Development of a versatile rotating ring-disc electrode for in situ pH measurements

There are some electrocatalytic reactions in which the key parameter explaining their behavior is a local change in pH. Therefore, it is of utter importance to develop an electrode that could quantify this parameter in situ, but also be customizable to be used in different systems. The purpose of this work is to build a versatile rotating ring/disc electrode (RRDE) with IrO_x deposited on a glass tube as a ring and any kind of material as disc. As the IrO_x is sensitive to pH variation, the reactions promoted on the disc can trigger proportional pH shifts on the ring. In such assembly, the IrO_x ring presents a fast response time even during the pH transients due to the small thickness of the ring (approximately 10 μm), which enables the detection of interfacial pH changes. The ring electrode was tested toward the interfacial pH shift observed during the electrolytic reduction of water on the disc and also characterized by acid–base titration to determine the response time. As the main conclusions, fast response and durable RRDE were obtained, and this assembly could be used to revisit many electrocatalytic reactions in order to test the importance of local pH on the process.     

Template carbon dispersed in polyaniline matrix electrodes: evaluation and application as electrochemical sensors to low concentrations of Cu and Pb

A new electrode, obtained by the dispersion of template carbon nanoparticles onto polyaniline, is presented in this paper. Template carbon was synthesized via the pyrolysis of the polyfurfuryl alcohol inside the nanometric pores of porous Vycor glass, and the electrodes were prepared by a polyaniline-template carbon mixture. Scanning electron microscopy showed that polyaniline-template carbon films presented a wholly modified morphology when compared to polyaniline and polyaniline-graphite films. Electrochemical characterization indicated that the interconversion reactions of polyaniline were strongly facilitated in the presence of the template carbon. The new electrode also exhibited excellent chemical and physical stabilities. Finally, anodic stripping voltammetry measurements revealed that the new electrode presented a noteworthy linear response to very low concentrations of Cu²⁺ and Pb²⁺ ions, under few minutes of pre-concentration.     

Determination of Rare Earth Elements in Natural Water Samples by Rapid Sequential High-Resolution Continuum Source Flame Atomic Absorption Spectrometry (HR CS FAAS) and inductively Coupled Plasma-Mass Spectrometry (ICP-MS)

A method was developed to sequentially assay ten rare earth elements by high-resolution continuum source flame atomic absorption spectrometry. The rare earth elements Nd, Sm, Eu, Tb, Ho, Er, Tm, Yb, Y, and Sc were assayed in environmental water samples which were also analyzed by a reference inductively coupled plasma-mass spectrometry protocol. The samples did not require pretreatment or preconcentration. Interferences for the method were evaluated. Experimental parameters, including the flame composition, burner height, ionization buffers and number of pixels, were optimized. The volume necessary to run measurements in triplicate was only 15?mL per sample. The accuracy, precision and linear range were evaluated. The limits of detection ranged from 0.003 to 0.473?µg mL^?1 for the most sensitive (Yb) to the least sensitive (Tb) element.     

Neutral pyridyl-functionalized C,N-ortho-chelated aminoaryl platinum(II) corner building blocks for application in coordination reactions

Two homoleptic pyridyl-functionalized C,N-ortho-chelating aminoaryl platinum(II) complexes, cis-[Pt(eta(2)-C,N)] (3a,b), were prepared via an unconventional method involving the initial synthesis of a bromide-functionalized C,N-chelating aminoaryl platinum(II) precursor complex 8, to which subsequently pyridyl groups were attached via a Suzuki-Miyaura C-C coupling reaction. The electron-donating properties of the pyridyl nitrogen atoms of the resulting complexes (3a,b) were used in complexation reactions with monocationic NCN-pincer (NCN = [C6H3(CH2NMe2)(2-)2,6]-) platinum(II) (11a) and palladium(II) (12a) nitrate complexes [M(NCN)(NO3)], thereby obtaining four trimetallic coordination complexes 16-19. The difference in the pyridine-metal coordination behavior between platinum and palladium was studied by varying the ratios of the reagents and by variable-temperature NMR experiments. IR and Raman analyses of 11a and 12a were performed to determine the coordination behavior of the nitrate counteranion, and it was found that both NO3- and H2O coordinate to the metal centers. The crystal structure determinations of free pyridyl complex 3a, [Pt(NCN)(NO3)] (11a), and [Pt(NCN)(NO3)].(H2O) (11b), as well as the crystal structure of trisplatinum coordination complex 16, are reported.     

Detailed 1H and 13C NMR structural assignment of ent-polyalthic acid,a biologically active labdane diterpene

In this paper, a complete ¹H and ¹³C NMR data assignment of ent-polyalthic acid, a biologically active labdane-type diterpene, is presented. The assignments were carried on the basis of spectroscopic data from ¹H NMR, ¹³C{¹H} NMR, gCOSY, gHMQC, and gHMBC experiments. Furthermore, a software-assisted methodology, using FOMSC3_rm_NB and NMR_MultSim programs, supported the detailed and unequivocal assignment of ¹H and ¹³C signals, allowing all hydrogen coupling constants to be determined and thus clarifying all hydrogen signal multiplicities.     

Detailed 1H and 13C NMR structural assignments of four sesquiterpene lactones isolated from Eremanthus elaeagnus (Asteraceae)

A complete ¹H and ¹³C NMR analysis for a group of four sesquiterpene lactones isolated from Eremanthus elaeagnus (Asteraceae) is described in this work. ¹H NMR, ¹³C {¹H} NMR, gCOSY, gHMQC, and gHMBC experiments were performed to provide sufficient structural information to allow an unequivocal assignment. All hydrogen coupling constants were measured, clarifying all hydrogen signal multiplicities.     

Needle-like IrO/Ag combined pH microelectrode

In this study, a combined pH microelectrode has been developed consisting of an indicator electrode made of IrO₂ prepared using the polymeric precursor method and deposited in a platinum microwire. This electrode was mounted inside a stainless steel needle, the external surface of which was painted with conductive silver ink which is used as reference electrode. This device was compared with a conventional glass electrode, and the results presented linear behavior in the pH range from 2.0 to 12.5, in Na⁺ and K⁺ solutions, exceeding glass electrodes in the alkaline range. The sensitivity was 56.9 ± 0.2 mV pH^? 1 and using ANOVA test we conclude that the electrode is not sensitive to the presence of alkaline cations such as Li⁺, Na⁺ or K⁺. Finally, the response time (t₉₅) was 4.9 to 9.0 s depending on the solution pH. The combined pH microelectrode can be used several times and, after three years, continues to have a response similar to that of a freshly produced one.     

1H and 13C NMR assignments of two new isomeric bisbenzylisoquinoline alkaloids from Cissampelos sympodialis Eichl. (Menispermaceae)

des‐7′‐O‐methylroraimine (compound 1) and epi‐des‐7′‐O‐methylroraimine (compound 2), two new isomeric bisbenzylisoquinoline alkaloids were isolated and characterized as a mixture from the rhizomes of Cissampelos sympodialis Eichl. The unambiguous structural elucidation of both isomers was performed with the aid of HR‐ESI‐MS, FT‐IR, and NMR techniques including COSY, HMQC, HMBC, and NOESY. Copyright © 2013 John Wiley & Sons, Ltd.