Switchable Cucurbituril–Bipyridine Beacons

4‐Aminobipyridine derivatives form strong inclusion complexes with cucurbit[6]uril, exhibiting remarkably large enhancements in fluorescence intensity and quantum yields. The remarkable complexation‐induced pK_a shift (ΔpK_a=3.3) highlights the strong charge–dipole interaction upon binding. The reversible binding phenomenon can be used for the design of switchable beacons that can be incorporated into cascades of binding networks. This concept is demonstrated herein by three different applications: 1) a switchable fluorescent beacon for chemical sensing of transition metals and other ligands; 2) direct measurement of binding constants between cucurbit[6]uril and various nonfluorescent guest molecules; and 3) quantitative monitoring of biocatalytic reactions and determination of their kinetic parameters. The latter application is illustrated by the hydrolysis of an amide catalyzed by penicillin G acylase and by the elimination reaction of a β‐cabamoyloxy ketone catalyzed by aldolase antibody 38C2.     

Experimental lifetime of some level belonging to the 5p46d configuration of XeII

Lifetimes of eight levels belonging to the 5p⁴6d configuration of singly ionized xenon have been measured by high frequency deflection technique with a delayed coincidence single photon counting arrangement. The results have been compared with other experimental and theoretical values. The lifetimes of the 6d ²F_3/2 and 6d ⁴F_3/2 levels have been measured for the first time.     

K2PdCl4 catalyzed efficient multicomponent synthesis of α-aminonitriles in aqueous media

An efficient, mild and environmentally friendly method has been developed for the Strecker reaction to synthesize α-aminonitriles in the presence of K₂PdCl₄ as a catalyst. The three-component one-pot condensation of an aldehyde, amine and trimethylsilyl cyanide proceeded smoothly in water to afford the corresponding product in high yield with short reaction times.     

Surface plasmon resonance in nano-gold antimony glass–ceramic dichroic nanocomposites: One-step synthesis and enhanced fluorescence application

A single-step melt-quench in situ thermochemical reduction technique has been used to synthesize a new series of Au° nanoparticles embedded antimony glass–ceramic (K₂O–B₂O₃–Sb₂O₃–ZnO) dichroic nanocomposites. X-ray and selected area electron diffractions manifest growth of Au° nanoparticles along (2 0 0) planes. The particle sizes obtained from X-ray diffraction patterns are found to vary in the range 4–21 nm. Dichroic behavior is attributed to the elliptical shape gold nanoparticles having aspect ratio 1.2, as observed from the transmission electron microscopy (TEM) images. The Au° nanoparticles exhibit surface plasmon resonance band (SPR) around 600 nm, which experiences red-shifts with increasing Au concentration. These nanocomposites when co-doped with Sm₂O₃ and excited at 949 nm, exhibit 2-fold intensification of 636 nm red emission transition (⁴G_5/2 → ⁶H_9/2) due to SPR induced local field enhancement of Au° nanoparticles and are promising materials for display applications.     

Homo and heteronuclear complexes of dioxime ligands

The mononuclear fragments [Cu(HDopn)(OH)2]+ and [Cu(HPopn)(OH)2]+, [H2Dopn=3,3-(trimethylene- dinitrilo)-dibutan-2–one dioximate and H2Popn, = 3, 3-(phenylenedinitrilo)-dibutan-2–one dioximate] were used to prepare four binuclear complexes [(OH2)Cu (Dopn)Cu(ditn)]2+, [(OH2)Cu(Dopn)Ni(ditn)(H2O)]2+ (ditn=diethylenetriamine) and [(OH2)Cu(Popn)Cu(L) (H2O)]2+ (L=2,2-bipyridine or 1,10–phenanthroline). Two trinuclear complexes, [{Cu(Popn)(OH2)}2M (H2O)n]2+ (when M=CuII, n=1; M=ZnII, n= 2), have been synthesised and characterised by elemental analyses, f.a.b. mass, i.r., electronic, e.s.r. spectroscopy and variable temperature (5–300K) magnetic susceptibility measurements. A strong antiferromagnetic interaction (J=–545cm–1 to –700cm–1) has been found for the binuclear copper(II) complexes. The X-band e.s.r. spectra of these complexes at 300K and for trinuclear complexes at 120K indicate square-pyramidal geometry for the copper centres with a (dx2–y2)1 ground state. The binuclear complex of copper(II)–nickel(II) centres with antiferromagnetic interaction (J=–107 cm–1) is described, and moderately strong zero-field splitting within the quartet state leads to Kramers doublet, as indicated by X-band e.s.r. spectra of this complex. The trinuclear copper(II) complex with an antiferromagnetic interaction (J= –350cm–1) is also described. The heterometallic trinuclear copper(II)–zinc(II)–copper(II) system shows a very weak interaction (J–1cm–1).     

High-gain W-band-printed antenna on flexible substrate

This article demonstrates a novel type of series-fed planar antenna array for a W-band (70 GHz) application. The proposed architecture is a 5-element antenna array with 10 numbers of gap-coupled parasitic patches in microstrip configuration over a thin, flexible and bio-compatible substrate named LCP (liquid crystal polymer). A detailed design methodology with all fabrication constraints has been elaborated on here. Full wave analysis of the whole structure has been carried out in the FEM-based 3D electromagnetic (EM) solver ANSYS HFSS Suite V.19.2. Parametric simulations were studied to achieve the optimized values of all design parameters. Further, an empirical electrical equivalent circuit model is proposed for the antenna array, and it was validated with the simulation results obtained from the FEM solver. Two prototypes have been fabricated, and measurements were carried out to fetch all the designed antenna parameters. The proto version of the antenna offers peak directive gain of about 19 dBi with better than 22 dB of return loss and 80% radiation efficiency for the frequency range of 67–85 GHz. Experimental and simulated results closely match each other. Small deviations are attributed to practical imperfections incurred by fabrication tolerances, measurement inaccuracies, testing, assembly-related issues and so forth. Finally, the current research work is compared with the recently reported literature.     

Concise syntheses of (+)- and (−)-methylenolactocins and phaseolinic acids

(+)- and (−)-Methylenolactocins and phaseolinic acids are synthesized in four steps via asymmetric syn- and anti-aldol reactions of chiral N-succinyl-2-oxazolidinones using the same set of reagents.     

Radiative lifetimes of some excited states of neutral xenon

The radiative lifetimes of ten levels belonging to the nf (n=4-7) and three levels belonging to the ns (n=8,9) configuration of XeI have been measured using the high frequency deflection technique together with a delayed coincidence single-photon counting arrangement. Lifetimes of some of the levels have been measured for the first time. The results have been compared with other experimental and theoretical values.     

Experimental lifetimes of some levels of KrI

Lifetime of nine levels belonging to the and configuration of neutral krypton have been measured by high-frequency deflection technique with a delayed coincidence single photon counting arrangement. The results have been compared with other experimental and theoretical values. The lifetimes of the 9s[3/2]₁ and 7p[1/2]₀ levels have been measured for the first time.     

Precise toppling balance, quenched disorder, and universality for sandpiles

A single sandpile model with quenched random toppling matrices captures the crucial features of different models of self-organized criticality. With symmetric matrices avalanche statistics falls in the multiscaling Bak-Tang-Wiesenfeld universality class. In the asymmetric case the simple scaling of the Manna model is observed. The presence or absence of a precise toppling balance between the amount of sand released by a toppling site and the total quantity the same site receives when all its neighbors topple once determines the appropriate universality class.