Ion exchange and ion transport properties of sulfonated organically modified silica hydrogels

Sulfonated ormosil hydrogels (~80% water) were prepared using tetramethyl orthosilicate as a silica precursor and 2(4-chlorosulfonylphenyl)ethyltrichlorosilane to provide sulfonate functionality for ion-exchange and ion conductivity. Ruthenium(III) hexamine was used as a redox probe in electrochemical studies performed on porous carbon fibre paper electrodes impregnated with the gel. The gel-modified electrodes extracted Ru(NH₃)₆³⁺ from solutions in 0.1 M CF₃CO₂Na_(aq) with a partition coefficient of ~36, and with ~100% of the sulfonate sites being accessible for ion exchange. The Ru(NH₃)₆^3+/2+ couple exhibited reversible and facile electrochemistry in the gel, with a Ru(NH₃)₆²⁺ diffusion coefficient of 4.9×10^–8 cm² s^–1 determined by chronoamperometry. This is an order of magnitude higher than the mobility of this complex in Nafion. The hydrogel-modified electrodes were stable for days, and could be repeatedly loaded with Ru(NH₃)₆³⁺.Special Issue to celebrate the 70^th birthday of Professor Zbigniew Galus     

Electronic structure and spectra of [Ru(NH3)5pyz]2+ and [(NH3)5Ru-pyz-Ru(NH3)5]4+

The electronic structure and spectra of [Ru(NH₃)₅pyz]²⁺ and [(NH₃)₅Ru-pyz-Ru(NH₃)₅]⁴⁺ are calculated by the INDO (CINDO-E/S) method. Changes in molecular orbitals, charge distributions, and bond order indices of the pyrazine molecule and [Ru(NH₃)₅pyz]²⁺ complex in the [(NH₃)₅Ru-pyz-Ru(NH₃)₅]⁴⁺ binuclear complex are analyzed. St. Petersburg State University. Translated fromZhurnal Strukturnoi Khimii, Vol. 35, No. 4, pp. 12–23, July–August, 1994. Translated by. O. Kharlamova     

Quartz crystal microbalance monitoring of density changes in mesoporous TiO2 phytate films during redox and ion exchange processes

Nanofilm deposits of TiO₂ nanoparticle phytates are formed on gold electrode surfaces by ‘directed assembly’ methods. Alternate exposure of a 3-mercapto-propionic acid modified gold surface to (i) a TiO₂ sol and (ii) an aqueous phytic acid solution (pH 3) results in layer-by-layer formation of a mesoporous film. Ru(NH₃)₆³⁺ is shown to strongly adsorb/accumulate into the mesoporous structure whilst remaining electrochemically active. Scanning the electrode potential into a sufficiently negative potential range allows the Ru(NH₃)₆³⁺ complex to be reduced to Ru(NH₃)₆²⁺ which undergoes immediate desorption. When applied to a gold coated quartz crystal microbalance (QCM) sensor, electrochemically driven adsorption and desorption processes in the mesoporous structure become directly detectable as a frequency response, which corresponds directly to a mass or density change in the membrane. The frequency response (at least for thin films) is proportional to the thickness of the mass-responsive film, which suggests good mechanical coupling between electrode and film. Based on this observation, a method for the amplified QCM detection of small mass/density changes is proposed by conducting measurements in rigid mesoporous structures.     

Sensitive Phenol Detection Using Tyrosinase‐Based Phenol Oxidation Combined with Redox Cycling of Catechol

This paper reports sensitive phenol detection using (i) tyrosinase (Tyr)‐based oxidation of phenol to catechol, combined with (ii) electrochemical‐chemical‐chemical (ECC) redox cycling involving Ru(NH₃)₆³⁺, catechol, and tris(2‐carboxyethyl)phosphine (TCEP). Phenol is converted into catechol by Tyr in the presence of dissolved O₂. Catechol then reacts with Ru(NH₃)₆³⁺, generating o‐benzoquinone and Ru(NH₃)₆²⁺. o‐Benzoquinone is reduced back to catechol by TCEP, and Ru(NH₃)₆²⁺ is accumulated over the course of the incubation. When Ru(NH₃)₆²⁺ is electrochemically oxidized to Ru(NH₃)₆³⁺, ECC redox cycling occurs. For simple phenol detection, bare ITO electrodes are used without modifying the electrodes with Tyr. The detection limit for phenol in tap water using Tyr‐based oxidation combined with ECC redox cycling is ca. 10^?9 M, while that using only Tyr‐based oxidation is ca. 10^?7 M.     

Study of nitrosation of hexaammineruthenium(II): Crystal structure of <Emphasis Type="Italic">trans</Emphasis>-[RuNO(NH<Subscript>3</Subscript>)<Subscript>4</Subscript>Cl]Cl<Subscript>2</Subscript>

The nitrosation of [Ru(NH₃)₆]²⁺ in hydrochloric acid and alkaline ammonia media has been studied; the patterns of interconversion of ruthenium complexes in reaction solutions have been proposed. In both cases, nitrogen(II) oxide acts as the nitrosation agent. The procedure for the synthesis of [Ru(NO)(NH₃)₅]Cl₃ · H₂O (yield 75–80%), the main nitrosation product of [Ru(NH₃)₆]²⁺, has been optimized. Thermolysis of [Ru(NO)(NH₃)₅]Cl₃ · H₂O in a helium atmosphere has been studied; the intermediates have been identified. One of these products is polyamidodichloronitrosoruthenium(II) whose subsequent decomposition gives an equimolar mixture of ruthenium metal and dioxide. The structure of trans-[RuNO(NH₃)₄Cl]Cl₂, formed in the second stage of thermolysis and as a by-product in the nitrosation of [Ru(NH₃)₆]Cl₂, has been determined by X-ray diffraction.     

A label-free electrochemical biosensor for trace uranium based on DNAzymes and gold nanoparticles

A novel and highly sensitive electrochemical DNAzymes biosensor was fabricated using Au nanoparticles (AuNPs) immobilized on the surface of Au electrode that had been previously modified with self-assembled monolayers of 1,6-hexanedithiol. Different modified electrodes were prepared and characterized by cyclic voltammetry and electrochemical impedance spectroscopy. The AuNPs were found to have a large surface area to anchor a large number of negatively charged phosphate backbones of DNAzymes, which further absorbed the electroactive indicator of hexaammineruthenium(III) ([Ru(NH₃)₆]³⁺) to amplify the electrochemical signal. In the presence of target molecules, a large amount of DNA partly associated with [Ru(NH₃)₆]³⁺ were removed from the electrode surface, leading to a significant decrease in peak current. Differential pulse voltammetry signals of [Ru(NH₃)₆]³⁺ provided quantitative measures of the concentrations of uranyl ion (UO₂ ²⁺), with linear calibration ranging from 13 pM to 0.15 nM and a detection limit of 5 pM. The presence of other metal ions did not affect the detection of UO₂ ²⁺, which indicated the high specificity of UO₂ ²⁺. Therefore, a new electrochemical DNAzymes sensor was designed with specific DNAzymes and AuNPs as immobilization platform and signal amplifier.     

Electronic tuning of ruthenium complexes by 8-quinolate ligands

A series of Ru(II) complexes were synthesized with the deprotonated forms of the ligands 8-hydroxyquinoline (quo⁻) and 5-NO₂-8-hydroxyquinoline (5-NO₂-quo⁻) as analogs to the prototypical complex [Ru(bpy)₃]²⁺ (bpy = 2,2′-bipyridine). Electrochemistry, spectroscopy and density functional theory calculations were utilized to investigate the electronic tuning of the occupied t_2g-type orbitals of the metal center with variation in the ligation sphere. The maximum of the lowest energy absorption of complexes containing one, two and three 8-quinolate ligands progressively redshifts from 452 nm in [Ru(bpy)₃]²⁺ to 510 nm in [Ru(bpy)₂(quo)]⁺, 515 nm in [Ru(bpy)(quo)₂] and 540 nm in [Ru(quo)₃]⁻ in water. This bathochromic shift results from the increase in energy of the occupied t_2g-type orbital across the series afforded by coordination of each subsequent quo⁻ ligand to the Ru(II) center. Time-dependent density functional theory calculations along with electrochemical analysis reveals that the lowest energy transition has contributions in the highest occupied molecular orbital from both the quo⁻ ligand and the metal, such that the lowest energy transition is not from an orbital that is purely metal-centered in character as in [Ru(bpy)₃]²⁺.     

Kinetic Study of the Ru(II) Catalyzed Oxidation of Pentacyanoferrate(ll) Complexes by Peroxydisulfate

The oxidation reactions of Fe(CN)₅L^3? (L = 4-ampy, py, dpa) complexes by S₂O₈^2? were catalyzed upon the addition of a trace amount of Ru(NH₃)₅L′²⁺ (L′ = pz, py or dcb) complex, and the reaction becomes zero-order in Fe(II). The reaction time is ～10² fold faster than the simple Fe(CN)₅L^3?-S₂O₈^2? system. The mechanism of this Ru(II) catalyzed redox reaction is proposed as Ru(NH₃)₅L′²⁺ + 1/2 S₂O₈^2? → Ru(NH₃)₅L′³⁺ + SO₄^2? Ru(NH₃)₅L′³⁺ + Fe(CN)₅L^3? ? Ru(NH₃)₅L′²⁺ + Fe(CN)₅L^2?     

Studies of the reactions of thiocyanate ion with pentammine dinitrogen ruthenium(II) dibromide at different temperatures

The salts of the linkage isomers of thiocyanatopentammineruthenium(III) [Ru(NH₃)₅(NCS)]²⁺, [Ru(NH₃)₅(SCN)]²⁺ and dithiocyanatotetrammineruthenium(III) [Ru(NH₃)₄(NCS)₂]⁺ along with those of tetrathiocyanatodiammineruthenate(III) [Ru(NH₃)₂(SCN)₄]^? have been synthesized. The insoluble polymeric complex [Ru(NH₃)₂(SCN)₂]_n has also been prepared. The compounds have been characterized by chemical analyses, spectral (IR, UV and visible), magnetic susceptibility, conductivity, cyclic voltammetry and chromatography studies.     

含噻吩环的吡啶Ru(II)配合物的电子结构和非线性光学性质

采用密度泛函理论(DFT) B3LYP方法对含有噻吩环的吡啶Ru(II)配合物的电子结构和非线性光学(NLO)性质进行理论研究. 结果表明: 配合物[Ru^II(NH₃)₅L]²⁺(L为含噻吩环的有机基团)中, 配位原子与中心金属离子间没有形成稳定的化学键, 但存在较强的供体-受体(D-A)相互作用; NH₃被羰基(CO)取代后, Ru-C间形成了稳定的σ-π配键, 降低了受体的空轨道能级. 噻吩环的增加增大了体系的共轭程度, 有利于分子内电荷转移, 使配合物的极化率α和一阶超极化率β明显增加. 结合配合物的前线分子轨道分析发现, 电荷转移过程中, 对体系二阶NLO系数贡献较大的是配体内电荷转移(ILCT)和配体间电荷转移(LLCT)跃迁, 羰基引入后配体到金属的电荷转移(LMCT)使配合物[Ru^II(CO)₅L]²⁺比对应的配合物[Ru^II(NH₃)₅L]²⁺的β值增大约7倍.     

Electronic structure of metastable isomers of Ru nitroso complexes

Geometrical structures of nitroso complexes trans- [Ru(NO)(NH₃)₄(Cl)]²⁺, trans-[Ru(NO)(NH₃)₄(H2O)]³⁺, [Ru(NO)(Cyclam)(Cl)]²⁺(Cyclam is 1,4,8,11-tetraazocyclodecane), and [Ru(NO)(Bipy)₂(Cl)]²⁺ (Bipy is 2,2-bipyridine) are optimized using the density functional method. The potential energy surface of all four complexes was found to contain local minima corresponding to a stable state with the ¹-coordination of NO through the N atom and to two metastable isomers with the ¹-O and ²-NO coordination. For [Ru(NO)Cl₅)]^2-, trans-[Ru(NO)(NH₃)₄(Cl)]²⁺, and trans-[Ru(NO)(NH₃)₄(H₂O)]³⁺, the lowest electronically excited triplet states are calculated, as well as the reduced complexes with one additional electron. It is shown that the electron excitation and reduction are accompanied by bending of the RuNO group with a substantial elongation of the Ru-O and N-O bonds, which makes this group unstable. These processes do not cause any significant changes in the metal or in the nitroso ligand oxidation states because of the electron density delocalization in the RuNO group.Translated from Koordinatsionnaya Khimiya, Vol. 31, No. 1, 2005, pp. 32–42.Original Russian Text Copyright © 2005 by Sizova, Lubimova.     

Electrochemical Studies of Thiol Self‐Assembled Monolayers at a Heated Gold‐Wire Microelectrode

Mercaptoundecanoic acid (MUA) and glutathione (GSH) self‐assembled monolayers were prepared on gold‐ wire microelectrode. Cyclic voltammetry was used to investigate the influence of temperature on electrochemical behaviors of Fe(CN)₆^3?/4? and Ru(NH₃)₆^3+/2+ at these SAMs modified electrodes in aqueous solution. It is found that temperature shows great influence on electron transfer (ET) and mass transport (MT) for the two SAMs modified electrodes and the influence of temperature depends on the charge properties of the redox couples and terminal groups of SAMs and the structure of the monolayer on gold surface. The temperature can greatly increase MT rate of Fe(CN)₆^3?/4? at both MUA and GSH modified electrodes. However, the increased MT rate doesn't have any effect on the CV's for Fe(CN)₆^3?/4? /MUA system. For Ru(NH₃)₆^3+/2+ , temperature can greatly improve the electrochemical reaction in both MUA and GSH modified electrodes, which is ascribed to temperature‐induced diffusion and convection and the electrostatic interaction between Ru(NH₃)₆^3+/2+ and negatively charged carboxyl groups on the electrode surface.     

Large lanthanide-induced chemical shifts in cobalt complexes of enethials (α,β-unsaturated thioaldehydes)

Eu(fod)₃-, Yb(fod)₃- and Pr(fod)₃-induced chemical shifts of the ‘thioaldehydic’ protons in enethial ligands complexed to a cobalt cyclopentadienyl group are unusually large and in the same direction (10–30 ppm downfield per mole of shift reagent per mole of substrate). The shifts of the protons induced by Eu(fod)₃ and Pr(fod)₃ in the enethial ligands show an alternation in sign on proceeding away from the sulfur atom. In contrast to the results with the fod reagents, the ytterbium and lanthanum shift reagents Yb(thd)₃ and La(thd)₃ caused only small shifts of protons in the 2-phenylpropenethial ligand. No induced shifts with the Eu or Pr reagents were observed for a cyclopentadienyl cobalt complex of dithioglyoxal. The induced shifts in these enethial complexes may be caused by varying blends of complex formation, contact and pseudocontact shifts. Caution is advised in assigning origins to lanthanide induced shifts in such organometallic systems.     

Direct cytochrome c electrochemistry at boron-doped diamond electrodes

Highly boron-doped diamond electrodes are characterized voltammetrically employing Ru(NH₃)₆^3+/2+, Fe(CN)₆^3−/4−, benzoquinone/hydroquinone, and cytochrome c redox systems. The diamond electrodes, which are polished to nanometer finish, are initially `activated' electrochemically and then pretreated by oxidation, reduction, or polishing. All electrodes give reversible cyclic voltammetric responses for the reduction of Ru(NH₃)₆³⁺ in aqueous solution.Redox systems other than Ru(NH₃)₆^3+/2+ show characteristic electrochemical behavior as a function of diamond surface pretreatment. In particular, the horse heart cytochrome c redox system is shown to give reversible voltammetric responses at Al₂O₃ polished boron-doped diamond electrodes. No voltammetric response for cytochrome c is detected at anodically pretreated diamond electrodes. The observations are attributed to preferential interaction of the polished diamond surface with the reactive region of the cytochrome c molecule and low interference due to a lack of protein electrode fouling.     

Excited State Tuning of Bis(tridentate) Ruthenium(II) Polypyridine Chromophores by Push–Pull Effects and Bite Angle Optimization: A Comprehensive Experimental and Theoretical Study

The synergy of push–pull substitution and enlarged ligand bite angles has been used in functionalized heteroleptic bis(tridentate) polypyridine complexes of ruthenium(II) to shift the ¹MLCT absorption and the ³MLCT emission to lower energy, enhance the emission quantum yield, and to prolong the ³MLCT excited‐state lifetime. In these complexes, that is, [Ru(ddpd)(EtOOC‐tpy)][PF₆]₂, [Ru(ddpd‐NH₂)(EtOOC‐tpy)][PF₆]₂, [Ru(ddpd){(MeOOC)₃‐tpy}][PF₆]₂, and [Ru(ddpd‐NH₂){(EtOOC)₃‐tpy}][PF₆]₂ the combination of the electron‐accepting 2,2′;6′,2′′‐terpyridine (tpy) ligand equipped with one or three COOR substituents with the electron‐donating N,N′‐dimethyl‐N,N′‐dipyridin‐2‐ylpyridine‐2,6‐diamine (ddpd) ligand decorated with none or one NH₂ group enforces spatially separated and orthogonal frontier orbitals with a small HOMO–LUMO gap resulting in low‐energy ¹MLCT and ³MLCT states. The extended bite angle of the ddpd ligand increases the ligand field splitting and pushes the deactivating ³MC state to higher energy. The properties of the new isomerically pure mixed ligand complexes have been studied by using electrochemistry, UV/Vis absorption spectroscopy, static and time‐resolved luminescence spectroscopy, and transient absorption spectroscopy. The experimental data were rationalized by using density functional calculations on differently charged species (charge n=0–4) and on triplet excited states (³MLCT and ³MC) as well as by time‐dependent density functional calculations (excited singlet states).     

Supramolecular microrods can be prepared by mixing aqueous Ru(NH<Subscript>3</Subscript>)<Subscript>6</Subscript>Cl<Subscript>3</Subscript> and K<Subscript>3</Subscript>Fe(CN)<Subscript>6</Subscript> solutions at room temperature

This paper describes the ionic self-assembly method to fabricate supramolecular one-dimensional microrods in solution. Such microrods were formed in a one-step process through the mixing aqueous Ru(NH₃)₆Cl₃ and K₃Fe(CN)₃ solutions at room temperature. Chemical composition of the resulting structures, which are composed of from Fe(CN)₆⁴⁻ and Ru(NH₃)₆³⁺, was determined by energy-dispersed spectroscopy. The data show that the formation of microrods depends on the molar ratio and concentration of the reactants.     

Elongated Thrombin Binding Aptamer: A G‐Quadruplex Cation‐Sensitive Conformational Switch

Aptamer‐based biosensors offer promising perspectives for high performance, specific detection of proteins. The thrombin binding aptamer (TBA) is a G‐quadruplex‐forming DNA sequence, which is frequently elongated at one end to increase its analytical performances in a biosensor configuration. Herein, we investigate how the elongation of TBA at its 5′ end affects its structure and stability. Circular dichroism spectroscopy shows that TBA folds in an antiparallel G‐quadruplex conformation with all studied cations (Ba²⁺, Ca²⁺, K⁺, Mg²⁺, Na⁺, NH₄⁺, Sr²⁺ and the [Ru(NH₃)₆]^2+/3+ redox marker) whereas other structures are adopted by the elongated aptamers in the presence of some of these cations. The stability of each structure is evaluated on the basis of UV spectroscopy melting curves. Thermal difference spectra confirm the quadruplex character of all conformations. The elongated sequences can adopt a parallel or an antiparallel structure, depending on the nature of the cation; this can potentially confer an ion‐sensitive switch behavior. This switch property is demonstrated with the frequently employed redox complex [Ru(NH₃)₆]³⁺, which induces the parallel conformation at very low concentrations (10 equiv per strand). The addition of large amounts of K⁺ reverts the conformation to the antiparallel form, and opens interesting perspectives for electrochemical biosensing or redox‐active responsive devices.     

Decomposition thermique du trichlorure de ruthenium hexammine

The thermal decomposition of [Ru(NH₃)₆]Cl₃ leads between 200 and 400° in inert gas to metallic ruthenium through the intermediates [Ru(NH₃)₅Cl]Cl₂, [Ru(NH₃)₄Cl₂]Cl and [Ru(NH₃)₃Cl₃]. In the total decomposition $$[Ru(NH_3 )_6 ]Cl_3 \to Ru + 1/2N_2 + 3NH_3 + HCl + 2NH_4 Cl$$ finely divided ruthenium is obtained above 240°. In oxygen the same intermediates are formed, the final product, however, being the metal and its dioxide.     

Clay modified electrodes: Part VI. Aluminum and silicon pillared clay-modified electrodes

Metal (Ru, Os, Fe) bipyridyl complexes and Ru(NH₃)³⁺₆ were incorporated into several montmorillonite clays and their aluminum and silicon-pillared analogues. Film concentrations and apparent diffusion coefficients were measured and compared by using spectrophotometry, cyclic voltammetry and chronocoulometry. The catalytic role of isomorphously substituted iron was evaluated and implicated by its effects on Ru(bpy)³⁺₃ voltammetric behavior. A model is proposed for charge transport within the novel silicon-pillared clay.     

Homo- und Hetero-Zweikernkomplexe des D2h-symmetrischen Bis(chelat)-Liganden 2,2′-Bipyrimidin mit den elektronenreichen Metallfragmenten Mo(CO)4, Re(CO)3Cl, [Cu(PPh3)2]+ und [Ru(bpy)2]2+

Homo- and Heterodinuclear Complexes of the D_2h-symmetric Bis(chelate) Ligand 2,2′-Bipyrimidine with Electron-Rich Metal Fragments Mo(CO)₄, Re(CO)₃Cl, [Cu(PPh₃)₂]⁺, and [Ru(bpy)₂]²⁺ All homo- and heterodinuclear complexes (L_nM)(μ-bpym)(ML_n)′, bpym = 2,2′-bipyrimidine, ML_n (ML_n)′ = Mo(CO)₄, Re(CO)₃Cl, [Cu(PPh₃)₂]⁺, [Ru(bpy)₂]²⁺, have been synthesized and studied by cyclic voltammetry, absorption spectroscopy, and by electron spin resonance of singly reduced forms. The individual capabilities of the low-valent metal fragments to undergo oxidation and to shift the reduction potential of the bpym π acceptor ligand on coordination combine to result in variable electrochemical potential differences. After consideration of different Franck-Condon factors, absorption intensities, additional low-lying unoccupied orbitals of the bridging acceptor ligand and solvatochromic effects, we have assigned the considerably varying metal-to-ligand charge transfer transitions in the visible.