Structure of the inclusion complexes of heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin with indole-3-butyric acid and 2,4-dichlorophenoxyacetic acid

The crystal structures of the complexes of heptakis(2,3,6-tri-O-methyl)-beta-cyclodextrin with indole-3-butyric acid and with 2,4-dichlorophenoxyacetic acid were studied by X-ray diffraction. The complexes crystallize in the monoclinic P2(1) space group. The host molecules are elliptically puckered and stacked along the a crystal axis, in a head-to-tail fashion, forming columns. One primary methoxy group of the host molecule of the complex with indole-3-butyric acid has the unusual trans-gauche conformation for permethylated CDs. All the secondary O-3-CH(3) methoxy groups, some secondary O-2-CH(3) and some primary methoxy groups pointing inwards the cavity enclose the indole or the 2,4-dichlorophenoxy moieties of the guest molecules inside the cavity, while the chains of the guests protrude between two adjacent host molecules of the columns. The mean planes of the indole and 2,4-dichlorophenoxy moieties of the guests are nearly perpendicular to the mean planes of the elliptical heptagons defined by the O-4n atoms of the hosts. The carboxyl group of the guests form hydrogen bonds with oxygen atoms of the host molecules or with the water molecules found in the space between the complexes of the same column.     

A structural and thermal investigation of the inclusion of parabens in heptakis(2,6-di-O-methyl)cyclomaltoheptaose

The structures of the inclusion complexes formed by heptakis(2,6-di-O-methyl)cyclomaltoheptaose and methyl-, ethyl-, propyl- and butyl parabens have been solved and analysed by X-ray diffraction. Each inclusion complex crystallises in the space group P2(1)2(1)2(1) with Z=4 and a host-to-guest ratio of 1:1. However the packing arrangements and modes of guest inclusion are not equivalent for the four structures. The analytical data indicated that two isostructural pairs, the methyl- and ethyl-paraben complexes, have similar cell parameters that differ from those of the propyl- and butyl paraben complexes. The results of thermogravimetric analysis and differential scanning calorimetry of the complexes are also reported.     

X-ray crystallography and solution NMR spectroscopy characterization of heptakis(2,3-di-O-acetyl-6-bromo-6-deoxy)cyclomaltoheptaose

Heptakis(2,3-di-O-acetyl-6-bromo-6-deoxy)cyclomaltoheptaose has been characterized in aqueous solution by 1D and 2D NMR spectroscopy and in the solid state by X-ray crystallography. In methanol solution, the acetyl groups were found to interact with both inward and outward-pointing protons. This and the strong deshielding of the bridging carbons, relative to the nonacetylated precursor, indicate macrocyclic flexibility. In the crystalline state the macrocycle exists as a methanol complex. It exhibits elliptical distortion, all glucose residues been tilted with their primary side toward the cavity. The existing strain due to the congestion of 14 acetyl groups at the secondary site is relieved by two glucose rings acquiring the rarely observed skew-boat conformation, (0)S(2), by the increased tilting of two glucose residues, as well as by minor variations of the torsion angles of the acetyl groups. The seven bromine atoms are quite accessible to nucleophiles.     

Fluorescence characterization of the interaction Suwannee river fulvic acid with the herbicide dichlorprop (2-(2,4-dichlorophenoxy)propionic acid) in the absence and presence of aluminum or erbium

This study uses fluorescence spectroscopy to better understand the role of environmental metal ions in the interaction of charged herbicides with biochemical degradation product Suwannee River fulvic acid (SRFA). The interactions between the widely-used herbicide dichlorprop (2-(2,4-dichlorophenoxy)propionic acid) (DCPPA) with Al³⁺ and the comparative metal Er³⁺ were probed at pH 4.0. Fluorescence experiments on binary solutions at pH 4.0 clearly indicated that Al³⁺ and Er³⁺ strongly interact with both SRFA and DCPPA alone in solution as demonstrated by fluorescence quenching with DCPPA and enhancement with SRFA by Al³⁺ and fluorescence quenching of both SRFA and DCPPA fluorescence by Er³⁺. Titrating Al³⁺ or Er³⁺ to SRFA-DCPPA quenched SRFA fluorescence as compared to the SRFA-metal ion binary complexes. Formation constants were determined using the Ryan-Weber model for the titration data. The DCPPA fluorescence results strongly support the formation of DCPPA-Al³⁺ and DCPPA-Er³⁺ complexes at pH values above the pK_a (3.0) of DCPPA. Excitation and emission data obtained on ternary solutions of SRFA-Al³⁺-DCPPA and SRFA-Er³⁺-DCPPA complexes at pH 4.0 suggest that at this pH where the predominant DCPPA species is negatively-charged, Al³⁺ and Er³⁺ metal ions may function to “bridge” negatively-charged fulvic acids to negatively-charged pesticides. Fluorescence data collected on UV-irradiated ternary complexes indicate that both metals can also bridge DCPPA interactions with SRFA under those conditions. The results of our studies suggest that creation of a herbicide-free boundary corridor is recommended near mines and runoff areas with metal ions in surface waters to control possible complexation among fulvic acids, DCPPA and metal ions that maintains these molecules in a bioavailable state to plants and animals.     

Syntheses and crystal structures of dimethyltin (IV) derivatives with 2,6-pyridinedicarboxylic acid

A novel cyclic dimethyltin complex [Me₂Sn(2,6-pdc)]₃ (1) (2,6-pdc = 2,6-pyridinedicarboxylate) was synthesized by the reaction of dimethyltin (IV) dichloride and 2,6-pyridinedicarboxylate acid in methanol under solvothermal conditions (150 °C). However, under room temperature (25 °C), we obtained a ladder complex [Me₂Sn(2,6-pdc)]₂(MeOH)₂ (2). Characterization of complexes 1 and 2 was achieved using elemental analysis, IR, ¹H, ¹³C and ¹¹⁹Sn NMR spectra and X-ray diffraction. X-ray data of 1 revealed that it was an unusual cyclic complex with a discrete cyclotrinuclear unit, in which the 12-membered cyclic cavity is almost completely planar. X-ray data of 2 showed that it was a ladder complex, in which a crystallizing methanol molecule is found in each formula unit.     

Evaluation of newly synthesized and commercially available charged cyclomaltooligosaccharides (cyclodextrins) for capillary electrokinetic chromatography

A highly new charged cyclodextrin (CD) derivatives, (6-O-carboxymethyl-2,3-di-O-methyl)cyclomaltoheptaoses (CDM-beta-CDs), was synthesized and characterized as anionic reagents for capillary electrophoresis (CE) in an electrokinetic chromatography mode of separation. Substitution with dimethyl groups at the secondary hydroxyl sites of the CD is aimed at influencing the magnitude and selectivity of analyte-CD interactions, while substitution by carboxymethyl groups at the primary hydroxyl sites provides for high charge and electrophoretic mobility. Full regioselective methylation at the secondary hydroxyl sites was achieved in this work, while substitution at the primary hydroxyl sites generated a mixture of multiply charged products. The separation performance of CDM-beta-CD was evaluated using a variety of analyte mixtures. The results obtained from commercially available negatively charged cyclodextrins, heptakis(2,3-di-O-methyl-6-O-sulfo)cyclomaltoheptaose (HDMS-beta-CD) and O-(carboxymethyl)cyclomaltoheptaose (CM-beta-CD) with an average degree of substitution one (DS 1), were compared to CDM-beta-CD using a sample composed of eight positional isomers of dihydroxynaphthalene. Four hydroxylated polychlorobiphenyl derivatives, a group of chiral and isomeric catchecins, and chiral binaphthyl compounds were also separated with CDM-beta-CD. The effect of adding neutral beta-cyclodextrin (beta-CD) into the running buffer containing charged cyclodextrins was investigated and provided evidence of significant inter-CD interactions. Under certain running buffer conditions, the charged cyclodextrins also appear to adsorb to the capillary walls to various degrees.     

Structure and luminescence of sodium and lanthanide(III) coordination polymers with pyridine-2,6-dicarboxylic acid

A series of coordination polymers constructed by sodium, lanthanide(III), and pyridine-2,6-dicarboxylate (dipic),NaLn(dipic)₂ · 7H₂O (Ln = Eu, Gd, Tb), have been prepared under a hydrothermal condition. The crystal structures of the three compounds which are isostructual were determined by single-crystal X-ray diffraction. The two-dimensional layers found in the compounds are built up from six-folded {NaO₆} polyhedra and nine-folded {LnN₂O₇} polyhedra, these being edge-shared each other along the c axis and bridged by carboxylate groups of dipic along the b axis, respectively. This two-dimensional framework provides cavities inside the layer and interlayer spaces outside the layer for accommodation of the two dipic molecules coordinated to a lanthanide(III) ions. The dehydrated materials obtained by heating the as-synthesized crystals at 200 °C held their crystal structure, and absorbed the same amounts of water molecules as those of the as-synthesized crystals upon the exposure of 100% relative humidity at room temperature. The Eu and Tb compounds showed strong red and green emissions, respectively, due to an energy transfer from dipic molecules to trivalent emission ions.     

New cyclomaltoheptaose (beta-cyclodextrin) derivative 2-O-(2-hydroxybutyl)cyclomaltoheptaose: preparation and its application for the separation of enantiomers of drugs by capillary electrophoresis

A new soluble cyclomaltoheptaose (cyclodextrin) derivative, 2-O-(2-hydroxybutyl)cyclomaltoheptaose [2-O-(2-hydroxybutyl)-beta-cyclodextrin, 2-HB-beta-CD], was prepared and studied as an efficient chiral selector in the separation of racemic mixtures of drugs by capillary electrophoresis (CE). Results showed that 2-HB-beta-CD could provide higher separating capability than that of beta-CD and the similarly substituted 2-HP-beta-CD.     

The determination of the stability constant for the iron(II) complex of the biochelator pyridine-2,6-bis(monothiocarboxylic acid)

Pyridine-2,6-bis(monothiocarboxylic acid), also known as pyridine-2,6-dithiocarboxylic acid (pdtc), is a unique and powerful metal chelator produced by Pseudomonas stutzeri and Pseudomonas putida. The actual physiological roles of pdtc in these pseudomonads are not known with certainty, though it is likely that the compound acts as a siderophore, an antibiotic, or both. The stability constant of Fe^III(pdtc)₂ ^2- was determined in previous work to be 10^33.36. Here we determined that the stability constant of Fe^II(pdtc)₂ ^2- is 10¹². We determined this stability constant through potentiometric and spectrophotometric measurements of a ligand-ligand competition study using 2,6-pyridine dicarboxylic acid as the competitor for iron. Comparing the stability constant for Fe^II(pdtc)₂ ^2- to the constant for Fe^III(pdtc)₂ ^2- shows that the stability constant of Fe^II(pdtc)₂ ^2- is approximately 21 orders of magnitude smaller. This represents a very significant decrease in the binding strength of pdtc toward iron. Thus, if the host cell produces pdtc as a siderophore for sequestering Fe(III), it is likely that a second metabolite or a membrane protein of the host cell is used for reduction of the chelated iron at or near the cell membrane in order to facilitate its release from pdtc for cellular use.     

An investigation of the inclusion complex of beta-cyclodextrin with p-nitrobenzoic acid in the solid state

The weak inclusion complex of cyclomaltoheptaose (beta-cyclodextrin, betaCD) with p-nitrobenzoic acid was investigated in the solid state. Crystallography shows that two betaCD molecules co-crystallize with two p-nitrobenzoic acids and 28.5 water molecules [2(C(42)H(70)O(35))x2(C(7)H(5)NO(4))x28.5H(2)O] in the triclinic system.     

Synthesis, crystal structure, luminescence and thermal decomposition kinetics of Eu(III) complex with 2,4-dichlorobenzoic acid and 2,2′-bipyridine

The complex of [Eu(2,4-DClBA)₃(bipy)]₂ (2,4-DClBA = 2,4-dichlorobenzoate; bipy = 2,2′-bipyridine) was obtained and characterized by elemental analysis, IR spectra, UV spectra, luminescence spectra, ¹H NMR spectra, single crystal X-ray diffraction and TG-DTG techniques. Two Eu³⁺ ions are connected by four carboxylate groups through bridging bidentate and bidentate chelating-bridging mode. The coordination number of europium ion is nine. The thermal decomposition behavior of the title complex under a static air atmosphere can be discussed by TG-DTG, SEM and IR techniques. The non-isothermal kinetics was investigated by using double equal-double steps method and Starink method. The mechanism function of the first decomposition step was determined. Meanwhile, the thermodynamic parameters (ΔH^≠, ΔG^≠ and ΔS^≠) and kinetic parameters (activation energy E and the pre-exponential factor A) were also calculated.     

Activity improvement of a regioselective nitrilase from Acidovorax facilis and its application in the production of 1-(cyanocyclohexyl) acetic acid

A nitrilase gene from Acidovorax facilis ZJB09122 was cloned and expressed in Escherichia coli BL21 (DE3). To improve the activity of this nitrilase, a key amino acid Phe168 was selected and mutated by site-directed mutagenesis, based on the homology modeling and previously described “hot spot” mutation. After mutation and screening, a mutant (Mut-F168V) with higher activity and stability was obtained. The nitrilase activity of Mut-F168V to hydrolyze 1-cyanocyclohexylacetonitrile was 39.52-fold compared with wild type A. facilis nitrilase (Wt-Acf-Nit). The values of K_m and V_max of Mut-F168V were markedly decreased to 1.89-fold and increased to 50.34-fold as compared to Wt-Acf-Nit, respectively. The biotransformation study showed that 1.0 M of 1-cyanocyclohexylacetonitrile could be regioselectively hydrolyzed to 1-(cyanocyclohexyl) acetic acid with 90% yield. The yield of 1-(cyanocyclohexyl) acetic acid by Mut-F168V was 66.19-fold compared to Wt-Acf-Nit after 1 h at the concentration of 1.0 M 1-cyanocyclohexylacetonitrile as substrate. The 1-(cyanocyclohexyl) acetic acid was subsequently isolated and characterized. The mutant (Mut-F168V) appears promising for potential applications for the industrial production of 1-(cyanocyclohexyl) acetic acid.     

Structure of the O-polysaccharide of Providencia alcalifaciens O8 containing (2S,4R)-2,4-dihydroxypentanoic acid, a new non-sugar component of bacterial glycans

A glycerol teichoic acid-like O-polysaccharide was obtained by mild acid degradation of the lipopolysaccharide of Providencia alcalifaciens O8 and studied by chemical methods and NMR spectroscopy, including 2D ROESY, {(1)H,(13)C} HSQC, and HMQC-TOCSY experiments. It was found that the compound contains a new component of bacterial lipopolysaccharides: ether-linked (2S,4R)-2,4-dihydroxypentanoic acid (Dhpa), which was identified by NMR spectroscopy. The following structure of the repeating unit of the polysaccharide was established:     

Ionic complexation properties of per(3,6-anhydro)cyclodextrin derivatives towards lanthanides

Using per(3,6-anhydro)cyclodextrin derivatives [per(3,6-anhydro)CD], it was possible to produce new lanthanide chelates by careful choice of the size and functional groups. Heptakis(3,6-anhydro-2-O-methyl)cyclomaltoheptaose fulfils the best criteria for complexation of lanthanide ions. Nuclear magnetic resonance was used to derive the association constants and the stoichiometries of these new complexes. Finally, a three-dimensional structure of these complexes consistent with the NMR data is proposed, to ascertain the position of lanthanide in the cavity of the per(3,6-anhydro)CD. For the present purposes, heptakis(2-O-acetyl-3,6-anhydro)cyclomaltoheptaose, octakis(2-O-acetyl-3,6-anhydro)cyclomaltooctaose, heptakis(3,6-anhydro-2-O-methyl)cyclomaltoheptaose and octakis(3,6-anhydro-2-O-methyl)cyclomaltooctaose have been synthesized and purified.     

Syntheses and characterizations of two lanthanide(III)-copper(II) coordination polymers constructed by pyridine-2,6-dicarboxylic acid

The hydrothermal reaction of La₂O₃ and Pr₂O₃ with pyridine-2,6-dicarboxylic acid (H₂pydc), CuO, and H₂O with a mole ratio of 1:2:4:300 resulted in the formation of two polymeric Cu(II)-Ln(III) complexes, [{Ln₄Cu₂(pydc)₈(H₂O)₈} · 18H₂O]_n (Ln = La (1); Pr (2)). 1 and 2 are isomorphous and crystallize in monoclinic space group C2/c. Complexes 1 and 2 have one-dimensional infinite chains with “∞” shape. The 1D chains are linked by the hydrogen bonds and π?π stacking interactions to form layer structures which are further linked by the hydrogen bonds and π?π stacking interactions to form the three-dimensional (3D) structures with nanoscale porosities. Temperature-dependent magnetic susceptibilities and the thermal stabilities of complexes 1 and 2 were studied.     

Crystal structure of the inclusion complex of the antibacterial agent triclosan with cyclomaltoheptaose and NMR study of its molecular encapsulation in positively and negatively charged cyclomaltoheptaose derivatives

The inclusion complexes of triclosan with native cyclomaltoheptaose (beta-cyclodextrin, betaCD) as well as with negatively and positively charged derivatives are studied. The structure of the inclusion complex betaCD/triclosan in the crystalline state [P1, a=15.189(5), b=15.230(6), c=16.293(6), alpha=91.07(4), beta=91.05(3) gamma=100.71(3)] comprises two crystallographically independent host macrocycles A and B. The packing results in betaCD dimers that align head-to-head and form infinite channels along the c-axis. Only one guest molecule statistically disordered over two positions, (the dichlorophenyl ring in the cavities of either A or B) corresponds to each dimer (a 2:1 host/guest complex). The enclosed dichlorophenyl ring enters the dimer through the primary side, whereas the hydrophilic chlorophenol ring extends in the space between dimers. Water molecules in five positions are also enclosed in the intradimer region, arranged on a plane perpendicular to the sevenfold axis of betaCD. The NMR spectroscopic studies in aqueous solution show the presence of both 1:1 and 2:1 betaCD/triclosan complexes. In the first case, two different 1:1 complexes are simultaneously present, each with either ring entering the narrow primary side of one betaCD molecule. In the 2:1 complex both rings of triclosan are included in two independent betaCD hosts, a precursor to the supramolecular arrangement found in the crystalline form. In the case of the negatively charged sodium heptakis[6-deoxy-6-(3-thiopropionate)]-betaCD, the NMR studies at pH 7.9 show a complete inclusion of triclosan inside the host in two orientations, one for the non-ionized (phenol) and reverse for the ionized (phenolate) form. Finally, for the positively charged heptakis(6-aminoethylamino-6-deoxy)-betaCD, inclusion of triclosan is possible only when the pH is raised to 10 and it is concluded that both aromatic rings are alternatively inside the cavity. However in that case also, inclusion of the entire guest in the elongated cavity is suggested.     

Equilibrium and structural studies on Co(II), Ni(II), Cu(II) and Zn(II) complexes with N-(2-benzimidazolyl)methyliminodiacetic acid: crystal structures of Ni(II) and Cu(II) complexes

Combined pH-metric, UV-Vis, ¹H NMR and EPR spectral investigations on the complex formation of M(II) ions (M=Co, Ni, Cu and Zn) with N-(2-benzimidazolyl)methyliminodiacetic acid (H₂bzimida, hereafter H₂L) in aqueous solution at a fixed ionic strength, I=10⁻¹ mol dm⁻³, at 25 ± 1 °C indicate the formation of M(L), M(H₋₁L)⁻ and M₂(H₋₁L)⁺ complexes. Proton-ligand and metal-ligand constants and the complex formation equilibria have been elucidated. Solid complexes, [M(L)(H₂O)₂] · nH₂O (n=1 for M = Co and Zn, n=2 for M = Ni) and {Cu (μ-L) · 4H₂O}_n, have been isolated and characterized by elemental analysis, spectral, conductance and magnetic measurements and thermal studies. Structures of [Ni(L)(H₂O)₂] · 2H₂O and {Cu(μ-L) · 4H₂O}_n have been determined by single crystal X-ray diffraction. The nickel(II) complex exists in a distorted octahedral environment in which the metal ion is coordinated by the two carboxylate O atoms, the amino-N atom of the iminodiacetate moiety and the pyridine type N-atom of the benzimidazole moiety. Two aqua O atoms function as fifth and sixth donor atoms. The copper(II) complex is made up of interpenetrating polymeric chains of antiferromagnetically coupled Cu(II) ions linked by carboxylato bridges in syn-anti (apical-equatorial) bonding mode and stabilized via interchain hydrogen bonds and π-π stacking interactions.     

2,4-Dichlorophenoxyacetic Acid (2,4-D) Utilization by Delftia acidovorans MC1 at Alkaline pH and in the Presence of Dichlorprop is Improved by Introduction of the tfdK Gene

Growth of Delftia acidovorans MC1 on 2,4-dichlorophenoxyacetic acid (2,4-D) and on racemic 2-(2,4-dichlorophenoxy)propanoic acid ((RS)-2,4-DP) was studied in the perspective of an extension of the strain’s degradation capacity at alkaline pH. At pH 6.8 the strain grew on 2,4-D at a maximum rate (μ_max) of 0.158 h⁻¹. The half-maximum rate-associated substrate concentration (K_s) was 45 μM. At pH 8.5 μ_max was only 0.05 h⁻¹ and the substrate affinity was mucher lower than at pH 6.8. The initial attack of 2,4-D was not the limiting step at pH 8.5 as was seen from high dioxygenase activity in cells grown at this pH. High stationary 2,4-D concentrations and the fact that μ_max with dichlorprop was around 0.2 h⁻¹ at both pHs rather pointed at limited 2,4-D uptake at pH 8.5. Introduction of tfdK from D. acidovorans P4a by conjugation, coding for a 2,4-D-specific transporter resulted in improved growth on 2,4-D at pH 8.5 with μ_max of 0.147 h⁻¹ and K_s of 267 μM. Experiments with labeled substrates showed significantly enhanced 2,4-D uptake by the transconjugant TK62. This is taken as an indication of expression of the tfdK gene and proper function of the transporter. The uncoupler carbonylcyanide m-chlorophenylhydrazone (CCCP) reduced the influx of 2,4-D. At a concentration of 195 μM 2,4-D, the effect amounted to 90% and 50%, respectively, with TK62 and MC1. Cloning of tfdK also improved the utilization of 2,4-D in the presence of (RS)−2,4-DP. Simultaneous and almost complete degradation of both compounds occurred in TK62 up to D = 0.23 h⁻¹ at pH 6.8 and up to D = 0.2 h⁻¹ at pH 8.5. In contrast, MC1 left 2,4-D largely unutilized even at low dilution rates when growing on herbicide mixtures at pH 8.5.     

6-(Pentadec-8-enyl)-2,4-dihydroxybenzoic acid from seeds of Ginkgo biloba

Novel phenolic lipids isolated from Ginkgo biloba were identified as 6-(pentadec-8-enyl)resorcylic (97%) and 6-tridecylresorcylic (3%) acids. They are 4-hydroxyanacardic acids and represent the postulated precursors of cardols (5-alkylresorcinols).     

Synthesis, characterization and crystal structure of manganese (IV) complex derived from salicylic acid

The binuclear manganese (IV) [Mn₂(Hsal)₄(OH)₄] (H₂sal = salicylic acid) complex has been obtained from a complex reaction mixture in methanol consisting of Mn(II)(OAc)₂ · 4H₂O, GS ( a reagent obtained by refluxing glycine and salicylaldehyde in 1:1 molar ratio in methanol), monosodium salicylate and pyridine. The compound contains a distorted octahedral MnO₆ coordination unit of potential importance to high oxidation state manganese bimolecules.