Self-assembled Supramolecular Architectures Research Articles

Insight into structural biophysics from solution X-ray scattering

The current challenges of structural biophysics include determining the structure of large self-assembled complexes, resolving the structure of ensembles of complex structures and their mass fraction, and unraveling the dynamic pathways and mechanisms leading to the formation of complex structures from their subunits. Modern synchrotron solution X-ray scattering data enable simultaneous high-spatial and high-temporal structural data required to address the current challenges of structural biophysics. These data are complementary to crystallography, NMR, and cryo-TEM data. However, the analysis of solution scattering data is challenging; hence many different analysis tools, listed in the SAS Portal (http://smallangle.org/), were developed. In this review, we start by briefly summarizing classical X-ray scattering analyses providing insight into fundamental structural and interaction parameters. We then describe recent developments, integrating simulations, theory, and advanced X-ray scattering modeling, providing unique insights into the structure, energetics, and dynamics of self-assembled complexes. The structural information is essential for understanding the underlying physical chemistry principles leading to self-assembled supramolecular architectures and computational structural refinement.

Investigating the impact of inbuilt cold atmospheric pressure plasma on molecular assemblies of tryptophan enantiomers: in vitro fabrication of self-assembled supramolecular structures.

The advancements in understanding the phenomenon of plasma interactions with matter, coupled with the development of CAPP devices, have resulted in an interdisciplinary research topic of significant importance. This has led to the integration of various fields of science, including plasma physics, chemistry, biomedical sciences, and engineering. The reactive oxygen species and reactive nitrogen species generated from cold atmospheric plasma on interaction with biomolecules like proteins and peptides form various supramolecular structures. CAPP treatment of amino acids, which are the fundamental building blocks of proteins, holds potential in creating self-assembled supramolecular architectures. In this work, we demonstrate the process of self-assembly of aromatic amino acid tryptophan (Trp) enantiomers (l-tryptophan and d-tryptophan) into ordered supramolecular assemblies induced by the reactive species generated by a cold atmospheric pressure helium plasma jet. These enantiomers of tryptophan form organized structures as evidenced by FE-SEM. To assess the impact of CAPP treatment on the observed assemblies, we employed various analytical techniques such as zeta potential, dynamic light scattering and FTIR spectroscopy. Also, photoluminescence and time-resolved lifetime measurements revealed the transfiguration of individual Trp enantiomers. The LC-ESI-QTOF-MS analysis demonstrated that CAPP irradiation led to the incorporation of oxygenated ions into the pure Trp molecule. These studies of the self-assembly of Trp due to ROS and RNS interactions will help us to understand the assembly environment. This knowledge may be utilized to artificially design and synthesize highly ordered functional supramolecular structures using CAPP.

Positional isomeric effect of acyclic hosts on supramolecular recognition of anionic guests

• Anion coordinated neutral/charged self-assemblies of positional isomeric receptors. • Acyclic positional isomeric receptor with different functionalities is discussed. • Anion-coordinated different types of molecular assemblies are summarized. • Aerial CO 2 uptake, extraction, transport phenomena are also discussed. Two or more supramolecular hydrogen-bonding receptor scaffolds having identical molecular formulas act as positional isomers only when the position of a substituent or a receptor arm or double/triple bond of one isomer differ from another isomer. The review summarizes the research on anion coordination chemistry of last decade affected by the positional isomeric acyclic receptors. The detailed and comprehensive account of reported examples of one or more anionic guest/hydrated-anionic guest assisted self-assemblies (neutral or charged) of artificial acyclic isomers (monopodal or linear, dipodal, triodal, hexapodal), affected by the terminal aryl substituents or the receptor arms with respect to central aryl spacer are systematically incorporated in the review. The review specifically consolidates the underexplored broad area of anion recognition chemistry affected by positional isomerism of acyclic amine, amide, urea, thiourea functionalized receptors/sensors in solid as well as in solution state. These substituent dependent isomeric systems could provide insights into the fundamental hydrogen-bonded anion-receptor chemistry and also useful for understanding the biological and environmental processes followed by the crystal engineering as well as extraction, aerial CO 2 fixation, sensing or transport phenomena of anions. Discussions relating to the construction of some typical examples of anion-coordinated self-assembled supramolecular architectures such as molecular capsules, barrels, helicates, foldamer, tetrahedral cages and mechanically interlocked systems by these positional isomeric podands are also included in this review.

Development of a tripeptide based arginine sensor via applying the concept of molecular engineering

In this present work, we have synthesized two tripeptides and one of them is the molecular engineered version of the other one. The study shows how a single nitro group can abruptly change the physicochemical properties of a tripeptide. Tripeptide 3 shows interesting self-assembled nanoscale supramolecular architectures. We experienced a gradual transition from toroid to sphere morphology. Contrary to this, 4, the molecular engineered version of 3, organizes in a completely different manner. Instead of producing aggregated spheres, it produces a structure similar to a chain of pearls. In the case of secondary structure, compound 3 shows beta sheet-like structure while compound 4 exhibits alpha helix-like assembly. Compound 4 acts as an arginine sensor with a detection limit of 1.38 μM in the water. Furthermore, using Density-functional theory, optimization of arginine bound 4, calculation of adsorption energies, and prediction of absorption spectra were obtained which support the experimental data.

Precise control over supramolecular nanostructures via manipulation of H-bonding in π-amphiphiles.

Self-assembled supramolecular architectures are ubiquitous in nature. A synchronized combination of dynamic noncovalent interactions is the major driving force in forming unique structures with high-precision control over the self-assembly of supramolecular materials. Herein, we have achieved programmable nanostructures by introducing single/multiple H-bonding units in a supramolecular building block. A diverse range of nanostructures can be generated in aqueous medium by subtly tuning the structure of π-amphiphiles. 1D-cylindrical micelles, 2D-nanoribbons and hollow nanotubes are produced by systematically varying the number of H-bonding units (0-2) in structurally near identical π-amphiphiles. Spectroscopic measurements revealed the decisive role of H-bonding units for different modes of molecular packing. We have demonstrated that a competitive self-assembled state (a kinetically controlled aggregation state and a thermodynamically controlled aggregation state) can be generated by fine tuning the number of noncovalent forces present in the supramolecular building blocks. The luminescence properties of conjugated dithiomaleimide (DTM) provided insight into the relative hydrophobicity of the core in these nanostructures. In addition, fluorescence turn-off in the presence of thiophenol enabled us to probe the accessibility of the hydrophobic core in these assembled systems toward guest molecules. Therefore the DTM group provides an efficient tool to determine the relative hydrophobicity and accessibility of the core of various nanostructures which is very rarely studied in supramolecular assemblies.

A Gold Nanocluster Constructed Mixed-Metal Metal-Organic Network Film for Combating Implant-Associated Infections.

The development of modular strategies for programming self-assembled supramolecular architectures with distinct structural and functional features is of immense scientific interest. We reported on the intrinsic antibacterial capability of anionic amphiphilic gold nanoclusters (GNCs) capped by para-mercaptobenzoic acid, which was closely related to the protonation level of terminal carboxylate groups. By using of the metal-ligand coordination-driven and solvent evaporation-induced self-assembly, we constructed GNCs-based mixed-metal metal-organic network (MM-MON) films on titanium disks as antibacterial nanocoatings. Taking the reasonable utilization of tetravalent metal ions M4+ (Ti, Zr, Hf; hard Lewis acid) and bactericidal divalent metal ions M2+ (Cu, Zn; borderline acid) co-incorporated metal-carboxylate coordination bonds, the MM-MON films exhibited superior stability due to the robust M4+-O bonds and M2+ releasing behavior resulting from the labile M2+-O coordinating. Together, the MM-MON films integrated the bacteria-responsive character of GNCs, exceptional chemical stability, and greatly enhanced antibacterial activity, ultimately killing adherent bacteria and initiating a self-defensive function. In a rat model for subcutaneous implant-associated infection, the MM-MON nanocoating showed an approximately 2 and 1 log lower multidrug-resistant Staphylococcus aureus implant and tissue colonization, respectively. The generalizable modular strategy of the GNC-metal networks is amenable to facilitate the functionalization of metal surfaces for combating implant-associated infections.

Self-Assembly of Supramolecular Architectures by the Effect of Amino Acid Residues of Quaternary Ammonium Pillar[5]arenes.

Novel water-soluble multifunctional pillar[5]arenes containing amide-ammonium-amino acid moiety were synthesized. The compounds demonstrated a superior ability to bind (1S)-(+)-10-camphorsulfonic acid (S-CSA) and methyl orange dye depending on the nature of the substituent, resulting in the formation one-to-one complexes with both guests. The formation of host-guest complexes was confirmed by ultraviolet (UV), circular dichroism (CD) and 1H NMR spectroscopy. This work demonstrates the first case of using S-CSA as a chiral template for the non-covalent self-assembly of architectures based on pillar[5]arenes. It was shown that pillar[5]arenes with glycine or L-alanine fragments formed aggregates with average hydrodynamic diameters (d) of 165 and 238 nm, respectively. It was established that the addition of S-CSA to the L-alanine-containing derivative led to the formation of micron-sized aggregates with d of 713 nm. This study may advance the design novel stereoselective catalysts and transmembrane amino acid channels.

Fabrication of Biobased Hydrophobic Hybrid Cotton Fabrics Using Molecular Self-Assembly: Applications in the Development of Gas Sensor Fabrics.

Inadvertent inhalation of various volatile organic compounds during industrial processes, such as coal and metal mining, metal manufacturing, paper and pulp industry, food processing, petroleum refining, and concrete and chemical industries, has caused an adverse effect on human health. In particular, exposure to trimethylamine (TMA), a fishy odor poisonous gas, resulted in numerous health hazards such as neurotoxicity, irritation in eyes, nose, skin, and throat, blurred vision, and many more. According to the environmental protection agency, TMA in the level of 0.10 ppm is generally considered as safe, and excess dose results in “trimethylaminuria” or “fish odor syndrome.” In order to avoid the health hazards associated with the inhalation of TMA, there is an urge to design a sensor for TMA detection even at low levels for use in food-processing industries, medical diagnosis, and environment. In this report, for the first time, we have developed a TMA sensor fabric using a sequential self-assembly process from silver-incorporated glycolipids. Formation of self-assembled supramolecular architecture, interaction of the assembled structure with the cotton fabric, and sensing mechanism were completely investigated with the help of various instrumental methods. To our surprise, the developed fabric displayed a transient response for 1–500 ppm of TMA and a stable response toward 100 ppm of TMA for 15 days. We believe that the reported flexible TMA sensor fabrics developed via the sequential self-assembly process hold great promise for various innovative applications in environment, healthcare, medicine, and biology.

Photoinduced LCST Behavior of Amphiphilic Diarylethene Assemblies: Phototransformative Supramolecular Architectures and Photodriven Actuation

Self-assembled supramolecular architectures of amphiphilic diarylethenes featuring tri(ethylene glycol) monomethyl ether chains showed photoinduced macroscopic morphological change upon alternate irradiation with UV and visible light in water. These suspensions containing supramolecular assembly of the diarylethene showed absorption spectral shifts at temperatures corresponding to the lower critical solution temperature (LCST) transition. The photoreversible morphological transformation can be rationalized as the photoinduced phase transition between the high- and low-temperature phases of the LCST transition. Colorless microspheres of the open-ring isomer had bicontinuous coacervate structures. The closed-ring isomers became hydrated state and formed rod-like micelle and bilayer structures depending on intermolecular interaction. The photoinduced change in nanostructure enables application to sophisticated photoactuators in aqueous media. The nanofibers formed bundles in a methylcellulose aqueous solution by depletion force. A submillimeter-sized bundle showed a photoinduced shrinking of more than 100 µm under visible light irradiation. Elongation of the fiber was observed in the direction of linearly polarized light. The diffusive motion was suppressed in the direction perpendicular to that of the generated fiber, as revealed by means of trajectory tracking of added polystyrene beads. Photoinduced clustering of polystyrene beads and photocontrol of their diffusion was achieved with thermal convection and assistance of the change in supramolecular architectures.

Effect of in situ gluten-chitosan interlocked self-assembled supramolecular architecture on rheological properties and functionality of reduced celiac-toxicity wheat flour

A new technology for reducing wheat flour toxicity for celiac disease patients through the in situ formation of gluten-chitosan interlocked self-assembled supramolecular architecture was developed. To have a deeper insight into the microstructure of this new molecular organization and its impact on the dough properties, its small and large deformation rheological properties and the macromolecular features of gluten-chitosan polymers were studied. The reduction of gluten proteins followed by spontaneous oxidation in the presence of the chitosan template in the range of 7.5:1 to 1.3:1 protein to chitosan weight ratio imposed a different reorganization of wheat flour proteins in the polymeric fraction changing conformation from homogeneous spherical molecules to polymer molecules with random-coil conformation. The polymeric fraction increased with decreasing protein to chitosan weight ratio attaining a maximum value at the 1.9:1 ratio. Moreover, the formation of the novel supramolecular architecture at this ratio allowed dough to maintain its ability to form a network after water addition and kneading showing a higher elastic and viscous moduli when compared to the control flour and the other studied formulations. It also presented a significantly higher resistance to extension, didn't inhibit the fermentation process, and retained the original dough ball shape while the dough made with the untreated flour presented a considerable extension during baking. Results show that it is possible to obtain a fully-functional wheat-based product when using a 1.9:1 protein to chitosan weight ratio with a reduced toxicity for celiac patients, opening in this way a new perspective concerning the quest for alternatives of gluten-exclusion diet.

In Situ Gluten-Chitosan Interlocked Self-Assembled Supramolecular Architecture Reduces T-Cell-Mediated Immune Response to Gluten in Celiac Disease.

The prevalence of celiac disease has increased since the last half of the 20th century and is now about 1% in most western populations. At present, people who suffer from celiac disease have to follow a gluten-exclusion diet throughout their lives. Compliance to this restrictive diet is demanding and the development of alternative strategies has become urgent. In this context, it is found that the biocompatible aminopolysaccharide chitosan imposes a different gluten reorganization after gluten redox reaction producing in situ mechanically interlocked supramolecular assemblies between gluten and chitosan. These new structures result in the decrease of gluten digestibility, tissue transglutaminase deamidation activity, and interferon-γ production in intestinal T cell lines generated from biopsy specimens of celiac disease patients. Overall, the results demonstrate the potential of this research avenue to celiac disease is problematic, as the reorganization of gluten proteins to a novel supramolecular architecture shows a positive impact on known pathogenesis mechanisms of the disease. At present, the only therapy for celiac disease is adherence to a gluten-free diet. Here, it is shown that chitosan-imposed gluten reorganization to an interlocked self-assembled supramolecular architecture reduces gluten digestibility, R5-reactivity, tissue transglutaminase deamidation activity, and its capacity to stimulate a T-cell-mediated immune response in celiac disease.

Competition between Hydrogen Bonds and Coordination Bonds Steered by the Surface Molecular Coverage.

In addition to the choices of metal atoms/molecular linkers and surfaces, several crucial parameters, including surface temperature, molecular stoichiometric ratio, electrical stimulation, concentration, and solvent effect for liquid/solid interfaces, have been demonstrated to play key roles in the formation of on-surface self-assembled supramolecular architectures. Moreover, self-assembled structural transformations frequently occur in response to a delicate control over those parameters, which, in most cases, involve either conversions from relatively weak interactions to stronger ones (e.g., hydrogen bonds to coordination bonds) or transformations between the comparable interactions (e.g., different coordination binding modes or hydrogen bonding configurations). However, intermolecular bond conversions from relatively strong coordination bonds to weak hydrogen bonds were rarely reported. Moreover, to our knowledge, a reversible conversion between hydrogen bonds and coordination bonds has not been demonstrated before. Herein, we have demonstrated a facile strategy for the regulation of stepwise intermolecular bond conversions from the metal-organic coordination bond (Cu-N) to the weak hydrogen bond (CH···N) by increasing the surface molecular coverage. From the DFT calculations we quantify that the loss in intermolecular interaction energy is compensated by the increased molecular adsorption energy at higher molecular coverage. Moreover, we achieved a reversible conversion from the weak hydrogen bond to the coordination bond by decreasing the surface molecular coverage.

Supramolecular architectures self-assembled using long chain alkylated spin crossover cobalt(ii) compounds.

Self-assembled hybrid supramolecular architectures formed between amphiphilic anions and long alkylated cationic cobalt(ii) complexes of type [Co(Cn-terpy)2](C12-Glu)2 (n = 15-20) have been synthesized and characterized by TEM, PXRD and magnetic susceptibility measurements. The hybrids display wire or rolled sheet supramolecular arrangements with odd and even alkyl chain dependence, with the cobalt(ii) centres exhibiting gradual spin-crossover behaviours.

External-stimuli responsiveness of self-assembled supramolecular architectures

Supramolecular materials are dynamic in nature which can reversibly dissociate and associate, deconstruct and reconstruct in response to external stimulus. These adaptive supramolecular materials are the materials of future which have shown a new path towards the chemistry of advanced and complex matter. In recent years these supramolecular materials are in the centre of attraction due to its wide range of applications in diversified fields like drug delivery, nanoelectronics, shape memory devices etc. In this short review, the supramolecular assembly-disassembly of molecules in response to the various external stimuli such as pH, light, redox, enzyme have been discussed which were developed in recent past.

Cover Picture: Binding Energies of the π-Stacked Anisole Dimer: New Molecular Beam-Laser Spectroscopy Experiments and CCSD(T) Calculations (Chem. Eur. J. 18/2015)

The unravelling of new fundamental information, the intersection between laser experiments and quantum calculations, with results that will lead to a better description of the structure of biomolecules and nanomaterials is the inspiration behind the cover. In their Full Paper on page 6740 ff., M. Becucci, P. Hobza et al. report on their developments in the experimental measurement of binding energies in π–π stacked complexes, complemented by theoretical calculations. The unravelling of new fundamental information, the intersection between laser experiments and quantum calculations, with results that will lead to a better description of the structure of biomolecules and nanomaterials is the inspiration behind the cover. In their Full Paper on page 6740 ff., M. Becucci, P. Hobza et al. report on their developments in the experimental measurement of binding energies in π–π stacked complexes, complemented by theoretical calculations. Sensing Nitroaromatics In their Concept article on page 6656 ff., S. Shanmugaraju and P. S. Mukherjee detail the adaptability of self-assembled molecular architectures for sensing nitroaromatic explosives. The observed reasonable sensitivity of self-assembled metallacycles/cages is owing to their π-electron-richness and intrinsic porous structures, which eventually accommodate electron-poor nitroaromatics through multiple supramolecular interactions. The synthetic simplicity and easy functionalization make self-assembled supramolecular architectures promising sensor materials.1 Pyridoazacarbazoles A facile and efficient synthetic route to a four-membered heterocyclic ring system, hitherto unknown to literature, is described. Utilizing commercially available building blocks in an elegant base-catalyzed one-pot procedure leads to novel 5,6-dihydro-11H-pyrido[3,2-i]-1-azacarbazoles with promising anticancer properties in only one step. More details of this chemistry and the formation mechanisms are given in the Communication by B. Clement and co-workers on page 6668 ff.1 G-Quadruplexes Duplex DNA formation allows the predictable construction of nanomaterials with a large number of potential applications. Additionally, duplexes and quadruplexes may be combined to form predictable supramolecular structures. In their Full Paper on page 6732 ff., J.-L. Mergny et al. show how classical duplex DNA can guide the strand polarity of a quadruplex motif in a duplex–quadruplex substrate.1

Tunable morphology and surface wettability of an amphiphilic azobenzene derivative and its melamine-induced self-assembly

Herein, a series of novel hydrogen-bonded complexes derived from 4-[[(dodecyloxy)benz-4-yl]azo]benzoic acid (DBA) and melamine are reported. The morphology and surface wettability of the resulting self-assembled supramolecular architectures can be easily modulated not only by varying the molar ratios of DBA and melamine, but also by external UV irradiation. Based on the results of atomic force microscope, X-ray diffractometer and contact angle measurements, orientation of the coassembled units with different molar ratios of DBA and melamine could be clearly confirmed. Moreover, the effect of photo-isomerisation of the azobenzene units on the wettability of the assemblies has been investigated in detail. As we know, the films derived from the cis-azobenzene derivative usually exhibit a more hydrophilic property than that from the trans-azobenzene derivative. However, the opposite results were obtained for the samples derived from the cis isomers of DBA–melamine (3:1) complexes or DBA. An explanation, based on the surfaces topography, has been proposed.

Nucleobase-functionalized ABC triblock copolymers: self-assembly of supramolecular architectures.

RAFT polymerization afforded acrylic ABC triblock copolymers with self-complementary nucleobase-functionalized external blocks and a low-Tg soft central block. ABC triblock copolymers self-assembled into well-defined lamellar microphase-separated morphologies for potential applications as thermoplastic elastomers. Complementary hydrogen bonding within the hard phase facilitated self-assembly and enhanced mechanical performance.

ChemInform Abstract: Dynamic Combinatorial Libraries: From Exploring Molecular Recognition to Systems Chemistry

AbstractReview: 182 refs.

Dynamic Combinatorial Libraries: From Exploring Molecular Recognition to Systems Chemistry

Dynamic combinatorial chemistry (DCC) is a subset of combinatorial chemistry where the library members interconvert continuously by exchanging building blocks with each other. Dynamic combinatorial libraries (DCLs) are powerful tools for discovering the unexpected and have given rise to many fascinating molecules, ranging from interlocked structures to self-replicators. Furthermore, dynamic combinatorial molecular networks can produce emergent properties at systems level, which provide exciting new opportunities in systems chemistry. In this perspective we will highlight some new methodologies in this field and analyze selected examples of DCLs that are under thermodynamic control, leading to synthetic receptors, catalytic systems, and complex self-assembled supramolecular architectures. Also reviewed are extensions of the principles of DCC to systems that are not at equilibrium and may therefore harbor richer functional behavior. Examples include self-replication and molecular machines.

Homochiral and heterochiral assembly preferences at different length scales – conglomerates and racemates in the same assemblies

Length scale dependent formation of conglomerates and racemic compounds has been observed in self-assembled hierarchical supramolecular architectures based on oligo(p-phenylenevinylene)-phenylglycinamide at the liquid-solid interface and in solution.