1D) ¹H, ¹³C, and two-dimensional (2D) ¹H–¹³C solid-state NMR measurements using fast magic-angle spinning (MAS) at a rate of 40 kHz revealed the molecular state of the encapsulated IBU in each ONT. Extremely mobile IBU was observed inside the hollow nanosapce of both ONT-1 and ONT-2 using ¹³C MAS NMR with a single pulse (SP) method. Interestingly, ¹³C cross-polarization (CP) MAS NMR demonstrated that IBU also existed on the outer surface of both ONTs. The encapsulation ratios of IBU inside the hollow nanospaces versus on the outer surfaces were calculated by waveform separation to be approximately 1:1 for ONT-1 and 2:1 for ONT-2. Changes in ¹³C chemical shifts showed the intermolecular interactions between the carboxyl group of IBU and the amino group on the ONT-2 inner surface. The cationic ONT-2 could form the stronger electrostatic interactions with IBU in the hollow nanosapce than anionic ONT-1. On the other hand, 2D ¹H–¹³C NMR indicated that the hydroxyl groups of the glucose unit on the outer surface of the ONTs interacted with the carboxyl group of IBU in both ONT-1 and ONT-2. The changes in peak shape and chemical shift of the ONT glucose group after IBU encapsulation were larger in ONT-2 than in ONT-1, indicating a stronger interaction between IBU and the outer surface of ONT-2. The smaller amount of IBU encapsulation and rapid IBU dissolution from ONT-1 could be due to the weak interactions both at the outer and inner surfaces. Meanwhile, the stronger interaction between IBU and the inner surface of ONT-2 could suppress IBU dissolution, although the IBU on the outer surface of ONT-2 was released soon after dispersal in water. This study demonstrates that the encapsulation amount and the dissolution rates of poorly water-soluble drugs, a class which makes up the majority of new drug candidates, can be controlled using the functional groups on the surfaces of ONTs by considering the host–guest interactions