Detection of trace levels of atrazine using surface-enhanced Raman scattering and information visualization

The detection of trace amounts of pesticides is essential for the quality control of waters, particularly with their inevitable increasing use with the growing demand for food. In this study, we report on the detection of atrazine, a highly toxic herbicide, down to 5?×?10^?12 M, which is sufficient to monitor the quality of drinking water even according to the most stringent international regulations. Such detection was performed with surface-enhanced Raman scattering (SERS) in atrazine incorporated into silver nanoparticles (AgNPs) colloids, with the SERS spectra being treated with Sammon’s mapping, an information visualization technique. In addition to providing a fingerprint of the atrazine molecules, SERS is advantageous in comparison with impedance spectroscopy and cyclic voltammetry applied to a sensor array of units made with layer-by-layer (LbL) films containing AgNPs and AuNPs. The combined use of SERS and information visualization methods is promising for monitoring water quality with regard to other pesticides, which may even approach single molecule detection.     

On Λ I s -sets and the related notions in ideal topological spaces

In this paper, we define and study the notions of Λ _I ^s -sets, Λ _I ^s -closed sets and I-generalized semi-closed (briefly I-gs-closed) sets by using semi-I-open sets in an ideal topological space. Moreover, we present and characterize two new low separation axioms using the above notions.     

Orderly generation of half-regular symmetric designs via Rahilly families of pre-difference sets

Rahilly families of pre-difference sets have been introduced by Rahilly, Praeger, Street and Bryant as a tool for constructing symmetric designs. Using orderly generation, we construct Rahilly families for various groups up to equivalence. For each equivalence class we determine the isomorphism type of the corresponding design. Some designs may be new, whilst others were already known in which case we identify them. For each design we test whether it admits as an automorphism group a regular extension of one of the given groups. If this is the case, the pre-difference set for the given group is also a difference set for the regular extension. We prove that there are examples of designs with a Rahilly family of pre-difference sets for a group which do not admit a regular extension.     

Photoinduced Oxygen Atom Transfer to α-Pinene and R-Carvone using a Dioxo-Molybdenum (VI) Complex Incorporated within a Modified UiO-67 (Zr/Ti) MOF

We report a highly selective (100 %) epoxidation of α-pinene and R-carvone using an oxygen atom transfer (OAT) reaction facilitated by a dioxo-Mo complex (Mo^(VI)O₂Cl₂Ln) incorporated into the ligand 5,5’-dicarboxylate-2,2’-bipyridine (bpydc) within a Metal-Organic Framework (MOF) type UiO-67. Photo-stimulated (350 nm) OAT reaction was carried out with oxygen molecular used as the oxidant for 10 h. UiO-67 was synthesized with a mixture of the ligands 2,2′-biphenyl-5,5′-dicarboxylate (bpdc) and 2,2-bipyridine-5,5-dicarboxylate (bpydc) in different molar ratios (67 : 33, 50 : 50, 70 : 30, 0 : 100 bpdc : bpydc) to promote a higher presence of catalytic sites, i. e., the dioxo-Mo complex units. Furthermore, a post-synthetic exchange of Zr for Ti, between 64 : 36 to 78 : 22 Ti : Zr molar ratio, was performed to improve the optical properties of the MOF and promote the photoinduced OAT reaction. The Catalytic system was characterized by FTIR, XRD, ¹H NMR, XPS, TGA, N₂ adsorption/desorption and UV-Vis-DR. The amount of the epoxide monoterpene is proportional to the number of the dioxomolybdenum^(VI) units (MoO₂) incorporated in the UiO-67 (Zr/Ti), and the OAT reaction selectivity is due to the absence of the oxygen radicals in the medium of reaction. Besides, The Mo complex exhibited excellent stability after five cycles of use.     

Methane Direct Conversion on Mo/ZSM-5 Catalysts Modified by Pd and Ru

The effect of addition of Ru and Pd to Mo/HZSM-5 catalysts used in the dehydroaromatiza-tion of methane was investigated. Catalytic tests and temperature-programmed oxidation results showed that Pd-based catalysts were more selective to naphthalene and suffered strong deactivation. The presence of Ru improved the activity and stability, with a decrease in the carbonaceous deposit probably because of a mechanism of protection of the Mo2C surface.     

Room-temperature phosphorimetry for the determination of trace contaminations of camptothecin in anticancer drugs

Campthotecin derivatives, irinotecan (CPT-11) and topotecan (TPT), have been used for the treatment of cancer and camptothecin (CPT) is a potential contaminant in these anticancer medicines. In this work, room-temperature phosphorimetry was used to quantify either CPT as trace contaminants in anticancer drugs and CPT-11 as the main ingredient in anticancer medicines. Phosphorescence from CPT-11 was induced using Pb(NO₃)₂ in SDS treated cellulose substrate while CPT was selectively detected using TlNO₃ as a phosphorescence enhancer in either cellulose or nylon substrates. The limit of quantification for CPT and CPT-11 was in ng order. A detailed metrological study was made to calculate the combined uncertainty associated to the CPT phosphorescence measurement. Satisfactory analyte recoveries were obtained for CPT-11 as a main active ingredient of a pharmaceutical formulation. The selective determination of CPT in a matrix containing TPT was made using the higher order (2nd) derivative of the excitation spectra. The results demonstrated the applicability of the method due its simplicity, cost effectiveness and selectivity.     

Isolation and Screening of Microorganisms for R-(+)-Limonene and (−)-β-Pinene Biotransformation

This work is focused on the biotransformation of R-(+)-limonene and (?)-β-pinene to bioflavor production. To carry out the present study, 405 microorganisms were tested for their ability to bioconvert the substrates. From the isolated microorganisms, 193 were selected in the prescreening using mineral medium for limonene degradation. At the screening step, eight strains were able to convert R-(+)-limonene and 15 to transform (?)-β-pinene, both in α-terpineol. The highest concentration in α-terpineol from R-(+)-limonene was about 3,450 mg/L for Penicillium sp. isolated from eucalyptus steam. From (?)-β-pinene, the highest product concentration of 675.5 mg/L was achieved using an Aspergillus sp. strain isolated from orange tree stem.     

Four 1‐naphthyl‐substituted tetrahydro‐1,4‐epoxy‐1‐benzazepines: hydrogen‐bonded structures in one,two and three dimensions

(2S*,4R*)‐2‐exo‐(1‐Naphthyl)‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C₂₀H₁₇NO, (I), crystallizes with Z′ = 2 in the space group P2₁; the two independent molecules have the same absolute configuration, although this configuration is indeterminate. The molecules of each type are linked by a combination of C—H...O and C—H...π(arene) hydrogen bonds to form two independent sheets, each containing only one type of molecule. (2SR,4RS)‐7‐Methyl‐2‐exo‐(1‐naphthyl)‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C₂₁H₁₉NO, (II), crystallizes as a true racemate in the space group P2₁/c, and a combination of C—H...N, C—H...O and C—H...π(arene) hydrogen bonds links the molecules into sheets, each containing equal numbers of the two enantiomorphs. (2S*,4R*)‐2‐exo‐(1‐Naphthyl)‐7‐trifluoromethyl‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C₂₁H₁₆F₃NO₂, (III), crystallizes as a single enantiomorph, as for (I), but now with Z′ = 1 in the space group P2₁2₁2₁; again, the absolute configuration is indeterminate. A single C—H...π(arene) hydrogen bond links the molecules of (III) into simple chains. (2S,4R)‐8‐Chloro‐9‐methyl‐2‐exo‐(1‐naphthyl)‐2,3,4,5‐tetrahydro‐1H‐1,4‐epoxy‐1‐benzazepine, C₂₁H₁₈ClNO, (IV), crystallizes as a single enantiomorph of well defined configuration, in the space group P2₁2₁2₁, where two independent C—H...π(arene) hydrogen bonds link the molecules into a single three‐dimensional framework structure.     

Exploring the coordination chemistry of isomerizable terpyridine derivatives for successful analyses of cis and trans isomers by travelling wave ion mobility mass spectrometry

The photochemical cis-trans isomerization of the 4-{4-[2-(pyridin-4-yl)ethenyl]phenyl}-2,2':6',2'-terpyridine ligand (vpytpy) was investigated by UV-vis, NMR and TWIM-MS. Ion mobility mass spectrometry was performed pursuing the quantification of the isomeric composition during photolysis, however an in-source trans-to-cis isomerization process was observed. In order to overcome this inherent phenomenon, the isomerization of the vpytpy species was suppressed by complexation, reacting with iron(ii) ions, and forming the [Fe(vpytpy)(2)](2+) complex. The strategy of "freezing" the cis-trans isomerizable ligand at a given geometric conformation was effective, preventing further isomerization, thus allowing the distinction of each one of the isomers in the photolysed mixture. In addition, the experimental drift times were related to the calculated surface areas of the three possible cis-cis, cis-trans and trans-trans iron(ii) complex isomers. The stabilization of the ligand in a given conformation also allows us to obtain the cis-cis and cis-trans complexes exhibiting the ligand in the metastable cis-conformation, as well as in the thermodynamically stable trans-conformation.