Plutonium-244 dating

Re-calculation of the²⁴⁴Pu ages of lunar rocks 10057 and 12013 indicates that, while the former started to retain its xenon (4,189 _?74 ⁺⁴⁵ ) million years ago, the latter was formed at a much later time, after the extinct nuclide²⁴⁴Pu had essentially decayed away.     

Anisotropic contributions in the ligand polarization model for the f-f transition probabilities of Eu(III) complexes

The intensities of the ΔM = ± 1 component of the ⁷f_o→ ⁵D₂ transition in D₃ complexes containing the [ EuO₉] cluster, and of other d-d or f-f transitions in D₃ complexes with the yz- and xz-components of the electric quadrupole as the leading moment, are found to be dependent upon the polarizability anisotropy of the ligands. The expectation is supported by determinations of the single-crystal absorption intensities of Na₃ [Eu(diglycollate)₃]·2NaClO₄·6H₂O and [Eu(H₂O)₉] (C₂H₅SO₄)₃.     

Alternating copolymer of thiophene andN‐(phenylethynyl)pyrrole. New π‐conjugated alternating five‐membered ring copolymer and its packing structure

An alternating copolymer, Copoly‐1 , of thiophene and N‐(phenylethynyl)pyrrole was prepared by palladium‐catalyzed polycondensation. Powder X‐ray diffraction (XRD) analysis indicated that Copoly‐1 formed a stacked packing structure with doubly‐running polymer main chains. Optical data support the molecular and packing structures of Copoly‐1 . © 2005 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 43: 2219–2224, 2005     

Chiral phosphinooxathiane ligands for catalytic asymmetric Diels-Alder reaction

Chiral cationic palladium[bond]phosphinooxathiane complexes have been found to be effective catalysts for enantioselective Diels-Alder (DA) reaction of cyclopentadiene with acyl-1,3-oxazolidin-2-ones to give the corresponding DA adducts in good yield and high enantioselectivity up to 93% ee.     

Formation of a new crystalline silicate structure by grafting dialkoxysilyl groups on layered octosilicate

Dialkoxydichlorosilanes ((RO)2SiCl2, R = alkyl) react almost completely with interlayer silanol groups in a layered silicate octosilicate to create a new crystalline silicate structure consisting of new five-membered rings arranged regularly on both sides of the silicate layers. The introduction of dialkoxysilyl groups to the interlamellar region of layered silicates with regular reaction sites provides a new methodology for the design and construction of novel crystalline silicate frameworks by a soft chemical route.     

Accurate mass measurement of low molecular weight compounds by matrix-assisted laser desorption/ionization time-of-flight mass spectrometry

We report the application of matrix-assisted laser desorption/ionization time-of-flight mass spectrometry (MALDI-TOF MS) for the accurate measurement of mass of low molecular weight compounds (smaller than 1500 Da), a linear peptide, two types of cyclic depsipeptides, a polyhydroxy-macrocyclic lactone, and two prenylated flavonoids, with delayed extraction in the reflector mode. The performance of the MALDI-TOF instrument was less than those of fast atom bombardment and Fourier-transform ion cyclotron resonance mass spectrometry instruments and insufficient to give acceptable accuracy for literature reporting. Nevertheless, when combined with NMR spectrometry and/or amino acid analysis to give information on the numbers of carbon atoms and index of hydrogen deficiency, MALDI was useful for determination of the elemental composition of the low molecular weight compounds available in small quantities.     

Distribution behavior of some drug enantiomers in an aqueous two-phase system using counter-current extraction with protein

Summary The partial resolution of some drug enantiomers by counter-current extraction in an aqueous two-phase system using bovine serum albumin (BSA) or ovomucoid (OVM) as chiral discriminator is described. The phase system was prepared with dextran 40, polyethylene glycol and a protein. Ofloxacin (OFLX) enantiomer was well recognized by the BSA system, whereas the enantiomers of carvedilol (-blocker) and DG-5128 (a new oral hypoglycaemic drug) were hardly recognized by the OVM system. The distribution coefficients of (S)-, (R)- and rac-OFLX varied with pH. Good enantioselectivity for OFLX was obtained at relatively high pH ( pH 9). The crude optically enriched OFLX enantiomers were extracted from the aqueous fractions and finally purified by thin-layer chromatography.     

Di-isotacticity of poly(methyl propenyl ether) and double-bond opening of methyl propenyl ether in cationic polymerization

The di-isotacticity of poly(methylpropenyl ether) obtained by the cationic polymerization has been studied by NMR spectra. The NMR spectra of β-methyl protons of the polymer are decoupled from the β-methine proton spectra to determine the di-isotactic fraction in a polymer. The signals of β-methyl protons at 8.78 and 8.89 τ are estimated as spectra based on threo- and erythro-di-isotactic diads, respectively. With BF₃·O(C₂H₅)₂ as a catalyst, the trans monomer yields a crystalline polymer and its structure is threo-di-isotactic. Otherwise, cis monomer produces an amorphous polymer, and it is a mixture of threo- and erythro-di-isotactic structure. From these results, it is concluded that the double bond in trans monomer is opened exclusively in the cis type, and in cis monomer cis- and trans-openings take place at almost the same rate.     

Substrate dependence in aqueous Diels-Alder reactions of cyclohexadiene derivatives with 1,4-benzoquinone

A reactivity difference based on the position of substituents on cyclohexa-1,3- diene was observed for the title reaction. The effect of water as solvent was more distinct for 1-methyl-4-isopropylcyclohexa-1,3-diene than for 2-methyl-5-isopropylcyclohexa- 1,3-diene or non-substituted cyclohexa-1,3-diene. The effect of NaCl (salting-out) and guanidium chloride (salting-in) was also large for 1-methyl-4-isopropylcyclohexa-1,3- diene.     

Low temperature properties of acetonitrile confined in MCM-41

The effect of confinement on the phase changes and dynamics of acetonitrile in mesoporous MCM-41 was studied by use of adsorption, FT-IR, DSC, and quasi-elastic neutron scattering (QENS) measurements. Acetonitrile molecules in a monolayer interact strongly with surface hydroxyls to be registered and perturb the triple bond in the C[triple bond]N group. Adsorbed molecules above the monolayer through to the central part of the cylindrical pores are capillary condensed molecules (cc-acetonitrile), but they do not show the hysteresis loop in adsorption-desorption isotherms, i.e., second order capillary condensation. FT-IR measurements indicated that the condensed phase is very similar to the bulk liquid. The cc-acetonitrile freezes at temperatures that depend on the pore size of the MCM-41 down to 29.1 A (C14), below which it is not frozen. In addition, phase changes between alpha-type and beta-type acetonitriles were observed below the melting points. Application of the Gibbs-Thomson equation, assuming the unfrozen layer thickness to be 0.7 nm, gave the interface free energy differences between the interfaces, i.e., Deltagamma(l/alpha) = 22.4 mJ m(-2) for the liquid/pore surface (ps) and alpha-type/ps, and Deltagamma(alpha/beta) = 3.17 mJ m(-2) for alpha-type/ps and beta-type/ps, respectively. QENS experiments substantiate the differing behaviors of monolayer acetonitrile and cc-acetonitrile. The monolayer acetonitrile molecules are anchored so as not to translate. The two Lorentzian analysis of QENS spectra for cc-acetonitriles showed translational motion but markedly slowed. However, the activation energy for cc-acetonitrile in MCM-41 (C18) is 7.0 kJ mol(-1) compared to the bulk value of 12.7 kJ mol(-1). The relaxation times for tumbling rotational diffusion of cc-acetonitrile are similar to bulk values.