A fluorinated ruthenium porphyrin as a potential photodynamic therapy agent: synthesis, characterization, DNA binding, and melanoma cell studies

When the new porphyrin 5,10-(4-pyridyl)-15,20-(pentafluorophenyl)porphyrin is reacted with 2 equiv of Ru(bipy)(2)Cl(2) (where bipy = 2,2'-bipyridine) formation of the target ruthenated porphyrin is achieved with 40% yield. Strong electronic transitions are observed in the visible region of the spectrum associated with the porphyrin Soret and four Q-bands. A shoulder at slightly higher energy than the Soret band is attributed to the Ru(dpi) to bipy(pi*) metal to ligand charge transfer (MLCT) band. The bipyridyl pi to pi* transition occurs at 295 nm. Cyclic voltammetry experiments reveal two single-electron redox couples in the cathodic region at E(1/2) = -0.80 and -1.18 V vs Ag/AgCl associated with the porphyrin. Two overlapping redox couples at E(1/2) = 0.83 V vs Ag/AgCl due to the Ru(III/II) centers is also observed. DNA titrations using calf thymus (CT) DNA and the ruthenium porphyrin give a K(b) = 7.6 x 10(5) M(-1) indicating a strong interaction between complex and DNA. When aqueous solutions of supercoiled DNA and ruthenium porphyrin are irradiated with visible light (energy lower than 400 nm), complete nicking of the DNA is observed. Cell studies show that the ruthenated porphyrin is more toxic to melanoma skin cells than to normal fibroblast cells. When irradiated with a 60 W tungsten lamp, the ruthenium porphyrin preferentially leads to apoptosis of the melanoma cells over the normal skin cells.     

Adsorptive stripping voltammetric properties of fentanyl at Hg electrode

Cyclic voltammetry shows that in a supporting electrolyte of NaOH, fentanyl (FENT) has a pair of cathodic and anodic peaks at Hg electrode. The peak potentials, E(pc) and E(pa), are -1.47 and -1.44 V (vs. Ag/AgCl), respectively. Fentanyl can be adsorbed on Hg surface, so the cathodic peak shows adsorptive properties. The adsorptive characteristics of fentanyl are explored in detail with various methods. The adsorbed species is considered to be fentanyl neutral molecule. The method for measuring trace amount of fentanyl by adsorptive stripping voltammetry is established. Under the optimised condition, the detection limit may reach 5 x 10(-8)M with a 10-min preconcentration.     

Synthetic nanocrystalline diamond as a third-generation biosensor support

Horseradish peroxidase (HRP) has been immobilized on the surface of functionalized nanocrystalline diamond (NCD) thin films. The structure of the modified NCD surface as well as the electrochemical behavior of the whole system was characterized by impedance spectroscopy and cyclic voltammetry. The proximity of HRP heme groups to the NCD surface allowed direct electron transfer between them, resulting in two separated one-electron-transfer peaks at 0.05 V and 0.29 V vs Ag/AgCl, corresponding to the cathodic and anodic process, respectively. The heterogeneous electron-transfer constant for both processes was calculated to be 0.066 s(-1), the charge-transfer coefficient alpha = 0.49, and the immobilized enzymatic layer about 2.10(-10) mol/cm2. The modified NCD electrode was used as a third-generation biosensor for hydrogen peroxide determination showing a linear response in the 0.1-45 mM H2O2 range, at +0.05 V vs Ag/AgCl.     

Molecular photoelectric switch using a mixed SAM of organic [60]fullerene and [70]fullerene doped with a single iron atom

We describe a photoswitch fabricated on indium tin oxide (ITO) as a self-assembled monolayer (SAM) of two fullerene molecules, a purely organic [60]fullerene that generates an anodic current and a [70]fullerene doped with a single iron atom. This device generates a bidirectional photocurrent upon irradiation at 340 and 490 nm. The new [70]fullerene iron complex bearing three rigid carboxylic acid legs, Fe[C(70)(C(6)H(4)C(6)H(4)COOH)(3)]Cp, generates only a cathodic current upon photoexcitation between 350 and 700 nm, whereas the organic [60]fullerene absorbs at wavelengths shorter than 500 nm. The quantum efficiency of the photocurrent generation by the mixed SAM is comparable to that of a single-component SAM, indicating that the individual diode molecules on ITO generate photocurrents independently with little cross talk.     

Voltammetric determination of dopamine in the presence of ascorbic acid at a chemically modified electrode

A Nafion/ruthenium oxide pyrochlore chemically modified electrode (CME) was used for the selective determination of dopamine (DA) in the presence of a high concentration of ascorbic acid by square-wave voltammetry. Compared to a bare glassy carbon electrode, the CME exhibits an apparent shift of the oxidation potentials in cathodic direction and a marked enhancement of the current response. The selective sensing of DA is achieved by combining the electrocatalytic function of the ruthenium oxide pyrochlore catalyst with the charge-exclusion and preconcentration features of Nation. With a preconcentration time of 60 s at a potential of −0.3 V (vs. Ag/AgCl), linear calibration plots are obtained for dopamine in 0.1 M, phosphate buffer (pH 7.4) over 0–20 μM with a detection limit (3σ) of 0.1 μM.     

Voltammetry of a Novel Antimycobacterial Agent 1‐Hydroxy‐N‐(4‐nitrophenyl)naphthalene‐2‐carboxamide in a Single Drop of a Solution

The aim of this study is the development of a miniaturized voltammetric method for the determination of an antimycobacterial agent 1‐hydroxy‐N‐(4‐nitrophenyl)naphthalene‐2‐carboxamide (HNN) in a single drop (20 μL) of a solution by cathodic and anodic voltammetry at a glassy carbon electrode. Cyclic voltammetry was used to investigate its redox properties followed by the optimization of differential pulse voltammetric determination in a regular 10 mL volume. The optimal medium for the analytical application of both cathodic and anodic voltammetry was found to be Britton‐Robinson buffer pH 7.0 and dimethyl sulfoxide (9 : 1, v/v). HNN gave one cathodic peak at around −0.6 V and one anodic peak at around +0.2 V vs. Ag|AgCl (3 mol L⁻¹ KCl) reference electrode. Determination of HNN in a 10 mL volume gave the limit of quantification around 10 nmol L⁻¹ by both adsorptive stripping anodic and cathodic voltammetry. Afterwards, miniaturized voltammetric methods in a single drop of solution (20 μL) were investigated. This approach requested some modifications of the cell design and voltammetric procedures. A novel method of removing dissolved oxygen in a single drop had to be developed and tested. Developed miniaturized voltammetric methods gave parameters comparable to the determination of HNN in 10 mL. The applicability of the miniaturized method was verified by the determination of HNN in a drop of a bacterial growth medium.     

聚吡咯纳米阵列电极的光电化学

以多孔的铝阳极氧化膜(AAO)为模板制备了直径约为80 nm聚吡咯(PPy)纳米线的阵列电极, 并研究了它的光电化学响应. 结果表明, 在电极电位低于－0.1 V(vs Ag/AgCl)时出现的阴极光电流是由聚吡咯纳米线的p型半导体性质引起的, 其平带电位为－0.217 V. 聚吡咯纳米线的长度对光电流的影响较大, 最佳长度为42 nm. 这是因为在很短的聚吡咯纳米线阵列中PPy太少, 产生的光电流弱, 而在过长的聚吡咯纳米线阵列中光生电子在到达电极基底前易于与光生空穴复合而消失. 聚吡咯纳米线有可能作为纳米光电器件用于未来微器件系统.     

Adsorption and release behavior of bare and DNA-wrapped-carbon nanotubes on self-assembled monolayer surface

The adsorption and release behavior of single-stranded DNA-wrapped single-walled carbon nanotubes (ssDNA-w-SWCNTs) on alkylthiol self-assembled monolayer (SAM) surface was systematically characterized by cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Fast electron transfer between bare Au electrode and redox species blocked by the alkylthiol SAM can be restored by SWCNTs or ssDNA-w-SWCNTs. The release of ssDNA-w-SWCNTs is carried out by positive or negative desorption potential. SWCNTs/SAM or ssDNA-w-SWCNTs/SAM is completely removed from Au surface at +0.90 V or -1.40 V (vs. 3.0 M KCl|Ag|AgCl). The controlled release of SWCNTs/SAM and ssDNA-w-SWCNTs/SAM holds great promise for gene delivering.     

银掺杂聚L-酪氨酸修饰电极同时测定多巴胺、肾上腺素和抗坏血酸

用循环伏安法制备银掺杂聚L-酪氨酸修饰玻碳电极,研究了多巴胺、肾上腺素和抗坏血酸在其电极上的电化学行为,建立了同时测定多巴胺、肾上腺素和抗坏血酸的新方法。当3种组分共存时,在磷酸盐缓冲溶液(pH6.0)中,扫描速率为140mV/s,多巴胺和肾上腺素在修饰电极上分别产生还原峰,峰电位分别为0.198和-0.205V,多巴胺和肾上腺素氧化峰重叠,峰电位为0.313V(vs.Ag/AgCl);抗坏血酸产生一个氧化峰,峰电位0.108V(vs.Ag/AgCl)。多巴胺和肾上腺素的ΔEpc=0.403V,抗坏血酸的氧化峰与多巴胺和肾上腺素的ΔEpa=0.205V,用还原峰和氧化峰可同时测定多巴胺、肾上腺素和抗坏血酸,3种组分同时测定的线性范围分别为5.0×10-6～1.0×10-4mol/L,8.0×10-6～1.0×10-4mol/L和3.0×10-5～1.0×10-3mol/L;检出限分别为5.0×10-7,8.0×10-7和5.0×10-6mol/L。本方法用于人尿液中多巴胺、肾上腺素和抗坏血酸的同时测定,结果满意。     

Indirect measurement of brucine by adsorptive stripping voltammetry at mercury electrode

After reaction with nitric acid, brucine can be transformed into cacotheline, and then measured indirectly by adsorptive stripping voltammetry. This method is based on the adsorptive accumulation of cacotheline at a hanging mercury drop electrode, followed by cathodic linear sweep voltammetry. The cathodic peak potential is about -0.35 V (vs. saturated Ag AgCl ). The detection limit of 2.0 x 10(-9) M is obtained under optimized conditions. The electrochemical behaviour of cacotheline and the mechanism of the electrode reactions are discussed.     

Differential pulse cathodic stripping voltammetry of the copper complexes of glycyl-L-histidyl-glycine at a hanging mercury drop electrode

The behaviour of the copper complexes of glycyl-L-histidyl-glycine (GHG) was investigated using cyclic voltammetry and differential pulse voltammetry after their adsorptive accumulation on the surface of a hanging mercury drop electrode (HMDE). The nature of the observed cathodic and anodic peaks was established and optimum conditions were found for the differential pulse cathodic stripping voltammetric detemination of GHG at the 1 x 10(-8)M concentration level using adsorptive accumulation at -0.20 V vs. Ag/AgCl reference electrode and the cathodic stripping peak around -0.4 V (pH 8.3). This peak corresponds to the reduction of the Cu(I)-GHG complex formed at the HMDE surface as an intermediate in the reduction of Cu(II)-GHG to Cu(O)amalgam.     

Redox characteristics of Schiff base manganese and cobalt complexes related to water-oxidizing complex of photosynthesis

In an effort to obtain synthetic analogues of water-oxidizing complex (WOC) of photosystem II (PS II) of plant photosynthesis, a Schiff base manganese and a cobalt complex, employing Niten, a SALEN type ligand, have been prepared. Cyclic and square wave voltammetric measurements have been performed to assess their redox characteristics. Both complexes undergo several reduction processes in cathodic negative potential region at more or less similar potentials. In view of these reductions being independent of the nature of the metal, they are thought to be ligand-localized. Although similar in negative region, a marked difference in the behavior of the complexes is observed in anodic region. While the cobalt complex is electrochemically inactive in the positive potentials up to +1.0 V vs. Ag/AgCl, the manganese complex displays two oxidation waves at +0.25 and +0.5 V vs. Ag/AgCl. The presence of oxidation wave in manganese complex at +0.5 V vs. Ag/AgCl or +0.7 V vs. NHE suggests that this complex can catalyze the oxidation of water and can, thus, simulate the WOC of PS II.     

Adsorptive stripping voltammetry of a fentanyl derivative at a mercury electrode

In a supporting electrolyte of NaOH, a pair of cathodic and anodic peaks of N,N'-diphenyl-N,N'-bis(1-phenylmethyl-4-piperidinyl)-ethanediamide (DBPPE) is found by cyclic voltammetry at a Hg electrode. The cathodic and anodic peak potentials are -1.53 and -1.46 V (vs. Ag/AgCl), respectively. The cathodic peak shows adsorptive characteristics when the concentration of DBPPE is low and the preconcentration time is long. The adsorbed species is most probably the DBPPE neutral molecule. The method for measuring trace amount of DBPPE by adsorptive stripping voltammetry is established and the detection limit can reach 5 x 10(-9)M with a 6-min preconcentration.     

First observation of luminescence from tris(2,2'-bipyridine)ruthenium(II) triggered by anodic oxidation of oligodeoxyribonucleotide.

Anodic oxidation of oligodeoxyribonucleotide in an alkaline aqueous medium containing tris(2,2'-bipyridine)ruthenium(II) (Ru(bpy)3(2+)) was shown to cause luminescence around +1.3 V (vs. Ag/AgCl) with a maximal intensity at approximately 600 nm, possibly originating from Ru(bpy)3(2+) in the d-pi* triplet state. A pivotal initial stage in the light production path was postulated to be the anodic oxidation of 2-deoxyribose residue. This reaction seems to be available for the determination of sub-micromol dm(-3) levels of oligodeoxyribonucleotide.     

The electrooxidation behavior of bilirubin in DMF and DMF + H_2O mixed solvent

The electrooxidation of Bilirubin (BR) in N,N'-dimethylformamide (DMF) and DMF + H_2O mixed solvent is investigated by voltammetry techniques, in situ rapid scan thin layer spectroelectrochemistry and in situ ESR spectroscopy. The data reveal that the oxidation process of BR undergoes many stages, which are all sped up by the introduction of water. The species of bilirubin taking part in the reaction is found to be changed from BR in DMF into BR' in the mixed solvents and the anodic peak potential is shifted correspondingly from +0.58 V to +0.026-+0.35 V (vs. Ag/AgCl, 1.0 M KCl). Free radicals and the dimerization of them are observed during the oxidation.     

Determination of Titanium in Water Solutions

Titanium(IV) dissolved in water solution can be successfully determined using adsorptive cathodic stripping square‐wave voltammetry in the presence of the mixed ligand system acetylacetone – lumazin (2,4‐dihydoxypteridin) maintaining pH at about 6. The method is additionally very sensitive due to the possibility of variation of square‐wave voltammetric parameters such as frequency and/or amplitude. The reduction peak of the titanium mixed ligand complex was detected at the potential of ?1.49 V (vs. Ag/AgCl) and a limit of detection was found to be 0.4 nM with the accumulation time of 20 minutes at the potential of ?1.2 V in the UV‐irradiated artificial seawater. Interferences of other trace metal ions and surface‐active substances were investigated as well.     

Voltammetric Studies on the Electrochemical Reduction of Methylmercury in HCl Aqueous Medium at a Carbon Microelectrode

Fast scan voltammetry applied to methylmercury in chloride medium at a carbon fiber microelectrode has shown two cathodic peaks located at ?0.45 and ?1.1 V and a single anodic peak at ?0.33 V (vs. Ag|AgCl). It was concluded that the reoxidation process, at high sweep rates, in acidic media behaves as a reversible one‐electron transfer process coupled to a chemical reaction, with the reaction product weakly adsorbed. Good linear calibration plots for the methylmercury determinations in the concentration range from 75 to 300 μM, have been obtained using the currents of the anodic peak measured on the CVs recorded, at 10 V s^?1, at a carbon fiber microelectrode, in a stationary solution of methylmercury chloride. Data have shown that the carbon microelectrode, cycled continuously in the analyte, can replace the dropping mercury electrode (DME), with the advantages that the carbon microelectrode is a promising tool for further studies in high resistive media, such as in natural waters.     

The inducing NO-vasodilation by chemical reduction of coordinated nitrite ion in cis-[Ru(NO(2))L(bpy)(2)](+) complex

The synthesis of [Ru(NO(2))L(bpy)(2)](+) (bpy = 2,2'-bipyridine and L = pyridine (py) and pyrazine (pz)) can be accomplished by addition of [Ru(NO)L(bpy)(2)](PF(6))(3) to aqueous solutions of physiological pH. The electrochemical processes of [Ru(NO(2))L(bpy)(2)](+) in aqueous solution were studied by cyclic voltammetry and differential pulse voltammetry. The anodic scan shows a peak around 1.00 V vs. Ag/AgCl attributed to the oxidation process centered on the metal ion. However, in the cathodic scan a second peak around -0.60 V vs. Ag/AgCl was observed and attributed to the reduction process centered on the nitrite ligand. The controlled reduction potential electrolysis at -0.80 V vs. Ag/AgCl shows NO release characteristics as judged by NO measurement with a NO-sensor. This assumption was confirmed by ESI/MS(+) and spectroelectrochemical experiment where cis-[Ru(bpy)(2)L(H(2)O)](2+) was obtained as a product of the reduction of cis-[Ru(II)(NO(2))L(bpy)(2)](+). The vasorelaxation observed in denuded aortic rings pre-contracted with 0.1 mumol L(-1) phenylephrine responded with relaxation in the presence of cis-[Ru(II)(NO(2))L(bpy)(2)](+). The potential of rat aorta cells to metabolize cis-[Ru(II)(NO(2))L(bpy)(2)](+) was also followed by confocal analysis. The obtained results suggest that NO release happens by reduction of cis-[Ru(II)(NO(2))L(bpy)(2)](+) inside the cell. The maximum vasorelaxation was achieved with 1 x 10(-5) mol L(-1) of cis-[Ru(II)(NO(2))L(bpy)(2)](+) complex.     

Electrochemical generation of free nitric oxide from nitrite catalyzed by iron meso-tetrakis(4-N-methylpyridiniumyl)porphyrin

Electrochemical generation of free nitric oxide (NO) from nitrite (NO(2)(-)) catalyzed by iron meso-tetrakis(4-N-methylpyridiniumyl)porphyrin, [Fe(III)(TMPyP)](5+), has been developed in this study. To obtain free NO, a cathodic electrolysis and an anodic electrolysis were performed in two connected flow electrolytic cells in sequence. The flow electrolytic cell upstream was used for cathodic electrolysis, where the solution of [Fe(III)(TMPyP)](5+) and NO(2)(-) was reduced at -0.25 V (vs Ag/AgCl) into [Fe(II)(NO(2)(-))(2)(TMPyP)](2+) and [Fe(II)(NO)(TMPyP)](4+) in sequence. The flow electrolytic cell downstream was utilized for anodic electrolysis, where [Fe(II)(NO)(TMPyP)](4+) formed from the upstream cell was oxidized at +0.40 V (vs Ag/AgCl) into [Fe(III)(TMPyP)](5+) and free NO. Finally, NO was bubbled out from anodic electrolyte by argon gas. The mechanism and the optimum conditions for electrochemical generation of NO from NO(2)(-) catalyzed by [Fe(III)(TMPyP)](5+) were studied in detail by voltammetric and spectroelectrochemical methods.     

Stripping voltammetric determination of traces of peptides and proteins containing disulphide linkages

Stripping voltammetry has been investigated for the determination of traces of ribonuclease, somatostatin, oxytocin, felypressin, insulin and oxidized glutathione at concentrations down to 1.5 × 10^?9 M. Repeated cyclic potential scans with an initial cathodic scan were used after accumulation at +0.1 to –0.3 V vs. Ag/AgCl at a hanging mercury drop electrode. In presence of excess of copper(II) ion, the first two compounds yield a well-defined peak couple at ?0.5 to ?0.6 V, with cathodic and anodic peaks of equal height, the accumulated product being adsorbed in both its oxidized and reduced state. Oxytocin and felypressin first yield two unresolved cathodic peaks, one of which disappears in the second scan cycle. Oxidized glutathione yields a large cathodic peak but a small anodic peak because of desorption in the reduced state. Excess of copper(II) is reduced during the accumulation, so that the electrode is actually copper amalgam. The peaks obtained with copper(II) present are considered to be due to redox reactions of copper complexes formed with the cysteine parts of the molecules. These peaks are suitable for quantitative purposes; calibration equations are given. Without copper(II), the substances show stripping responses of different complexity and magnitude. Insulin gives usable stripping peaks only without copper ions.