Solvent degradation of nylon-6 and its effect on fiber morphology of electrospun mats

In this work, we studied solvent-induced polymer degradation and its effect on the morphology of electrospun fibers. Nylon-6 in formic acid solvent was allowed to degrade by simply allowing it to stand for a long time, and nanofibrous mats were fabricated by taking a fraction of this solution at different time intervals via electrospinning under the same electrospinning conditions. FE-SEM images of the mats indicate that the nanofiber diameter gradually decreased with the standing time of solution, and large numbers of true nano fibers (<50 nm in diameter) were obtained. MALDI-TOF analysis revealed that the formation of low-molecular weight ions was caused by solvent degradation. FT-IR, DSC, XRD, and TGA analyses of electrospun mats showed that some physical properties, such as bond strength, crystallinity, and thermal stability also depended on solvent degradation. The obtained sub-nanofibrous mat has potential applications in different bioengineering fields.     

Steady state and time-resolved fluorescence study of isoquinoline: reinvestigation of excited state proton transfer

In the present work we report some hitherto unnoticed features in the steady state and time-resolved measurements of isoquinoline in water and trifluoroethanol (TFE). Absorption spectra reveal that in water, neutrals as well cationic species are present. Emission spectrum shows structured features at shorter wavelengths accompanied with a broad band around 375 nm, which correspond to neutrals and cations respectively. However, time-resolved data indicate that protonation does not take place in the excited state in water. On the contrary, in stronger hydrogen bonding solvent TFE, distribution of decay components is observed and at longer wavelengths a small rise time is present. This is ascribed to neutral and cation-like species present in the ground as well as in the excited state. The difference in the results is explained in terms of different excited state potential energy surfaces for water and TFE; particularly, the presence of a rather small barrier for protonation in case of TFE.     

Composition and antibacterial activity of essential oil from Scutellaria grossa Wall ex Benth

The chemical composition of the steam volatile oil of the whole aerial part of Scutellaria grossa Wall ex Benth. (Lamiaceae), obtained by steam distillation, has been analysed by capillary GC and GC-MS. The oil was found to be rich in oxygenated monoterpenes (88.6%). A total of 50 constituents were identified, representing 94.4% of the total oil composition. Linalool (37.0%) and 1-octen-3-ol (32.0%) were found to be the principal constituents. The antibacterial activity of the oil was determined against 10 bacterial strains by measuring the growth inhibitory zones. The oil showed significant antibacterial activity against Gram-positive bacteria, Bacillus subtilis and Enterococcus faecalis, and the Gram-negative, Klebsiella pneumoniae and Salmonella enterica enterica. A minimum inhibitory concentration of 31.25?μL mL(-1) was observed against E. faecalis.     

Enhanced optoelectronic properties with aromatic bridges: A computational study on N-methyl pyridinium and phenolate types of push-pull zwitterions

A series of zwitterions with varying bridges, connecting N-methyl pyridinium acceptor, with phenolate donor, are investigated using various methodologies like, HF, B3LYP, CAM-B3LYP and ωB97xD. In this systematic study effects of various mono aromatic rings as bridges, on the response properties like, the dipole moments (μ), polarizabilities (α), hyperpolarizabilities (β) and adiabatic absorptions were analyzed using CPHF and TDDFT (or TDHF) theories. Compared to many traditional bridges, as well as without a bridge, enhanced nonlinear optical (2ND order NLO) responses were observed for these aromatically bridged zwitterions (with benzene ring as bridge ~5.3 times and ~7.9 times enhanced hyperpolarizabilities were observed compared to either the ethylene bridge or without any bridge cases, respectively). Also, many significant differences and large enhancements in response properties were observed compared to our earlier works on non-zwitterionic system (~4.3 times enhanced hyperpolarizability—benzene as bridge case). For some bridge cases, 10- to 15-fold enhanced hyperpolarizabilities were observed compared to without any bridge case. This work reports a class of non-TICT chromophores, promoting bridge aromaticity control on structure–property correlation, as a suitable and efficient chromophore design strategy to create a wide range of function molecular chromophores. Also, unidirectional natures of response properties and large dipole moments can make these zwitterions suitable 1D-molecular materials for various contemporary technological applications, as poled polymer-based materials.     

Photonic-chip-based tunable slow and fast light via stimulated Brillouin scattering

We report the first (to our knowledge) demonstration of photonic chip based tunable slow and fast light via stimulated Brillouin scattering. Slow, fast, and negative group velocities were observed in a 7 cm long chalcogenide (As(2)S(3)) rib waveguide with a group index change ranging from ~-44 to +130, which results in a maximum delay of ~23 ns at a relatively low gain of ~23 dB. Demonstration of large tunable delays in a chip scale device opens up applications such as frequency sensing and true-time delay for a phased array antenna, where integration and delays ~10 ns are highly desirable.     

Simultaneous synthesis of TiO2 microrods in situ decorated with Ag nanoparticles and their bactericidal efficiency

In this study, we report a simple and cost-effective method for in situ decoration of Ag NPs onto nanoporous TiO₂ microrods by one medium (ethylene glycol) that can produce two different morphologies. In order to investigate the morphology, phase composition, crystalline structure, and chemical state (valency) of samples before and after annealing in air at different temperatures, field emission scanning electron microscopy (FESEM), transmission electron microscopy (TEM), X-ray diffraction (XRD) and X-ray photoelectron spectroscopy (XPS) were performed. The present results show that the size, morphology and crystallinity of both Ag NPs and TiO₂ microrod substrate depend on the post-annealing treatment temperatures. The annealed Ag–TiO₂ NP/microrod composites show large inhibition zones against E. coli bacteria. The obtained Ag–TiO₂ composites have the potential for use as a novel antibacterial material and in water treatment applications.     

Modification of the omega-meson lifetime in nuclear matter

Information on hadron properties in the nuclear medium has been derived from the photoproduction of omega mesons on the nuclei C, Ca, Nb, and Pb using the Crystal Barrel/TAPS detector at the ELSA tagged photon facility in Bonn. The dependence of the omega-meson cross section on the nuclear mass number has been compared with three different types of models: a Glauber analysis, a Boltzmann-Uehling-Uhlenbeck analysis of the Giessen theory group, and a calculation by the Valencia theory group. In all three cases, the inelastic omega width is found to be 130-150 MeV/c(2) at normal nuclear matter density for an average 3-momentum of 1.1 GeV/c. In the rest frame of the omega meson, this inelastic omega width corresponds to a reduction of the omega lifetime by a factor approximately 30. For the first time, the momentum dependent omegaN cross section has been extracted from the experiment and is in the range of 70 mb.     

Efficient synthesis of spirooxindole-pyrrolizidines and dispirooxindole-piperazines

A simple and efficient approach for the construction of spirooxindole-pyrrolizidines and dispirooxindole-piperazines by cycloaddition reaction of azomethine ylide generated by isatin and proline has been demonstrated successfully. The formation of two different types of frameworks by two different modes of cycloaddition is explored. The developed protocol highlights simple reaction conditions, easy workup processes, and very good yields of products.     

Internal heavy atom effect on the radiative and non-radiative rate constants in xanthene dyes

Flourescence quantum yield (ø_f), phosphorescence and fluorescence quantum yield ratio (ø_p/ø_f) and the observed triplet decay time (τ_po) of fluorescein and its halogen derivatives have been measured. On halogen substitution an increase in ø_p/ø_f and a decrease in ø_f and τ_po is observed in the sequence of Cl, Br, and I. The increase in ø_p/ø_f is not in the same proportion as the decrease in τ_po. Although ø_p/ø_f is higher for cations than for dianions, it increases more for dianions on halogen substitution. However, the increase in 1/τ_po is about 10³ times more for cations than for dianions. The radiative and non-radiative rate constants viz., k_is, k_p and k_qp have been calculated. On halogen substitution k_f remains almost constant, whereas an increase in k_p, k_is and k_qp is observed. For dianions the increase occurs in the order k_qp> k_is> k_p while for cations the order is k_qp> k_p> k_is. The deuterium solvent effect on triplet decay time and intensity is also observed.