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.     

Soft-surface DNA nanotechnology: DNA constructs anchored and aligned to lipid membrane

No strings attached: At least three attachment points are needed to align a two-dimensional DNA nanoconstruct to a soft lipid membrane surface with a porphyrin nucleoside as membrane anchor. The resulting freely diffusing DNA constructs can be reversibly assembled on the surface thus enabling the possibility of a self-repairing system.     

More than Meets the Eye: Conformational Switching of a Stacked Dialkoxynaphthalene–Naphthalenetetracarboxylic diimide (DAN–NDI) Foldamer to an NDI–NDI Fibril Aggregate

The thermally induced conformational switching of a stacked dialkxoynaphthalene–naphthalenetetracarboxylic diimide (DAN–NDI) amphiphilic foldamer to an NDI–NDI fibril aggregate is described. The aggregated fibril structures were explored by UV/Vis, circular dichroism (CD), atomic‐force microscopy (AFM), and TEM techniques. Our findings indicate that the aromatic DAN–NDI interactions of the original foldamer undergoes transformation to a fibrillar assembly with aromatic NDI–NDI stacked interactions. These structural insights could help inform new molecular designs and increase our understanding of fibrillar assembly and aggregation process in aqueous solution.     

Intermolecular Communication on a Liposomal Membrane: Enzymatic Amplification of a Photonic Signal with a Gemini Peptide Lipid as a Membrane‐Bound Artificial Receptor

A supramolecular system that can activate an enzyme through photo‐isomerization was constructed by using a liposomal membrane scaffold. The design of the system was inspired by natural signal transduction systems, in which enzymes amplify external signals to control signal transduction pathways. The liposomal membrane, which provided a scaffold for the system, was prepared by self‐assembly of a photoresponsive receptor and a cationic synthetic lipid. NADH‐dependent L ‐lactate dehydrogenase, the signal amplifier, was immobilized on the liposomal surface by electrostatic interactions. Recognition of photonic signals by the membrane‐bound receptor induced photo‐isomerization, which significantly altered the receptor’s metal‐binding affinity. The response to the photonic signal was transmitted to the enzyme by Cu²⁺ ions. The enzyme amplified the chemical information through a catalytic reaction to generate the intended output signal.     

Spontaneous Reconstitution of Functional Transmembrane Proteins During Bioorthogonal Phospholipid Membrane Synthesis

Transmembrane proteins are critical for signaling, transport, and metabolism, yet their reconstitution in synthetic membranes is often challenging. Non‐enzymatic and chemoselective methods to generate phospholipid membranes in situ would be powerful tools for the incorporation of membrane proteins. Herein, the spontaneous reconstitution of functional integral membrane proteins during the de novo synthesis of biomimetic phospholipid bilayers is described. The approach takes advantage of bioorthogonal coupling reactions to generate proteoliposomes from micelle‐solubilized proteins. This method was successfully used to reconstitute three different transmembrane proteins into synthetic membranes. This is the first example of the use of non‐enzymatic chemical synthesis of phospholipids to prepare proteoliposomes.     

Spatial Structuring of a Supramolecular Hydrogel by using a Visible‐Light Triggered Catalyst

Spatial control over the self‐assembly of synthetic molecular fibers through the use of light‐switchable catalysts can lead to the controlled formation of micropatterns made up of hydrogel structures. A photochromic switch, capable of reversibly releasing a proton upon irradiation, can act as a catalyst for in situ chemical bond formation between otherwise soluble building blocks, thereby leading to fiber formation and gelation in water. The use of a photoswitchable catalyst allows control over the distribution as well as the mechanical properties of the hydrogel material. By using homemade photomasks, spatially structured hydrogels were formed starting from bulk solutions of small molecule gelator precursors through light‐triggered local catalyst activation.     

Light Triggered Co‐Assembly of Photocleavable Copolymers and Polyoxometalates with Enhanced Photoluminescence

A novel co‐assembly based on the block copolymer bearing photocleavable groups and macroanionic polyoxometalates Na₉[Ln(W₅O₁₈)₂] (LnW₁₀, Ln = Eu, Dy) triggered by UV light is realized in aqueous solution. The copolymer synthesized by atom transfer radical polymerization (ATRP) undergoes irreversible cleavage upon UV irradiation to generate primary amine (pKa ≈ 8–9) residues which are completely protonated under a neutral pH in aqueous solution. Electrostatic attractions between the resulting positively charged copolymers and anionic LnW₁₀ drive the formation of assemblies. In situ small angle X‐ray scattering and transmission electron microscopy are used to characterize the morphology of the assemblies. The microenvironments around polyoxometalates in the core of hybrid assemblies become highly hydrophobic, resulting in dramatically enhanced photoluminescence with the obvious intensity enhancement. The solution parameters pH and salt additives show great effects on the formation of assemblies.

     

In Situ Vesicle Formation by Native Chemical Ligation

Phospholipid vesicles are of intense fundamental and practical interest, yet methods for their de novo generation from reactive precursors are limited. A non‐enzymatic and chemoselective method to spontaneously generate phospholipid membranes from water‐soluble starting materials would be a powerful tool for generating vesicles and studying lipid membranes. Here we describe the use of native chemical ligation (NCL) to rapidly prepare phospholipids spontaneously from thioesters. While NCL is one of the most popular tools for synthesizing proteins and nucleic acids, to our knowledge this is the first example of using NCL to generate phospholipids de novo. The lipids are capable of in situ synthesis and self‐assembly into vesicles that can grow to several microns in diameter. The selectivity of the NCL reaction makes in situ membrane formation compatible with biological materials such as proteins. This work expands the application of NCL to the formation of phospholipid membranes.     

Bilayer Molecular Assembly at a Solid/Liquid Interface as Triggered by a Mild Electric Field

The construction of a spatially defined assembly of molecular building blocks, especially in the vertical direction, presents a great challenge for surface molecular engineering. Herein, we demonstrate that an electric field applied between an STM tip and a substrate triggered the formation of a bilayer structure at the solid–liquid interface. In contrast to the typical high electric‐field strength (10⁹ V m^?1) used to induce structural transitions in supramolecular assemblies, a mild electric field (10⁵ V m^?1) triggered the formation of a bilayer structure of a polar molecule on top of a nanoporous network of trimesic acid on graphite. The bilayer structure was transformed into a monolayer kagome structure by changing the polarity of the electric field. This tailored formation and large‐scale phase transformation of a molecular assembly in the perpendicular dimension by a mild electric field opens perspectives for the manipulation of surface molecular nanoarchitectures.     

Sonication‐Triggered Instantaneous Gel‐to‐Gel Transformation

Two new peptide‐based isomers containing cholesterol and naphthalic groups have been designed and synthesized. We found that the position of L ‐alanine in the linker could tune the gelation properties and morphologies. The molecule with the L ‐alanine residue positioned in the middle of the linker ( 1 b ) shows better gelation behavior than that with L ‐alanine directly linked to the naphthalimido moiety ( 1 a ). As a result, a highly thermostable organogel of 1 b with a unique core–shell structure was obtained at high temperature and pressure in acetonitrile. Moreover, the gels of 1 a and 1 b could undergo an instantaneous gel‐to‐gel transition triggered by sonication. Ultrasound could break the core–shell microsphere of 1 b and the micelle structure of 1 a into entangled fibers. By studying the mechanism of the sonication‐triggered gel‐to‐gel transition process of these compounds, it can be concluded that ultrasound has a variety of effects on the morphology, such as cutting, knitting, unfolding, homogenizing, and even cross‐linking. Typically, ultrasound can cleave and homogenize π‐stacking and hydrophobic interactions among the gel molecules and then reshape the morphologies to form a new gel. This mechanism of morphology transformation triggered by sonication might be attractive in the field of material storage and controlled release.     

Mimicking the cell membrane with block copolymer membranes

Cell membranes are essential barriers in Nature. To understand their properties and functions and to develop desirable applications, a simple and elegant approach is to study membranes that mimic the cell membrane. Lipid bilayers represent simple models that are physiologically representative when in the form of mixtures of various lipids, but they are not adequately stable even when covered with amphipathic proteins or when combined with polymers, thus preventing technological applications. This makes necessary the design of completely synthetic membranes. In this respect, amphiphilic copolymers that self‐assemble under dilute aqueous conditions and generate supramolecular polymer vesicles or films are ideal candidates for synthetic membranes. Their versatility in terms of chemistry and properties (permeability, mechanical stability, thickness), if appropriately designed, enable the insertion of biological molecules, such as membrane proteins and biopores, or the attachment of biomolecules at their surfaces. Here, we present the domain of synthetic membranes based on amphiphilic copolymers beginning with their generation and up to their applications in medicine, the food industry, and technology. Even though significant progress has been made in combining them with membrane proteins, open questions remain with respect to desired properties that could accommodate biological molecules and support further development of the field, from both the point of view of fundamental understanding and of applications. © 2012 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem, 2012