A new saponin lactone from Astragalus corniculatus

A new oleanane-type saponin lactone was isolated from the ethanolic extract of the aerial parts of Astragalus corniculatus Bieb. The structure of the saponin was elucidated as 19-hydroxyolean-12-ene-28, 21beta-olide 3beta-D-xylopyranoside (1) by chemical and spectral methods.     

Tight binding of poly(carboxylate) ligand to calcium carbonate with intramolecular NH…O hydrogen bond

Novel poly(carboxylates), partially amidated poly(acry late), poly{[1-carboxylate-2-(N-t-butyl)carbamoyl)]ethylene-alt-ethylene}, poly[1-(N-oxysuccinyl-aminomethenyl)ethylene], poly[1-(N-oxymalenyl-aminomethnyl)ethylene] and poly[1-(N-oxyphthalyl-aminomethnyl)ethylene] with intramolecular NH…O hydrogen bond between amide NH and coordinating oxygen were synthesized as model ligands for CaCO₃ biominerallization. The FE/SEM and its backscatter of the CaCO₃ composite of gold colloid-conjugated poly{[1-carboxylate-2-(N-p-methylthiophenyl)carbamoyl]ethylene-alt-ethylene} indicate that the polymer ligand is located at the surface of vaterite crystals and the oriented carboxylate ligands control the CaCO₃ polymorph.     

The separation of daughter nuclides from90Sr−90Y and140La−140Ba systems by thin-layer chromatographic methods

The separation of daughter nuclides in the carrier-free state from⁹⁰Sr?⁹⁰Y and¹⁴⁰Ba?¹⁴⁰La aqueous solution systems was performed by thin-layer chromatographic methods. (1) When a silica gel adsorbent and a developer of 1N NaCl, KCl, NH₄Cl, CaCl₂, SrCl₂ or BaCl₂ solutions was employed,⁹⁰Y and¹⁴⁰La were retained at the origin, while⁹⁰Sr and¹⁴⁰Ba advanced with the developer front. Addition of gypsum as binder to the silica gel prevented the separation of the¹⁴⁰Ba?¹⁴⁰La system, retaining both components at the origin. (2) When the¹⁴⁰Ba?¹⁴⁰La system was developed with water on a silica gel adsorbent containing 5% of gypsum, which was treated with various concentrations of nitric acid, the Rf value of¹⁴⁰La increased with the concentration of nitric acid used, reaching a maximum of 0.98 at 0.1 N. The Rf value then decreased on the further increase of the concentration of nitric acid. When the same process was applied to the⁹⁰Sr?⁹⁰Y system, there was no separation. The radiochemical purities of⁹⁰Y and¹⁴⁰La obtained in the above two ways were more than 99%.     

The mechanism of photocatalytic hydrogen production from gaseous methanol and water: IR spectroscopic approach

IR spectroscopic and volumetric study under reaction conditions of the mechanism of photocatalytic hydrogen production from gaseous methanol and water revealed that CO₂ and H₂ were produced by reaction between adsorbed CH₃O(ad) and H₂O. Another reaction path for H₂ production, CH₃ OH(ad) → H₂ + HCHO, was suggested which is dominant in the absence of water.     

Diode laser spectra of cis-HONO near 850 cm−1 and trans-HONO near 1700 cm−1

Tunable diode laser spectra have been measured for the ν₄ band of cis-HONO near 850 cm^?1 and the ν₂ band of rans-HONO near 1700 cm^?1. The ν₄ band is completely unperturbed and 355 well-resolved transitions have been fit with a standard deviation of 0.0007 cm^?1. The ν₂ band appears to have some small perturbations, but about 190 transitions have been fit with a standard deviation of 0.0027 cm^?1. Rotational and centrifugal distortion constants are given for both bands.     

N-Heterocyclic carbene-catalyzed oxidations

N-Heterocyclic carbenes catalyze the oxidation of allylic and benzylic alcohols as well as saturated aldehydes to esters with manganese(IV) oxide in excellent yields. A variety of esters can be synthesized, including protected carboxylates. The oxidation proceeds under mild conditions, with low loadings of a simple triazolium salt pre-catalyst in the presence of base. Substrates containing potentially epimerizable centers are oxidized while preserving stereochemical integrity. The acyl triazolium intermediate generated under catalytic conditions can be employed as a chiral acylating agent in the desymmetrization of meso-diols.     

Are Unsaturated Isocyanides so Different from the Corresponding Nitriles?

Simple unsaturated and cyclopropylic isocyanides are synthesized by an efficient and simple approach. These compounds with gradually increasing distance between the unsaturated moiety and the isonitrile group are studied by UV photoelectron spectroscopy and quantum chemical calculations, and also compared to the corresponding nitriles. The first photoelectron band of the unsaturated compounds is linked to removal of an electron from the HOMO, which corresponds to CC multiple-bond ionization in antibonding interaction with the π-isocyanide bond (in the same plane) for conjugated systems, or in antibonding interaction with the pseudo-π-CH(2) group for isolated systems. For the 1-ethenyl derivatives, both cyano and isocyano groups act as a π-electron acceptor from the vinyl group, but the isocyano π system is much more strongly destabilized (ionization energies (IEs) shift to smaller values) by vinyl (3.12 eV) than the cyano π system is (2.70 eV). In comparison with the 1-ethynyl derivatives, a less pronounced destabilization (2.69 eV) of π(NC) by the ethynyl system (1.86 eV for π(CN)), and nearly the same order of magnitude of the energetic gap between the total antibonding (π(CC)-π(NC)) and the total bonding (π(CC)+π(NC)) IEs for ethenyl and ethynyl compounds are noted. The huge values of these last-named data for H(2)C=CH-NC (3.85 eV) and for HC≡C-NC (4.04 eV) reflect the strong interaction between the unsaturated carbon-carbon moiety and the isocyanide group, and thus more efficient conjugation than for the corresponding nitriles.     

Crystal structure and spin dynamics for the Li9V3P(8-δ)O(29-δ') insertion electrode system with a multiple-electron reaction

The crystal structure, the electron configurations of V ions and the spin dynamics for the Li(9)V(3)P(8-δ)O(29-δ') insertion electrode system that exhibits a multiple-electron reaction are explored through measurements of x-ray four-circle diffraction, magnetization and nuclear magnetic resonance. The structure for the stoichiometric composition with δ = δ' = 0 is refined precisely and the effective valences of all ions are determined. The electron configurations of V ions for the system annealed at various temperatures are considered in the framework of intermediate crystal field approach. For the system that often exhibits the charge-discharge performance better than the double-electron reaction, the spin dynamics mainly for the tetrahedral Li3 ions is understood on the basis of the relaxation mechanisms of quadrupole coupling and resonance shift anisotropy caused by the dipolar field of V ions. The correlation time of fluctuating fields is proportional to the temperature above 30 K, below which it follows the fractional Debye-Stokes-Einstein relation.     

Photochemical properties of a myoglobin-CdTe quantum dot conjugate

A myoglobin-cadmium telluride quantum dot conjugate was constructed using an artificial heme modified with a thiol moiety as a linker. Irradiation of the myoglobin-cadmium telluride conjugate generated the photoreduced ferrous myoglobin via an electron transfer from the photoexcited quantum dot, leading to the formation of CO-bound myoglobin under a CO atmosphere.     

Synthesis and pharmacological evaluation of 3-amino-1-(5-indanyloxy)-2-propanol derivatives as potent sodium channel blockers for the treatment of stroke

In investigating potent sodium (Na(+)) channel blockers for the treatment of ischemic stroke, we synthesized a novel series of 3-amino-1-(5-indanyloxy)-2-propanol derivatives and evaluated their inhibitory effects on neuronal Na(+) channels. The 3-amino-1-(5-indanyloxy)-2-propanol derivatives exhibited potent blocking activity for Na(+) channels and a significantly low affinity for dopamine D(2) receptors, which demonstrates a minimal clinical risk for extrapyramidal side effects. In particular, compound 4b, a 3-amino-1-(5-indanyloxy)-2-propanol derivative bearing a benzimidazole moiety, showed desirable neuroprotective activity in a rat transient middle cerebral artery occlusion model. Furthermore, compound 4b displayed a high binding affinity for neurotoxin receptor site 2 of the Na(+) channels, which suggests that 4b would act as a use-dependent Na(+) channel blocker in sustained depolarization during ischemic stroke.