Structural characterization of new Cd(2+) fluorescent sensor based on lumazine ligand: AM1 and ab initio studies

6-Thienyllumazine (TLM) is synthesized as a new fluorescent sensor that is capable of indicating selectively the presence of Cd(2+) ion via a fluorescence signal. Experiment has been performed in the presence of Ni(2+), Co(2+), Cu(2+), Ag(+), Mn(2+), Hg(2+), Zn(2+), Pb(2+), and Mg(2+) metal ions in aqueous solutions. The product was characterized by elemental analysis, mass, and NMR spectra. The spectral characteristics (maxima, quantum yields, Stokes shift, and lifetimes) of TLM in organic and aqueous solvents have been studied with the help of absorption and fluorescence spectroscopy, as well as, using time dependent spectrofluorimetry (single photon counting technique). The fluorescence dependence of TLM on the pH has also been investigated. The experimental results indicate that TLM exists in two ionic forms: neutral (acid) and anion (base). Electronic structure calculations of TLM were carried out using Semiempirical Austin Model 1 (AM1) and ab initio Hartree-Fock (HF) with 6-31G* basis set and using Gaussian 03 program. Absorption energies for TLM have been calculated using ZINDO method. The theoretical results confirm the presence of the thiophene and pteridine rings in two conformations: twisted at angle of about 35 degrees in the excited state and coplanar in the ground state.     

Spectroscopic and electronic structure studies of intermediate X in ribonucleotide reductase R2 and two variants: a description of the FeIV-oxo bond in the FeIII-O-FeIV dimer

Spectroscopic and electronic structure studies of the class I Escherichia coli ribonucleotide reductase (RNR) intermediate X and three computationally derived model complexes are presented, compared, and evaluated to determine the electronic and geometric structure of the FeIII-FeIV active site of intermediate X. Rapid freeze-quench (RFQ) EPR, absorption, and MCD were used to trap intermediate X in R2 wild-type (WT) and two variants, W48A and Y122F/Y356F. RFQ-EPR spin quantitation was used to determine the relative contributions of intermediate X and radicals present, while RFQ-MCD was used to specifically probe the FeIII/FeIV active site, which displayed three FeIV d-d transitions between 16,700 and 22,600 cm(-1), two FeIV d-d spin-flip transitions between 23,500 and 24,300 cm(-1), and five oxo to FeIV and FeIII charge transfer (CT) transitions between 25,000 and 32,000 cm(-1). The FeIV d-d transitions were perturbed in the two variants, confirming that all three d-d transitions derive from the d-pi manifold. Furthermore, the FeIV d-pi splittings in the WT are too large to correlate with a bis-mu-oxo structure. The assignment of the FeIV d-d transitions in WT intermediate X best correlates with a bridged mu-oxo/mu-hydroxo [FeIII(mu-O)(mu-OH)FeIV] structure. The mu-oxo/mu-hydroxo core structure provides an important sigma/pi superexchange pathway, which is not present in the bis-mu-oxo structure, to promote facile electron transfer from Y122 to the remote FeIV through the bent oxo bridge, thereby generating the tyrosyl radical for catalysis.     

Regioselective synthesis of some novel pyrazoles,isoxazoles, pyrazolo[3,4‐d]pyridazines and isoxazolo[3,4‐d]pyridazines pendant to benzimidazole

2‐Acetyl‐1‐methyl‐1H‐benzimidazole reacts with dimethylformamide‐dimethyl‐acetal (DMF‐DMA) to afford the corresponding E‐1‐(1‐methyl‐1H‐benzimidazol‐2‐yl)‐3‐N,N‐dimethylaminoprop‐2‐enone. The latter compound reacts regioselectively with some nitrilimines and nitrile oxides to afford the corresponding pyrazole and isoxazole derivatives, respectively. These reaction products react with hydrazine hydrate to give the novel pyrazolo[3,4‐d]pyridazine and isoxazolo[3,4‐d]pyridazine derivatives, respectively.     

Characterization by optical measurements of the effects of some stages of champagne technology on the adsorption layer formed at the gas/wine interface

This study analyzes the effects of some important factors of champagne technology on the ellipticity and Brewster angle microscopy (BAM) of the air/champagne interface in view of using the optical properties of the adsorption layer of base wine to forecast the stability of the champagne bubble collar. Using standard, ultrafiltered, and ultraconcentrated wines it was observed that champagne can lose amphiphilic macromolecules which adsorb on the inner glass wall of the bottle during storage, particles such as dead yeasts can adhere to the adsorption layer, a weak increase of the ethanol content during bottle fermentation can reduce significantly the ellipticity of the adsorption layer, and CO2 has no significant effect on the properties of that layer. Surprisingly, no visible differences of the adsorption layer were noticed between the experimental champagnes of the 2004 vintage of three vine varieties (Chardonnay, Pinot noir, and Pinot meunier). From analysis of all samples it is proposed that the mean value and standard deviation of the ellipticity measured during 30 min after pouring the wine in a Petri dish are physical quantities which satisfactorily characterize the adsorption layer of champagne. When needed, further characterization of the adsorption layer may be obtained by a detailed analysis of the kinetics of ellipticity during the same period and inspection of the BAM images of the interface.     

Discovery,Development, and Patent Trends on Molnupiravir: A Prospective Oral Treatment for COVID-19

The COVID-19 pandemic needs no introduction at present. Only a few treatments are available for this disease, including remdesivir and favipiravir. Accordingly, the pharmaceutical industry is striving to develop new treatments for COVID-19. Molnupiravir, an orally active RdRp inhibitor, is in a phase 3 clinical trial against COVID-19. The objective of this review article is to enlighten the researchers working on COVID-19 about the discovery, recent developments, and patents related to molnupiravir. Molnupiravir was originally developed for the treatment of influenza at Emory University, USA. However, this drug has also demonstrated activity against a variety of viruses, including SARS-CoV-2. Now it is being jointly developed by Emory University, Ridgeback Biotherapeutics, and Merck to treat COVID-19. The published clinical data indicate a good safety profile, tolerability, and oral bioavailability of molnupiravir in humans. The patient-compliant oral dosage form of molnupiravir may hit the market in the first or second quarter of 2022. The patent data of molnupiravir revealed its granted compound patent and process-related patent applications. We also anticipate patent filing related to oral dosage forms, inhalers, and a combination of molnupiravir with marketed drugs like remdesivir, favipiravir, and baricitinib. The current pandemic demands a patient compliant, safe, tolerable, and orally effective COVID-19 treatment. The authors believe that molnupiravir meets these requirements and is a breakthrough COVID-19 treatment.     

Alloy formation at the Ni–Al interface for nickel films deposited on Al(110) surfaces

Alloy formation at the Ni–Al interface for thin nickel films deposited on Al(110) surfaces has been studied using high-energy ion scattering/channeling (HEIS) and X-ray photoelectron spectroscopy (XPS). For nickel atoms deposited at room temperature on Al(110), a large amount of nickel–aluminum intermixing occurs at the interface. For the first two monolayers (ML) of deposited nickel, an NiAl-like compound is formed. The intermixing continues with a different rate, forming an Ni₃Al-like compound for nickel coverages from 2 to 8 ML, at which point a nickel metal film begins to grow on the surface. Nickel atoms deposited at 250°C on the Al(110) surface exhibit no surface compound formation, but diffuse up to 400 Å into the aluminum substrate. Interatomic potentials based on the embedded-atom method (EAM) are used in a Monte Carlo approach to simulate the evolution of the Ni–Al(110) interface as a function of the nickel coverage. The calculated ion-scattering yields and X-ray photoelectron intensities from nickel and aluminum atoms in these simulated interfaces are in good quantitative agreement with the experimental results. The simulations show a high-density Ni–Al alloy forming at the Al(110) surface which apparently inhibits outward diffusion of aluminum, leading to the more nickel-rich alloy and finally nickel film growth. The ion-scattering simulations show an unusually large amount of backscattering occurring below the Ni–Al(110) interface, apparently associated with defocusing of the incident ion beam.     

Exploiting the Chiral Ligands of Bis(imidazolinyl)- and Bis(oxazolinyl)thiophenes—Synthesis and Application in Cu-Catalyzed Friedel–Crafts Asymmetric Alkylation

Five new C₂-symmetric chiral ligands of 2,5-bis(imidazolinyl)thiophene (L1–L3) and 2,5-bis(oxazolinyl)thiophene (L4 and L5) were synthesized from thiophene-2,5-dicarboxylic acid (1) with enantiopure amino alcohols (4a–c) in excellent optical purity and chemical yield. The utility of these new chiral ligands for Friedel–Crafts asymmetric alkylation was explored. Subsequently, the optimized tridentate ligand L5 and Cu(OTf)₂ catalyst (15 mol%) in toluene for 48 h promoted Friedel–Crafts asymmetric alkylation in moderate to good yields (up to 76%) and with good enantioselectivity (up to 81% ee). The bis(oxazolinyl)thiophene ligands were more potent than bis(imidazolinyl)thiophene analogues for the asymmetric induction of the Friedel–Crafts asymmetric alkylation.     

Evaluation of spectral dispersion of optical constants of a-Se films from their normal-incidence transmittance spectra using Swanepoel algebraic envelope approach

Spectral dispersions of index of refraction \({n(\lambda )}\) and extinction coefficient \({\kappa (\lambda )}\) of undoped amorphous selenium (a-Se) films of three thicknesses (d?≈?0.5, 0.75, and 1.0 µm) were evaluated by analyzing experimental room-temperature normal-incidence transmittance-wavelength (\({{T_{{\text{exp}}}}(\lambda )} - \lambda\)) data (λ =?400–1100 µm) of their air-supported {a-Se film/thick glass slide}-stacks using Swanepoel’s transmission envelope theory of uniform films. Above a wavelength \({{\lambda _c}\,\, \approx \,\,640\;{\text{nm}}}\), as-measured \({{T_{{\text{exp}}}}(\lambda )}\,\, - \,\lambda\) spectra display well-resolved maxima and minima, with minor shrinkage in transparent and weak absorption regions (750–1100 nm). Below \({\lambda _{\text{c}}}\), a smeared sharp decline of \({{T_{{\text{exp}}}}(\lambda )}\) with decreasing λ, signifying strong absorption in a-Se films and existence of band-tail localized states. For λ > λ _c, the \({n\,(\lambda )}\, - \,\lambda\) data retrieved from algebraic envelope procedures followed a Sellmeier-like dispersion relation, with the best-fit values of high-frequency dielectric constant \({{\varepsilon _\infty }\, \approx \,\,{\text{4.9}}}\), static index of refraction \({{n_{\text{0}}} = n\left( {E\, \to \,{\text{0}}} \right)\,\, \approx \,\,{\text{2.43}}}\), and resonance wavelength \({{\lambda _0}\, \approx \,490\,\,{\text{nm}}}\), which may be assigned to onset of photogeneration in a-Se. Urbach-like dependency of absorption coefficient \({\alpha (h{{\nu }})}\) of a-Se films on photon energy \({h{{\nu }}}\) was realized with an Urbach-tail breadth of 85 meV. All achieved optical parameters were found to be slightly dependent on film thickness. Findings of present algebraic analysis are consistent with reported literature results obtained on the basis of other optical analytical approaches.     

Synthesis of ZnO2 nanoparticles by laser ablation in liquid and their annealing transformation into ZnO nanoparticles

A pulsed laser emitting UV radiations generated by the third harmonic of Nd:YAG was applied for the synthesis of nano-structured ZnO₂ and ZnO. For the synthesis of nanoparticles of ZnO₂, a high-purity metallic plate of Zn target was fixed at the bottom of a glass cell, in the presence of deionized water mixed with oxidizing agent H₂O₂, under repeated laser irradiation. The optical properties, size and the morphology of the synthesized ZnO₂ and ZnO by laser ablation was influenced strongly by post-annealing conditions which is not previously reported. By annealing ZnO₂ at 200 °C for 8 h, the product (ZnO₂) synthesized primarily was converted completely to ZnO. By variation of the annealing temperatures from 200 to 600 °C, the grain size of ZnO changes from 5 to 19 nm with a change in lattice parameters, the band gap and some other optical properties of nano-ZnO.