Biodegradable electrospun mat: Novel block copolymer of poly (p‐dioxanone‐co‐L‐lactide)‐block‐poly(ethylene glycol)

Ultrafine fibers of a laboratory‐synthesized new biodegradable poly(p‐dioxanone‐co‐L ‐lactide)‐block‐poly(ethylene glycol) copolymer were electrospun from solution and collected as a nonwoven mat. The structure and morphology of the electrospun membrane were investigated by scanning electron microscopy, differential scanning calorimetry (DSC), wide‐angle X‐ray diffraction (WAXD), and a mercury porosimeter. Solutions of the copolymer, ranging in the lactide fraction from 60 to 80 mol % in copolymer composition, were readily electrospun at room temperature from solutions up to 20 wt % in methylene chloride. We demonstrate the ability to control the fiber diameter of the copolymer as a function of solution concentration with dimethylformamide as a cosolvent. DSC and WAXD results showed the relatively poor crystallinity of the electrospun copolymer fiber. Electrospun copolymer membrane was applied for the hydrolytic degradation in phosphate buffer solution (pH = 7.5) at 37 °C. Preliminary results of the hydrolytic degradation demonstrated the degradation rate of the electrospun membrane was slower than that of the corresponding copolymers of cast film. © 2003 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 41: 1955–1964, 2003     

Fractal patterns on the onset of coherent structures in a coupled map lattice

We report the formation of Cantor set-like fractals during the development of coherent structures in a coupled map lattice (CML). The dependence of these structures on the size of the lattice as well as the first three dimensions of the associated fractal patterns are analyzed numerically.     

Asymptotic self invariant sets and functional differential equations in Banach spaces

Summary The stability properties of asymptotically self-invariant sets of functional differential equations in a Banach space are discussed using a nonlinear variation of constants formula analogous to Alekseev's formula in Euclidean spaces and Lyapunov functions. Entrata in Redazione il 14 aprile 1972.     

Palladium catalyzed insertion of carbon monoxide into benzyl-tetrahydroisoquinolines : A new synthesis of berbine alkaloids

A new total synthesis of the berbine alkaloid ring system has been achieved. Palladium catalyzed insertion of carbon monoxide into the 1 - (2 - bromobenzyl) - substituted - 1,2,3,4 - tetrahydroisoquinolines (1a–1d) by the use of catalytic amounts of palladium diacetate and triphenylphosphine in the presence of tri-n-butylamine afforded the berbin-8-ones (2a–2d) which, on reduction with lithium aluminium hydride gave the berbines (±)-berbine 3a, (±)2,3-dimethoxyberbine 3b, (±)-xylopinine 3c and (±)-pseudoepitetrahydroberbine 3d.     

GeO2 fibers: preparation, morphology and photoluminescence property

Nanomicron to submicron fibers of GeO(2) have been prepared using poly(vinyl acetate) and germanium dioxide sol by electrospinning followed by high temperature calcination. The morphology of the fibers have been studied by scanning electron microscopy, transmission electron microscopy, and atomic force microscopy. X-ray diffraction indicates that the fibers are single crystal with hexagonal alpha-phase quartz-like structure. At room temperature, the fibers show photoluminescence under excitation at 325 nm. The fibers may have potential applications in one-dimensional optoelectronic nanodevices.     

Large distinct diffusivity in binary mixtures confined to zeolite Nay

Mutual diffusion coefficients have been computed from molecular dynamics simulation of two different binary mixtures confined to zeolite NaY. In one of these mixtures, where one component is from the linear regime and the other from the anomalous regime of the levitation effect [S. Yashonath, P. Santikary, J. Phys. Chem., 1994, 98, 6368], the magnitude of distinct diffusivity, Dd, is unusually large and comparable to the mixture self-diffusivity Ds. Distinct van Hove correlations suggest that the large Dd seems to arise from the presence of distinct physisorption sites for the two components. The contribution from Dd might be important for achieving good separation of mixtures, for which zeolites are used extensively.     

Synthetic approach to seco-tetracenomycin natural products saccharothrixone A–C

Design and development of first synthetic approach to the functionalized tetracyclic framework of structurally novel seco-tetracenomycin natural products saccharothrixones A–C has been reported. A thermal dehydro Diels-Alder reaction of an arenyne-alkyne unit has been utilized as the key synthetic step. This strategy has been extended for the generation of a small library of diversely functionalized tetracyclic systems of seco-tetracenomycins. An approach for the synthesis of poly-hydroxyl tetracyclic system has also been described. This report represents the first synthetic approach to the tetracenomycin natural products saccharothrixones A–C.     

Synthesis and hydrolytic degradation of a random copolymer derived from 1,4‐dioxan‐2‐one and glycolide

Novel biodegradable copolymers, poly(1,4‐dioxan‐2‐one‐co‐glycolide) [P(DON‐co‐GA)] containing a high proportion of 1,4‐dioxan‐2‐one (DON), were synthesized by copolymerizations of DON and glycolide (GA) at 120 °C for 16 h using stannous octoate as catalyst. Chemical composition and microstructural variation of the resulting copolymer were investigated by ¹H‐ and ¹³C NMR and thermal properties by differential scanning calorimetry (DSC). From the ¹³C NMR spectra, it was observed that, apart from the expected preponderance of DON sequences, the minor component, GA, was indeed distributed at various points along the copolymer chain rather than incorporated as distinct blocks, which is consistent with a random sequence distribution. This view also was supported by the DSC results, which showed that most copolymers were amorphous except for one with a relatively high fraction of DON. The conclusion that it was a random structure rather than a statistical copolymer is discussed, using the theories about the mechanism of this type of polymerization in current as a reference. P(DON‐co‐GA) films were prepared by casting the copolymer solution in hexafluoroisopropanol (HFIP) with two concentrations of the polymeric solution (10 and 25 wt %). The in vitro hydrolytic degradation behaviors of these films were studied in phosphate buffer solution (pH = 7.4) at 37 °C and characterized by DSC, scanning electron microscopy, weight loss, and change in inherent viscosity. © 2004 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys 42: 2558–2566, 2004     

Reaction on Water: A Greener Approach for the Thia Michael Addition on N-Aryl Maleimides

A greener, economical, and efficient methodology for the Michael addition of thiols to N-aryl maleimides has been developed.     

Determination of naturally occurring radionuclides in selected rocks from Hetaunda area,central Nepal

The specific activities of the naturally occurring radionuclides ²³⁸U, ²³²Th, and ⁴⁰K were measured in rock samples from the Hetaunda area, central Nepal, using gamma spectrometry. The specific activities were found to be in the range of 17–95 Bq kg⁻¹ for ²³⁸U, 24–260 Bq kg⁻¹ for ²³²Th and 32–541 Bq kg⁻¹ for ⁴⁰K. From these data absorbed dose rates in air and annual effective doses were calculated and compared with respective data from the UNSCEAR compilation. The results from our study open the door to the safe applicability of most of the investigated materials as a cheep building material.