31P{1H}-n.m.r. as a tool for identification of ruthenium isomers containing PPh3 or 1,4-bis(diphenylphosphino)butane ligands. X-ray structures of the cis-{RuCl2(PPh3)2 [4,4′-(-X)2-2,2′-bipy]} complexes [X=-H, -Me, -SMe and (-Cl, -Me)]

A series of cis-{RuCl₂(PPh₃)₂[4,4-(X)₂-2,2-bipy]} [cis-chlorines; X=-H, -Me, -SMe, and (-Cl,-Me)] complexes have had their structures determined by single crystal X-ray diffraction. The geometry of these complexes, also determined in CH₂Cl₂ solution by ³¹P{¹H}-n.m.r. spectroscopy, showed that the chemical shifts for the phosphorus atoms are slightly dependent on the pKa of the 4,4-(-X)₂-2,2-bipy ligands.     

Selective Sulfenylative Desulfonylation or Decarbalkoxylation of α-Sulfonyl Malonates with DABCO or Bu3N: Reactivity and Conformational Analysis

The study on reactivity of several α-substituted α-sulfonyl malonates toward 1,4-diazabicyclo[2.2.2]octane (DABCO) and Bu₃N is described. The reactivity with DABCO revealed the possible competition between decarbalkoxylation and unexpected desulfonylation, depending on the α-substituent, because of sterical hindrance around the electrophilic centers (SO₂ and CO₂R). The derivatives with crowded α-substituents suffer selective desulfonylation, and a novel and efficient desulfonylation method can be proposed. The dependence of the reactivity of α-sulfonyl malonates on the sterical hindrance around the electrophilic centers is confirmed by conformational analysis (Macromodel/MM2? and Mopac/MP3). The carbanionic mechanism is proved because the corresponding protonated, deuterated, and sulfenylated products were obtained by addition of the corresponding electrophilic agents. Bu₃N showed itself to be a novel selective decarbalkoxylation agent for any α-substituted α-sulfonyl malonate.     

Hydrogel-filled micropipette contact systems for solid state electrochemical measurements

This paper reports on the use of a novel microcapillary system for solid contact electrochemical measurements. The probe is made of moveable micropipettes, with orifice of 1–30-μm radii, filled with a conducting hydrogel, which forms a thin-gelled meniscus at the pipette end. The hydrogel is made of 2 % (w/v) agarose and water solutions, containing KCl or KNO₃ as supporting electrolytes. The micropipette can be brought in contact with a conducting substrate to form a microcell, which allows performing voltammetric measurements confined within limited contact regions. The suitability of the proposed probe for local electrochemical measurements are tested using two electroactive species, dissolved in the hydrogel, namely [Fe (CN₆)]^4- and Ag⁺ ions. Mass transport characteristics of the two species, in bulk hydrogel and at micropipette meniscuses of different radii, are examined in detail in the frame of existing theory. For comparison, voltammetric measurements are also performed with micropipettes filled with the corresponding aqueous solutions. It is shown that the gel-filled micropipette, at variance with the aqueous one, prevents the spreading and leakage of solution on the sample surface. The microprobe developed here can be useful to perform electrochemical measurements on surfaces, which suffer from direct contact with liquid electrolytes. A proof-of-concept hydrogel-capillary measurement is performed to distinguish the presence of metallic silver deposited on a graphite-on-paper–based material, realized through simple pencil strokes.

Graphical abstract

     

Synthesis and electrochemical investigation of <Emphasis Type="Italic">beta</Emphasis>-substituted thiophene-based donor–acceptor copolymers with 3,4-ethylenedioxythiophene (EDOT)

The present work reports the synthesis of four electron-acceptor beta-substituted thiophenes that were studied as monomers for electrochemical polymerization with 3,4-ethylenedioxythiophene (EDOT), an electron-donating monomer, aiming the combination of electron-acceptor and donor monomer thiophene to a simpler and convenient build up of novel donor–acceptor copolymeric materials via electrochemical polymerization. Four novel copolymers poly(EDOT-co-3-thiophene phenylacetate), (PEDOT-co-PPhTAc-2a), poly(EDOT-co-3-thiophene(4-nitrophenyl)acetate) (PEDOT-co-PPhTAc-2b), poly(EDOT-co-3-thiophenephenylcarboxylate) (PEDOT-co-PPhTCb), and poly(EDOT-co-3-(phenoxymethyl)thiophene) (PEDOT-co-PPhOMT) were electrochemically polymerized. The monomers were characterized by spectrometric techniques (FTIR, ¹H NMR, and ¹³C NMR), and the copolymers were identified by electrochemical analyses and FT-IR. Although the corresponding homopolymers could not be obtained, in the presence of EDOT, the copolymers were formed in a quasi-reversible electrochemical kinetics. The infrared spectra of the copolymers as well the electrochemical profile corroborates their obtaining. The mass variation during the electrosynthesis was analyzed using a quartz crystal microbalance. The film’s morphologies were investigated by SEM. Interestingly, the combination of electron-rich monomer thiophene (EDOT) and these electron-deficient carboxy-substituted thiophenes might be a convenient building block couple to increase the performance control of physic-chemical properties of mixed polythiophenes with innovative applications and they also showed a possible applicability as charge storage device.     

Influence of oxidation state of sulfur on the dissociation of [Tz-(CH2)n-S(O)m-(CH2)n-Tz + Na+] adducts generated by electrospray ionization (Tz = tetrazole ring; n = 2, 3; m= 0, 1, 2)

Sodium adducts of six organosulfur‐α,ω‐ditetrazole compounds (Tz‐(CH₂)_n‐S(O)_m‐(CH₂)_n‐Tz; where Tz = tetrazole ring; n = 2, 3; m = 0, 1, 2) were generated via electrospray ionization (ESI) and their fragmentation pattern assessed via collision‐induced dissociation (CID). Two main dissociation channels were observed: (a) losses of N₂ and HN₃ from the tetrazole rings; (b) cleavage of the C–S bond. The sulfoxides pass predominantly through the second fragmentation pathway, but for the sulfides and sulfones the tetrazole ring fragmentation occurs. Theoretical calculations at the B3LYP/6‐31 + G(d,p) level indicate that for all the adducts (sulfide, sulfoxide, and sulfone) the dissociation pathway that leads to product ions arising from loss of N₂ was the most exothermic. Based on these results and assumptions, it was postulated that the dissociation of the sulfoxide adducts occurs under kinetic control (N₂‐loss pathway via a much more energetic transition state). For the sulfide and sulfone adducts, on the other hand, the dissociation process takes place via a thermodynamically controlled process. Copyright © 2011 John Wiley & Sons, Ltd.     

Multiple-scan voltammetry of immobilized particles of ancient copper/bronze coins

Journal of Solid State Electrochemistry - The application of a multiple-scan strategy to study the structure of the corrosion patina of copper/bronze ancient objects using the voltammetry of...     

Characterization of Inherently Chiral Electrosynthesized Oligomeric Films by Voltammetry and Scanning Electrochemical Microscopy (SECM)

A voltammetric and scanning electrochemical microscopy (SECM) investigation was performed on an inherently chiral oligomer-coated gold electrode to establish its general properties (i.e., conductivity and topography), as well as its ability to discriminate chiral electroactive probe molecules. The electroactive monomer (S)-2,2′-bis(2,2′-bithiophene-5-yl)-3,3′-bibenzothiophene ((S)-BT₂T₄) was employed as reagent to electrodeposit, by cyclic voltammetry, the inherently chiral oligomer film of (S)-BT₂T₄ (oligo-(S)-BT₂T₄) onto the Au electrode surface (resulting in oligo-(S)-BT₂T₄-Au). SECM measurements, performed in either feedback or competition mode, using the redox mediators [Fe(CN)₆]⁴⁻ and [Fe(CN)₆]³⁻ in aqueous solutions, and ferrocene (Fc), (S)-FcEA, (R)-FcEA and rac-FcEA (FcEA is N,N-dimethyl-1-ferrocenylethylamine) in CH₃CN solutions, indicated that the oligomer film, as produced, was uncharged. The use of [Fe(CN)₆]³⁻ allowed establishing that the oligomer film behaved as a porous insulating membrane, presenting a rather rough surface. This was inferred from both the approach curves and linear and bidimensional SECM scans, which displayed negative feedback effects. The oligomer film acquired semiconducting or fully conducting properties when the Au electrode was biased at potential more positive than 0.6 V vs. Ag|AgCl|KCl. Under the latter conditions, the approach curves displayed positive feedback effects. SECM measurements, performed in competition mode, allowed verifying the discriminating ability of the oligo-(S)-BT₂T₄ film towards the (S)-FcEA and (R)-FcEA redox mediators, which confirmed the results obtained by cyclic voltammetry. SECM linear scans indicated that the enantiomeric discriminating ability of the oligo-(S)-BT₂T₄ was even across its entire surface.     

2,2′-Bipyridine-6,6′-bis(carbothioamide) metal complexes

Complexes of 2,2-bipyridine-6,6-bis(carbothioamide), obtained with a variety of metal cations, were characterised by microanalyses, molar conductivities and by i.r. and n.m.r. (for diamagnetic compounds) spectra. The iron(II) complex was also characterised by Mössbauer spectroscopy. The spectral data indicate that, in all cases, the ligand coordinates to the metal through one pyridine nitrogen and one sulphur.     

Antimony(V) and bismuth(V) complexes of lapachol: synthesis, crystal structure and cytotoxic activity

Antimony(V) and bismuth(V) complexes of lapachol have been synthesized by the reaction of Ph?SbCl? or Ph?BiCl? with lapachol (Lp) and characterized by several physicochemical techniques such as IR, and NMR spectroscopy and X-ray crystallography. The compounds contain six-coordinated antimony and bismuth atoms. The antimony(V) complex is a monomeric derivative, (Lp)(Ph?Sb)OH, and the bismuth(V) complex is a dinuclear compound bridged by an oxygen atom, (Lp)?(Ph?Bi)?O. Both compounds inhibited the growth of a chronic myelogenous leukemia cell line and the complex of Bi(V) was about five times more active than free lapachol. This work provides a rare example of an organo-Bi(V) complex showing significant cytotoxic activity.     

In vivo Electrochemical Monitoring of Signaling Transduction of Plant Defense Against Stress in Leaves of Aloe vera L.

In situ recording of the voltammetric response of Aloe vera L. leaves using graphite and platinum microelectrodes inserted in the subcuticular region is described. The plant response against the mechanical stress results in changes of the voltammetric signals associated to signal transduction compounds salicylic and jasmonic acids and hydrogen peroxide, which were separately monitored. A kinetic model is proposed to describe the time variation of the respective voltammetric signatures, denoting the possibility of in vivo electrochemical monitoring of biochemical processes in plants. The obtained results suggest that two defense pathways with different participation of ROS are operative.