Uptake of some lanthanides on γ-zirconium phosphate-phosphite and its 1,10-phenanthroline and 2,2-bipyridyl intercalated products

γ-Zirconium phosphate-phosphite, γ-Zr·PO₄·H₂PO₃·2H₂O, (γ-ZrPP), was prepared and characterized. Direct treatment of γ-zirconium phosphate-phosphite with an ethanol solution of 0.1M 1,10-phenanthrolin and 2,2'-bipyridyl gave the well defined composites, γ-Zr·PO₄·H₂PO₃(phen)_0.15·H₂O and γ-Zr·PO₄·H₂PO₃(bipy)_0.18·0.6H₂O respectively.K _d values of a mixture of lanthanide ions: La³⁺, Sm³⁺, Eu³⁺ and Yb³⁺ for the intercalated products and for γ-ZrPP in HNO₃ solution at room temperature and at pH 2 and 4 were determined by a radiotracer technique.¹⁴⁰La,^152mEu,¹⁵³Sm and¹⁷⁵Yb radioisotopes were used for the equilibration experiment using 500 μl (4.0·10⁻⁵ mmole) each of the solutions of the tracers as a mixture in 7.5 M HNO₃ solution at the desired pH with 0.1 g of γ-ZrPP and of the intercalated products. The selectivity order was found to be dependent on the nature of the ligand and on the pH. The 2,2'-bipyridyl product posseses, at pH 2 in general, a highK _d value, specially for Sm³⁺ (9815.9) compared to that of the 1,10-phenanthrolin product (3375.5) and to γ-ZrPP (419.8). This could be attributed to partial deintercalation of the 2,2'-bipyridyl at pH 2 and increasing of ionogenic groups.     

Integrated enhancement- and depletion-mode FET's inmodulation-doped Si/SiGe heterostructures

We present results of enhancement and depletion mode transistors fabricated on the same layer structure of Si/SiGe, without using gate recess. The current in the enhancement mode device is controlled by a p-n junction, while that of the depletion-mode device is controlled by a Schottky barrier. A peak transconductance of 327 mS/mm and 417 mS/mm has been achieved in 0.5-μm gate length depletion and enhancement-mode transistors, respectively     

Fabrication and characterization of an InAlAs/InGaAs/InP ringoscillator using integrated enhancement- and depletion-modehigh-electron mobility transistors

The fabrication and characterization of an 11-stage ring oscillator utilizing integrated enhancement- and depletion-mode (E/D-mode) high-electron mobility transistors (HEMT's) in the lattice-matched InAlAs/InGaAs/InGaAs material system is demonstrated. The 0.5-μm gate length depletion-mode HEMT's (D-HEMT's) used in the circuit exhibit a threshold voltage (V_T) of -365 mV with a standard deviation of 19 mV, while the enhancement-mode HEMT's (E-HEMT's) with identical gate length display a V_T of 195 mV with a standard deviation of only 9 mV. The unity current gain cutoff frequency (f_t) for both devices is 70 GHz. The extremely high uniformity of the threshold voltages of these devices allowed for the implementation of a ring oscillator utilizing direct coupled FET logic (DCFL). At a supply voltage of 0.4 V, a room temperature propagation delay time (τ_pd) of 22.4 ps/stage, and a corresponding power dissipation of 120 μW/stage is measured, yielding a power delay product (PDP) of 2.65 fJ/stage. To the best of the authors knowledge, this is the first demonstration of a circuit employing E/D-HEMT technology in the lattice-matched InP-based material system     

0.3-μm gate-length enhancement mode InAlAs/InGaAs/InPhigh-electron mobility transistor

The fabrication and performance of ultra-high-speed 0.3-μm gate-length enhancement-mode high-electron-mobility transistors (E-HEMT's) are reported. By using a buried platinum-gate technology and incorporating an etch-stop layer in the heterostructure design, submicron E-HEMT devices exhibiting both high-threshold voltages and excellent threshold voltage uniformity have been achieved. The devices demonstrate a threshold voltage of +171 mV with a standard deviation of only 9 mV. In addition, a maximum DC extrinsic transconductance of 697 mS/mm is measured at room temperature. The output conductance is 22 mS/mm, which results in a maximum voltage gain (g_m/g₀ ) of 32. The devices show excellent RF performance, with a unity current-gain cutoff frequency (f_t) of 116 GHz and a maximum frequency of oscillation (f_max) of 229 GHz. To the best of the authors' knowledge, these are the highest reported frequencies for lattice-matched E-HEMT's on InP     

Studies on cobalt(II)azide complexes in different solvents

Complexation of cobalt(II) ion with azide ion is investigated, by spectroscopic methods, when water and absolute methanol are the solvents. In water the octahedral monoazidopentaaquocobalt(II) ion was obtained, whereas in alcohol the tetrahedral tetraazidocobalt(II) was obtained. Stability constants were computed for both complexes at different temperatures. An estimate of the standard enthalpy as well as the standard entropy of complexation was obtained.     

Induced fit conformational changes of a "reversed amidine" heterocycle: optimized interactions in a DNA minor groove complex

To better understand the molecular basis for recognition of the DNA minor groove by heterocyclic cations, a series of "reversed amidine" substituted heterocycles has been prepared. Amidine derivatives for targeting the minor groove have the amidine carbon linked to a central heterocyclic system, whereas in the reverse orientation, an amidine nitrogen provides the link. The reverse system has a larger dihedral angle as well as a modified spatial relationship with the groove relative to amidines. Because of the large dihedral, the reversed amidines should have reduced binding to DNA relative to similar amidines. Such a reduction is observed in footprinting, circular dichroism (CD), biosensor-surface plasmon resonance (SPR), and isothermal titration calorimetric (ITC) experiments with DB613, which has a central phenyl-furan-phenyl heterocyclic system. The reduction is not seen when a pyrrole (DB884) is substituted for the furan. Analysis of a number of derivatives defines the pyrrole and a terminal phenyl substituent on the reversed amidine groups as critical components in the strong binding of DB884. ITC and SPR comparisons showed that the better binding of DB884 was due to a more favorable binding enthalpy and that it had exceptionally slow dissociation from DNA. Crystallographic analysis of DB884 bound to an AATT site shows that the compound was bound in the minor groove in a 1:1 complex as suggested by CD solution studies. Surprisingly, unlike the amidine derivative, the pyrrole -NH of DB884 formed an H-bond with a central T of the AATT site and this accounts for the enthalpy-driven strong binding. The structural results and molecular modeling studies provide an explanation for the differences in binding affinities for related amidine and reversed amidine analogues.     

Electron trap centers in Ag-borate glasses

The center created by silver trapping an electron in borate glasses are considered. It is shown by ESR techniques that on trapping an electron, silver ions may form four types of centers: the single Ag⁰ or (Ag⁺ + e) centers, and, at higher Ag contents, the Ag⁰(Ag⁺) or (Ag⁺ + e) (Ag⁺) centers in which a second silver is involved. The formation and stability of these centers is critically dependent on the silver content, the concentration of alkali and the temperature of irradiation and measurement. The Ag⁰(Ag⁺) center is generally enhanced by increasing silver and decreasing alkali content and does not show separate signals for the two isotopes ¹⁰⁷Ag, ¹⁰⁹Ag because the two silvers in proximity occur in three different isotope combinations which are superimposed.Above 20% alkali the hyperfine splitting constant for the silver—electron trap center was found to decrease with increasing alkali content, probably in connection with the increasing appearances of non-bridging oxygens and the trapping of the electron in an oxygen vacancy in the vicinity of Ag⁺, i.e. a change from Ag⁰ to (Ag⁺ + e) center. A similar decrease was observed in high alkali (30% R₂O) glasses with changes of alkali from Li⁺ to K⁺.     

Novel Pyridinium Based Ionic Liquid Promoter for Aqueous Knoevenagel Condensation: Green and Efficient Synthesis of New Derivatives with Their Anticancer Evaluation

Herein, a distinctive dihydroxy ionic liquid ([Py-2OH]OAc) was straightforwardly assembled from the sonication of pyridine with 2-chloropropane-1,3-diol by employing sodium acetate as an ion exchanger. The efficiency of the ([Py-2OH]OAc as a promoter for the sono-synthesis of a novel library of condensed products through DABCO-catalyzed Knoevenagel condensation process of adequate active cyclic methylenes and ninhydrin was next investigated using ultimate greener conditions. All of the reactions studied went cleanly and smoothly, and the resulting Knoevenagel condensation compounds were recovered in high yields without detecting the aldol intermediates in the end products. Compared to traditional strategies, the suggested approach has numerous advantages including mild reaction conditions with no by-products, eco-friendly solvent, outstanding performance in many green metrics, and usability in gram-scale synthesis. The reusability of the ionic liquid was also studied, with an overall retrieved yield of around 97% for seven consecutive runs without any substantial reduction in the performance. The novel obtained compounds were further assessed for their in vitro antitumor potential toward three human tumor cell lines: Colo-205 (colon cancer), MCF-7 (breast cancer), and A549 (lung cancer) by employing the MTT assay, and the findings were evaluated with the reference Doxorubicin. The results demonstrated that the majority of the developed products had potent activities at very low doses. Compounds comprising rhodanine (5) or chromane (12) moieties exhibited the most promising cytotoxic effects toward three cell lines, particularly rhodanine carboxylic acid derivative (5c), showing superior cytotoxic effects against the investigated cell lines compared to the reference drug. Furthermore, automated docking simulation studies were also performed to support the results obtained.     

Water as a solvent for Ru‐catalyzed click reaction: Highly efficient recyclable catalytic system for triazolocoumarins synthesis

A new family of Ru (III) complexes has been synthesized, characterized and their catalytic performance has been tested for alkyne–azide cycloaddition (AAC) in water under ultrasonic irradiation conditions. These complexes are found to be effective heterogeneous catalysts for the regioselective synthesis of 1,4‐disubstituted‐1,2,3‐triazoles giving access to these products in excellent yields. The catalyst system is equally active for one‐pot multi‐component protocol of the AAC reactions. Also, successive sequencing of Huisgen reaction with Knoevenagel condensation reaction results in the effective assembly of a diversified hitherto unreported 1,2,3‐triazolyl coumarin frameworks. In present strategy, the catalyst could be easily isolated by simple filtration and reused up to eight consecutive cycles without significant drop in the reaction yields. During the leaching experiment, there is no leaching amount of the catalyst was detected, suggesting true heterogeneity in the catalytic system. The results of gram‐scale reaction and green metrics calculations also confirmed the sustainability and industrial applicability of the current catalytic protocol.