CAD-oriented lossy models for radial stubs

A lumped equivalent circuit model for both series and double-shunt (butterfly) connected radial stub has been developed. The model-simple and effective-not only includes conductor and dielectric losses but also radiation ones, which play an important role in microstrip circuit elements. Experiments widely demonstrate its suitability for implementation in available CAD (computer-aided design) programs. Furthermore, a synthesis procedure for using radial stubs in circuit design is described. An application of the proposed design procedure and simulation tools in the development of very broadband nongrounded termination is also presented     

Dual CD system-modified MEEKC method for the determination of clemastine and its impurities

A dual system of CDs was used for the first time in MEEKC with the aim of determining clemastine and its three main related impurities in both drug substances and tablets. The addition of methyl-β-cyclodextrin and heptakis(2,6-di-O-methyl)-β-cyclodextrin to the microemulsion pseudo-stationary phase was essential to increase the resolving power of the system to obtain a baseline separation among the compounds. The best microemulsion composition was identified by mixture design and the effects of the factors concentrations of CDs and voltage were investigated by a response surface study applying a Central Composite Design. In both cases, Derringer's desirability function made it possible to find the global optimum, which corresponded to the following combination: microemulsion, 89.8% 10 mM borate buffer pH 9.2, 1.5% n-heptane and 8.7% of SDS/n-butanol in 1:2 ratio; 18 mM methyl-β-cyclodextrin, 38 mM heptakis(2,6-di-O-methyl)-β-cyclodextrin, 17 kV. By applying these conditions, the separation was completed in about 5.5 min. The method was validated following International Conference on Harmonisation guidelines and was applied to a real sample of clemastine tablets.     

Biosensors for effective environmental and agrifood protection and commercialization: from research to market

Biosensors are projected to find many applications due to their high selectivity and sensitivity, rapid reaction, economy and ease of handling in field measurements. Even though biosensors for a wide range of environmental pollutants have been extensively reported in the literature, the decision to develop a suitable biosensing system that can be approved by a regulatory perspective for environmental applications is fraught with technical issues. These issues mainly concern the biological recognition element, the physico-chemical transducer and the interfaces between the biological and the physical components, but also aspects of fluidics, electronics, and software for data processing. This article reviews methods together with a process to move biosensor technology from research laboratories to market, focusing as a case in point on challenges and possible opportunities in the development of photosynthetic-based biosensors for environmental applications.     

Flexible Baseband Analog Circuits for Software-Defined Radio Front-Ends

This paper presents a novel approach to design a digitally programmable low pass filter (LPF) and variable gain amplifier (VGA) intended for a software-defined radio (SDR) front-end. These flexible analog circuits are driven by a network-on-chip (NoC) that is able to set performance parameters like cut-off frequency, selectivity, noise, and gain guaranteeing at any time a near-optimal power/performance trade-off. A design approach is proposed to tackle the challenges imposed by flexibility in analog design. A silicon prototype is realized in 0.13-mum CMOS technology with 1.2-V supply voltage to prove the validity of the proposed solution. The LPF provides a frequency tuning range between 0.35 MHz and 23.5 MHz with an adaptive integrated noise level between 85 muVrms and 163 muVrms whereby the power consumption conveniently varies from 0.72 mW to 21.6 mW according to the required performance. The VGA is made up of two cascaded gain stages and provides a gain range from about 0 dB to 39 dB with a reconfigurable power/bandwidth.     

Toggling enantioselective catalysis--a promising paradigm in the development of more efficient and versatile enantioselective synthetic methodologies

The increasingly needed synthesis of both enantiomers of a chiral compound usually requires the use of both enantiomers of a chiral catalyst. Several of the usually employed chiral ligands are naturally available in only one enantiomeric form, the antipode often being of labor-intensive preparation. Enantiodivergent asymmetric catalysis has accrued in importance in this regard, in that it allows expeditious access to both enantiomers of a product without any direct modification on the chemical structure of the chiral promoter. Various promising examples will be discussed throughout the review. If available or envisageable, a mechanistic rationale for the observed enantioinversion will be outlined.     

Opioid peptides: synthesis and biological properties of [(N gamma-glucosyl,N gamma-methoxy)-alpha, gamma-diamino-(S)-butanoyl]4-deltorphin-1-neoglycopeptide and related analogues

The [D-Ala2]deltorphin 1 sequence in which the aspartic acid residue is replaced by the N gamma-OCH3-alpha, gamma-diamino (S) butanoyl residue was synthesized using the Fmoc-chemistry-based solid phase procedure. The resulting deltorphin analogue was chemoselectively glucosylated by reaction with unprotected D-glucose (Glc). The Asn4-, (2-acetamido-3,4,6-tri-O-acetyl-2-deoxy-beta-D-galactopyranosyl)-Asn4- and the (2-acetamido-2-deoxy-D-galactopyranosyl)-Asn4-deltorphin I were also prepared for comparison. The affinity of the new compounds for the delta-opioid receptor was expressed by the inhibition constant (Ki) of the binding of the delta-receptor selective ligand [3H]naltrindole (NTI) to rat brain membrane preparations. The in vitro biological activity of the synthetic peptides was compared with that of the mu-opioid receptor agonist dermorphin in guinea pig ileum (GPI) preparations and with that of the delta-opioid receptor agonist deltorphin I in mouse vas deferens (MVD) preparations. The substitution of Asp4 with Asn failed to affect drastically the Ki and IC50 values for delta-sites, suggesting that an electrostatic interaction does not play an essential role in the binding to delta-opioid sites. The steric hindrance of the side chain of the residue in position 4 affects binding to delta-sites. The increase of the Ki value is smaller when the sugar-peptide linkage involves the gamma-nitrogen of the Dab residue in comparison with the Asn amide side chain.