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Lysine (K) is an important target residue for protein and peptide delivery across membranes. K is the most frequently exposed residue in proteins, leading to high demand for the development of K-compatible transport activators. However, designing activators for K-rich peptides and proteins is more challenging than for arginine-rich species because of the kosmotropic nature of K and its recognition difficulty. In this study, we designed a new amphiphilic sulfonatocalix[5]arene (sCx5-6C) as a K-compatible transport activator. sCx5-6C was tailored with two key elements, recognition of K and the ability to embed into membranes. We measured the membrane transport efficiencies of α-poly-l-lysine, heptalysine, and histones across artificial membranes and of α-poly-l-lysine into live cells, activated by sCx5-6C. The results demonstrate that sCx5-6C acts as an efficient activator for translocating K-rich peptides and proteins, which cannot be achieved by known arginine-compatible activators.

Cucurbit[n]urils (CBn, n = 6–8) serve as molecular receptors for imidazolium-based ionic liquids (ILs) in aqueous solution. The amphiphilic nature of 1-alkyl-3-methylimidazolium guests (Cnmim), with a cationic imidazolium residue and a hydrophobic alkyl chain, enabled their complexation with CBn through a combination of the hydrophobic effect and ion–dipole interactions. 1H NMR experiments revealed that the cavity of CBn can host the hydrophobic chain of the ILs, while one of the carbonyl rims served as a docking site for the imidazolium ring. The structure of the complexes was further analyzed by molecular dynamics (MD) simulations, which indicated that the cavity of CB6 can accommodate up to 5 carbon atoms, while the larger cavity of CB7 and CB8 can encapsulate longer alkyl chains in folded conformations. Isothermal titration calorimetry (ITC) experiments provided up to micromolar affinity of ILs to CBn in aqueous solution, which was independently quantified by indicator displacement titrations.

Following up on scattered reports on interactions of conventional chaotropic ions (for example, 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 (for example, borate clusters and polyoxometalates). In this Minireview, we present a continuous scale of water–solute interactions that 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.

We introduce herein boron-dipyrromethene (BODIPY) dyes as a new class of fluorophores for the design of reporter dyes for supramolecular host–guest complex formation with cucurbit[7]uril (CB7). The BODIPYs contain a protonatable aniline nitrogen in the meso-position of the BODIPY chromophore, which was functionalized with known binding motifs for CB7. The unprotonated dyes show low fluorescence due to photoinduced electron transfer (PET), whereas the protonated dyes are highly fluorescent. Encapsulation of the binding motif inside CB7 positions the aniline nitrogen at the carbonyl rim of CB7, which affects the pKa value, and leads to a host-induced protonation and thus to a fluorescence increase. The possibility to tune binding affinities and pKa values is demonstrated and it is shown that, in combination with the beneficial photophysical properties of BODIPYs, several new applications of host–dye reporter pairs can be implemented. This includes indicator displacement assays with favourable absorption and emission wavelengths in the visible spectral region, fluorescence correlation spectroscopy, and noncovalent surface functionalization with fluorophores.

We report the formation of supramolecular complexation between cucurbit[n]urils (CBn) and an amphiphilic pyridinium-functionalized anthracene (AnPy) in aqueous solution. The CB7 cavity is capable of accommodating the pyridinium moiety, while CB8 can encapsulate the pyridinium and anthracene moieties at once. The encapsulation of AnPy by CB7 leads to the formation of nanoparticles, while the complexation of AnPy with CB8 leads to the formation of nanorods.

1-Aminopyrene and 1-naphthylamine-5-sulfonic acid were converted to the putrescine (1,4-diaminobutane)-substituted derivatives (dyes 1 and 2). The diaminobutyl anchor serves as a common binding motive for cation-receptor macrocycles such as cucurbit[n]urils (n = 6–8) and p-sulfonatocalix[4]arene. When protonated, they are prone to undergo a rapid deprotonation in their excited state to result in fluorescence from the unprotonated form (Forster cycle). The deprotonation can be suppressed by complexation with cation-receptor macrocycles, which allows the fluorescence of the locally excited (protonated) state to be dramatically enhanced (factor 12 for dye 1 and 83 for dye 2). This host-retarded excited-dye deprotonation is a direct consequence of the previously established complexation-induced pKa shifts that dyes undergo upon binding to a macrocyclic host. The data set also allows a systematic comparison of complexation-induced pKa shifts in the ground and excited state of a dye. The trends are comparable, ...

Die Phosphorylierung und Dephosphorylierung von Peptiden durch Kinasen und Phosphatasen ist ein allgegenwartiger Mechanismus der Signaltransduktion in biologischen Systemen. Eine unnaturlich hohe oder niedrige Aktivitat dieser Enzyme steht im Zusammenhang mit vielen Krankheiten. Hier fuhren wir amphiphile Calixarene als supramolekulare Schlusselkomponenten fur einen Membrantransport von Peptiden ein, der sich durch Phosphorylierung regulieren lasst. Mithilfe von farbstoffbeladenen Liposomen zeigen wir, dass diese Calixarene als Gegenionen fur etablierte zellpenetrierende Peptide fungieren und deren Transport effizient aktivieren konnen. Die ermittelten EC50-Werte liegen im niedrigen nanomolaren Bereich. Die Calixarene aktivieren sogar den Membrantransport von kurzen Peptiden, die Substrate fur Kinasen in Signaltransduktionskaskaden sind. Dadurch dass das phosphorylierte Produkt viel weniger effektiv transportiert wird, ermoglicht dies die Regulierung des Membrantransports durch Proteinkinase A (PKA) und Proteinkinase C (PKC). Daraus folgt auch eine markierungsfreie Methode, um die Aktivitat dieser Enzyme mittels Fluoreszenz nachzuweisen.

Phosphorylation and dephosphorylation of peptides by kinases and phosphatases is essential for signal transduction in biological systems, and many diseases involve abnormal activities of these enzymes. Herein, we introduce amphiphilic calixarenes as key components for supramolecular, phosphorylation-responsive membrane transport systems. Dye-efflux experiments with liposomes demonstrated that calixarenes are highly active counterion activators for established cell-penetrating peptides, with EC50 values in the low nanomolar range. We have now found that they can even activate membrane transport of short peptide substrates for kinases involved in signal transduction, whereas the respective phosphorylated products are much less efficiently transported. This allows regulation of membrane transport activity by protein kinase A (PKA) and protein kinase C (PKC), as well as monitoring of their activity in a label-free kinase assay.

Cucurbit[7]uril (CB7), native α-cyclodextrin (αCD) and its tris-O-methylated derivative (TMαCD) as macrocyclic host molecules and amine-terminated poly(ethylene glycol) (PEG) as neutral guest were used for the synthesis of 3-CB7, 3-αCD and 3-TMαCD polyrotaxanes. The binding affinities of the neutral PEG guest into the CB7, αCD and TMαCD cavities were evaluated by isothermal titration calorimetry. The high value of the stability constant (1 × 104 M−1) indicates that PEG provides a preferential binding to CB7 over αCD. The polyrotaxane structure was confirmed by FT-IR and 1H NMR spectroscopy. The coverage ratio of the PEG with CB7, αCD and TMαCD macrocycles, were 63%, 71%, and 30%, respectively. The polyrotaxanes 3-CB7 and 3-αCD exhibit an enhancement in thermal stability compared with the non-rotaxane 3 counterpart. In addition, polyrotaxane 3-CB7 shows blue-shifted absorption by more than 20 nm and enhanced water solubility.

Cucurbit[n]urils stand out among supramolecular macrocycles with respect to their recognition propensity towards cationic and neutral guests in aqueous solution. Their ability to complex guests with ultra-high affinity can be understood in terms of multiple non-covalent interactions and the hydrophobic effect, to which the release of high-energy water from the cavity contributes considerably. This chapter focuses on the structure and physical properties of CB[n], including the peculiarities of their cavity, and their host–guest complexation with charged and neutral guests.

Chemical sensors and assays are essential to determine the concentration or functional activity of (bio)analytes. Most established assays rely on biomolecular recognition such as antibody–antigen interactions or protein–ligand interactions. However, during the past decade, supramolecular receptors have proven as useful alternatives affording new assays for hitherto undetectable analytes as well as for the development of refined assay procedures. Herein, we review sensors and assays, in which cucurbiturils (CBs) are key components. We focus on optical methods such as absorption, fluorescence, and circular dichroism spectroscopy, and we also include a summary of NMR-based bioimaging with CBs.

We report the modification of the 2-ammonio group at halogenated decaborate ions with 2,3-epoxypropane, the product of which reacts readily with nucleophiles to form previously inaccessible coupling of polyhedra with organic molecules and materials. We demonstrate that these ions present a good binding motif in supramolecular chemistry.

Whilst cucurbit[n]urils (CBn) have been utilized in gas encapsulation, only the smaller CBn (n = 5 and 6) have utility given their small cavity size. In this work, we demonstrate that the large cavity of CB8 can be tailored for gaseous and volatile hydrocarbon encapsulation by restricting its internal cavity size with auxiliary aryl-bisimidazolium (Bis, aryl = phenyl, naphthyl, and biphenyl) guests. The binding constants for light hydrocarbons \(C \le 4\) are similar to those measured with CB6, while larger values are obtained with Bis·CB8 for larger guests. A clear propensity for higher affinities of alkenes relative to alkanes is observed, most pronounced with the largest delocalized naphthalene residue in the auxiliary Bis guest, which provides unique evidence for sizable small-molecule \(\Pi-\Pi\) interactions.

The spatiotemporally resolved monitoring of membrane translocation, e.g., of drugs or toxins, has been a long-standing goal. Herein, we introduce the fluorescent artificial receptor-based membrane assay (FARMA), a facile, label-free method. With FARMA, the permeation of more than hundred organic compounds (drugs, toxins, pesticides, neurotransmitters, peptides, etc.) through vesicular phospholipid bilayer membranes has been monitored in real time (µs-h time scale) and with high sensitivity (nM-µM concentration), affording permeability coefficients across an exceptionally large range from 10–9–10–3 cm s–1. From a fundamental point of view, FARMA constitutes a powerful tool to assess structure-permeability relationships and to test biophysical models for membrane passage. From an applied perspective, FARMA can be extended to high-throughput screening by adaption of the microplate reader format, to spatial monitoring of membrane permeation by microscopy imaging, and to the compartmentalized monitoring of enzymatic activity., Biedermann et al develop a tool to monitor transport across membranes using fluorescent artificial receptors, thereby bypassing the need for analyte labelling. They show the utility of the method for a large number of compounds suggesting it can be widely applied to both basic research and drug screening.

[Image: see text] We demonstrate that the reproducibility of sensors for nitroaromatics based on surface-enhanced Raman spectroscopy (SERS) can be significantly improved via a hierarchical aqueous self-assembly approach mediated by the multifunctional macrocyclic molecule cucurbit[7]uril (CB[7]). Our approach is enabled by the novel host–guest complexation between CB[7] and an explosive marker 2,4-dinitrotoluene (DNT). Binding studies are performed using experimental and computation techniques to quantify key binding parameters for the first time. This supramolecular complexation allows DNT to be positioned in close proximity to the plasmonic hotspots within aggregates of CB[7] and gold nanoparticles, resulting in significant SERS signals with a detection limit of ∼1 μM. The supramolecular ensemble is selective against a structurally similar nitroaromatics owing to the molecular-recognition nature of the complexation as well as tolerant against the presence of model organic contaminants that bind strongly to the SERS substrates.

High binding constants of 19 inorganic cations with the cucurbit[n]uril homologues (CBn, n = 5, 6, 7, 8) in water were determined and the far-reaching consequences and interferences of the high affinities (millimolar to micromolar) are discussed.

Cucurbit[n]urils (CBn, n = 7, 8) serve as artificial receptors for steroids (21 tested), including the hormones testosterone and estradiol as well as steroidal drugs. Fluorescence displacement titrations and isothermal titration calorimetry (ITC) provided up to nanomolar binding affinities in aqueous solution for these hydrophobic target molecules, exceeding the values of known synthetic receptors. Remarkable binding selectivities, even for homologous steroid pairs, were investigated in detail by NMR, X-ray crystal diffraction, ITC, and quantum chemical calculations. Notably, the CBn•steroid complexes are stable in water and buffers, in artificial gastric acid, and even in blood serum. Numerous applications have been demonstrated, which range from the solubility enhancement of the steroids in the presence of the macrocycles (up to 100 times, for drug delivery) and the principal component analysis of the fluorescence responses of different CBn•reporter dye combinations (for differential sensing of steroids) to the real-time monitoring of chemical conversions of steroids as substrates (for enzyme assays).

We present novel active targeting luminescent gold nanoclusters (AuNCs), which are prepared through a one-pot procedure by using a pentapeptide (CRGDS) for stabilization and tumor recognition. CRGDS-AuNCs exhibit a high tumor-specific retention with an exceptionally high tumor-to-liver uptake ratio of 9.3. Their small hydrodynamic diameter and zwitterionic surface facilitate urinary excretion, which reaches 82% within 24 h after injection.

The supramolecular chemisorption of CO2 by the oligomeric chitin-acetate (CA) in DMSO as a green solvent offers a novel eco-friendly approach for CO2 capture. Since the amino groups in the sorbent material are blocked either by protonation or acetylation, the multi-armed hydroxyl based oligosaccharide captures CO2 through the formation of an organic carbonate species as confirmed by 13C NMR, in situ ATR-FTIR spectroscopy and conductivity. DFT calculations verified the formation of the CA-CO2 adduct, in which the organic carbonate group is stabilized through supramolecular ionic interaction and hydrogen bonding with the neighboring ammonium ion and hydroxyl functional group along the oligomer backbone. The use of other polar aprotic solvents (N,N-dimethylformamide (DMF), acetonitrile, and acetone) was not successful due to solubility issues.

The host-guest interactions of a third-generation fluoroquinone, danofloxacin (DOFL), with the macrocyclic host cucurbit[7]uril (CB7) have been investigated at different pH values (~3.5, 7.5, and 10). The photophysical properties have been positively affected, that is, the fluorescence yield and lifetime increased, as well as the photostability of DOFL improved in the presence of CB7. The antibacterial activity of DOFL is enhanced in the presence of CB7, as tested against four pathogenic bacteria; highest activity has been found towards B. cereus and E. coli, and lower activity towards S. aureus and S. typhi. The antibacterial activity of two additional second-generation fluoroquinones, i.e., norfloxacin and ofloxacin, has also been investigated in the absence as well as the presence of CB7 and compared with that of DOFL. In case of all drugs, the minimum inhibitory concentration (MIC) was reduced 3–5 fold in the presence of CB7. The extended shelf-life (antibacterial activity over time) of the fluoroquinone drugs in the presence of CB7, irrespective of four types of bacteria, can be attributed to the enhanced photostability of their CB7 complexes, which can act as better antibiotics with a longer expiry date than uncomplexed DOFL.

Competitive occupation of surface-bound supramolecular hosts allows precise control of surface coverage densities on particles., We report herein the controlled surface functionalization of micro- and nanoparticles by supramolecular host–guest interactions. Our idea is to exploit the competition of two high-affinity guests for binding to the surface-bound supramolecular host cucurbit[7]uril (CB7). To establish our strategy, surface azide groups were introduced to hard-sphere (poly)methylmethacrylate particles with a grafted layer of poly(acrylic acid), and a propargyl derivative of CB7 was coupled to the surface by click chemistry. The amount of surface-bound CB7 was quantified with the high-affinity guest aminomethyladamantane (AMADA), which revealed CB7 surface coverage densities around 0.3 nmol cm–2 indicative of a 3D layer of CB7 binding sites on the surface. The potential for surface functionalization was demonstrated with an aminoadamantane-labeled rhodamine (Ada-Rho) as a second high-affinity guest. Simultaneous incubation of CB7-functionalized particles with both high-affinity guests, AMADA and Ada-Rho, revealed a simple linear relationship between the resulting surface coverage densities of the model fluorescent dye and the mole fraction of Ada-Rho in the incubation mixture. This suggests a highly modular supramolecular strategy for the stable immobilization of application-relevant molecules on particle surfaces and a precise control of their surface coverage densities.

Polyhedral carboxymethyl carborane (C2 B10 H12 ) derivatives, including mono- and disubstituted o-, m-, and p-isomers, have been synthesized. Supramolecular host-guest complexation of these derivatives with cyclodextrins (CDs; namely, α-, β-, and γ-CD) has been investigated in water. The globular structure of the carborane binding moiety and its hydrophobic character qualify it as an ideal recognition site to form stable inclusion complexes with macrocyclic host molecules in aqueous solution. The measured binding affinities for the carborane derivatives were in the millimolar range (Ka =103 -104 m-1 ) with differently sized CDs, and preferential binding to β-CD.

Protein folding can be described as a probabilistic succession of events in which the peptide chain forms loops closed by specific amino acid residue contacts, herein referred to as loop nodes. To measure loop rates, several photophysical methods have been introduced where a pair of optically active probes is incorporated at selected chain positions and the excited probe undergoes contact quenching (CQ) upon collision with the second probe. The quenching mechanisms involved triplet-triplet energy transfer, photoinduced electron transfer, and collision-induced fluorescence quenching, where the fluorescence of Dbo, an asparagine residue conjugated to 2,3-diazabicyclo[2.2.2]octane, is quenched by tryptophan. The discrepancy between the loop rates afforded from these three CQ techniques has, however, remained unresolved. In analyzing this discrepancy, we now report two short-distance FRET methods where Dbo acts as an energy acceptor in combination with tryptophan and naphtylalanine, two donors with largely different fluorescence lifetimes of 1.3 and 33 ns, respectively. Despite the different quenching mechanisms, the rates from FRET and CQ methods were, surprisingly, of comparable magnitude. This combination of FRET and CQ data led to a unifying physical model and to the conclusion that the rate of loop formation in folding reactions varies not only with the kind and number of residues that constitute the chain but also in particular with the size and properties of the residues that constitute the loop node.

In aqueous solution, host–guest complexation is frequently driven by the hydrophobic effect, which also constitutes a popular approach in the design of supramolecular assemblies. Herein, we report an orthogonal assembly motif, the chaotropic effect, which exploits the tendency of chaotropic anions to associate with hydrophobic surfaces.

The driving forces of association between three different families of macrocycles as hosts, namely cyclodextrins (α-, β-, and γ-), p-sulfonatocalix[n]arenes (n = 4–6) as well as cucurbit[n]urils (n = 6–8), and three different bicyclic azoalkane homologues as guests, namely 2,3-diazabicyclo[2.2.1]hept-2-ene (DBH), 2,3-diazabicyclo[2.2.2]oct-2-ene (DBO) as well as 2,3-diazabicyclo[2.2.3]non-2-ene (DBN), were examined by means of calorimetric titrations, NMR spectroscopy and molecular dynamics simulation, all in aqueous solution. The small, spherical and uncharged guests preferably bind inside the cavities of the medium sized hosts. The inclusion complexation by β-cyclodextrin and p-sulfonatocalix[4]arene shows medium binding affinities (millimolar), while cucurbit[7]uril macrocycle shows very strong binding (micromolar). For all types of macrocycles, the complex formation is enthalpically driven (ΔH°

Dodecaborate anions of the type B12X12(2-) and B12X11Y(2-) (X=H, Cl, Br, I and Y=OH, SH, NH3(+), NR3(+)) form strong (K(a) up to 10(6) L mol(-1), for B12Br12(2-)) 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 B12I12(2-)), 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.

A poly[(2-ethyl-2-oxazoline)-ran-(2-nonyl-2-oxazoline)] random copolymer was synthesized and its thermoresponsive behavior in aqueous solution modulated by the addition of different supramolecular host molecules. The macrocycles formed inclusion complexes with the nonyl aliphatic side-chains present in the copolymer, increasing its cloud point temperature. The extent of this temperature shift was found to depend on the cavitand concentration and on the strength of the host-guest complexation. The cloud point temperature could be tuned in an unprecedented wide range of 30 K by supramolecular interactions. Since the temperature-induced breakage of the inclusion complexes constitutes the driving force for the copolymer phase transition, the shift in cloud point temperature could be utilized to estimate the association constant of the nonyl side chains with the cavitands.

1-Aminopyrene and 1-naphthylamine-5-sulfonic acid were converted to the putrescine (1,4-diaminobutane)-substituted derivatives (dyes 1 and 2). The diaminobutyl anchor serves as a common binding motive for cation-receptor macrocycles such as cucurbit[n]urils (n = 6-8) and p-sulfonatocalix[4]arene. When protonated, they are prone to undergo a rapid deprotonation in their excited state to result in fluorescence from the unprotonated form (Förster cycle). The deprotonation can be suppressed by complexation with cation-receptor macrocycles, which allows the fluorescence of the locally excited (protonated) state to be dramatically enhanced (factor 12 for dye 1 and 83 for dye 2). This host-retarded excited-dye deprotonation is a direct consequence of the previously established complexation-induced pK

The host-guest complexation of hydrocarbons (22 guest molecules) with cucurbit[7]uril (CB7) was investigated in aqueous solution. Association constants were determined by using the indicator displacement strategy, which allows binding constant determinations also for poorly water-soluble (hydrophobic) guests. The binding constants (103–109 M−1) increased with the size of the hydrocarbon, pointing to the hydrophobic effect and dispersion interactions as driving forces. Besides potential applications for the sensing and separation of hydrocarbons, the measured affinities provide unique benchmark data for the binding of neutral guest molecules. Consequently, a computational blind challenge, the HYDROPHOBE challenge, was conducted in order to allow a comparison with state-of-the-art computational methods for predicting host-guest affinity constants. In total, 5 computational data sets were submitted, which allowed the comparison of experimental binding constants with those predicted by coupled-cluster theory (DLPNO-CCSD(T)), dispersion-corrected density functional theory (DFT), and explicit solvent molecular dynamics (MD) simulations parameterized with two different force field combinations from the AMBER simulation package. All submissions were capable of predicting the general binding trend, with a slightly better correlation for the MD compared to the quantum-chemical (QM) data sets (R2MD = 0.80 vs R2QM = 0.66, average values for the submitted data sets). On the other hand, QM calculations showed better predictions for the absolute values of the binding affinities as reflected by the mean signed errors (4.3 kcal mol−1 for MD vs 1.8 kcal mol−1 for QM). When searching for sources of uncertainty in predicting the host-guest affinities, the experimentally known hydration energies of the investigated hydrocarbons could be employed, which provided a distinct advantage of the HYDROPHOBE challenge. The comparison with the employed solvation models (explicit solvent for MD and COSMO-RS for QM) confirmed a good correlation for both methods, but revealed a rather constant offset of the COSMO data, by ca. +2 kcal mol−1, which was traced back to a required reference-state correction in the QM submissions (2.38 kcal mol−1). Introduction of the reference-state correction improved the predictive power of the QM methods, particularly for small hydrocarbons up to C5. The correlations of both QM and MD submissions also exposed specific outliers, which could be due to peculiarities of the investigated guests, for example, different degrees of conformational changes upon complexation, such as helical structures of the longer n-alkyl chains within the cavity. The latter was confirmed by 2D NMR experiments and both the MD as well as QM calculations.

A fluorescent perylene dye with two aromatic units was designed for binding to cucurbit[8]uril. The binding affinity of the complexes increased about 3 orders of magnitude compared to the dye without a secondary aromatic unit. The high affinity allows the complexes to act as fluorescent probes for detection of strong binding guests with nanomolar sensitivity.

Nucleoli are important subnuclear structures inside cells. We report novel fluorescent gold nanoclusters (K-AuNCs) that are able to stain the nucleoli selectively and make it possible to explore the nucleolar morphology with fluorescence imaging technique. This novel probe is prepared through an easy synthesis method by employing a tripeptide (Lys-Cys-Lys) as the surface ligand. The properties, including deep-red fluorescence emission (680 nm), large Stocks shift, broad excitation band, low cytotoxicity, and good photostability, endow this probe with potential for bioanalytical applications. Because of their small size and their positively charged surface, K-AuNCs are able to accumulate efficiently at the nucleolar regions and provide precise morphological information. K-AuNCs are also used to monitor the nucleolar dynamics along the reverse-transformation process of malignant cells, induced by the agonist of protein A, 8-chloro-cyclic adenosine monophosphate. This gives a novel approach for investigating the working mechanism of antitumor drugs.

The weakly coordinating binary macropolyhedral anion closo,closo-[B

Undecahydro-mercapto-closo-dodecaborate (BSH), a purely inorganic cluster anion, serves as an unconventional stabilizing ligand for the preparation of gold nanoparticles (AuNPs). The BSH-capped AuNPs serve as nano-scaffolds, allowing for the creation of supramolecular architectures by using polycationic macrocyclic host molecules, through strong host–guest complexation. An amphiphilic calixarene (CX) forms first mono- and subsequently bi-layer assemblies on the BSH–AuNP surfaces depending on the CX concentration. The inorganic–organic hybrid materials, combined with host–dye displacement assays, serve as a chemosensing ensemble for negatively charged molecules, including DNA.

Polyamines play an important role in cell growth, differentiation, and cancer development, and the biosynthetic pathway of polyamines is established as a drug target for the treatment of parasitic diseases, neoplasia, and cancer chemoprevention. The key enzyme in polyamine biosynthesis is ornithine decarboxylase (ODC). We report herein an analytical method for the continuous fluorescence monitoring of ODC activity based on the supramolecular receptor cucurbit[6] uril (CB6) and the fluorescent dye trans-4-[4-(dimethylamino) styryl]-1-methylpyridinium iodide (DSMI). CB6 has a significantly higher binding constant to the ODC product putrescine (>10(7)M(-1)) than to the substrate L-ornithine (340 M-1). This enables real-time monitoring of the enzymatic reaction through a continuous fluorescence change caused by dye displacement from the macrocycle by the formed product, which allowed a straightforward determination of enzyme kinetic parameters (k(cat) = 0.12 s(-1) and K-M = 24 mu M) and inhibition constants of the two ODC inhibitors alpha-difluoromethylornithine (DFMO) and epigallocatechin gallate (EGCG). The potential for high-throughput screening (HTS) was demonstrated by excellent Z' factors (>0.9) in a microplate reader format, and the sensitivity of the assay is comparable to or better than most established complementary methods, which invariably have the disadvantage of not being compatible with direct implementation and upscaling to HTS format in the drug discovery process.

The weakly coordinating binary macropolyhedral anion closo,closo-[BH] (B21; D symmetry) has been synthesized using a simplified strategy compared to that in the literature. While gas-phase complexes of B21 with β- and γ-cyclodextrin (CD) were detected using ESI FT-ICR spectrometric measurements, α-CD did not bind to the B21 guest. This spectroscopic evidence has been interpreted using quantum-chemical computations, showing that β- and γ-CD are able to interact with B21 due to their larger cavities, in contrast to the smaller α-CD. The hydridic B-H vectors of the B21 anion interact with K counterions and, via dihydrogen bonding, also with the partially positively charged hydrogens of the CD sugar units in the modeled β- and γ-CD complexes. In summary, it has been shown by combined spectrometric/computational analysis that macropolyhedral boron hydride anions with two counterions can form stable complexes with β- and γ-CD in the gas phase, offering a new perspective for the future investigation of this remarkable anion in the areas of supramolecular and medicinal chemistries.

Der Makrocyclus p-Sulfonatocalix[4]aren (CX4) und der Fluoreszenzfarbstoff Lucigenin (LCG) bilden einen stabilen Wirt/Gast-Komplex, in dem die Fluoreszenz des Farbstoffs geloscht wird. Die Inkubation von lebenden V79- und CHO-Zellen mit dem chemosensorischen Ensemble CX4/LCG fuhrt zu dessen spontaner Aufnahme. Die nachfolgende Zugabe von Cholin, Acetylcholin oder Protamin, die alle eine hohe Affinitat fur CX4 haben und in der Lage sind, in die Zellen einzudringen, fuhrte zu einer positiven Fluoreszenzantwort der Zellen. Dies kann auf die Verdrangung des LCG aus CX4 durch die Analyten zuruckgefuhrt werden. Die Ergebnisse zeigen die grundsatzliche Funktionsfahigkeit von Indikatorverdrangungsassays mit synthetisch hergestellten Rezeptoren zur Detektion der Aufnahme bioorganischer Analyten in lebenden Zellen.

The intriguing dual-emission behavior of p- dimethylaminobenzonitrile (DMABN) and the identity of the associated excited states is, arguably, the most extensively investigated and also controversially discussed molecule- specific phenomenon of modern photochemistry. We have now found a new, third fluorescence band when DMABN is encapsulated within the water-soluble molecular container cucurbit[8]uril (CB8). It is centered between the previously observed emissions and assigned to the elusive excimer emission from DMABN through 1:2 CB8:DMABN complex formation. Heating of the CB8⋅(DMABN)2 complex from 0 to 100 °C results in the dissociation of the ternary complex and restoration of the dual-emission properties of the monomer. Alternatively, monomer emission can be obtained by selecting cucurbit[7]uril (CB7), a host homologue that is too small to accommodate two DMABN molecules, or by introducing ethyl instead of methyl groups at the amino terminus of the aminobenzonitrile guest.

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.

A new approach towards the rapid identification of quality binders to cucurbiturils--those that combine high affinity with high selectivity for a particular homologue--was developed. The assay exploits macrocycle-specific optical fingerprints (colorimetric or fluorimetric) of carefully selected indicators dyes. The screening of a guest library revealed known (e.g., adamantane derivatives) and new (e.g., terpenes) quality binders. The predictive power of the assay was underpinned by the modeling of the involved thermodynamic equilibria.

We report the self-assembly of a series of highly charged supramolecular complexes in aqueous media composed of cyclobis(4,4'-(1,4-phenylene)bispyridine-p-phenylene)tetrakis(chloride) (ExBox) and three dicationic perylene diimides (PDIs). Efficient energy transfer (ET) is observed between the host and guests. Additionally, we show that our hexacationic complexes are capable of further complexation with neutral cucurbit[7]uril (CB[7]), producing a 3-polypseudorotaxane via the self-assembly of orthogonal recognition moieties. ExBox serves as the central ring, complexing to the PDI core, while two CB[7]s behave as supramolecular stoppers, binding to the two outer quaternary ammonium motifs. The formation of the 3-polypseudorotaxane results in far superior photophysical properties of the central PDI unit relative to the binary complexes at stoichiometric ratios. Lastly, we also demonstrate the ability of our binary complexes to act as a highly selective chemosensing ensemble for the neurotransmitter melatonin.

Ternare Komplexe des makrocyclischen Wirts Cucurbit[8]uril mit dikationischen Farbstoffen und chiralen aromatischen Analyten zeigen starke induzierte Circulardichroismus(ICD)-Signale im Nah-UV- und sichtbaren Bereich. Dies ermoglicht eine neuartige Herangehensweise zur Chiralitatssensorik und Sequenzerkennung in Wasser mit mikromolaren Analytkonzentrationen. Chemische Reaktionen konnen zudem in Echtzeit verfolgt werden, da die reversible und nichtkovalente Bindung augenblicklich auf Konzentrationsanderungen anspricht. Die hier vorgestellte supramolekulare Methode eignet sich fur viele bioanalytische Anwendungen, z. B. fur Enzymassays, die Wirkstoffanalytik und die kontinuierliche Verfolgung enantioselektiver Reaktionen, insbesondere asymmetrischer Katalyse.

Die Effektivitat von Wirkstoffen und Biomolekulen basiert auf ihrer Fahigkeit, die Lipidmembran zu passieren. Die Entwicklung von Methoden, diese Transportprozesse direkt und mit hoher Empfindlichkeit zu verfolgen, bleibt eine Herausforderung. Der Einschluss eines chemosensorischen Ensembles, bestehend aus einem makrocyclischen Wirt (p-Sulfonatocalix[4]aren oder Cucurbit[7]uril) und einem Fluoreszenzfarbstoff (Lucigenin oder Berberin) in Liposomen ermoglicht es, den Membrandurchtritt von unmarkierten bioorganischen Molekulen direkt und in Echtzeit mittels Fluoreszenz zu verfolgen. Dieser In-vitro-Assay kann auf unterschiedliche Kanalproteine und Analyten angewendet werden, eignet sich zur schnellen Charakterisierung von Kanalmodulatoren und liefert zudem die absolute Kinetik der Translokation. Mit dieser neuen biophysikalischen Methode konnten wir erstmalig die direkte schnelle Translokation des antibiotisch wirksamen Peptids Protamin durch das bakterielle Transmembranprotein OmpF nachweisen.

A microcalorimetric study on the inclusion of monovalent and divalent metal cations by p-sulfonatocalix[4]arene was performed. The thermodynamic parameters for the complexation of alkali metal cations and Ag(+) were obtained for the first time at neutral pH. The Na(+) cation is routinely present as counterion of the calixarene in neutral aqueous solution, and this must be taken into account in the determination of the thermodynamic parameters for the complexation of Na(+) and the other cations by considering a sequential or a competitive binding scheme. The ΔH° and ΔS° values show that the inclusion process is entropically driven, although an influence of the temperature on the complexation reaction indicates that the enthalpic term is also an important contributor. The results also reveal that enthalpy/entropy compensation balances the gain in one contribution against a corresponding loss in the other. The obtained thermodynamic data are in contrast to the results from previous microcalorimetric studies, which showed binding constants that were orders of magnitude smaller and complexations, which were in part enthalpically driven but which neglected the influence of the alkali metal counterions.