Organic Capsule Research Articles

Interaction between Encapsulated Excited Organic Molecules and Free Nitroxides: Communication Across a Molecular Wall

Communication between two molecules, one confined and excited (triplet or singlet) and one free and paramagnetic, has been explored through quenching of fluorescence and/or phosphorescence by nitroxides as paramagnetic radical species. Quenching of excited states by nitroxides has been investigated in solution, and the mechanism is speculated to involve charge transfer and/or exchange processes, both of which require close orbital interaction between excited molecule and quencher. We show in this report that such a quenching, which involves electron-electron spin communication, can occur even when there is a molecular wall between the two. The excited state molecule is confined within an organic capsule made up of two molecules of a deep cavity cavitand, octa acid, that exists in the anionic form in basic aqueous solution. The nitroxide is kept free in aqueous solution. (1)H NMR and EPR experiments were carried out to ascertain the location of the two molecules. The distance between the excited molecule and the paramagnetic quencher was manipulated by the use of cationic, anionic, and neutral nitroxide and also by selectively including the cationic nitroxide within the cavity of cucurbituril. Results presented here highlight the role of the lifetime of the encounter complex in electron-electron spin communication when the direct orbital overlap between the two molecules is prevented by the intermediary wall.

Prussian Blue Nanocontainers: Selectively Permeable Hollow Metal–Organic Capsules from Block Ionomer Emulsion-Induced Assembly

Hollow polymer-based particles are useful for the encapsulation, protection, and release of active compounds. Adding a metal-organic coordination framework shell to nanocontainers is an attractive goal because it should help control their stability and permeability while yielding new properties and functions. We have discovered that polymer capsules with a Prussian blue analogue inner shell can be synthesized by emulsion-induced assembly of a metal-containing amphiphilic block ionomer. The capsules are selectively permeable and were used as nanocontainers to encapsulate and release a model compound. Further, these nanomaterials are tunable in size and organize into 2-D close-packed arrays in the solid state. Potential applications for these materials include the encapsulation and nanopatterning of pharmaceutical, biological, and catalytic compounds.

Ultrafast Singlet–Singlet Energy Transfer between an Acceptor Electrostatically Attached to the Walls of an Organic Capsule and the Enclosed Donor

Ultrafast Forster resonance energy transfer (FRET) between a donor (coumarin dye) and a cationic acceptor (rhodamine 6G) situated within and on the exterior walls, respectively, of a bimolecular capsule made up of anionic octa-acid (OA) is studied by femtosecond up-conversion. 1D and 2D 1H NMR spectral analyses reveal that donors coumarin-1, coumarin-153, and coumarin-480 form a 1:2 complex (guest to host) and are enclosed within the OA capsule. NMR and emission spectra suggest that the cationic acceptor rhodamine 6G is attached to the anionic exterior walls of the OA capsule. The acceptor emission displays a rise component of 1–3 ps which corresponds to a donor–acceptor distance (RDA) of ∼13 Å and thus indicates the occurrence of ultrafast FRET between the donor and acceptor at close contact.

The capsule: an organic skeletal structure in the Late Cretaceous belemnite Gonioteuthis from north-west Germany

An unusual, bilaterally symmetrical black structure that embraces the protoconch and the phragmocone and is overlain by a rostrum has been studied in the Santonian– early Campanian (Late Cretaceous) belemnite genus Gonioteuthis from Braunschweig, north-west Germany. The structure is here named the capsule. Energy dispersed spectrometry analyses of the capsule show a co-occurrence of sulphur with zinc, barium, iron, lead and titanium, suggesting their chemical association. The capsule was originally made of organic material that was diagenetically transformed into sulphur-containing matter. The material of the capsule differs from the chitin of the connecting rings in the same specimens. The capsule has a complex morphology: (1) ventral and dorsal wing-like projections that are repeated in a breviconic shape of the alveolus, (2) an aperture with lateral lobes and ventral and dorsal sinuses copied by growth lines and (3) a ventral ridge that fits with the position of the fissure in the rostrum. The alveolus in the most anterior part of the rostrum is crater-like. It is lined with thin, pyritized, laminated material, which appears to be the outermost portion of the capsule attached to the inner surface of the rostrum. A flare along the periphery of the alveolus marks a region where the rostrum was not yet formed, suggesting that the capsule extended beyond the rostrum. Modification of the skeleton in Gonioteuthis comprises a set of supposedly interrelated changes, such as innovation of the organic capsule, partial elimination of the calcareous rostrum and a diminishing of the pro-ostracum, resulting in the appearance of a new type of pro-ostracum that became narrower and shorter and lost the spatula-like shape and gently curved growth lines of a median field that are typical for the majority of Jurassic and Cretaceous belemnites. The partial replacement of a calcareous rostrum with an organic capsule in belemnitellids may have been an adaptive reaction to an unfavourable environmental condition, perhaps related to difficulties in calcium carbonate secretion during the Late Cretaceous that forced animals to reduce carbonate production and to secret an organic capsule around the protoconch and the phragmocone.

Restricted rotation due to the lack of free space within a capsule translates into product selectivity: photochemistry of cyclohexyl phenyl ketones within a water-soluble organic capsule

The rotational mobility of organic guest molecules when included within a confined capsule is restricted and this feature could be translated into product selectivity as established with the photochemical behavior of cyclohexyl phenyl ketones.

Encapsulation, storage and controlled release of sulfur hexafluoride from a metal–organic capsule

A metal-organic cage is shown to bind SF(6)--the most potent greenhouse gas known--and to release it under well-defined conditions.

Selective anion binding by a “Chameleon” capsule with a dynamically reconfigurable exterior

A new class of tetrahedral metal–organic capsules that can incorporate up to twelve different externally-directed amine residues is reported, allowing for very large dynamic libraries to be formed from mixtures of amines. Selectivity is observed both externally—more electron-rich amines are incorporated in favour of electron-poor amines—and internally—PF6− is bound in preference to CF3SO3− or BF4−.

A Colorimetric Sensor Array for the Detection of the Date‐Rape Drug γ‐Hydroxybutyric Acid (GHB): A Supramolecular Approach

γ-Hydroxybutyric acid (GHB), a colourless, odourless and tasteless chemical, has become one of the most dangerous illicit drugs of abuse today. At low doses, this drug is a central nervous system depressant that reduces anxiety and produces euphoria and relaxation, sedating the recipient. There is an urgent need for simple, easy-to-use sensors for GHB in solution. Here, we present a colorimetric sensor array based on supramolecular host-guest complexes of fluorescent dyes with organic capsules (cucurbiturils) for the detection of GHB.

Polymerizable gemini surfactants at solid/solution interfaces: Adsorption and polymerization on melamine formaldehyde particles and capsule fabrication

Organic capsules have been fabricated via three steps, by using the polymerizable gemini surfactant (1,2-bis(dimethyl(11-methacryloyloxy)undecylammonio) hexane dibromide, PC11-6-11) as a single wall component. In the first fabrication step, the surfactant spontaneously adsorbs on acid-dissolvable melamine formaldehyde (MF) particles in aqueous media. The adsorption isotherm data reveal that the adsorbed amount of PC11-6-11 (per chain) is greater than that of the corresponding monomeric surfactant ((11-methacryloyloxy)undecyltrimethylammonium bromide, PC11), resulting from the greater intermolecular association of PC11-6-11 at the solid/solution interface. The closely packed adsorbed layer of PC11-6-11 provides an opportunity to give a polymer thin film, as a result of in situ photo-polymerization on MF particles (in the second fabrication step) and subsequent acid dissolution of the core MF particles (in the third fabrication step). The dynamic light scattering (DLS) measurements have shown that the apparent hydrodynamic diameter of PC11-6-11 capsules is reversibly changed in response to a change in ionic strength: the increased background electrolyte concentration results in deswelling of the capsules, and vice versa. It seems likely that this swelling/deswelling behavior is primarily driven by the electrostatic interaction between quaternary ammonium groups within the polymerized film. We have also studied the capture and release capabilities of glucose into/from the capsule core and found that (i) glucose is encapsulated into the capsule core at high electrolyte concentrations and (ii) the glucose molecules encapsulated into the core are gradually released when the outer electrolyte solution is replaced by pure water. We believe, therefore, that the PC11-6-11 capsules fabricated here are useful as stimulus-responsive smart vehicles.

Induced‐Fit Formation of a Tetrameric Organic Capsule Consisting of Hexagram‐Shaped Amphiphile Molecules

Lieblingsgast: Nahezu sechseckige Amphiphile ordnen sich in einer wässrigen Methanol-Lösung um sphärische hydrophobe Gastmoleküle zu tetraedrischen organischen Kapseln an (siehe Bild). In Gegenwart von Adamantan wandelt sich eine hexamere Kapsel aus solchen sechseckigen Amphiphilen in eine 1.7 nm große tetramere Kapsel um, die das Adamantan-Templatmolekül einschließt.

Induced‐Fit Formation of a Tetrameric Organic Capsule Consisting of Hexagram‐Shaped Amphiphile Molecules

Fitting in: Hexagram-shaped amphiphiles self-assemble in the presence of a spherical, hydrophobic guest molecule to form a tetrahedron-shaped tetrameric organic capsule in an aqueous methanol solution (see picture). In the presence of adamantane, an aqueous solution of a box-shaped hexameric capsule composed of hexagram-shaped amphiphiles was converted into a novel 1.7 nm sized tetrameric capsule that has an encapsulated adamantane template molecule.

Template-Directed Synthesis of a Covalent Organic Capsule Based on a 3 nm-Sized Metallocapsule

A 4 nm-sized covalent organic capsule having 24 pyridyl groups was synthesized in extremely high yield (43% in three steps) using an octahedron-shaped metallocapsule as a template molecule. The entity was fully characterized by NMR and MALDI-TOF MS measurements. N-Methylation of the 24 pyridyl groups of the organic capsule produced a 5 nm-sized polycationic capsule, which is larger than the neutral precursory capsule because of the electrostatic repulsion between the positive charges on the pyridinium groups of the capsule.

Dual-response colorimetric sensor array for the identification of amines in water based on supramolecular host–guest complexation

Amines have been found as a challenging compound class in previous works on chemical tongues. Herein, we describe the successful application of libraries based on host–guest inclusion complexes in cyclodextrins (CDs) and cucurbiturils (CBs) for the discrimination of primary, secondary, tertiary, aliphatic and aromatic as well as linear and branched amines in water. Besides the clear need for new detection, identification and quantification techniques of organic compounds in water, the main advantage of our approach is that an array made by combining six simple basic dyes with seven commercial organic capsules allows a perfect discrimination among 14 amines ( see list in Table S1 in Supplementary data) with only very subtle structural differences.

Native Sn–Pb droplets in a zeolitic amygdale (Isle of Mull, Inner Hebrides)

Despite the particular scientific interest in the elements with high affinity to S and O 2, but found in zero-valence state in nature, the origin of these native minerals has been little explored and remains obscure. Here we describe unique Sn–Pb droplets found in a closed analcime–calcite amygdale collected from a basaltic unit cropping out at Carsaig Bay (Isle of Mull, Inner Hebrides). The droplets consist of intimate intergrowths of nearly pure Sn 0 and Pb 0 domains in proportion 88:12 and are enveloped in a thin, brownish film of organic composition. The occurrence of the Sn–Pb droplets in a closed amygdale, their relationship with the host analcime + calcite and their Pb isotope composition (which does not match any known anthropogenic Pb source) rule out the possibility of anthropogenic contamination and support the natural origin of the Sn–Pb alloy. The variable isotope (Pb, Sr, Nd) compositions in different members of the host basaltic sequence suggest that a parent basaltic magma was modified by crustal assimilation and post-emplacement alteration processes. Considering all possible explanations, it appears that the most likely source of Pb for the Sn–Pb alloy is a discrete basaltic unit with an isotopic composition comparable to the Antrim basalts (Northern Ireland). The amygdale phases, on the other hand, show isotopic evidence for incorporation of elements from both local basaltic and sedimentary units. The apparent isotopic disequilibrium between Sn–Pb droplets and amygdale phases indicates a complex, multi-stage fluid evolution. The occurrence of Sn–Pb droplets in organic capsules suggests that the droplets and the enveloping organic substances are co-precipitates. This implies that the transportation and deposition of Sn and Pb might have occurred through organometallic compounds. We assume interaction of seawater fluids carrying metals leached from basaltic rocks with hydrocarbons from sedimentary units as a prerequisite for the formation of the organometallic complexes. The zeolites lining the basaltic vesicles might have destabilized the migrating organo-Sn and Pb compounds causing their breakdown and precipitation of Sn–Pb alloy.

Recent developments in the chemical synthesis of inorganic porous capsules

The preparation of hollow inorganic capsules of defined shape, composition and with tailored properties is of immense scientific and technological interest. This article mainly features recent research progress towards various methods for preparing porous inorganic capsules. By choosing some typical inorganic porous capsules as examples, we present a comprehensive overview of synthetic strategies for inorganic capsules, and some typical organic capsules are also included. The available strategies are broadly categorized into three themes, i.e., hard-templating, soft-templating, and template-free routes, and each includes several well-established methods. The current methods show great success in controlling the size, composition, thickness, permeability and function of the finally achieved porous capsules. Applications of porous capsules in biomedicine, energy resources, environment protection and catalysis are also discussed. It is the intention of this contribution to provide a brief account of these research activities.

Cross‐talk between Adrenal Medulla and Adrenal Cortex in Stress

Response of the endocrine system to stress is characterized by the concomitant release of catecholamines from the adrenal medulla and of glucocorticoids from the adrenal cortex. Therefore, the activity of these two embryologically different endocrine organs that are united under one organ capsule has to be synchronized. The data summarized here indicate an involvement of intra-adrenal interactions in this coordination of the body's response to stress.

Consequences of controlling free space within a reaction cavity with a remote alkyl group: photochemistry of para-alkyl dibenzyl ketones within an organic capsule in water

With the aim of controlling free space available for the reactants, photochemical reactivity of several 4-alkyl dibenzyl ketones included within a water-soluble self-assembled organic capsule (octa acid) has been investigated. One and two-dimensional NMR spectroscopic techniques were employed to characterize the structure of the guest@host complexes. Free space controlled by the remote alkyl group influences the distribution of photoproducts. Correlation between the structures of the guest@host complexes and products selectivity suggested that the free space that could be controlled by a remote tether has a determining role during a photoreaction within the restricted space of the capsule. The fact that the same alkyl tether has no effect on the photobehavior of 4-alkyl dibenzyl ketones in hexane solution suggests that the role of substituents in free (solution) and restricted space (supramolecular assemblies) is different. The current observation suggests that rules of physical organic chemistry and photochemistry developed based on solution chemistry cannot be simply extended to supramolecular assemblies.

A Self-Assembled Organic Capsule Formed from the Union of Six Hexagram-Shaped Amphiphile Molecules

A discrete 2-nm-sized self-assembled organic capsule was formed from the union of six hexagram-shaped amphiphile molecules in aqueous methanol due to the hydrophobic effect, van der Waals forces, and CH-pi interactions between the chemical components. A couple of hexa-substituted benzene molecules were encapsulated inside the capsule in both solution and the solid state, as was evidenced by 1H NMR spectroscopy and single-crystal X-ray analysis.

Gold Nanoparticles in Organic Capsules: A Supramolecular Assembly of Gold Nanoparticles and Cucurbituril

Gold nanoparticles (<or=1 nm) have been encapsulated inside cucurbit[7]uril (CB[7]) by vapor deposition or chemical reduction in aqueous solutions. CB[7] has unique host properties compared with CB[5] and CB[6]. The particle size distribution obtained with CB[5] and CB[6] is similar to that obtained in the absence of CBs and the particles obtained are much too large to be incorporated inside the organic capsules. When gold nanoparticles are prepared inside CB[7] the resulting supramolecular assembly has shape-selective properties for gold interactions with amines, cyanide, and quaternary ammonium ions. Thus, CB[7] has the potential to be used in applications such as selective adsorption, sensing, and catalysis.

Temporal-spatial co-localisation of tissue transglutaminase (Tgase2) and matrix metalloproteinase-9 (MMP-9) with SBA-positive micro-fibres in the embryonic kidney cortex

Growth of the kidney is a complex process piloted by the collecting duct (CD) ampullae. The dichotomous arborisation and consecutive elongation of this tubular element determines the exact site and time for the induction of nephrons in the overlaying mesenchymal cap condensates. The mechanism by which the CD ampullae find the correct orientation is currently unknown. Recently, we have demonstrated micro-fibres that originate from the basal aspect of the CD ampullae and extend through the mesenchyme to the organ capsule. The micro-fibres are assumed to be involved in the growth and arborisation process of the CD ampulla. Therefore, we have investigated the specific distribution of the micro-fibres during branching morphogenesis. We have also analysed whether the micro-fibres co-localise with extracellular matrix (ECM)-modulating enzymes and whether the co-localisation pattern changes during CD ampulla arborisation. Micro-fibres were detected in all stages of CD ampulla arborisation. Tissue transglutaminase (Tgase2) co-localised with soybean agglutinin (SBA)-positive micro-fibres, whose presence depended upon the degree of CD branching. Matrix metalloproteinase-9 (MMP-9) also co-localised with micro-fibres, but its expression pattern was different from that for Tgase2. Western blotting experiments demonstrated that Tgase2 and MMP-9 co-migrated with SBA-labelled proteins. Thus, the micro-fibres are developmentally modulated by enzymes of the ECM in embryonic kidney cortex. These findings illustrate the importance of micro-fibres in directing CD ampulla growth.