Supramolecular Architectures Research Articles

Self-similar chiral organic molecular cages

The endeavor to enhance utility of organic molecular cages involves the evolution of them into higher-level chiral superstructures with self-similar, presenting a meaningful yet challenging. In this work, 2D tri-bladed propeller-shaped triphenylbenzene serves as building blocks to synthesize a racemic 3D tri-bladed propeller-shaped helical molecular cage. This cage, in turn, acts as a building block for a pair of higher-level 3D tri-bladed chiral helical molecular cages, featuring multilayer sandwich structures and displaying elegant characteristics with self-similarity in discrete superstructures at different levels. The evolutionary procession of higher-level cages reveals intramolecular self-shielding effects and exclusive chiral narcissistic self-sorting behaviors. Enantiomers higher-level cages can be interconverted by introducing an excess of corresponding chiral cyclohexanediamine. In the solid state, higher-level cages self-assemble into supramolecular architectures of L-helical or D-helical nanofibers, achieving the scale transformation of chiral characteristics from chiral atoms to microscopic and then to mesoscopic levels.

A Metal-Free Triazacoronene-Based Bimodal VOC Sensor.

Developing suitable sensors for selective and sensitive detection of volatile organic compounds (VOCs) is crucial for monitoring indoor and outdoor air quality. VOCs are very harmful to our health upon inhalation or contact. Bimodal sensor materials with more than one transduction capability (optical and electrical) offer the ability to extract complementary information from the individual analyte, thus improving detection accuracy and performance. The privilege of manipulating the optoelectronic properties of the polycyclic aromatic hydrocarbon-based semiconducting materials offers rapid signal transduction in multimodal sensing applications. A thiophene-functionalized triazacoronene (TTAC) donor-acceptor-donor (D-A-D) type sensor is reported here for VOC sensing. The single-crystal X-ray structure analysis of the TTAC revealed that a distinctive supramolecular polymer architecture was formed because of cooperative π-π and intermolecular D-A interactions and exhibited rapid signal transduction upon exposure to specific VOCs. The TTAC-embedded green luminescent paper-based test strip exhibited an on-off fluorescence response upon nitrobenzene vapor exposure for 120 s. The selective and rapid response is due to the fast photoinduced electron transfer, as is evident from the time-resolved excited-state dynamics and density functional theory studies. The thick-film-based prototype chemiresistive sensor detects harmful VOCs in a custom-made gas sensing system including benzene, toluene, and nitrobenzene. The TTAC sensor rapidly responds (200 s) at relatively low temperatures (180 οC) compared to other reported metal-oxide-based sensors.

Immunopotentiating Polyphosphazene Delivery Systems: Supramolecular Self-Assembly and Stability in the Presence of Plasma Proteins.

Studies on the biological performance of nanomedicines have been increasingly focused on the paradigm shifting role of the protein corona, which is imminently formed once the formulation is placed in a complex physiological environment. This phenomenon is predominantly studied in the context of protein adsorption science, while such interactions for water-soluble systems remain virtually unexplored. In particular, the importance of plasma protein binding is yet to be understood for pharmaceuticals designed on the basis of supramolecular architectures, which generally lack well-defined surfaces. Water-soluble ionic polyphosphazenes, clinically proven immunoadjuvants and vaccine delivery vehicles, represent an example of a system that requires supramolecular coassembly with antigenic proteins to attain an optimal immunopotentiating effect. Herein, the self-assembly behavior and stability of noncovalently bound complexes on the basis of a model antigen─hen egg lysozyme─and polyphosphazene adjuvant are studied in the presence of plasma proteins utilizing isothermal calorimetry, asymmetric flow field flow fractionation, dynamic light scattering, and size exclusion chromatography methods. The results demonstrate that although plasma proteins, such as human serum albumin (HSA), show detectable avidity to polyphosphazene, the strength of such interactions is significantly lower than that for the model antigen. Furthermore, thermodynamic parameters indicate different models of binding: entropy driven, which is consistent with the counterion release mechanism for albumin versus electrostatic interactions for lysozyme, which are characterized by beneficial enthalpy changes. In vitro protein release experiments conducted in Franz diffusion cells using enzyme-linked immunoassay detection suggest that the antigen-adjuvant complex stability is not adversely affected by the presence of the most physiologically abundant protein, which confirms the importance of the delivery modality for this immunoadjuvant. Moreover, HSA shows an unexpected stabilizing effect on complexes with high antigen load─an important consideration for further development of polyphosphazene adjuvanted vaccine formulations and their functional assessment.

Multi‐Length Scale Communication Effects in Catalysis: Thinking Big and Acting Small

AbstractThe use of hierarchically structured materials as catalysts has been finding increasing application in the past years. For these catalytic systems, not only the nano‐scale matters: a high degree of order across multiple length scales, along with its control and analytical assessment, is of paramount importance to obtain innovative properties that can find application in catalysis. Most reviews dealing with hierarchically structured materials are concerned with the “bottom‐up” transfer of structural information along the different length scales, with special emphasis on the transmission of chirality. Due to their mesoscale size together with their complex behaviour, these systems are often susceptible to feel the effects of macroscopic forces, that can exert a “top‐down” control of their catalytic properties, so that an external stimulus, acting at the level of the supramolecular architecture of the catalyst, can ultimately determine the outcome of the catalyzed reaction at the molecular level. We review in this paper some recent reports that deal with the experimental implementation of this concept, either by using a mechanical force in a full range direct transmission to the reaction coordinate, or by means of a stepwise relay transmission from the macroscopic level (purely supramolecular chirality) to the nanoscopic one. We focus in this review on these multi‐length scale communication control effects, identifying the different mechanisms that are affecting the catalytic activity.

Amplification of Light‐Induced Helix Inversion of Intrinsically Chiral Diarylethene Molecular Switches

AbstractPhotonics and tunable optics are rapidly developing fields that require materials with programmable properties and advanced functionalities. Cholesteric liquid crystals (CLCs) are unique materials that exhibit selective light reflection and can be tuned using stimuli‐responsive small organic molecules. The challenge lies in designing molecules that can convert external signals, such as light, into dynamic and invertible chiral states, which can be transduced to the CLC supramolecular structures inducing large differences in helicity and eventually to macroscopic properties. Here, novel intrinsically chiral phenanthrene‐based diarylethenes as light‐responsive chiral dopants for controlling the supramolecular helical architectures of CLCs are introduced. The substitution pattern and light‐invertible axial chirality of these diarylethenes make them highly compatible with liquid crystals and provide high twisting power. The light‐induced cyclization and molecular chirality transformation result in a wide tunability of the cholesteric helix pitch (reflection colors) and reversible inversion of helical handedness. These findings provide a powerful tool for controlling and manipulating the macroscopic properties of CLCs, opening new avenues for a range of applications, including diffractive optics and photonics, anticounterfeiting tags, and displays.

Self-Assembled Materials Based on Fully Aromatic Peptides: The Impact of Tryptophan, Tyrosine, and Dopa Residues.

Peptides are able to self-organize in structural elements including cross-β structures. Taking advantage of this tendency, in the last decades, peptides have been scrutinized as molecular elements for the development of multivalent supramolecular architectures. In this context, different classes of peptides, also with completely aromatic sequences, were proposed. Our previous studies highlighted that the (FY)3 peptide, which alternates hydrophobic phenylalanine and more hydrophilic tyrosine residues, is able to self-assemble, thanks to the formation of both polar and apolar interfaces. It was observed that the replacement of Phe and Tyr residues with other noncoded aromatic amino acids like 2-naphthylalanine (Nal) and Dopa affects the interactions among peptides with consequences on the supramolecular organization. Herein, we have investigated the self-assembling behavior of two novel (FY)3 analogues with Trp and Dopa residues in place of the Phe and Tyr ones, respectively. Additionally, PEGylation of the N-terminus was analyzed too. The supramolecular organization, morphology, and capability to gel were evaluated using complementary techniques, including fluorescence, Fourier transform infrared spectroscopy, and scanning electron microscopy. Structural periodicities along and perpendicular to the fiber axis were detected by grazing incidence wide-angle X-ray scattering. Finally, molecular dynamics studies provided interesting insights into the atomic structure of the cross-β that constitutes the basic motif of the assemblies formed by these novel peptide systems.

The effect of host size on binding in host-guest complexes of cyclodextrins and polyoxometalates.

Harnessing flexible host cavities opens opportunities for the design of novel supramolecular architectures that accommodate nanosized guests. This research examines unprecedented gas-phase structures of Keggin-type polyoxometalate PW12O40 3- (WPOM) and cyclodextrins (X-CD, X = α, β, γ, δ, ε, ζ) including previously unexplored large, flexible CDs. Using ion mobility spectrometry coupled to mass spectrometry (IM-MS) in conjunction with molecular dynamics (MD) simulations, we provide first insights into the binding modes between WPOM and larger CD hosts as isolated structures. Notably, γ-CD forms two distinct structures with WPOM through binding to its primary and secondary faces. We also demonstrate that ε-CD forms a deep inclusion complex, which encapsulates WPOM within its annular inner cavity. In contrast, ζ-CD adopts a saddle-like conformation in its complex with WPOM, which resembles its free form in solution. More intriguingly, the gas-phase CD-WPOM structures are highly correlated with their counterparts in solution as characterized by nuclear magnetic resonance (NMR) spectroscopy. The strong correlation between the gas- and solution phase structures of CD-WPOM complexes highlight the power of gas-phase IM-MS for the structural characterization of supramolecular complexes with nanosized guests, which may be difficult to examine using conventional approaches.

Incisive analysis of hydrogen-bonded supramolecular architectures in designer polycyclitols: observation of some interesting self-assembly patterns

This article examines C–H⋯O and O–H⋯O hydrogen-bonded patterns in polyoxygenated decalins, showcasing varied supramolecular architectures influenced by oxyfunctionalisation and surrogate carbonate groups.

Six polyoxotungstate-based transition metal compounds for electrochemical capacitor application and a comparative analysis of factors affecting capacitances.

Six different polyoxotungstate-based transition metal complexes were synthesized, namely [Cu5(2,2'-bpy)5(μ2-Cl)2(PO4)2(H2O)2][HPW12O40]·2H2O (1), [Cu1.5(2,2'-bpy)1.5(inic)2(H2O)1.5]3[H1.5PW12O40]2·16.25H2O (2), [Cu(2,2'-bpy)2]2[SiW12O40]·10H2O (3), [Zn(phen)3]2[PWVWVI11O40]·5H2O (4), [Zn(phen)2(H2O)]2[SiW12O40]·2H2O (5), and [Zn(2,2'-bpy)2]2[SiW12O40] (6) (2,2'-bpy = 2,2'-bipyridine, inic = isonicotinic acid, phen = 1,10-phenanthroline). Compound 1 is based on [HPW12O40]2- anions, which are accommodated within the open channels of a supramolecular network formed by novel Cu-P-Cl coordination clusters. Compound 2 is constructed from [H1.5PW12O40]1.5- and novel [Cu1.5(2,2'-bpy)1.5(inic)2(H2O)1.5]+ coordination fragments, and polyoxoanions are encapsulated within the pores created by the copper coordination fragments, resulting in a unique three-dimensional supramolecular architecture. Compound 3 is a two-dimensional structure formed through the covalent linkage between [SiW12O40]4- and [Cu(2,2'-bpy)2]2+. Compound 4 is a supramolecular architecture formed by [PWVWVI11O40]4- and [Zn(phen)3]2+ coordination fragments, while compound 5 is a supramolecular structure based on POM bi-supported Zn coordination complexes. Compound 6 is a two-dimensional framework structure constituted by [SiW12O40]4- and [Zn(2,2'-bpy)2]2+via covalent interactions. In addition, electrochemical measurement results show that the copper-based tungstate compounds 1-3 and zinc-based tungstate compounds 4-6 exhibit different performances and durabilities as electrochemical capacitors (compound 1 shows the highest specific capacitance of 94.0 F g-1 at 1.5 A g-1, whereas compound 6 maintains the best cycling stability with the capacity retention of 80.7% after 1000 cycles at 4 A g-1.). This study contributes to the development of POM-based transition metal complexes with high capacitance by providing insights into the design and synthesis process.

Multiple hydrogen bonding driven supramolecular architectures and their biomedical applications.

Supramolecular chemistry combines the strength of molecular assembly via various molecular interactions. Hydrogen bonding facilitated self-assembly with the advantages of directionality, specificity, reversibility, and strength is a promising approach for constructing advanced supramolecules. There are still some challenges in hydrogen bonding based supramolecular polymers, such as complexity originating from tautomerism of the molecular building modules, the assembly process, and structure versatility of building blocks. In this review, examples are selected to give insights into multiple hydrogen bonding driven emerging supramolecular architectures. We focus on chiral supramolecular assemblies, multiple hydrogen bonding modules as stimuli responsive sources, interpenetrating polymer networks, multiple hydrogen bonding assisted organic frameworks, supramolecular adhesives, energy dissipators, and quantitative analysis of nano-adhesion. The applications in biomedical materials are focused with detailed examples including drug design evolution for myotonic dystrophy, molecular assembly for advanced drug delivery, an indicator displacement strategy for DNA detection, tissue engineering, and self-assembly complexes as gene delivery vectors for gene transfection. In addition, insights into the current challenges and future perspectives of this field to propel the development of multiple hydrogen bonding facilitated supramolecular materials are proposed.

Engineering Supramolecular Hybrid Architectures with Directional Organofluorine Bonds

Engineering Supramolecular Hybrid Architectures with Directional Organofluorine Bonds

Multiscale organisation of lead carboxylates in artistic oil binders.

The supramolecular and mesoscopic architectures of lead-saponified linseed oil, used by painters since the Renaissance, have been characterised and linked to their rheological properties. The multi-scale organization of saponified oils has been demonstrated by SAXS (Small Angle X-ray Scattering), FF-TEM (Freeze-Fracture Transmission Electron Microscopy) and DIC (Differential Interference Contrast): some of the lead soaps (formed when the oil is heated in the presence of PbO) are organized into microscopic lamellar domains, distributed in a continuous matrix made up of unorganized species (partially saponified triglycerides, glycerol, remaining soaps, etc.). The concentration of lead soaps in the oil controls the average size and interaction between the lamellar domains. Linseed oil + PbO 17 mol% is viscous and consists of aggregates of lamellar domains isolated within the continuous unorganized matrix. In contrast, in linseed oil + PbO 50 mol%, the domains are homogeneously dispersed and form what can be described as a three-dimensional network, giving the system viscoelastic properties.

Cluster helicates: promising functional materials.

Cluster helicates are a new type of supramolecular architecture that consists of a metal cluster wrapped around by ligands arranged in a helical mode. This class of compounds combines the unique properties of metal clusters with the sophisticated chiral arrangement found in helicates. Therefore, these architectures show promising applications in the development of advanced materials with specific electronic, magnetic, optical, catalytic and biological properties. This review delves into a few pioneering studies on cluster helicates and their applications as nanomagnetic, nanoelectric and catalyst materials. Furthermore, it emphasises the necessity for further exploration in this area and the fields related to the functional applications that cluster helicates can bring to the future of materials science.

Two-component Supramolecular Adduct based on Hydroxyl Substituted Triptycene with 4,4’-bipyridine: Crystal Structure Analysis

A new cocrystal solvate possessing 2,7,14-trihydroxytriptycene (THT) and 4,4′-bipyridine (bpy) was grown from a MeOH solution by solvent evaporation to form THT·0.5bpy·MeOH·H2O (1).The crystal structure of 1 was determined by single-crystal X-ray diffraction in the monoclinic space group C2/c. In the new cocrystal solvate (1), the asymmetric unit consists of one unit of THT, a half unit of disordered bpy, one unit of a water molecule and one MeOH molecule. A 2D supramolecular architecture is observed in (1) linking THT, bpy and solvent water molecules via classical O-H···N and O-H···O hydrogen bonds. The MeOH and water molecules entrapped in (1) form stabilizing hydrogen bondswith the surrounding “trimeric cocrystals.” Furthermore, we investigated whether these hydrogen bonds stabilize the crystal packing. The calculations were carried out using Hydrogen Bond Statistics and Full Interaction Maps packages, and the results exhibit common bonding behaviour in terms of bond distances and strength.

Supramolecular architecture of theophylline polymorphs, monohydrate and co-crystals with iodine: study from the energetic viewpoint

The supramolecular features in five polymorphs and two co-crystals of theophylline were studied combining experimental and theoretical methods.

1,1'-Bis-(diphenylphosphino)ferrocene appended d8- and d10-configuration based thiosquarates: the molecular and electronic configurational insights into their sensitization and co-sensitization properties for dye sensitized solar cells.

Three new d8- and d10-configuration based 1,1'-bis-(diphenylphosphino)ferrocene (dppf) appended thiosquarates complexes with general composition [M(mtsq)2dppf] (M = Ni2+ (NiL2); Zn2+ (ZnL2) and Cd2+ (CdL2)) (mtsq = 3-ethoxycyclobutenedione-4-thiolate) have been synthesized and characterized spectroscopically as well as in case of NiL2 by single crystal X-ray diffraction technique. The single crystal X-ray analysis reveals square planar geometry around Ni(II) in NiL2, where Ni(II) coordinates with two sulfur centres of two mtsq ligands in monodentate fashion and two phosphorus of a dppf ligand in chelating mode. The supramolecular architecture of NiL2 is sustained by intermolecular C-H⋯O interactions to form one-dimensional chain. Further, the application of these newly synthesized complexes as sensitizers and co-sensitizers/co-absorbents with ruthenium based N719 sensitizer in dye-sensitized solar cells (DSSCs) have been explored. The DSSC set-up based on NiL2 offers best photovoltaic performance with photovoltaic efficiency (η) 5.12%, short-circuit current (Jsc) 11.60 mA cm-2, open circuit potential (Voc) 0.690 V and incident photon to current conversion efficiency (IPCE) 63%. In co-sensitized DSSC set-up, ZnL2 along with state-of-the-art N719 dye displays best photovoltaic performance with η 6.65%, Jsc 14.47 mA cm-2, Voc 0.729 V and IPCE 69%, thereby showing an improvement by 15.25% in photovoltaic efficiency in comparison to the photovoltaic efficiency of N719 sensitized DSSC set-up. Variation in co-sensitization behaviour have been ascribed to the differences in the excited state energy level of co-sensitizers. The ZnL2 and CdL2 have a higher energy level position than N719 dye, allowing efficient electron transfer to N719 during light irradiation, while excited state of NiL2 is lower than N719 dye, preventing photoexcited electron transfer to N719, resulting in its lowest overall efficiency among the three co-sensitized DSSC setups.

Role of tetrel bonds in the supramolecular architecture of tetranuclear Pb(ii)[LL′thiophene carboxylate] complexes – an experimental and computational study

Experimental and theoretical study of tetrel bonds in the 3D crystal arrangement.

Probing the molecular determinants of the activation of toll-like receptor 2/6 by amyloid nanostructures through directed peptide self-assembly.

Amyloid fibrils are proteinaceous nanostructures known for their ability to activate the innate immune system, which has been recently exploited for their use as self-adjuvanted antigen delivery systems for vaccines. Among mechanisms of immunostimulation, the activation of the heterodimeric toll-like receptor 2/6 (TLR2/TLR6) by the cross-β-sheet quaternary conformation appears important. Nonetheless, the lack of control over the process of self-assembly and the polydispersity of the resulting supramolecular architectures make it challenging to elucidate the molecular basis of TLR2/TLR6 engagement by amyloid assemblies. In this context, we harnessed the effects of N- and C-terminal modifications of a short 10-mer β-peptide derived from the islet amyloid polypeptide (I10) to investigate the relationships between the morphology and physicochemical properties of amyloid assemblies and their TLR2/TLR6 activity. Chemical substitutions at the N- and C-termini of the I10 peptide, including addition of charged residues at the N-terminus and α-amidation of C-terminus, allowed the controlled formation of a diversity of architectures, including belt-like filaments, rigid nanorods as well as flat and twisted fibrils. These fully cytocompatible peptide nanostructures showed different potencies to activate TLR2/TLR6, which correlated with the charge exposed on the surface. These results further demonstrate the potent modulatory effect of N- and C-terminal electrostatic capping on the self-assembly of short synthetic β-peptides. This study also indicates that self-assembly into cross-β-sheet nanostructures is essential for the activation of the TLR2/TLR6 by amyloidogenic peptides, albeit the structural requirements of the engagement of this promiscuous immune receptor by the nanostructures remain challenging to precisely untangle.

Structural, optical and magnetic properties of a new metal-organic CoII-based complex.

A mononuclear cobalt(ii) complex [C5H8N3]2[CoCl4(C5H7N3)2] (I) was synthesized and structurally characterized. Single crystal X-ray diffraction analysis indicates that monometallic Co(ii) ions acted as coordination nodes in a distorted octahedral geometry, giving rise to a supramolecular architecture. The latter is made up of a ½ unit form composed of an anionic element [Co0.5Cl2(C5H7N3)]- and one 2-amino-4-methylpyrimidinium cation [C5H8N3]+. The crystalline arrangement of this compound adopts the sandwich form where inorganic parts are sandwiched between the organic sheets following the [100] direction. More information regarding the structure hierarchy has been supplied based on Hirshfeld surface analysis; the X⋯H (X = N, Cl) interactions play a crucial role in stabilizing the self-assembly process of I, complemented by the intervention of π⋯π electrostatic interaction created between organic entities. Thermal analyses were carried out to study the thermal behavior process. Static magnetic measurements and ab initio calculations of compound I revealed the easy-axis anisotropy character of the central Co(ii) ion. Two-channel field-induced slow-magnetic relaxation was observed; the high-frequency channel is characterized by underbarrier relaxation with U eff = 16.5 cm-1, and the low-frequency channel involves a direct relaxation process affected by the phonon-bottleneck effect.

Energy landscape of perylenediimide chromophoric aggregates.

Understanding the self-assembly of conjugated organic materials at the molecular level is crucial in their potential applications as active components in electronic and optoelectronic devices. The type of aggregation significantly influences the intriguing electronic and optical characteristics differing from their constituent molecules. Perylenediimides (PDIs), electron-deficient molecules exhibiting remarkable n-type semiconducting properties, are among the most explored organic fluorescent materials due to their high fluorescence efficiency, photostability, and optoelectronic properties. PDI derivatives are reported to form well-tailored supramolecular architectures: cofacial with minor slip (H-aggregates), staggered with major slip (J-aggregates), magic angle stacking (M-aggregates), rotated (X-aggregates), rotated orthogonal ((+)-aggregates), etc. H*-aggregates are defined here as an ideal case of H-aggregate with an eclipsed configuration. Although numerous reports regarding the formation and optical properties of various PDI aggregates are known, the key driving force within the PDI units guiding the self-assembly to form distinct aggregate systems remains elusive. To unravel the molecular-level mechanisms behind the self-assembly of PDI units by probing the intermolecular interactions, symmetry-adapted perturbation theory-based energy decomposition, potential energy surface scans, and non-covalent interaction index analyses were employed on PDI dimer models. Quantum theory of atoms in molecules and frontier molecular orbital analyses were implemented on the dimer models to comprehend the effect of heteroatoms and orbital interactions in stabilising the X-aggregates over the other PDI aggregate systems. Competition between the attractive and repulsive non-covalent interactions dictates a stability order of X > H > J > M > (+) > H* for the PDI aggregate system, while in the parent perylene system, the stability order was found to be X > (+) > H > M > J > H*.