The beta-fluorine effect. Electronic versus steric effects in radical deoxygenations of fluorine-containing pentofuranose nucleosides

Stereoselective pyramidalization of free radicals by a vicinal fluorine substituent, the beta-fluorine effect, was invoked to rationalize a 77:23 anti/syn ratio of 2-deuterio-1-fluorocyclopentanes obtained by radical reduction of trans-2-fluoro-1-bromocyclopentane with tributyltin deuteride (Dolbier, W. R., Jr.; Bartberger, M. D. J. Org. Chem. 1995, 60, 4984-4985). We have evaluated analogous reductions of the four possible stereoisomers of some adenine 2'(3')-fluoro-3'(2')-O-phenoxythiocarbonyl nucleoside derivatives. In all cases, the steric effect of adenine on the beta face directs deuterium transfer from the stannane to C2'(C3') on the alpha face of the furanose ring. However, the beta-fluorine effect enhances ratios of deuterium transfer anti to the vicinal fluorine substituent.     

Rapid method for evaluating reversed-phase high-performance liquid chromatography column stability

A procedure is presented for the rapid evaluation of HPLC stationary phase stability at pH 8.4 or 10.1 using a temperature of 60 degrees C. Mobile phase (MeOH-0.1 mol l(-1) aqueous NaHCO3, 50:50, v/v) is continuously passed through the column with periodic injections of a test solution until the several chromatographic parameters of the resulting chromatograms are degraded. The tests were applied to several commercial and laboratory-made stationary phases. After degradation two of these phases, one commercial and one laboratory-made, were examined by elemental analysis and scanning electron microscopy to elucidate the degradation process.     

A low complexity pilot aided channel estimation method for WCDMA communication systems

This letter deals with the performance evaluation of a pilot aided method for estimating channel parameters in wideband code division multiple access (WCDMA) communication systems. Unlike previous approaches, a successive interference cancellation algorithm is used to reduce multipath and multiuser interference caused by pilot signal replicas on the channel parameter estimation, and on the detection of the information bearing signals. Comparisons with the ideal case of perfect knowledge of the channel parameters and the classical channel parameter estimation algorithm have highlighted the good performance of the proposed approach.     

Proposal of a Fixed Communication System Sharing the Bandwidth of an Existing Personal Communication Network

This paper deals with the proposal and performance evaluation of a fixed microwave communication (FMC) system that shares the same bandwidth with a wireless personal communication network. In particular, the focus here is on the case of an existing universal mobile telecommunication system (UMTS) network for which an FMC system is considered to provide a wireless connection between a remote base station not having the possibility of a wired connection to the core network and a base station having this possibility (a core network access point). This facility is of special interest in a dense urban environment or whenever a wired connection is prohibitive for service providers due to its implementation cost or lack of frequency spectrum. The mutual interference effects between the FMC systems and the existing UMTSs are investigated by focusing on typical application scenarios. A receiving scheme where interference signals are first detected and then canceled from the other received signals is proposed. The performance of the two interfering systems has been evaluated in terms of bit error rates (BERs) both by means of an analytical approach and computer simulations. The obtained results clearly demonstrate the effectiveness of the proposed method, in particular, by allowing efficient bandwidth sharing between the FMC system and the existing UMTS network.     

Photo-controlled release of zinc metal ions by spiropyran receptors anchored to single-walled carbon nanotubes

Light controllable release of antinflammatory zinc ions by a smart multifunctional material composed of spiropyrans and single walled carbon nanotubes (SWNTs) is demonstrated. The exploitation of a number of complementary characterization techniques allows the investigation of both composition and performance of the multifunctional SP/SWNT nanomaterial developed. Moreover, its suitability for potential applications in bio-systems is suggested by the effective removal of the metal catalyst and the introduction of biocompatible linkers into the SP/SWNT material. The realization of potential photo controllable SP/SWNTs based drug delivery systems (DDSs) is envisaged, where nanotubes act as intracellular carriers of light modulated receptors for bioactive agents.     

Perspectives for present and future CDMA-based communications systems

In this article the main boosters of future CDMA communication systems are presented and described in order to highlight the ways to cope with the more challenging requirements of future systems and services. Particular attention is devoted to the inherent weak points of CDMA systems and detection techniques that can be used to overcome their impairments. Moreover, high-data-rate transmissions in wireless channels require proper link adaptation techniques; these are thoroughly described as well. Finally, the last part of this article focuses on the design of suitable protocol strategies for new heterogeneous multimedia packet services characterized by strict QoS requirements     

Poly(alkylmethylsiloxanes) thermally immobilized on silica as stationary phases for high-performance liquid chromatography

Modifications have been made to the method of ion-exclusion pre-separation followed by ion exchange with conductivity detection for the determination of trace levels of chloride, sulfate and nitrate in concentrated phosphoric acid. Ion-exclusion separation and pre-concentration of impurity anions is performed using Dionex AS6-ICE and AS11-HC (4 mm) columns, respectively, with water eluent. Final separation is performed using Dionex AG11-HC and AS11-HC (2 mm) columns, KOH gradient elution, and suppressed conductivity detection. Improvements to the method include addition of an autosampler and eluent generator, and use of external standard calibration. These instrumental and procedural changes significantly improve the method's throughput, while the method's capability relative to phosphoric acid specifications is maintained, as verified through statistical evaluation of control sample analyses. Detection limits of 60, 680, and 4,0 ppb (w/w) are obtained vs. semiconductor-grade phosphoric acid specifications of 1000, 12,000, and 5000 ppb for chloride, sulfate, and nitrate, respectively.     

Reconfigurable Antenna for Future Wireless Communication Systems

This paper deals with the processing techniques which are known as reconfigurable antennas: these methods are foreseen to be a booster for the future high rate wireless communications, both for the benefits in terms of performance and for the capacity gains. In particular, adaptive digital signal processing can provide improved performance for the desired signal in terms of error probability or signal-to-noise ratio while the bandwidth efficiency can be increased linearly with the number of transmitting and receiving antennas. In this article, the main antenna processing techniques are reviewed and described, aiming at highlighting performance/complexity trade-offs and how they could be implemented in the future systems. The coexistence of all these different technologies in a wireless environment requires high efficiency and flexibility of the transceiver. Future transceiver implementations which are based on the Software Defined Radio technology are also reviewed and described.