Collagen-like peptides and peptide–polymer conjugates in the design of assembled materials

Collagen is the most abundant protein in mammals, and there has been long-standing interest in understanding and controlling collagen assembly in the design of new materials. Collagen-like peptides (CLPs), also known as collagen-mimetic peptides (CMPs) or collagen-related peptides (CRPs), have thus been widely used to elucidate collagen triple helix structure as well as to produce higher-order structures that mimic natural collagen fibers. This mini-review provides an overview of recent progress on these topics, in three broad topical areas. The first focuses on reported developments in deciphering the chemical basis for collagen triple helix stabilization, which we review not with the intent of describing the basic structure and biological function of collagen, but to summarize different pathways for designing collagen-like peptides with high thermostability. Various approaches for producing higher-order structures via CLP self-assembly, via various types of intermolecular interaction, are then discussed. Finally, recent developments in a new area, the production of polymer–CLP bioconjugates, are summarized. Biological applications of collagen contained hydrogels are also included in this section. The topics may serve as a guide for the design of collagen-like peptides and their bioconjugates for targeted application in the biomedical arena.     

Molecular design of specific metal-binding peptide sequences from protein fragments: theory and experiment

A novel strategy is presented for designing peptides with specific metal-ion chelation sites, based on linking computationally predicted ion-specific combinations of amino acid side chains coordinated at the vertices of the desired coordination polyhedron into a single polypeptide chain. With this aim, a series of computer programs have been written that 1) creates a structural combinatorial library containing Z(i)-(X)(n)-Z(j) sequences (n=0-14; Z: amino acid that binds the metal through the side chain; X: any amino acid) from the existing protein structures in the non-redundant Protein Data Bank; 2) merges these fragments into a single Z(1)-(X)(n(1) )-Z(2)-(X)(n(2) )-Z(3)-(X)(n(3) )--Z(j) polypeptide chain; and 3) automatically performs two simple molecular mechanics calculations that make it possible to estimate the internal strain in the newly designed peptide. The application of this procedure for the most M(2+)-specific combinations of amino acid side chains (M: metal; see L. Rulísek, Z. Havlas J. Phys. Chem. B 2003, 107, 2376-2385) yielded several peptide sequences (with lengths of 6-20 amino acids) with the potential for specific binding with six metal ions (Co(2+), Ni(2+), Cu(2+), Zn(2+), Cd(2+) and Hg(2+)). The gas-phase association constants of the studied metal ions with these de novo designed peptides were experimentally determined by MALDI mass spectrometry by using 3,4,5-trihydroxyacetophenone as a matrix, whereas the thermodynamic parameters of the metal-ion coordination in the condensed phase were measured by isothermal titration calorimetry (ITC), chelatometry and NMR spectroscopy methods. The data indicate that some of the computationally predicted peptides are potential M(2+)-specific metal-ion chelators.     

Near–Infrared‐Responsive Peptide that Targets Collagen Fibrils to Induce Cytotoxicity

A novel conjugate, PHG10 dye, was synthesized using a collagen peptide and a near–infrared (NIR)‐responsive dye to achieve targeted cytotoxicity. The collagen peptide motif, ‐(Pro‐Hyp‐Gly)₁₀‐ (PHG10), was incorporated for targeting collagen fibrils that are excessively produced by activated fibroblasts around tumor cells. PHG10 dye was purified by HPLC and identified by MALDI‐MS. The phototoxicity and cytotoxicity of PHG10 dye were examined using human glioma cells (HGCs). Fluorescent images indicated that PHG10 dye preferably assembled to collagen‐coated HGCs compared with noncoated HGCs. Under irradiation with NIR light, effective cytotoxicity was observed on collagen‐coated HGCs within 20 min. Because phototoxicity and cytotoxicity are dependent on the assembled amount of PHG10 dye, the targeting of collagen fibrils by the collagen peptide motif PHG10 is assured.     

Dynamics of Zn(II) binding as a key feature in the formation of amyloid fibrils by Aβ11-28

Supramolecular assembly of peptides and proteins into amyloid fibrils is of multifold interest, going from materials science to physiopathology. The binding of metal ions to amyloidogenic peptides is associated with several amyloid diseases, and amyloids with incorporated metal ions are of interest in nanotechnology. Understanding the mechanisms of amyloid formation and the role of metal ions can improve strategies toward the prevention of this process and enable potential applications in nanotechnology. Here, studies on Zn(II) binding to the amyloidogenic peptide Aβ11-28 are reported. Zn(II) modulates the Aβ11-28 aggregation, in terms of kinetics and fibril structures. Structural studies suggest that Aβ11-28 binds Zn(II) by amino acid residues Glu11 and His14 and that Zn(II) is rapidly exchanged between peptides. Structural and aggregation data indicate that Zn(II) binding induces the formation of the dimeric Zn(II)(1)(Aβ11-28)(2) species, which is the building block of fibrillar aggregates and explains why Zn(II) binding accelerates Aβ11-28 aggregation. Moreover, transient Zn(II) binding, even briefly, was enough to promote fibril formation, but the final structure resembled that of apo-Aβ11-28 amyloids. Also, seeding experiments, i.e., the addition of fibrillar Zn(II)(1)(Aβ11-28)(2) to the apo-Aβ11-28 peptide, induced aggregation but not propagation of the Zn(II)(1)(Aβ11-28)(2)-type fibrils. This can be explained by the dynamic Zn(II) binding between soluble and aggregated Aβ11-28. As a consequence, dynamic Zn(II) binding has a strong impact on the aggregation behavior of the Aβ11-28 peptide and might be a relevant and so far little regarded parameter in other systems of metal ions and amyloidogenic peptides.     

Octadecanuclear cluster or 1D polymer with [[ML](2)Nb(CN)(8)](n) motifs as a function of [ML] (M = Ni(II), n = 6; M = Mn(II), n = infinity; L = macrocycle)

A nanosized octadecaheteronuclear aggregate, [[NiL(2)](12)[Nb(CN)(8)](6)(H(2)O)(6)], and a 1-D coordination polymer, [[MnL(1)](2)[Nb(CN)(8)](H(2)O)]( infinity ), have been obtained by self-assembly between the octacyanometalate [Nb(CN)(8)](4)(-) and [ML](2+) complexes. The dimensionality of the supramolecular architectures was found to be controlled by the [ML] module for which the equatorial coordination sites are blocked by a macrocyclic ligand. The crystal structures and magnetic properties for both the compounds are described.     

Controlling and fine tuning the physical properties of two identical metal coordination sites in de novo designed three stranded coiled coil peptides

Herein we report how de novo designed peptides can be used to investigate whether the position of a metal site along a linear sequence that folds into a three-stranded α-helical coiled coil defines the physical properties of Cd(II) ions in either CdS(3) or CdS(3)O (O-being an exogenous water molecule) coordination environments. Peptides are presented that bind Cd(II) into two identical coordination sites that are located at different topological positions at the interior of these constructs. The peptide GRANDL16PenL19IL23PenL26I binds two Cd(II) as trigonal planar 3-coordinate CdS(3) structures whereas GRANDL12AL16CL26AL30C sequesters two Cd(II) as pseudotetrahedral 4-coordinate CdS(3)O structures. We demonstrate how for the first peptide, having a more rigid structure, the location of the identical binding sites along the linear sequence does not affect the physical properties of the two bound Cd(II). However, the sites are not completely independent as Cd(II) bound to one of the sites ((113)Cd NMR chemical shift of 681 ppm) is perturbed by the metalation state (apo or [Cd(pep)(Hpep)(2)](+) or [Cd(pep)(3)](-)) of the second center ((113)Cd NMR chemical shift of 686 ppm). GRANDL12AL16CL26AL30C shows a completely different behavior. The physical properties of the two bound Cd(II) ions indeed depend on the position of the metal center, having pK(a2) values for the equilibrium [Cd(pep)(Hpep)(2)](+) → [Cd(pep)(3)](-) + 2H(+) (corresponding to deprotonation and coordination of cysteine thiols) that range from 9.9 to 13.9. In addition, the L26AL30C site shows dynamic behavior, which is not observed for the L12AL16C site. These results indicate that for these systems one cannot simply assign a "4-coordinate structure" and assume certain physical properties for that site since important factors such as packing of the adjacent Leu, size of the intended cavity (endo vs exo) and location of the metal site play crucial roles in determining the final properties of the bound Cd(II).     

Reversible anion exchanges between the layered organic-inorganic hybridized architectures: syntheses and structures of manganese(II) and copper(II) complexes containing novel tripodal ligands

Six noninterpenetrating organic-inorganic hybridized coordination complexes, [Mn(3)(2)(H(2)O)(2)](ClO(4))(2).2 H(2)O (5), [Mn(3)(2)(H(2)O)(2)](NO(3))(2) (6), [Mn(3)(2)(N(3))(2)].2 H(2)O (7), [Cu(3)(2)(H(2)O)(2)](ClO(4))(2) (8), [Mn(4)(2)(H(2)O)(SO(4))].CH(3)OH.5 H(2)O (9) and [Mn(4)(2)](ClO(4))(2) (10) were obtained through self-assembly of novel tripodal ligands, 1,3,5-tris(1-imidazolyl)benzene (3) and 1,3-bis(1-imidazolyl)-5-(imidazol-1-ylmethyl)benzene (4) with the corresponding metal salts, respectively. Their structures were determined by X-ray crystallography. The results of structural analysis of complexes 5, 6, 7, and 8 with rigid ligand 3 indicate that their structures are mainly dependant on the nature of the organic ligand and geometric need of the metal ions, but not influenced greatly by the anions and metal ions. While in complexes 9 and 10, which contain the flexible ligand 4, the counteranion plays an important role in the formation of the frameworks. Entirely different structures of complexes 5 and 10 indicate that the organic ligands greatly affect the structures of assemblies. Furthermore, in complexes 5 and 6, the counteranions located between the cationic layers can be exchanged by other anions. Reversible anion exchanges between complexes 5 and 6 without destruction of the frameworks demonstrate that 5 and 6 can act as cationic layered materials for anion exchange, as determined by IR spectroscopy, elemental analyses, and X-ray powder diffraction.     

Molecular structures of edge-sharing square-planar dinuclear complexes with unsaturated bridges

The dinuclear complexes of transition metal ions of type [M(2)(mu,eta(1)-XY)(2)L(4)], where XY is an unsaturated ligand that can act as a four-electron or a two-electron donor through the X atom, appear in two molecular conformations depending on whether the coordination planes around the two metal atoms are coplanar or bent. In both structures the geometry of the X atom is planar, corresponding to an sp(2) hybridization. An ab initio theoretical study on 43 representative complexes, complemented with a structural database analysis, provides a rationale for the experimentally observed structures.     

Controlled polymerization and self-assembly of halogen-bridged diruthenium complexes in organic media and their dielectrophoretic alignment

Lipophilic paddlewheel biruthenium complexes [Ru(2)(μ-O(2)CR)(3)X](n) (O(2)CR = 3,4,5-tridodecyloxybenzoate, X = Cl, I) self-assemble in organic media to form halogen-bridged coordination polymers. The polymerization is accompanied by spectral changes in π(RuO,Ru(2)) → π*(Ru(2)) and π(axial ligand) → π*(Ru(2)) absorption bands. These polymeric complexes form lyotropic liquid crystals in n-decane at concentrations above ~100 unit mM. The bridging halogen axial ligands (X = Cl or I) exert significant influences on their electronic structures and self-assembling characteristics: the chloride-bridged polymers give hexagonally aligned ordered columnar structure (columnar hexagonal phase, Col(h)), whereas the iodide-bridged polymers form less ordered columnar nematic (Col(n)) phase, as revealed by small-angle X-ray diffraction measurements. Chloro-bridged coordination polymers dispersed in n-decane are thermally intact even at the elevated temperature of 70 °C. In contrast, iodo-bridged polymers show reversible dissociation and reassembly phenomena depending on temperature. These halogen-bridged coordination polymers show unidirectional alignment upon applying alternating current (ac) electric field as investigated by crossed polarizing optical microscopy and scanning electron microscopy. The unidirectionally oriented columns of chloro-bridged polymers are accumulated upon repetitive application of the ac voltage, whereas iodo-bridged coordination polymers show faster and reversible alignment changes in response to turning on-and-off the electric field. The controlled self-assembly of electronically conjugated linear complexes provide a potential platform to design electric field-responsive nanomaterials.     

Polytypism in columnar group 14 halide salts: structures of (Et2NH2)3Pb3X9 x nH2O (X = Cl,Br) and (beta-alaninium)2SnI4

The crystal structures of three hybrid organoammonium metal halide salts composed of edge-sharing MX(6) octahedra have been determined. The genesis of these structures can be traced to the parent hexagonal MX(2) structure via dimensional reduction and recombination arguments. The structures of (Et(2)NH(2))(3)Pb(3)X(9) x nH(2)O (X = Br, I) contain unique columnar (Pb(3)X(9))(n)(3)(n)(-) structures, built up of edge-shared PbX(6) octahedra. The interaction of the Et(2)NH(2)(+) cations with the parent PbX(2) structures leads to a rearrangement of the lattice into the observed columnar structure. Groups of six Et(2)NH(2)(+) cations are hydrogen bonded to these columns, girdling them at their narrowest points. These hydrogen bonds contribute to the formation of the zigzag nature of the columnar inorganic framework. The resultant structures are recombinate analogues (polytypes) of the (Pb(3)X(9))(n)(3)(n)(-) stacks that would be obtained by the dimensional reduction process of the parent layer PbX(2) structure into simple edge-shared ribbons of PbX(6) octahedra. These structures can be described in terms of the stacking of planar bibridged Pb(3)X(8)(2-) units decorated with a single halide ion at a terminal lead ion site. In a similar fashion, (beta-alaH)(2)Sn(2)I(6) contains corrugated (Sn(2)I(6))(n)(2)(n)(-) columns (beta-ala = beta-alanine), with the cations sitting in the clefts of the columns.     

Controlling the morphology of metal-promoted higher ordered assemblies of collagen peptides with varied core lengths

Self-assembling peptides have become an important subclass of next-generation biomaterials. In particular, materials that mimic the properties of collagen have received considerable attention due to the unique properties of natural collagen. Previous peptide-based designs have been successful in generating structures with morphological properties that were primarily determined by the type of self-assembling mechanism. Herein we demonstrate the metal ion-promoted, supramolecular assembly of collagen-based peptide triple helices into distinct morphologies that are controlled by defining the number of Pro-Hyp-Gly repeating units. We synthesized and characterized collagen-based peptides that incorporated either 5, 7, 9, or 11 Pro-Hyp-Gly repeating units. We found that the number of repeating units, and the resulting stability of the collagen triple helix, is intimately linked with the types of assemblies formed. For instance, collagen peptides that did not form a stable triple helix, such as NCoH5, did not participate in supramolecular assembly with added metal ions. Collagen peptides that formed stable triple helices, such as NCoH11, resulted in microsaddle structures with metal-promoted assembly, whereas a highly cross-linked, three-dimensional mesh formed with NCoH7, albeit at a higher metal ion concentration. These data provide evidence that triple helix formation is required for efficient metal-triggered assembly to the observed microstructures.     

Tunable self-assembled peptide amphiphile nanostructures

Peptide amphiphiles are capable of self-assembly into a diverse array of nanostructures including ribbons, tubes, and vesicles. However, the ability to select the morphology of the resulting structure is not well developed. We examined the influence of systematic changes in the number and type of hydrophobic and hydrophilic amino acids on the self-assembly of amphiphilic peptides. Variations in the morphology of self-assembled peptides of the form X(6)K(n) (X = alanine, valine, or leucine; K = lysine; n = 1-5) are investigated using a combination of transmission electron microscopy and dynamic light scattering measurements. The secondary structures of the peptides are determined using circular dichroism. Self-assembly is controlled through a combination of interactions between the hydrophobic segments of the peptide molecules and repulsive forces between the charged segments. Increasing the hydrophobicity of the peptide by changing X to a more lipophilic amino acid or decreasing the number of hydrophilic amino acids transforms the self-assembled nanostructures from vesicles to tubes and ribbons. Changes in the hydrophobicity of the peptides are reflected in changes in the critical micelle concentration observed using pyrene probe fluorescence analysis. Self-assembled materials formed from cationic peptide amphiphiles of this type display promise as carriers for insoluble molecules or negatively charged nucleic acids in drug or gene delivery applications.     

Morphology and persistence length of amyloid fibrils are correlated to peptide molecular structure

The formation of amyloid fibrils is a self-assembly process of peptides or proteins. The superior mechanical properties of these fibrils make them interesting for materials science but constitute a problem in amyloid-related diseases. Amyloid structures tend to be polymorphic, and their structure depends on growth conditions. To understand and control the assembly process, insights into the relation between the mechanical properties and molecular structure are essential. We prepared long, straight as well as short, worm-like β-lactoglobulin amyloid fibrils and determined their morphology and persistence length by atomic force microscopy (AFM) and the molecular conformation using vibrational sum-frequency generation (VSFG) spectroscopy. We show that long fibrils with near-100% β-sheet content have a 40-times higher persistence length than short, worm-like fibrils with β-sheet contents below 80%.     

Perylene bisimide dyes as versatile building blocks for functional supramolecular architectures

Perylene bisimide dyes and their organization into supramolecular architectures through hydrogen-bonding, metal ion coordination and pi-pi-stacking is discussed; further self-assembly leading to nano- and meso-scopic structures and liquid-crystalline compounds is also addressed.     

Transition metal complexes of the novel hexadentate ligand 1,4-bis(di(N-methylimidazol-2-yl)methyl)phthalazine

The novel polydentate ligand 1,4-bis(di(N-methylimidazol-2-yl)methyl)phthalazine, bimptz, has been synthesized and its coordination chemistry was investigated. Bimptz is neutral and contains a central phthalazine unit, to which two di-(N-methylimidazol-2-yl)methyl groups are attached in the 1,4-positions. This ligand therefore provides up to 6 donor sites for coordination to metal ions. A series of metal complexes of bimptz was prepared and their molecular structures were determined by X-ray diffraction. Upon reaction of bimptz with two equivalents of MnCl(2)·4H(2)O, CoCl(2)·6H(2)O and [Ru(dmso)(4)Cl(2)], the dinuclear complexes [Mn(2)(bimptz)(μ-Cl)(2)Cl(2)] (1), [Co(2)(bimptz)(CH(3)OH)(2)(μ-Cl)(2)](PF(6))(2) (3) and [Ru(2)(bimptz)(dmso)(2)(μ-Cl)(2)](PF(6))(2) (4), respectively, were isolated. The latter were found to have similar solid state structures with octahedrally coordinated metal centers bridged by the phthalazine unit and two chloro ligands. The cobalt and ruthenium complexes 3 and 4 were isolated as PF(6)(-) salts and contain neutral methanol and dmso ligands, respectively, at the terminal coordination sites of the metal centres. The mononuclear ruthenium complex [Ru(Hbimptz)(2)](PF(6))(4) (6) was obtained from the reaction of two equivalents bimptz with [Ru(dmso)(4)Cl(2)]. In complex 6, three donor sites per ligand molecule are used for coordination of the Ru(ii) center. In each bimptz ligand, one of the remaining, dangling N-methylimidazole rings is protonated and forms a hydrogen bond with the unprotonated N-methylimidazole ring of the other bimptz ligand.     

The first self-assembled trimetallic lanthanide helicates driven by positive cooperativity

The segmental tris-tridentate ligand L7 reacts with stoichiometric quantities of Ln(III) (Ln=La-Lu) in acetonitrile to give the complexes [Ln(2)(L7)(3)](6+) and [Ln(3)(L7)(3)](9+). Formation constants point to negligible size-discriminating effects along the lanthanide series, but Scatchard plots suggest that the self-assembly of the trimetallic triple-stranded helicates [Ln(3)(L7)(3)](9+) is driven to completion by positive cooperativity, despite strong intermetallic electrostatic repulsions. Crystallization provides quantitatively [Ln(3)(L7)(3)](CF(3)SO(3))(9) (Ln=La, Eu, Gd, Tb, Lu) and the X-ray crystal structure of [Eu(3)(L7)(3)](CF(3)SO(3))(9).(CH(3)CN)(9).(H(2)O)(2) (Eu(3)C(216)H(226)N(48)O(35)F(27)S(9), triclinic, P1, Z=2) shows the three ligand strands wrapped around a pseudo-threefold axis defined by the three metal ions rigidly held at about 9 A. Each metal ion is coordinated by nine donor atoms in a pseudo-trigonal prismatic arrangement, but the existence of terminal carboxamide units in the ligand strands differentiates the electronic properties of the terminal and the central metallic sites. Photophysical data confirm that the three coordination sites possess comparable pseudo-trigonal symmetries in the solid state and in solution. High-resolution luminescence analyses evidence a low-lying LMCT state affecting the central EuN(9) site, so that multi-metal-centered luminescence is essentially dominated by the emission from the two terminal EuN(6)O(3) sites in [Eu(3)(L7)(3)](9+). New multicenter equations have been developed for investigating the solution structure of [Ln(3)(L7)(3)](9+) by paramagnetic NMR spectroscopy and linear correlations for Ln=Ce-Tb imply isostructurality for these larger lanthanides. NMR spectra point to the triple helical structure being maintained in solution, but an inversion of the magnitude of the second-rank crystal-field parameters, obtained by LIS analysis, for the LnN(6)O(3) and LnN(9) sites with respect to the parameters extracted for Eu(III) from luminescence data, suggests that the geometry of the central LnN(9) site is somewhat relaxed in solution.     

Light-triggered disassembly of amyloid fibrils

There is growing demand for novel methods that could render the controlled disassembly of higher-order structures formed, for example, by peptides. Herein, we demonstrate such a method based on the application of a photocaged variant of the amino acid lysine, namely, lys(Nvoc). Specifically, we introduce lys(Nvoc) into the primary sequence of the amyloidogenic peptide, Aβ(16-22), at a position where the native side chain is known to play a key role in fibril formation via hydrophobic interactions. Both AFM and infrared spectroscopic measurements indicate that the resultant Aβ(16-22) mutant is able to form fibrils whereas, more importantly, the fibrils thus formed can be completely disassembled upon irradiation with near-UV light, which cleaves the photolabile Nvoc moiety and triggers the restoration of the lysine side chain. These results suggest that the generation of a single charge in a highly hydrophobic region of the fibrils is sufficient to promote their dissociation. Thus, we envisage that the current approach will find useful applications wherein controlled structural disassembly or content release is required.     

From terpyridine-based assemblies to metallo-supramolecular polyelectrolytes (MEPEs)

Introducing metal ion coordination as bonding motive into polymer architectures provides new structures and properties for polymeric materials. The metal ions can be part of the backbone or of the side-chains. In the case of linear metallo-polymers the repeat unit bears at least two metal ion receptors in order to facilitate metal-ion induced self-assembly. If the binding constants are sufficiently high, macromolecular assemblies will form in a solution. Likewise, polymeric networks can be formed by metal ion induced crosslinking. The metal ion coordination sites introduce dynamic features, e.g. for self-healing or responsive materials, as well as additional functional properties including spin-crossover, electro-chromism, and reactivity. Terpyridines have attracted attention as receptors in metallo-polymers due to their favorable properties. It is well suited to assemble linear rigid-rod like metallo-polymers in case of rigid ditopic ligands. Terpyridine binds a large number of metal ions and are readily functionalized giving rise to a plethora of available ligands as components in metallo-polymers. By the judicious choice of the metal ions, the design of the ligands, the counter ions and the boundary conditions of self-assembly, the final structure and properties of the resulting metallo-polymers can be tailored at all length scales. Here, we review recent activities in the area of metallo-polymers based on terpyridines as central metal ion receptors.     

Creating an Amyloid ‘Kaleidoscope’ Using Short Iodinated Peptides

Amyloid fibrils formed by peptides with different sequences exhibit diversified morphologies, material properties and activities, making them valuable for developing functional bionanomaterials. However, the molecular understanding underlying the structural diversity of peptide fibrillar assembly at atomic level is still lacking. In this study, by using cryogenic electron microscopy, we first revealed the structural basis underlying the highly reversible assembly of ¹GFGGNDNFG⁹ (referred to as hnRAC1) peptide fibril. Furthermore, by installing iodine at different sites of hnRAC1, we generated a collection of peptide fibrils with distinct thermostability. By determining the atomic structures of the iodinated fibrils, we discovered that iodination at different sites of the peptide facilitates the formation of diverse halogen bonds and triggers the assembly of entirely different structures of iodinated fibrils. Finally, based on this structural knowledge, we designed an iodinated peptide that assembles into new atomic structures of fibrils, exhibiting superior thermostability, that aligned with our design. Our work provides an in-depth understanding of the atomic-level processes underlying the formation of diverse peptide fibril structures, and paves the way for creating an amyloid “kaleidoscope” by employing various modifications and peptide sequences to fine-tune the atomic structure and properties of fibrillar nanostructures.     

Group 1 coordination chains and hexagonal networks of host cyclotriveratrylene with halogenated monocarbaborane anions

Halogenated carbaborane ions [CB(11)H(6)X(6)](-) in which X=Cl or Br have been combined with the host molecule cyclotriveratrylene (CTV) and Group 1 metal cations to give crystalline materials. The complexes [Na(ctv)(H(2)O)(CB(11)H(6)X(6))](CF(3)CH(2)OH) feature chiral Na-CTV coordination chains with complexation of the [CB(11)H(6)X(6)](-) ion by the Na(+) ion, together with the CTV molecular cavity. The coordination chains are hydrogen bonded together to give a puckered two-dimensional hexagonal grid structure. [K(ctv)(CB(11)H(6)Cl(6))(CF(3)CH(2)OH)(0.5)] is essentially isostructural. Complexes [Rb(ctv)(CB(11)H(6)Br(6))(H(2)O)] and [Cs(ctv)(CB(11)H(6)X(6))(CH(3)CN)] are coordination polymers with related distorted hexagonal grid structures. Use of N,N'-dimethylformamide (DMF) as a solvent results in an entirely different type of assembly, with [Na(2)(dmf)(4)(H(2)O)(2)(ctv)][(dmf)(0.5)(ctv)][CB(11)H(6)Br(6)](2) showing unusual [Na-mu-(dmf)-Na] bridges, and once again forming a distorted hexagonal coordination polymer.