Structure Of Supramolecular Complexes Research Articles

Species of Gold(III) Binding by Binuclear Zinc Dipropyldithiocarbamate: Supramolecular Self-Organization and Thermal Behavior of Ionic Complexes [Au(S2CNPr2)2]2[ZnCl4] and [Au(S2CNPr2)2]2[AuCl4][AuCl2

The reaction of binuclear zinc dipropyldithiocarbamate [Zn2{S2CN(C3H7)2}4] with an AuCl3/2 М HCl solution is studied. The double ionic complex [Au{S2CN(C3H7)2}2]2[ZnCl4] (I) is identified as the main species of gold(III) binding in the heterogeneous system under study and is characterized by 13С and 15N CP-MAS NMR spectroscopy. Single crystals of heterovalent compound [Au{S2CN(C3H7)2}2]2[AuCl4][AuCl2] (II) are sampled as a by-product. The crystal and supramolecular structures of complexes I and II are determined by the direct XRD method (CIF files CCDC nos. 2159171 and 2159170, respectively). The self-organization of the complex pseudopolymeric structures of compounds I and II are shown to be due to the binding of ionic structural units by secondary nonvalent interactions Au⋅⋅⋅S and S⋅⋅⋅Cl and hydrogen bonds C–H⋅⋅⋅Cl. The thermal behavior of the complexes is studied by simultaneous thermal analysis (STA), and the quantitative regeneration of bound gold (I and II) with the partial transformation of released ZnCl2 to ZnS (I) is found.

Binding of Gold(III) from Solutions by the [Ag6{S2CN(CH2)6}6] Cluster: Synthesis, Thermal Behavior, and Self-Organization of the Supramolecular Structure of the Double Complex [Au{S2CN(CH2)6}2]2[AgCl2]Cl\xb72CHCl3 (Role of Secondary Au\u22c5\u22c5\u22c5Cl, Ag\u22c5\u22c5\u22c5S, and Cl\u22c5\u22c5\u22c5Cl Interactions)

The capability of silver(I) cyclo-hexamethylenedithiocarbamate to concentrate gold(III) from solutions characterized by a high level of salinity (5.15 M NaCl) into the solid phase has been established. The double chloroform-solvated Au(III)–Ag(I) complex [Au{S2CN(CH2)6}2]2[AgCl2]Cl·2CHCl3 (I) was preparatively isolated as an individual form of binding of [AuCl4]– anions. The composition of the ionic structural units of compound I indicates that gold(III) binding from a solution to the solid phase is accompanied by the complete redistribution of the HmDtc ligands between the coordination spheres of Ag(I) and Au(III). Complex I characterized by IR spectroscopy, simultaneous thermal analysis, and X-ray structure analysis (CIF file CCDC no. 2051654) exhibits the supramolecular structure containing two oppositely charged pseudo-polymeric subsystems. Complex cations [Au{S2CN(CH2)6}2]+ and anions [AgCl2]– (in a ratio of 2 : 1) form a complicatedly organized cation-anionic pseudo-polymeric ribbon ({[Au(HmDtc)2]⋅⋅⋅[AgCl2]⋅⋅⋅[Au(HmDtc)2]}+)n due to secondary interactions Ag⋅⋅⋅S (3.2613 Å) and Au⋅⋅⋅Cl (3.2765 Å). The pseudo-polymeric ribbon consists of two rows of cations and a row of anions. The outer-sphere chloride ions combine the solvate chloroform molecules by two equivalent hydrogen bonds Cl⋅⋅⋅H–C yielding anion-molecular triads [Cl3CH⋅⋅⋅Cl⋅⋅⋅HCCl3]–, which are involved in the formation of the supramolecular ribbon due to the secondary Cl⋅⋅⋅Cl interactions (3.4058 Å) between the nonequivalent chlorine atoms of the nearest solvate molecules. The study of the thermal behavior of complex I makes it possible to determine the character of thermolysis and conditions for the quantitative regeneration of bound gold.

Cellulose cryogels prepared by regeneration from phosphoric acid solutions

The supermacroporous structure and ease of preparation of polysaccharide-based cryogels have led to their wide use in many areas and make them promising biomaterials for tissue engineering. One polysaccharide of particular interest for the production of tissue engineering scaffolds is cellulose, a natural biocompatible and nontoxic polymer. However, the complex supramolecular structure of cellulose creates difficulties in its dissolution and further processing into biomedical products. Conventional cellulose solvents have significant disadvantages, including poor removal from the resulting products. Therefore, this work proposes the preparation of cellulose-based cryogels using orthophosphoric acid, which can be easily removed and recovered. The effect of cellulose dissolution conditions on the structure and properties of cryogels were studied. Highly porous (88.3–93.4%) and light (ρ 0.091–0.161 g/cm3) cryogels with complex hierarchical morphologies were produced using a dissolution temperature of (20 ± 2) °C, a cellulose concentration in the solution > 3%, a dissolution time of 24–48 h (depending on the cellulose concentration), and precipitation with water or acetone. 13C CP-MAS NMR spectroscopy results confirmed that the regenerated cellulose is predominantly amorphous, with a crystallinity of 6.8–30.6% in the structure of cellulose II. The compressive modulus E for cryogels was from 330 to 3675 kPa. FTIR spectroscopy results showed that the regenerated cellulose had an increased number of aldehyde groups and a decreased number of hydrogen bonds decreases, indicating a decrease in crystallinity. No phosphoric acid esters of cellulose were detected in the cryogels by FTIR spectroscopy. These results pave the way for the easy preparation of biomaterials for tissue engineering.

Efficient isolation of organosolv lignin-carbohydrate complexes (LCC) with high antioxidative activity via introducing LiCl/DMSO dissolving

Lignin-carbohydrate complexes (LCC) have shown great potential as biocompatible antioxidants. But it is difficult to isolate LCC efficiently from lignocellulose by traditional Solid-Liquid Extraction method (SLE), which is blamed to the innate bioimpedance caused by the complex supramolecular structure of the lignocellulose, and a great mass transferring resistance between the extracting solution and solid lignocellulose. To release these restrictions above and improve the efficiency of LCC isolation, a modified isolating method named Liquid-Liquid Extraction (LLE) was proposed, in which ball-milled wheat stalk was dissolved in lithium chloride/dimethyl sulfoxide (LiCl/DMSO) solution, then regenerated by dioxane aqueous to extract LL-LCCs. The effect of the LLE on the LCC isolating was evaluated and results showed that both the total yield and antioxidant activity of LL-LCCs were higher than that of control group. It proved the dissolution of wheat stalk in LiCl/DMSO solution could reduce the mass transfer resistance during the extraction. Due to the catalyzation of LiCl as Lewis acid, LL-LCCs had lower molecular weight but more phenolic hydroxyl groups and higher S/G ratios. These factors of LL-LCCs resulted in greater free-radical scavenging ability than control sample. The modified isolation protocol could facilitate the isolation and utilization of LCCs as a free-radical scavenger.

Novel one‐dimensional polymeric Cu(II) complexes via Cu(II)‐assisted hydrolysis of the 2,4‐bis(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)‐6‐methoxy‐1,3,5‐triazine pincer ligand: Synthesis, structure, and antimicrobial activities

Two unexpected one‐dimensional coordination polymers, [Cu(PT)(H2O)Cl]n 1 and [Cu2(BPT)(ClO4)3(H2O)4]n·2nH2O 2, of symmetrical triazine‐based ligands were synthesized by Cu(II)‐mediated hydrolysis of the 2,4‐bis(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)‐6‐methoxy‐1,3,5‐triazine (MBPT) pincer ligand. The reaction of Cu(ClO4)2·6H2O with MBPT proceeded via hydrolysis of the methoxy group to produce the dicompartmental 4,6‐bis(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)‐1,3,5‐triazin‐2(1H)‐one ligand (HBPT) that then undergoes in situ complexation with Cu(II) to afford 2. In case of CuCl2, the reaction proceeds further with C–N cleavage of one pyrazolyl unit leading to the formation of 6‐(3,5‐dimethyl‐1H‐pyrazol‐1‐yl)‐1,3,5‐triazine‐2,4(1H,3H)‐dione ligand (HPT) that also undergoes in situ complexation with Cu(II) affording 1. The role of Cu(II) is to increase the Lewis acid reactivity of the water molecule where similar hydrolytic reactions for MBPT were observed in acidic medium in presence of an aqueous HCl (1:1 v/v) solution. The molecular and supramolecular structures of complexes 1 and 2 were investigated using X‐ray diffraction of single crystal, Hirshfeld analysis, and density functional theory calculations. The Cl…H (11.7%) and O…H (24.7%) contacts are the most important in 1, whereas the molecular packing of 2 is controlled mainly by the O…H (58.7%) hydrogen bonds. Complex 2 showed better activity against Escherichia coli, Bacillus subtilis, and Candida albicans compared with the standard antibiotics amoxicillin, tetracycline, and ampicillin. In general, complexes 1 and 2 showed good antimicrobial activity than these antibiotics and have the advantage to be used as both antibacterial and antifungal agents.

Novel lanthanide(III) complex [LaL2(NO3) (H2O)2]·5H2O with 2-pyridine carboxaldehyde isonicotinoyl hydrazine exhibiting a 3D supramolecular topology 3,6T49

A new coordination compound, namely [LaL2(NO3)(H2O)2]·5H2O (1), has successfully been synthesized from La(NO3)3·6H2O, 2-pyridinecarboxaldehyde isonicotinoylhydrazone (HL) and NaOH, as a deprotonated agent, in the CH3OH medium under mild solvothermal conditions at 120 °C. Both HL and 1 were characterized by FTIR spectroscopy and elemental analysis. Complex 1 was also studied by the simultaneous TG-DSC, powder and single crystal X-ray diffraction analyses. According to the single crystal diffraction analysis, the lanthanum (III) ion adopts a deca-coordinated mode, and five lattice water molecules exist in the asymmetric unit. The crystal structure of 1 is mainly stabilized by strong O–H⋯N and O–H⋯O and weak π⋯π and C–H⋯π interactions. As a result of hydrogen bonding, a 3D supramolecular structure is formed with a binodal (3,6)-connected network with a 3,6T49 topology having point symbol of {4∙62}{47∙65∙83}. As evidenced from the Hirshfeld surface analysis of [LaL2(NO3)(H2O)2], intermolecular H⋯H (40.1%), H⋯C (15.4%), H⋯N (12.2%) and H⋯O (20.3%) contacts occupy an overwhelming majority of a molecular surface of the complex molecule. Highly favoured intermolecular C⋯C (6.5%) and C⋯N (4.0%) contacts also play a vital role in the supramolecular structure of complex. Upon heating, complex 1 decomposes in few steps, consistently losing lattice water molecules, coordinated water molecules followed by the decomposition of organic ligands, yielding La(NO3)3 followed by the formation of a final residue La2O3.

Crystal structure, cytotoxicity and biological activity of hydrogen bonded networks based on dimethyltin (IV) and bipodal ligands

The supramolecular complexes (SC) of the type [Me2SnCl2L], L = 2,2′-bipyridine (2,2′-bpy), SC 1, 4,4′-bipyridine (4,4′-bpy), SC 2, and (1,10-phenanthroline), SC 3, have been synthesized and structurally characterized by elemental analysis, FT-IR, UV–Vis, 1H and 13C NMR spectra and X-ray single crystal. The X-ray data of SC 1 and SC 2 exhibited 1:1 stoichiometry for the dimethyltin dichloride: bipodal ligand. The structure of SC 1 extends along the a-axis in a parallel way forming 1D-chains via H-bonds while they further propagate creating 2D-network via extensive H-bonds. The extending structure of the SC 2 along the a-axis consists of parallel 1D-chains via H-bonds creating the A … A … A fashion. Molecular modeling studies of SC 3 indicated that Sn(IV) center acquires N2C2Cl2 octahedral geometry. The tested compounds SC 1, SC 2 and SC 3 were found to inhibit cell proliferation and induce high percent of apoptotic towards human breast adenocarcinoma (MCF7), liver carcinoma (HEPG2), colorectal carcinoma (HCT-116), cervical carcinoma (HELA) and prostate cancer (PC3) cell lines in vitro model within short times of treatment. The anti-Oxidant and anti-hemolytic assays employ that SC 1 exhibits moderate antioxidant activity as well as the most potent anti-hemolysis activities compared with ascorbic acid. The antimicrobial assessment has been also studied by disc diffusion method.

Lignocellulosic Film as a Valid Tool to Investigate Inhibitions to Cellulose Enzymatic Hydrolysis

The complex supramolecular structure of lignocellulose makes it difficult to clarify the recalcitrance to enzymatic digestibility. As an extensively used model mimicking the plant cell wall, assembled lignocellulosic film was applied to investigate inhibition factors of enzymatic hydrolysis for the first time. Xylan was deposited and then a model lignin compound was synthesized to equip bacterial cellulose films. Scanning electron microscopy and surface contact angle analyses revealed that lignin inhibited enzymatic hydrolysis by reducing cellulase accessibility to the cellulose surface. Moreover, xylan showed a good correlation (R2 = 0.969) with the decreased cellulose conversion, although xylan itself did not display inhibitions. The component and surface analyses revealed that xylan enhanced lignin formation on the cellulose surface, and thus increased lignin inhibition. These results highlighted the validity of lignocellulosic films in elucidating inhibitions of cellulose enzymatic hydrolysis. The research could thus open a new avenue for the mechanistic study of the recalcitrance of lignocellulose to enzymatic hydrolysis.

ТЕМПЕРАТУРНЫЕ ПЕРЕХОДЫ В НЕКРИСТАЛЛИЧЕСКИХ ДОМЕНАХ ЦЕЛЛЮЛОЗЫ

When samples of various polymers are heated, there is a monotonic change of various physico-chemical, physical and chemical properties until achieving of certain transition temperatures at which an abrupt change in properties of the polymers is observed. Cellulose is known to be a linear stereoregular semi-crystalline polysaccharide composed of anhydroglucose units joined by 1,4-β-glycosidic bonds. This polysaccharide has a complex supramolecular structure consisting of ordered crystallites and less ordered noncrystalline domains. This review article contains the description and discussion of temperature transitions in non-crystalline domains of cellulose. It has been shown that due to structural heterogeneity the non-crystalline domains have three temperature transitions of relaxation type, where the α 1 transition at 490-500 K and α 2 transition at 380-410 K are caused by the occurrence of segmentalmobility in dense mesomorphous and less packed amorphous clusters, respectively; whereas the β transition at 260-300 K is related to the mobility of small segments in loose packed amorphous clusters, which probably are located on the outer surface of cellulose fibrils. Under the action of water and other plasticizers all three isophase transitions are shifted to lower temperatures. Along with α and β transitions, also low-temperature γ transition at 180-200 K is observed due to mobility of hydroxy-methylene groups in noncrystalline domains of cellulose.

Functional Sulfur‐Doped Buckybowls and Their Concave–Convex Supramolecular Assembly with Fullerenes

AbstractBuckybowls are fascinating components of supramolecular assemblies owing to their unique bowl‐shaped π‐surfaces. Herein we present a protocol for the functionalization of a sulfur‐doped buckybowl, trithiasumanene, via a brominated intermediate, from which thiolated trithiasumanenes were derived. The curved surface and electron‐donating properties of thiolated trithiasumanenes promote their ready assembly with fullerenes to form concave–convex complexes. The supramolecular assembly behavior in solution was investigated by NMR analysis. The structures of supramolecular complexes were unambiguously characterized by crystallography. The crystals of the concave–convex complexes showed high thermal stability and photoconductivity.

Functional Sulfur-Doped Buckybowls and Their Concave-Convex Supramolecular Assembly with Fullerenes.

Buckybowls are fascinating components of supramolecular assemblies owing to their unique bowl-shaped π-surfaces. Herein we present a protocol for the functionalization of a sulfur-doped buckybowl, trithiasumanene, via a brominated intermediate, from which thiolated trithiasumanenes were derived. The curved surface and electron-donating properties of thiolated trithiasumanenes promote their ready assembly with fullerenes to form concave-convex complexes. The supramolecular assembly behavior in solution was investigated by NMR analysis. The structures of supramolecular complexes were unambiguously characterized by crystallography. The crystals of the concave-convex complexes showed high thermal stability and photoconductivity.

Cyanide-bridged bi- and trinuclear heterobimetallic Fe(III)–Mn(III) complexes: Synthesis, crystal structures and magnetic properties

By employing trans-dicyano or pentacyanometalate as building block and using a bicompartimental Schiffbase based manganese(III) compound as assemble segment, two new cyanide-bridged heterometallic Fe(III)–Mn(III) complexes {[Mn(L)(H2O)][Febpb(CN)2]}·2CH3OH (1) and {[Mn(L)(H2O)]2··[Fe(CN)5NO]} (2) (bpb2– = 1,2-bis(pyridine-2-carboxamido)benzenate, L = N,N'-ethylene-bis(3-ethoxysalicylideneiminate) have been synthesized and characterized by elemental analysis, IR spectroscopy and X-ray structure determination. Single X-ray diffraction analysis reveals binuclear FeMn and trinuclear FeMn2 structure, respectively, in which the cyanide precursor acts as mono- or bidentate ligand to connect the Mn(III) Schiff-base unit(s). Furthermore, these two complexes are self-complementary through coordinated aqua ligands from one complex and the free O4 compartments from the neighboring complex, giving dimeric and 1D single chain supramolecular structure. Investigation of the magnetic susceptibility of 1 reveals weak antiferromagnetic coupling between the adjacent Mn(III) ions. Based on the binuclear FeMn model, best fit of the magnetic susceptibilities of 1 leads to the magnetic coupling constants J =–1.37 cm–1 and zJ′ =–0.72 cm–1 (1).

Impact of the supramolecular structure of cellulose on the efficiency of enzymatic hydrolysis.

BackgroundThe efficiency of enzymatic hydrolysis is reduced by the structural properties of cellulose. Although efforts have been made to explain the mechanism of enzymatic hydrolysis of cellulose by considering the interaction of cellulolytic enzymes with cellulose or the changes in the structure of cellulose during enzymatic hydrolysis, the process of cellulose hydrolysis is not yet fully understood. We have analysed the characteristics of the complex supramolecular structure of cellulose on the nanometre scale in terms of the spatial distribution of fibrils and fibril aggregates, the accessible surface area and the crystallinity during enzymatic hydrolysis. Influence of the porosity of the substrates and the hydrolysability was also investigated. All cellulosic substrates used in this study contained more than 96% cellulose.ResultsConversion yields of six cellulosic substrates were as follows, in descending order: nano-crystalline cellulose produced from never-dried soda pulp (NCC-OPHS-ND) > never-dried soda pulp (OPHS-ND) > dried soda pulp (OPHS-D) > Avicel > cotton treated with sodium hydroxide (cotton + NaOH) > cotton.ConclusionsNo significant correlations were observed between the yield of conversion and supramolecular characteristics, such as specific surface area (SSA) and lateral fibril dimensions (LFD). A strong correlation was found between the average pore size of the starting material and the enzymatic conversion yield. The degree of crystallinity was maintained during enzymatic hydrolysis of the cellulosic substrates, contradicting previous explanations of the increasing crystallinity of cellulose during enzymatic hydrolysis. Both acid and enzymatic hydrolysis can increase the LFD, but no plausible mechanisms could be identified. The sample with the highest initial degree of crystallinity, NCC-OPHS-ND, exhibited the highest conversion yield, but this was not accompanied by any change in LFD, indicating that the hydrolysis mechanism is not based on lateral erosion.Electronic supplementary materialThe online version of this article (doi:10.1186/s13068-015-0236-9) contains supplementary material, which is available to authorized users.

Individual forms of gold(III) binding from solutions with zinc N,N-cyclo-hexamethylenedithiocarbamate: Structural self-organization and thermal behavior of gold complexes of composition [Au{S2CN(CH2)6}2][AuCl4] and ([Au{S2CN(CH2)6}2]3[AuCl4][AuCl2]2) n

A reaction of binuclear zinc N,N-cyclo-hexamethylenedithiocarbamate with [AuCl4]− anions in 2 M HCl solution was studied. Two types of crystals, plates and needles, were obtained from acetone solution of products of the heterogeneous reaction; the crystals are complexes of composition [Au{S2CN(CH2)6}2][AuCl4] (I) and ([Au{S2CN(CH2)6}2]3[AuCl4][AuCl2]2)n (II). Crystal and supramolecular structures of the prepared compounds were established by X-ray diffraction analysis. The structure of ionic complex I is built of alternating discrete [Au{S2CN(CH2)6}2]+ cations and [AuCl4]− anions. A complex supramolecular structure II, which includes isomeric [Au{S2CN(CH2)6}2]+ cations (A and B) with different structur functions, is formed due to secondary Au⋯S and Au⋯Cl bonds. Non-centrosymmetric cations B unite via pairs of secondary Au⋯S bond to form binuclear species [Au2{S2CN(CH2)6}4]2+ which together with centrosymmetric cations A participate in formation of polymeric chains (⋯[B⋯B]⋯A⋯)n. Moreover, each cation A binds a pair of [AuCl2]− anions due to secondary Au⋯S bonds. In its turn, [AuCl4]− anions unite the chains into 2D polymeric network to produce pairs of secondary Cl⋯Au bonds with gold atoms of binuclear cations [Au2{S2CN(CH2)6}4]2+ of neighboring chains. Thermal behavior of the complexes was studied by simultaneous thermal analysis and conditions of recovery of bound gold were revealed. The thermal destruction of I and II proceeds via intermediate stages of formation of Au2S and AuCl. Reduced elemental gold is the final product of thermal transformations of the complexes.

Structure of complexes of poly-γ-benzyl-L-glutamate with water and dioxane molecules studied by IR spectroscopy and quantum chemical calculations

The structure of supramolecular complexes of poly-γ-benzyl-L-glutamate (PBG) with water and dioxane molecules during sorption from pure liquids and their binary mixtures is studied by IR spectroscopy and quantum chemical calculations. It is shown that the sorption sites of water and dioxane in PBG are different in nature. Water molecules are bound in the monomeric form to the carbonyl groups of the ester moieties of the side chains and the helical backbone of the peptide to form complexes with two hydrogen bonds. Dioxane molecules are sorbed in a large amount in the region of the side chains of PBG, causing their repacking with preservation of the helicity of the polypeptide backbone. Under simultaneous sorption of water and dioxane vapors, the binding of the latter increases the number of water molecules bound to the carbonyl groups of PBG. In this case, there is also an additional absorption of water molecules on the oxygen atoms of dioxane molecules. Calculations have shown that in the most probable configuration of the complexes, the water molecule simultaneously forms hydrogen bonds with the carbonyl groups of the side chain and the peptide backbone. Dioxane molecules do not penetrate to the peptide groups of helical backbone of PBG due to steric hindrance and are localized in the region of the benzyl moieties of the side chains; such complexes are stabilized by weak CH…O interactions.

Study of the supramolecular structures of complexes of carborane-containing pyridazines with 2,3,5,6-tetrachloro-1,4-dihydroxybenzene

The structures and characteristic features of the molecular packing patterns of complexes of pyridazines containing heterocyclic substituents and the carborane moiety with 2,3,5,6-tetrachlorohydroquinone (TCHQ) were investigated. It was shown that TCHQ can form supramolecular assemblies with carborane-containing substituted pyridazines. The stoichiometry and three-dimensional structures of these assemblies depend on the substituents in the pyridazine ring and are formed via O-H…N hydrogen bonding between TCHQ and heterocyclic molecules.

Mass Spectrometry of Supramolecular Complexes of Glycyrrhizic Acid and Benzimidazole Derivatives

Low-dose drug substances based on glycyrrhizic acid (1) and known active ingredients are currently being actively investigated [1, 2]. The effective doses of drugs can be decreased by 100–200 times [3, 4]. The glycyrrhizic acid in such substances acts as a polydentate ligand that forms supramolecular complexes of various stoichiometries with the active ingredient. The formation mechanisms of such host–guest complexes, where a saponin host molecule can form an endolipophilic cavity for the guest molecule in a hydrophilic medium, must be studied in order to establish the fundamental structure–property relationships [5, 6]. Researchers have previously used quantum-chemical calculations and mass spectrometry to show [7] that 1 forms stable self-associated clusters of general form Xn (n = 6). Hence, self-associates of 1 that are formed from two and more molecules have a cavity between them that is capable of incorporating commensurate guest molecules. Therefore, the goal of the present work was to study the structure of supramolecular complexes of 1 and benzimidazole derivatives (2) (e.g., 9-diethylaminoethyl-2,3-dihydroimidazo[1,2-a]benzimidazole dihydrochloride) using mass spectrometry with electrospray ionization.

Tetraaqua(4,4′-dimethyl-2,2′-bipyridine-κ2N,N′)nickel(II) sulfate monohydrate: a simple molecule with an extremely complex hydrogen-bonding scheme

The title ionic compound, [Ni(C12H12N2)(H2O)4]SO4·H2O, is composed of an Ni(II) cation coordinated by a chelating 4,4'-dimethyl-2,2'-bipyridine ligand via its two N atoms [mean Ni-N = 2.056 (2) Å] and by four aqua ligands [mean Ni-O = 2.073 (9) Å], the net charge being balanced by an external sulfate anion. The whole structure is stabilized by a solvent water molecule. Even though the individual constituents are rather featureless, they generate an extremely complex supramolecular structure consisting of a central hydrogen-bonded two-dimensional hydrophilic nucleus made up of complex cations, sulfate anions and coordinated and solvent water molecules, with pendant hydrophobic 4,4'-dimethyl-2,2'-bipyridine ligands which interact laterally with their neighbours via π-π interactions. The structure is compared with closely related analogues in the literature.

Preparation and characterization of hydrogen-bonded P4VP-bisazobenzene complexes

Photoresponsive supramolecular complexes contain 4-hydroxyethyloxy-4′-(4-nitrophenylazo)azobenzene(BisAzo) molecule as a hydrogen bonding donor and poly(4-vinylpyridine) (P4VP) as a hydrogen bonding acceptor, and strong phenol pyridine hydrogen bonding is formed between them. FT-IR spectrum verifies the hydrogen bonding has formed between the phenol hydroxyl of BisAzo and pyridine ring of P4VP. The glass- transition temperature (Tg) is determined with differential-scanning calorimetry(DSC) and a decrease of complexes compared with pure P4VP is observed due to the attachment of BisAzo onto the backbone of P4VP. Polarized optical microscopy (POM) is performed to study the structure of supramolecular complexes,with a different texture observed which is different from both constituents alone. X-ray diffraction patterns are investigated with the same films already used for POM observation, indicating a lamellar structure with a periodic thickness of 4.1 nm. The supramolecular complexes P4VP/(BisAzo)x are prepared with the molar ratio of BisAzo to the pyridine group varied at x = 0.25, 0.5, 0.75 and 1.0, no mass aggregation is observed even at a high concentration of chromophore.

Structural and biochemical alterations during the healing process of tendons treated with Aloe vera

AimsThe tendon is composed of highly organized collagen fibers that form a complex supramolecular structure. After lesions, the organization and composition of the tendon are not completely restored. Our purpose was to evaluate if the application of Aloe vera improves tendon healing, considering the effectiveness in the stimulus of collagen synthesis. Main methodsThe calcaneal tendon of male Wistar rats was partially transected with subsequent topical application of A. vera ointment at the injury. The animals were separated into groups with tendons treated with the A. vera extract for 7days and excised on the 7th, 14th and 21st days after surgery; control rats received only ointment base without plant extract. Key findingsMorphological analysis using polarization microscopy showed that the entire tendon undergoes a remodeling process, with disorganized collagen fibers by days 7 and 14 in plant-treated and non‐treated groups and with a higher birefringence in tendons of the plant-treated group on the 21st day. A higher concentration of hydroxyproline was found in plant-treated tendons on days 7 and 14 compared with their controls. Western blots showed lower amounts of type I collagen in the plant-treated group on day 14 compared with the control. MMP-9 diminished 14days after lesion and the active isoform of MMP-2 increased on day 21 in plant-treated groups. SignificanceThe present study indicates a beneficial effect of A. vera in the tissue reorganization in the transected region of the tendon 21days after injury and is supported by an increase of active MMP-2.