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Self-assembled monolayers (SAMs) of 2-[(6-mercaptohexyl)oxy]methyl-12-crown-4 (1) and 2-[(6-mercaptohexyl)oxy]methyl-15-crown-5 (2) on gold are able to bind cations reversibly from aqueous solutions. This binding of the electrochemically inactive cations is monitored by cyclic voltammetry and impedance spectroscopy using the redox couple Ru(NH3)62+/3+ as "reporter ion". Gold electrodes modified with 1 detect Na+ even in the presence of a 100-fold excess of K+; SAMs of 2 are K+ selective. As a result of the high surface density of crown ethers, sandwich complexes are formed. Reduced surface concentrations of receptors in mixed monolayers of 2 with heptanethiol prevent the sandwich complexation and decreases the K+/Na+ selectivity of the SAM.

Die hohe Affinitat von Ag+-Ionen fur aromatische π-Donoren und Cyangruppen wird bei einer neuen MALDI-TOF-MS-Methode zur Identifizierung von H-Brucken-Aggregaten genutzt (MALDI-TOF-MS=Matrix-unterstutzte Laser-Desorptions-Ionisierungs-Flugzeit-Massenspektrometrie): Durch das Ag+-Ion, das z. B. sandwichartig von zwei Phenylgruppen komplexiert werden kann (siehe rechts), lassen sich die Aggregate - ohne Zersetzung - mit einer positiven Ladung versehen.

Highly stable films of tetranitrotetrapropoxycalix[4]arene (9) with second-order nonlinear optical (NLO) properties and a noncentrosymmetric structure were obtained by a novel crystallization process at 130-140 degrees C in a de electric field. The packing of 9 in these films was elucidated by a combination of X-ray diffraction, angle-dependent second- harmonic generation, and scanning force microscopy (SFM). The experimental results agree well with solid-state molecular dynamics calculations for these films. No crystalline phase was observed for nitrocalix[4]arene derivatives with longer or branched alkyl chains; this explains the limited NLO stability of films of these calixarenes. Scanning force microscopy o­n the aligned films of 9 showed two distinct surface lattice structures: a rectangular lattice (a = 9.3, b = 11.7 Angstrom) and a pseudohexagonal lattice (d approximate to 11.4 Angstrom). The combination of these data with the interlayer distance of 8.9 Angstrom (X-ray diffraction) allowed the packing of molecules of 9 in these structures to be fully elucidated at the molecular level.

A triclinic modification of triphenylphosphine, C18H15P, is reported. Two of the four unique molecules are in virtually the same conformation and are related by a local inversion centre; the other two molecules each have a different conformation. The structure contains a number of short C-H contacts.

The optical properties of different erbium (Er)-doped polydentate hemispherand organic cage complexes are studied, for use in polymer-based planar optical amplifiers. Room temperature photoluminescence at 1.54 um is observed, due to an intra-4 f transition in Er31. The Er is directly excited into one of the 4 f manifolds (at 488 nm), or indirectly (at 287 nm) via the aromatic part of the cage. The luminescence spectrum is 70 nm wide (full width at half maximum), the highest known for any Er-doped material, enabling high gain bandwidth for optical amplification. The absorption cross section at 1.54 um is 1.1x10 -20 cm2, higher than in most other Er-doped materials, which allows the attainment of high gain. Measurements were performed on complexes in KBr tablets, in which the complex is present in the form of small crystallites, or dissolved in the organic solvents dimethylformamide and butanol-OD. In KBr the luminescence lifetime at 1.54 um is

Three new metallohosts (2-4) were synthesized by the uranyl-templated macrocyclization of the appropriate dialdehydes 13a-c and 1,2-phenylenediamine in methanol. Cyclization of the dialdehyde 13b led to two isomers (3a, major, and 3b, minor), which only differed in the orientation of the isopropyl substituents on the outer phenolic rings of the terphenyl moiety. The binding constants in CDCl3 of ammonia and benzylamine were determined by 1H NMR spectroscopy. The binding of ammonia by these hosts follows 1 = 2 = 4 < 3b < 3a. The binding of benzylamine follows 1 = 2 = 4 = < 3b < 3a. Monte Carlo free-energy perturbation calculations reproduced the binding of ammonia and n-propylamine quite well. The much larger binding of benzylamine by host 3a was rationalized by a much deeper positioning of the guest in the cavity of the host compared to 3b.

Binding of halide has been studied for two thioureido-substituted resorcin[4]arenes and a model compound, with special attention to the NH stretching region and the bonding behaviour. Mathematical techniques such as curve fitting, Fourier self-deconvolution and Partial Least Squares analysis have been applied to investigate the characteristics of bonding, and the results are correlated with information obtained from a steric analysis.It is shown that association of the halide guest takes place via hydrogen bonding between halide ions and thioureido moieties solely for all ligands. Compared to a simple thiourea compound, pre-organisation of the thioureide side-chains on the upper rim by intramolecular bonding enhances the capability of association by a factor of 10 to 100.An analogy is found between complexation of a halide anion in the cavitands and complexation of an iodide anion by the model compound. This suggests that within the cavitand, chloride, bromide and iodide are all complexed by at least two thioureido moieties, whereas a simple thiourea binds chloride and bromide in a 1-to-1 fashion, and iodide in a 2-to-1 fashion.

A new method applying infrared spectroscopy in combination with multivariate regression for the determination of association constants has been developed to overcome the sensitivity problems arising when strongly associating complexes are investigated by NMR or UV–VIS methods. A concentration profile for the complex is derived by correction of multivariate regression data. Subsequent iterative fitting of the corrected data yields the association constant.The regression part is not integrated in the process of the association constant determination itself. Separating data treatment from the actual fitting procedure offers a means of evaluating the quality of the data set and the order of association before the actual calculation of the association constant. Furthermore, the method of regression can be varied and the applicability of the selected method can be assessed from the data-regression output.From simulated data, it is estimated that an association constant range of 102–106M–1 can be determined when measuring at millimolar concentration levels.Examples are shown for halide complexation of a thiourea compound and a urea-substituted resorcinarene cavitand.

Three sugar-integrated gelators bearing a p-nitrophenyl group as a chromophore were synthesised. D-Mannose-based compound 3 was too soluble in most organic solvents to act as a gelator whereas D-galactose-based compound 2 was sparingly soluble in most organic solvents. D-Glucose-based compound 1 was moderately soluble and acted as an excellent gelator, gelating 10 solvents tested. The possible correlation between the gelation ability and the gelator structure is discussed on the basis of the intermolecular hydrogen-bonding interactions detectable by FT-IR spectroscopy. CD spectral measurements showed that the p-nitrophenyl groups in the gel fibrils of 1 are stacked in the clockwise direction [i.e., with (R)-helicity]. SEM observation of the xerogels showed that in most cases the gelator forms a three-dimensional network with 30–100 nm frizzled fibrils. Only when they were prepared from the methylcyclohexane solution, was the helical structure (although in part) observed.

13C CP/MAS spectroscopy of calix[4]arene-based carceplexes shows that in the solid state the cavity walls of the carcerand are rigid, whereas the pendant groups of the resorcin[4]arene as well as the ends of the propyl goups of the calix[4]arene moiety exhibit some flexibility. Temperature dependent 2H measurements of the DMSO-d6 carceplex reveal that two different sites are present for the DMSO guest with an energy difference of 1.7 kcal mol-1.

Different siloxane copolymers have been used as membrane materials for Ca2+ selective chemically modified field effect transistors (CHEMFETs). CHEMFETs with 3-benzoylaminopropyl-functionalized polysiloxane membranes and 1 wt% borate anions are intrinsically selective for Ca2+ ions. This selectivity can be further enhanced by the incorporation of a Ca2+ selective 1,3 alternate calix[4]arene which is functionalized with four amido groups. The highest Ca2+ selectivties were obtained with CHEMFETs containing this calix[4]arene ionophore in 3-cyanopropyl-functionalized polysiloxane membranes.

Partially functionalized cavitands (7a–d) have been synthesized starting from the tetrakis(bromomethyl)cavitand 6. New cavitand‐based cation ligands, with one to three carbamoylmethylphosphane oxide (CMPO) moieties (11a–d), were prepared in good (66–90%) yields. The ligands 11a–d extract EuIII, but do so less effectively than the tetra‐CMPO cavitand 1. The decreasing number of CMPO groups which result in decreasing extraction percentages for EuIII, also decrease the selectivity of EuIII over that of FeIII, SrII, and UO2II. There is a difference in extraction behavior, determined by radio‐tracer experiments, between the distal and proximal disubstituted ligands, 11b and 11c, respectively. The extraction constants for the 1:1 complex of 11b and 11c with Eu(picrate)3 are Kex = 6.7 · 108 M−4 and 3.7 · 109 M−4, respectively.

The synthesis of 11 calix[4]arene‐based carceplexes obtained by solvent or doped inclusion is reported. Carceplexes with amides, for example, DMF, NMP, and 1,5‐dimethyl‐2‐pyrrolidinone, and sulfoxides, for example, DMSO and thiolane‐1‐oxide, were obtained by solvent inclusion. In these cases the yield of the carceplex decreases with increasing guest size. Potential guests that do not form carceplexes by solvent inclusion, such as 2‐butanone and 3‐sulfolene, could be incarcerated by doped inclusion with 1,5‐dimethyl‐2‐pyrrolidinone as a solvent “doped” with 5–15 vol% of potential guest. The amide bridges of the carceplexes were converted into thioamide bridges in essentially quantitative yield by means of Lawesson's reagent in refluxing xylene. The dynamic properties of the incarcerated guests were examined by 2D NMR spectroscopy. Whereas for most guests a preference for one orientation inside the calix[4]arene‐based (thia)carcerands was observed, for DMA, NMP, and ethyl methyl sulfoxide inside calix[4]arene‐based (thia)carcerands two different orientations were present. The energy barriers for interconversion between the various orientations of DMA, NMP, and ethyl methyl sulfoxide inside calix[4]arene‐based (thia)‐carcerands were determined with 2D EXSY NMR. The energy barriers are higher for the thiacarcerands than for the corresponding carcerands with amide bridges. This may be due to the stronger hydrogen‐bond‐donating character of the thioamide group. Furthermore, molecular modeling simulations indicate that in case of the thiacarcerand the cavity is smaller as a result of a smaller diametrical distance between the NH atoms. Our results demonstrate that molecular modeling can be used to estimate the energy barriers for interconversion; the calculated activation energies showed good quantitative agreement with the experimental values.

Combination of calix[4]arenes functionalized at the upper rim at the 5- and 17-positions with amino and formyl groups, respectively, gives a new series of "head-to-head" linked double calix[4]arenes in nearly quantitative yield. The X-ray structure of a modified double calix[4]arene is reported. The novel, highly preorganized receptor molecules complex silver(I) ions (K(ass) = 9.5 x 10(5) M(-)(1) in CDCl(3)); the selectivity of complexation was studied by supported liquid membrane transport experiments and chemically modified field effect transistor measurements.

New methods to obtain 1,2-bridged calix[4]arene-biscrowns in the 1,2-alternate conformation are described. The stereochemistry of the proximal double functionalization reaction is mainly governed by the solvent, the length of the polyether units and the base used to deprotonate the calix[4]arene.

The structure and orientation of calix[4]resorcinarene receptor adsorbate self-assembled monolayers (SAMs) on Au(111) were studied with atomic force microscopy (AFM). In molecularly-resolved images, two hexagonal periodicities with lattice constants of 11.6 ± 0.4 and 4.2 ± 0.2 A, respectively, were observed. These two periodicities could be observed separately as well as simultaneously by changing the imaging force. The experimentally determined distances are assigned to different parts of the adsorbates; the 11.6 A repeat distance is related to the lattice of the calix[4]resorcinarene recognition sites of the adsorbates, while the smaller repeat length fits well with the interchain distance of a closest packing of alkyl chains. These measurements confirm our previous assumption regarding the high degree of order of the calix[4]resorcinarene SAMs on gold.

A new type of soluble calix[4]arene-based polyimides was prepared by reaction of bis(3-aminopropyl) dipropyl functionalized tetranitrocalix[4]arenes with hexafluoroisopropylidene diphthalic anhydride. Spin-coating of these polymers and subsequent electric field poling results in films that are highly transparent above 410 nm and exhibit high and thermally stable second harmonic generation coefficients. These properties make these materials very suitable Ear frequency-doubling applications in the UV region (820-410 nm).

Calix[4]arenes diametrically substituted at the upper rim with two melamine units spontaneously form well-defined box-like assemblies in the presence of two equivalents of 5,5-diethylbarbituric acid. These assemblies, consisting of nine different components, are held together by 36 hydrogen bonds and are stable in apolar solvents at concentrations of up to 10-4M. This paper reports the first X-ray crystal structure, and the MALDI TOF mass spectra together with the complete 1H NMR spectroscopic characterization of these hydrogen-bonded assemblies. The crystal structure clearly shows that the assemblies are stereogenic, as a result of the antiparallel orientation of the two rosette motifs. Furthermore, the synthesis of twelve new 1,3-bis(melamine)calix[4]arenes carrying different numbers and types of functionalities at the upper rim is described. Detailed 1H NMR spectroscopic studies on the assembly behavior of these functionalized calix[4]arenes shows that 1) polar substituents (e.g. nitro, cyano) hardly affect the stability of the hydrogen-bonded assembly; 2) hydrogen bond donating or accepting groups, like amino and acetamido, can disturb assembly of the boxes under certain conditions by destabilizing the calix[4]arene pinched cone conformation as a result of intramolecular hydrogen bond formation; and 3) sterically bulky groups (e.g. tBu) can significantly inhibit the formation of the hydrogen-bonded assembly, but this effect very much depends on the exact positions of the groups.

new class of anion selective receptors is based on the neutral uranylsalophene building block as Lewis acidic binding site. Additional hydrogen bond accepting or donating moieties near the anion binding site offer the possibility of varying the binding selectivity. Field effect transistors chemically modified with such receptors exhibit anion selectivities that strongly deviate from the classical Hofmeister series favoring phosphate or fluoride anions, depending on the structure of the uranylsalophenes. The phosphate selective chemically modified field effect transistors (CHEMFETs) detect phosphate with high selectivity over much more lipophilic anions, such as nitrate (log = −1.3), at [H2PO4-] ≥ 6.3 × 10-4 M. CHEMFETs modified with salophenes with amido substituents result in a high fluoride selectivity; even in the presence of 0.1 M chloride, fluoride can be detected at [F-] ≥ 6 × 10-4 M (log = −2.0).

Two novel m-terphenyl-based organic ligands (2 and 3) have been synthesized. Photophysical studies show that the ligands form stable complexes with Eu3+, since typical Eu3+ luminescence is observed upon excitation of the ligand. The acyclic complex 2·Eu3+ shows relatively long lifetimes in methanol (e.g. = 0.72 ms in CH3OH). The acylic ligand 2 allows the additional coordination of two solvent molecules and their high-energy vibrational modes form the main quenching pathway for the Eu3+ luminescence. In comparison with 1·Eu3+, the more rigid dioxolane-containing complex 3·Eu3+ provides an additional donor atom, which reduces the solvent coordination of 3·Eu3+ (3·Eu3+ = 1.42 ms compared to 1·Eu3+ = 0.75 ms in CH3OH). The high-energy vibrational modes of the organic ligand 3 are the most important quenchers. Typical near-infrared Nd3+ emission at 1060 and 1350 nm resulting from 3·Nd3+ has been observed. Quenching by the solvent is still operative for 3·Nd3+, because of the larger ionic radius of the Nd3+ ion.

Aminocalix[4]arenes 7-12 react with triphosgene and thiophosgene to the corresponding iso(thio)cyanate-functionalized calix[4]arenes 13-20. Carbamate- (21-25) and ureasubstituted calix[4]arenes (26,27) can be obtained via isocyanatocalix[4]arenes using a one-pot synthesis starting from the corresponding aminocalix[4]arenes in moderate to good yields. Isothiocyanate-functionalized calix[4]arenes 16, 18 react selectively with amines to the corresponding thioureas 28-31 in 59-83% yield. Reaction of isothiocyanate-functionalized calix[4]arenes 16, 19, 20 with cavitands 34, 38 gives 2:2 products 42-45 in 35-42% yield.

The synthesis, characterization, and membrane-transport properties of a series of benzo-15-crown-5- andp-tert-butylcalix[4]arene-substituted polysiloxanes are described. Receptor-functionalized poly(dimethylsiloxane)s, randomly substituted with up to 37 mol % calix[4]arene or benzo-15-crown-5 moieties, were prepared by polymer-analogous hydrosilylation of the corresponding ω-alkenyl-substituted receptor molecules with poly(dimethylsiloxane-co-methylhydrosiloxane) copolymers of different compositions. It was attempted to increase the degree of substitution of these copolymers to such an extent that the receptor moieties no longer form isolated clusters in the bulk but associate into closely packed percolating arrays. In this way, ion transport through supported polymeric membranes containing these polymers no longer would take place by diffusion of host-guest complexes, but by hopping of the ions from one polymer-bound receptor side to another. First insight into these phenomena could be obtained from differential scanning calorimetry and transport experiments. The investigated polymeric membranes were prepared by gel crystallization of a xylene solution containing the functionalized polysiloxane and UHMW PE in a 1:1 ratio.

Quenching of the luminescent excited state of Eu3+ ions by C-H high-vibrational modes was studied by deuteration of the encapsulating ligand and the solvent. Novel polydentate hemispherands providing nine donor atoms, which form overall neutral complexes with rare earth ions, were synthesized in nine steps, allowing the easy incorporation of deuterium atoms (11a-d·Eu3+). The introduction of tert-butyl groups at the aromatic rings of the ligand further increased the solubility of the complexes in organic solvents (29·Eu3+ and 34·Eu3+). Photophysical studies, viz., luminescence spectra and lifetime measurements, revealed that significant quenching of the Eu3+ excited state is induced by nearby C-H vibrational modes. Substitution of these quenching C-H modes for C-D bonds in the azacrown bridge leads to an enhancement of the luminescent lifetime by a factor of 1.5. C-H high-vibrational modes of the pendant arms which are at a larger distance to the Eu3+ ion than the azacrown bridge hydrogen atoms (determined from the MD calculations) are less efficient quenchers. The number of coordinating methanol molecules to 11a·Eu3+, 29·Eu3+, and 34·Eu3+ estimated by the "Horrocks equation" is 0.9, 1.2, and 1.9, respectively, as was predicted by MD calculations. Moreover, the experimental data show that quenching of the excited state of well-shielded Eu3+ ions by the C-H modes of the ligand is of the same order of magnitude as quenching by one O-H mode.

Tetrafunctionalized resorcinarene cavitands (4-6) have been synthesized starting from tetrakis(bromomethyl)cavitand 3. New cavitand-based cation ligands with (carbamoylmethyl)phosphonate (CMP) and -phosphine oxide (CMPO) moieties (8a,b and 9a,b) were prepared via two different routes in good (45-86%) overall yields. The ligands (8a,b and 9b) are very effective europium extractants. Ph(2)CMPON(Pr)-cavitand 8b has the highest extraction constant, determined with radiotracer experiments, for 1:1 complexation with Eu(picrate)(3) (K(ex)(1) = 2.7 x 10(12) M(-)(4)). The steric preorganization of the four CMP(O) moieties on the resorcinarene cavitand improves the efficiency and selectivity [of Eu(III) over UO(2)(II) and Fe(III)] of the metal extraction processes, compared to simple CMP(O) extractants.

In this contribution, optically active and paramagnetic micelles of the ligand 1,4,7,10-tetraaza-1-(1-carboxymethylundecane)-4,7,10-triacetic acid cyclododecane (DOTAC10) have been incorporated inside capsids of the cowpea chlorotic mottle virus (CCMV) protein through a hierarchical process of self-assembly triggered by self-assembly. The DOTAC10 ligand was used to complex Gd-III , in order to form paramagnetic micelles, as well as to encapsulate an amphiphilic Zn-II phthalocyanine (ZnPc) dye that optically confirmed the encapsulation of the micelles. The incorporation of ZnPc molecules in the paramagnetic micelles led to high capsid loading of both Gd-III and ZnPc, as the micelles were stabilized by the amphiphilic dye encapsulation. The resulting protein cage nanoparticles (PCNs) show an improved r(1) relaxivity, suggesting the possible use of these nanostructures as contrast agents (CAs) for magnetic resonance imaging (MRI). Since the encapsulated ZnPc dye also has a potential therapeutic value, the present results represent a first step towards the consecution of fully selfassembled PCNs for multimodal imaging and therapy. (C) 2014 Elsevier Inc. All rights reserved.

Polysiloxane copolymers with different amounts and types of substituents have been synthesized and characterized. Polar substituents determine the polarity and methacrylate groups allow cross-linking and covalent binding of electroactive species. These chemically well-defined homogeneous polymers have been applied as ion-selective membrane material in nitrate-selective field effect transistors (CHEMFETs). The selectivity of the CHEMFETs is influenced by the nature of the polar substituents in the polymer. The incorporation of methacrylate moieties in the polysiloxane allows covalent attachment of quaternary ammonium sites to the membrane matrix and this enlarges the durability of the sensor.

A new method for the selective functionalization of resorcinarene cavitands is described starting from tetrakis(bromomethyl)cavitands.

First the cation, then the anion. This describes the complexation of alkali metal halides with bifunctional receptors like that on the right (R = n‐octyl) based on calix[4]arenes. The uncomplexed ligand has a strong intramolecular hydrogen bond between the urea moieties, which is disrupted by the conformational change induced by complexation of a Na+ ion. Only then is an anion like Cl− bound in the upper portion of the calixarene.

Als molekulare Plattformen und als Abstandshalter lassen sich melaminhaltige Calix[4]arene in Reaktionen mit Barbitur- sowie Cyanursäurederivaten verwenden, die zur Bildung großer Kästen führen (schematisch im Bild rechts gezeigt). Die Verbindungen wurden über 2D-NOESY-Experimente charakterisiert, die Auskunft über intramolekulare H-H-Abstände und über Kreuzrelaxationsgeschwindigkeiten geben.

New 25,27-dialkoxycalix-[4]arenecrown-5 conformers 8, 10, and 11 have been synthesized and studied. The compounds 8a and 8b, fixed in 1,3-alternate structure, have been obtained in 57 and 40% yield, respectively, by reaction of the corresponding 25,27-dialkoxycalix[4]arenes 7a-b with tetraethylene glycol di-p-toluenesulfonate in the presence of Cs2CO3. The cone 10a and 10b and the partial cone 11 conformers were obtained by selective demethylation of the 25,27-dimethoxycalix[4]arenecrown-5 (6a) and subsequent dialkylation with NaH/DMF and KOtBu/THF, respectively. In the solid state (X-ray), compound 6a adopts a flattened cone conformation, which is also found to be most abundant in CD3CN and CD3OD solution. Upon complexation with potassium picrate compound 6a was converted quantitatively into the 1,3-alternate conformation. All new ligands synthesized were used in the extraction of alkali metal cations from H2O into CHCl3, and as active components in supported liquid membranes and in chemically modified field effect transistors. Results were compared to those obtained with with the natural antibiotic valinomycin 1. All ligands showed high selectivity for potassium. Ligand 8a, fixed in the 1,3-alternate conformation, is more selective than valinomycin and shows the highest K+/Na+ selectivity known so far.

The calix[4]arene skeleton serves both as a spacer and as a molecular platform for preorganization in molecular boxes such as 1 constructed from calixarene‐based melamine and isocynanuric acid derivatives, which self‐assemble in double‐rosette structures (shown schematically on the right). These ensembles were characterized by 2D NOESY experiments, which provide information on intramolecular H-H distances and cross relaxation rates.

The Rebek self-replication reaction of 1 and 2, catalyzed by complexation of both reactants to the resulting product 3 (Tjivikua, T.; et al. J. Am. Chem. Soc. 1990, 112, 1249-1250. Nowick, J. S.; et al. J. Am. Chem. Soc. 1991, 113, 8831-8839. Wintner, E. A.; et al. Acc. Chem. Res. 1994, 27, 198-203. Conn, M. M.; et al. J. Am. Chem. Soc. 1994, 116, 8823-8824), and related work of Menger et al. (Menger, F. M.; et al. J. Am. Chem. Soc. 1994, 116, 3613-3614. Menger, F. M.; et al. J. Org. Chem. 1995, 60, 2870-2878) have been reinvestigated. On the basis of our experiments with the same systems and comparing the absolute rates of different (model) reactions, we have identified five pathways of the reaction between 1 and 2 in the presence of template 3: background (k1 = 0.035 M-1 min-1 ), preassociative (k2 = 0.0044 min-1), termolecular (k3 = 0.030 min-1), and two bimolecular (k4 = 0.130 M-1 min-1, k5 = 0.020 M-1 min-1). A general kinetic model for self-replicating reactions has been used to analyze the Rebek-Menger controversy. We conclude that self-replication as defined by Rebek et al. operates in this system; other pathways obscure the simple picture of a ternary complex as the only complex that leads to the rate enhancement and one of those (bimolecular) pathways is that proposed by Menger et al. Our results show that when 1 and 2 are complexed to 3 in a termolecular complex, the rate of reaction between 1 and 2 is 6.8 times (k3/k2) faster than when 3 is formed from the bimolecular complex of 1 and 2, and this rate enhancement factor represents the efficiency of template 3 in the self-replication process.

An assembly of cation receptor 1 and anion receptor 2 via the hydrogen bonding melamine-barbiturate structural motif complexes sodium thiocyanate, sodium iodide, and sodium azide in apolar solvents.

The overall dynamics of partially phosphorylated and thiophosphorylated p-tert-butylcalix[6]arenes has been studied by NMR spectroscopy. When p-tert-butylcalix[6]arene is monosubstituted with a phosphate or thiophosphate group, the calix[6]arene skeleton is remarkably rigidified. The 1,3- and 1,4-(thio)phosphorylated p-tert-butylcalix[6]arenes are more flexible. 2D NMR spectroscopy showed that these calix[6]arenes adopt syn conformations. A combination of 1H and 31P NMR spectroscopy revealed that the calix[6]arene (thio)phosphates are involved in at least three dynamic processes, viz., macrocyclic ring interconversion, hydrogen bond array reversal, and pinched conformer interconversion. The activation barrier (ΔGm⧧) for macrocyclic ring interconversion depends on the type and number of substituents and ranges from 67 to 86 kJ·mol-1. The activation barrier (ΔGh⧧) for hydrogen bond array reversal depends on the number of hydroxyl groups and ranges from 31 to 45 kJ·mol-1. For the pinched conformer interconversion an activation barrier (ΔGp⧧) ranging from 44 to 55 kJ·mol-1 was found. Pinched conformations have been frequently observed in the solid state, for example, for mono- and 1,4-bis(thiophosphorylated) p-tert-butylcalix[6]arene. These studies, however, show for the first time that these conformations also exist in solution and that differently pinched conformers may rapidly interconvert.

A series of crown boronic acids, 1-4, were synthesized and studied as carriers for catecholamine transport through bulk liquid membranes (BLMs) and supported liquid membranes (SLMs). Carrier 1 greatly facilitated the transport of primary catecholamines through BLMs; whereas, the more lipophilic analogues 3 and 4 were less effective. A combination of kinetic, mass spectral, and NMR evidence suggests that the transported species in BLMs is the cyclic, zwitterionic, 1:1 complex 7. The SLM transport studies used a liquid membrane of 2-nitrophenyl octyl ether supported by a thin, flat sheet of porous polypropylene. In the absence of carrier there was neglible dopamine transport ( epinephrine (1.5 × 10-7 mol/m2·s) > norepinephrine (0.8 × 10-7 mol/m2·s). SLMs containing carrier 3 were stable, implying that carrier 3 is a very good candidate for transport mechanism studies. Crown boronic acid 4 was an even better transport carrier of primary catecholamines with a transport order of norepinephrine (4.7 × 10-6 mol/m2·s) > dopamine (3.5 × 10-6 mol/m2·s) epinephrine (3 × 10-8 mol/m2·s). It is 10 times more effective than an equimolar mixture of boronic acid 5 and crown 6, which is one of best examples of ditopic cooperativity yet observed in SLM transport. SLMs containing 4, however, did not exibit long-term stability. Overall, it is possible that a device based on SLMs containing crown boronic acid carriers can be developed to selectively extract catecholamines from clinical samples.

Calix[4]arenes at the upper rim substituted with two (thio)urea moieties, 2a−c and 4, or substituted with two acetamido groups, 5, adopt a pinched cone conformation in CDCl3 solution. The pinched c...

Competition with a monovalent cyclodextrin host (blue cones) in solution drives the multivalent binding of a Eu(3+) complex and a sensitizer molecule to cyclodextrin monolayers through a nonlinear self-assembly process. Adamantyl groups (light-blue spheres) are attached to the EDTA ligand (black) and the antenna molecule (orange), which has a carboxylate group for coordination to the Eu(3+) ion (yellow or red in free or complexed form, respectively).

The synthesis of a new type of host adsorbate possessing a large resorcin[4]arene headgroup and four di-n-decyl sulfide chains underneath is described. The cross-sectional area of the alkyl chains is equal or larger than that of the headgroups which makes these resorcin[4]arene tetrasulfides suitable for self-assembly onto gold surfaces to form well-packed monolayers of which the outer interface is composed of receptor sites and the alkyl chains underneath the cavity headgroups passivate the gold surface. Resorcin[4]arene tetrasulfides with the following functionalities at the resorcin[4]arene headgroup were synthesized: methylene ether (the so-called cavitand), methyl ether, 2-fluoroethyl, several carboxyl esters, N-propylacetamide and hydroxy. New receptor adsorbates for self-assembling monolayers are described.

Calix[4]arene-crown-6 derivatives (1–3) in the 1,3-alternate conformation, incorporated in poly(vinylchloride) membranes of CHEMFETs, exhibit good Cs+-selectivity and Nernstian behaviour. The Cs+-selectivity over Na+, i.e., log KpotCs,Na = −3.3, is slightly better than observed for bis(18-crown-6) derivatives (log KpotCs,Na = −3.0). The CHEMFETs respond sub-Nernstian in the presence of NH+4 and K+. Model calculations show that this can be explained by the small difference between the stability constants of the Cs+− and K+-complexes and by the high partition coefficient of NH+4 in favour of the membrane phase, respectively.

The crystal and molecular structures of the 1,3-diisopropoxy-p-tertbutyl calix[4]arene crown-5 fixed in the partial cone conformation and that of its potassium picrate salt have been determined by single crystal X-ray diffraction studies. Energy calculations have been performed to gain more insight on the stabilizing cation…ligand interactions. The calculation of the total potential energy indicates that the contribution which comes from the electrostatic polarization induced by the electric field of the cation on the rotated nucleus gives a net stabilizing contribution of almost 6 kcal/mol. A comparison between the molecular geometry of some partial cone 1,3-disubstituted-p-tertbutylcalix[4]arene derivatives is reported and discussed in view of the preorganization principle.

The design of durable chemical sensors based on field-effect transistors (FETs) is described. After modification of an ion-sensitive FET (ISFET) with a polysiloxane membrane matrix, it is possible to attach all electroactive components covalently. Preliminary results of measurements with a sodium-selective CHEMFET have shown that the durability is improved by the covalent attachment of the electroactive components ( > 90 days).

Ethynylphenyl-methyldichlorosilane (EPDMS) has been prepared as a new monomer for the synthesis of polysilylenes with triple bonds attached to the catenated Si chain. A series of copolymers with methylphenyldichlorosilane (MPDS) as well as the homopolymer, PEPMS, have been synthesized. The content of ethynylphenyl substituents was quantitatively analyzed by FTIR spectroscopy. The optical properties of the new polymers were studied with respect to potential - interaction. No significant bathochromic shift of the UV-absorption maximum could be detected. Unexpectedly, increasing content of incorporated EPMS units led to a decrease of the (-*) absorption. The ethynylphenyl-substituted polysilylenes exhibited strong, temperature-dependent fluorescence in solution as well as in films.

We have studied the application of self-assembled resorcin[4]arene monolayers as chemically sensitive coating of quartz microalance sensors. Resorcin[4]arenes are typical supramolecular compounds with a molecular cavity formed by an aromatic ring system. The latter provides lipophilic binding sites and acts therefore as a molecular recognition structure for organic molecules. Reosrcinarenes are of particular interest for the selective detection of organic molecules in the gas and liquid phase. A high level of molecular order can be achieved by using modified cage compounds: dialkylsulfide-substituted resorcin[4]arene derivatives (with 4 aromatic rings) form well-ordered monolayers at Au surfaces by a self-assembling process which occurs spontaneously in ethanol/chloroform solutions of thes resorcin[4]arene derivatives. The driving force is the formation of very stable AuS bonds and the van der Waals interaction between the alkyl chains. We present results on the structure of resorcin[4]arene monolayers and their interactions with organic molecules. These results were obtained from angle-resolved X-ray photoelectron spectroscopy (AR-XPS) and thermal desorption spectroscopy (TDS). The latter techniques makes it possible to determine binding energies of the molecule/resorcin[4]arene ‘key-lock’ interaction. The binding energies are then compared with mass changes Δm which are obtained from quartz microbalance oscillators with their Au electrodes coated with resorcin[4]arene monolayers. We tested different organic molecules in the gas and liquid phase such as tetrachloroethane (C2Cl4), Trichloroethylene (HClCCCl2), tetrachloromethane (CCl4), chloroform (CHCl3) and toluene (H3C-C6H5). By far the most pronounced sensor response and hence highest selectivity was observed to tetrachloroethene (C2Cl4).

Dialkylsulfide substituted calix[4]arenes were synthesized and adsorbed onto gold substrates. Infrared spectroscopy, thickness, and wettability studies revealed that well-ordered monolayers were formed.

Combination of upper-rim-1,3-difunctionalized calix[4]arenes 14, 16, and 18 with tribridged resorcinarenes 4 and 6 and A,C-di-bridged resorcinarenes 10 and 13 yields both 1/1 calix-resorcinarenes (22–24) and 2/1 calix-resorcinarenes (25, 26). 1/1 Calix-resorcinarene 22 mainly exists as one conformer (a), but at low temperatures (−60°C) very small amounts ( < 5%) of a second conformer (b) can be observed. Both conformers equilibrate via rotation about one of the C(arene)-N bonds, with an activation free energy (Δ G≠) of 13 kcal/mol. 2/1 Calix-resorcinarenes 25 and 26 are more flexible and exist as a mixture of conformers. In order to be able to rigidify the structure of 2/1 calix-resorcinarenes via rigid spacers between the calix[4]arene fragments, 1,3-diaminocalix[4]arene derivatives 31, 32, and 34 were synthesized carrying nitro, carboxylic ester, and cyano groups at the unsubstituted aromatic rings. With these calix[4]arene derivatives, three new, functionalized 2/1 calix-resorcinarenes 35–37 have been synthesized.

The interaction of optically labeled saccharides with resorcin[4]arenes as synthetic saccharide receptors has been investigated by determination of the partition of the saccharides over an aqueous and 1-octanol phase in the absence and presence of the synthetic receptor. It is shown that the complexation of merocyanine labeled glucose, galactose and ribose with the resorcin[4]arenes can be optically detected and that the chosen receptors have a modest selectivity towards the labeled glucose.

Chemical reduction of mitosenes under aerobic conditions in DMSO showed characteristic ESR signals of the mitosene derived semiquinone free radicals. However, these signals diminished strongly upon addition of water to the reaction mixture, indicating a short lifetime of the mitosene semiquinone free radicals under aqueous conditions. In addition, enzymatic one-electron reduction of these mitosenes with either xanthine oxidase or purified NADPH cytochrome P450 reductase under anaerobic conditions showed no signals of the mitosene semiquinone free radicals. Subsequent cyclic voltammetry measurements demonstrated facilitation of the further one-electron reduction of the mitosene semiquinone free radicals in the presence of water in comparison with non-aqueous conditions. The present results strongly suggest that in the presence of water relatively stable hydroquinones are formed upon reduction of mitosenes. Consequently, the steady state concentrations of mitosene semiquinone free radicals will be lowered substantially in aqueous environment. Thus under physiological conditions, two-electron reduction and formation of the mitosene hydroquinone might be important in processes leading to DNA alkylation by these mitosenes. © 1995 Informa UK Ltd All rights reserved: reproduction in whole or part not permitted.

One of the problems preventing the widespread commercialization of ISFETs is the lack of reliable packaging. The most important parameter in the packaging is the interface adhesion between the encapsulant and the chip. This interface is characterized by two independent types of measurements. Long-term C-V measurements are used to check the water penetration along the interface. CO2 and NH3 response measurements are used to show the existence of condensed water at the interface. It is shown that the use of a suitable coupling agent improves the adhesion. However, vacuoles at the interface can still be formed and these can cause a breakdown of the packaging. The use of thicker layers of encapsulant will only postpone this breakdown.