Synthesis of novel benzopyrano[3,2-c]coumarins via tandem base promoted nucleophilic substitution and intramolecular electrophilic aromatic cyclization

Efficient and facile synthesis of 7H-benzopyrano[3,2-c]coumarins has been achieved by mild base promoted reaction of 4-chloro-3-formylcoumarin with diversely functionalized resorcinols. All the products were obtained as pure precipitates from the reaction mixture and the structure of the product was confirmed by X-ray analysis.     

Studies on organogelation of self assembling bis urea type low molecular weight molecules

A novel class of toluene based bis urea compounds carrying linear fatty acid units and semicarbazide linkages has been synthesised. The compounds were exhibiting thermoreversible gelation at concentrations below 10 mg/mL in common organic solvents, both aliphatic and aromatic. The effect of the chain length variation of fatty acid units on gelation properties like gelation concentration, gelation time and gel melting temperatures were studied. Choosing a particular gelator of fixed chain length and a specific solvent, the effect of the concentration on the gelation properties were studied. The thermal studies using DSC revealed the presence of phase transitions corresponding to the premelting and melting of the gels during the heating cycle. The morphology of the xerogels studied using SEM revealed a three dimensional network structure while the WAXS studies showed no crystallinity in the xerogels. IR spectra of the gels (solvent subtracted) and solutions in the corresponding solvent showed that a high degree of inter-molecular H bonding exists and absorptions corresponding to NH stretching shifted to lower wave numbers. Thus simple bisurea type of compounds exhibiting gelation ability in a wide range of solvents can be used for making functional gels for various applications.     

A compact four‐element MIMO antenna for WLAN/WiMAX/satellite applications

This paper presents a four‐element wideband monopole MIMO antenna. Initially, a single‐element wideband CPW‐fed antenna is designed operating in the range of 4.30 to 6.45 GHz. Using this design, an approach towards MIMO structure is studied. A two‐element structure is designed keeping them adjacent to each other, and the isolation between the antennas is observed. After which, a four‐element structure is designed having the best orientation in order to achieve good isolation between the antenna elements. The proposed antenna configuration has four identical CPW‐fed elements. The proposed configuration has a fractional bandwidth of 40.27% and has a simulated peak gain of 5.5 dBi. This antenna is intended to be used for WLAN, WiMAX, and satellite bands of range corresponding to 4.70–6.19, 5.5–5.7, and 5–6 GHz. All the necessary antenna simulations are simulated using Ansys HFSS and verified on NI AWR Design Environment. The fabricated model of the proposed design is measured for its performance parameters and validated.     

Preparation of vinylglycines by thermolysis of homocysteine sulfoxides

The synthesis and efficacy of preparing Cbz-VG-OMe (1) by thermolysis of alkyl and aryl homocysteine sulfoxides were surveyed. This investigation determined that aryl sulfoxide analogs were more effective for the reaction and that the 2-nitrophenyl analog 10f possessed a unique ability to syn eliminate at temperatures as low as 100 °C. The thermolysis of sulfoxide 10f was additionally discovered to occur under toluene reflux and when sodium acetate was added, Cbz-VG-OMe (1) could be obtained in high purity by simple filtration of the precipitated sulfenic acid byproduct 12. This mild protocol which was also applied in the synthesis of VG dipeptide 13 would have utility in the general synthesis of olefins and alkenes from 2-nitrophenylsulfoxides.     

An optimization technique for simultaneous reduction of PAPR and out-of-band power in NC-OFDM-based cognitive radio systems

Noncontiguous orthogonal frequency division multiplexing (NC-OFDM)-based cognitive radio (CR) systems achieve highly efficient spectrum utilization by transmitting unlicensed users' data on subcarriers of licensed users’ data when they are free. However, there are two disadvantages to the NC-OFDM system: out-of-band power (OBP) and a high peak-to-average power ratio (PAPR). OBP arises due to side lobes of an NC-OFDM signal in the frequency domain, and it interferes with the spectrum for unlicensed users. A high PAPR occurs due to the inverse fast Fourier transform (IFFT) block used in an NC-OFDM system, and it induces nonlinear effects in power amplifiers. In this study, we propose an algorithm called “Alternative Projections onto Convex and Non-Convex Sets” that reduces the OBP and PAPR simultaneously. The alternate projections are performed onto these sets to form an iteration, and it converges to the specified limits of in-band-power, peak amplitude, and OBP. Furthermore, simulations show that the bit error rate performance is not degraded while reducing OBP and PAPR.     

Mxene-Based Supramolecular Composite Hydrogels for Antioxidant and Photothermal Antibacterial Activities

Bacterial infections and oxidative damage caused by various reactive oxygen species (ROS) pose a significant threat to human health. It is highly desirable to find an ideal biomaterial system with broad spectrum antibacterial and antioxidant capabilities. A new supramolecular antibacterial and antioxidant composite hydrogel made of chiral L-phenylalanine-derivative (LPFEG) as matrix and Mxene (Ti₃C₂T_x) as filler material is presented. The noncovalent interactions (H-bonding and π–π interactions) in between LPFEG and Mxene and the inversion of LPFEG chirality are verified by Fourier transform infrared and circular dichroism spectroscopy. The composite hydrogels show improved mechanical properties revealed by rheological analysis. The composite hydrogel system exhibits photothermal conversion efficiency (40.79%), which enables effective photothermal broad-spectrum antibacterial activities against both Gram-positive (Staphylococcus aureus) and Gram-negative (Escherichia coli, Pseudomonas aeruginosa) bacteria. Furthermore, the Mxene also enables the composite hydrogel to exhibit excellent antioxidant activity by efficiently scavenging free radicals like DPPH•, ABTS•+, and •OH. These results indicate that the Mxene-based chiral supramolecular composite hydrogel, with improved rheological, antibacterial, and antioxidant properties has a great potential for biomedical applications.     

Apical functionalization of chiral heterohelicenes

We describe a synthetic protocol to selectively functionalize chiral bridged triarylamines at the apical position using regioselective copper-catalyzed amination reaction. This protocol allows the coupling of diphenylamines with a sterically hindered but electronically activated aryl-Br bond in the presence of a sterically unhindered but electronically unactivated aryl-Br bond. The unactivated aryl-Br bond was utilized further to synthesize a chiral heterohelicene homodimer using Stille coupling.     

"Silver effect" in gold(I) catalysis: an overlooked important factor

Clear experimental evidence from X-ray photoelectron spectroscopy and (31)P NMR spectroscopy has been obtained for the first time to confirm that the combination of Ag(+) cation with [L-Au](+) results in the formation of different complexes in solution. Re-evaluation of literature-reported gold-catalyzed reactions revealed a significant difference in the reactivities with and without silver. In extreme cases (more than "rare"), the conventional [L-Au](+) catalysts could not promote the reaction without the presence of silver. This investigation has therefore revealed a long-overlooked "silver effect" in gold catalysis and should lead to revision of the actual mechanism.     

LC‐MS/MS determination of cinacalcet enantiomers in rat plasma on Chirobiotic V column in polar ionic mode: application to a pharmacokinetic study

A simple and selective polar ionic liquid chromatography–tandem mass spectrometric method for separation and determination of cinacalcet enantiomers in rat plasma was developed and validated. The chromatographic separation was accomplished on a Chirobiotic V column packed with vancomycin as a chiral stationary phase using 2.5 mm ammonium formate in 100% methanol as a mobile phase in an isocratic mode of elution at a flow rate of 1.0 mL/min. The analytes were extracted from rat plasma by precipitating the proteins with acetonitrile. The developed method exhibited a linear dynamic range over 0.5–500 ng/mL in rat plasma for both enantiomers. The method was successfully applied to study the pharmacokinetics after a single dose by oral administration of 10 mg/kg of cinacalcet enantiomers to healthy male Wistar rats. Copyright © 2014 John Wiley & Sons, Ltd.