Molecular Capsules Research Articles

Efficient Catalytic Epoxidation in Water by Axial N-Ligand-Free Mn-Porphyrins within a Micellar Capsule.

Epoxidation of styrenes is efficiently catalyzed by micelle-like molecular capsules providing Mn-porphyrins in water at room temperature. In contrast to usual Mn-porphyrin catalysts, the encapsulated Mn-porphyrin catalysts show higher reactivities (up to 1350 TON for 1 h) even without the addition of imidazole ligands. Spectroscopic studies and competitive-binding experiments demonstrate that the efficient catalytic cycle stems from the enforced proximity of the catalyst and substrates as well as the smooth replacement of the products by substrates in the hydrophobic cavity of the capsule.

Functional heterocyclic molecular inclusion in p-sulfonatocalix[5]arene and lanthanide(iii) complexes

p-Sulfonatocalix[5]arene either self-assemble in the presence of lanthanide ions into dense packed arrays of calixarenes or a grid-like arrangement comprising molecular capsules from adjacent bilayers, with the ‘molecular capsules’ confining small to large molecules.

Supramolecular encapsulation of benzocaine and its metabolite para-aminobenzoic acid by cucurbit[7]uril

Cucurbit[7]uril forms 1 : 1 molecular capsules with benzocaine (an anesthetic agent) and its metabolite para-aminobenzoic acid, respectively, in aqueous solution.

A fluorescent molecular capsule with a flexible polyaromatic shell for the detection of monoterpene compounds in water.

A new molecular capsule with a flexible fluorescent shell was formed by the quantitative self-complementary assembly of amphiphilic, U-shaped polyaromatic subunits in water. The capsule can fully encapsulate a variety of non-fluorescent monoterpene compounds (e.g., menthone, menthol, and p-menthane) in the hydrophobic cavity and act as a fluorescent supramolecular probe for recognizing the structural identity of the analytes by emissive signals in water at room temperature.

Solid-state assembly of a resorcin[6]arene in twin molecular capsules

The solid state structures of a resorcin[6]arene macrocycle crystallized in two different forms are here reported. In both instances, the molecule adopts a pinched cone conformation very similar to that of p-tert-butylcalix[6]arene. In one case, the resorcin[6]arene macrocycle self-assembles in a molecular capsule able to host toluene and ethyl acetate solvent molecules.

Form and function of molecular cups and capsules

Form and function of molecular cups and capsules

Engineering an iridium-containing metal-organic molecular capsule for induced-fit geometrical conversion and dual catalysis.

By introducing photoactive fac-tris(2-phenylpyridine)iridium moieties as a ligand backbone to constrain the coordination geometry of cobalt ions, a multifunctional Ir2Co3-type capsule was achieved and showed induced-fit capsule-capsule conversion by cooperative binding one carbonate anion with the equatorial Co(ii) centers. The capsule combined photocatalysis and transition metal activation synergistically and exhibited efficient catalytic ability on visible light-activated α-trichloromethylation.

Gadolinium(iii)-mediated multi-component confinement of imidazolium cations in p-sulfonated calix[4]arene

Multi-component materials having supermolecules made up of mono- or bis-imidazolium cations shrouded by two p-sulfonated calix[4]arenes essentially form molecular capsules as part of the extended structure, with their formation mediated by Gd(iii), which is incorporated only in complex I.

Self-Assembled Supramolecular Structures as Catalysts for Reactions Involving Cationic Transition States

Self-assembled supramolecular structures represent easily accessible systems for the study of enzyme-like catalysis. The hydrophobic cavities of the assemblies provide a distinct chemical environment that can lead to unusual chemo- and stereoselectivities. This review summarizes the application of such host structures in the catalysis of reactions involving cationic transition states and includes detailed discussion of mechanisms and substrate–host interactions. The literature up to April 2015 is covered. 1 Introduction 2 Molecular Capsules: Structures and Background 3 Catalyzed Reactions 4 Summary and Outlook

Assembling of Supramolecular Capsules with Resorcin[4]arene and Calix[n]arene Building Blocks

Molecular capsules are containers endowed with isolated nanometer-sized cavities. In particular, supramolecular capsules generated by exploiting hydrogen bonds, metal-coordination bonds and/or hydrophobic effects represent an intriguing version of these fascinating molecules, and an impressive challenge for synthetic chemists. Resorcin[4]arene-based cavitands and conformationally preorganized calixarenes are two classes of receptors largely used as building blocks for the construction of these assemblies. This review focuses on the capsular self-assembly of suitably functionalized building blocks, analyzing from time to time the main driving force(s) involved for their formation. Keywords: Calix[n]arenes, hydrogen bond, metal-coordination, molecular recognition, resorcin[4]arene, self-assembly, supramolecular capsules.

ChemInform Abstract: A Unique Fluoride Nanocontainer: Porous Molecular Capsules Can Accommodate an Unusually High Number of “Rather Labile” Fluoride Anions.

AbstractPorous molecular nanocontainers of the {Mo132} Keplerate [{(MoVI)MoVI5O21 (H2O) 5F}12{MoV2O4(F) (H2O)}30]·≈250H2O (I) precipitates from an aqueous HF solution of [NH4]72 [{(Mo)Mo5O21 (H2O)6}12{Mo2O4 (CO3)}30]·≈260H2O (II) and Me2NH2F (air, 5 d, 66% yield).

Coordination of Ln3+ Ions to Perhydroxycucurbit[5]uril and the Formation of Supramolecular Self‐Assemblies in the Presence of [SiW12O40]4– Anions and Transition Metal Salts – Potential Application in the Isolation of Light Lanthanides

AbstractThe coordination and supramolecular assemblies of lanthanide cations and perhydroxycucurbit[5]uril {(HO)10Q[5]} in the presence of [SiW12O40]4– anions and transition metal salts show significant differences as the lanthanide atomic number increases. The molecular capsule (HO)10Q[5] coordinates with the light lanthanide cations Ce3+, Pr3+, Nd3+, Sm3+, Eu3+, Gd3+, and Tb3+ but does not coordinate with heavier Ln3+ cations. However, (HO)10Q[5]/Na+‐based molecular capsules form in the presence of the heavier lanthanide cations Ho3+, Er3+, Tm3+, Yb3+, and Lu3+ under the same synthetic conditions. These differences could be key in establishing a strategy for the isolation of light lanthanides from their heavier counterparts.

Halogen bonding molecular capsules.

Molecular capsules based solely on the interaction of halogen bonding (XB) are presented along with their host-guest binding properties in solution. The first example of a well-defined four-point XB supramolecular system is realized by decorating resorcin[4]arene cavitands with polarized halogen atoms for dimerization with tetra(4-pyridyl) resorcin[4]arene cavitands. NMR binding data for the F, Cl, Br, and I cavitands as the XB donor show association constants (Ka ) of up to 5370 M(-1) (ΔG283 K =-4.85 kcal mol(-1) , for I), even in XB-competitive solvent, such as deuterated benzene/acetone/methanol (70:30:1) at 283 K, where comparable monodentate model systems show no association. The XB capsular geometry is evidenced by two-dimensional HOESY NMR, and the thermodynamic profile shows that capsule formation is enthalpically driven. Either 1,4-dioxane or 1,4-dithiane are encapsulated within each of the two separate cavities within the XB capsule, with of up to Ka =9.0 10(8) M(-2) (ΔG283 K =-11.6 kcal mol(-1) ).

Investigating the formation of "molybdenum blues" with gel electrophoresis and mass spectrometry.

The reduction of solutions of acidified molybdate leads to the formation of a family of nanostructured molybdenum blue (MB) wheels which are linked together in a series of complex reaction networks. These networks are complex because the species which define the nodes are extremely labile, unstable, and common to many different networks. Herein, we combine gel electrophoresis and electrospray ionization mass spectrometry (ESI-MS) to investigate the effect of the pH and the ratio of reactants and reducing agents, R (R = [S2O4(2-)]/[MoO4(2-)]), on the complex underlying set of equilibria that make up MBs. By mapping the reaction parameter space given by experimental variables such as pH, R, solvent medium, and type of counterion, we show that the species present range from nanostructured MB wheels (comprising ca. 154 Mo atoms) to smaller molecular capsules, [(SO3)2Mo(V)2Mo(VI)16O54](6-) ({S2Mo18}), and templated hexameric [(μ6-SO3)Mo(V)6O15(μ2-SO3)3](8-)({S4Mo6}) anions. The parallel effects of templation and reduction on the self-assembly process are discussed, taking into consideration the Lewis basicity of the template, the oxidation state of the Mo centers, and the polarity of the reaction medium. Finally, we report a new type of molecular cage (TBA)5[Na(SO3)2(PhPO3)4Mo(V)4Mo(VI)14O49]·nMeCN (1), templated by SO3(2-) anions and decorated by organic ligands. This discovery results from the exploration of the cooperative effect of two anions possessing comparable Lewis basicity, and we believe this constitutes a new synthetic approach for the design of new nanostructured molecular metal oxides and will lead to a greater understanding of the complex reaction networks underpinning the assembly of this family of nanoclusters.

A unique fluoride nanocontainer: porous molecular capsules can accommodate an unusually high number of "rather labile" fluoride anions.

The present work refers to the challenging issue of fluoride anion recognition/binding in water by taking advantage of the unique possibilities offered by the porous molecular nanocontainers of the {Mo132} Keplerate type allowing the study of a variety of new phenomena. Reaction of the highly reactive carbonate-type capsule with aqueous HF results in the release of carbon dioxide and integration of an unprecedentedly large number of fluoride anions--partly as coordinated ligands at both the pentagonal units and the linkers, partly as a disordered water/fluoride assembly inside the cavity. The internal assembly and some of the fluoride ligands are easily released, which provides interesting options for future studies regarding coordination chemistry and catalysis under confined conditions.

A Unique Fluoride Nanocontainer: Porous Molecular Capsules Can Accommodate an Unusually High Number of “Rather Labile” Fluoride Anions

AbstractThe present work refers to the challenging issue of fluoride anion recognition/binding in water by taking advantage of the unique possibilities offered by the porous molecular nanocontainers of the {Mo132} Keplerate type allowing the study of a variety of new phenomena. Reaction of the highly reactive carbonate‐type capsule with aqueous HF results in the release of carbon dioxide and integration of an unprecedentedly large number of fluoride anions—partly as coordinated ligands at both the pentagonal units and the linkers, partly as a disordered water/fluoride assembly inside the cavity. The internal assembly and some of the fluoride ligands are easily released, which provides interesting options for future studies regarding coordination chemistry and catalysis under confined conditions.

A chromogenic molecular capsule attributable to dipolar amide resonance structure.

A new chromogenic, self-assembled molecular capsule G@22 is developed by introducing four (N,N-dimethyl-4-aminophenyl) azobenzyl moieties on the upper rim of a resorcin[4]arene-based amidoimino-cavitand. The tuning of conjugation between amido and (N,N-dimethyl-4-aminophenyl)azobenzyl groups by acid-base titration allows naked-eye detection of molecular capsule formation.

Bio-inspired self-assembled molecular capsules

Bowl shaped molecules are useful for making molecular capsules with suitable non-covalent bonds. We appended cyclotriguaiacylene with biologically important adenine and thymine to make capsule in solution by hydrogen bonding.

Diffusion NMR of molecular cages and capsules.

In the last decade diffusion NMR and diffusion ordered spectroscopy (DOSY) have become important analytical tools for the characterization of supramolecular systems in solution. Diffusion NMR can be used to glean information on the (effective) size and shape of molecular species, as well as to probe inter-molecular interactions and can be used to estimate the association constant (Ka) of a complex. In addition, the diffusion coefficient, as obtained from diffusion NMR, is a much more intuitive parameter than the chemical shift for probing self-association, aggregation and inter-molecular interactions. The diffusion coefficient may be an even more important analytical parameter in systems in which the formed supramolecular entity has the same symmetry as its building units, when there is a large change in the molecular weight, where many molecular species are involved in the formation of the supramolecular systems, and when proton transfer may occur which, in turn, may affect the chemical shift. Some of the self-assembled molecular capsules and cages prepared in the last decade represent such supramolecular systems and in the present review, following a short introduction on diffusion NMR, we survey the contribution of diffusion NMR and DOSY in the field of molecular containers and capsules. We will first focus on the role played by diffusion NMR in the field of hydrogen bond driven self-assembled capsules. We then survey the contributions of diffusion NMR and DOSY to the study and characterization of metal-ligand cages and capsules. Finally, we describe a few recent applications of diffusion NMR in the field of hydrophobic, electrostatic and covalent containers.

A hydrogen bonded molecular capsule versus a 3D network of tripodal organopolysilanols.

1,3,5-Triethylbenzene based tripodal trisilanols were synthesized. The X-ray crystal structures of trisilanols showed capsule formation as well as non-capsular network formation using silanol hydrogen bonds. The (1)H NMR and ESI-mass spectroscopy experiments for solution state binding supported encapsulation of the halide ions in the cavity of the molecular capsule with a C3 symmetry.