Reversible Self-assembly Research Articles

Synthesis and antibacterial activity of mesoporous zinc oxide particle with high specific surface area

Mesoporous ZnO particle with high specific surface area was synthesized by a reverse microemulsion-based evaporation-induced self-assembly (EISA) technique, using zinc nitrate as metal precursor and sucrose as porogen, respectively. Structural and morphological characterization indicated that the resulting ZnO possesses a wurtzite structure and spherical morphology with an average particle size of about 150nm. And, the effect of the molar ratio of sucrose to Zn2+ on the mesoporosity and antibacterial activity of the resulting ZnO was also investigated. The results of low temperature N2 adsorption–desorption analysis confirmed the formation of the mesoporous ZnO. When the molar ratio of sucrose to Zn2+ was 1.5, the resulting ZnO possessed the highest specific surface area of 233.56m2g−1 and the largest pore volume 0.89cm3g−1, respectively. The inhibition zone tests revealed that the mesoporous ZnO particle exhibits a strong antibacterial activity against both a Gram-negative bacterium Escherichia coli and a Gram-positive bacterium Staphylococcus aureus.

Reversible Self-Assembling of Comb-Like Functionalized Dextran Surfactant Polymers as an SPR-Sensing Surfaces

Novel surface plasmon resonance (SPR) sensing surfaces were developed from the perspective of reversible self-assembling of the mixed dextran surfactant polymers onto SPR gold chips. Two comb-like dextran surfactant polymers, which are different in their dextran molecular weight (MW) distribution and the presence of amine functional groups, and their characterization were synthesized. These structurally well-defined surfactant polymers include a bimodal amine dextran surfactant polymer and a monomodal dextran surfactant polymer. The bimodal one consists of poly (vinyl amine) (PVAm) backbone with amine functionalized high MW dextran, non-functionalized low MW dextran and hydrophobic hexyl pendant groups. Allyl high MW dextran aldonic acid and low MW dextran aldonic acid chains with various ratios were sequentially attached to PVAm. The unreacted amine groups on the backbone were further grafted with hexanoic acid and the allyl groups on the high MW dextran were finally converted to amine. The monomodal surfactant polymer, PVAm with non-functionalized low MW dextran and hexyl branches, was synthesized and characterized using similar procedures, except with the absence of allyl high MW dextran aldonic acid and the amine functionalization. The molecular compositions of the surfactant polymers were determined by FTIR and 1H-NMR. Surface active properties at the air-water interface were determined using tensiometer. Reduction in water contact angles was observed on the surfactant treated surfaces. Reversible self-assembling of the synthesized surfactant polymers on SPR gold chip surface was monitored using SPR analysis. Reproducibility of the mixed surfactant assembling process was preliminarily confirmed by a consistent increase in reflectivity change, while no detectable changes in the reflectivity under a 1-h buffer flow indicated stability of the absorbed surfactant layer. Moreover, a simple, quick flow of a basis regeneration solution completely removed the adsorbed surfactant from the surface. Our preliminary investigation also exhibited that the regenerated SPR gold chip was effectively reusable.

Shear Thinning Three-Dimensional Colloidal Assemblies of Chitosan and Poly(lactic acid) Nanoparticles

In this study, new materials capable of reversible self-assembly, based on concentrated negatively charged poly(lactic acid) nanoparticles and chitosan, a natural polycationic polymer, were successfully fabricated. Electrostatic interactions between oppositely charged components along with weaker interactions led to the formation of a 3D network. The resulting macroscopic assemblies were characterized by dynamic mechanical measurements, and the influences of various parameters such as chitosan/poly(lactic acid) weight ratio, duration and temperature of the mixture, and molecular weight or chitosan degree of acetylation were studied. Our results showed that the mechanical properties of assemblies were highly dependent on the nanoparticle solid content and chitosan/nanoparticle ratio. In particular, at an optimum weight ratio the colloidal assemblies exhibited remarkable high elastic moduli (about 300 kPa) for a particle solid content of 18% w/w. Thanks to the weak and reversible nature of the interactions, these materials exhibited shear thinning properties, and could instantly recover their cohesiveness at rest. The mode of interactions between PLA particles and chitosan was shown to be in part due to electrostatic interactions, but the cross-linking of chitosan-covered particles was attributed to hydrogen bonding. These materials could be envisaged as good candidates for injectable scaffolds for tissue engineering, taking advantage of the biocompatibility and bioactivity of both components. However, some issues concerning temperature stability must be resolved before applying these colloidal assemblies to cell growth in physiological conditions.

ChemInform Abstract: Supramolecular Chemical Biology; Bioactive Synthetic Self‐Assemblies

AbstractReview: 120 refs.

Reversible self-assembly of gels through metal-ligand interactions

Metal-ligand interactions with various proteins form in vivo metal assemblies. In recent years, metallosupramolecular approaches have been utilized to forge an assortment of fascinating two- and three-dimensional nano-architectures, and macroscopic materials, such as metal-ligand coordination polymeric materials, have promise in artificial systems. However to the best of our knowledge, the self-assembly of macroscopic materials through metal-ligand interactions has yet to be reported. Herein we demonstrate a gel assembly formed via metal-ligand interactions using polyacrylamide modified with Fe-porphyrin and L-histidine moieties. The stress values for the assembly increase as the concentration of Fe-porphyrin or L-histidine in the gels increases. Moreover, agitation of Fe-porphyrin gel, Zn-porphyrin gel, and L-histidine gel in an 80 mM Tris-acetate buffer (pH 9.0) results in selective adhesion of the Fe-porphyrin gel to the L-histidine gel based on the affinities of Fe-porphyrin and Zn-porphyrin with L-histidine.

Reversible multicomponent self-assembly mediated by bismuth ions

Bi(III) ions are capable of reversible, multicomponent self assembly with suitable tris-coordinate ligands. The nature of the self-assembled structures observed are dependent on the ligand coordination geometry, ligand protonation state and Bi concentration. These assemblies can exploit the maximum number of coordination sites at the Bi vertices (nine), and the self-assembly process has been studied by 1D NMR, Diffusion NMR, ESI-MS and X-ray crystallographic analysis. V-shaped coordinating ligands reversibly form discrete M2L4, M2L3, and M2L2 complexes dependent on ligand/bismuth concentration, whereas a linear coordinating ligand forms a single discrete M3L3 assembly.

Reversible self-assembly of ferritin molecules for fabrication of size controlled microspheres and microrods

The reversible self-assembly of ferritin molecules into stable size-tailored ferritin microspheres was achieved in 1-octanol, and microrods consisting of ferritin microspheres were prepared by the porous polycarbonate membrane templated deposition of these ferritin microspheres.

Reverse self-assembly of lipid onions induced by gadolinium and calcium ions

Self-assembly of lipids in water is well-known to result in nanostructures such as vesicles in dilute solution. In contrast, self-assembly in nonpolar organic solvents (oils) is much less established and there are hardly any known routes to forming structures such as reverse vesicles. Here, we build such structures based on our surprising recent discovery that salts can influence self-assembly of lipids in oil. We induce the self-assembly of nanoscale multilamellar vesicles (“onions”) in cyclohexane and toluene by combining the saturated phospholipid, 1,2-dimyristoyl-sn-glycero-3-phosphocholine (DMPC), with salts of di- or trivalent cations like calcium (Ca2+) or gadolinium (Gd3+) in the absence of water. DMPC–Gd3+ onions can be seen by a transmission electron microscope (TEM) without additional staining. They have sizes between ∼100 and 400 nm and have 6–18 concentric bilayer shells (lamellae) that are uniformly spaced. The presence of lamellae is further confirmed by small-angle X-ray scattering (SAXS), from which we find the inter-lamellar spacing to be 6.0 nm. The formation of reverse onions is driven by the binding of these multivalent cations with the lipid headgroups, which in turn brings adjacent lipids close and causes a tighter packing of the lipid tails. Evidence for such binding is provided by the cation-induced lowering of the lipid melting temperature.

Supramolecular chemical biology; bioactive synthetic self-assemblies

The regulation of recognition events in nature via dynamic and reversible self-assembly of building blocks has inspired the emergence of supramolecular architectures with similar biological activity. Synthetic molecules of diverse geometries self-assemble in water to target biological systems for applications ranging from imaging and diagnostics, through to drug delivery and tissue engineering. Many of these applications require the ability of the supramolecular system to actively recognize specific cell surface receptors. This molecular recognition is typically achieved with ligands, such as small molecules, peptides, and proteins, which are introduced either prior to or post self-assembly. Advantages of the non-covalent organization of ligands include the responsive nature of the self-assembled structures, the ease of supramolecular synthesis and the possibility to incorporate a multiple array of different ligands through pre-mixing of the building blocks. This review aims to highlight the diversity of self-assembled nanostructures constructed from mono-disperse synthetic building blocks; with a particular focus on their design, self-assembly, functionalization with bioactive ligands and effects thereof on the self-assembly, and possible applications.

Amidine functionality as a stimulus-responsive building block

This mini-review describes basic features and applications of small molecules and macromolecules containing amidine, and to a lesser extent, guanidine functional groups. The emphasis in this article is on the exploitation of such functionality as species that are capable of reversibly binding carbon dioxide in the presence of water, a process that also commonly involves a hydrophobic-to-hydrophilic transition. The review is not intended to be exhaustive but rather serves to highlight this one particular feature and demonstrate its application in areas ranging from reversible emulsion stabilization, purification and reversible self-assembly of polymeric nanoparticles.

Hydrophobic Interactions Modulate Self-Assembly of Nanoparticles

Hydrophobic interactions constitute one of the most important types of nonspecific interactions in biological systems, which emerge when water molecules rearrange as two hydrophobic species come close to each other. The prediction of hydrophobic interactions at the level of nanoparticles (Brownian objects) remains challenging because of uncontrolled diffusive motion of the particles. We describe here a general methodology for solvent-induced, reversible self-assembly of gold nanoparticles into 3D clusters with well-controlled sizes. A theoretical description of the process confirmed that hydrophobic interactions are the main driving force behind nanoparticle aggregation.

Specific and reversible DNA-directed self-assembly of oil-in-water emulsion droplets

Higher-order structures that originate from the specific and reversible DNA-directed self-assembly of microscopic building blocks hold great promise for future technologies. Here, we functionalized biotinylated soft colloid oil-in-water emulsion droplets with biotinylated single-stranded DNA oligonucleotides using streptavidin as an intermediary linker. We show the components of this modular linking system to be stable and to induce sequence-specific aggregation of binary mixtures of emulsion droplets. Three length scales were thereby involved: nanoscale DNA base pairing linking microscopic building blocks resulted in macroscopic aggregates visible to the naked eye. The aggregation process was reversible by changing the temperature and electrolyte concentration and by the addition of competing oligonucleotides. The system was reset and reused by subsequent refunctionalization of the emulsion droplets. DNA-directed self-assembly of oil-in-water emulsion droplets, therefore, offers a solid basis for programmable and recyclable soft materials that undergo structural rearrangements on demand and that range in application from information technology to medicine.

Fabrication and Manipulation of Gold 1D Chain Assemblies Using Magnetically Controllable Gold Nanoparticles

core/gold shell nanoparticles. The core/shell particles have the capability of forming gold 1D chains in thepresence of an external magnetic field. Here we demonstrate dynamic and reversible self-assembly of the gold1D chain structures in an aqueous solution without any templates or physical or chemical attachment. Thespatial configuration of gold chains can be arbitrarily manipulated by controlling the direction of a magneticfield. This technique can provide arbitrary manipulation of gold 1D chains for fabrication purpose. Todemonstrate this capability, we present a technique for immobilization of the gold particle chains on a glasssubstrate.Key Words : Magnetic core/gold nanoshell, Gold nanoparticle, Self-assembly, Magnetic manipulationIntroductionThe ability to assemble noble metal nanoparticles is animportant area of study due to their unique localized surfaceplasmon resonance (LSPR) properties

Accounting for Finite-Number Effects on Cluster Size Distributions in Simulations of Equilibrium Aggregation.

An approach is given to analyze aggregate size distributions obtained from simulations of a fixed number N of monomers undergoing reversible self-assembly. Equilibrium distributions are derived from size-dependent equilibrium association constants by appropriately weighted sums over all partitions of N monomers into aggregates. Conversely, equilibrium association constants can be obtained from an iterative fit to a finite-N equilibrium distribution. Model data for a micelle-forming system are used to show how results from simulations containing few micelles can yield infinite-N limiting distributions. A strategy is also suggested to exploit small-N effects on aggregate size distributions to enhance sampling of critical clusters in determination of nucleation free energy functions.

Light-Controlled Reversible Micellization of a Diblock Copolymer in an Ionic Liquid

We report the reversible photoinduced self-assembly of a diblock copolymer in a typical hydrophobic ionic liquid, 1-butyl-3-methylimidazolium hexafluorophosphate ([C4mim]PF6). A series of random copolymers consisting of 4-phenylazophenyl methacrylate and N-isopropylacrylamide (P(AzoMA-r-NIPAm)) show both photoresponsive solubility changes and upper critical solution temperature (UCST) phase transitions in [C4mim]PF6. The UCST phase transition temperature of the random copolymer depends strongly on the composition of AzoMA as well as on the photoisomerization state of the azobenzene moiety. The phase transition temperature of P(trans-AzoMA-r-NIPAm) in the dark is lower than that of P(cis-AzoMA-r-NIPAm) under UV-light irradiation. Reversible solubility changes by changing the wavelength of incident light were demonstrated by using the difference between the phase transition temperatures. On the basis of the results, we apply the thermo- and photoresponsive property of the random copolymer to a block copolym...

Supramolecular Assembly of Diplatinum Species through Weak PtII⋅⋅⋅PtII Intermolecular Interactions: A Combined Experimental and Computational Study

The present study elucidates the factors that govern the spontaneous self-assembly of a family of dimetal [Pt(2)L(4)] (L=dithiocarboxylato ligand) complexes. Experimental data show that variables such as temperature, concentration, solvent and the nature of the ligand L have a critical effect on the reversible self-assembly of supramolecular [Pt(2)L(4)](n) entities. In solution, new UV/Vis spectroscopic features emerge at low temperatures and/or high concentrations, which are attributed to the formation of oligomeric [Pt(2)L(4)](n) species. The description of intermolecular Pt⋅⋅⋅Pt interactions, the main driving force for the association, was addressed from a computational perspective. The contributions from intermolecular Pt⋅⋅⋅S and S⋅⋅⋅S interactions to these supramolecular assemblies were found to be repulsive. Experimental UV/Vis data have been interpreted by means of computational spectroscopy.

Macromol. Biosci. 9/2012

Front Cover: Reversible self-assembly of Poly(L-glutamic acid)-b-poly(L-lysine-r-dihydroxyphenyl alanine) at acidic and basic pHs forms an ellipsoidal morphology and vesicles, respectively. Subsequent O2-mediated oxidation of the phenolic groups of the DOPA at pH 12 lead to intermolecular dimerization to stabilize the vesicles via in situ cross-linking. Further details can be found in the article by A. Sulistio, A. Blencowe, J. Wang, G. Bryant, X. Zhang, G. G. Qiao* on page 1220.

Pattern Recognition of Cancer Cells Using Aptamer-Conjugated Magnetic Nanoparticles

Biocompatible magnetic nanosensors based on reversible self-assembly of dispersed magnetic nanoparticles into stable nanoassemblies have been used as effective magnetic relaxation switches (MRSw) for the detection of molecular interactions. We report, for the first time, the design of MRSw based on aptamer-conjugated magnetic nanoparticles (ACMNPs). The ACMNPs capitalize on the ability of aptamers to specifically bind target cancer cells, as well as the large surface area of MNPs to accommodate multiple aptamer binding events. The ACMNPs can detect as few as 10 cancer cells in 250 μL of sample. The ACMNPs' specificity and sensitivity are also demonstrated by detection in cell mixtures and complex biological media, including fetal bovine serum, human plasma, and whole blood. Furthermore, by using an array of ACMNPs, various cell types can be differentiated through pattern recognition, thus creating a cellular molecular profile that will allow clinicians to accurately identify cancer cells at the molecular and single-cell level.

Construction of photo-responsive micelles from azobenzene-modified hyperbranched polyphosphates and study of their reversible self-assembly and disassembly behaviours

Photo-responsive micelles with reversible self-assembly and disassembly behaviours were constructed via the supramolecular host–guest interaction of β-cyclodextrin (β-CD) and an amphiphilic azobenzene-containing hyperbranched polymer (denoted HPHEEP-Azo). The polymer was prepared through the carboxylation of hydroxyl groups in hyperbranched polyphosphate (HPHEEP-OH) with succinic anhydride and the subsequent esterification reaction with 4-hydroxyazobenzene. Dynamic light scattering (DLS) and transmission electron microscopy (TEM) measurements reveal that HPHEEP-Azo can self-assemble into spherical micelles with an average diameter of 169.9 nm in aqueous solution. The critical micelle concentration (CMC) of the micelles is 0.013 mg mL−1. After addition of β-CD into the micellar solution, the micelles dissociated gradually upon increasing the addition amount of β-CD. Irradiation experiments show that reversible self-assembly and disassembly behaviours can be controlled by irradiating with UV and visible light. These photo-responsive micelles self-assembled from hyperbranched polymers might have great potential in various practical applications such as controlled drug release.

Insight into peptide self-assembly from anisotropic rotational diffusion derived from 13C NMR relaxation

The NMR heteronuclear relaxation rate's dependency on the anisotropy of rotational diffusion motions can be exploited to investigate the supramolecular organization that results from reversible peptide self-assembly in solution. The measurement of longitudinal (R1) and transverse (R2) 13C relaxation rates for several peptide concentrations provides insight both into the orientation of individual molecules within the supramolecular assembly and its growth. The methodology was applied on the pore forming cyclic lipodepsipeptide pseudodesmin A, which reversibly assembles into supramolecular structures of indefinite size in non-polar organic solvents. The information extracted by correlating the 13C R1 and R2 relaxation rates—obtained at natural abundance and at multiple peptide concentrations—with the orientation of the C–H bonds in the monomer conformation demonstrates the existence of an axially symmetric assembly that exhibits unidimensional growth upon increased peptide concentrations. The orientation of the pseudodesmin A peptide within this assembly could be determined accurately and is consistent with the suggested model for the pore forming function and the peptide-peptide interactions within the oligomer.