Nuclear resonant magnetometry and its application to Fe/Cr multilayers

We introduce nuclear resonant magnetometry as a means to record the magnetization curve of isotopically enhanced regions of a sample. It is based on nuclear resonant scattering with circularly polarized synchrotron radiation and the use of a nuclear resonant reference sample. We apply this approach to study the interlayer coupling in Fe/Cr(100) multilayers and to obtain a layer-specific magnetization curve. Our measurements provide experimental evidence for the existence of a nontrivial interlayer-coupling angle in Fe/Cr/Fe.     

Rice straw and energy reed fibers reinforced phenol formaldehyde resin polymeric biocomposites

Cellulose - Herein, natural fiber (energy reeds and rice straw) reinforced with phenol formaldehyde (PF) polymeric resin biocomposites are developed and reported in this study. The dimensions of...     

Simultaneous determination of β-lactamic antibiotics by a new high-performance low-pressure chromatographic system using a multisyringe burette coupled to a monolithic column (MSC)

A technique based on multisyringe chromatography (MSC) was developed to determine three beta-lactamic antibiotics. Amoxicillin (AMOXI), ampicillin (AMPI) and cephalexin (CEPHA) were analyzed using a system with a very simple design and very low-cost equipment consisting of a multisyringe module, three low-pressure solenoid valves, a monolithic Chromolith Flash RP-18e column and a diode array spectrophotometric detector monitoring at 250 nm. Mobile phases containing methanol:acetic acid (0.1 M)-sodium acetate (0.1 M), pH 6.2, were tested for various ratios of methanol:acetic acid-sodium acetate, but a ratio of 10:90 gave optimum results with a flow rate of 2 ml min(-1). Validation parameters were evaluated for amoxicillin. The response to amoxicillin was linear over the range 0.04-0.4 mg/mL, with a correlation coefficient of 0.9996; precisions, evaluated as the repeatability for 0.04, 0.16 and 0.4 mg/mL amoxicillin, were 0.6%, 0.1% and 0.6%, respectively. Recovery from a generic formulation of amoxicillin was evaluated. The method showed selectivity in the presence of excipients commonly used in capsules, and satisfactory specificity was observed for amoxicillin and hydrolytic degradation products. The linearity was also evaluated for cephalexin and ampicillin. The conditions selected for MSC separation were compared with those for a HPLC system, and similar results were obtained in terms of chromatographic parameters but a difference in retention times was observed.     

Synthesis,Spectral, Thermal Studies of Co(II), Ni(II), Cu(II) and Zn(II)‐arginato Complexes. Crystal Structure of Monoaquabis(arginato‐κO,κN)copper(II). [Cu(arg)2(H2O)].NaNO3

Transition metal complexes of arginine (using Co(II), Ni(II), Cu(II) and Zn(II) cations separately) were synthesized and characterized by FTIR, TG/DTA‐DrTG, UV‐Vis spectroscopy and elemental analysis methods. Cu(II)‐Arg complex crystals was found suitable for x‐ray diffraction studies. It was contained, one mole Cu^II and Na⁺ ions, two arginate ligands, one coordinated aqua ligand and one solvent NO₃^? group in the asymmetric unit. The principle coordination sites of metal atom have been occupied by two N atoms of arginate ligands, two carboxylate O atoms, while the apical site was occupied by one O atom for Cu^II cation and two O atoms for Co^II, Ni^II, Zn^II atoms of aqua ligands. Although Cu^II ion adopts a square pyramidal geometry of the structure. Co^II, Ni^II, Zn^II cations have octahedral due to coordination number of these metals. Neighbouring chains were linked together to form a three‐dimensional network via hydrogen‐bonding between coordinated water molecule, amino atoms and O atoms of the bridging carboxylate groups. Cu^II complex was crystallized in the monoclinic space group P2₁, a = 8.4407(5) Å, b = 12.0976(5) Å, c = 10.2448(6) Å, V = 1041.03(10) ų, Z = 2. Structures of the other metal complexes were similar to CuII complex, because of their spectroscopic studies have in agreement with each other. Copper complex has shown DNA like helix chain structure. Lastly, anti‐bacterial, anti‐microbial and anti‐fungal biological activities of complexes were investigated.     

Synthesis and characterization of multiarm (Benzoin-PS)m-polyDVB star polymer as a polymeric photoinitiator for polymerization of acrylates and methacrylates

In this study, a new benzoin-based multi-arm star polymer was synthesized by using ATRP, and characterization was achieved by spectrophotometric and chromatographic methods. Obtained multiarm (Benzoin-PS)_m-polyDVB star polymer was employed as a polymeric photoinitiator for polymerization of methacrylates and acrylates. Photophysical properties of this initiator were determined by fluorescence and phosphorescence measurements, the phosphorescence lifetime was calculated as 29 ms hence the lowest triplet state nature was n-π* character, and laser flash photolysis technique was additionally used to get more information about triplet state and triplet lifetime which was calculated as 1.34 ms. Photokinetics of difunctional acrylate such as HDDA was studied with a multi-arm (Benzoin-PS)_m-polyDVB star polymeric initiator using Photo-DSC.     

Selective Recognition of Cobalt (II) Ion by a New Cryptand Compound with N2O2S2 Donor Atom Possessing 2-Hydroxy-1-Naphthylidene Schiff Base Moiety

A new cryptand compound carrying 2-hydroxy-1-naphthylidene Schiff base moiety (3) was designed and synthesized by reaction of the corresponding macrobicyclic amine compound (1) and 2-hydroxy-1-naphthaldehyde (2). The influence of metal cations such as Mg²⁺, Ca²⁺, Sr²⁺, Fe²⁺,Co²⁺, Mn²⁺, Zn²⁺, Cd²⁺, Hg²⁺, Al³⁺ and Pb²⁺ on the spectroscopic properties of the new fluoroionophore was investigated in acetonitrile-dichloromethane solution (9.5/0.5) by means of absorption and emission spectrometry. The blue shifts on the fluorescence spectrum were observed for all metal cations at 504nm. At the same time the fluorescence spectrum of the ligand showed quenching in the intensity of the signal at 504 nm for all metal cations except for Zn²⁺. Interaction of Co²⁺ with the ligand caused quenching of naphtyl fluorescence higher than 84%. The method showed good selectivity and sensitivity for Co²⁺ with respect to other metal cations with linear range and detection limit of 1.5 × 10⁻⁷ to 3.3 × 10⁻⁶M and 4.8 × 10⁻⁸M respectively.     

Crystal Structure and Conformational Analysis of 4-[(<Emphasis Type="Italic">p</Emphasis>-<Emphasis Type="Italic">N</Emphasis>,<Emphasis Type="Italic">N</Emphasis>-Dimethylamino)Benzylidene]-2-Phenyloxazole-5-One

Abstract  

Molecular and crystal structure of 4-[(p-N,N-dimethylamino)benzylidene]-2-phenyloxazol-5-one, C₁₈H₁₆N₂O₂, have been determined by single crystal X-ray diffraction study. The title compound is monoclinic, with a = 12.1704(23) ?, b = 3.9810(5) ?, c = 30.9603(56) ?, β = 101.176(15)°, Z = 4, D _x = 1.32 g/cm³, μ(Mo Kα) = 0.087 mm⁻¹, and space group is P12₁/c1. The structure was solved by direct methods and refined to a final R = 0.047 for 3166 reflections with I > 2σ(I). The crystal structure is stabilized by C–H⋯O and C–H⋯N type intra-molecular, C–H⋯O type inter-molecular interactions. To enlighten the flexibility and the geometric isomerism (E or Z) of the title compound, the selected torsion angle is varied from −180 to 180° in every 10° separately and molecular energy profile is calculated and analyzed.     

Modeling of copper(II) and lead(II) adsorption on kaolinite-based clay minerals individually and in the presence of humic acid

The aim of this study is to explain how clay minerals adsorb heavy metals individually and in the presence of humic acid, and to model heavy metal adsorption specifically based on surface-metal binary and surface-metal-ligand ternary complexation. The adsorption of Cu(II) and Pb(II) on kaolinite-based clay minerals has been modeled by the aid of the FITEQL3.2 computer program using single- and double-site binding models of the Langmuir approach. Potentiometric titrations and adsorption capacity experiments were carried out in solutions containing different concentrations of the inert electrolyte NaClO4; however, the modeling of binary and ternary surface complexation was deliberately done at high ionic strength (0.1 M electrolyte) for eliminating adsorption onto the permanent negatively charged sites of kaolinite. A "two-site, two pKa" model was adapted, and as for the two surface sites responsible for adsorption, it may be arbitrarily assigned that [triple bond]S1OH sites represent silanol and organic functional groups such as carboxyl having pKa values close to that of silanol, and [triple bond]S2OH sites represent aluminol and organic functional groups such as phenolics whose pKa values are close to that of aluminol, as all the studied clays contained organic carbon. Copper(II) showed a higher adsorption capacity and higher binding constants, while lead(II), being a softer cation (in respect to HSAB theory) preferred the softer basic sites with aluminol-phenol functional groups. Heavy metal cations are assumed to bind to the clay surface as the sole (unhydrolyzed) M(II) ion and form monodentate surface complexes. Cu(II) and Pb(II) adsorption in the presence of humic acid was modeled using a double-site binding model by the aid of FITEQL3.2, and then the whole system including binary surface-metal and surface-ligand and ternary surface-metal-ligand complexes was resolved with respect to species distributions and relevant stability constants. Electrostatic effects were accounted for using a diffuse layer model (DLM) requiring minimum number of adjustable parameters. Metal adsorption onto clay at low pH increased in the presence of humic acid, and the metal adsorption vs pH curves of metal-kaolinite-humic acid suspensions were much steeper (and distinctly S shaped) compared to the wider pH-gradient curves observed in binary clay-metal systems. The clay mineral in the presence of humic acid probably behaved more like a chelating ion-exchanger sorbent for heavy metals rather than being a simple inorganic ion exchanger.     

Emission-based optical carbon dioxide sensing with HPTS in green chemistry reagents: room-temperature ionic liquids

We describe the characterization of a new optical CO₂ sensor based on the change in the fluorescence signal intensity of 8-hydroxypyrene-1,3,6-trisulfonic acid trisodium salt (HPTS) in green chemistry reagents—room-temperature ionic liquids (RTILs). As far as we are aware, this is the first time RTILs, 1-methyl-3-butylimidazolium tetrafluoroborate (RTIL-I) and 1-methyl-3-butylimidazolium bromide (RTIL-II), have been used as matrix materials with HPTS in an optical CO₂ sensor. It should be noted that the solubility of CO₂ in water-miscible ionic liquids is approximately 10 to 20 times that in conventional solvents, polymer matrices, or water. The response of the sensor to gaseous and dissolved CO₂ has been evaluated. The luminescence intensity of HPTS at 519 and 521 nm decreased with the increasing concentrations of CO₂ by 90 and 75% in RTIL-I and RTIL-II, respectively. The response times of the sensing reagents were in the range 1–2 min for switching from nitrogen to CO₂, and 7–10 min for switching from CO₂ to nitrogen. The signal changes were fully reversible and no significant hysteresis was observed during the measurements. The stability of HPTS in RTILs was excellent and when stored in the ambient air of the laboratory there was no significant drift in signal intensity after 7 months. Our stability tests are still in progress.      

Rapid Hyperbranched Polythioether Synthesis Through Thiol-Michael Addition Reaction

In this study, two types of hyperbranched (HB) polythioether could readily be achieved in a short time at ambient temperature through a thiol-Michael addition reaction. Dimethyl acetylenedicarboxylate (DMADC) or methyl propiolate (A₂) and trimethylolpropane tris(3-mercaptopropionate) (B₃) monomers were reacted using an organobase 1,5,7-triazabicyclo[4.4.0]dec-5-ene (TBD) as a catalyst in chloroform at room temperature to provide subsequent HB polythioethers. The effect of TBD concentration on the polymerization was studied for the DMDAC case monitoring the molecular weight evolution against time. HB polythioethers were characterized using spectroscopic (nuclear magnetic resonance) and chromatographic (gel permeation chromatography with refractive index and light-scattering detectors) techniques. © 2020 Wiley Periodicals, Inc. J. Polym. Sci. 2020 , 58, 824–830