Regioselective Enzyme-Mediated Glycosylation of Natural Polyhydroxy Compounds. Part 1. Galactosylation of stevioside and steviolbioside

Bovine β-1,4-galactosyltransierase is an efficient catalyst for the regioselective transfer of galactose from UPD-galactose, generated in situ with the UDP-glucose/UDP-glucose-4-epimerase system, to the kaurane glycosides stevioside ( 1 ) and Steviolbioside ( 2 ), affording the corresponding galactosyl derivatives 3 and 4 in high yields. By a combination of 2D NMR techniques (COSY, TOCSY, ROESY, HMQC, and HMBC), the structure of the products is established as 13-[(β -D -galactopyranosyl-(1 → 4)-β-D -glucopyranosyl-(1 → 2)- β -D -glucopyranosyl)oxy]kaur-16-en-19-oic acid β -D -glucopyranosyl ester ( 3 ) and 13-[(β-D -galactopyranosyl-(1 → 4)- β-D -glu-copyranosyl-(1 → 2)- β-D -glucopyranosyl)oxy]kaur-16-en-19-oic acid ( 4 ).     

The dimeric and polymeric anhydride of 2,3-O-isopropylidene-β-D-ribofuranose. An NMR study

The ¹H- and ¹³C-NMR data of the dimeric anhydride 1 of 2,3-O-isopropylidene-β-D -ribofuranose are reported together with the ¹H-NOE values. The data show that the products of the polymerization of 1,5-anhydro-2,3-O-isopropylidene-β-D -ribofuranose are α- and β-D -ribofuranans and not an α-D -ribofuranan and a β-D -ribofuranan and a β D ribo-pyranan as claimed before [2] [3].     

Amperometric Immunosensor for the Detection of 2,4-Dichlorophenoxyacetic Acid (2,4-D) in Water

ABSTRACT

An amperometric immunosensor for the determination of the herbicide 2,4-dichlorophenoxyacetic acid (2,4-D) in water has been developed using sequential injection analysis techniques. The system is based on a rapid competitive enzyme immunoassay employing an alkaline phosphatase-labeled monoclonal antibody directed against the herbicide and an immunoreactor with 2,4-D immobilized via bovine serum albumin either to Eupergit in a column or directly to the surface of a glass capillary. The detection limit of the immunosensor at 0.1 μg 2,4-D/l without enrichment of the analyte makes automatic measurements of 2,4-D in drinking and ground water feasible.     

Upperbound procedures for the identification of similar three-dimensional chemical structures

Summary This paper describes techniques for calculating the degree of similarity between an input query molecule and each of the molecules in a database of 3-D chemical structures. The inter-molecular similarity measure used is the number of atoms in the 3-D common substructure (CS) between the two molecules which are being compared. The identification of 3-D CSs is very demanding of computational resources, even when an efficient clique detection algorithm is used for this purpose. Two types of upperbound calculation are described which allow reductions in the number of exact CS searches which need to be carried out to identify those molecules from a database which are similar to a 3-D target molecule.     

The separation of acyl protection groups in alkali-sensitive glucosides. Synthesis of podophyllotoxin-beta-D-glucoside

The synthesis of podophyllotoxin-β-D -glucoside (III), an antimitotic lignan compound isolated from Podophyllum species, is reported. Reaction of podophyllotoxin (I) with tetra-O-acetyl-α-D -glucopyranosyl bromide in acetonitrile in the presence of Hg(CN)₂ yields tetra-O-acetyl-podophyllotoxin-α-D -glucoside (II), which is converted into podophyllotoxin-β-D -glucoside (III) by ZnCl₂-catalysed methanolysis. This transesterification is an advantageous method for the preparation of glycosides, sensitive to base and acid, from their corresponding acetyl derivatives. Scope and conditions of the reaction are discussed.     

Multidimensional gas chromatography with capillary flow technology and LTM-GC

2-D GC is a logical and cost effective extension to 1-D GC for improving the separation resolution, selectivity, and peak capacity of an analytical system. The advent of electronic pressure control systems that are accurate to the third decimal place, combined with recently innovated chromatographic devices such as capillary flow technology, has eliminated many deficiencies encountered in current conventional 2-D GC by making the technique reliable and simple to implement in both production and research analytical facilities. Low thermal mass GC (LTM-GC) was successfully integrated with capillary flow technology to further enhance overall 2-D GC chromatographic system performance by providing not only faster throughput via rapid heating and cooling, but independent temperature control for each dimension to maximize separation power. As an example, despite the enhanced peak capacity obtained from conventional 2-D GC, alkyl naphthalene isomers such as 2,3-dimethyl and 1,4-dimethyl naphthalene coeluted. These two critical compounds were well resolved (R = 5.2) using 2-D GC with LTM-GC with a similar analytical time. This paper demonstrates the benefits of combining capillary flow technology with LTM-GC to provide major enhancements to conventional 2-D GC. The synergy of these techniques is highlighted with practical industrial applications.     

Acid-catalyzed polymerization of 1,6-anhydro-β-D-glucopyranose

A number of 1,6-anhydrides were polymerized in the melt at 115°C by use of monochloroacetic acid as catalyst. In the early stages of polymerization (up to 40–50% monomer consumed), each monomer was found to disappear by a first-order rate process. The 1,6-anhydrides investigated and their relative rates of polymerization were: 1,6-anhydro-2-O-methyl-β-D -glucopyranose, 1.0; 1,6-anhydro-3,4-di-O-methyl-β-D -glucopyranose, 1.4; 1,6-anhydro-2-O-methyl-β-D -galactopyranose, 2.3; 1,6-anhydro-3-O-methyl-β-D -glucopyranose, 2.6; 1,6-anhydro-4-O-methyl-β-D -glucopyranose, 6.3; 1,6-anhydro-4-O-(β-D -glucopyranosyl) β-D -glucopyranose, 9.0; 1,6-anhydro-β-D -galactopyranose, 17; 1,6-anhydro-β-D -glucopyranose, 37; 1,6-anhydro-β-D -mannopyranose, 91; and 1,6-anhydro-2-deoxy-β-D -arabino-hexopyranose, 240. The effect of substitution on the rate of polymerization suggests this reaction is mechanistically related to the acid hydrolysis of pyranosides. The results suggest that polymerization proceeds in two stages: (1) an initial build-up of dimer followed by (2) a slower growth to higher molecular weight material.     

Searching of chemical structure data bases with parallel computer hardware

The use of two types of parallel computer hardware for increasing the efficiency of processing in chemical structure data bases is discussed. The distributed array processor can be used for the clustering of 2-D chemical structure data bases by using the Jarvis—Patrick clustering method and for the ranking of output in an experimental system for substructure searching in the 3-D macromolecules in the Protein Data Bank. The Inmos transputer can be used in the construction of PC-based systems for 2-D substructure searching and in the identification of the maximal substructures common to pairs of 3-D molecules.     

Removal of 2,4-dichlorophenoxyacetic acid by calcined Zn-Al-Zr layered double hydroxide

The adsorption equilibrium, kinetics, and thermodynamics of removal of 2,4-dichlorophenoxy-acetic acid (2,4-D) from aqueous solutions by a calcined Zn-Al layered double hydroxide incorporated with Zr(4+) were studied with respect to time, temperature, pH, and initial 2,4-D concentration. Zr(4+) incorporation into the LDH was used to enhance 2,4-D uptake by creating higher positive charges and surface/layer modification of the adsorbent. The LDH was capable of removing up to 98% of 2,4-D from 5 to 400 ppm aqueous at adsorbent dosages of 500 and 5000 mg L(-1). The adsorption was described by a Langmuir-type isotherm. The percentage 2,4-D removed was directly proportional to the adsorbent dosage and was optimized with 8% Zr(4+) ion content, relative to the total metals (Zr(4+)+Al(3+)+Zn(2+)). Selected mass transfer and kinetic models were applied to the experimental data to examine uptake mechanism. The boundary layer and intra-particle diffusion played important roles in the adsorption mechanisms of 2,4-D, and the kinetics followed a pseudo-second order kinetic model with an enthalpy, ΔH(ads) of -27.7±0.9 kJ mol(-1). Regeneration studies showed a 6% reduction in 2,4-D uptake capacity over six adsorption-desorption cycles when exposed to an analyte concentration of 100 ppm.     

Structural Characterization of Composite Particles of Two Commonly Used Herbicides

A spray drying technique was applied to prepare composite microparticles of a water-insoluble herbicide, atrazine(AT) and a water-soluble herbicide 2,4-dichloro phenoxy acetic acid (2,4-D) for the purpose of improving the water solubility of AT. A homogenous mixture of an ethanol solution of AT and an aqueous 2,4-D solution at different ratios were spray dried using a laboratory scale spray drier. Quantitative elemental analysis suggested that the AT/2,4-D ratio in each composite microparticle was nearly the same as the desired formulation ratio. The resulting samples were characterized by powder x-ray diffractometry (XRD), differential scanning calorimetry (DSC), Fourier transform infra red (FT-IR) and scanning electron microscopy (SEM). It was found that the crystallinity of AT and 2,4-D were maintained in the composite particles. Moreover, the release of AT from dissolved composite microparticles was markedly improved because of an increase in the effective surface area following rapid dissolution of 2, 4 D. Hence, this study shows that it is possible to prepare AT-2,4-D composite microparticles using a laboratory scale spray drier and that this can improve the ability of AT to dissolve in water.     

Structural analysis of the recombinant therapeutic product rFVIII and its PEGylated variants using 2-D DIGE

2-D DIGE is a method that circumvents the gel-to-gel variability inherent in conventional 2-DE and is particularly useful for studying proteome changes in diverse applications such as developmental biology and tissue proteomics. We developed a 2-D DIGE protocol for recombinant factor VIII (rFVIII), a therapeutic protein used for the treatment of hemophilia A. The factor VIII heterodimer is composed of heterogeneous, heavily glycosylated heavy and light chains that are held together by a divalent cation. 2-DE of rFVIII led to a separation of the various fragments whose identity could be determined by Western blot. A comparison of two rFVIII batches by 2-D DIGE revealed their identical composition, whereas an rFVIII variant lacking its central B domain was congruent with the smallest heavy and light chain fragments of rFVIII only. A simpler pattern was obtained upon removal of the terminal sialic acids of rFVIII's glycans, due to a better focusing in the first dimension. 2-D DIGE was also well suited to structurally evaluate various PEGylated rFVIII conjugates. 2-D DIGE thus proved an excellent and straightforward method for structural analysis of rFVIII. Our data suggest that the method could serve as a tool for quality control of very complex pharmaceutically active ingredients.     

1-D Selenidoindates {[In2Se5]}∞ directed by chiral metal complex cations of 1,10-phenanthroline

Two 1-D selenidoindates {[M(phen)(3)]In(2)Se(5)·H(2)O}(n) (M = Ni, Fe) were synthesized by a solvothermal method. The 1-D {[In(2)Se(5)](2-)}(n) anion is a new type of single 1-D structure constituted by an alternately fused four-membered In(2)Se(2) ring and five-membered In(2)Se(3) ring. The chalcogenoindates were separated as mechanical racemic mixtures of single enantiomer crystals, in which the R-helix of 1-D InSe anion is directed by the related clockwise (Δ) cations of [M(phen)(3)](2+) or the L-helix of 1-D anion is directed by the related anticlockwise (Λ) cation. The π···π, C···Se, and C-H···Se oriented interactions of metal complex cations with selenidoindate anions play an important role in the formation of the chiral crystals. The embedded [M(phen)(3)](2+) cations improve the optical absorption of the 1-D semiconductor materials.     

2-D islanding of dodecane on an Au(111) surface: an investigation using he beam reflectivity and Monte Carlo modeling

Dodecane is deposited at submonolayer coverages onto an Au(111) surface forming two-dimensional (2-D) islands. The islands sublimate to a 2-D gas at higher substrate temperatures. We observe island formation and subsequent 2-D sublimation between substrate temperatures of 40 and 350 K, using low-energy helium reflectivity. A computer model of the submonolayer islanding process using Monte Carlo simulations shows significant agreement with experimental data and yields an intermolecular potential of 0.10+/-0.03 eV (about half that of the bulk substance) and a significantly higher corrugation potential of 0.3+/-0.1 eV.     

Apparent two-dimensional behavior of TiO2 nanotubes revealed by light absorption and luminescence

Optical absorption and photoluminescence (PL) properties of colloidal TiO(2) nanotubes, produced by the alkali hydrothermal method, were studied at room temperature in the range 300-700 nm. Nanotubes having an internal diameter in the range 2.5-5 nm have very similar optical properties, in contrast to the expected behavior for quasi-1-D systems. This is explained by the complete thermal smearing of all 1-D effects, due to the large effective mass of charge carriers in TiO(2), resulting in an apparent 2-D behavior of TiO(2) nanotubes.     

Development of a dipstick immunoassay for quantitative determination of 2,4-dichlorophenoxyacetic acid in water, fruit and urine samples

A sensitive dipstick assay for 2,4-dichlorophenoxyacetic acid (2,4-D) detection was developed. The assay was based on the competitive reaction of 2,4-D and enzyme tracer with monoclonal antibodies immobilised on an Ultrabind^? membrane. The binding of enzyme tracer on the test strip was determined by a simple, portable reflectometer as remission at 657 nm. Using this technique, 2,4-D could be detected in a concentration range of 0.5 μg/L to 100 μg/L. The center point of the 2,4-D test was found at a concentration of 6 μg/L. Cross-reactivity with 2,4,5-trichlorophenoxyacetic acid (2,4,5-T) as determined by this dipstick assay was 2.5% and 3% by standard ELISA technique using microtiter plates. The assay was applied in the detection of 2,4-D in real water samples, and sensitivity was comparable to spiked water samples. If combined with an effective extraction procedure that results in recovery rates of 90%, the dipstick assay can be used to monitor human exposure to 2,4-D from contamination in water, from oranges and in testing urine samples. Received: 2 September 1998 / Revised: 29 January 1999 / Accepted: 31 January 1999     

Structure elucidation of an unexpected product from dehydration of a beta-hydroxyketone

The structure of an unexpected compound from the dehydration of an aldol addition product has been determined using 1-D and 2-D NMR techniques. This reaction is the last step in a new synthetic approach to the galanthan ring system. Complete 1H and 13C NMR assignments for two synthetic precursors are also reported.     

Trace LC/MS quantitative analysis of polypeptide biomarkers: impact of 1-D and 2-D chromatography on matrix effects and sensitivity

We investigated the impact of one dimension (single reverse phase (RP) column) and two dimension (two different RP columns) chromatographic methods on SIM (MS) and multiple reaction monitoring (MRM; MS/MS) performance from human plasma. We find that MRM analysis is clearly preferable for 1-D applications; however, implementation of SIM detection in conjunction with 2-D separation technique resulted in an over 60-fold increase in analyte peak area and improved S/N compared to MRM for our analyte, human C-peptide. Implementation of a 2-D RP-RP technique with SIM detection is capable of eliminating matrix effects and greatly increases signal response and data quality. For two large peptides in complex biological samples, we found that a 2-D approach performed better than high quality sample preparation together with 1-D chromatography and MRM, even on a high-end mass spectrometer.     

Stepwise synthesis and magnetic control of trimetallic magnets [Co2Ln(L)2(H2O)4][Cr(CN)6].nH2O (Ln = La, Gd; H2L = 2,6-Di(acetoacetyl)pyridine) with 3-D pillared-layer structure

Integration of mononuclear [Cr(CN)6]3- and preorganized trinuclear [Co2Ln(L)2]3+ complexes provides novel trimetallic magnets having a 3-D pillared-layer framework with an alternate array of 2-D layer extended by Cr(III)-CN-Co(II) linkages and Ln(III) ion. The overall magnetic nature can be systematically controlled by Ln(III) ions inserted between the 2-D ferromagnetic layers.     

The influence of sterics on the formation of polar 1-D hydrogen-bonded networks

Polar, noncentrosymmetric packing of directional, 1-D hydrogen-bonded networks of chiral, 4-amino-2,6-bis(oxazolinyl)pyridines (ampybox) occurs for isopropyl-substituted ampybox; in contrast, 1-D networks of methyl-substituted ampybox pack in an antiparallel arrangement.