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Orthogonal Molecular Recognition of Chaotropic and Hydrophobic Guests Enables Supramolecular Architectures

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Abstract

The hydrophobic and chaotropic effect can be used as orthogonal assembly motifs in water. Cucurbit[7]uril, a water‐soluble macrocyclic host, and a ditopic guest molecule, carrying an organic‐hydrophobic (adamantane) and an inorganic‐chaotropic (dodecahydro‐closo‐dodecaborate dianion) binding site, have been used to construct hybrid supramolecular architectures. The hydrophobic effect drives the adamantane moiety into the host cavity, while the chaotropic effect allows the association of the dodecaborate cluster onto the host exterior surface. The new strategy facilitates potential applications in surface modification, separation, and purification.

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... [10,18] Der chaotrope Effekt erstreckt sich über die molekulare Erkennung mit makrocyclischen Wirten, [10,12,[21][22][23][24][25][26][27] biologisch relevante Wechselwirkungen mit Proteinen und Peptiden, [13,[28][29][30][31][32] die Assoziation an niedermolekulare organische Verbindungen [10,33] sowie die Bindung an Membranen, [17,[34][35][36][37][38] Polymere [39] und Kolloide [15,18,40] und wird in Festphasenstrukturen zwischen superchaotropen Ionen und organischen Komponenten manifest. [10,12,26,41,42] Die Begriffe "chaotroper Effekt" und "superchaotrope Ionen" wurden rasch in der chemischen Literatur in verschiedenen Zusammenhängen aufgenommen. [11-13, 15-18, 22, 24, 28, 40, 41, 43-54] Diese Bedeutung auf verschiedenen Gebieten der Chemie verdeutlicht den chaotropen Effekt als eine generische Antriebskraft, die orthogonal zum hydrophoben Effekt ist. ...
... Vor kurzem haben andere Autoren und wir -in Analogie zu superhydrophobden Begriff "superchaotrop" für Ionen eingeführt, deren Eigenschaften über die der üblichen chaotropen Ionen hinausgehen. [10,15,16,18,23,41,64] Superchaotrope Ionen haben keine hydrophoben Eigenschaften nach herkçmmlichen Definitionen, sondern verursachen besondere Effekte, die in diesem Kurzaufsatz zusammengefasst und als Folge des chaotropen Effekts verstanden werden kçnnen. Die kontinuierliche Skala für wässrige Solvatation lässt sich auf superhydrophobe Spezies (vernachlässigbare Dispersion) bis zum Vakuum (keine Wechselwirkung) erweitern; letztere Situation beschreibt die Solvatation um einen geformten Leerraum in Wasser (Kavitation). ...
... [41, 64" 94, 154] So assoziieren superchaotrope Anionen wie POMs und Dodecaborat-Cluster an die hydrophobe Außenseite von makrocyclischen Cucurbit[n]urilen (CBn) (Abbildung 6). [41,64,94,154] Aufgrund ihrer Grçße kçnnen superchaotrope Anionen mit mehreren Makrocyclen mehrzähnig wechselwirken, was rasch zu ihrer Ausfällung führen kann, z. B. von CBn. ...
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Following up on scattered reports on interactions of conventional chaotropic ions (e.g., I−, SCN−, ClO4−) with macrocyclic host molecules, biomolecules, and hydrophobic neutral surfaces in aqueous solution, the chaotropic effect has recently emerged as a generic driving force for supramolecular assembly, orthogonal to the hydrophobic effect. The chaotropic effect becomes most effective for very large ions that extend beyond the classical Hofmeister scale, and that can be referred to as superchaotropic ions (e.g., borate clusters and polyoxometalates). In this review, we present a continuous scale of water‐solute interactions which includes the solvation of kosmotropic, chaotropic, and hydrophobic solutes, as well as the creation of void space (cavitation). Recent examples for the association of chaotropic anions to hydrophobic synthetic and biological binding sites, lipid bilayers, and surfaces are discussed.
... [40] Moreover, addition of H + , i.e. acidification, was shown to control the complexation of superchaotropic dodecaborate clusters with macrocyclic guests. [41]. ...
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Hofmeister effects of ions in aqueous solution strongly affect chemical and biological systems. High and low charge density anions, such as SO42- and SCN- respectively, decrease (salting-out) or increase (salting-in) the solubility of organic solutes in water. Due to their very low charge-density, nanometric anions, e.g. polyoxometalates (POMs), increase the solubility of organic solutes tremendously (highly salting-in) as they bind to neutral hydrated solutes strongly – a property that is attributed to the (super-)chaotropic effect. Here, we show that salting-out anions can be turned into salting-in anions in the presence of a superchaotropic POM, α-PW12O403-. The effect of salts composed of salting-out anions, e.g. SO42-, was investigated on the cloud point (CP) of an ethoxylated surfactant (C8E4) and a propoxylated co-solvent (C3P2) in the presence of SiW12O404- and PW12O403- with different counter-cations (H+, Li+, Na+, K+). SiW12O404- and PW12O403- lead to a monotonic strong CP-increase regardless of the counterion, except for PW12O403- combined with H+. Indeed, H3PW12O40 shows a CP decrease at high POM concentrations. This peculiar behavior is attributed to the formation of large H3PW12O40-C3P2 (and H3PW12O40-C8E4) co-assemblies, as shown by SAXS. The formation of these co-assemblies results from the “bridging” effect of H+ and the lower charge density of PW12O403- compared to SiW12O404-. The addition of (basic) salting-out anions leads to (i) the consumption of H+, then to (ii) the disruption of the large H3PW12O40-C3P2 (and H3PW12O40-C8E4) co-assemblies and subsequently to (iii) a CP-increase. In the peculiar case, this shows how commonly used salting-out anions can become apparently salting-in.
... The 1 2 3 4 5 6 7 8 9 10 11 12 13 14 15 16 17 18 19 20 21 22 23 24 25 26 27 28 29 30 31 32 33 34 35 36 37 38 39 40 41 42 43 44 45 46 47 48 49 50 51 52 53 54 55 56 57 large ΔH values are compensated by large entropic penalties, which are jointly in line with the thermochemical fingerprint of the chaotropic effect. [11,13,[15][16][17]19,20,25,26] We also used a computational model to gain deeper insight into the binding of B21 to γ-CD and expanded this investigation, for comparison, to other compounds with icosahedral γ-CD binding motifs, specifically ortho-COSAN, meta-COSAN (ortho and meta define the positions of the respective C atoms in the COSAN framework), [ . For all these compounds, association constants (K a ) are known under the same conditions (as sodium salts, in H 2 O) and a predominant 1 : 1 binding stoichiometry can be assumed. ...
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The supramolecular recognition of closo,closo ‐[B 21 H 18 ] − by cyclodextrins (CDs) has been studied in aqueous solution by isothermal titration calorimetry and nuclear magnetic resonance spectroscopy. These solution studies follow up on previous mass‐spectrometric measurements and computations, which indicated the formation and stability of CD•B 21 H 18 − complexes in the gas phase. The thermodynamic signature of solution‐phase binding is exceptional, the association constant for the γ‐CD complex with B 21 H 18 − reaches 1.8 × 10 6 M −1 , which is on the same order of magnitude as the so far highest observed value for the complex between γ‐CD and a metallacarborane. The nature of the intermolecular interaction is also examined by quantum‐mechanical computational protocols . These suggest that the desolvation penalty, which is particularly low for the B 21 H 18 − anion, is the decisive factor for its high binding strength. The results further suggest that the elliptical macropolyhedral boron hydride is another example of a CD binder, whose extraordinary binding affinity is driven by the chaotropic effect, which describes the intrinsic affinity of large polarizable and weakly solvated chaotropic anions to hydrophobic cavities and surfaces in aqueous solution.
... In recent years, our group has been doing plenty of work on the applications of boron cluster, especially in the fabrication of new and multi-functional nanomaterials. [39][40][41][42][43] Driven by the inherent reducibility and superchaotropic effect of boron cluster, we hope to further build boron clusterbased well-ordered metal NPs-coated nanocomposite materials. Based on this purpose, we first screened a series of support materials and found that commercial Fe3O4 NPs, with both easy separation and surface modification, met our requirement perfectly. ...
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Amphiphilic polyhedron-shaped p-sulfonatocalix[4]arene building blocks, which have been previously shown to assemble into bilayers in an antiparallel fashion, have been assembled in a parallel alignment into spherical and helical tubular structures by the addition of pyridine N-oxide and lanthanide ions. Crystallographic studies revealed how metal ion coordination and substrate recognition direct the formation of these supramolecular assemblies. The addition of greater amounts of pyridine N-oxide changed the curvature of the assembling surface and resulted in the formation of extended tubules.
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Dodecaborate anions of the type B12X122− and B12X11Y2− (X=H, Cl, Br, I and Y=OH, SH, NH3+, NR3+) form strong (Ka up to 106 L mol−1, for B12Br122−) inclusion complexes with γ-cyclodextrin (γ-CD). The micromolar affinities reached are the highest known for this native CD. The complexation exhibits highly negative enthalpies (up to −25 kcal mol−1) and entropies (TΔS up to −18.4 kcal mol−1, both for B12I122−), which position these guests at the bottom end of the well-known enthalpy-entropy correlation for CDs. The high driving force can be traced back to a chaotropic effect, according to which chaotropic anions have an intrinsic affinity to hydrophobic cavities in aqueous solution. In line with this argument, salting-in effects revealed dodecaborates as superchaotropic dianions.
Article
Nichtkovalente Wechselwirkungen sind die Grundlage der Informationsübertragung zwischen Molekülen sowohl in der belebten Natur als auch in synthetischen supramolekularen Strukturen. Trotz der immer genaueren Beschreibung biologischer Systeme und trotz der rasch zunehmenden Vielfalt synthetischer Wirt-Gast-Komplexe sind wir von einem systematischen und allgemein anwendbaren Verständnis der zugrundeliegenden zwischenmolekularen Kräfte noch weit entfernt. Die Organische Chemie ermöglicht den gezielten Aufbau nahezu beliebig variierbarer Wirtverbindungen mit komplementären, multiplen Wechselwirkungszentren und damit systematische experimentelle Analysen auf der Grundlage von weitgehend additiven Bindungsinkrementen. Obwohl selbst bei einfachen Ionenpaaren mehrere Mechanismen gleichzeitig wirken und wechselnde Entropie- wie Enthalpiebeiträge maßgebend sind, lassen sich in Analogie zu den Freie-Enthalpie-Beziehungen der Physikalisch-Organischen Chemie einzelne Wechselwirkungen identifizieren und praktisch nutzbar machen. Aufbauend auf klassischen physikalisch-chemischen Konzepten wird der Anteil an solvophoben Effekten, an Wechselwirkungen mit permanenten und mit induzierten Dipolen sowie an Wasserstoffbrücken soweit wie möglich empirisch quantifiziert. Bei Wasser als Solvens spielt neben hydrophoben Effekten seine geringe Polarisierbarkeit eine besondere Rolle. Die Quantifizierung von paarweisen Wechselwirkungen und ihrer Steuerung durch die Mikroumgebung sollte Hilfestellung leisten nicht nur bei der Konzeption neuer synthetischer Wirt-Gast-Komplexe, sondern unter anderem auch bei der rationalen Entwicklung von Wirkstoffen, von molekularen Schaltern, z. B. in der Sensortechnik, von enzymanalog arbeitenden Katalysatoren sowie bei Planung und Analyse biochemischer Experimente unter Einschluß gentechnologischer Verfahren.
Article
Traditional descriptions of the hydrophobic effect on the basis of entropic arguments or the calculation of solvent-occupied surfaces must be questioned in view of new results obtained with supramolecular complexes. In these studies, it was possible to separate hydrophobic from dispersive interactions, which are strongest in aqueous systems. Even very hydrophobic alkanes associate significantly only in cavities containing water molecules with an insufficient number of possible hydrogen bonds. The replacement of high-energy water in cavities by guest molecules is the essential enthalpic driving force for complexation, as borne out by data for complexes of cyclodextrins, cyclophanes, and cucurbiturils, for which complexation enthalpies of up to −100 kJ mol−1 were reached for encapsulated alkyl residues. Water-box simulations were used to characterize the different contributions from high-energy water and enabled the calculation of the association free enthalpies for selected cucurbituril complexes to within a 10 % deviation from experimental values. Cavities in artificial receptors are more apt to show the enthalpic effect of high-energy water than those in proteins or nucleic acids, because they bear fewer or no functional groups in the inner cavity to stabilize interior water molecules.
Article
Die traditionelle Beschreibung des hydrophoben Effekts, die auf entropischen Gesichtspunkten oder auf der Berechnung von lösungsmittelzugänglichen Oberflächen basiert, wird insbesondere durch neue Ergebnisse zu supramolekularen Wirt-Gast-Komplexen infrage gestellt. Dadurch können nun hydrophobe von dispersiven Wechselwirkungen separiert werden, wobei letztere vornehmlich in wässrigen Systemen von Bedeutung sind. Selbst die sehr hydrophoben Alkane werden allerdings nur dann stark gebunden, wenn die Kavität des Wirtes mit Wassermolekülen gefüllt ist, die nur eine kleine Zahl von Wasserstoffbrücken bilden können. Im Unterschied dazu bilden Wassermoleküle in der kondensierten Phase im Durchschnitt vier H-Brücken, wie Röntgenstreuungsexperimente und neuere Rechnungen belegen. Daten für Komplexe von Cyclodextrinen, Cyclophanen und Cucurbiturilen zeigen, dass die Verdrängung des “High-Energy”-Kavitätswassers durch Komplexierung des Gastes eine bedeutende enthalpische Bindungstriebkraft ist, wobei Komplexierungsenthalpien von bis zu −100 kJ mol−1 erreicht werden. Wasserboxsimulationen untermauern diesen enthalpischen Wasserverdrängungseffekt, wobei dieser für Cucurbiturile bis auf 10 % Abweichung mit dem experimentellen Enthalpiewert übereinstimmt. Kavitäten synthetischer Rezeptoren, besonders solche ohne nach innen ausgerichtete, H-Brücken bildende funktionelle Gruppen, sind dabei eher prädestiniert, einen High-Energy-Wassereffekt hervorzurufen, als diejenigen von Proteinen und Nukleinsäuren.
Article
Efficient assembly in host–guest interactions is crucial to supramolecular nanotechnology. Cyclodextrins (CDs), which possess a hydrophilic exterior surface and hydrophobic interior cavity on the truncated cone, improve the biocompatibility of nanodelivery systems, and hence, supramolecular approaches utilizing CDs can improve and expand the design and applications of functional delivery systems. Owing to good inclusion ability, αCD and βCD are commonly used in the design and construction of supramolecular structures.
Article
Host⋅guest complexes between cucurbit[7] (CB[7]) or CB[8] and diamantane diammonium ion guests 3 or 6 were studied by 1H NMR spectroscopy and X-ray crystallography. 1H NMR competition experiments revealed that CB[7]⋅6 is among the tightest monovalent non-covalent complexes ever reported in water with Ka=7.2×1017 M−1 in pure D2O and 1.9×1015 M−1 in D2O buffered with NaO2CCD3 (50 mM). The crystal structure of CB[7]⋅6 allowed us to identify some of the structural features responsible for the ultratight binding, including the distance between the NMe3+ groups of 6 (7.78 Å), which allows it to establish 14 optimal ion-dipole interactions with CB[7], the complementarity of the convex van der Waals surface contours of 6 with the corresponding concave surfaces of CB[7], desolvation of the CO portals within the CB[7]⋅6 complex, and the co-linearity of the C7 axis of CB[7] with the N+⋅⋅⋅N+ line in 6. This work further blurs the lines of distinction between natural and synthetic receptors.
Article
In this review, we highlight recent advancements on pillararene-based assemblies. The driving forces for the formation of the pillararene-based assemblies are discussed first. The host-guest interactions are deemed as not only general strategy for constructing assemblies but also essential components for preventing the assemblies from the dissociation. Solvent effect is also important in the assembling process, since it could influence the host-guest interactions and provide solvophobic effect on pillararenes for the assembly. Then, several pillararene-based assembly architectures are introduced, including pillararene-based interlocked structures, such as (poly)pseudorotaxanes, (poly)rotaxanes, and daisy chains, classified by their topological structures and synthetic strategy. The morphologies of the supramolecular assemblies are divided into several types, for example, nanospheres, nanotubes and supramolecular polymers. Furthermore, the functions and potential applications are summarized accompanied with related assembly structures. The review not only provides fundamental findings, but also foresights future research directions in the research area of pillararene-based assemblies.
Article
The term hydrophobic interactions denotes the tendency of relatively apolar molecules to stick together in aqueous solution. These interactions are of importance in many chemical disciplines, including the chemistry of in vivo processes. Enzyme-substrate interactions, the assembly of lipids in biomembranes, surfactant aggregation, and kinetic solvent effects in water-rich solutions are all predominantly governed by hydrophobic interactions. Despite extensive research efforts, the hydration of apolar molecules and the noncovalent interactions between these molecules in water are still poorly understood. In fact, the question as to what the driving force for hydrophobic intractions is shifts the study into a quest for a detailed understanding of the remarkable properties of liquid water. This review highlights some of the novel insights that have been obtained in the past decade. The emphasis is on both hydrophobic hydration and hydrophobic interactions since both phenomena are intimately connected. Several traditional views have been found to be deeply unsatisfactory, and courageous attempts have been made to conceptualize the driving force behind pairwise and bulk hydrophobic interactions. The review presents an admittedly personal selection of the recent experimental and theoretical developments, and when necessary, reference is made to relevant studies of earlier date.
Article
Noncovalent interactions constitute the basis for information transfer between molecules in living systems as well as in synthetic supramolecular structures. Despite ever more accurate descriptions of biological systems and a dramatically increasing diversity of synthetic host guest complexes, a systematic and general understanding of the underlying intermolecular forces is still in its infancy. Organic chemistry makes possible the targeted construction of infinitely variable host compounds with multiple centers interacting in complementary ways. This in turn opens the door to systematic experimental analyses based on binding increments, which can be shown to have a high degree of additivity. Even in the case of relatively simple ion pairs, several mechanisms are at work simultaneously, and either entropy or enthalpy contributions may prove to be decisive. Nevertheless, it is possible to identify individual interactions and then use them to practical advantage in ways analogous to the free-energy relationships of physical organic chemistry. Contributions due to solvophobic effects, to interactions with permanent and induced dipoles, and to hydrogen bonds lend themselves to a high degree of empirical quantification on the basis of classical physical-chemical principles. Water as a solvent plays a special role due to its low polarizability, apart from hydrophobic effects. Quantification of pairwise interactions and ultimate control over them through manipulation of the microenvironment should prove useful not only in the design of new synthetic host–guest complexes but also, for example, in the rational development of biologically active substances, molecular switches (e.g., for sensor technology), and catalysts that function analogously to enzymes. The results should also assist in the planning and analysis of biochemical experiments including techniques of genetic engineering.
Article
We report on the noncovalent interactions of nanodiamond carboxylic acids derived from adamantane, diamantane, and triamantane with β- and γ-cyclodextrins. The water solubility of the nanodiamonds was increased by attaching an aromatic dicarboxylic acid via peptide coupling. Isothermal titration calorimetry experiments were performed to determine the thermodynamic parameters (K(a), ΔH, ΔG and ΔS) for the host-guest inclusion. The stoichiometry of the complexes is invariably 1:1. It was found that K(a), ΔG and ΔH of inclusion increase for larger nanodiamonds. ΔS is generally positive, in particular for the largest nanodiamonds. β-Cyclodextrin binds all nanodiamonds, γ-cyclodextrin clearly prefers the most bulky nanodiamonds. The interaction of 9-triamantane carboxylic acid shows one of the strongest complexation constants towards γ-cyclodextrin ever reported, K(a) = 5.0 × 10(5) M(-1). In order to gain some insight into the possible structural basis of these inclusion complexes we performed density functional calculations at the B97-D3/def2-TZVPP level of theory.
Article
A system of chemical reactions has been developed which permits the controlled growth of spherical silica particles of uniform size by means of hydrolysis of alkyl silicates and subsequent condensation of silicic acid in alcoholic solutions. Ammonia is used as a morphological catalyst. Particle sizes obtained in suspension range from less than 0.05 μ to 2 μ in diameter.
Article
Supramolecular polymers can be random and entangled coils with the mechanical properties of plastics and elastomers, but with great capacity for processability, recycling, and self-healing due to their reversible monomer-to-polymer transitions. At the other extreme, supramolecular polymers can be formed by self-assembly among designed subunits to yield shape-persistent and highly ordered filaments. The use of strong and directional interactions among molecular subunits can achieve not only rich dynamic behavior but also high degrees of internal order that are not known in ordinary polymers. They can resemble, for example, the ordered and dynamic one-dimensional supramolecular assemblies of the cell cytoskeleton and possess useful biological and electronic functions.
Article
Construction of supramolecular self-assemblies whose self-assembling process and self-assembled architectures can be controlled by external stimuli is a fascinating and challenging topic for supramolecular chemists. The modification of photochromic molecules with noncovalent interaction sites or the incorporation of photochromic molecules into self-assembling modules makes light an ideal external input, providing high-performance photoresponsive multicomponent self-assemblies. Among such systems, in this tutorial review we deal with several photoresponsive supramolecular self-assemblies showing a unique mechanism and/or type of photoresponse. These examples illustrate that we would be able to produce further new photoresponsive molecular ensembles if one can elaborately hybridize photochromic molecules to specifically-designed supramolecular self-assemblies. We believe that the accumulation of insight into the construction principle, mechanism and concept of such smart supramolecular self-assemblies should realize practical smart functional materials.
Article
The first organic-inorganic hybrid complexes between CB[n] and polyoxometalates not only display a surprisingly high structural complementarity, the right pairing also allows their chemical and physical properties to be coupled, as illustrated by two examples.
Article
We determined the values of Ka for a wide range of host-guest complexes of cucurbit[n]uril (CB[n]), where n = 6-8, using 1H NMR competition experiments referenced to absolute binding constants measured by UV/vis titration. We find that the larger homologues--CB[7] and CB[8]--individually maintain the size, shape, and functional group selectivity that typifies the recognition behavior of CB[6]. The cavity of CB[7] is found to effectively host trimethylsilyl groups. Remarkably, the values of Ka for the interaction of CB[7] with adamantane derivatives 22-24 exceeds 10(12) M(-1)! The high levels of selectivity observed for each CB[n] individually is also observed for the CB[n] family collectively. That is, the selectivities of CB[6], CB[7], and CB[8] toward a common guest can be remarkably large. For example, guests 1, 3, and 11 prefer CB[8] relative to CB[7] by factors greater than 10(7), 10(6), and 3000, respectively. Conversely, guests 23 and 24 prefer CB[7] relative to CB[8] by factors greater than 5100 and 990, respectively. The high levels of selectivity observed individually and collectively for the CB[n] family renders them prime components for the preparation of functional biomimetic self-sorting systems.
Article
Supramolecular chemistry has developed over the last forty years as chemistry beyond the molecule. Starting with the investigation of the basis of molecular recognition, it has explored the implementation of molecular information in the programming of chemical systems towards self-organisation processes, that may occur either on the basis of design or with selection of their components. Supramolecular entities are by nature constitutionally dynamic by virtue of the lability of non-covalent interactions. Importing such features into molecular chemistry, through the introduction of reversible bonds into molecules, leads to the emergence of a constitutional dynamic chemistry, covering both the molecular and supramolecular levels. It considers chemical objects and systems capable of responding to external solicitations by modification of their constitution through component exchange or reorganisation. It thus opens the way towards an adaptive and evolutive chemistry, a further step towards the chemistry of complex matter.
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