Deep-cavity Cavitands Research Articles

Nature of Supramolecular Complexes Controlled by the Structure of the Guest Molecules: Formation of Octa Acid Based Capsuleplex and Cavitandplex

Factors that govern inclusion of organic molecules within octa acid (OA), a synthetic deep cavity cavitand, have been delineated by examining the complexation behavior of a number of organic molecules with varying dimensions and functionalities with OA. The formation of two types of complexes has been noted: the one which we call cavitandplex is a partially open complex in which a part of the guest molecule remains exposed to water, and the other termed capsuleplex is formed through assembly of two OA molecules. In capsuleplex, the guest is protected from water. Generally, guest molecules that possess ionic head groups form cavitandplex, and all others form capsuleplex. Capsuleplex may contain one or two guest molecules within the capsule. Small organic molecules (<10 A in length) may form both 2:1 and 2:2 capsuleplex, while longer ones (>12 A) preferentially form 2:1 capsuleplex. Extensive 1H NMR experiments have been carried out to characterize host-guest complexes. In the absence of the guest, OA tends to aggregate in water. The extent of aggregation depends on the concentration of OA and the presence of salts in solution. We expect the information obtained from this study to be of great value in predicting the nature of complexes with a given guest and facilitating appropriate guest chosen by researchers.

Divergent Dendronization of Deep‐Cavity Cavitands to Tune Host Solubility

AbstractResorcinarene‐based deep‐cavity cavitands (DCCs) are useful components in supramolecular chemistry because their extended cavity enables the encapsulation of relatively large guests. To provide H2O solubility, they have been modified with hydroxyl functionalized dendrons. This has been carried out by the divergent dendronization of aliphatic poly(ester) dendrons through the third dendritic generation. The resultant macromolecule demonstrated the desired H2O solubility.

Cavitand Octa Acid Forms a Nonpolar Capsuleplex Dependent on the Molecular Size and Hydrophobicity of the Guest

We have been exploring the use of a deep cavity cavitand known by the trivial name 'octa acid' as a photochemical reaction cavity for manipulating photochemical and photophysical properties of organic molecules. In the current study, we have monitored the micropolarity of the interior of the cavitand by recording the fluorescence of five different organic probes. They all indicate that the interior of octa acid capsuleplex (2:1, H/G complex) is nonpolar and does not contain water molecules in spite of the complex being present in water. The nature of the octa acid-probe complex in each case has been characterized by 1H NMR data to be a 2:1 capsuleplex. Photophysical and 1H NMR experiments were employed to probe the factors that control the structure of the complex, 2:2, 2:1, and 1:1. The data we have on hand suggest that the structure of the host/guest complex depends on the size and hydrophobicity of the guest molecule.

Dendronized supramolecular nanocapsules: pH independent, water-soluble, deep-cavity cavitands assemble via the hydrophobic effect.

At neutral pH, dendronized deep-cavity cavitands were shown to form supramolecular nanocapsules via assembly around a range of guest molecules.

Ferrocene Derivatives Included in a Water-Soluble Cavitand: Are They Electroinactive?

The formation in aqueous solution of kinetically stable inclusion complexes between a deep-cavity cavitand and several redox active ferrocene derivatives was demonstrated using (1)H NMR spectroscopy. The electrochemical kinetics of the inclusion complexes was strongly attenuated as compared to that observed with the free guests.

Encapsulation of Ferrocene and Peripheral Electrostatic Attachment of Viologens to Dimeric Molecular Capsules Formed by an Octaacid, Deep‐Cavity Cavitand

In aqueous media the deep-cavity cavitand octaacid 1 forms stable dimeric molecular capsules 1(2), which are stabilized by hydrophobic effects. In this work we investigate the binding interactions in aqueous solution between these capsules and the redox active guests, ferrocene (Fc) and three 4,4'-bipyridinium (viologen) dications: methyl viologen (MV(2+)), ethyl viologen (EV(2+)), and butyl viologen (BV(2+)). Using NMR spectroscopic and electrochemical techniques we clearly show that the hydrophobic Fc guest is encapsulated inside 1(2). An interesting effect of this encapsulation is that the reversible voltammetric response of Fc is completely eliminated when it resides inside the 1(2) capsular assembly, a finding that is attributed to very slow electrochemical kinetics for the oxidation of Fc@1(2). Diffusion coefficient measurements (PGSE NMR spectroscopy) reveal that all three viologen guests are strongly bound to the dimeric capsules. However, the (1)H NMR spectroscopic data are not consistent with encapsulation and the measured diffusion coefficients indicate that two viologen guests can strongly associate with a single dimeric capsule. Furthermore, the (V(2+))(2)*1(2) complex is capable of encapsulating ferrocene, clearly suggesting that the viologen guests are bound externally, via coulombic interactions, to the anionic polar ends of the capsule. The electrochemical kinetic rate constants for the reduction of the viologen residue in the V(2+)*1(2) complexes were measured and found to be substantially lower than those for the free viologen guests.

Synthesis of nanoscale carceplexes from deep-cavity cavitands

Deep-cavity cavitands were shown to undergo carceplex reactions in which two cavitand tetrols were covalently linked using bromochloromethane; the efficiency of the "dimerization" was closely tied to the templating guest molecule incarcerated within the host.

Calorimetric Analysis of the 1:1 Complexes Formed between a Water-soluble Deep-cavity Cavitand, and Cyclic and Acyclic Carboxylic Acids

A water-soluble cavitand was shown to form 1:1 complexes with a series of acyclic and cyclic aliphatic carboxylic acids. Isothermal titration calorimetry was used to determine the standard molar enthalpy change (ΔH°) and binding constant (K a), and hence the Gibbs free energy (ΔG°) and entropy (ΔS°) change for the different complexes. The thermodynamic determinations were carried out from 288 to 318 K, allowing the standard molar heat capacity changes () also to be derived. Typical of the processes driven by the hydrophobic effect, was observed to be proportional to the accessible (non-polar) surface area of the guest. The cyclic and acyclic guests displayed opposite trends; the heat capacity penalty upon binding increased with longer aliphatic chains, while the opposite was observed with the cyclic guests.

Controlling Photochemical Geometric Isomerization of a Stilbene and Dimerization of a Styrene Using a Confined Reaction Cavity in Water

Utility of a water-soluble deep cavity cavitand, octa acid, as a reaction medium is illustrated by carrying out photochemical reactions of a stilbene and a styrene included within the octa acid in water. Geometric isomerization of trans-4,4'-dimethyl stilbene is restricted while dimerization of 4-methyl styrene is facilitated within the octa acid cavity. The excited-state chemistry of both systems is different in this medium from that in organic solvents. The change in chemistry is attributed to the supramolecular effects provided by the host cavity.

Making a Difference on Excited-State Chemistry by Controlling Free Space within a Nanocapsule: Photochemistry of 1-(4-Alkylphenyl)-3-phenylpropan-2-ones

The free space within a reaction cavity plays a determining role during the excited-state reaction of 1-(4-alkylphenyl)-3-phenylpropan-2-ones included within a capsule formed by two molecules of a deep cavity cavitand. By controlling the free space within the reaction cavity through remote alkyl substitution on the reactant ketone it is possible to control the yield of the rearrangement product shown above.

Controlling Photoreactions with Restricted Spaces and Weak Intermolecular Forces: Exquisite Selectivity during Oxidation of Olefins by Singlet Oxygen

Highly regioselective photooxidation of methyl cycloalkenes has been performed in an aqueous medium by selectively blocking two of the three allylic hydrogens through supramolecular steric effect. Hydrophobic, steric, and weak intermolecular C−H−π interactions are suggested to be responsible for the specific orientation of the olefin within a water-soluble, deep-cavity cavitand with eight carboxylic acid groups.

Electrophilic Substitution of Deep Cavity Cavitands: Selective Exo Functionalization of Molecular Concavity

[reaction: see text] The functionalization of deep-cavity cavitands via electrophilic substitution was investigated. In the parent structures, substitution occurs both at the exo position of the bowl-shaped hosts and on the convex face. Little or no endo substitution was observed. In contrast, derivatives in which methyl groups blocked the reaction sites on the convex face reacted selectively at the exo positions.

Photo-Fries reaction in water made selective with a capsule

The water soluble capsule formed by a deep cavity cavitand with eight carboxylic acid groups controls product distribution during photo-Fries rearrangement of naphthyl esters in water by restricting the mobility of primary singlet radical pair.

Templated Assembly of Water-Soluble Nano-Capsules: Inter-Phase Sequestration, Storage, and Separation of Hydrocarbon Gases

In aqueous solution, a deep-cavity cavitand was shown to self-assemble into dimeric nano-capsules via the sequestration of gaseous-phase hydrocarbons. The sequestration, assembly, and entrapment process was shown to be dependent on the hydrocarbon. Thus, by way of example, butane could be selectively sequestered from a propane-butane mixture.

A deuterated deep-cavity cavitand confirms the importance of C–H⋯X–R hydrogen bonds in guest binding

A deuterated cavitand host was examined for its affinity to a series of guests; for halogenated, preorganized guests binding was significantly stronger than the corresponding protium host.

Well-defined, organic nanoenvironments in water: the hydrophobic effect drives a capsular assembly.

The synthesis of a water-soluble, deep-cavity cavitand is reported. A blend of molecular curvature and amphiphilicity, this molecule has a hydrophobic concave surface and a hydrophilic convex surface. As a result, in aqueous solution and in the presence of a guest molecule, the host self-assembles to form a capsular assembly with an interior cavity large enough to entrap steroidal guests.

Towards Multi-generation Assemblies with Tetraphenylmethane Subunits

The synthesis of tetra(4-hydroxymethylphenyl)methane is reported. Possessing four benzyl alcohol groups, this molecule is anticipated to undergo self-assembly processes analogous to previously studied benzyl alcohol derived, deep-cavity cavitands (Gibb, C. L. D.; Stevens, E. D.; Gibb, B. C. Chem. Commun. 2000, 363–364). Towards such assembly processes, a bis-protected derivative was synthesized and its ability to undergo a macrocyclization reaction determined. Both the protection strategy employed and the macrocyclization approach are important models for more complex, repetitive self-assembly processes that can be envisaged with these types of molecules.

Reduced-symmetry deep-cavity cavitands

The syntheses of reduced-symmetry deep-cavity cavitands by two-stage stereoselective bridging with substituted benzal bromides is reported. Conditions for the optimal formation of the trisbridged derivatives were readily established. However, it was not possible to determine conditions which selectively promoted formation of either one of the two bisbridged species, or the monobridged compound, above the other products. A comparison of yields for A/B bisbridged derivatives verses A/C bisbridged derivatives may indicate that the one-pot formation of deep-cavity cavitands occurs primarily through the former species.

The self-assembly of benzyl alcohol derived deep-cavity cavitands: a new, highly efficient moiety for irreversible assemblies?

In the absence of an apparent (single) molecular template, the irreversible self-assembly of benzyl alcohol substituted, deep-cavity cavitands is shown to be a highly efficient process.

Deep-cavity cavitands: synthesis and solid state structure of host molecules possessing large bowl-shaped cavities

A novel family of deep-cavity cavitands is prepared via the first examples of the stereoselective bridging of resorcin- [4]arenes with carbon electrophiles.