Allosteric effect of the first lead ion on stepwise extraction of the second lead ion with p-t-butylcalix[5]arene pentacarboxylic acid derivative

A calix[5]arene-based solvent extraction reagent displaying very high selectivity for lead has been prepared, one molecule of which extracts two lead ions in a stepwise manner. The first Pb²⁺ ion is bound to five phenoxy oxygen atoms inside the calixarene cavity due to which the ligand undergoes conformational freezing in stable cone conformer. This causes positive allosteric effect for co-extraction of the second lead ion due to the aggregation of functional groups.     

Determination of amoxapine and nortriptyline in blood plasma and serum by salt-assisted liquid-liquid microextraction and high-performance liquid chromatography

A new, selective and sensitive method has been developed for the determination of tricyclic antidepressant drugs, amoxapine and nortriptyline, in human blood plasma and serum, involving their reaction with allyl isothiocyanate and extraction of thiourea derivatives with water-miscible organic solvent acetonitrile. The phase separation was effected by addition of ammonium sulphate, a process called salt-assisted liquid-liquid microextraction. The extract was analyzed by HPLC with UV detection at 254?nm. The method has been optimized for derivatization reaction time and temperature, solvent for extraction, and salt for solvent phase separation. Under the optimal conditions, a linear calibration graph was obtained between the amount of drug and the peak area of thiourea derivatives in the range of 0.002-20?mg/L drugs. The correlation coefficient and limit of detection values for amoxapine and nortriptyline in serum/plasma samples were in the range of 0.9953-0.9999 and 0.46-0.58?μg/L, respectively. The recovery in spiking experiments ranged, respectively, 75-88% (RSD 3.4-7.2%) and 79-97% (RSD 3.7-7.9%) for the two drugs.     

Resolving overlaps in diffusion encoded spectra using band-selective pulses in a 3D BEST-DOSY experiment

A novel diffusion-edited 3D NMR experiment that incorporates a BEST-HMQC pulse sequence in its implementation is presented. Heteronuclear 3D DOSY NMR experiments are useful in elucidating the diffusion coefficients of individual constituents of a mixture, especially in cases where the proton NMR 2D DOSY spectra show considerable overlap. The present 3D BEST-DOSY pulse sequence provides a more sensitive and less time-consuming alternative to standard 3D HMQC-DOSY experiments. Cleanly separated subspectra of individual mixture components are obtained, leading to the determination of diffusion coefficients with better accuracy. The feasibility of the technique is demonstrated on a mixture of amino acids, on a mixture of small molecules with similar diffusion coefficients, and on a complex mixture with large dynamic range (commercial gasoline). The implications of using adiabatic decoupling schemes and band-selective shaped pulses for selective BEST-DOSY experiments on proteins are also discussed.     

Performance of two-hop infrastructure based multi-antenna regenerative relaying in Rayleigh fading channel

Cooperative relaying is considered as an effective technique to enlarge the coverage area and enhance the system capacity for the future wireless systems. In this paper, an infrastructure based multi-antenna cooperative relay network has been investigated. Closed form expressions of outage probability and average error rate have been derived, when the relay and the destination perform selection combining of the signals. The relay is assumed to operate in the adaptive decode and forward mode. The effect of number of antennas installed on the relay and their placement has also been studied.     

Reputation-based network selection mechanism using game theory

Current and future wireless environments are based on the coexistence of multiple networks supported by various access technologies deployed by different operators. As wireless network deployments increase, their usage is also experiencing a significant growth. In this heterogeneous multi-technology multi-application multi-terminal multi-user environment users will be able to freely connect to any of the available access technologies. Network selection mechanisms will be required in order to keep mobile users “always best connected” anywhere and anytime. In such a heterogeneous environment, game theory techniques can be adopted in order to understand and model competitive or cooperative scenarios between rational decision makers. In this work we propose a theoretical framework for combining reputation-based systems, game theory and network selection mechanism. We define a network reputation factor which reflects the network’s previous behaviour in assuring service guarantees to the user. Using the repeated Prisoner’s Dilemma game, we model the user–network interaction as a cooperative game and we show that by defining incentives for cooperation and disincentives against defecting on service guarantees, repeated interaction sustains cooperation.