Binding of Stimuli-Responsive Ruthenium Aqua Complexes with 9-Ethylguanine.

Stimuli-responsive ruthenium complexes proximal- and distal-[Ru(C10tpy)(C10pyqu) OH2]2+ (proximal-1 and distal-1; C10tpy = 4'-decyloxy-2,2':6',2″-terpyridine and C10pyqu = 2-[2'-(6'-decyloxy)-pyridyl]quinoline) were experimentally studied for adduct formation with a model DNA base. At 303 K, proximal-1 exhibited 1:1 adduct formation with 9-ethylguanine (9-EtG) to yield proximal-[Ru(C10tpy)(C10pyqu)(9-EtG)]2+ (proximal-RuEtG). Rotation of the guanine ligand on the ruthenium center was sterically hindered by the presence of an adjacent quinoline moiety at 303 K. Results from 1H NMR measurements indicated that photoirradiation of a proximal-RuEtG solution caused photoisomerization to distal-RuEtG, whereas heating of proximal-RuEtG caused ligand substitution to proximal-1. The distal isomer of the aqua complex, distal-1, was observed to slowly revert to proximal-1 at 303 K. In the presence of 9-EtG, distal-1 underwent thermal back-isomerization to proximal-1 and adduct formation to distal-RuEtG. Kinetic analysis of 1H NMR measurements showed that adduct formation between proximal-1 and 9-EtG was 8-fold faster than that between distal-1 and 9-EtG. This difference may be attributed to intramolecular hydrogen bonding and steric repulsion between the aqua ligand and the pendant moiety of the bidentate ligand..

Deep-sea in situ determination of sulfide using a sensitized chemiluminescent terbium complex.

A new chemiluminescence (CL) method based on the chemiluminescent reaction between sulfide and an acidic permanganate solution was used to quantify sulfide in seawater. A terbium-pipemidic acid complex was used as CL enhancer. The method was used to determine sulfide in the concentration range of 1-30 µmol/L in artificial seawater samples. The limit of detection of the method was 21 nmol/L sulfide. The sensitivity of the CL method was eight times higher than that of the CL method reported previously. Br- ions, which are conservative ions, interfered with sulfide. We investigated the effects of salinity, water temperature, and interfering chemicals,such asheavy-metal ions and organic matter, on the performance of the CL method. In addition, sulfite-spiked natural seawater samples were analyzed. The results demonstrate that the CL method can be used to develop a deep-sea sulfide analyzer.

A visible-light and temperature responsive host-guest system: the photoisomerization and inclusion complex formation of a ruthenium complex with cyclodextrins.

In the present study, we investigated the visible-light- and thermal-stimuli-responsive properties of a host-guest system based on proximal- and distal-[Ru(C10tpy)(C10pyqu)OH2]2+ complexes (proximal and distal-1; C10tpy = 4'-decyloxy-2,2':6',2''-terpyridine and C10pyqu = 2-[2'-(6'-decyloxy)-pyridyl]quinoline). The analogs of such ruthenium aqua complexes are well-known as metallodrugs and catalysts. The proximal isomer has a dicationic ruthenium center and hydrophobic alkyl chains on both ligands, with the two alkyl chains located close together. According to titration experiments, proximal-1 binds to γ-cyclodextrin (γ-CD) in aqueous media with a binding constant of K1:1 = 520 ± 60 M-1, which is much higher than the corresponding values for α-CD and ß-CD. Additional experiments indicated that the two alkyl chains were incorporated into the cavity of γ-CD. The photoisomerized complex, distal-1, exhibits thermal isomerization back to proximal-1 in the dark with a kobs = 7.26 ± 0.01 × 10-6 s-1. In the presence of γ-CD, the corresponding rate constant is 1.3 times higher, which is attributed to the steric repulsion of cyclodextrin and the aqua ligand by the inclusion complex formation between distal-1 and the cyclodextrins. The distal isomer has a lower affinity for CDs because the two alkyl chains are more separated. The repeated application of external stimuli to a mixture of proximal-1 and γ-CD resulted in a reproducible and reversible host-guest complex formation.

Proton spin relaxation study with pulsed NMR on the plasticization of Na+ ion-selective electrode membranes prepared from PVCs with different degrees of polymerization.

The proton spin-spin relaxation times (T2) of ion-selective electrode membranes with differences in the polymerization degree of the incorporated poly(vinyl chloride) (PVC) polymers were investigated. T2 measurements were performed using Hahn-Echo, Solid-Echo and Carr-Purcell-Meiboom-Gill (CPMG) pulse sequences. Analyses of the T2 measurements by Hahn-Echo pulse sequences could realize the estimation of the homogeneity and compatibility for a series of ion-selective electrode membranes and reveal a relationship with the electromotive force (EMF) response in the low-concentration region of the Na+ ions. On the other hand, the normalized derivative spectra from T2 measurements by Solid-Echo and CPMG pulse sequences could approximately visualize the degree of plasticization for such potentiometric polymeric membranes. Moreover, differences in the polymerization degrees of the incorporated PVCs were scarcely found to affect the selectivity coefficients of the Na+-ISEs based on bis(12-crown-4).

Investigation of Polyurethane Matrix Membranes for Salivary Nitrate ISFETs to Prevent the Drift.

We have investigated human-stress monitoring by making use of salivary nitrate, which can be a candidate for stress markers, with ion-selective field-effect transistors (ISFETs). ISFETs are suitable for on-site single-drop analysis of salivary nitrate within 10 s. However, when ISFETs are used for salivary nitrate, ISFETs have a problem that is called the initial drift. The initial drift makes accurate nitrate monitoring difficult. Thus, the purpose of this study is to prevent the initial drift and to search for a new, simple polymer to possess a better performance of sensor responses than conventional matrix membranes, such as PVC. In this research, we investigated ISFETs using specific matrix membranes, for example KP-13, Pellethane®--, and P7281-PU. The initial drift was evaluated from the fluctuations of the response values generated by the ISFETs when immersed in saliva or aqueous solution. As a result, P7281-PU showed a prevention effect on the initial drift, both in the whole saliva and in various solutions. Furthermore, the cause of drift may be H+ diffusion, and the drift prevention effect of P7281-PU may be affected by urethane bond capturing H+ in the ion-selective membrane. This result suggests that a continuous nitrate monitoring is feasible and may be applied to wearable sensors.

A C3-substituted cyclotriveratrylene derivative with 8-quinolinyl groups as a fluorescence-enhanced probe for the sensing of Cu2+ ions.

C 3-Substituted cyclotriveratrylene (CTV) derivatives were considered suitable candidates for recognition compounds due to their unique structures. In this study, a C3-substituted CTV derivative with three fluorogenic 8-quinolinyl groups (1) was designed and prepared as a fluorescent probe. The synthesized CTV derivative 1 exhibited a selective response of fluorescence enhancement toward Cu2+ ions among the examined cations. The sensing ability of CTV derivative 1 toward Cu2+ ions was superior to that of the previously reported C3-substituted CTV derivative with three 2-quinolinyl groups (2). It is, thus, suggested that the CTV structure plays an important role in selective sensing ability toward Cu2+ ions since the mono-quinoline compound 5 showed fluorescence properties toward the Cr3+, Fe2+ and Fe3+ ions in addition to Cu2+ ions. In other words, the high Cu2+ ion-selectivity of CTV derivative 1 was demonstrated even in the presence of other co-existing examined cations. Moreover, it was found that CTV derivative 1 could work as a reversible fluorescence-enhanced probe toward Cu2+ ions by the simple addition of Et3N.

Bis(1-pyrenylmethyl)-2-benzyl-2-methyl-malonate as a Cu2+ Ion-Selective Fluoroionophore.

A new malonate possessing two pyrene moieties was synthesized as a fluoroionophore, and its structure and fluorescence spectroscopic properties were investigated. When excited at 344 nm in acetonitrile/chloroform (9:1, v/v), the synthesized bispyrenyl malonate has the fluorescence of intramolecular excimer (λem = 467 nm) emissions and not a pyrene monomer emission (λem = 394 nm). A large absolute fluorescence quantum yield was obtained in the solid state (ΦPL = 0.65) rather than in solution (ΦPL = 0.13). X-ray crystallography analysis clarified the molecular structure and alignment of the bispyrenyl malonate in the crystal phase, elucidating its fluorescence spectroscopic properties. Such analysis also suggests there are intramolecular C-H···π interactions and intermolecular π···π interactions between the pyrenyl rings. Interestingly, the synthesized bispyrenyl malonate exhibits excellent fluorescence sensing for the Cu2+ ion. Remarkable fluorescence intensity enhancement was only observed with the addition of the Cu2+ ion.

Enhanced chemiluminescence for trazodone trace analysis based on acidic permanganate oxidation in concurrent presence of rhodamine 6G.

A new sensitized chemiluminescence method by acidic permanganate oxidation was developed for the sensitive determination of trazodone. A fluorescent dye as used rhodamine 6G to increase a chemiluminescence intensity. Under optimum conditions, the liner range of the calibration curve was obtained for 1-5000 nmol/L. The limit of detection was calculated from 3σ of a blank was 0.23 nmol/L. The coexistent ions and substances had no interference with the chemiluminescence measurement. The chemiluminescence spectra were measured to elucidate a possible mechanism for the system. The present method was satisfactorily used in the determination of the drugs in pharmaceutical samples and animal serums.

Influence of Introduced Substituents on the Anion-selectivity of [14]Tetraazaannulene Complexes.

Nickel(II) complexes of [14]tetraazaannulene derivatives incorporating aromatic rings into their azaannulene framework were synthesized, and the anion-selectivity of the [14]tetraazaannulene nickel complexes 1 - 4 was evaluated by potentiometric measurements with solvent polymeric membrane electrodes. All of the [14]Tetraazaannulene nickel complexes, except 3, were found to exhibit high selectivity for the I(-) ion over the SCN(-) ion, although considerable interference of the ClO4(-) ion was observed in all 1 - 4 complexes. Concerning the anion-selectivities of 1 and 4, the incorporation of naphthalene rings into the azaannulene framework decreased not only the interference of the ClO4(-) ion but also the I(-) ion-selectivity over the SCN(-) ion. Comparison studies between the dibenzotetraaza[14]annulene nickel complexes 1 - 3 indicated that differences in the attached substituents of the [14]tetraazaannulene nickel complexes greatly influenced the ion-selectivity as ionophores. According to our computational results, the ionophoric properties of [14]tetraazaannulene nickel complexes 1 - 4 were influenced by their electrostatic properties rather than their topological properties.

Evaluation of the plasticization of ion-selective electrode membranes by pulsed NMR analyses.

The potentiometric polymeric membranes for ion-selective electrodes were evaluated by analyses of the proton spin-spin relaxation times T2 with pulsed NMR. The T2 measurements were performed using the Hahn-Echo, Solid-Echo and CPMG pulse sequences. The T2 values and fractions F of each component were obtained by analyses of the FID signals measured with the Hahn-Echo pulse sequence. The softer potentiometric polymeric membrane possessed the main fraction F(L), providing a relatively longer T(2L) value. A linear relationship existed between the weight ratio of the membrane solvent and ln T(2L) (or ln total T2×F). This analysis method could quantify the degree of hardness or softness of the potentiometric polymeric membranes with the differences in the membrane solvent weight. The normalized derivative spectra were acquired from the transverse magnetization M(t) data measured by using the Solid-Echo and CPMG pulse sequences. In the normalized derivative spectra of the potentiometric polymeric membranes, most PVC peaks in the short time region shifted to a larger area of long time regions by plasticization, and the softer potentiometric polymeric membrane incorporating more membrane solvent exhibited a relaxation peak in the relatively longer time region. Thus, the normalized derivative spectra were effective in elucidating the compatibility of the PVC with the membrane solvent.

Ion-selective electrodes based on L-tryptophan and L-tyrosine.

Novel ion-selective electrodes (ISEs) based on amino acids have been developed. L-Tryptophan and L-tyrosine, which are amino acids, are employed as ionophores for solvent polymeric membrane electrodes. The proposed ISEs show rapid Nernstian responses for the Cu(2+) ion over the concentration ranges of 3.0×10(-4)-1.0×10(-1) M. These ISEs exhibit comparatively good selectivity with respect to alkaline, alkaline earth, and some transition and heavy metal ions and the ammonium ion. The ISE based on tryptophan also indicates the Nernstian response for the benzylammonium ion.

A new solvent polymeric membrane electrode incorporating poly(N-isopropylacrylamide) as a polymer.

Here, we report on a new solvent polymeric membrane electrode incorporating thermoresponsive poly(N-isopropylacrylamide) (PIPA) as a polymer with the lower critical solution temperature (LCST) of ca. 32 °C. The response of the solvent polymeric membrane electrode to the ions changes at 25 and 40 °C. Pulsed NMR analyses demonstrated the novel effects of the LCST behaviour on the potentiometric polymeric membrane.

Determination of sulfide with acidic permanganate chemiluminescence for development of deep-sea in-situ analyzers.

A new chemiluminescence method is proposed for the determination of sulfide in seawater based on the chemiluminescence reaction between sulfide and an acidic permanganate solution. 3-Cyclohexylaminopropanesulfonic acid was used as a chemiluminescence enhancer. By use of this method, 1-150 µM of sulfide could be determined in artificial seawater. The limit of detection was 0.17 µM sulfide. We investigated the effects of salinity, water temperature, and interfering chemicals such as heavy-metal ions and organic matter. In addition, natural seawater spiked with sulfide was analyzed. The results showed that the CL method could be applied to a deep-sea sulfide analyzer.

Pulsed NMR analysis of ion-selective electrode membranes.

A novel method for evaluation of ion-selective electrode membranes was reported with the proton spin-spin relaxation time T(2) by pulsed NMR. The proton spin-spin relaxation time T(2) measurements provided valuable information about properties of the whole membrane matrix. The softer potentiometric liquid membrane possessed a large fraction F(L) providing relatively longer T(2) value. Pulsed NMR method can quantify the degree of the plasticization of ion-selective electrode membranes.

A Cu2+ ion-selective fluoroionophore with dual off/on switches.

A new malonamide fluoroionophore possessing two pyrene moieties was synthesized. This bispyrene exhibited the fluorescence of the pyrene monomer (lambda(em) = 395 nm) and intramolecular excimer (lambda(em) = 467 nm) emissions. The designed derivative showed the excellent ion sensing ability to Cu2+. The "on-off-off" and "off-on-off" fluorescence responses were demonstrated by the addition of the variable Cu2+ concentration. The utilization of the dual off/on responses could apply to the estimation of the rough Cu2+ concentration.

C(3)-functionalized cyclotriveratrylene derivative bearing quinolinyl group as a fluorescent probe for Cu(2+).

A new C(3)-functionalized cyclotriveratrylene (CTV) bearing three fluorogenic quinolinyl groups was synthesized and studied as a fluorescent probe. The CTV derivative exhibited a selective response of fluorescence enhancement toward Cu(2+). The fluorescence intensity in CH(3)CN was increased until the [Cu(2+)]/[CTV derivative] mole ratio was 3. Moreover, C(3)-functionalized CTV(2-quinolinemethyl)(3) was applied to a visible fluorescent probe by using a plasticized polymeric membrane. The emission profile was observed by a fluorescence microscope after immersing the membrane in a 1 x 10(-5) M aqueous solution of Cu(2+).