Capsular Complexes Research Articles

Advancement of Periosteal and Capsular Complexes With or Without Augmentation Using a Free Graft From Lower Extensor Retinaculum: A Comparative Study With Propensity Score Matching.

This study compared the outcome of the L-shaped (L-AD) advancement of the periosteal and capsular complexes with or without augmentation using a free graft of the lower extensor retinaculum (AUG) in patients with chronic lateral ankle instability. A matched pair analysis was performed of retrospectively collected medical records of patients undergoing lateral ankle ligament repair who had completed at least 2 years of follow-up. Patients who underwent L-AD with AUG and patients undergoing L-AD alone were matched for age, sex, stress radiography findings, and body mass index. Patients with general joint laxity, osteoarthritic changes in the ankle, and subtalar symptoms and who underwent simultaneous surgical treatment for conditions other than that for lateral ankle ligament were excluded. A total of 46 patients were included in the study (23 patients in each group). Clinical outcome scores and postoperative mechanical instability were compared. The median American Orthopaedic Foot & Ankle Society (AOFAS) score improved significantly (P < .001) from 72 to 97 in the L-AD alone group and from 77 to 100 in the L-AD with AUG group. The mean (±SD) talar tilt angles improved significantly from 11.1 to 4.7 degrees postoperatively (P < .001) in the L-AD alone group vs 9.7 to 5.2 degrees (P < .001) in the L-AD with AUG group. The mean anterior drawer distances were improved significantly postoperatively from 6.4 to 4.7 mm (P < .001) in the L-AD alone group, and from 6.5 to 4.5 mm (P < .001) in the L-AD with AUG group. The L-AD technique significantly improved AOFAS scores and mechanical instability of ankles with chronic lateral instability with a very low complication rate. Additional augmentation using a free graft showed no advantages in the ankle with a talar tilt of <20 degrees. Level III, retrospective case-control series.

Two‐ and Three‐Phase Self‐assembly of Molecular Capsules

AbstractTwo‐ and three‐phase molecular encapsulations of Me4N+ or C7H7+ in the hydrogen‐bonded dimers of resorcin[4]arene tetraphosphates enable ion pair separations, dissolution of solid capsule components, and stabilization of capsule‐separated ion pairs in solution. Self‐assembly of the capsular ion pairs, the exchange of the encapsulated cations and external anions as well as the formation of heterodimeric capsular complexes are slow on hours time scale in heterogeneous systems and instantaneous in solutions. Spectroscopic studies and molecular modeling related the properties of the capsule‐separated ion pairs to the energies of induced conformational changes, hydrogen bonding, host‐guest interactions, ion pair separation, and the relative polarity of the solvent.

Cavitand Complexes in Aqueous Solution: Collaborative Experimental and Computational Studies of the Wetting, Assembly, and Function of Nanoscopic Bowls in Water.

Water is the dominant liquid on Earth. Despite this, the main focus of supramolecular chemistry research has been on binding and assembly events in organic solvents. This arose because it is more straightforward to synthesize organic-media-soluble hosts and because of the relative simplicity of organic solvents compared to water. Nature, however, relies on water as a solvent, and spurred by this fact, supramolecular chemists have recently been making forays into the aqueous domain to understand water-mediated non-covalent interactions. These studies can benefit from the substantial understanding of the hydrophobic effect and electrostatic interactions developed by physical chemists. Nearly 20 years ago, the Gibb group first synthesized a class of water-soluble host molecules, the deep-cavity cavitands, that possess non-polar pockets that readily bind non-polar moieties in aqueous solution and are capable of assembling into a wide range of complexes with distinct stoichiometries. As such, these amphipathic host species are ideal platforms for studying the role of negatively curved features on guest complexation and the structural requirements for guided assembly processes driven by the hydrophobic effect. Here we review the collaborative experimental and computational investigations between Gibb and Ashbaugh over the past 10 years exploring questions including the following: How does water wet/solvate the non-polar surfaces of non-polar pockets? How does this wetting control the binding of non-polar guests? How does wetting affect the binding of anionic species? How does the nature and size of a guest size impact the assembly of cavitand hosts into multimeric capsular complexes? What are the conformational motifs of guests packed within the confines of capsular complexes? How might the electrostatic environment engendered by hosts impact the properties and reactivity of internalized guests?

Chalcogen Bonding and Hydrophobic Effects Force Molecules into Small Spaces.

Supramolecular capsules are desirable containers for the study of molecular behavior in small spaces and offer applications in transport, catalysis, and material science. We report here the use of chalcogen bonding to form container assemblies that are stable in water. Cavitands 1-3 functionalized with 2,1,3-benzoselenadiazole walls were synthesized in good yield from resorcin[4]arenes. The solid-state single-crystal X-ray structure of 3 showed a dimeric assembly cemented together through multiple Se···N chalcogen bonds. Binding of hydrophobic and amphiphilic guests in D2O was investigated by 1H NMR methods and revealed host-guest assemblies of 1:1, 2:1, and 2:2 stoichiometries. Small guests such as n-hexane or cyclohexane assembled as 2:2 capsular complexes, larger guests like cyclohexane carboxylic acid or cyclodecane formed 1:1 cavitand complexes, and longer linear guests like n-dodecane, cyclohexane carboxylic acid anhydride, and amides created 2:1 capsular complexes. The 2:1 complex of the capsule with cyclohexane carboxylic acid anhydride was stable over 2 weeks, showing that the seam of chalcogen bonds is "waterproof". Selective uptake of cyclohexane over benzene and methyl cyclohexane over toluene was observed in aqueous solution with the capsule. Hydrophobic forces and hydrogen-bonding attractions between guest molecules such as 3-methylbutanoic acid stabilized the assemblies in the presence of the competing effects of water. The high polarizability and modest electronegativity of Se provide a capsule lining complementary to guest C-H bonds. The 2,1,3-benzoselenadiazole walls impart an unusually high magnetic anisotropy to the capsule environment, which is supported by density functional theory calculations.

Theoretical studies of capsular complexes of C2V-symmetrical resorcin[4]arene tetraesters with tetramethylammonium cation

Dimeric capsular complexes of two C2V-symmetrical resorcin[4]arene tetraesters with tetramethylammonium cation have been analyzed by a number of theoretical tools to rationalize the experimentally observed preferential formation of heterodimeric complexes over homodimeric ones. These tools range from purely empirical (force fields) to quantum chemical (density-functional theory) approaches. The importance of solvent and thermal effects on the final stabilities of capsular complexes has also been addressed. It has been clearly demonstrated that the quality of results obtained with the empirical force fields improves through the respective molecular dynamics simulations employing Mulliken atomic charges in both gas phase and in a solvent. On the quantum chemical side, density-functional theory calculations including the solvent model based on density (SMD) and thermal corrections resulted in a correct energetic preference of a heterodimeric structure over homodimeric ones.

Supramolecular-Surface Photochemistry: Assembly and Photochemistry of Host-Guest Capsules on Silica Surface.

Host cavitands and organic guest molecules independently adsorbed on silica particles when mixed and shaken in the presence of a few drops of water underwent intra- and interparticle migration to form capsular complexes that were not formed either in water or organic solvents. Importance of cavitand migration and tumbling on silica surface was established by demonstrating that covalently linked cavitands do not form capsular complexes. The encapsulated guests exhibited selective photochemistry as they do within an organic capsule in solution.

Template-directed self-assembly of dynamic covalent capsules with polar interiors.

Chiral polyimine molecular capsules with polar interiors have been prepared through template covalent dynamic self-assembly. An aryl-extended tetraaldehyde calix[4]pyrrole scaffold was condensed with suitable diamines as linkers using templates for efficient self-assembly. The capsular complexes were characterized in solution, gas phase and the solid-state. Unprecedented transfer of asymmetry was observed from a chiral diamine linker to the resulting supramolecular capsular assembly.

Cavitand Chemistry – Towards Metallocapsular Catalysts

Two diphosphanes with widely separated P centres and cores that consists of two covalently linked resorcinarene cavitands were synthesised. Their ability to bind transition‐metal ions in a chelating fashion with the concomitant formation of capsular complexes was shown in their reactions with metal centres with two available binding sites. The solid‐state structure of one of the complexes, a capsule with a partially embedded “trans‐PtCl2” unit, was determined by single‐crystal X‐ray diffraction. Upon reaction with SnCl2, this complex developed good activity for the hydroformylation of styrene. Its activity and selectivity towards the branched aldehyde were significantly superior to those observed for the reference complex trans‐PtCl2L2, in which L is a monophosphane monocavitand ligand. The higher activity is likely to reflect the initial formation of a hydrido intermediate with a somewhat distorted trigonal‐bipyramidal structure that facilitates the intracapsular olefin/PtH insertion step. The observed aldehyde selectivity is probably controlled by the shape of the capsule, which is sterically better suited for hosting a branched Pt–alkyl unit than a linear one.

MANAGEMENT OF MYCOBACTERIUM CHELONAE ENDOPHTHALMITIS WITH COMPLETE SURGICAL DEBRIDEMENT.

To report the clinical course and histopathologic findings of two consecutive patients with resolution of Mycobacterium chelonae endophthalmitis and favorable visual outcomes after complete removal of intraocular implants and lens capsular complexes and prolonged sensitivity-guided combination antibiotic therapy. Medical records and histopathologic findings were reviewed for two consecutive patients with M. chelonae endophthalmitis. Two consecutive patients with M. chelonae endophthalmitis had prolonged clinical courses with refractory endophthalmitis before complete removal of intraocular implants and lens capsular complexes. One patient had histopathologic evidence of lens remnant-associated acid-fast bacilli. Surgical explantation of intraocular implants and lens capsular complexes appears to play an important role in the management of M. chelonae endophthalmitis, which may be closely associated with crystalline lens remnants.

α,ω-Alkanediyldiammonium dications sealed within calix[5]arene capsules with a hydrophobic bayonet-mount fastening

A combined XRD and 1H NMR study revealed that two molecules of tetrakis-(tert-butyloxycarbonylmethoxy)-calix[5]arene carboxylic acid are able to efficiently encapsulate α,ω-diaminoalkanes of suitable length as a result of proton-transfer-mediated recognition. In the case of 1,10-diaminodecane and 1,11-diaminoundecane, rim-to-rim attractive van der Waals interactions drive the formation of capsular complexes with a packing coefficient close to 70%. The two calixarene bowls in these capsules are seen in an eclipsed conformation. On the other hand, when the longer 1,12-diaminododecane guest is used, a quasi-capsular complex is formed in which the capsule seal is lost and the two calixarenes are arranged in a staggered conformation as a result of a reciprocal rotation of the two facing macrocyclic cavities. A comparison with similar capsular complexes confirms that a hydrophobic ‘bayonet-mount’ fastening is mandatory for the encapsulation of suitably sized guests.

Cationic Tripodal Receptor Assisted Formation of Anion and Anion–Water Clusters: Structural Interpretation of Dihydrogen Phosphate Cluster and Sulfate–Water Tetramer [(SO4)2–(H2O)2]4–

Well-defined anion and anion–water clusters based on tetrahedral oxyanions are reported herein. Self-assembled infinite dihydrogen phosphate anion clusters of 10 H2PO4– ions consist of a hexameric cluster linked to tetrameric and trimeric clusters. Octahedrally arranged discrete anionic [Na(ClO4)6]5– cluster is found to stabilize by self-complementary H-bonding and electrostatic interactions in noncapsular complexes. Our findings also indicate the presence of discrete sulfate–hydrogen sulfate anion trimers [SO4—(HSO4)2]4– and sulfate–water tetramers [(SO4)2—(H2O)2]4– in the bimolecular capsular complexes of the tripodal receptor. All complexes were well characterized by FT-IR and NMR spectroscopies, TGA, DSC, and XRD.

Encapsulation of divalent tetrahedral oxyanions of sulfur within the rigidified dimeric capsular assembly of a tripodal receptor: first crystallographic evidence of thiosulfate encapsulation within neutral receptor capsule

A simple tris(2-aminoethyl)amine based meta-chloro substituted tripodal thiourea receptor L has been extensively studied with two divalent oxyanions of sulfur, such as sulfate and thiosulfate, with identical dimensionality. The solid state crystal structure of the anion complexes with L reveal that the anions are encapsulated within the dimeric rigid capsular assembly of the receptor via N-H···anion interactions. To the best of our knowledge this is the first report on the encapsulation of thiosulfate within dimeric capsular assembly of a neutral receptor. The tight capsular sizes for both anion complexes are quite comparable, whereas the coordination mode of the anions and the hydrogen bonding parameters are significantly varied. The three dimensional solid state structural orientations of the capsular complexes are mainly governed by the Cl···Cl (for thiosulfate complex) and Cl···S (for sulfate complex) halogen bonding interactions. The solution-state binding and encapsulation of oxyanions by N-H···anion hydrogen bonding has also been confirmed by quantitative (1)H NMR titration and 2D NOESY NMR experiments. Both the experiments confirm that in contradiction of 2:1 solid state binding, in solution the studied anions are bound within the pseudocavity of the receptor with 1:1 binding stoichiometry. Moreover, the change in chemical shifts of thiourea -NH protons and the binding constant values suggest the receptor-sulfate interaction is more energetically favorable compared to the receptor thiosulfate interaction.

Capsular Complexes of Nonpolar Guests with Octa Amine Host Detected in the Gas Phase

Nanocapsules, made up of the deep cavitand octa amine and several guests, were prepared in aqueous acidic solution and were found to be stable in the gas phase as detected by electrospray ionization mass spectrometry (ESI-MS). The observed gas phase host-guest complexes contained five positive charges and were associated with several acid molecules (HCl or HBr).

Complexation of Sc3N@C80 Endohedral Fullerene with Cyclic Zn-Bisporphyrins: Solid State and Solution Studies

We report the synthesis of two cyclic β-pyrrole unsubstituted meso-tetraphenyl bisporphyrins in which the porphyrin units are connected by two 2,3-hexadiynyl-1,6-dioxo or two hexyl-1,6-dioxo spacers, respectively. Both cyclic porphyrin dimers exist in solution as mixtures of two conformational isomers. In the solid state, the receptor with diynyl spacers forms a 1:1 complex with the icosahedral (I(h)) isomer of the trimetallic nitride endohedral fullerene Sc(3)N@C(80). In this complex the receptor adopts a scoop-shaped conformation having a dihedral angle of 87.25° between the two porphyrin planes. The hexyl spaced analogue, however, adopts a similar conformation upon encapsulation of one molecule of Sc(3)N@C(80) in a self-assembled dimeric capsule. The capsular complexes pack in columns and render the fullerene units completely isolated. In toluene solution, (1)H NMR experiments indicate that the endohedral fullerene Sc(3)N@C(80) is exclusively bound by the expanded isomer of both dimers. UV-vis and fluorescence titration experiments confirmed the existence of strong π-π interactions between the fullerene Sc(3)N@C(80) and the flexible bisporphyrin dimer with hexyl spacers. At micromolar concentration, the flexible receptor forms only a 1:1 complex with the endohedral fullerene with stability constant value of K(a) = 2.6 ± 0.3 × 10(5) M(-1).

Solvent denaturation of supramolecular capsules assembled via the hydrophobic effect

The organic co-solvent induced denaturation of a series of capsular complexes formed between trioxolane guests and a water-soluble deep-cavity cavitand was examined. The results obtained demonstrate a wide range of denaturation properties, and suggest the important factors governing capsule stability.

Capsular polysaccharide of the bacterium Azospirillum lipoferum Sp59b: Structure and antigenic specificity

Antigenic differences were revealed between the cell wall outer membrane lipopolysaccharides and the capsular high molecular weight bioglycans for a typical strain of the nitrogen-fixing rhizobacterium Azospirillum lipoferum Sp59b using antibodies prepared against the homologous lipopolysaccharide and lipopolysaccharide-protein complex. From the capsular lipopolysaccharide-protein and polysaccharide-lipid complexes of A. lipoferum Sp59b, polysaccharides were isolated and their structure was for the first time established in Azospirillum by monosaccharide analysis which included determination of the absolute configurations, methylation, O-deacetylation, and one- and two-dimensional NMR spectroscopy. The polysaccharides of the capsular complexes were shown to have identical structure of the branched tetrasaccharide repeating unit, which differs from the structure of the O-specific polysaccharide within the outer membrane lipopolysaccharide of this strain.

Van der Waals Nanocapsular Complexes of Amphiphilic Calixarenes

The inclusion complexes of p-alkanoyl calix[4]arenes with alkanoyl chain lengths from C4 to C10 (C4OH−C10OH) and tetrahydrofuran, dioxane, and some halocarbons as guests were prepared and their structures were studied by single-crystal X-ray diffraction, TGA, DSC, and 13C CP-MAS NMR. The complexes of C6OH are nanocapsules stabilized by van der Waals interactions between the calixarene cavity as extended by the alkanoyl chains and one or more guest molecules. The stability of the nanocapsule compounds depends strongly on the size and saturation vapor pressure of the guests, as well as on the presence of halogen atoms in the guest molecule. In the presence of the latter, the C6OH capsular complexes have markedly lower stability and easily eject the guests. C4OH calixarene prefers to form open-container type complexes, whereas it is possible to prepare quasicapsular complexes of C10OH with dioxane as a guest. In this case, two dioxane molecules are encapsulated by two molecules of calixarene and the third dioxane molecule provides interlayer stabilization of the crystal lattice by hydrogen bonding of dioxane oxygens with OH groups of the neighboring calixarenes. The general trends in the formation and stability of van der Waals capsular complexes of amphiphilic calixarenes are discussed, as well as how they relate to the formation of solid lipid nanoparticles.

ChemInform Abstract: The Design of Molecular Hosts, Guests, and Their Complexes

The origins, definitions, tools, and guiding principles of host-guest chemistry are developed. Perching, nesting, and capsular complexes are exemplified through molecular model and crystal structure comparisons. The degree of preorganization of a host for binding is a central determinant of its binding power. Complementarity of binding site placement in host and guest is a central determinant of structural recognition in complexation. Examples are given of chiral recognition in complexation, of partial transacylase mimics, of caviplexes, and of a synthetic molecular cell.

The design of molecular hosts, guests, and their complexes

The origins, definitions, tools, and guiding principles of host-guest chemistry are developed. Perching, nesting, and capsular complexes are exemplified through molecular model and crystal structure comparisons. The degree of preorganization of a host for binding is a central determinant of its binding power. Complementarity of binding site placement in host and guest is a central determinant of structural recognition in complexation. Examples are given of chiral recognition in complexation, of partial transacylase mimics, of caviplexes, and of a synthetic molecular cell.

The Design of Molecular Hosts, Guests, and Their Complexes

The origins, definitions, tools, and guiding principles of host-guest chemistry are developed. Perching, nesting, and capsular complexes are exemplified through molecular model and crystal structure comparisons. The degree of preorganization of a host for binding is a central determinant of its binding power. Complementarity of binding site placement in host and guest is a central determinant of structural recognition in complexation. Examples are given of chiral recognition in complexation, of partial transacylase mimics, of caviplexes, and of a synthetic molecular cell.