Synthon Modularity in 4-Hydroxybenzamide-Dicarboxylic Acid Cocrystals

A family of 4-hydroxybenzamide-dicarboxylic acid cocrystals has been designed and subsequently isolated and characterized. The design strategy follows from an understanding of synthon modularity in crystal structures of monocomponent crystals such as gamma-quinol, 4,4'-biphenol and 4-hydroxybenzoic acid. These monocomponent structures contain infinite O-H center dot center dot center dot O-H center dot center dot center dot O-H center dot center dot center dot cooperative synthons linked with molecular connectors such as phenyl and biphenyl, and supramolecular connectors such as the acid dimer in 4-hydroxybenzoic acid. The cocrystal design was influenced by the anticipation that dicarboxylic acids can form a supramolecular connector mediated by acid-amide synthons with 4-hydroxybenzamide, which can then form the phenol O-H center dot center dot center dot O-H center dot center dot center dot O-H center dot center dot center dot infinite synthon. Effectively, the acid-amide and phenol synthons are insulated. The short axis of such a structure will be around 5.12 angstrom and this is borne out in 2:1 cocrystals of 4-hydroxybenzamide with oxalic, succinic, fumaric, glutaric (two forms) and pimelic acids. Hydrated variations of this structure type are seen in the cocrystals obtained with adipic and sebacic acids.

Assembly of 12-tungstosilicic acid and 4-aminobenzo-15-crown-5 ether based on the electrostatic attraction through bridging of oxonium ions on different substrates

Based on the electrostatic attraction Keggin-type polyoxometalate H4SiW12O40 (SiW12) and small molecule 4-aminobenzo-15-crown-5 ether (4-AB15C5) were alternately deposited on poly (allylamine hydrochloride) (PAH)-derived indium tin oxide (ITO) substrate through a layer-by-layer (LBL) self-assembly, forming a supramolecular multilayer film (film-A). SiW12 was also deposited on a glassy carbon electrode (GCE) derived by 4-AB15C5 via covalent bonding in 0.1 M NaCl aqueous solution and formed a composite monolayer film (film-B). UV-vis absorption spectroscopy, X-ray photoelectron spectroscopy (XPS) and Fourier-transform infrared (FTIR) spectroscopy measurements demonstrated that the interactions between SiW12 and 4-AB15C5 in both two film electrodes were the same and caused by the bridging action of oxonium ions. But, the nanostructure in the two film electrodes was different. 4-AB15C5 in film-A was oriented horizontally to ITO substrate, however, that in film-B was oriented vertically to GCE. Namely film-A corresponded to a layer structure, and film-B corresponded to an intercalation structure.

Introduction of 4-chloro-alpha-cyanocinnamic acid liquid matrices for high sensitivity UV-MALDI MS

Matrix-assisted laser desorption/ionization (MALDI) is a key ionization technique in mass spectrometry (MS) for the analysis of labile macromolecules. An important area of study and improvements in relation to MALDI and its application in high-sensitivity MS is that of matrix design and sample preparation. Recently, 4-chloro-alpha-cyanocinnamic acid (ClCCA) has been introduced as a new rationally designed matrix and reported to provide an improved analytical performance as demonstrated by an increase in sequence coverage of protein digests obtained by peptide mass mapping (PMM) (Jaskolla, T. W.; et al. Proc. Natl. Acad. Sci. U.S.A. 2008, 105, 12200-12205). This new matrix shows the potential to be a superior alternative to the commonly used and highly successful alpha-cyano-4-hydroxycinnamic acid (CHCA). We have taken this design one step further by developing and optimizing an ionic liquid matrix (ILM) and liquid support matrix (LSM) using ClCCA as the principle chromophore and MALDI matrix compound. These new liquid matrices possess greater sample homogeneity and a simpler morphology. The data obtained from our studies show improved sequence coverage for BSA digests compared to the traditional CHCA crystalline matrix and for the ClCCA-containing ILM a similar performance to the ClCCA crystalline matrix down to 1 fmol of BSA digest prepared in a single MALDI sample droplet with current sensitivity levels in the attomole range. The LSMs show a high tolerance to contamination such as ammonium bicarbonate, a commonly used buffering agent.

Piperonylic Acid, a Selective, Mechanism-Based Inactivator of the trans-Cinnamate 4-Hydroxylase: A New Tool to Control the Flux of Metabolites in the Phenylpropanoid Pathway1

Piperonylic acid (PA) is a natural molecule bearing a methylenedioxy function that closely mimics the structure of trans-cinnamic acid. The CYP73A subfamily of plant P450s catalyzes trans-cinnamic acid 4-hydroxylation, the second step of the general phenylpropanoid pathway. We show that when incubated in vitro with yeast-expressed CYP73A1, PA behaves as a potent mechanism-based and quasi-irreversible inactivator of trans-cinnamate 4-hydroxylase. Inactivation requires NADPH, is time dependent and saturable (KI = 17 μm, kinact = 0.064 min−1), and results from the formation of a stable metabolite-P450 complex absorbing at 427 nm. The formation of this complex is reversible with substrate or other strong ligands of the enzyme. In plant microsomes PA seems to selectively inactivate the CYP73A P450 subpopulation. It does not form detectable complexes with other recombinant plant P450 enzymes. In vivo PA induces a sharp decrease in 4-coumaric acid concomitant to cinnamic acid accumulation in an elicited tobacco (Nicotiana tabacum) cell suspension. It also strongly decreases the formation of scopoletin in tobacco leaves infected with tobacco mosaic virus.

Hydrogen bonding in proton-transfer compounds of 5-sulfosalicylic acid with a series of aliphatic nitrogen Lewis bases

The crystal structures of the proton-transfer compounds of 5-sulfosalicylic acid (3-carboxy-4-hydroxybenzenesulfonic acid) with the aliphatic nitrogen Lewis bases, hydroxylamine, triethylamine, pyrrolidine, morpholine, N-methylmorpholine and piperazine, viz. hydroxyammonium 3-carboxy-4-hydroxybenzenesulfonate (1), triethylaminium 3-carboxy-4-hydroxybenzenesulfonate (2), pyrrolidinium 3-carboxy-4-hydroxybenzenesulfonate monohydrate (3), morpholinium 3-carboxy-4-hydroxybenzenesulfonate monohydrate (4), N-methylmorpholinium 3-carboxy-4-hydroxybenzenesulfonate monohydrate (5) and piperazine-1,4-diium bis(3-carboxy-4-hydroxybenzenesulfonate) hexahydrate (6) have been determined and their comparative structural features and hydrogen-bonding patterns described. Crystals of 4 are triclinic, space group P-1 while the remainder are monoclinic with space group either P21/c (1 - 3) or P21/n (5, 6). Unit cell dimensions and contents are: for 1, a = 5.0156(3), b = 10.5738(6), c = 18.4785(9) Å, β = 96.412(5)o, Z = 4; for 2, a = 8.4998(4), b = 12.3832(6), c = 15.4875(9) Å, β = 102.411(5)o, Z = 4; for 3, a = 6.8755(2), b = 15.5217(4), c = 12.8335(3) Å, β = 92.074(2)o, Z = 4; for 4, a = 6.8397(2), b = 12.9756(5), c = 15.8216(6) Å, α = 90.833(3), β = 95.949(3), γ = 92.505(3)o, Z = 4; for 5, a = 7.0529(3), b = 13.8487(7), c = 15.6448(6) Å, β = 90.190(6)o, Z = 4; for 6, a = 7.0561(2), b = 15.9311(4), c = 12.2102(3) Å, β = 100.858(3)o, Z = 2. The hydrogen bonding generates structures which are either two-dimensional (2 and 5) or three-dimensional (1, 3, 4 and 6). Compound 6 represents the third reported structure of a salt of 5-sulfosalicylic acid having a dicationic piperazine species.

Poly[di-mu-aqua-bis(mu-2-amino-4-nitrobenzoato)dicaesium]

In the structure of title compound [Cs2(C7H5N2O4)2(H2O)2]n the asymmetric unit comprises two independent and different Cs centres, one nine-coordinate, the other seven coordinate, with both having irregular stereochemistry. The CsO9 coordination comprises oxygen donors from three bridging water molecules, one of which is doubly bridging, three from carboxylate groups, and three from nitro groups, of which two are bidentate chelate bridging. The CsO6N coordination comprises the two bridging water molecules, one amine N donor, one carboxyl O donor and four O donors from nitro groups (two from the chelate bridges). The extension of the dimeric unit gives a two-dimensional polymeric structure which is stabilized by both intra- and intermolecular amine N-H...O and water O-H...O hydrogen bonds to carboxyl O acceptors, as well as inter-ring pi-pi interactions [minimum ring centroid separation, 3.4172(15)A].

Poly[[diaquabis[mu-2-(4-fluorophenoxy)acetato-k2O1:O1']magnesium] 0.4-hydrate]

In the structure of the title compound, [Mg(H2O)2(C8H6FO3)2]n(0.4H2O)n, slightly distorted octahedral MgO6 complex units have crystallographic inversion symmetry, the coordination polyhedron comprising two trans-related water molecules and four carboxyl O-atom donors, two of which are bridging. Within the two-dimensional complex polymer which is parallel to (100), the coordinating water molecules form intermolecular O---H...O hydrogen-bonds with carboxylate and phenoxy O-atom acceptors, as well as with the partial-occupancy solvent water molecules.

Poly[μ-aqua-aqua-μ5-(4-nitrobenzoato)-caesium]

In the structure of the title complex [Cs(C7H4N2O2)(H2O)2]n, the Cs salt of 4-nitrobenzoic acid, the irregular CsO9 coordination sphere comprises three bridging nitro O-donors, a bidentate carboxyl (O,O')-chelate interaction, a triple-bridging water molecule and a monodentate water molecule. A three-dimensional framework polymer is generated, within which there are water O-H...Ocarboxyl and water O-H...O(water) hydrogen-bonding interactions.

Poly[μ-aqua-bis(μ5-2,4-dichlorobenzoato)dipotassium

In the title compound, [K2(C7H3Cl2O2)2(H2O)]n, the potassium salt of 2,4-dichlorobenzoic acid, the repeating unit in the polymeric structure consists of two identical irregular KO6Cl complex units related by twofold rotational symmetry, linked by a bridging water molecule lying on the twofold axis. The coordination polyhedron about each K+ comprises a carboxyl O-atom and a Cl-atom donor from a bidentate chelate ligand interaction, four O-atom donors from a doubly bridging bidentate carboxyl (O,O')-chelate interaction and the water molecule. A two-dimensional layered coordination polymer structure lying parallel to (100) is generated through a series of conjoined cyclic bridges between K centres and is stabilized by water O-H...O(carboxyl) hydrogen-bonding interactions.

Poly[di-mu-aqua-bis{2-amino-4-nitrobenzoato)]-dirubidium

In the structure of title compound [Rb2(C7H5N2O4)2(H2O)2]n the asymmetric unit comprises two independent and different seven-coordinate Rb centres, one RbO7, the other RbO6N, with both having irregular stereochemistry. The RbO7 coordination comprises bridging oxygen donors from two water molecules, three carboxylate groups, and a nitro group, with one doubly bridging. The RbO6N coordination comprises the two bridging water molecules, one monodentate amine N donor, one carboxyl O donor and three O donors from nitro groups (one from the chelate bridge). The extension of the dinuclear unit gives a three-dimensional polymeric structure which is stabilized by both intra- and intermolecular amine N-H...O and water O-H...O hydrogen bonds to carboxyl and water O-atom acceptors, as well as a number of inter-ring \p--\p interactions [minimum ring centroid separation, 3.364(2) \%A]. This complex is both isostructural with the analogous Cs -nitroanthranilate monohydrate complex.

Adsorption of the herbicide 2,4-D on organo-palygorskite

Among the clay minerals, montmorillonite is the most extensively studied material using as adsorbents, but palygorskite and its organically modified products have been least explored for their potential use in contaminated water remediation. In this study, an Australian palygorskite was modified with cationic surfactants octadecyl trimethylammonium bromide and dioctadecyl dimethylammonium bromide at different doses. A full structural characterization of prepared organo-palygorskite by X-ray diffraction, infrared spectroscopy, surface analysis and thermogravimetric analysis was performed. The morphological changes of palygorskite before and after modification were recorded using scanning electron microscopy, which showed the surfactant molecules can attach on the surface of rod-like crystals and thus can weaken the interactions between palygorskite single crystals. Real surfactants loadings on organo-palygorskites were also calculated based on thermogravimetric analysis. 1 CEC, 2 CEC octadecyl trimethylammonium bromide modified palygorskites, 1 CEC and 2 CEC dioctadecyl dimethylammonium bromide modified palygorskites absorbed as much as 12 mg/g, 42 mg/g, 9 mg/g and 25 mg/g of 2,4- dichlorophenoxyacetic acid respectively. This study has shown a potential on organo-palygorskites for organic herbicide adsorption especially anionic ones from waste water. In addition, equilibration time effects and the Langmuir and Freundlich models fitting were also investigated in details.

The bentiromide test using plasma p-aminobenzoic acid for diagnosing pancreatic insufficiency in young children. The effect of two different doses and a liquid meal

The bentiromide test was evaluated using plasma p-aminobenzoic acid as an indirect test of pancreatic insufficiency in young children between 2 months and 4 years of age. To determine the optimal test method, the following were examined: (a) the best dose of bentiromide (15 mg/kg or 30 mg/kg); (b) the optimal sampling time for plasma p-aminobenzoic acid, and; (c) the effect of coadministration of a liquid meal. Sixty-nine children (1.6 ± 1.0 years) were studied, including 34 controls with normal fat absorption and 35 patients (34 with cystic fibrosis) with fat maldigestion due to pancreatic insufficiency. Control and pancreatic insufficient subjects were studied in three age-matched groups: (a) low-dose bentiromide (15 mg/kg) with clear fluids; (b) high-dose bentiromide (30 mg/kg) with clear fluids, and; (c) high-dose bentiromide with a liquid meal. Plasma p-aminobenzoic acid was determined at 0, 30, 60, and 90 minutes then hourly for 6 hours. The dose effect of bentiromide with clear liquids was evaluated. High-dose bentiromide best discriminated control and pancreatic insufficient subjects, due to a higher peak plasma p-aminobenzoic acid level in controls, but poor sensitivity and specificity remained. High-dose bentiromide with a liquid meal produced a delayed increase in plasma p-aminobenzoic acid in the control subjects probably caused by retarded gastric emptying. However, in the pancreatic insufficient subjects, use of a liquid meal resulted in significantly lower plasma p-aminobenzoic acid levels at all time points; plasma p-aminobenzoic acid at 2 and 3 hours completely discriminated between control and pancreatic insufficient patients. Evaluation of the data by area under the time-concentration curve failed to improve test results. In conclusion, the bentiromide test is a simple, clinically useful means of detecting pancreatic insufficiency in young children, but a higher dose administered with a liquid meal is recommended.

A new mode of ring cleavage of 2,3-dihydroxybenzoic acid in Tecoma stans (L.). Partial purification and properties of 2,3-dihydroxybenzoate 2,3-oxygenase.

2,3-Dihydroxybenzoic acid has been shown to be oxidized via the 3-oxoadipate pathway in the leaves of Tecoma stans. The formation of 2-carboxy-cis,cis-muconic acid, a muconolactone, 3-oxoadipic acid and carbon dioxide during its metabolism has been demonstrated using an extract of Tecoma leaves. The first reaction of the pathway, viz., the conversion of 2,3-dihydroxybenzoate to 2-carboxy-cis,cis-muconic acid has been shown to be catalysed by an enzyme designated as 2,3-dihydroxybenzoate 2,3-oxygenase. The enzyme has been partially purified and a few of its properties studied. The enzyme is very labile with a half-life of 3--4 h. It is maximally active with 2,3-dihydroxybenzoate as the substrate and does not exhibit any activity with catechol, 4-methyl catechol, 3,4-dihydroxybenzoic acid, etc. However, 2,3-dihydroxy-p-toluate and 2,3-dihydroxy-p-cumate are also oxidized by the enzyme by about 38% and 28% respectively, compared to 2,3-dihydroxybenzoate. Sulfhydryl reagents inhibit the enzyme reaction and the inhibition can be prevented by preincubation of the enzyme with the substrate. Substrate also affords protection to the enzyme against thermal inactivation. Sulfhydryl compounds strongly inhibit the reaction and the inhibition cannot be prevented by preincubation of the enzyme with its substrates. Data on the effect of metal ions as well as metal chelating agents suggest that copper is the metal cofactor of the enzyme. Evidence is presented which suggests that iron may not be participating in the overall catalytic mechanism.

Purification and Properties of l-4-Hydroxymandelate Oxidase from Pseudomonas convexa

An inducible membrane-bound l-4-hydroxymandelate oxidase (decarboxylating) from Pseudomonas convexa has been solubilized and partially purified. It catalyzes the conversion of l-4-hydroxymandelic acid to 4-hydroxybenzaldehyde in a single step with the stoichiometric consumption of O2 and liberation of CO2. The enzyme is optimally active at pH 6.6 and at 55 oC. It requires FAD and Mn2+ for its activity. The membrane-bound enzyme is more stable than the solubilized and purified enzyme. After solubilization it gradually loses its activity when kept at 5 oC which can be fully reactivated by freezing and thawing. The Km values for DL-4-hydroxymandelate and FAD are 0.44 mM and 0.038 mM respectively. The enzyme is highly specific for DL-4-hydroxymandelic acid. DL-3,4-Dihydroxymandelic acid competitively inhibited the enzyme reaction. From the Dixon plot the Ki for DL-3,4-dihydroxymandelic acid was calculated to be 1.8 × 10−4 M. The enzyme is completely inactivated by thiol compounds and not affected by thiol inhibitors. The enzyme is also inhibited by denaturing agents, heavy metal ions and by chelating agents.

Purification and properties of Image -mandelate-4-hydroxylase from Pseudomonas convexa

An inducible Image -mandelate-4-hydroxylase has been partially purified from crude extracts of Pseudomonas convexa. This enzyme catalyzed the hydroxylation of Image -mandelic acid to 4-hydroxymandelic acid. It required tetrahydropteridine, NADPH, Fe2+, and O2 for its activity. The approximate molecular weight of the enzyme was assessed as 91,000 by gel filtration on Sephadex G-150. The enzyme was optimally active at pH 5.4 and 38 °C. A classical Michaelis-Menten kinetic pattern was observed with Image -mandelate, NADPH, and ferrous sulfate and Km values for these substrates were found to be 1 × 10−4, 1.9 × 10−4, and 4.7 × 10−5 Image , respectively. The enzyme is very specific for Image -mandelate as substrate. Thiol inhibitors inhibited the enzyme reaction, indicating that the sulfhydryl groups may be essential for the enzyme action. Treatment of the partially purified enzyme with denaturing agents inactivated the enzyme.