Effect of Photoinduced Size Changes on Protein Refolding and Transport Abilities of Soft Nanotubes

Self‐assembly of azobenzene‐modified amphiphiles (Gly_nAzo, n=1–3) in water at room temperature in the presence of a protein produced nanotubes with the protein encapsulated in the channels. The Gly₂Azo nanotubes (7 nm internal diameter [i.d.]) promoted refolding of some encapsulated proteins, whereas the Gly₃Azo nanotubes (13 nm i.d.) promoted protein aggregation. Although the 20 nm i.d. channels of the Gly₁Azo nanotubes were too large to influence the encapsulated proteins, narrowing of the i.d. to 1 nm by trans‐to‐cis photoisomerization of the azobenzene units of the Gly₁Azo monomers packed in the solid bilayer membranes led to a squeezing out of the proteins into the bulk solution and simultaneously enhanced their refolding ratios. In contrast, photoinduced transformation of the Gly₂Azo nanotubes to short nanorings (<40 nm) with a large i.d. (28 nm) provided no further refolding assistance. We thus demonstrate that pertubation by the solid bilayer membrane wall of the nanotubes is important to accelerate refolding of the denatured proteins during their transport in the narrow nanotube channels.     

Protein Recognition by an Ensemble of Fluorescent DNA G‐Quadruplexes

Sniffing out proteins : Fluorescent DNA G‐quadruplexes have been used for building versatile signaling receptors for proteins in a single solution. Introducing a protein sample to the ensemble results in a unique emission signature for unambiguous identification (see scheme, R=fluorophore). The self‐assembled, pattern‐based protein detection systems are easily fabricated, have the potential for high‐throughput operations, and have the ability to handle small protein samples.

     

Photoinduced Morphological Transformations of Soft Nanotubes

In water, synthetic amphiphiles composed of a photoresponsive azobenzene moiety and an oligoglycine hydrogen‐bonding moiety selectively self‐assembled into nanotubes with solid bilayer membranes. The nanotubes underwent morphological transformations induced by photoisomerization of the azobenzene moiety within the membranes, and the nature of the transformation depended on the number of glycine residues in the oligoglycine moiety (i.e., on the strength of intermolecular hydrogen bonding). Upon UV‐light irradiation of nanotubes prepared from amphiphiles with the diglycine residue, trans‐to‐cis isomerization induced a transformation from nanotubes (inner diameter (i.d.) 7 nm), several hundreds of nanometers to several tens of micrometers in length, to imperfect nanorings (i.d. 21–38 nm). The cis‐to‐trans isomerization induced by continuous visible‐light irradiation resulted in the stacking of the imperfect nanorings to form nanotubes with an i.d. of 25 nm and an average length of 310 nm, which were never formed by a self‐assembly process. Time‐lapse fluorescence microscopy enabled us to visualize the transformation of nanotubes with an i.d. of 20 nm (self‐assembled from amphiphiles with the monoglycine residue) to cylindrical nanofibers with an i.d. of 1 nm; shrinkage of the hollow cylinders started at the two open ends with simultaneous elongation in the direction of the long axis.     

Chirality in Dynamic Supramolecular Nanotubes Induced by a Chiral Solvent

Amplification of chirality has been reported in polymeric systems. It has also been shown that related effects can occur in polymer‐like dynamic supramolecular aggregates, if a subtle balance between noncovalent interactions allows the coupling between a chiral information and a cooperative aggregation process. In this context, we report a strong majority‐rules effect in the formation of chiral dynamic nanotubes from chiral bisurea monomers. Furthermore, similar helical nanotubes (with the same circular dichroism signature) can be obtained from racemic monomers in a chiral solvent. Competition experiments reveal the relative strength of the helical bias induced by the chiral monomer or by the chiral solvent. The nanotube handedness is imposed by the monomer chirality, whatever the solvent chirality. However, the chirality of the solvent has a significant effect on the degree of chiral induction.     

DNA-Directed Three-Dimensional Protein Organization

All bound together: Self-assembled symmetric DNA polyhedra were used to organize proteins in 3D space. Biotin moieties were incorporated into the self-assembled symmetric DNA polyhedra. Upon incubation with streptavidin (STV) protein, an STV protein became bound to each polyhedral face, thus resulting in well-structured DNA polyhedra/STV complexes (see picture, TET=tetrahedron). This strategy was also applied to different 3D DNA nanostructures and different proteins.     

Self‐Assembled Fluorescent Organic Nanoparticles for Live‐Cell Imaging

Fluorescent, cell‐permeable, organic nanoparticles based on self‐assembled π‐conjugated oligomers with high absorption cross‐sections and high quantum yields have been developed. The nanoparticles are generated with a tuneable density of amino groups for charge‐mediated cellular uptake by a straightforward self‐assembly protocol, which allows for control over size and toxicity. The results show that a single amino group per ten oligomers is sufficient to achieve cellular uptake. The non‐toxic nanoparticles are suitable for both one‐ and two‐photon cellular imaging and flow cytometry, and undergo very efficient cellular uptake.     

Protein nanotubes with an enzyme interior surface

This report describes the synthesis and enzyme activities of multilayered protein nanotubes with an α-glucosidase (αGluD) interior surface. The nanotubes were prepared by using an alternating layer-by-layer (LbL) assembly of human serum albumin (HSA) and oppositely charged poly-L-arginine (PLA) into a track-etched polycarbonate (PC) membrane (pore size=400 nm) followed by addition of αGluD as the last layer of the wall. Subsequent dissolution of the PC template yielded (PLA/HSA)(2)PLA/αGluD nanotubes. SEM measurements revealed the formation of uniform hollow cylinders with (413±17) nm outer diameter and (52±3) nm wall thickness. In aqueous media, the nanotubes captured a fluorogenic glucopyranoside, 4-methyl-umbelliferyl-α-D-glucopyranoside (MUGlc), into their one-dimensional pore space and hydrolyzed the substrate efficiently to form α-D-glucose. We determined the enzyme parameters (Michaelis constant, K(M), and catalytic constant, k(cat), values) of the protein nanotubes. The several-micrometers-long cylinders were of sufficient length to be spun down by centrifugation at 4000 g, so the product could therefore be easily separated. Similar biocatalysts were prepared by complexation of biotinylated-αGluD into HSA-based nanotubes bearing a single avidin layer as an internal surface. The obtained hybrid nanotubes also exhibited the same enzyme activity for the MUGlc hydrolysis.     

Construction of Supramolecular Self‐Assembled Microfibers with Fluorescent Properties through a Modified Ionic Self‐Assembly (ISA) Strategy

Highly ordered supramolecular microfibers were constructed through a simple ionic self‐assembly strategy from complexes of the N‐tetradecyl‐N‐methylpyrrolidinium bromide (C₁₄MPB) surface‐active ionic liquid and the small methyl orange (MO) dye molecule, with the aid of patent blue VF sodium salt. By using scanning electron microscopy and polarized optical microscopy, the width of these self‐assembled microfibers is observed to be about 1 to 5 μm and their length is from tens of micrometers to almost a millimeter. The ¹H NMR spectra of the microfibers indicates that the supramolecular complexes are composed of C₁₄MPB and MO in equal molar ratio. The electrostatic, hydrophobic, and π–π stacking interactions are regarded as the main driving forces for the formation of microfibers. Furthermore, through characterization by using confocal fluorescence microscopy, the microfibers were observed to show strong fluorescent properties and may find potential applications in many fields.     

Robust Ordered Bundles of Porous Helical Nanotubes Assembled from Fully Rigid Ionic Benzene‐1,3,5‐tricarboxamides

Size‐controlled and ordered assemblies of artificial nanotubes are promising for practical applications; however, the supramolecular assembly of such systems remains challenging. A novel strategy is proposed that can be used to reinforce intermolecular noncovalent interactions to construct hierarchical supramolecular structures with fixed sizes and long‐range ordering by introducing ionic terminals and fully rigid arms into benzene‐1,3,5‐tricarboxamide (BTA) molecules. A series of similar BTA molecules with distinct terminal groups and arm lengths are synthesized; all form hexagonal bundles of helical rosette nanotubes spontaneously in water. Despite differences in molecular packing, the dimensions and bundling of the supramolecular nanotubes show almost identical concentration dependence for all molecules. The similarities of the hierarchical assemblies, which tolerate certain molecular irregularities, can extend to properties such as the void ratio of the nanotubular wall. This is a rational strategy that can be used to achieve supramolecular nanotubes in aqueous environments with precise size and ordering at the same time as allowing molecular modifications for functionality.     

Protein nanotubes comprised of an alternate layer-by-layer assembly using a polycation as an electrostatic glue

We present the synthesis and structure of various protein nanotubes comprised of an alternate layer-by-layer (LbL) assembly using a polycation as an electrostatic glue. The nanotubes were fabricated by sequential LbL depositions of positively charged polycations and negatively charged proteins into a porous polycarbonate (PC) membrane, followed by release of the cylindrical core by quick dissolution of the template with CH(2)Cl(2). This procedure provides a variety of protein nanotubes without interlayer cross-linking. The three-cycle depositions of poly-L-arginine (PLA) and human serum albumin (HSA, M(w)=66.5 kDa) into the porous PC template (pore diameter, D(p)=400 nm) yielded well-defined (PLA/HSA)(3) nanotubes with an outer diameter of 419+/-29 nm and a wall thickness of 46+/-8 nm, revealed by scanning electron microscopy (SEM) and transmission electron microscopy (TEM) observations. The outer diameter of the tubules can be controlled by the pore size of the template (200-800 nm), whereas the wall thickness is always constant, independent of the D(p) value. The (PEI/HSA)(3) (PEI: polyethylenimine) nanotubes showed a slightly thin wall of 39+/-5 nm. CD spectra of the multilayered (PEI/HSA)(n) film on a flat quartz plate suggested that the secondary structure of HSA between the polycations was almost the same as that in aqueous solution. The three-cycle LbL depositions of PLA and ferritin (M(w)=460 kDa) or myoglobin (Mb, M(w)=1.7 kDa) into the porous PC membrane also gave cylindrical hollow structures. The wall thickness of the (PLA/ferritin)(3) and (PLA/Mb)(3) nanotubes were 55+/-5 nm and 31+/-4 nm; it depends on the globular size of the protein (ferritin>HSA>Mb). The individual ferritin molecule was clearly seen in the tubular walls by SEM and TEM measurements.     

含有二十分子水簇的金属—水二维网的构成

以醋酸铜、1,10-邻菲啰啉和顺丁烯二酸在去离子水和乙醇的混合溶液中反应得到了配合物单晶[Cd(phen)2(male)(H2O)]·9.5H2O (1) (phen＝1,10－邻菲啰啉; H2male＝顺丁烯二酸)。采用元素分析、红外光谱和热重分析对化合物进行了表征。用X－射线单晶衍射分析了晶体结构,结果表明：在化合物１中存在着由二十分子水簇构成的结构新颖的一维水链。一维水链和[Cd(phen)2(male)(H2O)]依靠氢键作用构成了独特的包含金属－水网的二维结构。