Encapsulated Molecule Research Articles

Adaptations of guest and host in expanded self-assembled capsules

Reversible encapsulation complexes create spaces where two or more molecules can be temporarily isolated. When the mobility of encapsulated molecules is restricted, different arrangements in space are possible, and new forms of isomerism ("social isomerism") are created: the orientation of one encapsulated molecule influences that of the other in the confined space. Expansion of a capsule's length is possible through addition of small-molecule spacer elements. The expanded capsules have dimensions that permit the observation of social isomerism of two identical guests, and they adopt arrangements that properly fill the host's space. The host also can adapt to longer guests by incorporating additional spacers, much as protein modules are added to a viral capsid in response to larger genomes. Arachidonic and related fatty acid derivatives act in this way to induce the assembly of further extended capsules having sufficient length to accommodate them.

Nonvolatile Memory Elements Based on the Intercalation of Organic Molecules Inside Carbon Nanotubes

We propose a novel class of nonvolatile memory elements based on the modification of the transport properties of a conducting carbon nanotube by the presence of an encapsulated molecule. The guest molecule has two stable orientational positions relative to the nanotube that correspond to conducting and nonconducting states. The mechanism, governed by a local gating effect of the molecule on the electronic properties of the nanotube host, is studied using density functional theory. The mechanisms of reversible reading and writing of information are illustrated with a F4TCNQ molecule encapsulated inside a metallic carbon nanotube. Our results suggest that this new type of nonvolatile memory element is robust, fatigue-free, and can operate at room temperature.

Synthetic Micelle Sensitive to IR Light via a Two-Photon Process

A micellar assembly of molecules constituted of poly(ethylene glycol) as the hydrophilic component and 2-diazo-1,2-naphthoquinone as the hydrophobic component was shown to be destroyed in a two-photon photoreaction triggered by infrared light with release of an encapsulated fluorescent probe molecule.

Host to Guest Energy Transfer in a Self-assembled Supramolecular Nanocage Observed by Picosecond Fluorescence Quenching

Abstract The host–guest energy transfer process in a self-assembled system was investigated by picosecond time-resolved fluorescence spectroscopy. A self-assembled coordination nanocage (Pd6L4) was photoexcited and the appearance of the fluorescence from an encapsulated guest acridine dye molecule was observed. The time constant (1.3 ns) as well as the efficiency (9%) of the energy transfer from the nanocage to the guest molecule was determined.

Dimeric capsules of tetraurea calix[4]arenes. MD simulations and X-ray structure, a comparison

The single crystal X-ray structure of a homodimer of a tetra(tolylurea) calix[4]arene including a tetraethylammonium cation as guest shows an expansion of the capsule and a distortion of its shape, in comparison to the structure of a similar dimer with an encapsulated benzene molecule. Thus, only 8 of 16 possible hydrogen bonds are present in the hydrogen bonded belt holding together the two hemispheres. The encapsulated cation is disordered over two equivalent positions with two methyl groups pointing to the equator, while two methyl groups pointing to the poles form CH–π interactions with the inner surfaces of the calixarene cavities. MD simulations are in agreement with the distorted X-ray structure for a short simulation time of 1–2 ns with a given orientation of the included cation and approach for longer simulation times (9 ns) the fourfold symmetry found by 1H NMR spectroscopy in solution.

Cyclo-[Ni(μ2-SPh)2]9and cyclo-[Ni(μ2-SPh)2]11: new oligomeric types of toroidal nickel(ii) thiolates containing geometrically unprecedented 9- and 11-membered ring systems

Two new oligomeric types of toroidal nickel(II) monothiolate ring systems, cyclo-[Ni(SPh)2]11 (1) and cyclo-[Ni(SPh)2]9 (2), containing heretofore unknown 11-membered (n = 11) and 9-membered (n = 9) ring-geometries, respectively, are reported. Our initial isolation of 1 was as an unexpected by-product that resulted from unsuccessful attempts to produce crystalline nanostructural gold thiolate clusters from reactions of alkyl/phenyl thiols with the recently prepared nanostructural [Au16Ni24(CO)40]4− cluster. The unique architecture of 1 led to a designed preparation of it by a direct synthetic route involving reactions of PhSNa with Ni(ClO4)2 in THF or DMF. Slow addition of the reactants at low temperature afforded two crystal forms of 1: namely, the previously isolated triclinic crystals (P) as well as solvated monoclinic crystals (C2/c) (1a). Normal mixing of the reactants at room temperature gave rise to a trigonal crystal form (P12/c) that was determined to be cyclo-[Ni(SPh)2]9 (2). The atomic arrangements and stoichiometries of both 1 and 2 were unequivocally established from low-temperature CCD area-detector X-ray diffractometry studies; particularly noteworthy is that the structures of both crystal forms of 1 possess nearly identical molecular geometries (including the phenyl-ring orientations) along with an encapsulated THF molecule. These new air-stable molecular additions to the cyclo-[Ni(μ2-SR)2]n family (with n = 4, 5, 6, and 8) are of particular stereochemical interest in that: (1) in sharp contrast to the previously known monodentate thiolate-bridged members which ideally possess regular convex Ni–S toroids, the assembled n-localized edge-fused square-planar [NiS4] subunits found in the triclinic and monoclinic crystal forms of undecanickel 1 and in the trigonal crystal form of nonanickel 2 have irregularly-shaped mixed concave/convex toroidal pseudo-C2v and pseudo-D3h ring geometries, respectively, that are geometrically unique; (2) 1 is the first host member of any known cyclo-[Ni(SR)2]n oligomer to have a co-crystallized solvated guest molecule (viz., THF); and (3) the observed orientations of adjacent phenyl rings attached to the highly pyramidal sulfur atoms in both 1 and 2 suggest the occurrence of weakly attractive pairwise phenyl⋯phenyl dispersion forces that are presumed to stabilize these novel nickel(II) phenylthiolate oligomers. A comparative analysis of the salient solid-state structural features of the idealized Ni–S ring geometries of the resulting entire cyclo-[Ni(SPh)2]n family (n = 4, 5, 6, 8, 9, and 11) is presented (under the assumed absence of sterically crowded R-substituents and/or abnormal packing effects). The unsymmetrical enlargement of the pseudo-threefold 9-membered ring in 2 by the formal insertion of two adjacent [Ni(SPh)2] units to give an otherwise analogous Ni–S framework of the 11-membered ring in 1 is attributed to the elongated template-geometry of the guest molecule coupled with the maintenance of attractive pairwise phenyl ring interactions.

A new approach to lithium–heavier alkali metal interchange reactions: synthesis of a tetralithium pentasodium mixed alkoxide–amide dome-shaped cage compound with an encapsulated hydroxide molecule †

An investigation of metal–metal interchange reactions between alkali metal amides and alkali metal alkoxides, relevant to the area of ‘superbases’, has uncovered a novel adduct containing both components, which has been isolated from solution and crystallographically characterised. Formulated as [Li4Na4(ButO)4{PhN(H)}4(NaOH)(4-Me-py)4], this tetralithium pentasodium mixed alkoxide–amide can be synthesized either by reaction of lithium anilide with sodium t-butoxide or of sodium anilide with lithium t-butoxide, in the presence of the co-ordinating solvent 4-methylpyridine (4-Me-py). The single sodium hydroxide molecule in the formulation occurs adventitiously, but consistently. X-Ray crystallographic studies reveal a 17-vertex dome-shaped structure founded on a (NaN)4 basal ring, above which lies a smaller (LiO)4 ring then an apical Na atom: the OH− ion occupies an internal position within the dome. Discussion focuses on the striking resemblance between this structure and that of the previously reported tetralithium pentapotassium mixed alkoxide–enolate [Li4K4(ButO)4(C6H11O)4(KOH)(THF)5], and it is pointed out that the dominant factor in their common architectural design appears to be the encapsulated hydroxide molecule.

Stability of SUV liposomes in the presence of cholate salts and pancreatic lipases: effect of lipid composition

The effect of bile salts (sodium cholate and sodium taurocholate), and pancreatic lipases on the structural integrity of SUV liposomes of different lipid compositions was studied. Liposomal membrane integrity was judged by bile salt or pancreatin-induced release of vesicle encapsulated 5,6-carboxyfluorescein, and vesicle size distribution before and after incubations. Bile salt concentration was 10 mM, while a saturated solution of pancreatin (mixed with equal volume of liposomes) was utilized. Results agree with earlier studies, demonstrating the instability of liposomes composed of lipids with low transition temperatures (PC and DMPC) in presence of cholates. Addition of cholesterol (1:1 lipid:chol molar ratio) does not substantially increase the encapsulated molecule retention. Nevertheless, liposomes composed of lipids with high transition temperatures (DPPC, DSPC and SM), retain significantly higher amounts of encapsulated material, under all conditions studied. Furthermore, the vesicles formed by mixing cholesterol with these lipids will possibly be sufficiently stable in the gastrointestinal tract for long periods of time. Sizing results reveal that in most cases release of encapsulated molecules is mainly caused by their leakage through holes formed on the lipid bilayer. However, in stearylamine containing DPPC and DSPC vesicles, the cholate-induced drastic decrease in vesicle size suggests total liposome disruption as the possible mechanism of encapsulated material immediate release.

The methylgallium-2-carboxylatobenzimidazolato hexamer, [MeGa·C8H4N2O2]6·C6H6·(Me2C6H4)2; synthesis and X-ray crystal structure

The room-temperature reaction of Me3Ga with benzimidazole 2-carboxylic acid in xylene solvent has yielded a novel crystalline hexameric gallium compound with "MeGa" moieties bridged by the doubly depronotated ligand precursor. Crystals of [MeGa(4,5-benzimidazolato-2-carboxylato)]6·(C6H6)·(m-Me2C6H4)2 are monoclinic, a = 18.091(2), b = 17.094(2), c = 13.2215(5) Å, Z = 2, space group C2/m. The structure was solved by direct methods and refined by full-matrix least-squares procedures to R (F, I [Formula: see text] 3σ(I)) = 0.064 (Rw (F2, all data) = 0.134). The hexameric Ga complex contains a six-membered ring of Ga atoms, bridged by the benzimidazolate ligands with the benzo rings projecting alternately above and below the Ga plane, thus forming a ball-shaped molecule. The complex could have ideal D3d symmetry, but it contains an encapsulated molecule of benzene, which distorts the regularity of the Ga6 hexagon, and reduces the symmetry of the complex to the crystallographically observed C2h. The coordination geometry at each of the two independent GaO2N2C centres approximates a trigonal bipyramid, with a N2C trigonal plane, and the O atoms above and below; average dimensions are Ga-O = 2.176(2), Ga-N = 1.973(3), Ga-C = 1.927(5) Å, O-Ga-O = 165°. The unit cell also contains four m-xylene solvent molecules (outside the molecular cage).Key words: gallium, crystal structure, benzene intercalate, benzimidazolecarboxylic acid.

The methylgallium-2-carboxylatobenzimidazolato hexamer, [MeGa·C<sub>8</sub>H<sub>4</sub>N<sub>2</sub>O<sub>2</sub>]<sub>6</sub>·C<sub>6</sub>H<sub>6</sub>·(Me<sub>2</sub>C<sub>6</sub>H<sub>4</sub>)<sub>2</sub>; synthesis and X-ray crystal structure

The room-temperature reaction of Me3Ga with benzimidazole 2-carboxylic acid in xylene solvent has yielded a novel crystalline hexameric gallium compound with "MeGa" moieties bridged by the doubly depronotated ligand precursor. Crystals of [MeGa(4,5-benzimidazolato-2-carboxylato)]6·(C6H6)·(m-Me2C6H4)2 are monoclinic, a = 18.091(2), b = 17.094(2), c = 13.2215(5) Å, Z = 2, space group C2/m. The structure was solved by direct methods and refined by full-matrix least-squares procedures to R (F, I 3σ(I)) = 0.064 (Rw (F2, all data) = 0.134). The hexameric Ga complex contains a six-membered ring of Ga atoms, bridged by the benzimidazolate ligands with the benzo rings projecting alternately above and below the Ga plane, thus forming a ball-shaped molecule. The complex could have ideal D3d symmetry, but it contains an encapsulated molecule of benzene, which distorts the regularity of the Ga6 hexagon, and reduces the symmetry of the complex to the crystallographically observed C2h. The coordination geometry at each of the two independent GaO2N2C centres approximates a trigonal bipyramid, with a N2C trigonal plane, and the O atoms above and below; average dimensions are Ga-O = 2.176(2), Ga-N = 1.973(3), Ga-C = 1.927(5) Å, O-Ga-O = 165°. The unit cell also contains four m-xylene solvent molecules (outside the molecular cage).Key words: gallium, crystal structure, benzene intercalate, benzimidazolecarboxylic acid.

Hydrophobic Concave Surfaces and Cavities by Combination of Calix[4]arenes and Resorcin[4]arenes

AbstractCoupling reactions of calix[4]arenes and modified resorcin[4]arenes have been investigated. Reaction of mono(chloroacetamido)calix[4]arene 4 with tetrahydroxycavitand 9 gave the 1:1 coupled product 13 in 61% yield. Combination of upper‐rim 1,3‐difunctionalized calix[4]arene 5 with 9 afforded predominantly the 2:1 calix‐resorcinarene 18 in 47% yield. Reaction of 1,2‐difunctionalized calix[4]arene 6 with 9 gave five products, namely, endo 1:1 (19), exo 1:1 (20), endo‐endo 2:1 (21), endo‐exo 2:1 (22), and exo‐exo 2:1 (23) in ratios that depend on the reaction conditions. The stereochemistry of the different products was determined with NOESY experiments. The structures of 21 a and 23 b were calculated by using molecular mechanics, which revealed that intramolecular hydrogen bonds are only present in the former. Reaction of 1,2‐bis(chloroacetamido)calix[4]arene 26, which has two additional nitro groups at the remaining aromatic rings, with 9 yielded three different products, namely, endo 1:1 (28), endo‐endo 2:1 (30), and endo‐exo 2:1 (32) in ratios that depend on the reaction conditions. There is a preference for the endo orientation in the formation of the 1:1 coupled product, probably owing to an interaction of the nitro groups with the cavitand in the transition state. After conversion of the nitro groups in 28 into chloroacetamido moieties, reaction with Cs2CO3 in DMF under high‐dilution conditions afforded holand 33 in 26% yield together with calix[4]arene‐based carceplex 34 with an encapsulated DMF molecule (27% yield). Holand 33 was obtained in 33% yield by reaction of the tetrakis(chloroacetamide) endo‐endo 2:1 isomer 31 with tetrahydroxycavitand 9. Holand 33 contains a cavity of nanosize dimensions. Molecular mechanics simulations indicate that holand 33 adopts a conformation with eight hydrogen bonds and a large, preorganized cavity with two entrances of smaller dimensions. Molecular dynamics simulations of holand 33 in both CHCl3 and THF showed that four solvent molecules can be accommodated in the cavity at well‐defined positions.