Effects of Residual Silanol on Solid Phase Extraction of Organic Compounds to Octadecylsilyl Silica.

Batchwise equilibrium study was carried out on the retention of nonpolar and polar organic compounds to octadecylsilyl (ODS) silicas of different properties at atmospheric pressure. While nonpolar compounds were retained only by distribution on the ODS phase, polar compounds were retained by both distribution and Langmuir-type adsorption on residual silanol. Retention on ODS silica with more silanol proceeded at a higher rate than retention on ODS silica with less silanol and was reversible on this solid phase extraction time-scale. An increase in surface density of ODS decreased the distribution constant, due to a decrease in fraction of ODS functioning as an extracting medium and also decreased the saturated adsorption amount, due to reductions of the residual silanol and the functioning ODS. The ODS silica with the lowest ODS density showed a distribution constant 31 times higher and a saturated adsorption amount 27 times higher than the ODS silica with the highest ODS density. On the other hand, because the interaction between the organic part and the ODS group introduced at higher density is strengthened, the adsorption constant is increased by about 5 times compared to the low density ODS silica. The electronic effects of substituents to nitrogen- and oxygen-containing compounds on retention were discussed. In conclusion, ODS silica with an appreciable amount of residual silanol is superior for solid phase extraction.

Effects of Functional Group Density in Stylene-Divinylbenzene Copolymer Phase and of Supporting Electrolyte Concentration in Aqueous Phase on Performance of Iminodiacetate-type Chelating Resin in Terms of Contribution of Ion-Exchange Mechanism.

The effects of the functional group density in the stylene-divinylbenzene copoymer phase and of the supporting electrolyte concentration in the aqueous phase on the perfomance of the iminodiacetate (IDA)-type chelating resin were studied in terms of contribution of an ion-exchange mechanism. High hydrophobicity of the resin having a low functional group density interfered with penetration of aqueous solutions into the resin phase to slow the acid-base reaction and the adsorption reaction. Uptake of the cation in the supporting electrolyte into the resin phase was clearly indicated in each of two acid dissociation reactions. The high concentration of the supporting electrolyte enhanced acid dissociation of the IDA group, and a singly deprotonated species interacting with the supporting electrolyte cation strongly interfered with adsorption by the ion-exchange mechanism, while only slightly interfering with adsorption by the complexation. Both the complexed and ion-exchanged species respectively involving two or more IDA groups were destabilized to reduce the adsorption capacity of the resin having the low functional group density.

Interactions of Anion-Exchange Resins with Polyacrylates in Atmosphere.

The interactions of polyacrylates (PAs with mean molecular weight of 4.5, 25, and 250 kDa; Na+,pa-) with anion exchange resins in the Br- form (AXRs; -R+,Br-) were studied under practical conditions by reaction stoichiometry and spectroscopy. The stoichiometric or an excess amount of PA(4.5 kDa) completely replaced Br- in the AXRs of the cross-linking degree of 2 or 8%, respectively, to give (-R+,pa-), due to enhancement in selectivity of carboxylate group by multiple interactions. In contrast, PA(250 kDa) exchanged Br- only on the surface of AXRs and did not penetrate into the resins; CO2 was involved in the system to induce exchange with CO32-. Using the slightly acidic condition caused substantially no exchange by CO32- but induced coextraction of PA with proton as free Hpa. PA(4.5 kDa) once penetrating into the resin phase as (-R+,pa-) or free Hpa was reversibly eluted under the appropriate conditions.

Erratum: Analytical Sciences, 2016, Vol. 32, No. 3, p. 343, Enhanced Retention of Chelating Reagents in Octadecylsilyl Silica Phase by Interaction with Residual Silanol Groups in Solid Phase Extraction of Divalent Metal Ions.

On page 343, the abstract, the second line,with which octadecylsilyl silica (ODS), was impregnated with was studiedshould readwith which octadecylsilyl silica (ODS) was impregnated, was studied.

Enhanced Retention of Chelating Reagents in Octadecylsilyl Silica Phase by Interaction with Residual Silanol Groups in Solid Phase Extraction of Divalent Metal Ions.

Solid-phase extraction (SPE) of divalent metal ions with a lipophilic and potentially divalent hexadentate chelating reagent (H2L), with which octadecylsilyl silica (ODS), was impregnated with was studied to gain more insight into and develop the potential of this methodology. This is the first time to demonstrate that this reagent as well as other common nitrogen-containing reagents were retained both by adsorption due to hydrogen bonding between nitrogen atoms of the reagent and residual silanol groups in the ODS phase and by simple distribution into the hydrophobic space. An appreciably large amount of this reagent could be retained by the adsorption mechanism even with a relatively thin loading solution. The divalent metal ions of Mn(2+), Co(2+) and Zn(2+) were extracted as 1:1 neutral complexes ([ML]), while Ni(2+) and Cu(2+) as ion-pairs of 1:1 cationic complex ([MHL](+)) with anion in SPE with H2L. The extractability and selectivity were substantially the same as that in liquid-liquid extraction.

Iridium(III) Bis-Pyridine-2-Sulfonamide Complexes as Efficient and Durable Catalysts for Homogeneous Water Oxidation.

A family of tetradentate bis(pyridine-2-sulfonamide) (bpsa) compounds was synthesized as a ligand platform for designing resilient and electronically tunable catalysts capable of performing water oxidation catalysis and other processes in highly oxidizing environments. These wrap-around ligands were coordinated to Ir(III) octahedrally, forming an anionic complex with chloride ions bound to the two remaining coordination sites. NMR spectroscopy documented that the more rigid ligand frameworks-[Ir(bpsa-Cy)Cl2](-) and [Ir(bpsa-Ph)Cl2](-)-produced C1-symmetric complexes, while the complex with the more flexible ethylene linker in [Ir(bpsa-en)Cl2](-) displays C2 symmetry. Their electronic structure was explored with DFT calculations and cyclic voltammetry in nonaqueous environments, which unveiled highly reversible Ir(III)/Ir(IV) redox processes and more complex, irreversible reduction chemistry. Addition of water to the electrolyte revealed the ability of these complexes to catalyze the water oxidation reaction efficiently. Electrochemical quartz crystal microbalance studies confirmed that a molecular species is responsible for the observed electrocatalytic behavior and ruled out the formation of active IrOx. The electrochemical studies were complemented by work on chemically driven water oxidation, where the catalytic activity of the iridium complexes was studied upon exposure to ceric ammonium nitrate, a strong, one-electron oxidant. Variation of the catalyst concentrations helped to illuminate the kinetics of these water oxidation processes and highlighted the robustness of these systems. Stable performance for over 10 days with thousands of catalyst turnovers was observed with the C1-symmetric catalysts. Dynamic light scattering experiments ascertained that a molecular species is responsible for the catalytic activity and excluded the formation of IrOx particles.

Disposable molecular valve consisting of alginate gel.

A disposable molecular valve, consisting of a membrane coated with alginate gel, which is partially cross-linked with Ca(2+), was developed based on a volume change and/or dissolution of the gel in response to the cation concentration. The valve automatically opened upon an increase in the concentration of cations such as H(+), Na(+), Ca(2+), Mg(2+), Cu(2+), or Al(3+). The concentration where the valve opens was 1 x 10(-4) to 2 x 10(-4) M for Ca(2+), Cu(2+), and Al(3+), but the solution volume passed vs. concentration increased in the order of Ca(2+), Cu(2+), and Al(3+). For Na(+) and Mg(2+) the valve opening concentration was ca. 1 x 10(-2) and 1 x 10(-3) M, respectively. Two mechanisms were proposed to account for the opening of the valve. One is due to a shrinking of the gel caused by cations; the other is due to dissolution of the gel. The former corresponds for the cases of Ca(2+), Cu(2+), and Al(3+), and the latter does for Na(+) and Mg(2+). The valve closed over the pH range from 3 to 12, whereas it opened below and above this range. The effects of anions and pressure were also studied.

Biosensing of an indoor volatile organic compound on the basis of fungal growth.

A fungal biosensor plate was applied to assessment of the harmfulness of air polluted by formaldehyde. Alternariaalternata, Eurotiumherbariorum and Aspergilluspenicillioides were used as fungal species. Fungal mycelium length and optical transparency of the biosensor plate were employed as indices of the fungal growth. Formaldehyde in air was detected on the basis of growth inhibition, reflected by suppression of the growth indices. Dynamic range of the measurement was 700-4000 microg m(-3) or broader. Eurotiumherbariorum and Aspergilluspenicillioides were the most suitable fungal species to formaldehyde sensing based on the mycelium length and that based on the transparency, respectively.

Electrochemiluminescence of Ru(II) complexes immobilized on a magnetic microbead surface: distribution of magnetic microbeads on the electrode surface and effect of azide ion.

The electrochemiluminescence (ECL) of magnetic microbeads modified with tris(2,2'-bipyridine)ruthenium(II) ([Ru(bpy)3]2+) was studied in the presence of tri-n-propylamine (TPA) to develop highly sensitive ECL detection system, where the employed microbead has a diameter of 4.5 microm. The ECL signal of the [Ru(bpy)3]2+ derivative-modified magnetic microbeads was found to be affected by the geometrical distribution of the magnetic microbeads on the electrode surface. The ECL peak intensity increased with increasing the number of the beads on the electrode surfaces up to 1.6 x 10(6) beads cm(-2), although above 1.6 x 10(6) beads cm(-2), it decreased. The ECL decrease arises from the physical prevention of the ECL from reaching the photomultiplier tube by the excessive beads. The observed peak ECL signal of the [Ru(bpy)3]2+ derivative-modified magnetic microbeads in the presence of NaN3, which serves as a preservative substance, mainly appeared at a potential of +0.90 V vs Ag/AgCl where [Ru(bpy)3]2+ is hardly oxidized, whereas the ECL signal in the absence of NaN3 appeared at a potential of +1.15 V. The presence of NaN3 on the electrode surface retards formation of an oxide layer on the electrode surfaces and promotes TPA oxidation. The ECL response at +0.90 V was mainly attributed to ECL reaction of excited-state [Ru(bpy)3]2+* formed by oxidation of [Ru(bpy)3]+ with TPA radical cation, where the [Ru(bpy)3]+ was generated by reduction of [Ru(bpy)3]2+ with TPA radical.

Three-dimensional motion and transformation of a photoelectrochemical actuator.

A new "photoelectrochemical actuator" consisting of poly(acrylic acid)/copper gel and TiO2 nanoparticles has been developed, which undergoes reversible expansion/contraction upon UV light irradiation/termination, likely due to dissociation/formation of carboxylic group/Cu2+ binding.

Dinitrophenyl ligand substrates and their application to immunosensors.

We present an approach for the development of highly specific and sensitive antibody based biosensors by chemically tailoring the sensor surface with materials that control specific and nonspecific binding of biologically relevant molecules. As a model system we employed surface immobilized 2,4-dinitrophenyl (DNP)-ligands that bind specifically to anti-DNP antibodies. Self-assembling characteristics and minimization of the nonspecific interactions were used in the ligand design. The redox activity of the DNP-head group was used to calculate the surface density (coverage) of these assemblies using cyclic voltammetry. Quartz crystal microbalance (QCM) and impedance analysis were used to assess the ligand-antibody interaction and estimate the quantity of antibodies bound to the surface. The ligand surface density and the QCM data were useful in determining the sensitivity of our model system. A simple two-step kinetic model was shown to fit the experimental data.

Electrodes modified with the phase transition polymer and heme peptide: biocatalysis and biosensing with tunable activity and dynamic range.

An electrode was modified with a phase transition polymer, poly(N-isopropylacrylamide), and the polymer was further modified with a peroxidase model compound, heme peptide (HP). As the polymer layer shrank at temperatures above 30-40 degrees C, the catalytic activity of the HP molecules for H(2)O(2) reduction improved, and simultaneously, the number of HP molecules that can communicate electrochemically with the electrode increased. As a result, the catalytic current for H(2)O(2) reduction in the shrunken state was 4 times larger than that in the swollen state. This reversible change was exploited for tuning the sensitivity and dynamic range of the HP electrode in H(2)O(2) biosensing. The dynamic range in inhibition-based biosensing of imidazole derivatives was also tunable.

Amperometric biosensing systems based on motility and gravitaxis of flagellate algae for aquatic risk assessment.

Electrochemical biosensing systems for toxic substances were developed on the basis of motility and negative gravitaxis of the unicellular flagellate Chlamydomonas reinhardtii. Changes in the flagellar movement of the flagellates in response to three toxic chemicals, toluene, copper(II) sulfate, and nickel(II) chloride, were monitored as changes in the redox currents for a coexisiting redox marker. The gravitaxis-based flagellate biosensing system was more sensitive to toluene than the motility-based system. A thin-layer flagellate biosensor was also developed. In comparison with the conventional algal biosensors monitoring the photosynthetic activity, the gravitaxis-based thin-layer sensor was more sensitive by more than 1 order of magnitude.

Toward selectivity control of a heme peptide electrode by modification with a phase-transition polymer.

Reduction currents for H2O2 at a heme peptide (HP)-modified electrodes are suppressed by inhibitors, such as imidazole derivatives. Although this inhibition effect allows determinations of the total inhibition ability of imidazole derivatives, it has no selectivity. In this study the selectivity control of HP-modified electrodes for imidazole derivatives was performed utilizing the thermoresponsive phase transition of poly(N-isopropylacrylamide), which was chemically immobilized on HP-modified electrodes. The inhibition ratios for imidazole derivatives appeared to be small at temperatures below the lower critical solution temperature (LCST), and to be large above the LCST. This change was ascribed to a steric hindrance caused by a phase transition of the polymer. On the other hand, the inhibition ratio for histamine, which has a larger molecular size relative to imidazole, was not significantly changed by the phase transition. Thus, the selectivity of the HP-modified electrode was found to be controllable using an immobilized phase-transition polymer.

Iron(II) and copper(I) coordination polymers: electrochromic materials with and without chiroptical properties.

The electrochemical and optical properties of films prepared from two different Fe(II) coordination polymers (TPT[Fe(II)TPT](n)(PF(6))(2)(n) (TPT = terpyridine-phenyl-terpyridine) and CTPCT[Fe(II)CTPCT](n)(PF(6))(2)(n) (CTPCT = chiral terpyridine-phenyl-chiral terpyridine)) and a coordination polymer based on Cu(I) metal centers (PDP[Cu(I)PDP](n)(BF(4))(n)) (PDP = phenanthroline-dodecane-phenanthroline) have been studied. The oxidation of a PDP[Cu(I)PDP](n)(BF(4))(n) film coated on an indium-tin oxide (ITO) electrode by stepping the potential from 0.0 to +1.4 V vs Ag/AgCl led not only to the complete bleaching of the absorption in the visible region of the spectrum within 5 min but also to a redox-induced dissociation and dissolution of the polymer. The reverse reaction of binding and reassembling the polymer at the electrode surface, upon stepping the potential back to 0.0 V, occurred with a rate which was at least 1 order of a magnitude slower. In contrast, the bis(2,2':6',2' '-terpyridine)iron(II)-based redox polymers TPT[Fe(II)TPT](n)(PF(6))(2)(n) and CTPCT[Fe(II)CTPCT](n)(PF(6))(2)(n), during similar spectroelectrochemical experiments, not only exhibited a dramatically enhanced switching rate but also displayed symmetric switching kinetics. The films did not show signs of deterioration over 150 switching cycles. Additionally, in an effort to assemble an electrochromic device with chiroptical properties, the electrochromism of films generated from the enantiomerically pure CTPCT[Fe(II)CTPCT](n)(PF(6))(2)(n) polymer was studied through circular dichroism.

Photophysics and redox behavior of chiral transition metal polymers.

The absorption and emission spectra, excited-state lifetimes, quantum yields, and electrochemical measurements have been obtained for a new series of chiral complexes based on three different chiral 2,2':6',2' '-terpyridine ligands, (-)-ctpy, (-)-[ctpy-x-ctpy], and (-)-[ctpy-b-ctpy], with one, two, or multiple Ru metal centers. The room-temperature absorption and emission maxima of [[((-)-ctpy)Ru]-(-)-[ctpy-b-ctpy]-[Ru((-)-ctpy)]](PF(6))(4) and ((-)-[ctpy-b-ctpy])-[[Ru((-)-[ctpy-b-ctpy])](PF(6))(2)](n) were shifted to lower energies and also exhibited significantly longer luminescence lifetimes when compared to [Ru((-)-ctpy)(2)](PF(6))(2), [[((-)-ctpy)Ru]-(-)-[ctpy-x-ctpy]-[Ru((-)-ctpy)]](PF(6))(4), and ((-)-[ctpy-x-ctpy])-[[Ru((-)-[ctpy-x-ctpy])](PF(6))(2)](n). In terms of their electrochemical behavior, all of the complexes studied exhibited one Ru-centered and two ligand-centered redox waves and the [[((-)-ctpy)Ru]-(-)-[ctpy-x-ctpy]-[Ru((-)-ctpy)]](PF(6))(4), ((-)-[ctpy-x-ctpy])-[[Ru((-)-[ctpy-x-ctpy])](PF(6))(2)](n), and ((-)-[ctpy-b-ctpy])-[[Ru((-)-[ctpy-b-ctpy])](PF(6))(2)](n)() complexes were found to electrodeposit upon ligand-based reduction. The difference between the formal potentials of the Ru-centered and the first ligand-centered (least negative) waves corresponded linearly with the changes in the observed emission energies. The shifts in energy are discussed using a particle-in-a-box model, and the luminescence lifetimes are discussed in terms of the structure of the excited-state manifold.

Redox induced reversible structural transformations of dimeric and polymeric phenanthroline-based copper chelates.

The synthesis and characterization of copper complexes of the phenanthroline based bridging ligands, 9-methyl-2-(2-[4-[2-(9-methyl-1,10-phenanthrolin-2-yl)ethyl]phenyl]ethyl)-1,10-phenanthroline, 1, and 1,12-bis(9-methyl-1,10-phenanthroline-2-yl)dodecane, 2, are presented. Whereas in the first case a discrete dimeric complex [Cu(2)(1)(2)](BF(4))(2) was formed, in the latter, a coordination polymer [2(Cu(2))(n)](BF(4))(n) resulted. Both of these materials have been characterized by cyclic voltammetry (CV), the electrochemical quartz crystal microbalance (EQCM), and UV-vis spectroscopy and the results compared to those of the monomeric [Cu(dmp)(2)](BF(4)) (dmp is 2,9-dimethyl-1,10-phenanthroline) species. Oxidation of the dimeric species results in its precipitation and reduction results in stripping of the deposited layer as ascertained from CV and EQCM measurements. The electrooxidation of the copper centers in the coordination polymer results in changes in the coordination which are fully reversible upon reduction. The dissociation/regeneration of the coordination polymer as a function of the redox state of the copper centers has been characterized by CV, EQCM, and UV-vis spectroelectrochemistry.

Catechol-Pendant Terpyridine Complexes: Electrodeposition Studies and Electrocatalysis of NADH Oxidation.

The synthesis, spectroscopic characterization, and electrochemical characterization, including the electrodeposition onto glassy carbon (GC) and platinum (Pt) electrodes, of electroactive films of the homoleptic catechol-pendant terpyridine complexes [M(L(2))(2)](2+) (where M = Co, Cr, Fe, Ni, Ru, and Os, and L(2) = 4'-(3,4-dihydroxyphenyl)-2,2':6',2' '-terpyridine) are described. The potential dependence of the deposition was probed through electrochemical quartz crystal microbalance (EQCM) studies. Multilayer equivalent films were found to deposit at potentials less than that of the catechol oxidation process. Whereas the heteroleptic ruthenium(II) complex [Ru(tpy)(L(2))](2+) (tpy = 2,2':6',2' '-terpyridine) did not deposit onto electrode surfaces, the corresponding osmium(II) heteroleptic complex [Os(tpy)(L(2))](2+) deposited onto Pt and GC electrodes, suggesting that the metal center can play an important role in the deposition process. The heteroleptic cobalt(II) complex [Co(v-tpy)(L(2))](2+) (v-tpy = 4'-vinyl-2,2':6',2' '-terpyridine) was found to deposit onto Pt or GC electrodes through either a catechol-based deposition or a v-tpy-based electropolymerization, depending on the potential range over which a homogeneous solution of the complex was cycled. The electrochemical response of [Co(L(2))(2)](2+)-modified GC electrodes in aqueous solution was robust and pH-dependent over the pH range 1-11, suggesting that the catechol moieties retain their pH-dependent redox activity upon immobilization. The application of these complexes, in solution and as electrodeposited films, to the electrocatalytic oxidation of NADH was also probed. [Co(L(2))(2)](2+) in solution plus [Co(L(2))(2)](2+)- and [Co(v-tpy)(L(2))](2+)-modified GC electrodes were found to catalyze the oxidation of NADH in pH 7 phosphate buffer solution.