A sequential injection method for the fluorimetric determination of aluminum in drinking water using 8-hydroxy-7-(4-sulfo-1-naphthylazo)-5-quinoline sulfonic acid

A robust and simple sequential injection (SI) method for the assay of aluminum ions in drinking water is described. The method is based on the complex formation between aluminum and 8-hydroxy-7-(4-sulfo-1-naphthylazo)-5-quinoline sulfonic acid (HSNQ). The fluorescence of the complex is monitored at an emission wavelength of 492 nm with excitation at 357 nm. The HSNQ concentration, aspirated reagent and sample volumes were optimized simultaneously using 3(3) full factorial design. The optimum operating conditions are aspirated sample and reagent volumes of 90 and 70 microL, respectively, and HSNQ concentration of 20 microM. With these conditions linear calibration curves were obtained from 100 to 800 ppb. The detection limit was 4 ppb. The maximum relative standard deviation of the method was 1.43% (n=5). The method was successfully applied for the determination of aluminum in drinking water samples.     

Anomeric effects in the symmetrical and asymmetrical structures of triethylamine. Blue-shifts of the C-h stretching vibrations in complexed and protonated triethylamine

Quantum mechanical calculations using density functional theory with the hybrid B3LYP functional and the 6-31++G(d,p) basis set are performed on isolated triethylamine (TEA), its hydrogen-bond complex with phenol, and protonated TEA. The calculations include the optimized geometries and the results of a natural bond orbital (NBO) analysis (occupation of sigma* orbitals, hyperconjugative energies, and atomic charges). The harmonic frequencies of the C-H stretching vibrations of TEA are predicted at the same level of theory. Two stable structures are found for isolated TEA. In the most stable symmetrical structure (TEA-S), the three C-C bond lengths are equal and one of the C-H bond of each of the three CH2 groups is more elongated than the three other ones. In the asymmetrical structure (TEA-AS), one of the C-C bonds and two C-H bonds of two different CH2 groups are more elongated than the other ones. These structures result from the hyperconjugation of the N lone pair to the considered sigma*(C-H) orbitals (TEA-S) or to the sigma*(C-C) and sigma*(C-H) orbitals of the CH2 groups (TEA-AS). The formation of a OH...N hydrogen bond with phenol results in a decrease of the hyperconjugation, a contraction of the C-H bonds, and blue-shifts of 28-33 cm-1 (TEA-S) or 40-48 cm-1 (TEA-AS) of the nus(CH2) vibrations. The nu(CH3) vibrations are found to shift to a lesser extent. Cancellation of the lone pair reorganization in protonated TEA-S and TEA-AS results in large blue-shifts of the nu(CH2) vibrations, between 170 and 190 cm-1. Most importantly, in contrast with the blue-shifting hydrogen bonds involving C-H groups, the blue-shifts occurring at C-H groups not participating in hydrogen bond formation is mainly due to a reduction of the hyperconjugation and the resulting decrease in the occupation of the corresponding sigma*(C-H) orbitals. A linear correlation is established between the C-H distances and the occupation of the corresponding sigma*(C-H) orbitals in the CH2 groups.     

Recrystallization of Zeolite Y to Analcime and Zeolite P with <SC>d</SC>‐Methionine as Structure‐Directing Agent (SDA)

In this study, the synthesis of template free zeolite Y and its recrystallization to two types of pure zeolite P and analcime in the presence of the amino acid d‐methionine as structure‐directing agent were investigated. The recrystallization occurred solely when specific heating cycles were applyed. A completely crystallized phase of zeolite Y for the mixture of zeolite P and analcime was observed in the presence of d‐methionine at a concentration of 0.015 <SC>m</SC>. The effect of different Si/Al ratios (2.3–9.3), crystallization temperatures (40–160 °C), and crystallization times (28–96 hours) on the achievement of two different zeolite types were studied as well. Pure zeolite P was obtained during conventional heating to 100 °C for 42 hours, whereas pure analcime zeolite was achieved by heating the mixture to 160 °C for 96 hours. The products were characterized by X‐ray diffraction, scanning electron microscopy, and IR spectroscopy.     

Water‐Mediated Proton Conduction in a Robust Triazolyl Phosphonate Metal–Organic Framework with Hydrophilic Nanochannels

The development of water‐mediated proton‐conducting materials operating above 100 °C remains challenging because the extended structures of existing materials usually deteriorate at high temperatures. A new triazolyl phosphonate metal–organic framework (MOF) [La₃ L ₄(H₂O)₆]Cl ? x H₂O ( 1 , L ^2?=4‐(4H‐1,2,4‐triazol‐4‐yl)phenyl phosphonate) with highly hydrophilic 1D channels was synthesized hydrothermally. Compound 1 is an example of a phosphonate MOF with large regular pores with 1.9 nm in diameter. It forms a water‐stable, porous structure that can be reversibly hydrated and dehydrated. The proton‐conducting properties of 1 were investigated by impedance spectroscopy. Magic‐angle spinning (MAS) and pulse field gradient (PFG) NMR spectroscopies confirm the dynamic nature of the incorporated water molecules. The diffusivities, determined by PFG NMR and IR microscopy, were found to be close to that of liquid water. This porous framework accomplishes the challenges of water stability and proton conduction even at 110 °C. The conductivity in 1 is proposed to occur by the vehicle mechanism.     

Design,Microwave-Assisted Synthesis and In Silico Prediction Study of Novel Isoxazole Linked Pyranopyrimidinone Conjugates as New Targets for Searching Potential Anti-SARS-CoV-2 Agents

A series of novel naphthopyrano[2,3-d]pyrimidin-11(12H)-one containing isoxazole nucleus 4 was synthesized under microwave irradiation and classical conditions in moderate to excellent yields upon 1,3-dipolar cycloaddition reaction using various arylnitrile oxides under copper(I) catalyst. A one-pot, three-component reaction, N-propargylation and Dimroth rearrangement were used as the key steps for the preparation of the dipolarophiles3. The structures of the synthesized compounds were established by ¹H NMR, ¹³C NMR and HRMS-ES means. The present study aims to also predict the theoretical assembly of the COVID-19 protease (SARS-CoV-2 M^pro) and to discover in advance whether this protein can be targeted by the compounds 4a–1 and thus be synthesized. The docking scores of these compounds were compared to those of the co-crystallized native ligand inhibitor (N3) which was used as a reference standard. The results showed that all the synthesized compounds (4a–l) gave interesting binding scores compared to those of N3 inhibitor. It was found that compounds 4a, 4e and 4i achieved greatly similar binding scores and modes of interaction than N3, indicating promising affinity towards SARS-CoV-2 M^pro. On the other hand, the derivatives 4k, 4h and 4j showed binding energy scores (−8.9, −8.5 and −8.4 kcal/mol, respectively) higher than the M^pro N3 inhibitor (−7.0 kcal/mol), revealing, in their turn, a strong interaction with the target protease, although their interactions were not entirely comparable to that of the reference N3.     

Impact of phase out of leaded gasoline on the air quality in Budapest

As part of an air pollution study in Budapest, size-fractionated aerosol samples were collected by stacked filter units and cascade impactors, and some criteria pollutants and meteorological parameters were recorded in 1996, 1998 and 1999. The samplings were performed at three urban locations including an urban background site, a downtown site, and a tunnel. Elemental composition of the aerosol samples was measured by instrumental neutron activation analysis and/or particle-induced X-ray emission spectrometry; and black carbon (BC) was determined by a light reflectance technique. Since leaded gasoline was completely phased out in Hungary on 1 April 1999, the atmospheric concentrations of some typical transportation-related air pollutants (i.e. Pb, Br, BC and CO) were used for overviewing the actual impact of the phase out on the air quality and on the aerosol characteristics. For the background site, mean concentration of Pb and Br was not changed significantly. In the downtown site, the phase out resulted in a concentration decrease by a factor of 3–4 for Pb and Br. For the tunnel, concentrations of Pb and Br were decreased by a factor up to 9 and 28, respectively. Correlation between the pollutants, their crustal enrichment factors, and average elemental mass size distributions are also presented and discussed.     

Induced Nematic Phase of New Synthesized Laterally Fluorinated Azo/Ester Derivatives

A new series of laterally fluorinated mesomorphic compounds, namely 2-fluoro-4-((4-(alkyloxy)phenyl)diazenyl)phenyl 4-substitutedbenzoate (In_x) were prepared and evaluated for their mesophase behavior. The synthesized series constitutes five members that possess different terminally attached polar groups (X). Their molecular structures were confirmed by elemental analyses and both FT-IR and NMR spectroscopy. Examination of the prepared derivatives was conducted via experimental and theoretical tools. Mesomorphic investigations were carried by polarized optical microscopy (POM) and differential scanning calorimetry (DSC). DSC and POM measurements indicated that except for the un-substituted analogue, all other derivatives were purely nematogenic, possessing their nematic (N) mesophase enantiotropically. This is to say that insertions of terminal polar substituents on their mesogenic structures induced the N phase. In addition, the location of lateral and terminal polar moieties played a considerable role in achieving good thermal N stability. Computational calculations were investigated to determine the deduced optimized molecular structures. Theoretical data indicated that both size and polarity of the terminal substituent (X) have essential impact on the thermal parameters and optical properties of possible geometries.     

The composition and antimicrobial activities of Cyperus conglomeratus, Desmos chinensis var. lawii and Cyathocalyx zeylanicus essential oils

The essential oil compositions of the rhizomes of Cyperus conglomeratus (Cyperaceae) collected from Oman and the leaves of two Annonaceae plants, Desmos chinensis var. lawii and Cyathocalyx zeylanicus collected from India were studied by GC, GC-MS and 13C NMR spectroscopy. Twenty-six compounds, representing 84.4% of the oil were identified in C. conglomeratus, where eugenol (31.3%), alpha-cyperone (10.5%) and cyperotundone (8.4%) were the major compounds. Twelve compounds, constituting 100%, were identified in D. lawii oil, of which benzyl benzoate (58.7%), beta-caryophyllene (23.2%), limonene (4.9%) and alpha-humulene (4.0%) were the major constituents. Thirty-two compounds, comprising 98.0%, were identified in C. zeylanicus oil, of which beta-caryophyllene (21.6%), alpha-pinene (20.4%) and E-beta-ocimene (11.8%) were the major components. The antibacterial and antifungal activities of the oils were tested against a panel of five bacterial and two fungal strains. The oils showed moderate activity against all the tested microbial strains. The minimum inhibitory concentrations of the oils were also determined.     

A note on Schanuel’s conjectures for exponential logarithmic power series fields

In Ax (Ann. Math. 93(2):252–268, 1971), J. Ax proved a transcendency theorem for certain differential fields of characteristic zero : the differential counterpart of the still open Schanuel conjecture about the exponential function over ${\mathbb{C}}$ (Lang, Introduction to transcendental numbers, 1966). In this article, we derive from Ax’s theorem transcendency results in the context of differential valued exponential fields. In particular, we obtain results for exponential Hardy fields, Logarithmic-Exponential power series fields, and Exponential-Logarithmic power series fields.