[show abstract][hide abstract] ABSTRACT: In order to investigate possible isostructural solid solutions of disubstituted N-phenylformamides and thioamides, we have studied the re-crystallization of pairs of compounds selected from 2,6-difluoro-N-phenylformamide (I), 2,6-dichloro-N-phenylformamide (II), 2,6-dimethyl-N-phenylformamide (III), 2,6-dichloro-N-phenylthioamide (IV), 2,6-dimethyl-N-phenylthioamide (V), 2,6-diisopropyl-N-phenylformamide (VI) and 2,6-diisopropyl-N-phenylthioamide (VII). For single-component 2,6-disubstituted-N-phenylformamides only the trans form occurs in the pure crystal, while for thioamides the cis form occurs, with only one exception. By forming solid solutions of pairs of these molecules the resulting structures all adopt similar N-H...O/S chains in the crystals. Solid solutions (1), (2) and (3), resulting from the mixing of (I) and (II), (II) and (III), and (IV) and (V), respectively, are all isostructural with each other (space group Pbca). Only co-crystal (1) is isostructural to both starting materials, while (2) is isostructural to only one of the starting pair, (II). Solid solution (3), which adopts the same Pbca structure as (1) and (2), is different to the monoclinic structures of both the reactants. Solid solution (4) is monoclinic, with similar hydrogen-bonded chains, and isostructural to the two components, resulting from the composition from the mixing of (VI) and (VII). Isostructural indices were used to quantify crystal-packing similarities and differences. Occupancy factors of the reactants in each co-crystal differ widely.
[show abstract][hide abstract] ABSTRACT: An octadentate cyclen-based europium complex with amidic and hydroxyalkyl pendent moieties exhibits pH dependent ligand denticity associated with anion recognition. Unusually high hydration numbers are determined for ortho-phthalate ternary outer-sphere complexes for which modulation of lanthanide-based luminescence is observed.
Chemical Communications 01/2014; · 6.38 Impact Factor
[show abstract][hide abstract] ABSTRACT: In this work, 2-((2-((2-hydroxyethyl)amino)ethyl)amino)cyclohexanol, HEAC, was prepared in solvent by the ring opening of cyclohexene oxide with 2-(2-amino-ethylamino)ethanol. Four complexes of HEAC, including [Pd(HEAC)Cl2] (1), [Cd2(HEAC)2(μ-Br)2Br2] (2), [Cd(HEAC)(OAc)2] (3) and [Hg(HEAC)Cl2] (4), were prepared and identified by elemental analysis, FT-IR, Raman, 1H NMR spectroscopy and single-crystal X-ray diffraction. Redox properties of HEAC before and after complexation were investigated in DMSO. In the crystal structure of HEAC, the two hydroxyl arms are trans to each other and the cyclohexane ring has a chair conformation with two C-chiral centers. Two new N-chiral centers are produced during the complexation process. In the crystal structure of 1, the palladium atom has a distorted square planar PdN2Cl2 environment. X-ray analysis of 2 reveals a dimer structure containing two bromide bridges. Each cadmium atom in 2 is found to be in a CdN2OBr3 distorted octahedral environment. The Cd2(μ-Br)2 moiety is placed on a plane and forms a parallelogram. The complex has a center of inversion at the center of the parallelogram and Ci symmetry. In the crystal structure of 3, the cadmium atom with a CdN2O5 environment has a distorted capped trigonal prismatic geometry. Complex 4 also has a distorted square-pyramidal geometry (HgN2OCl2). In the networks of HEAC and the complexes 1–4, intermolecular hydrogen bonds form different types of hydrogen bond motifs between adjacent molecules.
[show abstract][hide abstract] ABSTRACT: Cob(i)alamin reacts with phenylacetylene to produce two diastereomers in which the organic ligand is coordinated to the upper (β) and lower (α) face of the corrin ring, respectively. The isomers were separated chromatographically and characterised by ESI-MS and, in the case of the β isomer, by (1)H and (13)C NMR. Only the β isomer crystallised and its molecular structure, determined by X-ray diffraction, shows that the organic ligand coordinates Co(iii) through the β carbon of the phenylvinyl ligand. The Co-C bond length is 2.004(8) Å while the Co-N bond length to the trans 5,6-dimethylbenzimidazole (dmbzm) base is 2.217(8) Å, one of the longest Co-Ndmbzm bond lengths known in an organocobalamin. Unlike benzylcobalamin (BzCbl), phenylvinylcobalamin (PhVnCbl) is stable towards homolysis. DFT calculations (BP86/TZVP) on model compounds of BzCbl and PhVnCbl show that the Co-C bond dissociation energy for homolysis to Co(ii) and an organic radical in the former is 8 kcal mol(-1) lower than in the latter. An analysis of the electron density at the Co-C bond critical point using Bader's QTAIM approach shows that the Co-C bond in PhVnCbl is shorter, stronger and somewhat more covalent than that in BzCbl, and has some multiple bond character. Together with calculations that show that the benzyl radical is more stable than the phenylvinyl radical, this rationalises the stability of PhVnCbl compared to BzCbl. The phenylvinyl ligand has a large trans influence. The pKa for deprotonation of dmbzm and its coordination by the metal in β-PhVnCbl is 4.60 ± 0.01, one of the highest values reported to date in cobalamin chemistry. The displacement of dmbzm ligand by CN(-) in β-PhVnCbl occurs with log K = 0.7 ± 0.1; the trans influence order of C-donor ligands is therefore CN(-) < CCH < CHCH2 = PhVn < Me < Et.
[show abstract][hide abstract] ABSTRACT: The title indole derivative, C(17)H(15)NO(3)S, crystallizes with two independent mol-ecules in the asymmetric unit. The benzene ring of the tosyl group is almost perpedicular to the indole ring in both mol-ecules, with inter-planar angles of 82.60 (5)° and 81.82 (6)°. The two mol-ecules are, as a consequence, able to form an almost centrosymmetric non-bonded dimer, in which the molecules are linked by pairs of C-H⋯π inter-actions. The crystal structure displays a three-dimensional network of C-H⋯O inter-actions. A π-π inter-action occurs between inversion-related indole rings with a centroid-centroid distance of 3.6774 (16) Å and an inter-planar angle of 1.53 (15)°. This inter-action leads to a stacking of mol-ecules along the a axis.
[show abstract][hide abstract] ABSTRACT: The HIV protease plays a major role in the life cycle of the virus and has long been a target in antiviral therapy. Resistance of HIV protease to protease inhibitors (PIs) is problematic for the effective treatment of HIV infection. The South African HIV-1 subtype C protease (C-SA PR), which contains eight polymorphisms relative to the consensus HIV-1 subtype B protease, was expressed in Escherichia coli, purified, and crystallized. The crystal structure of the C-SA PR was resolved at 2.7 Å, which is the first crystal structure of a HIV-1 subtype C protease that predominates in Africa. Structural analyses of the C-SA PR in comparison to HIV-1 subtype B proteases indicated that polymorphisms at position 36 of the homodimeric HIV-1 protease may impact on the stability of the hinge region of the protease, and hence the dynamics of the flap region. Molecular dynamics simulations showed that the flap region of the C-SA PR displays a wider range of movements over time as compared to the subtype B proteases. Reduced stability in the hinge region resulting from the absent E35-R57 salt bridge in the C-SA PR, most likely contributes to the increased flexibility of the flaps which may be associated with reduced susceptibility to PIs. An animated interactive 3D complement (I3DC) is available in Proteopedia at http://proteopedia.org/w/Journal:JBSD:36.
[show abstract][hide abstract] ABSTRACT: The title macrocyclic amino alcohol compound, C14H30N4O, is investigated as a solid-state synthon for the design of a self-assembled tubular structure. It crystallizes in a helical column constructed by stereospecific O—H- - - -N and N—H- - - -N interactions. The hydrogen-bonding interactions, dependent upon macrocyclic ring helicity and molecular conformation, link R,R and S,S enantiomers in a head-to-tail fashion, forming a continuous hydrophilic inner core.
Acta Crystallographica Section C. 10/2012; C(68):o383-o386.
[show abstract][hide abstract] ABSTRACT: The supramolecular reagent isonicotinamide (isonico) was used to co-crystallize with three liquid carboxylic acids, cyclopropanecarboxylic acid (C3A), cyclobutanecarboxylic acid (C4A) and cyclopentanecarboxylic acid (C5A), and a solid carboxylic acid, cyclohexanecarboxylic acid (C6A). A total of six co-crystal structures resulted, which are an illustration of the co-crystal space observed in the ever-expanding research on co-crystallization of multiple molecular components. Co-crystal 1, (C3A)·(isonico), has a crystal structure with one of the highest reported Z′ values. 12 acid and 12 isonico molecules combine in the asymmetric unit to give a Z′ = 12, all forming 1-D ribbons. Co-crystals 2a and 2b, both having a formula of (C4A)2·(isonico), having, respectively, a Z′ of 1 and 2, illustrate both stoichiometric variation as well as polymorphism, resulting in different packing architectures. Co-crystals (C5A)·(isonico) 3 and (C6A)·(isonico) 4 have isostructural structures at low temperature, and both show phase transitions above room temperature. For (C6A)·(isonico), we determined the structure of both the low temperature phase, 4a, as well as a high temperature phase, 4b, by single crystal X-ray diffraction, and monitored the transition of 3 by variable temperature powder X-ray diffraction. In all of the compounds reported here, synthesized from two components that are not necessarily solids at ambient conditions and which we have called co-crystals, the primary hydrogen bonded interaction is the carboxylic acidpyridine hydrogen bond.
New Journal of Chemistry 10/2012; 36(11):2242-2252. · 2.97 Impact Factor
[show abstract][hide abstract] ABSTRACT: An alternative procedure is described for producing diffraction-quality crystals of the sodium salt of the water-soluble porphyrin diaqua-5,10,15,20-tetra-p-phenylsulfonyporphinatocobalt(III), Na[Co(TPPS)(H2O)2]·4H2O by vapour diffusion of ethyl acetate into an aqueous solution of the porphyrin overlaid with a layer of acetone. The structure contains a large amount of disordered solvent in channels but application of an appropriate algorithm (SQUEEZE – an algorithm incorporated into PLATON that applies a Fourier transform of the observed density in the solvent areas and incorporates its contribution to the structure factors) permits a structure solution.
[show abstract][hide abstract] ABSTRACT: The reaction between [V(IV)OSO(4)] and the tetradentate N(2)O(2)-donor Schiff base ligand, N,N-bis(o-hydroxybenzaldehyde)phenylenediamine (sal-HBPD), obtained by the condensation of salicylaldehyde and o-phenylenediamine in a molar ratio of 2 : 1 respectively, resulted in the formation of [V(IV)O(sal-HBPD)]. The molecular structure of [V(IV)O(sal-HBPD)] was determined by single crystal X-ray diffraction, and confirmed the distorted square pyramidal geometry of the complex with the N(2)O(2) binding mode of the tetradentate ligand. The formation of the polymer-supported p[V(IV)O(sal-AHBPD)] proceeded via the nitrosation of sal-HBPD, followed by the reduction with hydrogen to form an amine group that was then linked to Merrifield beads followed by the reaction with [V(IV)OSO(4)]. XPS and EPR were used to confirm the presence of oxovanadium(iv) within the beads. The BET surface area and porosity of the heterogeneous catalyst p[V(IV)O(sal-AHBPD)] were found to be 6.9 m(2) g(-1) and 180.8 Å respectively. Microanalysis, TG, UV-Vis and FT-IR were used for further characterization of both [V(IV)O(sal-HBPD)] and p[V(IV)O(sal-AHBPD)]. Oxidation of dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) was investigated using [V(IV)O(sal-HBPD)] and p[V(IV)O(sal-AHBPD)] as catalysts. Progress for oxidation of these model compounds was monitored with a gas chromatograph fitted with a flame ionization detector. The oxidation products were characterized using gas chromatography-mass spectrometry, microanalysis and NMR. Dibenzothiophene sulfone (DBTO(2)) and 4,6-dimethyldibenzothiophene sulfone (4,6-DMDBTO(2)) were found to be the main products of oxidation. Oxovanadium(iv) Schiff base microspherical beads, p[V(IV)O(sal-AHBPD)], were able to catalyse the oxidation of sulfur in dibenzothiophene (DBT) and 4,6-dimethyldibenzothiophene (4,6-DMDBT) to a tune of 88.0% and 71.8% respectively after 3 h at 40 °C. These oxidation results show promise for potential application of this catalyst in the oxidative desulfurization of crude oils.
[show abstract][hide abstract] ABSTRACT: The ion channel protein CLIC1 exists in both a soluble conformation in the cytoplasm and a membrane-bound conformation. The conformational stability of soluble CLIC1 demonstrates pH sensitivity which may be attributable to very specific residues that function as pH sensors. These sensors could be histidine or glutamate residues with pK(a) values that fall within the physiological pH range. The role of Glu81, a member of a topologically conserved buried salt bridge in CLIC1, as a pH sensor was investigated here. The mutants E81M, R29M, and E81M/R29M were designed to break the salt bridge between Glu81 and Arg29 and examine the effect of each member on the stability of the protein. Spectroscopic studies and the solved crystal structures indicated that the global structure of CLIC1 was not affected by the mutations. Urea-induced equilibrium unfolding unexpectedly showed E81M to stabilize CLIC1 at pH 7. This was due to stabilizing hydrophobic interactions with Met81 and a water-mediated compensatory H-bond between Met81 and Arg29. R29M and E81M/R29M destabilized CLIC1 at pH 7, and the unfolding transition changed from two-state to three-state, mimicking the wild type at pH 5.5. This observation points out the significance of the salt bridge in stabilizing the native state. The total unfolding free energy change of E81M CLIC1 does not change with pH, implying that Glu81 forms one of a network of pH-sensor residues in CLIC1 responsible for destabilization of the native state. This allows detachment of the N-domain from the C-domain at low pH.
[show abstract][hide abstract] ABSTRACT: Methodology for the synthesis of the benzo-fused acetal core of marticin is described in this paper. Condensation of readily available 1-(2-allyl-3,6-dimethoxyphenyl)ethanone with diethyl oxalate under Claisen condensation conditions furnished (Z)-ethyl 4-(2-allyl-3,6-dimethoxyphenyl)-2-hydroxy-4-oxobut-2-enoate. Treatment of this with LiAlH4 resulted in the formation of the diol, 1-(2-allyl-3,6-dimethoxyphenyl)-3,4-dihydroxybutan-1-one. Conversion of primary alcohol of the diol into the TBDMS ether followed by further reaction with LiAlH4 and exposure to Wacker oxidation conditions resulted in the formation of (3,6-dimethoxy-9-methyl-10,13-dioxatricyclo[7.3.1.02,7]trideca-2,4,6-trien-11-yl)methanol, the core of marticin.
[show abstract][hide abstract] ABSTRACT: In the crystal structure of the 1:1 title salt, C(4)H(12)NO(2) (+)·C(6)H(4)BrO(-), hydrogen-bonding inter-actions originate from the ammonium cation, which adopts a syn conformation. A gauche relationship between the C-O and C-N bonds of the 2-hy-droxy-ethyl fragments also facilitates O-H⋯O inter-actions of bis-(2-hy-droxy-eth-yl)ammonium cation chains to phenolate O atoms. The resulting double-ion chains along  are further linked by N-H⋯O inter-actions, forming chains parallel to .
[show abstract][hide abstract] ABSTRACT: The title organic salt, 6C(3)H(10)N(+)·C(10)H(2)O(8) (4-)·C(10)H(4)O(8) (2-)·4H(2)O, contains seven independent entities in the asymmetric unit which comprises three propyl-ammonium cations, two water mol-ecules, half a 2,5-dicarb-oxy-benzene-1,4-carboxyl-ate dianion (H(2)btc(2-)) and half a benzene-1,2,4,5-tetra-carboxyl-ate tetra-anion (btc(4-)), the latter two anions being located about centres of inversion. One of the water mol-ecules is disordered over two positions in a 0.55 (2):0.45 (2) ratio. The combination of mol-ecular ions and water mol-ecules results in an extensive and complex three-dimensional network of hydrogen bonds, the network being made up of nine unique N-H⋯O inter-actions between the ammonium cations and the anions, as well as four unique O-H⋯O inter-actions between the water mol-ecules and the anions.
[show abstract][hide abstract] ABSTRACT: The synthesis of two closely related pyranonaphthoquinones, dehydroherbarin and anhydrofusarubin, is described. The construction of the naphthalene nuclei was achieved using the Stobbe condensation reaction using 2,4-dimethoxybenzaldehyde and 2,4,5-trimethoxybenzaldehyde as their respective starting materials. Two key steps en route include a PIFA-mediated addition of a methoxy substituent onto the naphthalene skeleton and a Wacker oxidation reaction to construct the benzo[g]isochromene nucleus. Two interesting oxidation reactions of the intermediate isochromene enol ether of 7,9-dimethoxy-3-methyl-1H-benzo[g]isochromene-5-ol were observed. Treatment of the substrate with salcomine resulted in the formation of (3-formyl-4-hydroxy-6,8-dimethoxynaphthalene-2-yl)methyl acetate, while treatment of the same substrate with CAN resulted in the formation of racemic (3R,4R)-3-hydroxy-7,9-dimethoxy-3-methyl-5,10-dioxo-3,4,5,10-tetrahydro-1H-benzo[g]isochromen-4-yl nitrate.
[show abstract][hide abstract] ABSTRACT: The title salt, C(4)H(10)Br(2)N(+)·Br(-), crystallizes with four cations and four anions in the asymmetric unit. In the crystal, the bis-(2-bromo-eth-yl)ammonium cations and bromide anions are linked into chains by N-H⋯Br hydrogen bonds describing a binary C(2) (1)(4) motif along . Each of these chains is formed by a unique cation and anion pair. The ammonium cations occur in the less preferred anti conformation, characterized by different NCCBr torsion angles. Adjacent chains are linked by weak C-H⋯Br inter-actions, forming a three-dimensional network. The crystal studied was a pseudo-merohedral twin with twin ratio 0.640 (2):0.360 (2).
[show abstract][hide abstract] ABSTRACT: In the crystal structure of the title compound, C(21)H(14)ClN(3)OS, mol-ecules assemble into inversion dimers via pairs of N-H⋯N hydrogen bonds involving the N-H hydrogen of the thia-zine ring and the N atom of the pyridine ring. There is a close intra-molecular contact [2.570 (2) Å] between the carbonyl O atom of the benzamide and the S atom of the puckered thia-zine ring. The title compound can exist in two tautomeric forms, viz. amino or imino. The observed structure is compatible with the imino form on the basis of observed residual electron density and the two C-N bond lengths of 1.308 (2) and 1.353 (2) Å.
[show abstract][hide abstract] ABSTRACT: The title compound, [Fe(η(5)-C(5)H(5))(NH(2)CH(2)CHBrCH(2)Br)(CO)(2)](BF(4)) contains an Fe(II) cation with a three-legged piano-stool coordination. The NH(2)CH(2)CHBrCH(2)Br ligand contains a chiral carbon atom. The Fe-N bond length is 2.011 (3) Å and the Fe-Cp centroid distance is 1.7189 (5) Å. In the crystal, the ions are linked via two N-H⋯F inter-actions and a weak N-H⋯Br inter-action.
[show abstract][hide abstract] ABSTRACT: In the title compound, [Fe(C(10)H(15))(C(6)H(12)N(4))(CO)(2)]BF(4), the arrangement around the Fe(II) atom corresponds to a three-legged piano stool. The penta-methyl-cyclo-penta-dienyl (Cp*) ligand occupies three coordination sites, while two CO ligands and one N atom of the hexa-methyl-ene-tetra-mine ligand occupy the remaining coordination sites, completing a pseudo-octahedral geometry. Both the complex cation and the BF(4) (-) anion reside on crystallographic mirror planes. The Fe-N bond length is 2.069 (2) and the Fe-Cp*(centroid) distance is 1.7452 (3) Å.