Reversible One-electron Redox Processes Research Articles

Novel 2,6-dimethoxyphenoxy alpha substituted phthalocyaninato metal complexes: Electrochemistry, In situ spectroelectrochemistry and oxygen electrocatalysis

Non-peripherally tetra-2,6-dimethoxyphenoxy substituted Co(II) 3, Fe(II) 4, Mn(III) 5, and Ni(II) 6 phthalocyanines were prepared by refluxing the n-pentanol solution of their metal-free analogue H2Pc 2, (obtained by using 3-(2,6-dimethoxyphenoxy)phthalonitrile), metal salts (Co(CH3COO)2.4 H2O, Fe(CH3COO)2, Mn(CH3COO)2.4 H2O or NiCl2) and 1,8-diazabicyclo[5.4.0]undec-7-ene(DBU) as the catalyst under N2 atmosphere for 2 h. The molecular structure of metallophthalocyanines 3–6 were explained by common methods which are elemental analysis, MALDI-TOF mass, FTIR, and UV-Vis spectroscopies. The complexes are well dissolved in various solvents (dichloromethane, tetrahydrofuran, dimethylsulfoxide, dimethylformamide, and toluene. Electrochemical redox, electrocatalytic oxygen reducing and electrocolorimetric properties of the phthalocyanine complexes were also measured by voltammetric and in situ UV-Vis spectroelectrochemical techniques. The phthalocyanine complexes displayed highly reversible sequential one-electron redox processes occurring at metal and/or phthalocyanine ring. The association of these processes with net colour changes pointed out their functionality as electrochromic material. Furthermore, the phthalocyanine complexes 3-5 and especially Fe(II)Pc 4, showed striking electrocatalytic oxygen reducing activity, owing to the metal centres with redox activity, increasing their interplay with the O2 molecule.

Functional mimic for amine and catechol oxidases: Structural, spectral, electrochemical and catalytic properties of mononuclear copper(II) complex

A mononuclear copper(II) complex, [Cu(L)(Hdpa)](ClO4) (where H(L) is 1-(2-diethylamino)- ethyliminomethyl)naphthol, the tridentate N,N,O-donor Schiff base formed by 2-hydroxy-1-naphthaldehyde and N,N’-diethylethylenediamine and Hdpa is 2,2′-dipyridylamine) have been synthesized and structurally characterized by different spectral and electrochemical methods including single crystal X-ray diffraction study. The Cu(II) center in the complex adopts a square pyramidal geometry with an N4O coordination environment. It exhibits inter-pair dimeric association in its solid-state due to (a) inter-pair π-π interactions, (b) intermolecular NH⋯O hydrogen bonding, and (c) CH⋯π non-covalent interactions and it is weakened in solution. The complex shows a reversible one-electron redox process (Cu(II) ⇌ Cu(I)) with high positive potential. The benzylamine was used as the substrate in methanol solution, revealing that the complex exhibits greater catalytic activity with an 83% isolated yield of benzaldehyde. Also, the complex effectively catalyze the oxidation of 3,5-di-tert-butylcatechol (3,5-DTBC) in methanol (M) and buffer solution (BS, pH 7.0) to the corresponding 3,5-di-tert-butyl-o-quinone (3,5-DTBQ) with significant turnover number, Kcat (h−1) = 1.96 × 103 (M) and 2.26 × 105 (BS), which are comparable to the best values reported in the literature. The complex mimics the functional activities of both amine and catechol oxidases and can thus be regarded as models.

Synthesis, crystal structure and electrochemical properties of a new methylammonium sodium decavanate salt Na3(CH3NH3)3[V10O28].(CH3NH2).14H2O

A new hybrid decavanadate Na3(CH3NH3)3[V10O28].(CH3NH2).14H2O was obtained by a simple synthesis in solution and the crystal structure was determined by single-crystal X-ray diffraction. The compound consists of decavanadate anions [V10O28]6- isolated between sodium and methylammonium cations. The UV–Visible absorption, IR spectroscopy as well as electrochemical properties were characterized. The compound crystalizes in a triclinic system (space group P-1) with the unit cell parameters: a = 10.1584(11) Å, b = 10.8123(5) Å, c = 11.1582(7) Å, α = 107.723(4)°, β = 106.811(5)°, γ = 94.238(7)°. UV–Visible absorption spectroscopy shows a strong absorption band at 300 nm. The main IR absorption bands appear at: 954 cm-1, 800 cm-1, 732 cm-1 and 580 cm-1.The electrochemical measurement of this compound shows two reversible one-electron redox process -105 mV (I-I’) and 335mV(II-II’), which was attributed to two consecutive one-electron VV → VIV reductions.

Synthesis, electrochemistry, DNA binding and in vitro cytotoxic activity of tripodal ferrocenyl bis-naphthalimide derivatives

A series of tripodal ferrocenyl bis-naphthalimide derivatives were synthesized and characterized. All of the bis-naphthalimide derivatives exhibited good DNA binding ability which was confirmed by ethidium bromide (EB) displacement experiment and ultraviolet (UV)-visible absorption titration. And the binding mode of these compounds was proved to be a hybrid binding mode by experiments. The cytotoxicity of synthesized compounds against 4 different human cancer cell lines (EC109, BGC823, SGC7901 and HEPG2) was evaluated by thiazolyl blue tetrazolium bromide (MTT) assay. All of the bis-naphthalimide derivatives exhibited good anticancer activity than the positive control drug (amonafide), which was due to the promotion of reactive oxygen species (ROS) level in test cancer cells by the reversible one-electron redox process of ferrocenyl bis-naphthalimide derivatives. Although there was no obvious relationship between the binding constants and the chain length, the structure cytotoxicity relationship revealed that the linker of n = 3, m = 1 was the best choice for the tested tripodol bis-naphthalimide derivatives. SynopsisA series of tripodal ferrocenyl bis-naphthalimide derivatives were synthesized to study the DNA binding ability and the cytotoxicity induced by reactive oxygen species. All of the compounds exhibited good DNA binding ability. And the structure cytotoxicity relationship revealed that the structure of 5h was the best choice.

Polyoxometalate/Hydroquinone Hybrid Redox Electrolyte for Electrochemical Energy Storage

There has been progress and growing interest in the development of novel and efficient energy storage systems meeting high power and energy demands of modern devices and advanced technologies. Among important requirements for such charge storage devices are high volumetric and gravimetric energy and power, large number of charging/discharging cycles, improved safety and reasonable cost. At the current stage of technology, common charge storage systems, such as batteries and electrochemical capacitors, rarely meet those expectations. Indeed the present systems offer either high energy density (batteries) or high peak power (electrochemical capacitors) but barely both characteristics. Lately, there have been attempts to consider aqueous electrolytes containing dissolved redox species capable of undergoing fast electrode reactions at the interfaces formed with highly porous carbon electrodes. Consequently, the energy density significantly increases while keeping the power performance of a typical double-layer capacitor. Since most of redox-electrolyte-based systems utilize aqueous solutions, such advantages as enhanced safety, environment-friendliness and reasonable cost could be retained. Such redox-active species as iodide, quinone, phenelenediamine, ferrocyanide, methylene blue, thiocyanide and cerium sulphate have been successfully applied as positive or negative electrode-supporting electrolytes. The redox processes (battery-type characteristics) are typically observable in the potential range of a single electrode only and, therefore, the opposite electrode operating according to the electrical double-layer mechanism (capacitive behavior) limits the overall cell performance in terms of capacity and energy. To overcome this drawback, application of dual redox-type electrolytes comprising two independent redox couples separated in the positive and negative electrode compartments has been recently proposed. From the mechanistic point of view, such devices resemble conventional redox-flow batteries but operating in static conditions, i.e. more favourable from the practical and economical point of view.By taking into account the above deliberations, a dual redox-active (proton-conductive) electrolyte composed of the mixture of two different soluble redox species is considered here for application in energy storage devices with an enhanced specific energy [1]. The Keggin-type polyoxometalate (phosphotungstic acid), undergoing fast (electrochemically reversible) one-electron redox processes has been selected to support the negative electrode. In order to develop the potential difference in the cell, the hydroquinone, capable of oxidation/reduction according to the fast two-electron mechanism has been adopted and its electroactivity was predominantly confined to the positive electrode. It enabled us to design a hybrid charge storage cell with the operating voltage of 0.8 V and the specific energy of 20 Wh kg-1 (per total mass of both electrodes). In the constant power discharge mode, 13 Wh kg-1 of the energy has been preserved at the power of 1 kW kg-1 during discharging down to ½ of the maximum voltage which is consistent with the fast charging/discharging dynamics of the proposed hybrid system. A mixed hierarchical micro-porous (predominantly mesoporous) porous carbon of high (>2 cm3g-1) total pore volume and the BET surface area approaching 1000 m2 g-1 has been selected as the electrode material permitting electrical double layer charging and supporting electroactivity of redox species and unimpeded mass transport. Also, the normalization of electrical parameters against the total mass of electrodes and electrolyte resulted in a ca. five-fold increase of discharge capacity and specific energy in comparison to the performance of a simple electrical double-layer capacitor. Acknowledgement Financial support was provided by the National Centre for Research and Development (NCBR, Poland) under Techmatstrateg Grant no. 347431/14/NCBR/2018 as well as by the NCBR in the framework of European Union POWER 3.2 Project no. POWR.03.02.00-00-I007/16-00. 1. M. Skunik-Nuckowska, K. Węgrzyn, S. Dyjak, N. H. Wisińska, P. J. Kulesza, Energy Storage Mater., 21 (2019) 427-438

Propentdyopents: Brief history of a family of dipyrrolic pigments

Propentdyopents are naturally occurring dipyrroles deriving from the metabolism of heme and characterized by a dipyrrin-1,9-dione motif. The unusual name propentdyopent is due to the first colorimetric method (the Stokvis reaction) for the detection of these compounds, which were initially isolated from urine samples. Upon reduction in alkaline solutions, they produced red species that were termed pentdyopents to describe with Greek numerals their absorption maximum (525 nm) in the visible range. The precursors to the red pentdyopents were thus indicated as propentdyopents.Over the course of several decades, these dipyrrolic compounds have appeared in several studies of human physiology, typically associated to conditions of abnormal heme metabolism and/or oxidative stress. Concurrently, synthetic investigations have confirmed their chemical structure, reactivity, and ability to coordinate metals as bidentate monoanionic ligands. Notably, the planar dipyrrindione platform can undergo reversible one-electron redox processes and thereby act as an electron reservoir in metal complexes. In combination with the documented ability of the carbonyl groups to act as hydrogen-bonding acceptors, the coordination chemistry of propentdyopents could lead to new applications for this old class of pigments. Furthermore, the observation of these pigments in several clinical contexts could potentially delineate a role of propentdyopents as diagnostic biomarkers. This mini-review summarizes both the chemistry and biology of propentdyopents while highlighting the ample space for new discoveries.

Polyoxometalate/hydroquinone dual redox electrolyte for hybrid energy storage systems

A dual redox-active (proton-conductive) electrolyte composed of the mixture of two different soluble redox species is considered here for application in hybrid (battery-type) energy storage devices operating like high-power supercapacitor-type systems with an enhanced specific energy. The Keggin-type polyoxometalate (phosphotungstic acid), undergoing fast (electrochemically reversible) one-electron redox processes has been selected to support the negative electrode. In order to develop the potential difference in the cell, the hydroquinone, capable of oxidation/reduction according to the fast two-electron mechanism has been adopted and its electroactivity was predominantly confined to the positive electrode. It enabled us to design a hybrid charge storage cell with the operating voltage of 0.8 V and the specific energy of 20 Wh kg−1 (per total mass of both electrodes). In the constant power discharge mode, 13 Wh kg−1 of the energy has been preserved at the power of 1 kW kg−1 during discharging down to ½ of the maximum voltage which is consistent with the fast charging/discharging dynamics of the proposed hybrid system. A mixed hierarchical micro-porous (predominantly mesoporous) carbon of high (>2 cm3g-1) total pore volume and the BET surface area approaching 1000 m2 g−1 has been selected as the electrode material permitting electrical double layer charging, supporting electroactivity of redox species and unimpeded mass transport. Also, the normalization of electrical parameters against the total mass of electrodes and electrolyte resulted in a ca. five-fold increase of discharge capacity and specific energy in comparison to the performance of a simple electrical double-layer capacitor.

Electroreductive dechlorination of γ-Hexachlorocyclohexane catalyzed by Rh2(dpf)4 in nonaqueous media, where dpf = N,N′-Diphenylformamidinate (1-) ion

The electroreductive dechlorination of γ-hexachlorocyclohexane (lindane) was investigated in non-aqueous media using as a catalyst the dirhodium complex Rh2(dpf)4, where dpf=the anion of N, N′-diphenylformamidinate. Rh2(dpf)4 undergoes two reversible one-electron redox processes in pyridine and/or N,N′-dimethylformamide (DMF), corresponding respectively to Rh24+/Rh25+ and Rh24+/Rh23+. Electrochemical and spectroelectrochemical measurements indicate that lindane reacts with the Rh23+ center in singly reduced [Rh2(dpf)4]−, giving a transient carbon-bonded dirhodium complex along with Cl−. Further catalytic dechlorination of lindane subsequently occurs with the activity of Rh2(dpf)4 as a catalyst depending upon the solvent conditions. Rh2(dpf)4 shows a higher catalytic reduction current in pyridine than in DMF for the degradation of lindane. This catalytic current can be further enhanced if 6% water (v/v) is added to the pyridine solution. Bulk controlled-potential electrolysis combined with GC–MS verified that although the addition of water to the neat pyridine increased the catalytic activity of Rh2(dpf)4, neat pyridine is still a better solvent for the formation of more extensively dechlorinated products of lindane. In neat pyridine, lindane can be converted stepwise to tetrachlorocyclohexene, dichlorobenzene isomers, chlorobenzene and the fully dechlorinated product benzene, the last of which becomes predominant at the end of the electrolysis. In pyridine having 6% added water, other than those dechlorinated products seen above, trichlorobenzene isomers are formed upon lindane degradation. Meanwhile, the relative concentrations of dichlorobenzene isomers and chlorobenzene become higher, while the yield of benzene becomes lower than the corresponding results obtained in neat pyridine. Based on the measured distribution of the products under the different solvent conditions, an overall pathway for the degradation of lindane is proposed.

Tuneable reversible redox of cobalt(iii) carbazole complexes.

Four tridentate carbazole-based ligands, HLtBu/H {3,6-di(tert-butyl)-1,8-bis[5-(3-benzyl-1,2,3-triazole)]-9H-carbazole}, HLtBu/tBu {3,6-di(tert-butyl)-1,8-bis[5-(3-(4-tert-butyl)benzyl-1,2,3-triazole)]-9H-carbazole}, HLH/H {1,8-bis[5-(3-benzyl-1,2,3-triazole)]-9H-carbazole} and HLH/tBu {1,8-bis[5-(3-(4-tert-butyl)benzyl-1,2,3-triazole)]-9H-carbazole}, were prepared and complexed with cobalt(ii) tetrafluoroborate. In situ air oxidation resulted in cobalt(iii) complexes 1-4 with the general formula [CoIII(L)2]BF4·xH2O (1: L = LtBu/H, x = 2; 2: L = LtBu/tBu, x = 1; 3: L = LH/H, x = 0.5; 4: L = LH/tBu, x = 2). X-ray structural characterisation confirmed that the four complexes are isostructural, with two orthogonally coordinated deprotonated tridentate ligands providing an octahedral N6-donor set to the cobalt(iii) ion. 1H NMR studies show that this structure is maintained in CDCl3 and DMSO-d6 solution. Cyclic voltammetry on 1-4 in MeCN showed that all of the complexes exhibit two reversible, one-electron oxidation processes (probably due to ligand oxidations), and an irreversible or quasi-reversible reduction process (probably due to reduction of Co(iii) to Co(ii)). As expected, the oxidations move 120-140 mV to lower potentials on adding tert-butyl substituents to the 3 and 6 positions of the carbazole rings, and unsurprisingly the potentials are far less sensitive to the nature of the benzyl ring substituents.

Electrochemical Investigation of Benzil in Ionic Liquids

The voltammetric behavior of benzil (1,2-ethanedione, 1,2-diphenyl) has been investigated by cyclic voltammetry in the ionic liquids 1-ethyl-3-methylimidazolium tetrafluoroborate (EMImBF4), 1-butyl-2,3-dimethylimidazolium tetrafluoroborate (BDMIm BF4), and 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate BMPY TfO. At 100 mV/s, protonation of the radical anions of benzil by the EMIm cation is extensive and leads to complicated voltammetry; however, the protonation reaction is slow and is much less significant at 1000 mV/s. Use of BDMIm BF4, in which the acidic imidazolium 2-position is substituted, precludes protonation of these radical anions. It has been found that addition of BF3 etherate to solutions of benzil in EMImBF4 results in the complexation of benzil by BF3. Benzil has been found to undergo two successive reversible one-electron redox processes in the ionic liquid 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate (BMPY TfO). This behavior is observed due to the very low proton-donating ability of the BMPY cation. Upon addition of acetonitrile, however, the second redox process becomes irreversible as is observed in acetonitrile alone. The benzil dianion is evidently undergoing protonation by acetonitrile, and the resulting voltammogram is very similar to that in acetonitrile itself.

Electrochemical Explorations of 9,10-Anthraquinone/Hafnium(IV) Ion Interactions in Nonaqueous Solvents

The effect of hafnium(IV) trifluoromethanesulfonate [Hf(TfO)4] on the electrochemical behavior of 9,10-anthraquinone (AQ) has been studied in adiponitrile (ADN). AQ undergoes two successive reversible one-electron redox processes in ADN. Addition of Hf(TfO)4 produces a positive reduction peak potential shift due to formation of the complexes Hf(AQ)4+, then Hf2(AQ)8+, as Hf(TfO)4 is added. The reduction of these complexes leads to the appearance of the same oxidation peak, which is assigned to oxidation of Hf(AQ)3 2-. The peak potential shift is greater than that observed for addition of Al(TfO)3, indicating that Hf4+ interacts more extensively with AQ than does Al3+.

Nitride-bridged triiron complex and its relevance to dinitrogen activation.

Using a simple metathesis approach, the triiron(II) tribromide complex Fe3Br3L (1) reacts with tetrabutylammonium azide to afford the monoazide dibromide analogue Fe3(Br)2(N3)L (2) in high yield. The inclusion of azide was confirmed by IR spectroscopy with a ν(N3) = 2082 cm(-1) as well as combustion analysis and X-ray crystallography. Heating 2 in the solid state results in the complete loss of the azide vibration in the IR spectra and the isolation of the olive-green mononitride complex Fe3(Br)2(N)L (3). Solution magnetic susceptibility measurements support that the trimetallic core within 2 is oxidized upon generation of 3 (5.07 vs 3.09 μB). Absorption maxima in the UV-visible-near-IR (NIR) spectra of 2 and 3 support the azide-to-nitride conversion, and a broad NIR absorption centered at 1117 nm is similar to that previously reported for the intervalence charge-transfer band for a mixed-valent nitridodiiron cluster. The cyclic voltammograms recorded for 3 are comparable to those of 1 with no reductive waves observed between ∼0 and -2.5 V (vs Fc/Fc(+)), whereas a reversible one-electron redox process is observed for Fe3(NH2)3L (4). These results suggest that intercluster cooperativity is unlikely to predominate the dinitrogen reduction mechanism when 1 is treated with KC8 under N2.

Synthesis and Electrochemical Properties of N-(Ferrocenylmethyl)Aminobenzonitrile and N-(Ferrocenylmethyl)Nitroaniline Derivatives

Seven novel ferrocene derivatives containing (methylamino)benzonitrile and N-methylnitroaniline groups (3a-3f and 4) have been synthesized by conventional methods and characterized by FT-IR, NMR and cyclic voltammetry. The electrochemical behavior of these compounds (3a-3f) has been studied by cyclic voltammetry measurements at a platinum electrode in acetonitrile/0.1 M TBAP. The ferrocenyl group in all compounds showed similar reversible one-electron redox process, suggesting that the ferrocene moieties are equivalent and that there are no interactions among them. The formal potential, , is shifted to the more positive potential, indicating that the (methylamino)benzonitrile and N-methylnitroaniline introduced to ferrocene moiety exercise an electron-withdrawing effect.

Synthesis and Electrochemical Properties of N-(Ferrocenylmethyl)Aminobenzonitrile and N-(Ferrocenylmethyl)Nitroaniline Derivatives

Seven novel ferrocene derivatives containing (methylamino)benzonitrile and N-methylnitroaniline groups (3a-3f and 4) have been synthesized by conventional methods and characterized by FT-IR, NMR and cyclic voltammetry. The electrochemical behavior of these compounds (3a-3f) has been studied by cyclic voltammetry measurements at a platinum electrode in acetonitrile/0.1 M TBAP. The ferrocenyl group in all compounds showed similar reversible one-electron redox process, suggesting that the ferrocene moieties are equivalent and that there are no interactions among them. The formal potential, , is shifted to the more positive potential, indicating that the (methylamino)benzonitrile and N-methylnitroaniline introduced to ferrocene moiety exercise an electron-withdrawing effect.

A facile one step electrostatically driven electrocodeposition of polyviologen–reduced graphene oxide nanocomposite films for enhanced electrochromic performance

Polyviologen (PV)–reduced graphene oxide (rGO) nanocomposite films were fabricated by simple, one-step reductive electropolymerization of cyanopyridinium based precursor monomer (CNP) in an aqueous dispersion of graphene oxide (GO). Since the polymer formation and reduction of graphene oxide occurs within the same potential window, electrocodeposition method was preferred for obtaining nanostructured PV–rGO films. Cyclic voltammetry experiments of PV–rGO displayed two well resolved, reversible one-electron redox processes typical of viologen. Being a redox polymer, incorporation of rGO further enhances the electroactivity of the PV in the composite films. Vibrational spectral analysis with surface characterization revealed structural changes after composite formation along with subsequent reduction of GO within the polymer matrix. The PV–rGO nanostructured film exhibits a high-contrast electrochromism with low driving voltage induced striking color changes from transparent (0V) to purple (−0.6V), high coloration efficiency, fast response times and better cycling stability compared to a pristine PV film. This improved performance can be attributed to the high stability of the electrochrome in the composite assembly induced by electrostatically driven non-covalent interactions between redox PV2+ and negatively charged rGO, improved electrical conductivity and enlarged surface area accessed through reinforced nanostructured graphene sheets for tethering PV molecules.

Electrochemical Investigations of Benzil in Nonaqueous Media

Benzil has been found to undergo two successive reversible one-electron redox processes in the ionic liquid 1-butyl-1-methylpyrrolidinium trifluoromethanesulfonate (BMPY TfO). This behavior is observed due to the very low proton donating ability of the BMPY cation. Upon addition of acetonitrile, however, the second redox process becomes irreversible. The benzil dianion is evidently undergoing protonation by acetonitrile, and the resulting voltammogram is very similar to that in acetonitrile itself. The benzil dianion also undergoes protonation in adiponitrile.

Synthesis, Crystal Structure and Electrochemical Property of New Ferrocenyl Schiffbase

s: A novel Schiff-base compound based on ferrocene I has been synthesized and characterized by X-ray diffraction. Electrochemical measurements exhibit that this new ferrocenyl schiffbase undergoes a reversible one-electron redox process.

DNA Binding and Cleavage Activity of cis‐Cobalt Aromatic Oxime Complexes and Its Pyridine/imidazole Adducts

Abstractcis‐Cobalt complexes with salicycaldoxime(SAO), (Z)‐1‐(2‐hydroxyphenyl)ethanonoxime (HEO), (Z)‐1‐(2,5‐dihydroxyphenyl)ethanonoxime (DEO), (Z)‐1‐(2,5‐dihydroxyphenyl)(phenyl)methanonoxime (DPO) and their adducts with pyridine (Py) and imidazole (Im) were synthesized and characterized by elemental analysis, magnetic susceptibility, UV‐Vis and IR spectra. The electrochemical studies were carried by cyclic voltammeter, the peak potential separation and formal potential of complexes were independent of sweep rate or scan rate (ν) indicating a quasi reversible one‐electron redox process. Absorption studies and thermal denature studies revealed that each of these octahedral complexes is an avid binder of calf thymus DNA. The apparent binding constants for mixed ligand complexes are in order of ∼103‐103 M−1. Based on the data obtained in the DNA binding studies a partial intercalative mode of binding is suggested for these complexes. The nucleolytic cleavage activity of parent complexes and their pyridine adduct were carried out on double stranded pBR322 circular plasmid DNA by using a gel electrophoresis experiment in the presence and absence of oxidant (H2O2). All the metal complexes show enhanced cleavage activity in presence of oxidant. The hydrolytic cleavage of DNA of Co(DEO)2 and Co(DPO)2 is evidenced from the control experiments showing discernable cleavage inhibition in the presence of the hydroxyl radical inhibitor DMSO and EDTA.

Probing the Role of the Linker in Ferrocene-ATP Conjugates: Monitoring Protein Kinase Catalyzed Phosphorylations Electrochemically

The synthesis and electrochemical properties of ferrocene conjugates are presented for the purpose of investigating adenosine 5'-[γ-ferrocenoylalkyl] triphosphate (1 a-4 a, ferrocene (Fc)-ATP) as co-substrates for phosphorylation reactions. Compounds 1 a-4 a were synthesized, purified by HPLC, and characterized by NMR spectroscopy and mass spectrometry. In solution, all Fc-ATP bioconjugates exhibit a reversible one-electron redox process with a half-wave potential (E(1/2)) in the 390-430 mV range, peak separations (ΔE(p)) in the 40-70 mV range, and the peak current ratio (i(pa)/i(pc)) near unity. The peptide-modified surface Glu-Gly-Ile-Tyr-Asp-Val-Pro was used to study the sarcoma-related protein (Src) kinase activity by employing the Fc-ATP bioconjugates as co-substrates. Subsequent kinase-catalyzed transfer of the γ-Fc-phosphate group to the tyrosine residues of the surface-bound peptides was characterized by a formal potential (E°) ≈390 mV (vs. Ag/AgCl). The Fc-coverage, estimated by time-of-flight secondary-ion mass spectrometry (TOF-SIMS) and cyclic voltammetry (CV), suggested validity of Fc-ATP conjugates as kinase co-substrates. Depending on the length of the alkyl spacer of the Fc-ATP conjugate, different current densities were obtained, pointing to a direct correlation between the two. Molecular modeling revealed that the structural constraint imposed by the short alkyl spacer (1 a) causes a steric congestion and negatively affects the outcome of phosphorylation reaction. An optimal analytical response was obtained with the Fc-ATP conjugates with linker lengths longer than six CH(2) groups.

Syntheses, Characterizations and Crystal Structures of Two Copper Coordination Polymers Both Having Cu2Cl2 Bridging Subunit [CuI(bipy)1/2Cl]n(1) and {[(CuII)4(phen)4(SSA)2Cl2](H2O)2(DMF)2}n(2)

Two copper coordination polymers [CuI(bipy)1/2Cl] n (1) and {[(CuII)4(phen)4(SSA)2Cl2] (H2O)2(DMF)2} n (2)(bipy = 4,4′-bipyridine, phen = 1,10-phenanthroline, H3SSA = 5-sulfosalicylic acid, DMF = N,N-dimethylformamide) have been prepared and characterized by X-ray diffraction, elemental analysis, IR spectrum and 2 was also studied by cyclic voltammetric method. X-ray analysis indicates that both of them have Cu2Cl2 bridging subunit. Complex 1 is a two dimensional network structure. While 2 shows a one dimensional zigzag chain. Electrochemistry studies reveal that complex 2 undergo a quasi reversible one-electron metal-centered redox process at E 1/2 = +0.062 V. [Two copper coordination polymers [CuI(bipy)1/2Cl] n (1) and {[(CuII)4(phen)4(SSA)2Cl2] (H2O)2(DMF)2} n (2) (bipy = 4,4′-bipyridine, phen = 1,10-phenanthroline, H3SSA = 5-sulfo salicylic acid, DMF = N,N-dimethylformamide) have been prepared and characterized. Both of them have Cu2Cl2 bridging subunit. Compound 2 undergo a quasi reversible one-electron metal-centered redox process at E 1/2 = +0.062 V.]