Investigation of the mechanism of living cationic polymerization of isobutylene by B11 NMR spectroscopy

Summary The living carbocationic polymerization of isobutylene initiated by tri-cumyl-ether (1)/BCl₃ and tricumyl-acetate(2)/BCl₃ was investigated by B¹¹ NMR spectroscopy in the presence and absence of DMSO. With BCl₃, 1 yields tri-cumyl-chloride and BCl₂OMe due to fast exchange reaction, while 2 forms complexes. If the 1/BCl₃ mixture contains DMSO, well defined complexes can be detected, i.e., DMSO.BCl₃ and BCl₂OMe.DMSO. In the system 2/BCl₃/DMSO neutral complexes with broad NMR signals are formed. In the presence of isobutylene (real polymerization mixture) the same complexes can be detected.     

Natural Taxanes: From Plant Composition to Human Pharmacology and Toxicity

Biologically active taxanes, present in small- to medium-sized evergreen conifers of various Taxus species, are widely used for their antioxidant, antimicrobial and anti-inflammatory effects, but mostly for their antitumour effects used in the treatment of solid tumours of the breast, ovary, lung, bladder, prostate, oesophagus and melanoma. More of the substances found in Taxus plant extracts have medical potential. Therefore, at the beginning of this review, we describe the methods of isolation, identification and determination of taxanes in different plant parts. One of the most important taxanes is paclitaxel, for which we summarize the pharmacokinetic parameters of its different formulations. We also describe toxicological risks during clinical therapy such as hypersensitivity, neurotoxicity, gastrointestinal, cardiovascular, haematological, skin and renal toxicity and toxicity to the respiratory system. Since the effect of the drug-form PTX is enhanced by various Taxus spp. extracts, we summarize published clinical intoxications and all fatal poisonings for the Taxus baccata plant. This showed that, despite their significant use in anticancer treatment, attention should also be focused on the risk of fatal intoxication due to ingestion of extracts from these plants, which are commonly found in our surroundings.     

Layer by layer deposition of hydroxyapatite onto the collagen matrix

Layer by layer (LbL) deposition is a useful method for deposition of many inorganic (including metals, oxides and phosphates) and organic (including polymers and proteins) components on a large range of substrates. The LbL deposition of hydroxyapatite (HA) onto a collagen matrix involves HA synthesis on the collagen matrix starting from electrically charged precursors such as Ca²⁺ and PO₄³⁻ at a proper pH to precipitate the desired calcium phosphate.The LbL deposition process was continuously monitored in order to study the amount of HA deposited in each layer. The deposition of the first layers of HA was concluded to be highly influenced by the collagen matrix. When the collagen matrix is crosslinked with glutaraldehyde, the matrix structure is not modified during the deposition, and the porosity will decrease with the number of layers until saturation is reached. Following pore saturation, HA will be only deposited onto the mineralized collagen matrix surface. The obtained composite materials were characterized by XRD, SEM, DTA-TG and FTIR.     

Avoidance of multicast incapable branching nodes for multicast routing in WDM networks

In this article we study the multicast routing problem in all-optical WDM networks under the spare light splitting constraint. To implement a multicast session, several light-trees may have to be used due to the limited fanouts of network nodes. Although many multicast routing algorithms have been proposed in order to reduce the total number of wavelength channels used (total cost) for a multicast session, the maximum number of wavelengths required in one fiber link (link stress) and the end-to-end delay are two parameters which are not always taken into consideration. It is known that the shortest path tree (SPT) results in the optimal end-to-end delay, but it can not be employed directly for multicast routing in sparse light splitting WDM networks. Hence, we propose a novel wavelength routing algorithm which tries to avoid the multicast incapable branching nodes (MIBs, branching nodes without splitting capability) in the shortest-path-based multicast tree to diminish the link stress. Good parts of the shortest-path-tree are retained by the algorithm to reduce the end-to-end delay. The algorithm consists of tree steps: (1) a DijkstraPro algorithm with priority assignment and node adoption is introduced to produce a SPT with up to 38% fewer MIB nodes in the NSF topology and 46% fewer MIB nodes in the USA Longhaul topology, (2) critical articulation and deepest branch heuristics are used to process the MIB nodes, (3) a distance-based light-tree reconnection algorithm is proposed to create the multicast light-trees. Extensive simulations demonstrate the algorithm’s efficiency in terms of link stress and end-to-end delay.     

Combined Effect of Nitrogen‐ and Oxygen‐Containing Functional Groups of Microporous Activated Carbon on its Electrochemical Performance in Supercapacitors

Microporous activated carbon originating from coconut shell, as received or oxidized with nitric acid, is treated with melamine and urea and heated to 950 °C in an inert atmosphere to modify the carbon surface with nitrogen‐ and oxygen‐containing groups for a systematic investigation of their combined effect on electrochemical performance in 1 M H₂SO₄ supercapacitors. The chemistry of the samples is characterized using elemental analysis, Boehm titration, potentiometric titration, and X‐ray photoelectron spectroscopy. Sorption of nitrogen and carbon dioxide is used to determine the textural properties. The results show that the surface chemistry is affected by the type of nitrogen precursor and the specific groups present on the surface before the treatment leading to the incorporation of nitrogen. Analysis of the electrochemical behavior of urea‐ and melamine‐treated samples reveal pseudocapacitance from both the oxygen and the nitrogen containing functional groups located in the pores larger than 10 Å. On the other hand, pores between 5 Å and 6 Å are most effective in a double‐layer formation, which correlates well with the size of hydrated ions. Although the quaternary and pyridinic‐N‐oxides nitrogen groups have enhancing effects on capacitance due to the positive charge, and thus an improved electron transfer at high current loads, the most important functional groups affecting energy storage performance are pyrrolic and pyridinic nitrogen along with quinone oxygen.     

Effect of silver-nanoparticles generated in poly(vinyl alcohol)membranes on ethanol dehydration via pervaporation

Pervaporation is an important membrane separation method of chemical engineering. In this work,silver-nanoparticles-poly(vinyl alcohol) nanocomposite membranes(AgNPs-PVA) are produced for the sake of improving its potentials for pervaporation of ethanol–water mixture so that the usual opposite trend between membrane selectivity and permeation can be reduced. The nanocomposite membranes are fabricated from an aqueous solution of poly(vinyl alcohol) with silver nanoparticles via the in-situ generation technique in the absence of any reducing agent. Successful generation of the nano size silver is measured by the UV–vis spectrum showing a single peak at 419 nm due to the plasmonic effect of silver nanoparticles. Our nanocomposite AgNPs-PVA membranes are characterized using scanning electron microscope(SEM), Fourier-transform infrared(FT-IR) spectroscopy, X-ray diffraction and thermogravimetric analysis(TGA). The pervaporation tests of our new AgNPs-PVA membranes show good results since at a higher temperature and higher ethanol concentration in the feed, the prepared membranes are highly permeable for the water having stable selectivity values and therefore our membranes show better performance compared to that of the other PVA-based nanocomposite membranes.     

A Partially-Blocking Queueing System with CBR/VBR and ABR/UBR Arrival Streams

In this paper we consider an ATM transmission link, to which CBR or VBR and ABR or UBR calls arrive according to independent Poisson processes. CBR/VBR calls (characterized by their equivalent bandwidth) are blocked and leave the system if the available link capacity is less than required at the time of arrival. ABR/UBR calls, however, accept partial blocking, meaning that they may enter service even if the available capacity is less than the specified required peak bandwidth, but greater than the so called minimal accepted bandwidth. Partially blocked ABR/UBR calls instead experience longer service time, since smaller given bandwidth entails proportionally longer time spent in the system, as first suggested in [3] and analyzed in details herein. Throughout the life time of an ABR/UBR connection, its bandwidth consumption fluctuates in accordance with the current load on the link but always at the highest possible value up to their peak bandwidth (greedy sources). Additionally, if this minimal accepted bandwidth is unavailable at the time of arrival, ABR/UBR calls are allowed to wait in a finite queue. This system is modeled by a Continuous Time Markov Chain (CTMC) and the CBR/VBR and ABR/UBR blocking probabilities and the mean ABR/UBR waiting- and service times are derived.     

Optical detection in microscopic domains. 3. Confocal analysis of fluorescent amphiphilic molecules

This series of papers demonstrates the feasibility of novel optical methodologies for microchemistry and analysis in aqueous samples of nano-, pico-, and femtoliter in volume. Not a conventional glass cuvette, but water-immiscible organic liquid, is used as the container for microscopic sample droplets in this approach. In part 1, absorption spectra of excellent quality were obtained and used for analysis from samples as small as a few tens of a micrometer in diameter. In part 2, an inert fluorescence marker as an internal standard was employed for indirectly detecting absorbing but nonfluorescent reagents in microsamples, employing inner filter effects. In this part 3, a third modality, confocal fluorescence microscopy, is added to the techniques being examined. A clearly visible emission ring emanating from an amphiphilic molecule, doxorubicin, at the sample boundary is demonstrated for the first time in "optically sliced" microdroplets. Relative intensity of this ring with respect to sample bulk can be used to study adsorption phenomena at liquid-liquid interfaces with proper calibrations for bulk and boundary. Quantitative separation of these two domains, a precondition to such calibrations, is also discussed.