Total synthesis and stereochemistry of the antitumor antibiotic PD 113,271

[Structure: see text] A total synthesis of PD 113,271, an antitumor fostriecin analogue isolated from Streptomyces pulveraceus, was achieved by the chiral pool approach starting with D-galactose and L-tartaric acid. The synthesis of PD 113,271 led to unambiguous assignment of the relative and absolute stereochemistry of its stereocenters.     

Generic initial ideals of some monomial complete intersections in four variables

Let R = K[x ₁, x ₂, x ₃, x ₄] be the polynomial ring over a field of characteristic zero. For the ideal (x₁^a, x₂^b, x₃^c, x₄^d) ì R{(x_1^a, x_2^b, x_3^c, x_4^d) \subset R}, where at least one of a, b, c and d is equal to two, we prove that its generic initial ideal with respect to the reverse lexicographic order is the almost revlex ideal corresponding to the same Hilbert function.     

Guaranteed error bounds for finite element approximations of noncoercive elliptic problems and their applications

In this paper, we discuss with guaranteed a priori and a posteriori error estimates of finite element approximations for not necessarily coercive linear second order Dirichlet problems. Here, ‘guaranteed’ means we can get the error bounds in which all constants included are explicitly given or represented as a numerically computable form. Using the invertibility condition of concerning elliptic operator, guaranteed a priori and a posteriori error estimates are formulated. This kind of estimates plays essential and important roles in the numerical verification of solutions for nonlinear elliptic problems. Several numerical examples that confirm the actual effectiveness of the method are presented.     

Preparation of 3-bromo-2-methylfuran and 4-bromo-2-methylfuran

4-endo-5-exo-Dibromo-3-methyl-3,6-endo-oxyperhydrophthalic anhydride 3b and 4-exo-5-endo-dibro-mo-3-methyl-3,6-endo-oxyperhydrophtbalic anhydride 3c were isolated from the bromo-adducts of 3-methyl-3,6-endo-oxy-1,2,3,6-tetrahydrophthalic anhydride 2. When 3b or 3c was heated in quinoline, only 3-bromo-2-methylfuran 4 was obtained from 3b and only 4-bromo-2-methylfuran 5 from 3c.     

Single DNA molecule isolation and trapping in a microfluidic device.

This paper presents a systematic method to isolate and trap long single DNA segments between integrated electrodes in a microfluidic environment. Double stranded lambda-DNA molecules are introduced in a microchip and are isolated by electrophoretic force through microfluidic channels. Downstream, each individual molecule is extended and oriented by ac dielectrophoresis (900 kHz, 1 MV m(-1)) and anchored between aluminium electrodes. With a proper design, a long DNA segment (up to 10 microm) can be instantly captured in stretched conformation, opening way for further assays.     

Molecular design of calixarene-based ion-selective electrodes

In order to obtain insights into relationships between the calix[4]arene structure and the ion selectivity in the electrode system, 20 ionophoric calix[4]arenes were synthesized and their ion selectivity (with Na⁺ as a standard) estimated. Among these ionophoric calix[4]arenes, 25,26,27,28-tetrakis[(ethoxycarbonyl)methoxy]-p-t-octylcalix[4]arene afforded the highest logK _NA,M ^pot value (–3.1) in the presence of 2-fluorophenyl-2-nitrophenylether (10) as the best of 13 plasticizers. This is the first example in which the Na⁺/K⁺ selectivity exceeds a factor of 10³ in the electrode system based on the neutral carrier. The high Na⁺ selectivity is attributed to modification of the upper rim which ostensibly has no relation with the component of the cavity. This paper demonstrates the potential relationships between the unique structure of the calix[4]arene-based ligands and selectivity performance for the design of ion-selective electrodes.     

Enhancement of the Coulomb correlations in type-II quantum dots

We report on calculation of binding energies of excitons as well as positively and negatively charged excitons and biexcitons in type-II quantum dots. The shape of the GaSb/GaAs quantum dot is assumed lens-like and the energies are calculated within the Hartree–Fock approximation. A large enhancement of the binding energies has been estimated in comparison with the type-I quantum dots (InAs/GaAs) which is in good agreement with the recent experimental findings.     

High-performance liquid chromatographic detector based on near-infrared semiconductor laser fluorimetry

Three polymethine dyes, which fluoresce at 780–820 nm, are separated by reversed-phase chromatography and detected fluorimetrically with a semiconductor laser for excitation. The detection limit for anhydro-3,3,3′,3′-tetramethyl-1,1′-bis(4-sulfomethyl)-4,5,4′,5′-dibenzoindotricarbocyanine hydroxide (sodium salt) is 0.3 pg, which is almost three orders of magnitude better than the value obtained by conventional fluorimetry.