No abstract

Traditional aqueous self-assembly of tubular structures (as well as other aggregates) usually relies on the hydrophobic effect, a relatively weak and nondirectional interaction. The resultant aggregates are inherently soft, fluid, and less-ordered. Alternatively, we report a novel kind of nonamphiphilic selfassembly of microtubes in aqueous solutions of cyclodextrin/ionic surfactant (CD/IS) complexes. This self-assembly is driven exclusively by H-bonds, relatively strong, directional interactions. The CD/IS microtubes feature an unbundling nature, ultralong persistence lengths, highly monodispersed diameters, and remarkable rigidity. Every single CD/IS microtube is constituted by a set of coaxial, equally spaced, hollow cylinders, resembling the annular rings of trees (thus termed as ''annular ring'' microtubes). Furthermore, bearing in mind the fundamental difference between the amphiphilic counterpart in driving forces, this H-bond-driven hydrophilic self-assembly is envisioned to complement its counterpart and expand the field of molecular self-assembly.

Proteins can readily assemble into rigid, crystalline and functional structures such as viral capsids and bacterial compartments. Despite ongoing advances, it is still a fundamental challenge to design and synthesize protein-mimetic molecules to form crystalline structures. Here we report the lattice self-assembly of cyclodextrin complexes into a variety of capsid-like structures such as lamellae, helical tubes and hollow rhombic dodecahedra. The dodecahedral morphology has not hitherto been observed in self-assembly systems. The tubes can spontaneously encapsulate colloidal particles and liposomes. The dodecahedra and tubes are respectively comparable to and much larger than the largest known virus. In particular, the resemblance to protein assemblies is not limited to morphology but extends to structural rigidity and crystallinity—a well-defined, 2D rhombic lattice of molecular arrangement is strikingly universal for all the observed structures. We propose a simple design rule for the current lattice self-assembly, potentially opening doors for new protein-mimetic materials.

All salts studied effectively reduce critical micelle concentration (CMC) values of the cationic gemini surfactants. The ability to promote the surfactant aggregation decreases in the order of C(6)H(5)COONa > p-C(6)H(4)(COONa)(2) > Na(2)SO(4)> NaCl. Moreover, only C(6)H(5)COONa distinctly reduces both the CMC values and the surface tension at CMC. For 12-4-12 solution, the penetration of C(6)H(5)COO(-) anions and charge neutralization induce a morphology change from micelles to vesicles, whereas the other salts only slightly increase the sizes of micelles. The 12-4(OH)(2)-12 solution changes from the micelle/vesicle coexistence to vesicles with the addition of C(6)H(5)COONa, whereas the other salts transfer the 12-4(OH)(2)-12 solution from the micelle/vesicle coexistence to micelles. As compared with 12-4-12, the two hydroxyls in the spacer of 12-4(OH)(2)-12 promote the micellization of 12-4(OH)(2)-12 and reduce the amounts of C(6)H(5)COONa required to induce the micelle-to-vesicle transition.

No abstract

The vesicle-to-micelle transition (VMT) was realized in catanionic surfactant systems by the addition of two kinds of bile salts, sodium cholate (SC) and sodium deoxycholate (SDC). It was found that steric interaction between the bile salt and catanionic surfactant plays an important role in catanionic surfactant systems that are usually thought to be dominated by electrostatic interaction. The facial amphiphilic structure and large occupied area of the bile salt are crucial to the enlargement of the average surfactant headgroup area and result in the VMT. Moreover, bile salts can also induce a macroscopic phase transition. Freeze-fracture transmission electron microscopy, dynamic light scattering, isothermal titration calorimetry, and absorbance measurements were used to follow the VMT process.

Self-assembly is ubiquitous in nature, science, and technology and provides a general route to achieve order from disorder at various length scales. [1] Extensive effort has been exerted to molecular and colloidal self-assembly, where molecules and colloids, respectively, organize into larger-scale ordered structures. Although these two research areas have developed separately to a great extent, their combination would be very promising. Nature, for instance, utilizes hierarchical selfassembly across different length scales to construct complex, dynamic functional entities such as cells. Here we bridge the nano-and microscale by the hierarchical co-assembly between molecules and colloids, where molecular self-assembly induces the self-assembly of colloids into ordered structures.Colloidal self-assembly is widely employed in analogues of molecular systems and processes encountered in chemistry, physics, and biology. [2][3][4][5][6][7][8][9][10][11] Colloids mimic naturally occurring systems such as microorganisms, [10] micelles, [3] molecules, [6] and polymers. [7] The directed organization into such specific ordered structures is fuelled by the rapidly advancing availability of colloidal building blocks that are asymmetric in shape and chemical functionality. [2][3][4][5][6]12] Of particular interest is the creation of colloidal helical structures, for instance, as models of the DNA helix. Colloidal structures with a helical twist have been assembled from complex anisotropic magnetic colloids [4] and amphiphilic Janus spheres. [5] These sophisticated building blocks are believed to be essential for inducing directionality and chirality in self-assembly. [13] Here we demonstrate that the simplest of building blocks, namely the isotropic sphere, already suffices to generate a library of ordered structures, including helical sphere chains. These structures form through the spontaneous co-assembly of colloidal spheres and confining surfactant-cyclodextrin microtubes, [14] thereby coupling molecular and colloidal selfassembly. We introduce these microtubes as a novel versatile platform for the self-assembly of colloid-in-tube structures, as depicted in Figure 1 a. Microtube precursors sodium dodecyl sulfate (SDS) and b-cyclodextrin (b-CD) are mixed with colloidal particles at elevated temperatures to obtain isotropic mixtures (see the Supporting Information for experimental details). The microtubes form upon cooling to room temperature and, simultaneously, the colloids co-assemble inside the microtubes into ordered, chain-like structures throughout the sample volume. The elementary building block of the straight and rigid microtubes consists of one SDS molecule and two b-cyclodextrin molecules, forming an aqueous inclusion complex (Figure 1 a). These building blocks in turn assemble into multiple curved SDS/b-CD bilayers with in-plane order, thereby forming a set of coaxial hollow cylinders. The thus formed microtubes exhibit a rather uniform pore diameter of 0.9 mm and prefer to align parallel with each other (Figu...

To carry doxorubicin (DOX) on breast cancer site effectively, halloysite nanotubes conjugated with poly­(ethylene glycol) and folate (HNTs-PEG-FA) is designed as a targeted drug delivery system. Halloysite nanotubes (HNTs) are shortened to ∼200 nm by ultrasonic scission and functionalized with amide groups to conjugate with N-hydroxylsuccinimide-polyethylene glycol carboxylic acid (NHS-PEG-COOH) and folate (FA). DOX@HNTs-PEG-FA is prepared by loading DOX on HNTs-PEG-FA via physical adsorption. The sustained and controlled release of DOX from DOX@HNTs-PEG-FA is up to 35 h in an acidic environment (pH 5.3). DOX@HNTs-PEG-FA, performed as a new nanodelivery system, shows significant inhibition of proliferation and induction of death in MCF-7 cells with positive FA receptor but not in L02 cells with negative FA receptor. Results of acridine orange/ethidium bromide and flow cytometric assay indicate that DOX@HNTs-PEG-FA induces cell death through apoptosis. Compared to the same dose of DOX, DOX@HNTs-PEG-FA generates more reactive oxygen species (ROS) in MCF-7 cells, which lead to mitochondrial damage and apoptosis. Furthermore, with fluorescence images and transmission electron microscopy, uptake of DOX@HNTs-PEG-FA by tumor cells is both through endocytosis and direct penetration mechanism. The in vivo antibreast cancer activity of DOX@HNTs-PEG-FA is further confirmed in 4T1-bearing mice. In contrast to DOX, DOX@HNTs-PEG-FA effectively reduces heart toxicity and inhibits solid tumor growth with higher cleaved caspase-3 protein level in tumor tissue of 4T1-bearing mice. DOX@HNTs-PEG-FA reveals a higher DOX fluorescence intensity in tumor tissue than in other normal tissues including heart, spleen, lung, and kidney at different time points. All these results suggest that FA-conjugated HNTs may be designed to be a novel drug delivery system for targeted therapy of breast cancer via intravenous injection.