Explicit upper bounds for exponential sums over primes

We give explicit upper bounds for linear trigonometric sums over primes.

     

Sur l'acylation et l'alkylation de l'amino-4 pyrazolo [3,4-d] pyrimidine

New derivatives of 4-amino [3,4-d] pyrazolo pyrimidine have been prepared. Mono, di- and tri-substitution products are characterised by unequivocal synthesis. Several compounds are being tested for possible carcinostatic activity.     

Avidin: a natural bridge for quantum dot-antibody conjugates

We describe the preparation and characterization of bioinorganic conjugates in which luminescent semiconductor CdSe-ZnS core-shell nanocrystal quantum dots (QDs) were coupled to antibodies through the use of an avidin bridge adsorbed to the nanocrystal surface via electrostatic self-assembly. Avidin, a highly positively charged protein, was found to adsorb tightly to QDs modified with dihydrolipoic acid, which gives their surface a homogeneous negative charge. QD conjugation to biotinylated antibodies subsequently is readily achieved. Fluoroimmunoassays utilizing these antibody conjugated QDs were successful in the detection of protein toxins (staphylococcal enterotoxin B, cholera toxin). QD-antibody conjugates formed in such a facile manner permit their use as a common immuno reagent, and in the development of multianalyte detection.     

Synthesis,structural and complex impedance spectroscopy studies of Ni0.4Co0.4Mg0.2Fe2O4 spinel ferrite

Spinel ferrite having composition Ni_0.4Co_0.4Mg_0.2Fe₂O₄ was prepared by sol-gel method. X-ray diffraction result indicates that the ferrite sample has a cubic spinel type structure. FT-IR showed two absorption bands (ν₁ and ν₂) that are attributed to the stretching vibration of tetrahedral and octahedral sites. Complex impedance properties have been investigated in 200–420 K temperature range with varying frequency between 40 and 10⁷ Hz. Frequency and temperature dependency of imaginary part of permittivity (?″) and dielectric loss (tanδ) has been discussed in terms of hopping of charge carriers between Fe²⁺ and Fe³⁺ ions. Activation energy has been estimated from both temperature dependency of dc conductivity and relaxation time data, which indicates that the relaxation process and conductivity have the same origin. Nyquist plots of impedance show semicircle arcs for sample and an electrical equivalent circuit has been proposed to explain the impedance results.     

On the pH-dependent quenching of quantum dot photoluminescence by redox active dopamine

We investigated the charge transfer interactions between luminescent quantum dots (QDs) and redox active dopamine. For this, we used pH-insensitive ZnS-overcoated CdSe QDs rendered water-compatible using poly (ethylene glycol)-appended dihydrolipoic acid (DHLA-PEG), where a fraction of the ligands was amine-terminated to allow for controlled coupling of dopamine-isothiocyanate onto the nanocrystal. Using this sample configuration, we probed the effects of changing the density of dopamine and the buffer pH on the fluorescence properties of these conjugates. Using steady-state and time-resolved fluorescence, we measured a pronounced pH-dependent photoluminescence (PL) quenching for all QD-dopamine assemblies. Several parameters affect the PL loss. First, the quenching efficiency strongly depends on the number of dopamines per QD-conjugate. Second, the quenching efficiency is substantially increased in alkaline buffers. Third, this pH-dependent PL loss can be completely eliminated when oxygen-depleted buffers are used, indicating that oxygen plays a crucial role in the redox activity of dopamine. We attribute these findings to charge transfer interactions between QDs and mainly two forms of dopamine: the reduced catechol and oxidized quinone. As the pH of the dispersions is changed from acidic to basic, oxygen-catalyzed transformation progressively reduces the dopamine potential for oxidation and shifts the equilibrium toward increased concentration of quinones. Thus, in a conjugate, a QD can simultaneously interact with quinones (electron acceptors) and catechols (electron donors), producing pH-dependent PL quenching combined with shortening of the exciton lifetime. This also alters the recombination kinetics of the electron and hole of photoexcited QDs. Transient absorption measurements that probed intraband transitions supported those findings where a simultaneous pronounced change in the electron and hole relaxation rates was measured when the pH was changed from acidic to alkaline.     

Adsorption of CO2, CH4, and N2 on Zeolitic Imidazolate Frameworks: Experiments and Simulations

Experimental measurements and molecular simulations were conducted for two zeolitic imidazolate frameworks, ZIF‐8 and ZIF‐76. The transferability of the force field was tested by comparing molecular simulation results of gas adsorption with experimental data available in the literature for other ZIF materials (ZIF‐69). Owing to the good agreement observed between simulation and experimental data, the simulation results can be used to identify preferential adsorption sites, which are located close to the organic linkers. Topological mapping of the potential‐energy surfaces makes it possible to relate the preferential adsorption sites, Henry constant, and isosteric heats of adsorption at zero coverage to the nature of the host–guest interactions and the chemical nature of the organic linker. The role played by the topology of the solid and the organic linkers, instead of the metal sites, upon gas adsorption on zeolite‐like metal–organic frameworks is discussed.     

Antimicrobial and antioxidant activities of Artemisia herba-alba essential oil cultivated in Tunisian arid zone

This study was conceived to examine the antimicrobial and antioxidant activities of four essential oil types extracted by hydrodistillation from the aerial parts of Artemisia herba-alba cultivated in southern Tunisia. The chemical composition was investigated using both capillary GC and GC/MS techniques. β-thujone, α-thujone, α-thujone/β-thujone and 1,8-cineole/camphor/α-thujone/β-thujone were respectively, the major components of these oil types. The antimicrobial activity of different oils was tested using the diffusion method and by determining the inhibition zone. The results showed that all examined oil types had great potential of antimicrobial activity against strains. In addition, antioxidant capacity was assessed by different in vitro tests and weak activity was found for these A. herba-alba oils.     

Experimental observation of quantum confinement in the conduction band of CdSe quantum dots

X-ray absorption spectroscopy has been used to characterize the evolution in the conduction band (CB) density of states of CdSe quantum dots (QDs) as a function of particle size. We have unambiguously witnessed the CdSe QD CB minimum (CBM) shift to higher energy with decreasing particle size, consistent with quantum confinement effects, and have directly compared our results with recent theoretical calculations. At the smallest particle size, evidence for a pinning of the CBM is presented. Our observations can be explained by considering a size-dependent change in the angular-momentum-resolved states at the CBM.     

Study on the dynamic metabolic characteristic of main active ingredients in Danggui Buxue Decoction by liquid chromatography-tandem mass spectrometry based on in situ sequential metabolism strategy

Danggui Buxue Decoction is a classic formula for replenishing qi and nourishing blood. Despite its widespread use, its dynamic metabolism involved remains unclear. Based on the sequential metabolism strategy, blood samples from different metabolic sites were obtained via in situ closed intestine ring integrated with a jugular venous continuous blood supply technique. An ultra-high-performance liquid chromatography-linear triple quadruple-Orbitrap-tandem mass spectrometry method was developed for the identification of prototypes and metabolites in rat plasma. The dynamic absorption and metabolic landscape of flavonoids, saponins, and phthalides were characterized. Flavonoids could be deglycosylated, deacetylated, demethylated, dehydroxylated, and glucuronicated in the gut and then absorbed for further metabolism. Jejunum is an important metabolic site for saponins biotransformation. Saponins that are substituted by Acetyl groups tend to lose their acetyl groups and convert to Astragaloside IV in the jejunum. Phthalides could be hydroxylated and glucuronidated in the gut and then absorbed for further metabolism. Seven components serve as crucial joints in the metabolic network and are potential candidates for the quality control of Danggui Buxue Decoction. The sequential metabolism strategy described in this study could be useful for characterizing the metabolic pathways of Chinese medicine and natural products in the digestive system.     

SYNTHÈSE ET RÉACTIVITÉ DES 2-PHOSPHONOMETHYLBENZIMIDAZOLES N-ETHOXYCARBONYLES: NOUVELLE VOIE D'ACCÈS AUX 2-PHOSPHONOMETHYL N-AMIDOBENZIMIDAZOLES ET AUX 2-PHOSPHONOMETHYL N-HYDRAZIDOBENZIMIDAZOLES

Abstract

A variety of 2-phosphonomethyl N-amidobenzimidazoles and 2-phosphonomethyl N-hydrazidobenzimidazoles has been efficiently synthesized by treatment of 2-phosphonométhyl N-ethoxycarbonylbenzimidazoles respectively with the appropriate prim amines and hydrazines. The structure of these products was confirmed by IR, NMR(¹H, ¹³C, ³¹P) spectroscopy and mass spectra.