Electrogenerated chemiluminescence reaction of tris(2,2'-bipyridine)ruthenium(II) with 2,5-dimethylthiophene as co-reactant in aqueous solution

A novel effective co-reactant for electrogenerated chemiluminescence (ECL) of Ru(bpy)(3)(2+) has been found. Alpha-position-dialkylated thiophene derivatives such as 2,5-dimethylthiophene (DMT) could be used as a co-reactant for Ru(bpy)(3)(2+) ECL. The reaction mechanism of the Ru(bpy)(3)(2+)/DMT system was proposed on the basis of the identification of the reaction product, the relationship between the molecular structure and the chemiluminescent intensity, and the electrochemical study. The obtained reaction mechanism was similar to that of the Ru(bpy)(3)(2+)/aliphatic tertiary amine system. Based on these results, the preliminary studies of the Ru(bpy)(3)(2+) ECL detection system using DMT as a co-reactant were performed. Under the optimal ECL conditions, the plot of ECL intensity versus the concentration of Ru(bpy)(3)(2+) was linear over the concentration range 1.0x10(-8) to 1.5x10(-7) M (determination coefficient=0.9996).     

Electrogenerated chemiluminescence. 81. Influence of donor and acceptor substituents on the ECL of a spirobifluorene-bridged bipolar system

The electrochemistry and radical ion annihilation electrogenerated chemiluminescence (ECL) of 9,9'-spirobifluorene-bridged bipolar systems containing 1,3,4-oxadiazole-conjugated oligoaryl and triarylamine substituents were investigated. The stability of the oxidized spirobifluorenes was improved by functionalization with triarylamine centers. These donor-acceptor (DA) compounds exhibited a good fluorescence efficiency with an emission maximum that correlated with the potential difference between radical anion and cation formation, suggesting a charge transfer (CT) emission band. An ECL mechanism based on the formation of the CT excited state by radical ion annihilation or production of the triplet state followed by triplet-triplet annihilation, with perhaps some excimer contribution, is proposed.     

Electrochemiluminescent detection of labile radical intermediates of electrochemical reactions

The article considers the basic principles of electrochemiluminescent spin traps diagnostic method which consists of efficient trapping of intermediate labile radical products (free radicals of complex organic molecules) by electrogenerated radical ions of electrochemiluminescers in different liquid-phase systems including bioobjects. The method permits qualitative and quantitative identification of such particles by measurement of electrolysis radical recombination luminescence (electrogenerated chemiluminescence) intensity which is emitted by electrolyzed solutions of organic electrochemiluminescers. The unique possibilities of the method are illustrated on examples of experimental study of systems with sodium tetraphenylborate and chloride ion.     

Persistent Chemiluminescent Glow of Phenoxy-dioxetane Luminophore Enables Unique CRET-Based Detection of Proteases

Chemiluminescence is being considered an effective imaging modality as it offers low background and high sensitivity. Recent discovery by our group has led to development of new phenoxy-dioxetane chemiluminescence luminophores, which are highly bright under physiological conditions. However, the current scope of probes based on these luminophores is limited, as they can only be turned on by phenol protecting group removal. Here we present a new chemiluminescence resonance energy transfer (CRET) system, Glow-CRET, in which light emission is triggered by proteolytic cleavage of a peptide substrate that links a dioxetane luminophore and a quencher. In order to compose such system, a new phenoxy-dioxetane luminophore, 7-HC-CL, was developed. This luminophore exhibits intense and persistent glow chemiluminescence; it undergoes very slow chemiexcitation, and it has the highest chemiluminescence quantum yield ever reported under physiological conditions. Based on 7-HC-CL, a Glow-CRET probe for matrix metalloproteinases, MMP-CL, was synthesized. Incubation of MMP-CL with its cognate protease resulted in 160-fold increase in chemiluminescence signal. MMP-CL was also able to detect matrix metalloproteinase activity in cancer cells with significantly higher signal-to-background ratio than an analogous fluorescence resonance energy transfer (FRET)-based probe. This work is expected to open new horizons in chemiluminescence imaging, as it enables to use the dioxetanes in ways that had not been possible. We anticipate that 7-HC-CL and future derivatives will be utilized not only for the construction of further Glow-CRET probes, but also for other applications, such as chemiluminescence tagging of proteins.     

Electrochemistry, spectroscopy, and electrogenerated chemiluminescence of some star-shaped truxene-oligofluorene compounds

We report electrochemical studies, spectroscopy, and electrogenerated chemiluminescence (ECL) of four monodisperse star-shaped truxene core-oligofluorene compounds (T1-T4). All oligomers produced stable radical anions and radical cations and showed blue ECL by ion annihilation with an intensity that could be seen with the naked eye. ECL spectra showed that all ECL emissions were at the same position as the fluorescence emission, except for T1, the compound with the shortest fluorene arms that produced some longer wavelength emission in addition to that seen in the fluorescence spectrum. When tetra-n-butylammonium oxalate was used as a coreactant for T1, the emission was much weaker than that in ion annihilation with the same long-wavelength emission observed, making it unlikely that this emission can be ascribed to excimer formation. The ECL intensity of T4 was about 80% of the common blue ECL emitter, 9,10-diphenylanthracene (DPA), under similar conditions.     

Scanning electrochemical microscopy study of ion annihilation electrogenerated chemiluminescence of rubrene and [Ru(bpy)3]2+

Scanning electrochemical microscopy (SECM) was used for the study of electrogenerated chemiluminescence (ECL) in the radical annihilation mode. The concurrent steady-state generation of radical ions in the microgap formed between a SECM probe and a transparent microsubstrate provides a distance-dependent ECL signal that can provide information about the kinetics, stability, and mechanism of the light emission process. In the present study, the ECL emission from rubrene and [Ru(bpy)(3)](2+) was used to model the system by carrying out experiments with the SECM and light-detecting apparatus inside an inert atmosphere box. We studied the influence of the distance between the two electrodes, d, and the annihilation kinetics on the ECL light emission profiles under steady-state conditions, as well as the ECL profiles when carrying out cyclic voltammetry (CV) at a fixed d. Experimental results are compared to simulated results obtained through commercial finite element method software. The light produced by annihilation of the ions was a function of d; stronger light was observed at smaller d. The distance dependence of the ECL emission allows the construction of light approach curves in a similar fashion as with the tip currents in the feedback mode of SECM. These ECL approach curves provide an additional channel to describe the reaction kinetics that lead to ECL; good agreement was found between the ECL approach curve emission profile and the simulated results for a fast, diffusion-limited second-order annihilation process (k(ann) > 10(7) M(-1) s(-1)). In the CV mode at fixed distance, the ECL emission of rubrene showed two distinct signals at different potentials when fixing the substrate to generate the radical cation and scanning the tip to generate the radical anion. The first signal (pre-emission) corresponded to an emission well before reaching the generation of the radical anion and was more intense on Au than on Pt. The second ECL signal showed the expected steady-state behavior from the second-order annihilation reaction and agreed well with the simulation. A comparison of the emission obtained with rubrene and [Ru(bpy)(3)](2+) to test the direct formation of lower energy triplets directly at the electrode showed that triplets are not the cause of the pre-emission observed. Wavelength selection experiments for the rubrene system showed that the pre-emission ECL signal also appeared slightly red-shifted with respect to the main luminophore emission; a possible explanation for this phenomenon is inverse photoemission, where the injection of highly energetic holes by the oxidized species into the negatively biased tip electrode causes emission of states in the metal that appear at a different wavelength than the singlet emission from the ECL luminophore.     

Solvent Effect on the Chemiluminescence of Acridinium Thioester: A Computational Study

Chemiluminescent labelling, which is one of the promising procedures of modern immunodiagnostics, is increasingly carried out using acridinium derivatives, an oxidant, and an alkaline aqueous environment. However, the efficiency of the chemiluminescence of luminol or acridinium esters is higher in non-aqueous solvents such as dimethyl sulfoxide or acetonitrile. Therefore, the search for a new environment for the chemiluminescence reaction, especially the one characterized by a higher quantum yield of chemiluminescence, is one of the aims of current research. Using computational methods (DFT and TD DFT with PCM model of solvent), we examined thermodynamic and kinetic data concerning the chemiluminescence and competitive dark pathways. Our results suggest that better characteristics of the chemiluminescence reaction of acridinium thioester are observed in nonpolar solvents, such as methylcyclohexane, n-hexane and n-pentane, than in aqueous media used so far. Further experimental verification is necessary to confirm the possible application of proposed nonpolar solvents in chemiluminescent labelling and hence in immunodiagnostics.     

Electrogenerated chemiluminescence of the lithium salts of 8-hydroxyquinoline and 2-methyl-8-hydroxyquinoline

The spectroscopy, electrochemistry, and electrogenerated chemiluminescence (ECL) of [(q)(qH)Li]x (qH=8-hydroxyquinolinato) and [(Meq)(MeqH)Li]x (MeQH=2-methyl-8-hydroxyquinolinato) have been investigated. In both acetonitrile and aqueous solutions, [(q)(qH)Li]x and [(Meq)(MeqH)Li]x have absorption maxima at 320 and 309 nm, respectively. When excited at these wavelengths, the complexes emit around 500 nm (blue-green) in acetonitrile. Photoluminescence efficiencies (phiem) were 0.036 for [(q)(qH)Li]x and 0.012 for [(Meq)(MeqH)Li]x when compared to Ru(bpy)3(2+) (bpy=2,2'-bipyridine) with phiem=0.042. No photoluminescence was observed in aqueous media. The complexes show irreversible oxidative electrochemistry and quasi-reversible reductions in acetonitrile. ECL efficiencies (phiecl) were 0.097 for [(q)(qH)Li]x and 0.080 for [(Meq)(MeqH)Li]x when compared to Ru(bpy)(3)2+ (phiecl=1) in aqueous buffered solution and 0.035 for [(q)(qH)Li]x and 0.028 for [(Meq)(MeqH)Li]x in acetonitrile (0.05 M tri-n-propylamine (TPrA) as an oxidative-reductive ECL co-reactant). The ECL peaks at a potential corresponding to oxidation of both the TPrA and [(q)(qH)Li]x or [(Meq)(MeqH)Li]x. Also, qualitative studies using transmission filters suggest that both complexes emit ECL in approximately the same blue-green region as their photoluminescence, indicating that the same excited state is formed in both experiments.     

Current efficiency and titration efficiency in coulometric titrations with electrogenerated ceric ion determination of iodide

The current efficiency for the electrogeneration of cerie ion at a platinum anode falls considerably below 100% at both very small and at large current densities in both sulfuric and perchloric acid media. The maximal current efficiency is about 99.8%.Iodide ion can be titrated to iodine with an error of only about +0.3%, even under conditions where the cerie ion generation efficiency is only 98%. High titration efficiency, in spite of poor efficiency for ceric ion generation, is obtained because iodine is oxidized to iodate ion at a potential slightly in advance of the potential at which cerous ion is oxidized. Since the electrogenerated iodate ion oxidizes iodide ion only a minor fraction of the total quantity of electricity results from ceric ion generation, so the effect of its inefficient generation is greatly minimized. Satisfactory titrations of iodide ion to iodine can be performed without any cerous salt present, provided the generating current density is smaller than the limiting current density for oxidation of iodine to iodate ion.     

13-Hydroxyacenaphato[1,2-b]quinolizinium bromide as a new flouorescence indicator

13-Hydroxyacenaphtho[1,2-b]quinolizinium bromide (13-HQBr)was selected as a fluorescence indicator to determine basic compounds in non-aqueous media. This compound possesses an acidic phenolic hydroxyl group. It presents varying absorption (ROH, 408, 430 nm; RO(-) 456, 478 nm) and excitation spectra (ROH, 425 nm; RO, 471 nm) depending on the pH of the media, but the same emission fluorescence spectrum (ROH = RO(-), 526 nm) at different pH in buffered aqueous solutions. However, in acidic non-aqueous media (acetic, formic and trifluoroacetic acids), it can be observed that the fluorescence emission spectra differ for the ionized (lambda(em) = 530 nm) and non-ionized (lambda(em) = 440, 470 nm) forms. The fluorescence intensity at the characteristic peaks depends on the acid-base equilibria in the ground and excited states. Therefore, this property could be used to evaluate the concentration of basic compounds, showing a good linearity range between fluorescence intensity and basic sample concentration.     

In Process Citation

Oxidation with vanadium pentoxide in aqueous sulphuric acid has certain limitations, mainly because of the instability of vanadosulphate complexes in aqueous media. Hence the possibility of use of less strongly dissociative solvents than water has been examined with a view to enhancing the stability and oxidizing power of these complexes. Some simple organic oxygen compounds (alcohols, aldehydes, ketones and acids) have been examined as reductants, together with some others (acetals and esters) which are difficult to study in aqueous media because of the hydrophobic character. The results show that alcohols are more resistant to attack in non-aqueous medium than in water, and that the longer-chain alcohols are more easily oxidized. The aldehydes are more difficult to oxidize than ketones, as is also the case in water. The acids, also as in water, react only very feebly. The use of non-aqueous media extends the range of oxidation with vanadate to some substances insoluble in water (such as epoxides) which display sufficient reactivity.     

Highly efficient quenching of coreactant electrogenerated chemiluminescence by phenolic compounds

We describe the quenching effects of phenolic compounds on the electrogenerated chemiluminescence (ECL) of the Ru(bpy)3(2+) (bpy = 2,2'-bipyridine)/tri-n-propylamine (TPrA) system in aqueous solution. First, the emissions via different ECL routes were examined in the presence of 1,4-benzoquinone. It was found that the interception of the ECL intermediate radicals by the quencher molecules significantly influenced the light emission, especially when the direct coreactant oxidation played a predominant role in producing ECL. The most efficient quenching was observed for the low-oxidation-potential (LOP) ECL at a low concentration of TPrA (<5 mM). The Stern-Volmer constant (K(SV)) of the LOP ECL quenching could be as high as 1.3 x 10(6) M(-1), approximately 700 times larger than that of the photoluminescence quenching. Other phenolic compounds, such as phenol, hydroquinone, catechol, and dopamine, would be oxidized at the potential where the ECL was generated, and the benzoquinone-containing products exhibited ECL quenching effects similar to that of 1,4-benzoquinone. The highly efficient quenching of the LOP ECL by the phenolic compounds may provide a new approach for the determination of these pharmaceutically and environmentally important molecules.     

The mechanism of the electrogenerated chemiluminescence of luminol in aqueous alkaline solution

The mechanism of the electrogenerated chemiluminescence of luminol in aqueous alkaline solution based on the rotating ring—disc electrode system is discussed. The disc electrode is maintained at a negative potential and the ring electrode at a symmetrically changing double-step potential. Hydrogen peroxide generated at the disc electrode by the reduction of oxygen is immediately transported to the ring electrode because of electrode rotation. Hydrogen peroxide and luminol are oxidized at the ring electrode during the positive pulse of the double-step potential. These oxidation processes generate a superoxide radical and a luminol radical as intermediates. The luminol radical reacts with the superoxide radical (or oxygen) emitting light.     

Determination coulometrique d'alcaloides et de sels de bases organiques apres precipitation sous forme de tetraphenylborates

A coulometric microdetermination of salts of certain organic bases and alkaloids is described, based on precipitation as the tetraphenylborates and the coulometric determination of the tetraphenylborate content of the precipitate with electrogenerated silver ion. Eleven compounds were determined with satisfactory accuracy.     

Evidence for a radical intermediate in the anodic oxidation of reduced nicotinamide adenine dinucleotides obtained by electrogenerated chemiluminescence

Electrogenerated chemiluminescence is used to show that the radicals NAD and NADP are intermediates in the electro-oxidation of NADH and NADPH at a platinum anode in anhydrous or partly aqueous (up to 15% v/v) dimethyl sulfoxide. An ECE mechanism seems to predominate. The use of dimethyl sulfoxide proved to be very convenient, with the advantage of enabling electrogenerated chemiluminescence to be obtained in partly aqueous media even with ionic substances as substrates. The method is useful in proving the existence of unstable radical intermediates in redox processes, even for relatively large molecules like NADH and NADPH.     

Revealing Crystallization-Induced Blue-Shift Emission of a Di-Boron Complex by Enhanced Photoluminescence and Electrochemiluminescence

Elucidating the effects of crystallization-induced blue-shift emission of a newly synthesized di-boron complex (DBC) by enhanced photoluminescence (PL) and electrochemiluminescence (ECL) in the annihilation pathway was realized for the first time. The 57 nm blue-shift and great enhancement in the crystalline lattice relative to the DBC solution were attributed to the restriction of intramolecular rotation (RIR) and confirmed by PL imaging, X-ray diffraction, as well as DFT calculations. It was discovered that ECL at crystalline film/solution interfaces can be further enhanced by means of both co-reactant route and RIR. The RIR contributions with co-reactant increased ECL up to 5 times more. Very interestingly, the co-reactant system was found to give off a red-shifted light emission. Mechanistic studies reveal that a difference between location of the ECL in the co-reactant route and that in the annihilation pathway leads to an alternative emission wavelength.     

Electrogenerated chemiluminescence of single conjugated polymer nanoparticles

We demonstrate a novel and powerful method to study electrogenerated chemiluminescence (ECL) of single nanoparticles (NPs) (r = 25 +/- 15 nm) of a conjugated polymer, F8BT, on an ITO electrode in the presence of a co-reactant, such as tri-n-propylamine (TPrAH) in acetonitrile solution. The results reveal that the maximum formation rate of ECL of individual NPs is achieved after a long "build-up" time (10-40 s after pulse application). The high number of detected ECL photons from individual NPs (1500 photons during 100 s) highlights the potential of this technique as a very sensitive analytical method. Additionally, TPrAH acts as a very efficient protecting agent against irreversible electrochemical processes occurring in F8BT, as found in photoluminescence studies. This protection mechanism probably involves the neutralization of holes at the particle surface via electron transfer by both TPrAH and TPrA radical (TPrA*).     

Color‐Tunable Electrogenerated Chemiluminescence of Ruthenium N‐Heterocyclic Carbene Complexes

Ru(II) complexes 1 – 3 bearing various N‐heterocyclic carbene (NHC) ligands were synthesized, and their photophysical, electrochemical, and electrogenerated chemiluminescence (ECL) properties were discussed to evaluate a potential of their use as multicolor ECL labels. Interestingly, they exhibited ECL emission ranging from greenish‐yellow to red both in nonaqueous and mixed aqueous solutions, which might show the potential of the Ru(II) complexes as multicolor ECL labels.     

Flow Injection Chemiluminescence Determination of Gentamycin Using On-Line Electrogenerated Co(III) As the Oxidant

ABSTRACT

A novel flow-injection Chemiluminescence (CL) system for the determination of gentamycin is described, based on the direct chemiluminescence reaction of gentamycin and Co(III) in sulfuric acid media. The unstable strongly oxidative Co(III) was electrogenerated on-line with constant current electrolysis. The chemiluminescence intensity was linear with gentamycin concentrations of 0.01～80μg/ml, the detection limit being 0.005μg/ml. The whole process could be completed in 1 min with a relative standard deviation of less than 3.2%. The proposed method is rapid and simple and is suitable for automatic and continuous analysis. This method has been applied satisfactorily to the analysis of gentamycin in pharmaceutical preparations.     

Efficient emission from charge recombination during the pulse radiolysis of electrochemical luminescent substituted quinolines with donor-acceptor character

Efficient emission from various donor-acceptor quinolines with an ethynyl linkage (PnQ), which are known as efficient electrogenerated chemiluminescent molecules, was observed with time-resolved fluorescence measurement during the pulse radiolysis in benzene. On the basis of the transient absorption and emission measurements, and steady-state measurements, the formation of PnQ in the singlet excited state can be interpreted by charge recombination between the PnQ radical cation and the PnQ radical anion which are generated initially from the radiolytic reaction in benzene. The strong electronic coupling between the donor and acceptor through conjugation is responsible for the efficient emission during the pulse radiolysis of PnQ in benzene. It is suggested that the positive and negative charges are localized on the donor and acceptor moieties in the radical cation and anion, respectively. This mechanism is reasonably explained by the relationship between the annihilation enthalpy changes and singlet excitation energies of PnQ. The formation of the intramolecular charge transfer state is assumed for PnQ in the singlet excited state with a strong electron donating substituent. The emission from PnQ is suggested to originate from PnQ in the singlet excited state formed from the charge recombination between the PnQ radical cation and the PnQ radical anion during the pulse radiolysis. This is strong evidence for the efficient electrogenerated chemiluminescence of PnQ.