Showing papers in "Journal of The Chinese Chemical Society in 1999"

The Constituents of Cananga odorata

Abstract: Sixteen compounds, (+)-ushinsunine-β-N-oxide (1), cleistopholine (2), liriodenine (3), (-)-anonaine (4), (+)-nornuciferine (5), (+)-N-acetylnornuciferine (6), (-)-ushinsunine (7), (-)-norushinsunine (8), (-)-asimilobine (9), (+)-reticuline (10), N-trans-feruloyltyramine (11), β-sitosterol (12) and stigmasterol (13), lyscamine (14), (-)-anaxagoreine (15) and trans-cinnamic acid (16) were isolated from the methanolic extract of the Cananga odorata. Among them, 1 is a new stereoisomer of ushinsunine-β-N-oxide. The structures of these compounds were established by means of spectral experiments.

Chemotaxonomy of Triterpenoid Pattern of HPLC of Ganoderma lucidum and Ganoderma tsugae

Abstract: Three strains of Ganoderma tsugae (CCRC36065, CCRC37034, CCRC37038) and three strains of Ganoderma lucidum (CCRC36021, CCRC37029, CCRC37033) were cultivated. Their triterpenoid patterns of the fruit body were analyzed by reverse phase HPLC using a gradient elution of acetonitrile/2% acetic acid (1/4 and 1/2). The triterpenoid patterns of G. tsugae and G. lucidum are different. But similar 2 and 3 dimensional patterns are obtained among three strains of G. tsugae. Different patterns are found among different strains of G. lucidum. Ganoderic acid A(1), B(2), C(3) and D(4) were isolated from the ethanol extract of G. tsugae.

Lignans, Flavonoids and Phenolic Derivatives from Taxus mairei

Abstract: From the twigs of Taxus mairei, 35 lignans, 2 sesquilignans, 4 flavonoids, 3 bisflavonoids, 13 phenolic derivatives, 2 sesquiterpenes, 3 bisnorsesquiterpenes, 3 long-chain carboxylic acids and 4 steroids were isolated. The new lignans and phenolic glucosides include 7′-hydroxynortrachelogenin, 7-hydroxymatairesinol, 3′-O-demethylepipinoresinol, taxiresinol 9-acetate, 3′-O-demethyltanegool, 8′-epitanegool, 3,3′-dimethoxy-4,4′,9-trihydroxy-7,9′-epoxylignan-7′-one, 3-O-demethyldihydrodehydrodiconiferyl alcohol, taxumaiglucoside A heptaacetate, taxumaiglucoside B heptaacetate, and taxumaiglucoside C heptaacetate. Their structures were determined by spectral methods.

Metal String Complexes: Synthesis, Crystal Structures and Magnetic Properties of Heptanuclear Nickel(II) Complexes, [Ni7(μ7-teptra)4X2] (teptra = tetrapyridyltriamido, X = Cl−, NCS−)

Abstract: The synthesis, crystal structures and magnetic properties of linear heptanuclear nickel(II) complexes [Ni7(μ7-teptra)4X2], (teptra = tetrapyridyltriamido), with the axial ligand X = Cl− (1), NCS− (2), are reported. The hepta-nuclear metal chain is helically wrapped by four syn-syn-syn-syn-syn-syn teptra3− ligands. Both of the [Ni7(μ7-teptra)4]2+ moiety are isostructural involving a Ni7 linear chain unit with all of the ∠Ni-Ni-Ni being 180°, terminated by two axial ligands. Three types of NiNi distances are found in these complexes. The longest ones bonded with the axial ligands are 2.383(1), 2.374(2) and 2.375(2), 2.354(2), and the intermediate ones are 2.310(1), 2.304(1) and 2.300(2), 2.303(2) A for (1) and (2), respectively. The innermost NiNi distances are the shortest ones with the distances of 2.226(2), 2.214(2) and 2.194(2), 2.206(2) A for (1) and (2), respectively. Two terminal Ni(II) ions bonded with the axial ligands are in a square-pyramidal (NiN4X) environment and exhibit long NiN bonds (−2.10 A) which are consistent with a high-spin Ni(II) configuration. The inner five Ni(II) ions displayed short NiN (∼1.90 A) bond distances which are consistent with a square-planar (NiN4), diamagnetic arrangement of a low-spin Ni(II) configuration. The magnetic measurement of (1) shows an antiferromagnetic interaction of two terminal high-spin Ni(II) ions with the coupling constant J = −3.8 cm−1. The NiNi, NiN distances and magnetic behavior among tri-, penta-, and hepta-nickel(II) complexes are compared and discussed.

Chemical Constituents of the Pericarp of Platycladus orientalis

Abstract: In previous papers, we have reported two new compounds, 15-hydroxypinusolidic acid and platydiol, from the pericarp of Platycladus orientalis. In addition to the above compounds, the isolation and identification of twenty-one compounds from the same source are described. Their structures were determined on the basis of spectral evidence as well as direct comparison with authentic samples. These compounds included four fatty alcohols and acids, three monolignols, one sesquiterpene, nine diterpenes, two steroids, one flavone, and one sugar. Among these, docosyl 3-hydroxyferulate is a new compound. And docosyl trans- and cis-ferulates were isolated in pure form.

Applications of Highly Sulfated Cyclodextrins for Enantiomeric Separation by Capillary Electrophoresis

Abstract: Separation of enantiomeric pairs of compounds by capillary electrophoresis (CE) was performed using highly sulfated α-, β- and γ-cyclodextrins (HS-CDs). CE analysis of the HS-CDs using indirect absorbance detection showed that the new class of chiral selectors has substantially higher degrees of sulfation and narrower heterogeneity than those used in previous reports. Elemental analyses showed that the average number of sulfate groups per cyclodextrin was 11, 12, and 13, for HS-α, β and γCD, respectively. Our earlier 13C NMR data of HS-CDs were consistent with the structural assignment of complete sulfation at the C-6 primary hydroxyl groups, greater than 70% sulfation at the C-2 secondary hydroxyls and absence of substitution at the C-3 hydroxyls. CE-based chiral separations were performed using a generalized procedure with phosphate buffer (pH 2.5) containing 5% (w/v) HS-CD in a 50 μm I.D. × 31 cm (total length) fused silica capillary. Quantitation of enantiomeric impurity of less than 1% was demonstrated for pseudoephedrine and phenylpropanolamine. The HS-α, β and γCD complement each other by exhibiting different chiral selectivity. The combination of HS-α, β and γCD resolved more than 140 chiral compounds of neutral, acidic and basic drugs with very different structural features. The HS-CDs were synthesized under conditions of controlled sulfation to produce chiral reagents with consistent composition, making them excellent chiral selectors for capillary electrophoretic analysis of enantiomeric impurities.

Polar chemical constituents from phoebe formosana

Abstract: A chemical investigation on the H2O-soluble constituents from the leaf of Phoebe formosana. led to the characterization often compounds including two C-glycosylflavone — vitexin (1), isovitexin (2); six O-glycosylflavonol — quercetin 3-O-galactoside (3), quercetin 3-O-α-L-arabinopyranoside (4), kaempferol 3-O-α-L-arabinofuranoside (5), kaempferol 3-O-α-L-rhamnoside (6), kaempferol 3-O-β-D-xylopyranoside (7); one dihydroflavonol -(+)-dihydroquercetin (8) and two nucleosides -adenosine (9), and adenine (10). Their structures were determined on the basis of spectral analysis.

Design and Synthesis of Carbohydrate Mimetics: A New Strategy for Tackling the Problem of Carbohydrate‐Mediated Biological Recognition

Abstract: Carbohydrates have been known as poor candidates for drug development. Recent studies have, however, shown that structurally simplified small molecules as mimics of complex carbohydrates recognized by receptors can be developed as inhibitors of carbohydrate-mediated biological recognition. In addition, small molecules with higher affinity and specificity than the parent ligands can be developed by incorporating additional hydrophobic or charged groups in the carbohydrate mimetic which contains essential functional groups for receptor binding. Representative examples are illustrated in the studies of sialyl Lewis x - selectin interactions, glycosidase and glycosyltransferase reactions and aminoglycoside antibiotic - RNA interactions.

Influence of Short‐Chain Alcohols on the Micellization Parameters of Sodium Dodecyl Sulfate (SDS)

Abstract: The in flu ence of short-chain al co hol on the ag gre ga tion be hav ior of So dium Dodecyl Sul fa te (SDS) is in ves ti gated within a wide range of al co hol con cen tra tion by potentiometric tech nique. It is ob served that ag gre ga tion be hav ior of SDS is a func tion of al co hol con cen tra tion. Vari a tion of mice llization pa ram e ters are stud ied in a wide range of al co hol con cen tra tion and the trend of chang ing of micellizat ion pa ram e ters have been in ves ti gated. The vari a tions of micellization pa ram e ters show sev eral reg u lar i ties. Finally, the re la tion ships be tween these reg u lar i ties and al co hol-surfactant in ter ac tions have been ex plained.

Chemical Constituents of a Formosan Soft Coral Sinularia sp.

Abstract: A new marine sterol 7β-hydroperoxy-24-methylenecholesterol (1) along with five known compounds sarcophytol A (2), (Z)-N-[2-(4-hydroxyphenyl)ethyl]-3-methyldodec-2-enamide (3), 5α,7αH-eduesm-11(13)en-4α-ol (4), 24-methylenecholesterol (5) and 1β-hydroxy-α-cyperone (6) have been isolated from a Formosan soft coral Sinularia sp. The structures of the above compounds were determined by spectral analyses. Cytotoxicity of compounds 1–6 toward various cancer cell lines also is reported.

A sensitive colorimetric method for the determination of arsenic in environmental and biological samples

Abstract: Results of a thorough study and application of leucocrystal violet for the determination of arsenic in parts per million (ppm) levels in environmental and biological samples is described here. The proposed method is based on the reaction of arsenic with potassium iodate to liberate iodine. The liberated iodine selectively oxidises leucocrystal violet to form crystal violet dye in the presence of sodium hydroxide. The dye formed shows maximum absorbance at 592 nm. The detection limit of arsenic is 0.002 μgmL−1 and the method obeys Beer's law over the concentration range of 0.1 μg - 1.0 μg of per 25 mL of final solution (0.004–0.04 ppm). The molar absorptivity was found to be 1.49 × 106 L mol−1 cm−1. The proposed method was successfully applied for the determination of arsenic in various environmental and biological samples. The results are in good agreement with the standard reported method.

Tannin and Related Compounds from Terminalia catappa and Terminalia parviflora

Abstract: Continuing chemical examination on tannins and related compounds of Combretaceous plants has led to the isolation of one novel complex type tannin, catappanin A, together with two phenolcarboxylic acids, two phenol glucoside gallates, seven ellagic tannins, one other hydrolyzable tannin, four flavan-3-ols and two complex type tannins from the bark of Terminalia catappa. In addition, from the bark of Terminalia parviflora one new methyl glucoside gallate, methyl 3,6-di-O-galloyl-β-D-glucoside, three phenolcarboxylic acids, three gallotannins, six ellagitannins and three other hydrolyzable tannins were isolated. Their structures were elucidated on the basis of chemical and spectroscopic evidence.

Synthesis and Biological Activity of ω‐(5‐Aryl‐1,3,4‐oxadiazol‐2‐thio)‐ and ω‐(5‐Aryl‐1,3,4‐oxadiazol‐2‐thioacetoxyl)‐ω‐(1‐H‐1,2,4‐triazol‐1‐yl)acetophenones

Abstract: Eighteen novel ω-(5-Aryl-1,3.4-oxadiazol-2-thio)-ω-(1-H-1,2,4-triazol-1-yl)acetophenones (4a-4i) and ω-(5-Aryl-1,3,4-oxadiazol-2-thioacetoxyl)-ω-(1-H-1,2,4-triazol-1-yl)acetophenones (5a-5i) were synthesized. All the compounds synthesized were confirmed by elemental analyses and spectral data. The biological activity of representative compounds was evaluated.

The Synthesis and Application of the Mesoporous Molecular Sieves MCM‐41 — A Review

Abstract: We report a “delayed neutralization” process for the preparation of highly-ordered aluminosilicate MCM-41 molecular sieves with high thermal and hydrothermal stability, and sharp pore size distribution. However, the structural order and pore size are dependent on the carbon chain length. In the mixture surfactant systems, the pore size of the MCM-41 materials could be fine-tuned. The pore size can be extended from 2.5 to 4.5 nm by adding a suitable amount of hydrocarbons. The tubular morphology of the MCM-41 material of 0.3 to 10 micrometers diameter, where the wall consists of coaxial cylindrical pores of nanometers MCM-41, can be obtained by careful control of the surfactant-water content and the rate of condensation of silica. An optimum condition for automatic synthesis of the hierarchical TWT structure has been accomplished. The addition of 1-alkanols as cosurfactant would not only improve the order of the MCM-41 hexagonal structure but also promote the formation of micrometer-sized hierarchical materials, for example: tubules-within-tubule and uniform-sized hollow spheres of diameter 5.0 ± 1.0 μm. However, the inside of the micron spheres has intricate structures possessing various topological genus ranks. The MCM-41 is a good supporter for Molybdenum oxide catalysts. The rate of deactivation in the catalytic reaction of ethyl-benzene dehydrogenation to styrene increases in the order: MT < MP < SiO2. The physically mixed samples have higher catalytic activity than impregnated ones.

Studies on the Synthesis of New 3‐(3,5‐Diamino‐1‐substituted‐pyrazol‐4‐yl)azo‐thieno[2,3‐b]pyridines and 3‐(2‐Amino‐5,7‐disubstituted‐pyrazolo[1,5‐a]pyrimidine‐3‐yl)azothieno[2,3‐b]pyridines

Abstract: Coupling the diazonium salt of 3-amino-2-cyano-4,6-dimethylthieno[2,3-b]pyridine 1 with malononitrile 2 gave 2-cyano-3-(hydrazonomalononitrile)-4,6-dimethylthieno[2,3-b]pyridine 3 which then reacted with hydrazine compounds 4a-4h to yield corresponding 2-cyano-3-(3,5-diamino-1-substituted-pyrazol-4-yl)azo-4,6-dimethylthieno[2,3-b]pyridines 5a-5h. The 2-cyano-3-(2-amino-5,7-disubstituted-pyrazolo-[1,5-a]pyrimidine-3-yl)azo-4,6-dimethylthieno[2,3-b]pyridines 7a-7f were obtained in good yield by the cyclocondensation reaction of 2-cyano-3-(3,5-diamino-pyrazol-4-yl)azo-4,6-dimethylthieno[2,3-b]pyridine 5a with the appropriate 1,3-diketones 6a-6f under acidic condition.

Biochemistry and Molecular Biology of Snake Neurotoxin

Abstract: A review of research on snake neurotoxin is presented, with emphasis on the chemical modification studies and molecular cloning of postsynaptic and presynaptic neurotoxins from Naja naja atra (Taiwan cobra) (Fig. 1a) and Bungarus multicinctus (Taiwan banded krait) (Fig. 1b). Cobrotoxin and α-bungarotoxin are the primary postsynaptic neurotoxins isolated from the venom of N. naja atra and B. multicinctus, respectively. Although they share a common three-dimensional structure, the functional elements essential for the manifestation of their toxicity are different. Selective and stepwise chemical modification of cobrotoxin indicate that at least two cationic groups, an ϵ-amino group of Lys-47 and a guanidino group of Arg-33 common to all known postsynaptic neurotoxins, are functionally important for its neuromuscular blocking activity. However, for α-bungarotoxin, the side chains of several basic amino acid residues are involved in the multipoint contact between the toxin and acetylcholine receptor. Moreover, the conserved Trp residue is essential for the neurotoxicity of cobrotoxin, but not for α-bungarotoxin. The cDNAs encoding cobrotoxin and α-bungarotoxin was constructed from the cellular RNA isolated from the venom glands of N. naja atra and B. multicinctus by polymerase chain reaction. The sequence of their 3′-untranslational region, signal peptide and 5′-untranslational region share a high degree of homology, suggesting that they are evolutionarily related. Expression of both neurotoxic protein in E. coli generated polypeptide chains for reactions with the antisera against the native neurotoxins. Presynaptic neurotoxins constitute a different group of neurotoxic proteins in snake venom proteins. These presynaptic neurotoxins are either basic phospholipase A2 (PLA2) per se or contain basic PLA2 as an indispensible part of their structures. Thus, the presynaptic neurotoxins usually show both PLA2 activity and presynaptic neurotoxicity. β-Bungarotoxin (β-Bgt), the main presynaptic PLA2 neurotoxin isolated from the venom of B. multicinctus (Taiwan banded krait), consists of two dissimilar polypeptide chains, a PLA2 subunit (A chain) and potassium channel recognition subunit (B chain). Chemical modification studies show that the toxin might possess two functional sites, one responsible for the catalytic activity and the other for its pharmacological properties. Molecular cloning and expression of the A chain and B chain of β-Bgt reveal that the A chain of β-Bgt is an active subunit with PLA2 activity, and that the B chain is involved in voltage-gated potassium channel blocking action observed with β-Bgt.

Beckmann Rearrangement of Cyclohexanone Oxime over Borate-Pillared LDHs

Abstract: Borate-pillared layered double hydroxides (LDHs) were studied as catalysts in vapor-phase Beckmann rearrangement of cyclohexanone oxime to caprolactam under atmospheric pressure. The results were compared with those over the physical admixture of LDH and boria, the co-precipitate of B-Mg-Al hydroxide, and the pristine LDH and boria compounds. Although oxime conversion and caprolactam selectivity declined with time-on-stream over all the catalysts, borate-pillared LDH catalysts could retain activity longer than pure boria or those prepared by other methods. The decay rate however was affected by the Mg/Al ratio, the boron content and the form of LDH precursor used. The LDH itself functioning as a basic catalyst contributed to the formation of side products such as cyclohexanone and 2-cyclohexen-1-one. The physical admixtures of LDH and boria had catalytic properties more close to that of pure boria, which gave high caprolactam selectivities but lost the activity in several hours on stream. The high resistance to decay of the pillared catalysts was attributed to that boria in the interlayer of LDH was stabilized and prevented from structural transformation to a glassy state of no activity.

On the Search for H5O2+centered Water Clusters in the Gas Phase

Abstract: In searching for H5O2+-centered water clusters, we employed vibrational predissociation spectroscopy and ab initio calculations. Structures of the clusters were characterized by the free- and hydrogen-bonded-OH stretches of ion cores and solvent molecules. Systematic examination of H+(H2O)5–7 in a supersonic expansion reveals the presence of both cyclic and noncyclic forms of H5O2+-centered water clusters. The proton transfer intermediate H5O2+(H2O)4 was identified, for the first time, by its characteristic hydrogen-bonded-OH stretches of the ion core at 3178 cm−1. Also discovered at n = 7 is the H5O2+-containing five-membered ring isomer, whose existence is evidenced by the observation of a bonded-OH stretching doublet at 3544 and 3555 cm−1 of the solvent molecules. The observations are in accord with ab initio calculations which forecast that H5O2+(H2O)4 and H5O2+(H2O)5 are, respectively, the lowest-energy isomers of protonated water hexamers and heptamers.

Application of Cryptand/Polystyrene Drift-Type Phase Transfer Catalysts for Reduction of Ketones

Abstract: A drift-type phase transfer catalyst, cryptand-22, adsorbed on poly(styrene/diviny benzene)-sulfonic resin was prepared and applied to catalyze the reduction of ketones, e.g., acetophenone, benzophenone and benzaldehyde with NaBH4 as a reducing agent. Before the reaction, cryptand-22 was adsorbed on the sulfonic resin with ion-pairing, resin-SO3− +NH-cryptand-22. The ion-pairs can be destroyed by adjusting the basicity of the reaction solution with NaOH and the cryptand can be released from the resin into the reaction solution as a homogeneous catalyst during the reaction period. After the reaction, the cryptand catalyst can be readsorbed on the resin by adjusting the acidity of the solution with HCl and can be readily recovered by filtration like a heterogeneous catalyst. The draft-type cryptand catalyst exhibited better catalytic ability than some common crown ethers, e.g., 15-crown-5, benzo-15-crown-5, 12-crown-4 and dibenzo-18-crown-6 for the reduction of acetophenone with NaBH4. Effects of solvents, pH of solutions, concentration of the catalyst, reducing agents and resin property on the reduction of ketones were investigated and discussed. The reaction mechanism of the cryptand catalyzed reduction was also studied.

Design and Synthesis of an Activity Probe for Protein Tyrosine Phosphatases

Abstract: Protein tyrosine phosphatases (PTPases) are an important class of enzymes involved in the regulation of many cellular events. Here we describe the design and synthesis of an activity probe 2 targeting these PTPases. This mechanism-based activity probe adopts a cassette-like design; a phosphate group serves as the recognition head and a fluorescent diethylaminocoumarin derivative acts as the reporter group. Compound 3 was phosphorylated with diallyl phosphorochloridate and then fluorinated with DAST to give versatile intermediate 5. The Boc protective group of compound 5 was removed by TEA to make available the amino group where a diethylaminocoumarin chromophore was later attached. Final deprotection of the allyl group from the phosphate head gives our complete activity probe 2. It will be used in the labeling study of PTPases from various sources.

High Performance Liquid Chromatographic Enantioresolution of Benzoyl Amino Acid, Dipeptides and Tripeptide on β-Cyclodextrin Bonded Stationary Phase Using Polar-Organic Acetonitrile as the Mobile Phase

Abstract: The enantiomeric resolution of several dipeptides, amino acid (i.e., isoleucine) and tripeptide (i.e., Leu-Gly-Phe) with two stereogenic centers on β-cyclodextrin bonded chiral stationary phase (β-CD CSP) using polar-organic acetonitrile as the mobile phase is examined through pre-column chemical derivatization with a series of tagging reagents such as benzoyl chloride, benzenesulfonyl chloride and 1-naphthalenesulfonyl chloride. These tagging reagents are similar in structure; however, the enantioselectivity for the same analyte derivatized with these tagging reagents is quite different and found to be the best with benzoyl chloride. In the reversed-phase mode or on the γ-CD CSP under the same chromatographic conditions, the enantioresolution diminishes for all tagged enantiomers that were examined in this study. Dipeptides derivatized by benzoyl chloride appear to be better resolved than by dansyl chloride as reported previously. Interestingly, no enantioresolution for most derivatized amino acids with single stereogenic center was observed. Finally, enantioresolution can be enhanced by replacing the basic additive such as triethylamine with tripropylamine in the polar-organic mobile phase.

Thermodynamics of Binding 2,2′‐Bipyridineglycinato Palladium (II) Chloride on Human Serum Albumin

Abstract: The interaction of human serum albumin (HSA) with 2,2′-bipyridineglycinato palladium (II) chloride was studied by isothermal titration microcalorimetry at 27°C and equilibrium dialysis and UV-Vis. spectrophotometry techniques at temperatures of 27 & 37°C in 2.5 mM phosphate buffer solution at pH = 7.0. The enthalpy of binding was calculated from binding data, which were obtained from equilibrium dialysis in terms of the Wyman binding potential theory related to the van't Hoff relation. The enthalpy of HSA unfolding was determined by subtraction of the microcalorimetric enthalpy (binding and unfolding enthalpies) and the enthalpy of binding. The enthalpy of HSA unfolding, due to the binding of that ligand, was 491.43 kJ mol−1.

Chiral ruthenium-oxo complexes for enantioselective epoxidation of trans-stilbene

Abstract: Two oxoruthenium(IV) complexes containing C2 symmetric 1,1′-biisoquinoline (biqn) and (R,R)-3,3′-(1,2-dimethylethylenedioxy)-2,2′-bipyridine (diopy*) were prepared, and both are active oxidants for alkene epoxidations. The oxidation of styrene and cis- and trans-β-methylstyrenes by [(Cn)(diopy*)-RuIV(O)](ClO4)2 did not proceed enantioselectively, but the same oxidant can attain a moderate enantioselectivity of 33%ee for the trans-stilbene oxidation to trans-stilbene oxide. A head-on approach model, where the C=C is directed from the top to the O=Ru moiety, is proposed to account for the facial differentiation of the trans-stilbene oxidation.

Some New Radical Reactions of Xanthates

Abstract: Xanthates are convenient precursors of a variety of radicals that can be captured in an inter- or intramolecular fashion. Overall, the process involves rupture of the sulfide C-S bond and addition of the elements of the xanthate to the olefinic trap. The xanthate in the product can be used in another radical sequence or ionically modified in a great variety of ways. S-Propargyl xanthates exhibit a special but interesting behaviour which involves a sigmatropic rearrangement to the corresponding allene and ring closure to a novel betaine.

Ion‐Solvent Interaction of Biunivalent Electrolytes in Dioxane‐Water Mixtures from Conductivity Data at Different Temperatures

Abstract: This paper presents the conductivity measurements for some alkaline earth metal salts MgCl2, MgBr2, Mg(NO3)2, CaCl2, CaBr2 and Ca(NO3)2 by which the ion-solvent interactions are reported in the concentration range in dioxane-water mixtures at mass fraction of 0, 3, 10, 20 and 30% at 30°, 35°, 40° and 45°C ± 0.01. The conductance data were analyzed for the limiting molar conductivity, Ao, by the Fuoss-Edelson conductivity equation for the 2:1 unsymmetrical electrolytes. The results were discussed in terms of the solute-solvent interaction from the temperature coefficient of Walden product, Λoη of the electrolyte solutions. Moreover, Λoη was found to exhibit a linear relationship with the dielectric constant, ϵ, of the dioxane-water mixtures. The study gives information regarding the ion-solvent interactions from the mobilities and Walden product of the ions in the solvent. The ions appear to interact appreciably and the ion-solvent interaction tends to increase in the order Ca > Mg for the same anion while for the anions, the trend decreases in the order Cl− < Br− < No−3.

Systematic nmr assignments of dna exchangeable protons

Abstract: Exchangeable proton information is of critical importance in the NMR structural studies of DNA/RNA oligomers and/or their complexes with protein. However, no systematic NMR assignment strategy about these protons has been reported until now, although similar studies about non-exchangeable proton assignment have been well established in the past decade. We now report detailed NMR studies of a DNA duplex (d20-mer) containing the recognition site (5′-ATGAC-3′) of GCN4 basic zinc finger protein. All exchangeable and non-exchangeable protons except H5′/H5″ protons could be assigned from a single H2O/NOESY spectrum at 25°C. The assignment strategy reported in this paper shall be useful to NMR studies of unusual DNA/RNA structures and their complexes with peptides/proteins.

Bisabolane Sesquiterpenes from Ligularia thyrsoidea

Abstract: Phytochemistry investigation of the whole plants of Ligularia thyrsoidea, has led to the isolation of five new bisabolane sesquiterpenes along with three known compounds. The structures of these new compounds were elucidated by spectroscopic methods and 2D NMR techniques.

Removal of Heavy Metals from Plating Wastewater by Crystallization/Precipitation of Gypsum

Abstract: A high surface area was created during nucleation and crystal growth of gypsum by mixing calcium and sulfate ions, causing adsorption of heavy metals on the colloids of gypsum and capsulation in the subsequent precipitation process. In addition to the effect of surface area, zeta potential and surface pH of the gypsum colloids, ionic strength of solution, as well as solubility and particle size of the metal hydroxide influenced the extent of uptake of heavy metals from wastewater.

New Approaches for Solving Crystal Structures from Powder Diffraction Data

Abstract: The determination of crystal structures from single crystal diffraction data can generally be carried out routinely and straightforwardly. However, many crystalline solids can be obtained only as microcrystalline powders and are not suitable for investigation by conventional single crystal diffraction methods. In the past, this problem has limited the ability to elucidate the structural properties of such materials. For the wide range of materials in this category, there is clearly a pressing need to develop and exploit techniques that allow crystal structures to be solved from powder diffraction data. Although traditional techniques for structure solution from powder diffraction data have been applied successfully in several cases, these techniques have certain intrinsic limitations, and for the case of organic molecular crystals the challenges that must be overcome are particularly severe. For these reasons, our recent research has focused on the development and implementation of new methodologies for structure solution from powder diffraction data, leading to new “direct-space” techniques for structure solution in which a hypersurface based on the profile R-factor is searched using Monte Carlo or Genetic Algorithm techniques. This paper presents a brief overview of the problems and challenges associated with structure solution from powder diffraction data. The foundations of the techniques that we have developed are described, and illustrative examples (from the field of organic molecular crystals) are given to highlight the application of these techniques.