Phosphorylation of Dialkylaminomethyl-substituted Calix[4]resorcinolarenes with Hexaalkylphosphorous Triamides and Phosphorus(V) Dichlorides

A series of aminophosphino cavitands were synthesized by reactions of dialkylaminomethyl-substituted calix[4]resorcinolarenes with hexaalkylphosphorous triamides, and their properties were studied. New aminoalkylated (thio)phosphato(phosphonato) cavitands were prepared by phosphorylation of dialkylaminomethyl-substituted calix[4]resorcinolarenes with phosphorus(V) dichlorides in the presence of a base. Their reactions with electrophilic alkylating agents (methyl trifluoromethanesulfonate, methyl iodide, and triethyloxonium tetrafluoroborate) were examined.     

Tetrathiafulvalene-functionalized Cavitands as Building Blocks for Redox Active Hemicarcerands

Two new cavitands bearing four upper-rim tetrathiafulvalene (TTF) units were synthesized. One of these cavitands was used to prepare a redox-active hemicarcerand containing four TTF subunits covalently appended to its equatorial region. Preliminary electrochemical characterization data show that the four TTF residues in all these compounds behave as independent, non-interacting groups in their heterogeneous electron transfer reactions.     

Cavitands bearing four fluorophores

The synthesis of novel cavitands containing four fluorophores [tert-butoxycarbonyl protected 2,2′-bis(furyl)benzidine (t-BOC FurylBz) or 5,5′-bis(4-aminophenyl)-2,2′-bifuryl (t-BOC PFDA)] and ionophoric functional groups on the upper rim is reported. The cavitands bearing the four fluorophores emit blue light photoluminescence. In particular, the cavitand containing PFDA moieties exhibits a high photoluminescence quantum yield.     

Syntheses and Cation Complexation Studies of New Cavitand Derivatives

A series of new cavitands containing four esters, nitriles, 2-pyridyl, or 3-pyridyl groups were synthesized fromtetrahydroxycavitand. Their binding properties towards various metal ions are investigated.     

State-of-the-art and recent progress in resorcinarene-based cavitand

Compartmentalization in the biological world brings excellent efficiency and specificity to the formation of complex compounds, inspiring supramolecular chemists to continuously search for defined spaces that can mimic such natural binding sites. Bowl-shaped cavitands built up from resorcinarenes (RA) present rigid and preorganized concave surfaces, which are capable of mimicking the molecular recognition properties of enzymes. The versatile scaffold of RA endows the cavitand with terrific variety and excellent binding behavior. This review provides a comprehensive overview over the structural modification to date in the high attention field of RA-based cavitands development. Different strategies for synthesizing diverse cavitands, such as small cavity cavitands, wider cavity cavitands, deep cavity cavitands, biscavitands, and asymmetric cavitands, are discussed in details. Furthermore, insights into their applications including catalysis, separations and sensing are provided.     

Cyclic Phosphorochloridites and Phosphorochloridates Derived from Bromocalix[4]resorcinolarenes

Reactions of bromocalix[4]resorcinolarenes with PCl₃ and POCl₃ in the presence of triethylamine give the corresponding phosphorochloridito and phosphorochloridato cavitands in good yields. Phosphorochloridito cavitands were converted into phosphoramidito cavitands by treatment with piperidine.     

Complexing and self-complexing of peptide-cavitands

Resorc[4]arene based peptide-cavitands with four identical chiral amino acids at their upper rim were synthesized and investigated for the complexation of small guest molecules. Competition experiments show, that the tetra amino acid cavitands complex small organic guests in chloroform in the order ethyl acetate <dichloromethane < acetonitrile < ethanol < acetamide < acetic acid. The peptide-cavitands containing aspartic and glutamic acid derivatives enclose parts of their attached amino acids in the cavity, so that these peptide-cavitands are host and guest at the same time. The starting material for the cavitands, the resorc[4]arenetetraamine 3, is made by a new synthetic route using the Delépine-reaction.     

Metal-free synthesis of calixsalen-type cavitands for the recognition of fluoride ion

Novel calixsalen-type cavitands have been synthesized using metal-free synthesis from simple and inexpensive materials, such as ethylenediamine and 5,5′-methylene-bis-salicylaldehyde derivatives. The cavitand 1 containing salen functionality recognizes fluoride ion. Fluoride ions switch on fluorescence on binding with the cavitand 1. Substitution on bis-salicylaldehyde part of calixsalen-type cavitand shows change in recognition behavior. On the attachment of electron withdrawing substituent, such as nitro group, the cavitand lost its fluorescence properties but proved to be a better colorimetric probe showing marked color change from pale yellow to red on addition of tetrabutyl ammonium salt of fluoride ion to the solution of cavitand. The nitro substituted cavitand is highly sensitive and selective for fluoride anion and hence is a promising candidate for development of colorimetric chemosensor. The binding of the cavitands with fluoride ion is investigated using ¹H NMR-titration experiments.     

Synthesis of polyhydroxy cavitands and intramolecular inclusion of their octaester derivatives

A facile and efficient synthesis of novel cavitands containing eight hydroxyl groups was accomplished in eight steps beginning from commercially available resorcinol and the corresponding aldehydes. The synthesis combines two classical approaches to cavitand chemistry and yields the target octol cavitand molecules in gram quantities with no chromatographic separations. A variety of octaester cavitand derivatives were then prepared from the parent octols and their spectral properties are reported.     

Supramolecular sensing with phosphonate cavitands

Phosphonate cavitands are an emerging class of synthetic receptors for supramolecular sensing. The molecular recognition properties of the third-generation tetraphosphonate cavitands toward alcohols and water at the gas-solid interface have been evaluated by means of three complementary techniques and compared to those of the parent mono- and diphosphonate cavitands. The combined use of ESI-MS and X-ray crystallography defined precisely the host-guest association at the interface in terms of type, number, strength, and geometry of interactions. Quartz crystal microbalance (QCM) measurements then validated the predictive value of such information for sensing applications. The importance of energetically equivalent multiple interactions on sensor selectivity and sensitivity has been demonstrated by comparing the molecular recognition properties of tetraphosphonate cavitands with those of their mono- and diphosphonate counterparts.     

Deep cavitand vesicles - multicompartmental hosts

The synthesis and characterization of vesicles assembled from deep cavitands in water is reported. These vesicles act as hosts for three different types of guests: the cavitands bind small guest molecules, the bilayer attracts larger hydrophobic guests and the inner aqueous compartment contains hydrophilic molecules.     

Cavitand-porphyrins.

The synthesis and characterization of new nanoscale container molecules 7 and 8 are described. They are covalent hybrids of deepened, self-folding cavitands and metalloporphyrins. In receptor 7, the Zn-porphyrin wall is directly built onto the cavitand skeleton. Host 8 features a large unimolecular cavity containing two cavitands attached with the Zn-porphyrin wall. Its dimensions, approximately 10 x 25 A, place it among the largest synthetic hosts prepared to date. A series of adamantyl- and pyridyl-containing guests 14-20 of various lengths were prepared and used to determine the hosts' binding abilities in solution using UV/vis and (1)H NMR spectroscopy. Intramolecular hydrogen bonds at the upper rims of the cavitands resist the unfolding of the inner cavities and thereby increase the energetic barrier to guest exchange. The exchange is slow on the NMR time scale (at < or =300 K), and kinetically stable complexes result. When the cavities and metalloporphyrins participate simultaneously in the binding event, very high affinities for guests are found (-DeltaG295 up to 10 kcal x mol(-1) in toluene), to which the porphyrin fragments contribute significantly (-DeltaG295 up to 6 kcal x mol(-1)). The pairwise selection of two different guests by molecular container 8 is reported, and the termolecular complex formed raises the possibility of metal-catalyzed bimolecular reactions in these containers.     

Effect of <Emphasis Type="Italic">ortho</Emphasis>-methyl groups in the benzene rings of the macrocyclic frame on the chemistry of phosphacavitands

Effect of ortho-methyl groups in the benzene rings of the macrocyclic matrix on the chemistry of cavitands with phosphorous amide bridges in the upper rim is studied. The presence of ortho-methyl groups is shown to prevent formation of phosphacavitands of C _4v symmetry and favor formation of macrocyclic systems of C _2v symmetry, enhance solubility of phosphacavitands in organic solvents, hinder oxidation of phospha(III)cavitands and decrease the yield of phospha(V)cavitands, prevent formation of binuclear molybdenum complexes of phosphorous amide cavitands, and favor formation of their tetranuclear analogs.     

Exploiting Cavities in Supramolecular Gels

Endowing supramolecular gelators with cavities opens up a number of opportunities not possible with other gel systems. The well‐established host–guest chemistry of cavitands can be utilized to build up and break down gel structures, introduce responsive functionalities, or enhance selectivity in applications such as catalysis and extraction. Cavity‐containing gelators provide an excellent case study for how different aspects of supramolecular chemistry can be used intelligently to create responsive materials.     

One-dimensional void-space arrays constructed from a coordination polymer with bowl-like frameworks of cavitands

A one-dimensional coordination polymer of [Mn(II)(hfac)2] bridged by new bowl-like ligands of cavitands was prepared and the crystal structure was determined by X-ray crystal analysis. Ethyl acetate molecules are necessarily included as guest molecules in each of the void-space cavities of the cavitands, and then are held by weak interaction forces.     

Gold nanoparticles functionalized with deep-cavity cavitands: synthesis, characterization, and photophysical studies

In this report, we present methods of functionalization of AuNP's with deep-cavity cavitands that can include organic molecules. Two types of deep-cavity cavitand-functionalized AuNP's have been synthesized and characterized, one soluble in organic solvents and the other in water. Functionalized AuNP soluble in organic solvents forms a 1:1 host-guest complex where the guest is exposed to the exterior solvents. The one soluble in water forms a 2:1 host-guest complex where the guest is protected from solvent water. Phosphorescence from thiones and benzil included within heterocapsules attached to AuNP was quenched by gold atoms present closer to the guests included within deep-cavity cavitands. During this investigation, we have synthesized four new deep-cavity cavitands. Of these, two thiol-functionalized hosts allowed us to make stable AuNP's. However, AuNP's protected with two amine-functionalized cavitands tended to aggregate within a day.     

Oligo Tröger's bases--new molecular scaffolds

Oligo Tr?ger's bases are compounds containing two or more Tr?ger's base subunits (1,5-methanodiareno[b,f][1,5]diazocines) sharing one or more arene parts. Due to their interesting molecular shapes, these compounds are studied as chiral molecular tweezers, clips, cavitands, clefts, calixes, etc. This review includes all available data on oligo Tr?ger's bases, and introduces their preparation and properties to a wide audience.     

ESI-FTICR mass spectrometric study of alcohol complexation properties of mono- and diphosphonate-bridged cavitands

Alcohol complexation properties of eight mono- and diphenyl phosphonate-bridged cavitands were studied by electrospray ionization Fourier transform ion cyclotron resonance mass spectrometry (ESI-FTICR) and theoretical calculations. The cavitands varied in number and position of phenyl phosphonate bridges and their orientation with respect to the cavity, length of the lower rim alkyl chains, and substituents at apical positions of the resorcarene skeleton. The specificities of the different cavitands toward primary, secondary, and tertiary alcohols varying long of the alkyl chain were investigated, together with the stabilities of the formed complexes. The number, position, and orientation of the P = O moieties affected the complex formation of the cavitands and stability of the complexes dramatically. Methyl groups at apical positions of the resorcarene skeleton also affected the complexation properties. Although length and branching of the alkyl chain of the alcohol influenced the complex formation, the effect on stability of the complexes was negligible.     

Expanding cavitand chemistry: the preparation and characterization of [n]cavitands with n>=4

The preparation of cavitands composed of 4, 5, 6, and 7 aromatic subunits ([n]cavitands, n=4-7) is described. The simple, two-step synthetic procedure utilized readily available starting materials (2-methylresorcinol and diethoxymethane). The two cavitand products having 4 and 5 aromatic subunits exhibited highly symmetric cone conformations, while the larger cavitands (n = 6 and 7) adopt conformations of lower symmetry. 1H NMR spectroscopic studies of [6]cavitand and [7]cavitand revealed that these hosts undergo exchange between equivalent conformations at room temperature. The departure of these two cavitands from cone conformations is related to steric crowding on their Ar-O-CH2-OAr bridges and is predicted by simple molecular mechanics calculations (MM2 force field). X-ray diffraction studies on single crystals of the [4]cavitand, [5]cavitand, and [6]cavitand hosts afforded additional experimental support for these conclusions.     

Recent Advances in the Applications of Water-soluble Resorcinarene-based Deep Cavitands

We review here the use of container molecules known as cavitands for performing organic reactions in water. Central to these endeavors are binding forces found in water, and among the strongest of these is the hydrophobic effect. We describe how the hydrophobic effect can be used to drive organic molecule guests into the confined space of cavitand hosts. Other forces participating in guest binding include cation−π interactions, chalcogen bonding and even hydrogen bonding to water involved in the host structure. The reactions of guests take advantage of their contortions in the limited space of the cavitands which enhance macrocyclic and site-selective processes. The cavitands are applied to the removal of organic pollutants from water and to the separation of isomeric guests. Progress is described on maneuvering the containers from stoichiometric participation to roles as catalysts.