Supramolecular Recognition Research Articles

Temperature-responsive supramolecular hydrogels.

Hydrogels comprise a class of soft materials which are extremely useful in a number of contexts, for example as matrix-mimetic biomaterials for applications in regenerative medicine and drug delivery. One particular subclass of hydrogels consists of materials prepared through non-covalent physical crosslinking afforded by supramolecular recognition motifs. The dynamic, reversible, and equilibrium-governed features of these molecular-scale motifs often transcend length-scales to endow the resulting hydrogels with these same properties on the bulk scale. In efforts to engineer hydrogels of all types with more precise or application-specific uses, inclusion of stimuli-responsive sol-gel transformations has been broadly explored. In the context of biomedical uses, temperature is an interesting stimulus which has been the focus of numerous hydrogel designs, supramolecular or otherwise. Most supramolecular motifs are inherently temperature-sensitive, with elevated temperatures commonly disfavoring motif formation and/or accelerating its dissociation. In addition, supramolecular motifs have also been incorporated for physical crosslinking in conjunction with polymeric or macromeric building blocks which themselves exhibit temperature-responsive changes to their properties. Through molecular-scale engineering of supramolecular recognition, and selection of a particular motif or polymeric/macromeric backbone, it is thus possible to devise a number of supramolecular hydrogel materials to empower a variety of future biomedical applications.

Carbohydrate supramolecular chemistry: beyond the multivalent effect.

It has been amply constated that sugar ligand multivalency increases lectin-binding avidities dramatically, thereby modulating the capacity of carbohydrates to participate in supramolecular recognition processes involving transfer of biological information. The importance of this concept, the multivalent or glycoside cluster effect, in cell biology in general and in the glycosciences in particular is reflected in the ever-growing number of papers in the field. An impressive range of glycoarchitectures has been conceived to imitate the glycan coating of cells (the glycocalyx) in order to target complementary lectin receptors. However, these models rarely address the heterogeneity and the fluidity of the densely glycosylated cell membrane. They also disregard the impact that high-density nanosized arrangements could have in their interactions with the whole spectrum of carbohydrate-interacting proteins, among which glycosidases are notable representatives. For many years it has been tacitly assumed that: (i) efficient recognition by lectins generally requires high densities of the putative primary ligand and (ii) the mechanisms governing binding of a carbohydrate motif by a lectin or a glycosidase are totally disparate. Notwithstanding, an increasing amount of evidence seriously questions this paradigm. First, it was shown that secondary "innocent" ligands can play important roles in the recognition of heteroglycocluster constructs by lectins through synergistic or antagonistic contributions, a phenomenon termed the heterocluster effect. Second, the existence of multivalent effects in the inhibition of certain glycosidases by glycomimetic- and, even more disturbing, glyco-coated architectures (multivalent enzyme inhibition) was demonstrated. These observations call for a generalized multivalent effect governing the supramolecular chemistry of carbohydrate or glycomimetic structures in a biological context, with (hetero)multivalency acting as a multimodal switcher to drive the encoded information through different pathways. In this Feature Article we review the advancements made in the last few years in our understanding of the mechanisms underpinning the generalized multivalent effect, with an emphasis on the potential risks and opportunities derived from (hetero)multivalency-elicited promiscuity.

Development of copper-catalyzed enantioselective decarboxylative aldolization for the preparation of perfluorinated 1,3,5-triols featuring supramolecular recognition properties.

Fluorine is able to confer unique properties to organic molecules but the scarcity of natural organofluorine sources renders the development of new synthetic methods highly desirable. Using a chiral BOX/Cu combination, enantioselective decarboxylative aldolization of perfluorinated aldehydes has been developed. Most notably, the reaction occurring under mild conditions and with high enantiocontrol can create ketodiols in one single synthetic operation, which are precursors of crucial perfluorinated 1,3,5-triols. In addition, the reaction performed with chloral, validates the proposed transition state model based on steric interactions and provides the first enantioselective synthesis of hexachlorinated ketodiol of great synthetic utility. The ability of perfluorinated 1,3,5-triols to form a central hydrogen-bonding framework allows strong coordination of anions and the chirality obtained through the catalyst-controlled synthetic sequence demonstrates the selective chiral anion recognition ability of polyols.

Supramolecular recognition of phosphocholine by an enzyme-like cavitand receptor.

The first example of supramolecular recognition of phosphocholine by a cavitand receptor has been reported here. The chemical structure of the receptor has been optimized by DFT calculations. The recognition mechanism is based on a "multi-topic approach", which leads to highly efficient (K value up to 107 M-1), selective and sensitive (ppb level) sensing of phosphocholine. The recognition mechanism proposed here is similar to those exploited by Nature, and paves the way for the realization of new sensors with important applications in medicine and security fields.

A two-dimensional metallosupramolecular framework design based on coordination crosslinking of helical oligoamide nanorods

Coordination crosslinking of oligoamide nanorods yields two dimensional metallosupramolecular framework.

Host-guest controlled assembly and recognition of perylene bisimide-based glycocluster with cyclodextrin

Carbohydrate-protein interactions are the very important recognition processes involved in cell adhesion, viral infection and immune response in live cells. In this paper, host-guest controlled supramolecular assemblies based on an asymmetrical perylene bisimide derivative, PBI-ADA-Lac, and β-cyclodextrin was achieved. Importantly, the self-assembly of PBI-ADA-Lac showed adjustable carbohydrate-protein interactions based on the host-guest interactions between PBI-ADA-Lac and β-cyclodextrin, indicating enhanced carbohydrate-protein binding interactions. In addition, PBI-ADA-Lac and its host-guest complexes with β-cyclodextrin showed fluorescence imaging in HeLa cells through interaction with the galectin proteins. This work developed a new method for host-guest controlled supramolecular multivalent recognition.

Molecular and supramolecular recognition patterns in ternary copper(II) or zinc(II) complexes with selected rigid-planar chelators and a synthetic adenine-nucleoside

Four ternary metal-complexes with Cu(II) or Zn(II), 2,6-pyridine-dicarboxylate (pdc) or glycyl-glycinate (GG) and the synthetic nucleoside 9-(2-hydroxyethyl)adenine (9heade) have been synthesized and studied by single-crystal X-ray diffraction and other physical methods. Relevant supramolecular assemblies found in the solid state structures have been further studied using density functional theory (DFT) calculations. In addition, the energetic features of the non-covalent interactions as well as the cooperativity effects have been calculated and characterized using the non-covalent interaction plot computational tool. Compounds trans-[Cu(pdc)(9heade)(H2O)2]·3H2O (1a) and [Cu(pdc)(9heade)(H2O)]·H2O (1b), trans-[Zn(pdc)(9heade)(H2O)2] (2), share the same molecular recognition pattern consisting in the cooperation of the metal-N7(9heade) bond and an interligand (9heade)N6-H···O(pdc) interaction, regardless of the nature of the metal, the coordination environment and the water content. At a supramolecular level, these compounds exhibit pairs of complex molecules linked by H-bonds and interesting anion–π/π–π/π–anion assemblies (in 1a and 1b) or the unprecedented π-π interactions (in 2), involving the purine moieties or the exocyclic –6NH2 purine groups, respectively. Compound 3, {[Cu(GG)(9heade)(H2O)·Cu(GG)(μ2-9heade)]·8H2O}n, consists in asymmetric dinuclear complex units (Cu···Cu 7.83 Å) that connect with adjacent ones by pairs of very weak Cu-O(carboxylate) bonds (Cu···Cu 3.81 Å) building a polymeric chain. The supramolecular transition from a single molecule to dinuclear units and finally a polymeric chain is also observed in the electron paramagnetic resonance spectra and discussed from a structural point of view as well as by DFT calculations. The unprecedented N7 and μ-N7,O(ol) metal binding patterns of 9heade differs from that recently reported (μ-N1,N7) in a Cd(II) polymer.

Curvature sculptured growth of plasmonic nanostructures by supramolecular recognition

Nanoscale curvature is an important and powerful tool in understanding and tailoring chemical/surface functionalities of nanostructures that dictate a host of important applications from biochemical recognitions, catalysis to spectroscopy. However, it is a critical challenge in materials chemistry to rationally shape the local nanoscale curvatures of colloidal nanoparticles during the growth owing to the constraints of their flat facets. Here we demonstrate a synthetic mechanism that could cooperatively mediate local nanoparticle surface curvature patchiness and shape symmetries during one-step colloidal growth. The idea is to tailor host-guest supramolecular recognition using fluorocarbon and hydrocarbon molecules that regulate interfacial energy during the nanoparticle growth. Such delicate regulation enables a degree of freedom in control over the local nanoparticle curvatures during the growth, resulting in intriguing plasmonic properties. More interestingly, a morphological shape transformation was induced by such curvature changes from anisotropic nanorods to isotropic nanospheres. This unique approach of the spontaneous curvature/structural transformation of plasmonic nanoparticles exploits the mutual interplay between competing supramolecules and colloidal growth. It may ultimately allow for accurate controlling nanoscale objects with varied degree of complexity that could open the door to a myriad of surface chemical, optical, and biomedical applications.

The Stability of the Complex and the Basicity of the Anion Impact the Selectivity and Affinity of Tripodal Gadolinium Complexes for Anions.

The affinities and selectivities of lanthanide complexes with open coordination sites for anions vary considerably with the chelate. In order to determine the effect of the stability of a lanthanide complex on its affinity for anions, five different complexes featuring different bidentate chelating moieties were synthesized, and their affinity for anions in water at neutral pH were evaluated by longitudinal relaxometry measurements. The chelates comprise both oxygen and nitrogen donors including maltol, 1,2-hydroxypyridinone, hydroxamic acid, pyridin-2-ylmethanol, and carbamoylmethylphosphonate diester. They were chosen to span a range of basicities all the while maintaining a similar tripodal tris-bidentate architecture, thereby allowing for a direct study of the role of the coordinating motif on the supramolecular recognition of anions by the corresponding GdIII complex. Overall, for ligands containing the same number of protonation steps, and therefore the same charge at neutral pH, the lower the acidity of the chelate (higher ∑pKa's), the less stable the corresponding GdIII complex, and the higher its affinity for anions. Regardless of the number of protonation steps, the more stable GdIII complexes form ternary or quaternary assemblies with coordinating anions. In contrast, the same anions readily displace the chelate of the least stable complexes, resulting instead in the formation of GdIII·anion precipitates. Irrespective of the chelate, in the absence of steric hindrance at the open coordination site, the affinity of GdIII complexes for anions follows the order phosphate > arsenate > bicarbonate > fluoride. Hence, the selectivity and affinity of GdIII complexes of tripodal tris-bidentate chelates for anions is a function of the stability of the GdIII complex and the basicity of the anion.

A domino reaction for generating \u03b2-aryl aldehydes from alkynes by substrate recognition catalysis

The development of universal catalyst systems that enable efficient, selective, and straightforward chemical transformations is of immense scientific importance. Here we develop a domino process comprising three consecutive reaction steps based on the strategy of supramolecular substrate recognition. This approach provides valuable β-aryl aldehydes from readily accessible α-alkynoic acids and arenes under mild reaction conditions, employing a supramolecular Rh catalyst containing an acylguanidine-bearing phosphine ligand. Furthermore, the synthesis of a key intermediate of Avitriptan using this protocol is accomplished. The first step of the reaction sequence is proved to be the regioselective hydroformylation of α-alkynoic acids. Remarkably, molecular recognition of the ligand and the substrate via hydrogen bonding plays a key role in this step. Control experiments indicate that the reaction further proceeds via 1,4-addition of an arene nucleophile to the unsaturated aldehyde intermediate and subsequent decarboxylation.

Designing electrochemical interfaces based on nanohybrids of avidin functionalized-carbon nanotubes and ruthenium nanoparticles as peroxidase-like nanozyme with supramolecular recognition properties for site-specific anchoring of biotinylated residues

We are reporting an original supramolecular architecture based on a rationally designed new nanohybrid with enhanced peroxidase-like activity and site-specific biorecognition properties using avidin-functionalized multi-walled carbon nanotubes (MWCNTs-Av) and Ru nanoparticles (RuNPs). The nanohybrid-electrochemical interface was obtained by drop-coating of MWCNTs-Av dispersion at glassy carbon electrodes (GCE) followed by solvent evaporation and further electrodeposition of RuNPs (50 ppm RuCl2 for 15 s at -0.600 V). The simultaneous presence of MWCNTs and RuNPs produces a synergic effect on the non-enzymatic catatalytic reduction of H2O2 and allows the quantification of H2O2 in a wide linear range (from 5.0 × 10−7 M to 1.75 × 10−3 M) with a low limit of detection (65 nM). The avidin residues present in MWCNTs-Av/RuNPs hybrid nanomaterial allowed the anchoring by bioaffinity of biotinylated glucose oxidase (biot-GOx) as proof-of-concept of the analytical application of MWCNTs-Av platform for biosensors development. The resulting nanoarchitecture behaves as a bienzymatic-like glucose biosensor with a competitive analytical performance: linear range between 2.0 × 10−5 M and 1.23 × 10−3 M, sensitivity of (0.343 ± 0.002) μA mM−1 or (2.60 ± 0.02) μA mM−1 cm−2, detection limit of 3.3 μM, and reproducibility of 5.2% obtained with five different GCE/MWCNTs-Av/RuNPs/biot-GOx bioplatforms prepared the same day using the same MWCNTs-Av dispersion, and 9.1% obtained with nine biosensors prepared in different days with nine different MWCNTs-Av dispersions. The average concentrations of glucose in Gatorade®, Red bull® and Pepsi® with the biosensor demonstrated excellent agreement with those reported in the commercial beverages.

A facile one-pot green synthesis of β-cyclodextrin decorated porous graphene nanohybrid as a highly efficient adsorbent for extracting aflatoxins from maize and animal feeds

In this paper, β-cyclodextrin (β-CD) supported on porous graphene nanohybrid (β-CDPG) was obtained by self-assembly of functionalized graphene nanosheets into a three-dimensional network in the presence of ascorbic acid via an in situ graphene oxide reduction and β-CD functionalization process during a hydrothermal reaction. The prepared supramolecular nanohybrid was further packed into a reusable syringe filter holder and applied as an adsorbent for solid phase extraction of four aflatoxins (B1, B2, G1, G2). Under optimal conditions, the detection limits and linear dynamic ranges were achieved in the range of 0.0075–0.030 μg kg−1 and 0.025–100 μg kg−1, respectively and the relative standard deviations were less than 6.1%. Good recoveries were observed for analyzing target AFs in maize and cereal-based chicken feed samples ranged from 90.5 to 105%. The method offered simultaneous advantages of high supramolecular recognition and enrichment capability of β-CD and the high specific surface area of the porous graphene.

Self-Assembled Supramolecular Polyoxometalate Hybrid Architecture as a Multifunctional Oxidation Catalyst.

Polyoxometalates (POMs) are widely applied as tuneable and versatile catalysts for a variety of oxidation reactions in an aqueous/organic two-phase system. However, the practical applications of POMs-based biphasic catalysis are hampered by low space-time yields and mass-transport limitation between two layers due to extremely low solubility of the organic reactants in the aqueous phase. Here, we first introduced β-cyclodextrin (β-CD) as an inverse phase transfer agent and a supramolecular nanoreactor to construct a supramolecular POM inorganic-organic hybrid framework (KCl4)Na7[(β-CD)3(SiW12O40)]·9H2O {3CD@SiW12} for various oxidation catalyses. In contrast to free CD, Keggin [SiW12O40]4- catalysts, and their mixture, the {3CD@SiW12} catalyst, efficiently catalyze oxidation reactions of alcohol, alkene, and thiophene. A comprehensive strategy of experimental, crystallographic, and density functional theory (DFT) calculations elucidates that the catalytic pathway involved three combined aspects of supramolecular recognition, phase transfer property, and POM catalysis. The strategic combination of supramolecular characteristic and POM-based catalysts to fabricate supramolecular POM hybrid materials opens up new economic and green tuning options, thus paving the way to informed catalyst design.

Brice Bosnich. 3 June 1936—13 April 2015

Brice Bosnich, an Australian inorganic chemist, graduated from the University of Sydney and obtained his PhD at the Australian National University, Canberra. He then worked successively at University College London, the University of Toronto and the University of Chicago. He had an abiding interest in stereochemistry and its relationship with chemical reactivity, and in the chirality and optical activity of coordination and organometallic complexes, mainly those of the d-block elements. His early studies concerned the topological and conformational behaviour of classical coordination compounds, mainly of cobalt(III), and made extensive use of the technique of circular dichroism. He put this background to elegant use in perhaps his most distinctive work, namely, the design and synthesis of a C 2 -symmetric ditertiary phosphine, ( S , S )-chiraphos, the rhodium(I) complex [Rh{Ph 2 PCH(CH 3 )CH(CH 3 )PPh 2 }] + of which catalysed efficiently the homogeneous hydrogenation of prochiral enamides to amino acids in high optical purity. Bosnich traced the high enantioselectivity to the chiral array of P-phenyl substituents that is generated on coordination of ( S , S )-chiraphos. In principle, catalytic enantioselective synthesis represents a powerful and economic method of introducing chirality into the synthesis of biologically active molecules, which, since the thalidomide tragedy, are required to be marketed only in optically pure forms. Dissymmetric ligands similar to ( S , S )-chiraphos are now routinely employed in this type of synthesis. Bosnich developed several other enantioselective processes based on organo-transition metal chemistry. He also had several quasi-theoretical interests, including the possible use of circular dichroism to determine the absolute configuration of chiral metal complexes, and the development of a molecular mechanics force field for metallocenes. He maintained a strong interest in the properties of multimetallic proteins and devoted much effort to the construction of chiral binucleating ligands. During the 7–8 years before his retirement from the University of Chicago in 2006, he shifted his research to supramolecular recognition by suitably designed metal complexes.

Multistimuli Responsive Nanocomposite Tectons for Pathway Dependent Self-Assembly and Acceleration of Covalent Bond Formation.

Nanocomposite tectons (NCTs) are a recently developed building block for polymer–nanoparticle composite synthesis, consisting of nanoparticle cores functionalized with dense monolayers of polymer chains that terminate in supramolecular recognition groups capable of linking NCTs into hierarchical structures. In principle, the use of molecular binding to guide particle assembly allows NCTs to be highly modular in design, with independent control over the composition of the particle core and polymer brush. However, a major challenge to realize an array of compositionally and structurally varied NCT-based materials is the development of different supramolecular bonding interactions to control NCT assembly, as well as an understanding of how the organization of multiple supramolecular groups around a nanoparticle scaffold affects their collective binding interactions. Here, we present a suite of rationally designed NCT systems, where multiple types of supramolecular interactions (hydrogen bonding, metal complexation, and dynamic covalent bond formation) are used to tune NCT assembly as a function of multiple external stimuli including temperature, small molecules, pH, and light. Furthermore, the incorporation of multiple orthogonal supramolecular chemistries in a single NCT system makes it possible to dictate the morphologies of the assembled NCTs in a pathway-dependent fashion. Finally, multistimuli responsive NCTs enable the modification of composite properties by postassembly functionalization, where NCTs linked by covalent bonds with significantly enhanced stability are obtained in a fast and efficient manner. The designs presented here therefore provide major advancement for the field of composite synthesis by establishing a framework for synthesizing hierarchically ordered composites capable of complicated assembly behaviors.

Catalyst: Can Systems Chemistry Unravel the Mysteries of the Chemical Origins of Life?

Daniela Kroiss obtained her MSc degree in biotechnology at BOKU and is currently a PhD student in the biochemistry program at CUNY, where she works on a joint project between the Nanoscience Initiative and the University of Strathclyde. Gonen Ashkenasy is head of the Laboratory for Systems Chemistry at the Ben-Gurion University Chemistry Department. His research focuses on the design and analysis of synthetic replication networks. Adam Braunschweig earned his PhD in organic chemistry at the University of California and is an associate professor in the CUNY Nanoscience Initiative. His research focuses on the interface of organic chemistry with biology and material science. Tell Tuttle obtained his PhD in theoretical chemistry at Goteborg University and is a professor of theoretical chemistry at the University of Strathclyde. His research focuses on the directed discovery of peptide-based materials. Rein Ulijn gained his PhD in physical chemistry at the University of Strathclyde and is founding director of the Nanoscience Initiative at the CUNY Advanced Science Research Center. His research focuses on nanotechnology inspired by living systems.

Applications of macrocyclic compounds for electrochemical sensors to improve selectivity and sensitivity

Electrochemical sensing is a promising analytic method with its advantages, such as low cost, fast response, simple operation, high accuracy, low detection limit and so on. With the rapid development of electroanalysis, various modified electrodes were synthesized for constructing different kinds of electrochemical sensors on purpose. Macrocyclic compounds with their superior supramolecular recognition properties have aroused the research interest, as they can be used as modifiers for enhancing the sensitivity and selectivity of electrodes. All five classic macrocyclic compounds, which are crown ethers, cyclodextrins, calixarenes, cucurbiturils, and pillararenes, have been employed as receptors for electrochemical sensors, and these macrocycles have led to a wilder detection range, a lower detection limit, and superior ability of anti-interferences against coexisting ions or molecules. The macrocycles modified electrodes have shown greater sensitivity and selectivity in detection. Therefore, this review focuses on the results of the studies published in recent 8 years on macrocycles improved electrochemical sensing. In this review, the recent development of functionalization of macrocyclic compounds including crown ethers, cyclodextrins, calixarenes, cucurbiturils, pillararenes, on electrochemical sensors has been summarized.

Racemic Salts and Solid Solutions of Enantiomers of the Antihypertensive Drug Carvedilol

The R and S enantiomers of the antihypertensive drug carvedilol (CVD) can display remarkable miscibility in the crystalline state allowing this active pharmaceutical ingredient (API) to form a solid-solution of enantiomers (SSEs) as well as racemic compounds. Although rare and still little explored, these intriguing systems can also be used to design racemic multicomponent crystal forms toward the improvement of undesirable pharmaceutical properties of APIs. In this study, aiming to understand why there is miscibility between the enantiomers during the supramolecular recognition and crystallization processes of the CVD in the presence of salt formers, two SSEs and one racemic salt were prepared from the reaction of CVD with pharmaceutically acceptable HCl, HBr, and oxalic acids. Two monohydrated isostructural salts, hydrochloride (CVD-HCl-H2O) and hydrobromide (CVD-HBr-H2O), crystallize as racemic SSEs. These unique systems are formed from the miscibility of the R···R and S···S homochiral units that propa...

On‐Surface Cucurbit[n]uril Supramolecular Recognition for an Optical Sensor Design

AbstractA novel optical sensor, based on the use of the macrocyclic receptor cucurbit[7]uril as molecular selector taking part of a sensing poly(vinyl chloride)‐based membrane immobilized onto a quartz slide surface, has been developed and tested to thiabendazole analysis. The method is built upon the increase of the thiabendazole fluorescence as a result of the supramolecular recognition event. Variables involved in the membrane construction and fluorescence measurements have been evaluated and optimized. The sensing membrane is prepared by a spin‐coating procedure (1 min at 800 r.p.m.). An increase of more than 2 fold in the fluorescence signal is observed when the supramolecular complex is immobilized into the membrane respect to that observed for the free guest. Under optimized conditions, the dispositive responds in a few seconds to thiabendazole concentrations at 10−7 M level. In addition, the characterization of the supramolecular complex together with lifetime measurements is included.

Controlled assembly of Ag nanoparticles on the surface of phosphate pillar [6]arene functionalized single-walled carbon nanotube for enhanced catalysis and sensing performance

We developed a green and facile approach for synthesizing Ag@PP6@SWCNT nano-material via in-situ loading silver nanoparticles on the surface of phosphate pillar [6]arene (PP6) functionalized single-walled carbon nanotubes (SWCNT) at room temperature and without using either toxic or organic solvents. Ag nanoparticles (with an average size of 3–4 nm) were uniformly dispersed on the surface of SWCNT via the anchoring effect of PP6. PP6 provided a coordination environment between Ag and –PO32– groups in PP6, and there were the π-π interactions between SWCNT and benzene rings of PP6. The obtained hybrid nano-material Ag@PP6@SWCNT was characterized using UV-vis absorption spectrum, transmission electron microscopy (TEM), X-ray diffraction (XRD), and X-ray photoelectron spectroscopy (XPS). Compared to commercial Pd/C and Ag@SWCNT catalysts, Ag@PP6@SWCNT exhibited higher catalytic activity for 4-nitrophenol (4-NP) reduction and methylene blue (MB) degradation, respectively. Moreover, because of the excellent supramolecular host-guest recognition capability of PP6, a sensitive and convenient electrochemical sensing platform for detecting paraquat (PQ) was constructed, and had potential applications in sensing highly toxic herbicides.