Cage-like Complexes Research Articles

Discrete and infinite cage-like frameworks with inclusion of anionic and neutral species and with interpenetration phenomena.

Complex [Ag(tpba)N(3)] (1) was obtained by reaction of novel tripodal ligand N,N',N"-tris(pyrid-3-ylmethyl)-1,3,5-benzenetricarboxamide (TPBA) with [Ag(NH(3))(2)]N(3). While the reactions between 1,3,5-tris(imidazol-1-ylmethyl)-2,4,6-trimethylbenzene (TITMB) and silver(I) salts with different anions and solvent systems give six complexes: [Ag(3)(titmb)(2)](N(3))(3).CH(3)OH.4 H(2)O (2), [Ag(3)(titmb)(2)](CF(3)SO(3))(2)(OH).5 H(2)O (3), [Ag(3)(titmb)(2)][Ag(NO(3))(3)]NO(3).H(2)O (4), [Ag(3)(titmb)(2)(py)](NO(3))(3).H(2)O (py=pyridine) (5), [Ag(3)(titmb)(2)(py)](ClO(4))(3) (6), and [Ag(3)(titmb)(2)](ClO(4))(3).CHCl(3) (7). The structures of these complexes were determined by X-ray crystallography. The results of structural analysis of complexes 1 and 2, with the same azide anion but different ligands, revealed that 1 is a twofold interpenetrated 3D framework with interlocked cage-like moieties, while 2 is a M(3)L(2) type cage-like complex with a methanol molecule inside the cage. Entirely different structure and topology between 1 and 2 indicates that the nature of organic ligands affected the structures of assemblies greatly. While in the cases of complexes 2-7 with flexible tripodal ligand TITMB, they are all discrete M(3)L(2) type cages. The results indicate that the framework of these complexes is predominated by the nature of the organic ligand and geometric need of the metal ions, but not influenced greatly by the anions and solvents. It is interesting that there is a divalent anion [Ag(NO(3))(3)](2-) inside the cage 4 and an anion of ClO(4)(-) or NO(3)(-) spontaneously encapsulated within the cage of complexes 5, 6 and 7.

Rare-earth doped polymers for planar optical amplifiers

Optical waveguide amplifiers based on polymer materials offer a low-cost alternative for inorganic waveguide amplifiers. Due to the fact that their refractive index is similar to that of standard optical fibers, they can be easily coupled to existing fibers with low coupling losses. Doping the polymer with rare-earth ions that yield optical gain is not straightforward, as the rare-earth salts are poorly soluble in the polymer matrix. This review article focuses on two different approaches to dope a polymer waveguide with rare-earth ions. The first approach is based on organic cage-like complexes that encapsulate the rare-earth ion and are designed to provide coordination sites to bind the rare-earth ion and to shield it from the surrounding matrix. These complexes also offer the possibility of attaching a highly absorbing antenna group, which increases the pump efficiency significantly. The second approach to fabricate rare-earth doped polymer waveguides is obtained by combining the excellent properties of SiO2 as a host for rare-earth ions with the easy processing of polymers. This is done by doping polymers with Er-doped silica colloidal spheres.

Self-assembly of frameworks with specific topologies: construction and anion exchange properties of M3L2 architectures by tripodal ligands and silver(I) salts.

Three five-component architectures, compounds 3, 4, and 5 were obtained by self-assembly of tripodal 1,3,5-tris(imidazol-1-ylmethyl )-2,4,6-trimethylbenzene (6) and 1,3,5-tris(benzimidazol-2-ylmethyl)benzene (7) ligands with silver(I) salts. The structures of these novel complexes have been determined by X-ray crystallography. The results of structural analysis indicate that these frameworks have same M3L2 components, but different structures. Compounds 3 and 4 are both M3L2 type cage-like complexes, while the 5 is an open trinuclear complex. The complex 3 is a cylindrical cage with simultaneous inclusion of a perchlorate anion inside of the cage as a guest molecule. Such guests can be exchanged for other anions through the open edge of the cage as evidenced by crystal structure of 4. The results demonstrate that the molecular M3L2 type cage can act as a host for anions and provide a nice example of supramolecular architectures with interesting properties and possible applications.

Isolation and Single X-ray Crystal Structure of a Flattened M3L2 Type Metallosupramolecular Cage Obtained by Self-Assembly of Tripodal Ligand with Zinc(II) Chloride

Abstract A novel cake-like complex, Zn3(tbib)2Cl6·3DMF·2H2O [tbib = 1,3,5-tris(benzimidazol-2-ylmethyl)benzene], was synthesized by self-assembly of tripodal ligand tbib with zinc(II) chloride. The X-ray crystal structural analysis indicates that the framework is a flattened M3L2 type cage-like complex in which the tbib ligand has a cis, trans, trans conformation.

Zinc and cadmium complexes with versatile hexadentate Schiff base ligands. The supramolecular self-assembly of a 3-D cage-like complex †

Mono- and poly-nuclear neutral complexes have been obtained by electrochemical reaction of zinc or cadmium anodes with potentially hexadentate ligands H4Ln (n= 1–3). The ligands were prepared by 2∶1 condensation of 3-hydroxysalicylaldehyde and 1,2-diaminopropane, 1,3-diaminopropane or 1,4-diaminobutane, respectively. They can act either as N2O2 dianionic in mononuclear complexes or as N2O4 tetraanionic in polynuclear complexes, where metal ions are held together by μ-phenoxo bridges. X-Ray diffraction study of self-assembled [Zn8(L3)4(H2O)3]·H2O·¼MeCN shows a 3-D cage-like crystal structure, where the ligand units display O2 + N2O2 + O2 polynucleating behaviours.

Highly stable cage-like complexes by self-assembly of tetracationic Zn(II) porphyrinates and tetrasulfonatocalix[4]arenes in polar solvents

Tetracationic Zn(II) porphyrinates and tetraanionic calix[4]arenes can be assembled in polar solvents to obtain cage-like complexes in an entropy driven process. These structures are remarkably stable even in the presence of water or competing salts.

The first X-ray structurally characterized M3L2 cage-like complex with tetrahedral metal centres and its encapsulation of a neutral guest molecule

The first X-ray structurally characterized M3L2 cage-like complex with tetrahedral metal centres [Zn3(tib)2- (OAc)6]·xH2O [tib = 1,3,5-tris(imidazol-1-ylmethyl)benzene, x ≈ 4] obtained by reaction of zinc(II) acetate with the tripodal ligand tib exhibits guest inclusion properties of neutral molecule such as synthetic camphor in aqueous solution.

ISCOMs: an adjuvant with multiple functions.

Aluminum salts are currently the only widely used adjuvant for human vaccines. Over the past 10-15 years, a large research effort has attempted to find novel adjuvants with ability to induce a broad range of immune responses, including cell-mediated immunity. The immunostimulating complex or ISCOM is one adjuvant with multiple adjuvant properties. ISCOMs are open cage-like complexes typically with a diameter of about 40 nm that are built up by cholesterol, lipid, immunogen, and saponins from the bark of the tree Quillaia saponaria Molina. ISCOMs have been demonstrated to promote antibody responses and induce T helper cell as well as cytotoxic T lymphocyte responses in a variety of experimental animal models, and have now progressed to phase I and II human trials. This review describes recent developments in the understanding of the structure, composition, and preparation of ISCOMs and will cover important aspects of the understanding of the adjuvant functions of ISCOMs and how they act on the immune system.

Guest-Induced Organization of a Three-Dimensional Palladium(II) Cagelike Complex. A Prototype for "Induced-Fit" Molecular Recognition.

Guest-Induced Organization of a Three-Dimensional Palladium(II) Cagelike Complex. A Prototype for "Induced-Fit" Molecular Recognition.

Photosensitization study of cage-like metal complexes with hexadentate ligands, tptn and tpen. Part 1. Photochemistry and spectroelectrochemistry of iron(II), cobalt(III) and nickel(II) complexes

Abstract Two hexadentate ligands, N,N,N′,N ′-tetrakis(2-pyridylmethyl)-1,3-propanediamine (tptn) and N,N,N′,N ′-tetrakis(2-pyridylmethyl)ethylenediamine (tpen), were used to prepare cage-like metal complexes of Fe(II), Co(III) and Ni(II). As expected, these complexes are photochemically inert. The electrochemical behaviour of these complexes was studied by spectroelectrochemical methods. The iron(II) complexes exhibit chemical irreversibility on reduction and the nickel(II) complexes show reversible reduction behaviour. The potential of cobalt(III) complexes as photosensitizers is discussed.

Photosensitization study of cage-like metal complexes with hexadentate ligands, tptn and tpen. Part 2. Electron transfer photosensitization via ion pairs: cobalt(III)(tptn)—iodide ion and cobalt(III)(tpen)—iodide ion systems

Abstract Co(tptn)3+ and Co(tpen)3+ (where tptnN,N,N′,N′-tetrakis(2-pyridylmethyl)-1,3-propanediamine and tpen N,N,N′,N′-tetrakis(2-pyridylmethyl)ethylenediamine) are demonstrated to have a similar photosensitization capacity to other caged Co(III) complexes such as Co(sepulchrate)3+. In oxygen-saturated aqueous solutions at pH 4.0, a photoassisted oxidation of I− to I3− by O2 is obtained with a turnover number of greater than 12 for both Co(tptn)3+ and Co(tpen)3+. Quantum yields for the formation of 1 2 I3− are 8.7x 10−4 and 1.6x 10−2 respectively at pH 4.0 in solution with a constant supply of air.

The structure of the cage-like complex anion formed by sodium borate and 1,1,1-tris(hydroxymethyl)ethane

The triol 1,1,1-tris(hydroxymethyl)ethane combines with tetrahydroxy borate [B(OH) 4] − in alkaline aqueous solution to form a mixture of complex anions, one of which is isolated upon crystallization. The structure of [Na(H 2O) 3][CH 3C(CH 2O) 3B(OH)] has been determined by X-ray crystallography. The complex anion is a cage in which all three oxygen atoms of 1,1,1-tris(hydroxymethyl)ethane are attached to the tetrahedrally-coordinated boron atom. These BO bond lengths are 1.492 Å the BOH bond length is 1.407 Å. The sodium ion is surrounded octahedrally by six oxygen atoms at distances from 2.33 to 2.51 Å, one from the hydroxyl group on boron and the remainder from water molecules. The water molecules form hydrogen bonds with the oxygen atoms of the anion cage.

Molecular receptors. Synthesis and X-ray crystal structure of an 18-crown ether phenol complex of 1,2-diaminoethane

Treatment of 18-crown-5 p-nitrophenol (1) with 1,2-diaminoethane produces a 1:2 cage-like complex (2) in which proton transfer has occurred to both amino groups. The crystal structure of (2) has been determined. Crystals of (2)·2EtOH are monoclinic, space group P21/n with two formula units in a cell of dimensions a= 11.903(2), b= 14.361(3), c= 13.014(2)A, β= 95.98(2)°. The structure was solved by direct methods and refined by full-matrix least-squares calculations; R= 0.058 for 961 reflections with I > 2σ(I). The diammonium cation lies about a crystallographic inversion centre and the asymmetric crystal unit contains half a dication, one crown-ether phenolate, and one ethanol. Reception of the NH3 moiety by the corwn-ether phenolate after proton transfer involves N–H ⋯ O hydrogen bonding to three ethereal oxygen atoms [N⋯· O 2.952(8), 2.789(8), and 2.899(8)A]; the phenolate oxygen atom does not participate in receptor binding via hydrogen bonding, but instead is linked to ethanol of solvation via an O–H ⋯ O hydrogen bond [O ⋯ O 2.820(8)A]. The structure is thus unlike that of the monoammonium salt of (1) in that the N–H moieties hydrogen bond to the macrocycle only and in an endo rather than an exo fashion.

Models for deploymerizing enzymes: criteria for discrimination of models

Several models for the action of alpha amylase have been proposed to account for the nonrandom distribution of oligosaccharides in the amylase digests of polysaccharides. The preferred-attack model attempts to account for the nonrandom distribution by assuming that the probability for bond cleavage depends upon the position of the bond in the chain. The repetitive, or multiple-attack, model suggests that the nonrandom distribution of oligosaccharides arises because an amylase can form a cage-like complex with a substrate and attack it several times during a single encounter. The multiple-enzyme or dual-site model suggests that the nonrandom yield of oligosaccharides arises from the combined action of exo- and endo-enzymes. The effects of pH, inhibitors, and substrate chain-length on enzyme action have been studied in several laboratories to determine which of the three action-patterns best describes the action of alpha amylase. The influence of these variables on product distributions or enzyme action-patterns are mathematically modeled in the Appendix. The experimental data on porcine-pancreatic alpha amylase are discussed in the light of the derivations.