Coordination supramolecular structures

Supramolecular coordination ensembles with d-metal ions directly incorporated into their structures are the subject of the present review. Diversity of such structures considerably exceeds that of purely organic supramolecules due to inclusion of additional polyvalent metal atoms (totally sixty) with diverse coordination geometry. Such metal-containing constructions are generated by self-assembling and (or) by templating, as 2D and 3D geometric figures (polygons and polyhedra) and “furniture” constructions (ladders, racks, grids) together with helicates, interwoven species and metallodendrimers as combinations of 1D coordination compounds. Besides, is presented a numerous of coordination polymers and supramolecular crystal lattices as infinite structures.     

Self-assembly of heterogeneous supramolecular structures with uniaxial anisotropy

Uniaxial anisotropy in two-dimensional self-assembled supramolecular structures is achieved by the coadsorption of two different linear molecules with complementary amine and imide functionalization. The two-dimensional monolayer is defined by a one-dimensional stack of binary chains, which can be forced to line up along steps in vicinal surfaces. The competing driving forces in the self-organization process are discussed in light of the structures observed during single molecule adsorption and coadsorption on flat and vicinal surfaces and the corresponding theoretical calculations.     

Syntheses of fluorescent thiocyanate supramolecular compounds with unusual two-dimensional structures

Three novel thiocyanate supramolecular compounds have been synthesized and characterized by X-ray diffraction and fluorescent spectra. Compound [pipH]₂[Co(NCS)₄] (pip=piperazine) 1 possesses a two-dimensional layer connected by the combination of N-H?N hydrogen bonds and weak S?S contacts. Under the same conditions, using nickel salt instead of cobalt salt as a starting material, we obtained a different two-dimensional supramolecular layer [pipH]₂[Ni(NCS)₄] 2 connected by unusual N-H?S hydrogen bonds and weak S?S contacts. In order to observe the influence of the dimension of ligand on the self-assembly structure, dabco was used for substituting pip, and compound [dabcoH]₂[Ni(NCS)₄] (dabco=1,4-Diazabicyclo[2.2.2] octane) 3 was gained, which constructed two-dimensional, highly wavy network with hourglass-shaped cavities only through N-H?S hydrogen bonds.     

Topology of supramolecular structures in ethanol solutions

A quantitative topological analysis of supramolecular structures in ethanol solutions with methanol, propanol, water, benzene, and hexane is performed by the MDGT method previously proposed by the authors. The method is based on a combination of molecular dynamics calculations and the graph theory, which enables the recognition and memorization of supramolecular structures observed in each snapshot of the molecular dynamic trajectory, the averaging of data for any number of these snapshots. Thus, the averaged concentrations of associates (dimers, trimers, etc.) are represented and then the concentrations and characteristics of isomers (e.g., chains, branched chains, rings, etc.), bond lengths, angles, etc. are determined in each group of associates.     

Mechanism of N-octadecyl-N'-maleoyl-L-phenylalanine self-assembled into supramolecular structures

N-Octadecyl-N'-maleoyl-L-phenylalanine (ODMA-L-Phe) was synthesized through the condensation, deprotection and aeid-ylation reaction of BOC-L-phenylalanine, octadecylamine and maleic anhydride. ODMA-L-Phe can self-assemble in some organic solvents and turned them into thermally reversible physical supramolecular organogels. The morphology of ODMA-L-Phe aggregates was characterized by polarized optical microscopy (POM) and field emission scanning electron microscope (FE-SEM). The aggregates of ODMA-L-Phe were needle-like fibrils with diameters of approximately 100-200 nm. The mechanism of ODMA-L-Phe self-assembly in organic solvents was investigated using 1H NMR and circular dichroism (CD). The results indicated that hydrogen bonding was one of the main driving forces for the self-assembly of ODMA-L-Phe.     

Assembly of ethylzincate compounds into supramolecular structures

Sodium and potassium triethylzincate were isolated by Wanklyn in 1858, and are corner stones in the history of organometallic chemistry. Crystallisation of organozincates from neat dialkylzinc, in the absence of a coordinating solvent, can be expected to result in assembly of supramolecular structures, rather than formation of discrete molecules in the crystalline state. This inspired us to reinvestigate Wanklyn’s classical compounds. Crystallisation of sodium triethylzincate from benzene led to metallation of benzene and the formation of diethylphenylzincate anions. The compound is a two-dimensional network where Na⁺ ions link the zincate anions by coordination to both ethyl- and phenyl groups. We have also, accidently, isolated crystals of the two-dimensional coordination network [K₂(ZnEt₂)₄O]_n, displaying a rare oxo-centred core with an octahedral oxide ion surrounded by four zinc atoms and two potassium atoms.     

Solid-state supramolecular structures of resorcinol-arylboronic acid compounds

[structure: see text] An X-ray crystallographic study of unique hydrogen-bonded supramolecular solid-state networks comprised of a tetraarylboronic acid resorcinarene is described. When 1 is recrystallized from 9:1 MeOH:EtOH, partial esterification takes place to give compound 2, the corresponding half methyl ester, which forms an infinite two-dimensional array. Each molecule participates in 12 hydrogen bonds with other macrocycles. These hydrogen bonds are both B-OH- - - OH (phenolic) and OH (phenolic)- - -OH (phenolic).     

Approaches to supramolecular structures with various topologies in the crystal lattice

Simple molecular building blocks for creating supramolecular architectures in the crystal lattice are described. Combination of hydrogen bonding and alkyl chain crystallization is used to explore self-assembly¹ of molecular building blocks 1, 2, 3 and 4 in the crystal lattice. The crystal lattice of pure acids and its equimolar mixtures with bifunctional hydrogen bond acceptors are characterized by singe crystal analysis.     

Solution NMR techniques for large molecular and supramolecular structures

Transverse relaxation-optimized spectroscopy (TROSY) or generation of heteronuclear multiple quantum coherences during the frequency labeling period and TROSY during the acquisition period have been combined either with cross-correlated relaxation-induced polarization transfer (CRIPT) or cross-correlated relaxation-enhanced polarization transfer (CRINEPT) to obtain two-dimensional (2D) solution NMR correlation spectra of (15)N,(2)H-labeled homo-oligomeric macromolecules with molecular weights from 110 to 800 kDa. With the experimental conditions used, the line widths of the TROSY-components of the (1)H- and (15)N-signals were of the order of 60 Hz at 400 kDa, whereas, for structures of size 800 kDa, the line widths were about 75 Hz for (15)N and 110 Hz for (1)H. This paper describes the experimental schemes used and details of their setup for individual measurements. The performance of NMR experiments with large structures depends critically on the choice of the polarization transfer times, the relaxation delays between subsequent recordings, and the water-handling routines. Optimal transfer times for 2D [(15)N,(1)H]-CRIPT-TROSY experiments in H(2)O solutions were found to be 6 ms for a molecular weight of approximately 200 kDa, 2.8 ms for 400 kDa, and 1.4 ms for 800 kDa. These data validate theoretical predictions of inverse proportionality between optimal transfer time and size of the structure. The proton longitudinal relaxation times in H(2)O solution were found to be of the order of 0.8 s for structure sizes around 200 kDa, 0.4 s at 400 kDa, and 0.3 s at 800 kDa, which enabled the use of recycle times below 1 s. Since improper water handling results in severe signal loss, the water resonance was kept along the z-axis during the entire duration of the experiments by adjusting each water flip-back pulse individually.     

New titanium imido synthons: syntheses and supramolecular structures

Reactions of Ti(NMe(2))(2)Cl(2) with a wide range of primary alkyl and arylamines RNH(2) afforded the corresponding 5-coordinate imido titanium compounds Ti(NR)Cl(2)(NHMe(2))(2) (R = (t)Bu (1), (i)Pr (2), CH(2)Ph (3), Ph (4), 2,6-C(6)H(3)Me(2) (5), 2,6-C(6)H(3)(i)Pr(2) (6), 2,4,6-C(6)H(2)F(3) (7), 2,3,5,6-C(6)HF(4) (8), C(6)F(5) (9), 4-C(6)H(4)Cl (10), 2,3,5,6-C(6)HCl(4) (11), 2-C(6)H(4)CF(3) (12), 2-C(6)H(4)(t)Bu (13)). The compounds 1-13 are monomeric in solution but in the solid state form either N-H...Cl hydrogen bonded dimers or chains or perfluorophenyl pi-stacked chains, depending on the imido R-group. The compound 13 was also prepared in a "one-pot" synthesis from RNH(2) and Ti(NMe(2))(4) and Me(3)SiCl. Reaction of certain Ti(NR)Cl(2)(NHMe(2))(2) compounds with an excess of pyridine afforded the corresponding bis- or tris-pyridine analogues [Ti(NR)Cl(2)(py)(x)](y) (x = 3, y = 1; x = y = 2), and the structure of Ti(2)(NC(6)F(5))(2)Cl(2)(mu-Cl)(2)(py)(4) shows pi-stacking of perfluorophenyl rings. Reaction of Ti(NMe(2))(2)Cl(2) with cross-linked aminomethyl polystyrene gave quantitative conversion to the corresponding solid-supported titanium imido complex. This paper represents the first detailed study of how supramolecular structures of imido compounds may be influenced by simple variation of the imido ligand N-substituent.     

Photostability and skin penetration of different E-resveratrol-loaded supramolecular structures

It is desirable and challenging to prevent E-resveratrol (E-RSV) from photoisomerizing to its Z-configuration to preserve its biological and pharmacological activities. The aim of this research was to evaluate the photostability of E-RSV-loaded supramolecular structures and the skin penetration profile of chemically and physically stable nanoestructured formulations. Different supramolecular structures were developed to act as carriers for E-RSV, that is, liposomes, polymeric lipid-core nanocapsules and nanospheres and solid lipid nanoparticles. The degrees of photostability of these formulations were compared with that of an ethanolic solution of E-RSV. The skin penetration profiles of the stable formulations were obtained using vertical diffusion cells (protected from light and under UVA radiation) with porcine skin as the membrane, followed by tape stripping and separation of the viable epidermis and dermis in a heated water bath. Photoisomerization was significantly delayed by the association of resveratrol with the nanocarriers independently of the supramolecular structure. Liposomes were the particles capable of maintaining E-RSV concentration for the longest time. On the other hand, E-RSV-loaded liposomes reduced in size showing low physical stability under UVA radiation. In the dark, the skin penetration profiles were very similar, but under UVA radiation the E-RSV-loaded nanocarriers showed increasing amounts in the total epidermis.     

A smart supramolecular phototherapeutics for specific cancer therapy

正Phototherapeutics provides opportunities for cancer therapy because of its high spatiotemporal controllability and minimal invasiveness. For example, photodynamic therapeutics,often termed as photosensitizer (PS), can be administered to the patients with subsequent exposure to a specific light that leads to the death of the disease cells via oxidative damage.However, the efficacy of traditional PS has been limited by several issues including poor tumor specificity, fast renal clearance, and phototoxic side effect on normal tissues [1].     

Two nickel(II) carboxyphosphonates with different supramolecular structures: synthesis,crystal structures and magnetic properties

Transition Metal Chemistry - Two Ni(II) carboxyphosphonates, namely [Ni(H4L)2] (1) and [Ni(H3L)(H2O)]·2H2O (2) (H5L=HOOCC6H4CH2N(CH2PO3H2)2), have been hydrothermally synthesized. Structural...     

Hydrogen-bonded supramolecular structures constructed from trinuclear copper units

Four copper complexes with similar trinuclear copper units, [Cu₆(Bmshp)₂(SO₄)₂(H₂O)₇]·2H₂O (1), [Cu₃(Bmshp)(ClO₄)₂(H₂O)₄]·5H₂O (2), [Cu₃(Bmshp)(DMF)₄(H₂O)₂]·H₂O·2DMF·2ClO₄ (3) and [Cu₃(H₂Bcshp)(ClO₄)₂(H₂O)₄]·3H₂O (4) (H₄Bmshp = 2,6-bis[(3-methoxysalicylidene)hydrazinocarbonyl]pyridine, H₆Bcshp = 2,6-bis[(3-carboxylsalicylidene)hydrazinocarbonyl]pyridine), were synthesized and characterized by elemental analysis, IR and single crystal X-ray diffraction analysis. Due to the different anions, solvents and ligands used in the syntheses, complexes 1–4 exhibit diverse supramolecular structures constructed from the corresponding trinuclear copper units via H-bonds.     

Fundamental problems of the chemistry of supramolecular and nanosized structures

A series of problems presently being solved in the framework of two new complementary directions of chemistry, viz., supramolecular chemistry and chemistry of nanosized systems, which have been formed and intensively developed for the recent 2–3 decades, are discussed.     

Solid-state molecular folding and supramolecular structures of triptycene-derived secondary dicarboxamides

The synthesis and X-ray crystal structures of triptycene-derived secondary dicarboxamides 1 and 4-7 and reference compounds 2, 3, and 8 are reported. For comparison, molecular conformations of 1-8 in the gas phase and those of 1 and 3-6 in CD2Cl2 investigated by AM1 modeling and 1H NMR spectroscopy, respectively, are also included. The solid-state conformations of 1 and 5-8 are folded and compact, resulting from the cooperative effects of intramolecular amide-amide hydrogen bonding and edge-to-face arene-arene interactions between the triptycene and the N-acetylsulfanilyl groups. The sulfonyl ester groups are also essential in the folding of 1 and 5-8 and function as structural turn units. In contrast, the conformations of 2-4 are unfolded due to the lack of one of these three essentials. The extended triptycene ring systems in 6 and 7 provide an arene-arene contact mode that is different from that for 1 and 5. While AM1 calculations suggest that the two possible arene-arene contact modes in 6 and 7 have similar conformational energies, the one observed in the solid state is also favored in solutions. To achieve a more regular shape for compact crystal packing, the bulky triptycene groups tend to pack in pairs. As a result, the intermolecular amide-amide hydrogen bonding is perturbed and modified with the participation of either the sulfonyl groups or the methanol solvent molecules, leading to various hydrogen-bonding motifs for these triptycene diamides.     

Microstructures and supramolecular structures of butadiene-nitrile rubbers: Paramagnetic-probe study

The chain microstructures and supramolecular structures of butadiene-nitrile rubbers are studied by ESR spectroscopy. On the temperature dependences of the rotational mobility (correlation time τ_c) of paramagnetic probes differing in size (2,2,6,6-tetramethylpiperidine-1-oxyl and 4-benzoate-2,2,6,6-tetramethylpiperidine-1-oxyl), relaxation transitions are observed. It is shown that there is a correlation between the Arrhenius parameters of rotational mobility of radicals and the copolymer composition and that different brands of rubbers differ in microstructure and supramolecular structure.     

Polyhedral structures with an odd number of vertices: nine-atom clusters and supramolecular architectures

The geometries of metal clusters and supramolecular architectures that contain nine metal atoms are analyzed within the framework of continuous shape measures (CShM). The most common polyhedra in nine coordinate complexes, the capped square antiprism and the tricapped trigonal prism, are also found among these families of compounds, even if much more scarcely. In addition, a variety of new shapes, not found among coordination polyhedra, can be identified and their proximity to the ideal geometries quantified. These include a linear chain, two types of trigonal columns, the planar regular enneagon, two-dimensional hexagonal and square grids, fragments of a close-packed structure, the triangular cupola, the tridiminished icosahedron or different fragments of the icosahedron. Among the nine-atom boranes and related clusters of the groups 13 and 14 elements, those having between 18 and 20 framework electrons present the structure of the tricapped trigonal prism, the expected closo structure. However, clusters with 21 and 22 framework electrons present a variety of structures with geometries covering nearly all the path that takes one from the capped square antiprism (nido form) to the tricapped trigonal prism (closo form).