Self‐Recognition Between Two Almost Identical Macroions During Their Assembly: The Effects of pH and Temperature

Two Keplerate‐type macroions, [Mo^VI₇₂Fe^III₃₀O₂₅₂‐ (CH₃COO)₁₂{Mo₂O₇(H₂O)}₂{H₂Mo₂O₈(H₂O)}(H₂O)₉₁]?ca. 150 H₂O= {Mo₇₂Fe₃₀} and [{Na(H₂O)₁₂}?{Mo^VI₇₂Cr^III₃₀O₂₅₂(CH₃COO)₁₉‐ (H₂O)₉₄}]?ca. 120 H₂O= {Mo₇₂Cr₃₀} , with identical size and shape but different charge density, can self‐assemble into spherical “blackberry”‐like structures in aqueous solution by means of electrostatic interactions. These two macroanions can self‐recognize each other and self‐assemble into two separate types of homogeneous blackberries in their mixed dilute aqueous solution, in which they carry ?7 and ?5 net charges, respectively. Either adjusting the solution pH or raising temperature is expected to make the self‐recognition more difficult, by making the charge densities of the two clusters closer, or by decreasing the activation energy barrier for the blackberry formation, respectively. Amazingly, the self‐recognition behavior remains, as confirmed by dynamic and static light scattering, TEM, and energy dispersive spectroscopy techniques. The results prove that the self‐recognition behavior of the macroions due to the long‐range electrostatic interaction is universal and can be achieved when only minimum differences exist between two types of macroanions.     

Monitoring and Targeting the Initial Dimerization Stage of Amyloid Self‐Assembly

Amyloid deposits are pathological hallmark of a large group of human degenerative disorders of unrelated etiologies. While accumulating evidence suggests that early oligomers may account for tissue degeneration, most detection tools do not allow the monitoring of early association events. Here we exploit bimolecular fluorescence complementation analysis to detect and quantify the dimerization of three major amyloidogenic polypeptides; islet amyloid polypeptide, β‐amyloid and α‐synuclein. The constructed systems provided direct visualization of protein‐protein interactions in which only assembled dimers display strong fluorescent signal. Potential inhibitors that interfere with the initial intermolecular interactions of islet amyloid polypeptide were further identified using this system. Moreover, the identified compounds were able to inhibit the aggregation and cytotoxicity of islet amyloid polypeptide, demonstrating the importance of targeting amyloid dimer formation for future drug development.     

An M12(L1)12(L2)12 Cantellated Tetrahedron: A Case Study on Mixed‐Ligand Self‐Assembly

In the self‐assembly of Pd^II ions and two different, but similarly shaped, ligands ( 1 and 2 ), neither random mixing nor self‐sorting of the two ligands into two unmixed structures was observed. Instead a mixed, yet sorted, Pd₁₂( 1 )₁₂( 2 )₁₂ cantellated tetrahedron (and its pseudoisomer) was selectively formed, thus revealing a fine example of intramolecular self‐sorting. A case study showed that a homothetic ratio of >2 is necessary to observe cantellated tetrahedra.     

pH‐Triggered Self‐Assembly of Cellulose Oligomers with Gelatin into a Double‐Network Hydrogel

Multicomponent systems for self‐assembled molecular gels provide huge opportunities to generate collective or new functions that are not inherent in individual single‐component gels. However, gelation tends to require careful and complicated procedures, because, among a myriad of kinetically trapped structures related to the degree of mixing of multiple components over a wide range of scales, from molecular level to macroscopic scale, a limited number of structures that exhibit the desired function need to be constructed. This study presents a simple method for the construction of double‐network (DN) hydrogels with improved stiffness composed of crystalline cellulose oligomers and gelatin. The pH‐triggered self‐assembly of cellulose oligomers leads to the formation of robust networks composed of crystalline nanofibers in the presence of dissolved gelatin, followed by cooling to allow for the formation of soft gelatin networks. The resultant DN hydrogels exhibit improved stiffness; the improvement in gel stiffness with double networking is comparable to that of previously reported DN hydrogels produced via a time‐consuming enzymatic reaction.     

In Situ Visualization of Block Copolymer Self‐Assembly in Organic Media by Super‐Resolution Fluorescence Microscopy

Analytical methods that enable visualization of nanomaterials derived from solution self‐assembly processes in organic solvents are highly desirable. Herein, we demonstrate the use of stimulated emission depletion microscopy (STED) and single molecule localization microscopy (SMLM) to map living crystallization‐driven block copolymer (BCP) self‐assembly in organic media at the sub‐diffraction scale. Four different dyes were successfully used for single‐colour super‐resolution imaging of the BCP nanostructures allowing micelle length distributions to be determined in situ. Dual‐colour SMLM imaging was used to measure and compare the rate of addition of red fluorescent BCP to the termini of green fluorescent seed micelles to generate block comicelles. Although well‐established for aqueous systems, the results highlight the potential of super‐resolution microscopy techniques for the interrogation of self‐assembly processes in organic media.     

Synthesis and Characterisation of Self‐Assembled and Self‐Adjuvanting Asymmetric Multi‐Epitope Lipopeptides of Ovalbumin

Designing a lipopeptide (LP) vaccine with a specific asymmetric arrangement of epitopes may result in an improved display of antigens, increasing host‐cell recognition and immunogenicity. This study aimed to synthesise and characterise the physicochemical properties of a library of asymmetric LP‐based vaccine candidates that contained multiple CD4⁺ and CD8⁺ T‐cell epitopes from the model protein antigen, ovalbumin. These fully synthetic vaccine candidates were prepared by microwave‐assisted solid phase peptide synthesis. The C12 or C16 lipoamino acids were coupled to the N or C terminus of the OVA CD4 peptide epitope. The OVA CD4 LPs and OVA CD8 peptide constructs were then conjugated using azide–alkyne Huisgen cycloaddition to give multivalent synthetic vaccines. Physiochemical characterisation of these vaccines showed a tendency to self‐assemble in aqueous media. Changes in lipid length and position induced self‐assembly with significant changes to their morphology and secondary structure as shown by transmission electron microscopy and circular dichroism.     

Synthesis,self‐assembly,fluorescence, and thermosensitive properties of star‐shaped amphiphilic copolymers with porphyrin core

Star‐shaped amphiphilic poly(ε‐caprolactone)‐block‐poly(oligo(ethylene glycol) methyl ether methacrylate) with porphyrin core (SPPCL‐b‐POEGMA) was synthesized by combination of ring‐opening polymerization (ROP) and atom transfer radical polymerization (ATRP). Star‐shaped PCL with porphyrin core (SPPCL) was prepared by bulk polymerization of ε‐caprolactone (CL) with tetrahydroxyethyl‐terminated porphyrin initiator and tin 2‐ethylexanote (Sn(Oct)₂) catalyst. SPPCL was converted into SPPCLBr macroinitiator with 2‐bromoisobutyryl bromide. Star‐shaped SPPCL‐b‐POEGMA was obtained via ATRP of oligo(ethylene glycol) methyl ether methacrylate (OEGMA). SPPCL‐b‐POEGMA can easily self‐assemble into micelles in aqueous solution via dialysis method. The formation of micellar aggregates were confirmed by critical micelle formation concentration, dynamic light scattering, and transmission electron microscopy. The micelles also exhibit property of temperature‐induced drug release and the lower critical solution temperature (LCST) was 60.6 °C. Furthermore, SPPCL‐b‐POEGMA micelles can reversibly swell and shrink in response to external temperature. In addition, SPPCL‐b‐POEGMA can present obvious fluorescence. Finally, the controlled drug release of copolymer micelles can be achieved by the change of temperatures. © 2011 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2011     

Synthesis of a Benzenethiol‐derivatized Porphyrin for Self‐assembly

The synthesis of a benzenethiol‐derivatized porphyrin for flat‐lying self‐assembly on gold substrates is described. Acetyl protected thiol is not stable enough in Pd‐catalyzed reactions. While acrylate derivatives protected thiol group shows good tolerance in Pd‐catalyzed borylations and Suzuki‐Miyaura coupling reactions and no catalyst poisoning was observed.     

Hydrogen‐bonding‐aided synthesis of novel ladderlike organobridged polysiloxane containing side‐chain naphthyl groups

With a hydrogen‐bonding template, a novel soluble aryl amide‐bridged ladderlike polysiloxane, containing naphthyl as the side‐chain group, has been successfully synthesized via a stepwise coupling polymerization. It is proposed that the monomer, N,N′‐di(3‐naphthyldiethoxylsilyl‐propyl)‐[4,4′‐oxybis(benzyl amide)], prepared by Grignard and hydrosilylation reactions, undergoes self‐assembly first via amido hydrogen bonding and then via hydrolysis, followed by condensation under controlled reaction conditions to yield a high molecular weight, soluble, dark yellow polymer. The analytical results (Fourier transform infrared, ¹H NMR, ²⁹Si NMR, X‐ray diffraction, differential scanning calorimetry, and vapor pressure osmometry) show that the polymer possesses an ordered ladderlike architecture. © 2003 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 41: 636–644, 2003     

Self‐assembling directed synthesis of a novel terephthalamide‐bridged ladderlike polysiloxane

A novel, soluble terephthalamide‐bridged ladderlike polysiloxane ( L ) was synthesized successfully for the first time by stepwise coupling polymerization. The process involved the hydrogen‐bonding self‐assembly of amido groups, which resulted in the formation of a more highly ordered polymeric structure. A novel monomer, bis(3‐methyldimethoxysilylpropyl) terephthalamide ( M ), was prepared by a hydrosilylation reaction in the presence of dicyclopentadienyl platinum dichloride as a catalyst. The structures of the monomer ( M ) and the polymer ( L ) were characterized by Fourier transform infrared, ¹H NMR, ¹³C NMR, ²⁹Si NMR, mass spectrometry, X‐ray diffraction, differential scanning calorimetry, and vapor pressure osmometry. All the characterization data indicated that the synthesized polymer ( L ) possessed an ordered ladderlike structure. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3161–3170, 2002     

Self－assembly of Novel Hetero[3]rotaxane, [2]Rotaxanes and [2]Catenane

One linear template 13 and one cyclophane template 15, both incorporating two electron rich 1,4‐dialkoxybenzene units and one diamide unit, have been synthesized. By utilizing donor‐acceptor interaction and/or intermolecular hydrogen bonding assembling principles, one novel hetero[3]rotazane 22·4Cl, possessing one neutral and one tetracationic ring components, has been synthesized from 13, through neutral [2]rotaxane 21 as intermediate. With 15 as template, tetracationic [2]catenane 23·4PF₆ was assembled by using donor‐acceptor interaction, but no neutral [2]rotaxane could be obtained under the typical conditions of hydrogen bonding assembling principle. The interlocked supramolecular compounds have been characterized and their spectral properties are investigated.     

Cholesterol-substituted Tetrathiafulvalene(TTF)Compound:Formation of Organogel and Supramolecular Chirality

A new tetrathiafulvalene (TTF) derivative with two cholesterol units (compound 1 ) was synthesized and characterized. Gelation of n‐hexane occurred after the hot solution of 1 was subjected to ultrasonic treatment for a few minutes. The resulting organogel was characterized with SEM, XRD and AFM. Besides heating the gel‐sol transition also occurred upon addition of I₂ which can oxidize the TTF unit in 1 . This result provides a new example of organogels responding to redox reactions. Interestingly, gelation‐induced CD signals were observed and the CD signals can be tuned with the gel‐sol transition which can be effected by heating and chemical reaction with I₂.     

Entropically Driven Self‐Assembly of Lysinibacillus sphaericus S‐Layer Proteins Analyzed Under Various Environmental Conditions

S‐Layer proteins are an example of bionanostructures that can be exploited in nanofabrication. In addition to their ordered structure, the ability to self‐assembly is a key feature that makes them a promising technological tool. Here, in vitro self‐assembly kinetics of SpbA was investigated, and found that it occurs at a rate that is dependent on temperature, its concentration, and the concentration of calcium ions and sodium chloride. The activation enthalpy (120.81 kJ · mol^?1) and entropy (129.34 J · mol^?1 · K^?1) obtained infers that the incorporation of monomers incurs in a net loss of hydrophobic surface. By understanding how the protein monomers drive the self‐assembly at different conditions, the rational optimization of this process was feasible.

     

Self‐Healing Colloidal Crystals

Healing hands : A complex interplay between colloidal and polymeric energetics in microgel self‐assembly behavior results in soft colloidal assemblies with self‐healing properties. Repulsive soft spheres can adopt highly compressed conformations in colloidal crystalline lattices without directly contacting the nearest neighbors (see picture). This distant action is directly responsible for the self‐healing of the assemblies.

     

Interactions of KLVFF-PEG peptide conjugate with fibrinogen in neutral aqueous solutions

In this work we report on the interaction of KLVFF-PEG with fibrinogen (Fbg) in neutral aqueous solutions at 20 degrees C, for particular ratios of KLVFF-PEG to Fbg concentration, Delta = c(KLVFF-PEG)/c(Fbg). Our results show the formation of Fbg/KLVFF-PEG complexes for Delta > 0, such that there is not an extended network of complexes throughout the solution. In addition, cleaved protein and Fbg dimers are identified in the solution for Delta >or= 0. There is a dramatic change in the tertiary structure of the Fbg upon KLVFF-PEG binding, although the KLVFF-PEG binds to the Fbg without affecting the secondary structure elements of the glycoprotein.     

Synthesis of Copper Oxide Hierarchical Nanostructures

The copper oxide (CuO) hierarchical nanostructures were synthesized by a simple hydrothermal reaction, using copper(II) acetylacetonate and NaOH as the reactants. The morphologies of CuO nanostructures are strongly influenced by the dosage of copper(II) acetylacetonate, alkali concentration and reaction temperature. The possible formation process was also discussed on the basis of time‐dependent experiments. This simple solution‐phase method may be useful for morphological synthesis of other oxides nanocrystals.