Solvent-accessible Channel Research Articles

Crystal structure of tris-{N,N-diethyl-N'-[(4-nitro-phen-yl)(oxo)meth-yl]carbamimido-thio-ato}cobalt(III).

The synthesis, crystal structure, and a Hirshfeld surface analysis of tris-{N,N-diethyl-N'-[(4-nitro-phen-yl)(oxo)meth-yl]carbamimido-thio-ato}cobalt(III) conducted at 180 K are presented. The complex consists of three N,N-diethyl-N'-[(4-nitro-benzene)(oxo)meth-yl]carbamimido-thio-ato ligands, threefold sym-metric-ally bonded about the CoIII ion, in approximately octa-hedral coordination, which generates a triple of individually near planar metallacyclic (Co-S-C-N-C-O) rings. The overall geometry of the complex is determined by the mutual orientation of each metallacycle about the crystallographically imposed threefold axis [dihedral angles = 81.70 (2)°] and by the dihedral angles between the various planar groups within each asymmetric unit [metallacycle to benzene ring = 13.83 (7)°; benzene ring to nitro group = 17.494 (8)°]. The complexes stack in anti-parallel columns about the axis of the space group (P), generating solvent-accessible channels along [001]. These channels contain ill-defined, multiply disordered, partial-occupancy solvent. Atom-atom contacts in the crystal packing predominantly (∼96%) involve hydrogen, the most abundant types being H⋯H (36.6%), H⋯O (31.0%), H⋯C (19.2%), H⋯N (4.8%), and H⋯S (4.4%).

Nanoporous {Co3}-Organic framework for efficiently seperating gases and catalyzing cycloaddition of epoxides with CO2 and Knoevenagel condensation

Enhancing the catalysis of metal–organic frameworks (MOFs) by regulating inherent Lewis acid-base sites to realize the efficient seperation and chemical fixation of inert carbon dioxide (CO2) is crucial but challenging. Herein, the solvothermal self-assembly of Co2+, 5′-(4-carboxy-2-nitrophenyl)-2,2′,2′',4′,6′-pentanitro-[1,1′:3′,1′'-terphenyl]-4,4′'-dicarboxylic acid (H3TNBTB) and 4′-phenyl-4,2′:6′,4′'-terpyridine (PTP) generated a highly robust cobalt-organic framework of {[Co3(TNBTB)2(PTP)]·7DMF·6H2O}n (NUC-82). In NUC-82, the tri-core clusters of {Co3} with linear shape are bridged by TNBTB3– to form two-dimensional structure in ac plane, which is further linked by PTP to generate a three-dimensional framework with two kinds of solvent-accessible channels: rhombic-like (ca. 11.57 × 10.76 Å) along a axis and rectangular-like (ca. 7.32 × 11.56 Å) along b axis. Furthermore, it is worth emphasizing that the confined pore environments are characterized by plentiful Lewis acid-base sites of tricobalt clusters, grafted nitro groups and free pyridinyl, high specific surface area and solvent-free nano-caged windows. Activated NUC-82a owns the ultra-high ethylene (C2H2) separation performance over the mixture of C2H2/CH4 and CO2/CH4 with the selectivity of 223.1 and 44.7. Thanks to the great Lewis-acid sites as well as the large pore volume, activated NUC-82a displays the high catalytic performace on the cycloaddition of CO2 with epoxides under wield condtions such as amibient pressure. Furthermore, because of the rich Lewis base sites, NUC-82a can efficiently catalyze Knoevenagel condensation of aldehydes and malononitrile. In the above organic reactions, NUC-82a not only shows the high catalytic activity, but also exhibits the high selectivity, satifactory recyclability and easy-to-separate heterogeneity, confirming that NUC-82a is a promising catalyst. Hence, this work provides in-depth insight into the construction of multifunctional MOFs by modifying the traditional ligands with as many Lewis acid-base active sites as possible.

A new heteroleptic cuprous polymer constructed by a cyanopyridine ligand exhibiting a supramolecular framework structure and luminescence.

Luminescent cuprous complexes are of great importance among coordination compounds due to their relative abundance, low cost and ability to display excellent luminescence. The title heteroleptic cuprous polymer solvate, catena-poly[[[(9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphane)-κ2P,P'](μ-pyridine-3-carbonitrile-κ2N1:N3)copper(I)] hexafluorophosphate dichloromethane trisolvate], {[Cu(C6H4N2)(C39H32OP2)]PF6·3CH2Cl2}n, conventionally abbreviated as {[Cu(3-PyCN)(Xantphos)]PF6·3CH2Cl2}n, where Xantphos and 3-PyCN represent (9,9-dimethyl-9H-xanthene-4,5-diyl)bis(diphenylphosphane) and pyridine-3-carbonitrile, respectively, has been described. In this polymer solvate, the asymmetric unit consists of three dichloromethane solvent molecules, a hexafluorophosphate anion and a polymeric heteroleptic cuprous complex cation, in which the cuprous centre is in a CuP2N2 tetrahedral coordination and is coordinated by two P atoms from the Xantphos ligand and two N atoms from two 3-PyCN ligands (the pyridyl and cyano N atoms). It is through the connection of the μ2-bridging 3-PyCN ligand that these cuprous centres are linked into a one-dimensional helical chain structure. The chains are further assembled through C-H...π interactions to form a supramolecular metal-organic framework containing solvent-accessible channels. The UV-Vis absorption and photoluminescence properties of this heteroleptic cuprous polymer have been studied on as-synthesized samples. Its luminescence emission should mainly originate from the metal-to-ligand charge transfer excited state.

Aqueous Stability and Ligand Substitution of a Layered Cu(I)/Isocyanide-Based Organometallic Network Material with a Well-Defined Channel Structure.

Isocyanide coordination networks (ISOCNs), which consist of multitopic isocyanide linker groups and transition-metal-based secondary building units (SBUs), are a promising class of organometallic framework materials for the inclusion of low-valent metal centers as primary structural components. Previously, it was demonstrated that the ditopic m-terphenyl isocyanide ligand, [CNArMes2]2 (ArMes2 = 2,6-(2,4,6-Me3C6H2)2C6H3), could provide single-metal node frameworks based on Cu(I) and Ni(0) centers. However, the relatively short linker length in [CNArMes2]2 precluded the formation of networks with significant porosity. Here, it is shown that expansion of the [CNArMes2]2 scaffold with a central phenylene spacer allows for the formation of a robust Cu(I)-based framework with a distinct and solvent accessible channel structure. This new framework, denoted Cu-ISOCN-4, is prepared as single-crystalline samples from a solvothermal reaction between [Cu(NCMe)4]PF6 and expanded linker 1,4-(CNArMes2)2C6H4. Crystallographic characterization of Cu-ISOCN-4 revealed mononuclear [Cu(THF)(CNR)3]+ structural nodes. The expanded diisocyanide linker results in fourfold interpenetrated (6,3) internal morphology. However, interpenetration in Cu-ISOCN-4 results in discrete layer domains, each of which possesses well-defined 29 × 19 Å channels along the crystallographic b axis. Thermogravimetric analysis on Cu-ISOCN-4 revealed THF solvent loss from the channels between 100-200 °C and dissociation of the Cu-coordinated THF ligand at 290 °C. The overall integrity of the network remains intact up to 400 °C, thereby signifying the robust nature of materials produced from metal-isocyanide M-C linkages. Aqueous stability studies revealed that Cu-ISOCN-4 remains chemically resistant to exposure to liquid water for several days. In addition, ligand exchange studies in both THF and aqueous solution demonstrate that the Cu-coordinated THF group in Cu-ISOCN-4 can be readily substituted with pyridine. This ligand exchange process occurs via single-crystal-to-single-crystal transformations and can also be readily monitored by infrared spectroscopy.

Underlying molecular alterations in human dihydrolipoamide dehydrogenase deficiency revealed by structural analyses of disease-causing enzyme variants.

Human dihydrolipoamide dehydrogenase (hLADH, hE3) deficiency (OMIM# 246900) is an often prematurely lethal genetic disease usually caused by inactive or partially inactive hE3 variants. Here we report the crystal structure of wild-type hE3 at an unprecedented high resolution of 1.75Å and the structures of six disease-causing hE3 variants at resolutions ranging from 1.44 to 2.34Å. P453L proved to be the most deleterious substitution in structure as aberrations extensively compromised the active site. The most prevalent G194C-hE3 variant primarily exhibited structural alterations close to the substitution site, whereas the nearby cofactor-binding residues were left unperturbed. The G426E substitution mainly interfered with the local charge distribution introducing dynamics to the substitution site in the dimer interface; G194C and G426E both led to minor structural changes. The R460G, R447G and I445M substitutions all perturbed a solvent accessible channel, the so-called H+/H2O channel, leading to the active site. Molecular pathomechanisms of enhanced reactive oxygen species (ROS) generation and impaired binding to multienzyme complexes were also addressed according to the structural data for the relevant mutations. In summary, we present here for the first time a comprehensive study that links three-dimensional structures of disease-causing hE3 variants to residual hLADH activities, altered capacities for ROS generation, compromised affinities for multienzyme complexes and eventually clinical symptoms. Our results may serve as useful starting points for future therapeutic intervention approaches.

Crystal structures of the disease-causing D444V mutant and the relevant wild type human dihydrolipoamide dehydrogenase

We report the crystal structures of the human (dihydro)lipoamide dehydrogenase (hLADH, hE3) and its disease-causing homodimer interface mutant D444V-hE3 at 2.27 and 1.84 Å resolution, respectively. The wild type structure is a unique uncomplexed, unliganded hE3 structure with the true canonical sequence. Based on the structural information a novel molecular pathomechanism is proposed for the impaired catalytic activity and enhanced capacity for reactive oxygen species generation of the pathogenic mutant. The mechanistic model involves a previously much ignored solvent accessible channel leading to the active site that might be perturbed also by other disease-causing homodimer interface substitutions of this enzyme.

Solvatochromism as a probe to observe the solvent exchange process in a 1-D porous coordination polymer with 1-D solvent accessible channels.

A one-dimensional porous coordination polymer (PCP) {[Cu2(acetate)2(3,6-di(pyridin-4-yl)-1,2,4,5-tetrazine)]·2CHCl3}n possesses pleochroic properties. Solvent exchange with acetonitrile and nitromethane reveals that single crystals of the PCP are also solvatochromic, with the solvent exchange process occurring in an unexpected double V-shaped pattern. Crystal surface adsorption modeling shows that the origin of this effect is preferential sorption at two faces of the crystal.

Molecular Dynamics and Free Energy Simulations of Phenylacetate and CO2 Release from AMDase and Its G74C/C188S Mutant: A Possible Rationale for the Reduced Activity of the Latter.

Arylmalonate decarboxylase (AMDase) catalyzes the decarboxylation of α-aryl-α-methyl malonates to produce optically pure α-arylpropionates of industrial and medicinal importance. Herein, atomistic molecular dynamics simulations have been carried out to delineate the mechanism of the release of product molecules phenylacetate (PAC) and carbon dioxide (CO2), from the wild-type (WT) and its G74C/C188S mutant enzymes. Both of the product molecules follow a crystallographically characterized solvent-accessible channel to come out of the protein interior. A higher free energy barrier for the release of PAC from G74C/C188S compared to that in the WT is consistent with the experimentally observed compromised efficiency of the mutant. The release of CO2 precedes that of PAC; free energy barriers for CO2 and PAC release in the WT enzyme are calculated to be ∼1-2 and ∼23 kcal/mol, respectively. Postdecarboxylation, CO2 moves toward a hydrophobic pocket formed by Pro 14, Leu 38, Leu 40, Leu 77, and the side chain of Tyr 48 which serves as its temporary "reservoir". CO2 releases following a channel mainly decorated by apolar residues, unlike in the case of oxalate decarboxylase where polar residues mediate its transport.

Crystal structure of bis-(ethyl-enedi-thio)-tetra-thia-fulvalenium μ2-acetato-bis-[tri-bromido-rhenate(III)] 1,1,2-tri-chloro-ethane hemisolvate.

The asymmetric unit of the title salt, (C10H8S8)[Re2Br6(CH3COO)]·0.5C2H3Cl3, contains one bis-(ethyl-enedi-thio)-tetra-thia-fulvalene (ET) radical cation, one μ2-acetato-bis-[tri-bromido-rhenate(III)] anion and a 1,1,2-tri-chloro-ethane mol-ecule with half-occupancy disordered about a twofold rotation axis. The tetra-thia-fulvalene fragment adopts an almost planar configuration typical of the ET radical cation. The C atoms of both ethyl-enedi-thio fragments in the cation are disordered over two orientations with occupancy factors 0.65:0.35 and 0.77:0.23. In the anion, six Br atoms and a μ2-acetate ligand form a strongly distorted cubic O2Br6 coordination polyhedron around the Re2 dinuclear centre. In the crystal, centrosymmetrically related ET cations and Re2O2Br6 anions are linked into dimers by π-π stacking inter-actions [centroid-to-centroid distance = 3.826 (8) Å] and by pairs of additional Re⋯Br contacts [3.131 (3) Å], respectively. The dimers are further packed into a three-dimensional network by non-directional inter-ionic electrostatic forces and by C-H⋯Br and C-H⋯S hydrogen bonds. The disordered 1,1,2-tri-chloro-ethane mol-ecules occupy solvent-accessible channels along the b axis.

Horizontal membrane-intrinsic α-helices in the stator a-subunit of an F-type ATP synthase.

ATP, the universal energy currency of cells, is produced by F-type ATP synthases, which are ancient, membrane-bound nanomachines. F-type ATP synthases use the energy of a transmembrane electrochemical gradient to generate ATP by rotary catalysis. Protons moving across the membrane drive a rotor ring composed of 8-15 c-subunits. A central stalk transmits the rotation of the c-ring to the catalytic F1 head, where a series of conformational changes results in ATP synthesis. A key unresolved question in this fundamental process is how protons pass through the membrane to drive ATP production. Mitochondrial ATP synthases form V-shaped homodimers in cristae membranes. Here we report the structure of a native and active mitochondrial ATP synthase dimer, determined by single-particle electron cryomicroscopy at 6.2Å resolution. Our structure shows four long, horizontal membrane-intrinsic α-helices in the a-subunit, arranged in two hairpins at an angle of approximately 70° relative to the c-ring helices. It has been proposed that a strictly conserved membrane-embedded arginine in the a-subunit couples proton translocation to c-ring rotation. A fit of the conserved carboxy-terminal a-subunit sequence places the conserved arginine next to a proton-binding c-subunit glutamate. The map shows a slanting solvent-accessible channel that extends from the mitochondrial matrix to the conserved arginine. Another hydrophilic cavity on the lumenal membrane surface defines a direct route for the protons to an essential histidine-glutamate pair. Our results provide unique new insights into the structure and function of rotary ATP synthases and explain how ATP production is coupled to proton translocation.

The Interactions in the Carboxyl Terminus of Human 4-Hydroxyphenylpyruvate Dioxygenase Are Critical to Mediate the Conformation of the Final Helix and the Tail to Shield the Active Site for Catalysis

4-Hydroxylphenylpyruvate dioxygenase (4-HPPD) is an important enzyme for tyrosine catabolism, which catalyzes the conversion of 4-hydroxylphenylpyruvate (4-HPP) to homogentisate. In the present study, human 4-HPPD was cloned and expressed in E. coli. The kinetic parameters for 4-HPP conversion were: k cat = 2.2±0.1 s−1; and K m = 0.08±0.02 mM. Sequence alignments show that human 4-HPPD possesses an extended C-terminus compared to other 4-HPPD enzymes. Successive truncation of the disordered tail which follows the final α-helix resulted in no changes in the K m value for 4-HPP substrate but the k cat values were significantly reduced. The results suggest that this disordered C-terminal tail plays an important role in catalysis. For inspection the effect of terminal truncation on protein structure, mutant models were built. These models suggest that the different conformation of E254, R378 and Q375 in the final helix might be the cause of the activity loss. In the structure E254 interacts with R378, the end residue in the final helix; mutation of either one of these residues causes a ca. 95% reductions in k cat values. Q375 provides bifurcate interactions to fix the tail and the final helix in position. The model of the Q375N mutant shows that a solvent accessible channel opens to the putative substrate binding site, suggesting this is responsible for the complete loss of activity. These results highlight the critical role of Q375 in orientating the tail and ensuring the conformation of the terminal α-helix to maintain the integrity of the active site for catalysis.

Coordination polymers of flexible poly-carboxylic acids with metal ions. IV. Syntheses, structures, and magnetic properties of polymeric networks of 5-(3,5)-(dicarboxybenzyloxy)isophthalic acid with Cd(ii), Cu(ii), Co(ii) and Mn(ii) ions

Four new framework solids consisting of coordination polymers [Cd2(L)(H2O)2(DMA)]n (1), [Cu2(L)(H2O)2]n (2), [Co2(L)(H2O)5]n (3) and [Mn2(L)(H2O)5]n (4) (H4L = 5-(3,5-dicarboxybenzyloxy)isophthalic acid; DMA = dimethyl acetamide) have been synthesized under hydro(solvo)thermal conditions and characterized by X-ray crystallography. In all cases, the metal-ion connectors consist of di-nuclear clusters. The fully de-protonated flexible tetradentate organic linker assumes a flat conformation with laterally oriented carboxylate functions in 1 and 2, but a twisted conformation with one carboxyphenyl residue rotated by nearly 90° with respect to the other in the isomorphous structures of 3 and 4. The resulting polymeric metal–organic lattices in 1 and 2 are perforated by wide (accounting for more than 50% of the crystal volume) solvent-accessible channel voids. In 3 and 4 the organic linker is characterized by tetrahedral tetra-carboxylate functionality, inducing the formation of open polymeric architectures with diamondoid geometries which interweave into one another in the crystal to fill most of the empty space. The remaining voids are filled by molecules of water. Thermal analysis (TGA and DTA) features of 1–4, nitrogen gas sorption behavior of 2 and solid-state variable temperature magnetic susceptibility data of 3 and 4 are reported as well.

Hydrogen bonding interactions and supramolecular networks of pyridine-aryl based thiosemicarbazides and their Zn(ii) complexes

The synthesis of five pyridyl derived thiosemicarbazides, 1–5, is presented. All five were formed in a single step from 2-hydrazinopyridine with commercially available isothiocyanates using microwave assisted synthesis. Compounds 1–4 were structurally characterised by single crystal diffraction analysis, and showed extended supramolecular hydrogen bonding arrays. Furthermore, the Zn(II) complexes 6 and 7 have been prepared using ligands 1 and 5, and structurally characterised, again showing elegant assemblies of metal-supramolecular structures with solvent accessible channels, demonstrating that these building units are excellent candidates for use in supramolecular chemistry and crystal engineering.

Mechanism of reactant and product dissociation from the anthrax edema factor: A locally enhanced sampling and steered molecular dynamics study

The anthrax edema factor is a toxin overproducing damaging levels of cyclic adenosine monophosphate (cAMP) and pyrophosphate (PPi) from ATP. Here, mechanisms of dissociation of ATP and products (cAMP, PPi) from the active site are studied using locally enhanced sampling (LES) and steered molecular dynamics simulations. Various substrate conformations and ionic binding modes found in crystallographic structures are considered. LES simulations show that PPi and cAMP dissociate through different solvent accessible channels, while ATP dissociation requires significant active site exposure to solvent. The ionic content of the active site directly affects the dissociation of ATP and products. Only one ion dissociates along with ATP in the two-Mg(2+) binding site, suggesting that the other ion binds EF prior to ATP association. Dissociation of reaction products cAMP and PPi is impaired by direct electrostatic interactions between products and Mg(2+) ions. This provides an explanation for the inhibitory effect of high Mg(2+) concentrations on EF enzymatic activity. Breaking of electrostatic interactions is dependent on a competitive binding of water molecules to the ions, and thus on the solvent accessibility of the active site. Consequently, product dissociation seems to be a two-step process. First, ligands are progressively solvated while preserving the most important electrostatic interactions, in a process that is dependent on the flexibility of the active site. Second, breakage of the electrostatic bonds follows, and ligands diffuse into solvent. In agreement with this mechanism, product protonation facilitates dissociation.

Prediction of Hydration Structures around Hydrophilic Surfaces of Proteins by Using the Empirical Hydration Distribution Functions from a Database Analysis

We developed a knowledge-based program to predict hydration structures around hydrophilic surfaces of proteins as probability density. In the program, we assume that the three-dimensional distribution of hydration water molecules on a hydrophilic surface is reconstructed by summing up the empirical hydration distribution function of each solvent-exposed polar atom composing the surface. The probability functions of polar atoms in the CO, NH(n) (n = 1,3), and OH groups were calculated from the 17 984 protein structures solved by X-ray crystallography better than resolutions of 2.2 A (Matsuoka, D.; Nakasako, M. J. Phys. Chem. B 2009, 113, 11274-11292). The program was first tested for human lysozyme. The predicted probability density enveloped more than 85% of crystal water sites found in the crystal structure refined at a resolution of 0.95 A, and the density peaks suggested as hydration sites were located within 1.5 A from more than 75% of the crystal water sites. The density reproduced the hydration structure in a solvent accessible narrow channel from the surface to the lysozyme interior. We also tested the feasibility of the program to predict the water clusters existing in the transmembrane channels of bacteriorhodopsin and aquaporin. In bacteriorhodopsin, the distributions were distinct between the ground state and the photoreaction intermediate indispensable for its function. The program reproduced the interfacial hydration in Per-Arnt-Sim-related protein-protein complex and the hydration of metastable conformations in domain motion of glutamate dehydrogenase. Taking the results for the various types of protein hydration, the present program may be a useful tool to characterize the surface properties of proteins and discuss the relevance of hydration structures to the biological functions of proteins. In addition, it will be used to predict hydration structures of proteins available at resolutions insufficient to identify water molecules.

Crystal structure and substrate specificity of plant adenylate isopentenyltransferase from Humulus lupulus: distinctive binding affinity for purine and pyrimidine nucleotides

Cytokinins are important plant hormones, and their biosynthesis most begins with the transfer of isopentenyl group from dimethylallyl diphosphate (DMAPP) to the N6-amino group of adenine by either adenylate isopentenyltransferase (AIPT) or tRNA–IPT. Plant AIPTs use ATP/ADP as an isopentenyl acceptor and bacterial AIPTs prefer AMP, whereas tRNA–IPTs act on specific sites of tRNA. Here, we present the crystal structure of an AIPT–ATP complex from Humulus lupulus (HlAIPT), which is similar to the previous structures of Agrobacterium AIPT and yeast tRNA–IPT. The enzyme is structurally homologous to the NTP-binding kinase family of proteins but forms a solvent-accessible channel that binds to the donor substrate DMAPP, which is directed toward the acceptor substrate ATP/ADP. When measured with isothermal titration calorimetry, some nucleotides displayed different binding affinities to HlAIPT with an order of ATP > dATP ∼ ADP > GTP > CTP > UTP. Two basic residues Lys275 and Lys220 in HlAIPT interact with the β and γ-phosphate of ATP. By contrast, the interactions are absent in Agrobacterium AIPT because they are replaced by the acidic residues Asp221 and Asp171. Despite its structural similarity to the yeast tRNA–IPT, HlAIPT has evolved with a different binding strategy for adenylate.

Channel-forming solvates of 6-chloro-2,5-dihydroxypyridine and its solvent-free tautomer 6-chloro-5-hydroxy-2-pyridone

On crystallization from CHCl3, CCl4, CH2ClCH2Cl and CHCl2CHCl2, 6-chloro-5-hydroxy-2-pyridone, C5H4ClNO2, (I), undergoes a tautomeric rearrangement to 6-chloro-2,5-dihydroxypyridine, (II). The resulting crystals, viz. 6-chloro-2,5-dihydroxypyridine chloroform 0.125-solvate, C5H4ClNO(2).0.125CHCl3, (IIa), 6-chloro-2,5-dihydroxypyridine carbon tetrachloride 0.125-solvate, C5H4ClNO(2)..0.125CCl4, (IIb), 6-chloro-2,5-dihydroxypyridine 1,2-dichloroethane solvate, C5H4ClNO2.C2H4Cl2, (IIc), and 6-chloro-2,5-dihydroxypyridine 1,1,2,2-tetrachloroethane solvate, C5H4ClNO2.C2H2Cl4, (IId), have I4(1)/a symmetry, and incorporate extensively disordered solvent in channels that run the length of the c axis. Upon gentle heating to 378 K in vacuo, these crystals sublime to form solvent-free crystals with P2(1)/n symmetry that are exclusively the pyridone tautomer, (I). In these sublimed pyridone crystals, inversion-related molecules form R(2)(2)(8) dimers via pairs of N-H...O hydrogen bonds. The dimers are linked by O-H...O hydrogen bonds into R(4)(6)(28) motifs, which join to form pleated sheets that stack along the a axis. In the channel-containing pyridine solvate crystals, viz. (IIa)-(IId), two independent host molecules form an R(2)(2)(8) dimer via a pair of O-H...N hydrogen bonds. One molecule is further linked by O-H...O hydrogen bonds to two 4(1) screw-related equivalents to form a helical motif parallel to the c axis. The other independent molecule is O-H...O hydrogen bonded to two 4 related equivalents to form tetrameric R(4)(4)(28) rings. The dimers are pi-pi stacked with inversion-related dimers, which in turn stack the R(4)(4)(28) rings along c to form continuous solvent-accessible channels. CHCl3, CCl4, CH2ClCH2Cl and CHCl2CHCl2 solvent molecules are able to occupy these channels but are disordered by virtue of the 4 site symmetry within the channels.

Self-assembly of a hydrogen bonded framework from a gold phosphine complex with a pendant uracil group

The easily prepared complex AuCl(PPh(2)Ur) (Ur = uracil) self-assembles in the solid state to form crystals containing solvent-accessible channels, the structure remains crystalline even after removal and re-addition of solvent.

Layer-pillared metal-organic framework showing two-fold interpenetration and considerable solvent-accessible channels

Via solvothermal synthesis, the self-assembly of CuCl 2, 1,4-benzenedicarboxylic acid, and N, N′-bis(4-pyridylformamide)-1,4-benzene in DMF generated a layer-pillared metal-organic coordination polymer, which affords two-fold interpenetration and considerable solvent-accessible channels where the guest water molecules reside. Further, the TG and XRD researches disclose that such interpenetrating net stabilized by H-bonds can be maintained up to 350 °C even after the release of free water molecules, and through the calcination and immersion experiments, it is suggested that the guest water molecules in the channels are reversible, which is traced by XRD and IR studies.

Framework coordination polymers of tetra(4-carboxyphenyl)porphyrin and lanthanide ions in crystalline solids

Targeted synthesis of framework coordination polymers was achieved by reacting meso-tetra(4-carboxyphenyl)porphyrin with common salts of lanthanide metal ions. The large size, high coordination numbers and strong affinity for oxo ligands of the latter, combined with favourable hydrothermal reaction conditions in acidic environments, allowed the formation of open three-dimensional single-framework architectures in which the tetra-dentate porphyrin units are inter-coordinated by multinuclear assemblies of the bridging metal ions, which serve as construction pillars, into infinite architectures. Three different modes of coordination polymerisation were characterized by single-crystal X-ray diffraction. They differ by the nuclearity of the metal connectors. All structures exhibit, however, layered organization of the porphyrin-metal domains, and periodically spaced solvent accessible channel voids that penetrate through these layers throughout the corresponding crystals. Thermal analysis provided additional insight into the stability of these polymeric materials.