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Aim. To study the effect of 5,11,17,23-tetrakis(diisopropoxyphosphonyl)-25,26,27,28-tetrapropoxycalix[4]arene and oсtаkis(diethoxyphosphoryloxy)-tert-butylcalix[8]аrene additives to the MeCN – H2O mobile phase (86:14) on the selectivity of the separation of aromatic compounds by the reversed-phase high performance liquid chromatography (RP HPLC) using a Separon SGX C18 support.Results and discussion. The process of complexation of phosphorylated calix[4,8]arenes with benzene derivatives in the mobile phase plays a key role in the RP HPLC separation of analytes. The stability constants of the inclusion complexes and the chromatographic separation coefficients of the analytes depend on the nature of the aromatic compounds and the cavity size of the calixarene macrocycle.Experimental part. The HPLC analysis was performed in acetonitrile – water (86:14) solution using a Separon SGX C18 column. The stability constants of the calixarene complexes were determined using the dependence of 1/k’ chromatographic parameters of benzene derivatives on the calixarene concentration in the mobile phase. Molecular modelling of the calixarene complexes was carried out using a Hyper Chem 8.0 program.Conclusions. The phosphorus-contained calixarenes due to their ability to form supramolecular complexes with aromatic molecules can be used as additives to the RP HPLC mobile phase and improve separation of benzene derivatives.Received: 14.05.2020Revised: 24.06.2020Accepted: 27.08.2020

We describe a synthetic method for the synthesis of merocyanine dyes containing a bridge with three conjugated double bonds. This method consists of two successive condensation reactions. The first one is made between CH-acidic indane-1,3-dione acceptor units and an appropriate ketone (here acetone or hexan-2-one). The extended acceptor thus obtained is condensed with an aldehyde in the next step. The dyes show high tinctorial strength due to intense absorption bands at wavelengths between 500 and 750 nm.

A series of 1-mono- and 1,7-disubstituted perylene bisimides (PBIs) with voluminous phenoxy groups at bay positions has been synthesized. These dyes show absorption and emission properties typical for PBIs in solution with high fluorescence quantum yields close to unity. In the solid state, the voluminous substituents at bay positions effectively wrap the dye core and prevent π–π interactions between twofold substituted chromophores. The comparison of UV–vis absorption and fluorescence properties for solutions as well as solid-state thin films, powders, and microcrystals in combination with the respective single-crystal structures allows for establishing the packing structure–optical property relationships. According to this analysis, only with two bulky 2,4,6-tris­(4-tert-butylphenyl)-phenoxy or 2,4,6-tris­(3,5-di-tert-butylphenyl)-phenoxy substituents functionalized PBI chromophores are completely jacketed to afford efficient solid-state emitter materials with fluorescence quantum yields of over 60%. A comparative evaluation of PBIs bearing bulky substituents at imide positions reveals significantly higher solid-state fluorescence quantum yields of the 1,7-substituted PBIs.

1,1′-Binaphthol (BINOL) is a versatile chiral reagent with widespread applications in asymmetric catalysis and fluorescent bio-sensing and imaging. However, unsubstituted BINOLs exhibit only weak and short-wavelength emission, limiting their scope for the latter applications. Herein, we report axially chiral 1,1′-bi(2-naphthol-4,5-dicarboximide)s which show two reversible reductions, bright blue light fluorescence with fluorescence quantum yields up to 0.67, and aggregation-enhanced emission characteristics. Single crystal X-ray analysis revealed an intriguing double helical supramolecular polymer motif formed by π–π stacking interactions between 2-naphthol-4,5-dicarboximide units. The enantiomers of racemic 1,1′-bi(2-naphthol-4,5-dicarboximide)s were resolved on chiral columns and studied by CD spectroscopy.

Two novel unnatural amino acids, prepared by linking a dicationic purple-coloured and fluorescent naphthalene diimide (NDI) at core position to amino acid side chains of variable length, strongly interacted with ds-DNA/RNA by threading intercalation. Different from a reference NDI dye with identical visible range absorbance (520–540 nm) and Stokes shifts in emission (+60 nm, quantum yield > 0.2), only these amino acid–NDI conjugates showed selective fluorimetric response for GC-DNA in respect to AT(U)-polynucleotides. The DNA/RNA binding-induced circular dichroism (ICD) response of NDI at 450–550 nm strongly depended on the length and rigidity of the linker to the amino acid unit, which controls the orientation of the NDI unit inside within the intercalative binding site. The ICD selectivity also depends on the type of polynucleotide, thus the studied NDI dyes act as dual fluorimetric/ICD probes for sensing the difference between here used GC-DNA, AT-DNA and AU-RNA.

Using results of X-ray diffraction study supramolecular architecture of crystals of 2-(4-iodophenyl)-1,10-phenanthroline has been analyzed on the basis of quantum-chemical calculations of intermolecular interactions energy. It is demonstrated that these crystals have three levels of organization. Molecules form stacked dimers with the highest binding energy (first level). These dimers represent basic unit of infinite columns stabilized by stacking interactions between dimers (second level). The energy of intermolecular interactions between neighbouring stacked columns is very close. This does not allow to figure out any layers in the crystal. Therefore crystals of this compound have columnar structure with almost isotropic packing of stacked columns (third level).

The concept of sublinks has been further developed and has been used in the new form for the analysis of the graphs of complex mechanically bound molecules. This analysis is additionally supported by the Brunnian numbers M, µ for topologically non-trivial and their complements L and λ for topologically trivial systems (like (n)-rotaxanes). The detailed topological analysis has been thus performed for more than thirty topologically different structures. The different orders of (sub)links, single and multiple mechanical bonds ought to be discerned to analyze connections within the larger structures. The new nomenclature recommendations developed suggest to indicate the number of the mechanical bonds, their (highest) multiplicities together with the number of covalent units and the number of interlocked rings or rings and dumbbells.

2-Mono- and 2,9-di-substituted 1,10-phenanthrolines with 4-pyridine units attached either via 1,4-phenylene- or 4-ethynyl-phenyl spacers, have been synthesised. The strategy is based on the introduction of 4-trimethylsilylphenyl group(s) at the phenanthroline core with the subsequent ipso-substitution of TMS groups by bromine or iodine and successive Suzuki or Sonogashira reactions with 4-pyridineboronic acid or 4-ethynylpyridine, respectively.

The exclusive formation of hydrogen-bonded dimers between tetraaryl and tetratosylurea calix[4]arenes has been used to prepare a series of ten "bisloop" tetraurea calix[4]arenes 3, in which adjacent phenylurea groups are covalently linked through alpha,omega-dioxyalkane chains. This dimerization with tetratosylurea 2 as template preorganizes the alkenyl residues of tetra(m-alkenyloxyphenyl) ureas 1 and enables their selective connection in high yield (up to 95 %) by olefin metathesis followed by hydrogenation. The "bisloop" calixarenes 3 also exclusively form heterodimers with 1. Thus, in a separated metathesis/hydrogenation sequence, a series of 14 cyclic bis[2]catenanes 4, in which two calix[4]arenes are connected through their wide rims by two pairs of interlocked rings (total size 29 to 41 atoms), were prepared in yields of up to 97 %. Optical resolution of these chiral bis[2]catenanes was studied by HPLC on chiral stationary phases. The single-crystal X-ray structure of one example (4(P,10)) confirmed the interlocking rings and revealed that the hydrogen-bonded dimeric capsule of the calix[4]arene can be "completely" opened.

Molecular dynamics (MD) simulations have been performed for complexes of a dimeric capsule of a tetraurea calixarene with a series of twelve aromatic guests. A distinct orientational preference and a restriction of the internal mobility was found which depend on the size and electronic properties of the guests. The results are in agreement with the CIS values obtained from (1)H NMR spectroscopic measurements and with complexation selectivities obtained by competition experiments.

Calix[5]arenes substituted at their wider rim by five urea residues do not form hydrogen bonded dimeric capsules in aprotic, apolar solvents, in contrast to their calix[4]arene analogs, although molecular dynamic simulations predict very similar geometrical parameters for both cases. The reason for this different behavior is most probably the higher energetic cost which must be paid to arrange the calix[5]arene skeleton in the C 5-symmetrical conformation required for the dimerization.

Bis-loop tetraurea calix[4]arene 6 has been prepared by acylation of the wide-rim calix[4]arene tetraamine 1 with the activated bis(urethane) 8 under dilution conditions. Similarly the bis(Boc-protected) tetraamine 2 is converted into the mono-loop derivative 3 which after deprotection and acylation gives the bisalkenyl derivative 5. In apolar solvents this tetraurea calix[4]arene 5 forms regioselectively a single hydrogen-bonded homodimer, from which the bis[2]catenane 10 a is formed in 49 % by a metathesis reaction followed by hydrogenation. Bis-loop derivative 6 forms no homodimers for steric reasons, but a stoichiometric mixture with the open-chain tetraalkenyl derivative 7 a contains exclusively the heterodimer. Metathesis and subsequent hydrogenation now yields 65 % of the pure bis[2]catenane 10 a which could not be isolated from the complex reaction mixture obtained from the homodimer 7 a⋅7 a. The chirality of 10 a (D2 symmetry) has been verified by optical resolution using HPLC on a chiral stationary phase.

The dimerization of tetratolyl- and tetratosyl-urea derivatives 1 and 2, derived from a tetrapentoxy calix[4]arene in the cone conformation and of the corresponding tetra-urea derivatives 3 and 4, in which the cone conformation is rigidified by the two crown-3 tethers, have been studied. All six possible equimolar mixtures were examined by 1H NMR using CDCl3 and CD2Cl2 as solvents. While no heterodimers are found for the combinations 1/3 and 2/4 in either solvent, all remaining combinations lead to the (exclusive) formation of heterodimers in CD2Cl2. In CDCl3 heterodimers are only observed for the combinations of 3 with 2 or 4. These results are discussed in terms of entropic and enthalpic contributions and compared with MD-simulations in a box of chloroform solvent molecules.

A new strategy is proposed for the synthesis of tetraether derivatives of calix[4]arenes bearing at the wide rim nitro and phthalimido groups in well defined positions. Since both groups are precursors of amino functions, calix[4]arenes substituted by different N-acylamino residues are easily available in four steps. The essential steps during the synthesis of the precursor consist in the protection of amino groups by the formation of their phthalimides followed by ipso-nitration of the remaining tert-butylphenol ether units. This nitration occurs without side reactions at the phthalimido substituted units, in contrast to simple N-acyl derivatives.

A calix[4]arene tetrapentyl ether in the cone conformation substituted at its wide rim by four m-(omega-octenyloxy)phenyl urea groups forms hydrogen-bonded dimeric capsules in dichloromethane/benzene (95:5). Metathesis reaction with Grubbs' catalyst under high-dilution conditions (1.1 x 10(-4) M) followed by hydrogenation leads to a covalent connection of all the urea groups within a dimer. Three topologically different products may be expected in such a reaction: a bis[2]catenane, a doubly bridged monocatenane and a tetrabridged capsule. All three possible reaction products could be isolated in an overall yield up to 60 % for the separated and purified compounds. Their identification was based on the NMR patterns which reflect the characteristic symmetry properties of the isomeric products especially in the region of the hydrogen-bonded NH protons and were further confirmed by MALDI-TOF mass spectra. Further structural support for the bis[2]catenane comes from a single-crystal X-ray structure, although severe disorder prevents the localization of all atoms in the aliphatic chains connecting the two calix[4]arenes. Kinetic studies for the guest release/exchange (cyclohexane against the solvent [D(6)]benzene) do not show remarkable differences between the starting dimer and the additionally linked dimers, while the mobility of an included tetraethylammonium cation is obviously more restricted.

A series of symmetrical and inherently chiral water-soluble calix[4]arenes bearing one, two or four proton-ionisable dihydroxyphosphoryl groups at the narrow rim of the macrocycle has been synthesised by consecutive treatment of appropriate diethoxyphosphoryl derivatives with bromotrimethylsilane and methanol. The calix[4]arene phosphoric acids synthesised possess pKa-values 2.85–3.10 (CH3OH–H2O 70 : 30) and form salts with L-(−)-α-phenylethylamine or (1S,2R)-(+)-ephedrine in methanol solution. The salts of the inherently chiral calixarene phosphoric acids with chiral amines are easily separated into diastereomeric forms by the RP HPLC method on Separon SGX C18 or Partisil 5 ODS 3 achiral columns.

Surface plasmon resonance (SPR) properties were measured for porphyrin Langmuir–Blodgett (LB) films and the response to NO 2 gas was investigated. The porphyrin molecule was 5,10,15,20-tetrakis(3,4-bis[2-ethylhexyloxyphenyl])-21H,23H-porphine (EHO). The EHO porphyrin LB films were deposited onto the cover glass with evaporated Ag thin films by vertical dipping method with a very fast deposition rate of 1000 mm min −1 . The SPR measurements were carried out at wavelengths of 488 and 632.8 nm. The SPR properties measured at 488 nm were considered to be related to the dispersion properties due to the optical absorption band of the EHO LB films. The thickness and the complex dielectric constants of the EHO LB films evaluated from the SPR properties measured at 632.8 nm were thought to be related to the island structure of the EHO LB films. From the NO 2 gas response measurements, the SPR properties at 488 nm were found to be more sensitive to NO 2 gas than those at 632.8 nm. The response rate to NO 2 gas and the recovery properties were also examined.

The UV–vis absorbance spectrum of LB film assemblies of 5,10,15,20-tetrakis(3,4-bis[2-ethylhexyloxyphenyl])-21H,23H-porphine is very sensitive to low concentrations of NO2. LB films prepared at very high deposition rates (∼1000 mm min−1) yield t50 response and recovery times of 25 and 33 s, respectively, and show a sensitivity of 60% relative absorbance change (at 430 nm) for 4.4 ppm NO2. Atomic force microscopy shows that the morphology of these films is characterised by isolated micron-size domains, which are themselves composed of grains of several nm in diameter. This unconventional LB structure leads to a useful sensing material as a result of the molecular functionality of the porphyrin coupled to the enhanced surface area of the porous film assembly. The optical response of the EHO gradually decreases as its temperature is increased, resulting from the shift in the adsorption-desorption equilibrium towards desorption. An activation energy for adsorption of 0.68 eV is obtained. The spectrum recovers fully after exposure to NO2 and the rate of recovery can be accelerated dramatically with gentle heating (∼350 K) for a few seconds. The concentration dependence of the optical response over the range 0.8–4.4 ppm follows a Langmuir model.

The single crystal X-ray structure of a homodimer of a tetra(tolylurea) calix[4]arene including a tetraethylammonium cation as guest shows an expansion of the capsule and a distortion of its shape, in comparison to the structure of a similar dimer with an encapsulated benzene molecule. Thus, only 8 of 16 possible hydrogen bonds are present in the hydrogen bonded belt holding together the two hemispheres. The encapsulated cation is disordered over two equivalent positions with two methyl groups pointing to the equator, while two methyl groups pointing to the poles form CH–π interactions with the inner surfaces of the calixarene cavities. MD simulations are in agreement with the distorted X-ray structure for a short simulation time of 1–2 ns with a given orientation of the included cation and approach for longer simulation times (9 ns) the fourfold symmetry found by 1H NMR spectroscopy in solution.

Structural models for self-assembled dimers composed of two urea calix[4]arenes which entrap benzene or cyclohexane are developed using Fourier transform infrared (FTIR) spectroscopy. Based on the host–guest ratio determined by 1H NMR spectroscopy in solution, and confirmed for the solid state by a thermogravimetric analysis, it is possible to prove by a comparison of the FTIR data of host, guest, complex and model compounds, that the capsule is held together by a cyclic array of weak and strong hydrogen bonds between the urea units attached at the wide rim of the calixarenes. The dimerization of the two urea units leads to a loss of symmetry, and an averaged C4 symmetrical arrangement is probable. Guest molecules, such as benzene or cyclohexane, are enclosed inside the container rotating fast on the IR timescale around a longitudinal axis of the guest. From the observed splitting of absorption bands upon dimerization and inclusion it follows that either two crystallographically independent types of capsules exist in the crystal lattice or that the guests are occupying two major orientations in the capsule. As indicated by a higher complexation induced shift for cyclohexane, this guest exhibits a tighter interaction with the host molecules compared to benzene.

Hydrogen-bonded, dimeric capsules of calix[4]arenes substituted at the wide rim by four urea functions show unprecedented dynamic features when a tetraethylammonium cation is included as a guest. The seam of hydrogen bonds C=O...(HN)2C=O in the equatorial region which holds the two calixarene counterparts together changes its directionality fast (at 25 degrees C), while the dimer itself is kinetically stable on the NMR time scale. An energy barrier of deltaG++ = 49.9 kJmol(-1) (Tc 276 K) was estimated for this reorientation from variable-temperature (VT) NMR measurements. Lowering the temperature to about -50 degrees C restricts also the rotation of the encapsulated tetraethylammonium cation around a pseudo C2-symmetry axis in the equatorial plane of the capsule, while its rotation around the C4 axis is still fast. As a result of this restriction two ethyl groups of the tetraethylammonium cation point towards the "poles" of the capsule, while the other pair lies in the "equator" region. Variable-temperature 1H NMR experiments led to a barrier of deltaG++=54.8kJ mol(-1) (Tc 306 K) for the exchange of these different ethyl groups. Studies with the ternary complex formed by a C2v-symmetrical tetraurea proved that both processes, reorientation of the hydrogen bonds and rotation of the guest, take place independently. Molecular dynamics simulations suggest that the capsule is strongly expanded by the larger tetraethylammonium cation in comparison with benzene as guest. Thus, on average only one N-H...O hydrogen bond is formed per urea function and the interaction energy between the two tetraurea calixarenes is less favorable by about 15 kcal mol(-1). This is overcompensated by an energy gain of about 36 kcal mol(-1) due to cation-pi interactions. These results provide a rationale to understand the high stability of the complex inspite of the mobility of the hydrogen-bonded belt.

The discipline of molecular electronics has grown rapidly over the last 10 years and is driven by the promise of the enhanced applied physical properties of functionalised organic materials compared to their inorganic partners. The subject can be divided generally into two broad themes, namely active molecular-scale electronics (or photonics), in which the control or generation of charge (or photons) at the nanoscale is attempted, and passive supra-molecular electronics (or photonics), in which the specific functionality of the molecules is modified by some interaction or process. In this paper, an example of the latter approach to molecular electronics will be given and this will describe the gas sensing properties of a tetra-substituted porphyrin molecule. The optical absorbance spectrum of LB film assemblies of 5,10,15,20-tetrakis(3,4-bis[2-ethylhexyloxy]phenyl)-21H,23H-porphine (EHO) is highly sensitive to low concentrations of NO 2 . LB films prepared at much faster than conventional deposition rates (∼1000 mm min −1 ) yield t 50 response and recovery times of 25 and 33 s, respectively, and show a sensitivity of 60% relative absorbance change (at 430 nm) for 4.4 ppm NO 2 . The morphology of these films is revealed using atomic force microscopy to contain isolated micron-size domains which are composed of grains of several nm in diameter. This unconventional structure leads to a useful sensing material as a result of the molecular functionality of the porphyrin coupled to the enhanced surface area of the porous film assembly. The EHO film shows a gradually diminishing optical response as its temperature is increased, resulting from the shift in the adsorption–desorption equilibrium towards desorption. The spectrum recovers fully after exposure to NO 2 . The rate of recovery is slow at room temperature but can be accelerated dramatically with gentle heating (∼350 K) for a few seconds. The kinetics of the gas sensing process have been modelled and found to fit Elovichian surface adsorption for an initial fast surface adsorption process. This is followed by a much slower diffusive process in which the NO 2 molecules diffuse through the bulk of the assembly. The concentration dependence of the optical response over the range 0.8–4.4 ppm follows a Langmuir model.

Reversible zinc-pyridine coordination and hydrogen-bonding interactions have been used to assemble a [2]rotaxane from three components. Cooperativity in the macrocyclization process that results in the porphyrin dimer makes the system exceptionally stable. However, the kinetic lability of the zinc-porphyrin interaction means the dimer is in dynamic equilibrium with its monomer, and this has been exploited in the construction of a [2]rotaxane.

Phosphorylation of p-tert-butylcalix[4]arene 9 or calix[4]arene 10, having two diethoxyphosphoryl groups at distal positions on their narrow rim (phenolic oxygen atoms), by dibutyloxophosphinechloride or alkylation of 10 by methyl bromoacetate led to the corresponding tetrasubstituted calix[4]arenes 8b–d fixed in a cone conformation. The latter compounds and the similar derivative of calix[4]arene 8a with four diethoxyphosphoryl groups were found to exhibit lithium cation selectivity, which was supported by UV–Vis spectra of THF solutions of the alkali metal picrates and their water–chloroform extraction in the presence of ligands 8a–d. Calculated K/K selectivities range from 2.9 (8d) to 9.5 (8a), which are among the highest values for the calixarene-based Li+-selective receptors reported to date. Copyright © 2001 John Wiley & Sons, Ltd.

The optical absorbance spectrum of LB film assemblies of 5,10,15,20-tetrakis[3,4-bis(2-ethylhexyloxy)phenyl]-21H,23H-porphine (EHO) is highly sensitive to low concentrations of NO2 in nitrogen. LB films prepared at much faster than conventional deposition rates (∼1000 mm min−1) yield t50 response and recovery times of 25 s and 33 s respectively and show a sensitivity of 60% relative absorbance change (at 430 nm) for 4.4 ppm NO2. The morphology of these films is revealed using atomic force microscopy to contain isolated micron-size domains which are themselves composed of grains of several nm in diameter. This unconventional structure leads to a useful sensing material as a result of the molecular functionality of the porphyrin coupled to the enhanced surface area of the porous film assembly. The EHO film shows a gradually diminishing optical response as its temperature is increased, resulting from the shift in the adsorption–desorption equilibrium towards desorption as expected. The UV–visible spectrum recovers fully after exposure to NO2. The rate of recovery is slow at room temperature but can be accelerated dramatically with gentle heating (∼350 K) for a few seconds. The concentration dependence of the optical response over the range 0.8–4.4 ppm follows a Langmuir model.

Inclusion complexes of self-assembled molecular dimers composed of two tetratolylurea calix[4]arenes show strongly different kinetic stability for different guests. In cyclohexane-d12, half-life ti...

1H and 13C NMR spectra of the complexes of camphor enantiomers with α-cyclodextrin in D2O manifest splittings due to chiral recognition. The complexes were found to be of 1:2 guest-to-host stoichiometry. Free energies of the complex formation obtained from 1H NMR titration data are equal to −7.95 ± 0.09 kcal mol-1 for the complex with (1S,4S)- and −7.61 ± 0.06 kcal mol-1 for that with (1R,4R)-enantiomer. Thus, the free energy difference between the complexes is equal to 0.34 ± 0.11 kcal mol-1, with the complex involving the (1S,4S)-camphor more stable. A strong positive cooperativity of the guests binding has been found. In agreement with experimental results, molecular dynamics simulations yielded greater stability of the complex with (1S,4S)-camphor. However, they reproduced only qualitatively the experimental trend since the corresponding difference in average energies obtained from molecular dynamic simulations carried out in a water solution is equal to 5 kcal/mol with the CVFF force field.

Three types of inherently chiral calix[4]arenes( AAHH BHBH , AHHH HBBH , AAHH HHBH ) with asymmetrical superposition of ethyl, diethoxyphosphoryl groups at the lower rim of the macrocycle and bromine atoms at the upper rim, have been synthesized. The key steps of the synthesis are O,O′-phosphorotropic rearrangements of 1,3-distally disubstituted calix[4]arenes into 1,2-proximal isomers, regioselective bromination of the upper rim and hydrolytic removing of phosphoryl or benzoyl group from the lower rim.

The title compound, C75H68N2O3·3CH3OH·H2O, was synthesized starting from the corresponding acid and p-tritylaniline. Single crystals were obtained from a methanol solution as a solvate, with three methanol mol­ecules and one water mol­ecule. The solid-state structure proves the existence of an intra­molecular bifurcated hydrogen bond between one amide H atom and the carbonyl and xanthene O atoms. The packing is stabilized by inter­molecular hydrogen bonds.

A solid powder of hydrogen bonded dimers of a tetraurea calix[4]arene is able to exchange the encapsulated guest in contact with the vapor of a second guest. The molecules of a guest-free powder obtained from a polar solvent cannot rearrange in the solid phase to form new guest-filled capsules under these conditions.

The mol­ecule of the title compound, C48H60N4O12, is located on a crystallographic twofold rotation axis. It is found in the typical pinched cone conformation. The dihedral angles between the reference plane (defined by the C atoms of the methyl­ene bridges) and the benzene rings are 83.33 (6) and 141.61 (5)°.

A multicatenane is described in which two belts consisting of four annelated rings attached to the wide rims of two calix[4]arenes are interwoven in such a way that each ring of one belt penetrates two adjacent rings of the other belt and vice versa. The key step of the synthesis of this [8]catenane is the exclusive formation of preorganized heterodimers between a multimacrocyclic tetraurea calix[4]arene and an “open-chain” tetraurea calix[4]arene containing eight ω-alkenyl groups. When a tetraurea calix[4]arene containing four alkenyl groups is used, a bis-[3]catenane is formed analogously.

The analysis of suit[2]-, suit[3]ane and tetrafould [2]-rotaxanes on the bases of calix[4]- arene with the help of the "mechanical disconnection operation" show that these structures possess only one mechanical bond, which is suggested to be called bi-, tri- and tetrafurcated one, respectively, since such structures bear two, three and four divergent mechanical entanglements. In the same time, introduction of the external bulky groups to these structures transforms such unique mechanical bonds into several single ones. There can be several different invariants which have only one mechanical bond, but possess different number of the intrinsic mechanical entanglements like, for example, in [2]-catenane and doubly braided [2]-catenane. The mechanical bond in the last case is proposed to be called the tight one. The constrictive bonds in carceplexes are classified as the spherical mechanical bonds. Thus, the whole classification of the mechanical bonds (together with the previously proposed ones), is presented.

A series of symmetrical and inherently chiral water-soluble calix[4]arenes bearing one, two or four proton-ionisable dihydroxyphosphoryl groups at the narrow rim of the macrocycle has been synthesised by consecutive treatment of appropriate diethoxyphosphoryl derivatives with bromotrimethylsilane and methanol. The calix[4]arene phosphoric acids synthesised possess pKa-values 2.85–3.10 (CH3OH–H2O 70 : 30) and form salts with L-(−)-α-phenylethylamine or (1S,2R)-(+)-ephedrine in methanol solution. The salts of the inherently chiral calixarene phosphoric acids with chiral amines are easily separated into diastereomeric forms by the RP HPLC method on Separon SGX C18 or Partisil 5 ODS 3 achiral columns.

Calix[4]arenes bearing at their wide rim four urea residues easily form hydrogen bonded dimeric capsules. This has been used to preorganise alkenyl functions attached to these urea groups for their controlled connection via metathesis reaction. Multimacrocyclic tetraurea derivatives are thus obtained in excellent yields via heterodimers which are formed exclusively with tetratosylurea derivatives. Heterodimerisation of such bis- and tetraloop tetraureas leads analogously to multicatenanes, or to rotaxanes by stoppering. Huge macrocycles are detached from tetraloop derivatives by cleavage of the urea function.

Macrocycles with up to 100 atoms have been synthesised using two calix[4]arenes as templates: first, (3,5-dialkenyloxy)phenyl groups are attached to the wide rim of a calix[4]arene via urea links, then the alkenyl groups are connected via a metathesis reaction using a tetratosylurea calix[4]arene for their correct prearrangement and finally the urea functions are cleaved to detach the newly formed macrocycles.

Tetraurea calix[4]arenes with four loops form exclusively heterodimers with open-chain urea calix[4]arenes when they are dissolved in aprotic solvents. These assemblies can be considered as pseudorotaxanes. If open-chain tetraureas ending with maleic imide functions are used, their Diels-Alder reaction with 1,4,5,8-tetrapentoxyanthracene leads to tetra[2]rotaxanes which cannot be split into the single calixarene parts by hydrogen bond breaking solvents.

Wide rim tetraurea derivatives (2a,b) have been prepared from a calix[4]arene rigidified in the cone conformation by two diethyleneglycol ether bridges between adjacent oxygens. In comparison to the analogous tetraurea derivatives (3a,b) of a tetrapentoxy calix[4]arene, 2a,b show an increased thermodynamic stability in mixtures of CDCl(3) and DMSO-d(6). Their kinetic stability as expressed by the rate of guest exchange (benzene or cyclohexane against the solvent benzene-d(6)) is also strongly increased by factors of 30-38. Noticeable differences for the inclusion of selected guests are found.

In solvents such as chloroform or benzene, tetraurea calix[4]arenes 1 form dimeric capsules in which one solvent molecule is usually included as guest. To explore the structural requirements for the formation of such hydrogen-bonded dimers we replaced one p-tolylurea residue by a simple acetamide function. The resulting calix[4]arene 2 a, substituted at its wide rim with one acetamide and three p-tolylurea functions, assumes a C(1)-symmetrical conformation in apolar solvents as shown by (1)H NMR, which is not compatible with the usual capsule. In the crystalline state, four molecules of 2 a, adopting a pinched cone conformation, assemble into a quasi S(4)-symmetrical tetramer stabilized by a cyclic array of 24 NH.O==C hydrogen bonds and four NH.pi interactions. Four acetamide groups are hydrogen-bonded to each other and pack tightly in the center of the assembly. All polar residues are buried inside the tetramer, the surface of which is lipophilic. Extensive NMR studies revealed similar structures in apolar solvents such as [D]chloroform or [D(6)]benzene for calixacetamides 2 a-c. The formation of these tetramers in solution is critically dependent on the size of the amide fragment, so that propionamide 2 d, butyramide 2 e, and p-tolylamide 2 f form only ill-defined aggregates. This is caused by steric crowding inside the tetrameric assembly. The tetramers persist during molecular dynamics simulations, and the optimized average structure of the MD run is similar to that found in the crystalline state. Theoretical studies revealed that cooperation of hydrogen bonds with multiple NH.pi, C--H.pi, and pi.pi attractions make the tetramer more stable than the capsular dimer with the solvent as guest. In the presence of tetraethylammonium salts, however, compounds 2 a-e form dimeric capsular assemblies, each incorporating a single ammonium cation. Only one of two possible regioisomeric dimers is formed, in which both acetamide groups are surrounded by two urea residues. These examples give striking evidence of how self-assembly in solution can be strongly dependent on subtle structural factors and of how the formation of dimeric capsules can be induced by the presence of an appropriate guest.

Half-life times up to 4 days in DMSO at room temperature are observed for the decomposition of dimeric capsules of urea substituted calix[4]arenes held together by a combination of hydrogen bonds, mechanical entanglement and cation–π interactions.