Electrochemical Titrations Research Articles

Towards the rational design of N-(1,3-dimethylbutyl)-N'-phenyl-1,4-benzenediamine (6PPD) electrochemical sensor.

N-(1,3-Dimethylbutyl)-N'-phenyl-1,4-benzenediamine (6PPD) is a common additive in tires. 6PPD protects rubber from oxidative damage by ozone. Leaching of 6PPD in the environment leads to the formation of harmful byproducts such as 6PPD quinone. In this work we provide the fundamental basis for the detection of 6PPD by electrochemical techniques. We use cyclic voltammetry to study the adsorption of 6PPD on glassy carbon. We show that adsorbed 6PPD can be reversibly oxidized and reduced without disturbing the adsorption process. This result enables repeated electrochemical titrations. We determine, in neutral condition at 22 °C, an adsorption constant of Kads = 1.2 ± 0.5 μM-1 and kinetics of adsorption kads∈[0.74-5.60] × 104 L mol-1 s-1. Based on this knowledge we demonstrate the lowest concentration of 6PPD ever detected electrochemically, 10 nM. We also identify current challenges for electrochemical sensing of 6PPD. Multiple layers are formed at concentrations above 4.6 μM and the slow kinetics of adsorption requires long (hour) measurement time to reach maximum sensitivity.

An Integrated Analysis of Mechanistic Insights into Biomolecular Interactions and Molecular Dynamics of Bio-Inspired Cu(II) and Zn(II) Complexes towards DNA/BSA/SARS-CoV-2 3CLpro by Molecular Docking-Based Virtual Screening and FRET Detection.

Novel constructed bioactive mixed-ligand complexes (1b) [CuII(L)2(phen)] and (2b) [ZnII(L)2(phen)] {where, L = 2-(4-morpholinobenzylideneamino)phenol), phen = 1,10-phenanthroline} have been structurally analysed by various analytical and spectroscopic techniques, including, magnetic moments, thermogravimetric analysis, and X-ray crystallography. Various analytical and spectral measurements assigned showed that all complexes appear to have an octahedral geometry. Agar gel electrophoresis's output demonstrated that the Cu(II) complex (1b) had efficient deoxyribonucleic cleavage and complex (2b) demonstrated the partial cleavage accomplished with an oxidation agent, which generates spreadable OH● through the Fenton type mechanism. The DNA binding constants observed from viscosity, UV-Vis spectral, fluorometric, and electrochemical titrations were in the following sequence: (1b) > (2b) > (HL), which suggests that the complexes (1b-2b) might intercalate DNA, a possibility that is supported by the biothermodynamic measurements. In addition, the observed binding constant results of BSA by electronic absorption and fluorometric titrations indicate that complex (1b) revealed the best binding efficacy as compared to complex (2b) and free ligand. Interestingly, all compounds are found to interact with BSA through a static approach, as further attested by FRET detection. The DFT and molecular docking calculations were also performed to realize the electronic structure, reactivity, and binding capability of all test samples with CT-DNA, BSA, and the SARS-CoV-2 3CLPro, which revealed the binding energies were in a range of -8.1 to -8.9, -7.5 to -10.5 and -6.7--8.8 kcal/mol, respectively. The higher reactivity of the complexes than the free ligand is supported by the FMO theory. Among all the observed data for antioxidant properties against DPPH᛫, ᛫OH, O2-• and NO᛫ free radicals, complex (1a) had the best biological efficacy. The antimicrobial and cytotoxic characteristics of all test compounds have been studied by screening against certain selected microorganisms as well as against A549, HepG2, MCF-7, and NHDF cell lines, respectively. The observed findings revealed that the activity enhances coordination as compared to free ligand via Overtone's and Tweedy's chelation mechanisms. This is especially encouraging given that in every case, the experimental findings and theoretical detections were in perfect accord.

Reversible Multielectron Release from Redox-Active Three-Dimensional Molecular Barrels with Ruthenium-Alkenyl Moieties.

Three-dimensional molecular barrels Ru6-4 and Ru6-5 were synthesized in high yields from dinuclear ruthenium-vinyl clamps and tritopic triphenylamine-derived carboxylate linkers and characterized by multinuclear NMR spectroscopy including 1H-1H COSY and 1H DOSY measurements, high-resolution electrospray ionization mass spectrometry, and X-ray crystallography. The metal frameworks of the cages adopt the shape of twisted trigonal prisms, and they crystallize as racemic mixtures of interdigitating Δ- and Λ-enantiomers with a tight columnar packing in Ru6-4. Electrochemical studies and redox titrations revealed that the cages are able to release up to 11 electrons on the voltammetric timescale and that their cage structures persist up to the hexacation level. IR and UV-vis-near-infrared spectroelectrochemical studies confirm substituent-dependent intramolecular electronic communication within the π-conjugated 1,3-divinylphenylene backbone in the tricationic states, where all three divinylphenylene-bridged diruthenium clamps are present in mixed-valent radical cation states. The formation of 1:3 charge-transfer salts with 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane as the electron acceptor is also demonstrated.

Examining Some of Students’ Challenges and Use of Algorithmic Problem-Solving Approaches in Electrochemical Titrations

Examining Some of Students’ Challenges and Use of Algorithmic Problem-Solving Approaches in Electrochemical Titrations

Comprehensive Assessment of Biomolecular Interactions of Morpholine-Based Mixed Ligand Cu(II) and Zn(II) Complexes of 2,2'-Bipyridine as Potential Anticancer and SARS-CoV-2 Agents: A Synergistic Experimental and Structure-Based Virtual Screening.

A new class of pharmacologically active mixed-ligand complexes (1a-2a) [MII(L)2 (bpy)], where L = 2-(4-morpholinobenzylideneamino)phenol), bpy = 2,2'-bipyridine, MII = Cu (1a), and Zn (2a), were assigned an octahedral geometry by analytical and spectral measurements. Gel electrophoresis showed that complex (1a) demonstrated the complete DNA cleavage mediated by H2O2. The overall DNA-binding constants observed from UV-vis, fluorometric, hydrodynamic, and electrochemical titrations were in the following sequence: (1a) > (2a) > (HL), which suggests that the complexes might intercalate DNA, a possibility that is further supported by the biothermodynamic characteristics. The binding constant results of BSA by electronic absorption and fluorometric titration demonstrate that complex (1a) exhibits the highest binding effectiveness among others, which means that all compounds could interact with BSA through a static approach, additionally supported by FRET measurements. Density FunctionalTheory (DFT) and molecular docking calculations were relied on to unveil the electronic structure, reactivity, and interacting capability of all substances with DNA, BSA, and SARS-CoV-2 main protease (Mpro). These observed binding energies fell within the following ranges: -7.7 to -8.6, -7.2 to -10.2, and -6.7 to -8.2 kcal/mol, respectively. The higher reactivity of the complexes compared to free ligand is supported by the Frontier MolecularOrbital (FMO) theory. The in vitro antibacterial, cytotoxic, and radical scavenging characteristics revealed that complex (1a) has the best biological efficacy compared to others. This is encouraged because all experimental findings are closely correlated with the theoretical measurements.

Molecular recognition: Evidence of the redox role of ferrocenyl-imine derivatives in the presence of copper (II) ions

The design and development of new selective and sensitive chemosensors for metal ions is an area of intense research activity due to their important roles in medicine, living systems, and the environment. In this work, novel ferrocenyl derivatives functionalized with a crown ether linked via an olefin-imine spacer have been designed as versatile molecular recognizers for a series of metal ions (Na+, Ca+2, Cu2+, and Cd2+). By using UV-vis titrations, these systems showed a high affinity for Cu2+ among other metal ions, nevertheless, with unexpected optical behavior. With Spectroelectrochemical studies and electrochemical titrations we revealed that redox reactions between the ferrocenyl and the imine moieties of the spacer and the copper ions took place. These experimental results prove a redox reaction mechanism between both ferrocenyl and imine moieties in the presence of Cu2+. Therefore, this work puts a notice about the redox reaction that takes place between copper (II) and ferrocenyl-imine derivatives, and this information should be considered when designing metal ion chemosensors based on ferrocenyl and imine units, because this redox interaction would become a possible competition reaction.

Ferrocenylmethylthio-maleonitrile for selective recognition of Hg(II) ion

A new ferrocene based receptor 1,2-bis(ferrocenylmethylthio)-maleonitrile (FcMNT) was synthesized and characterized by elemental analysis, FTIR, NMR and X-ray single crystal diffraction. The ligand showed a high selection for Hg2+ in DMF or DMF/H2O mixed solution. Upon addition of Hg2+ in DMF, the receptor showed an obvious color change and significant UV–vis spectroscopic response. Electrochemical titrations revealed that the receptor sensed Hg2+ in high selectivity with an anodic shift of 307 mV. The 13CNMR titrations confirmed that the Hg2+ interacted with the S atoms of FcMNT when the amount of Hg2+ was under 1.0 equiv.; the Hg2+ interacted with CC and CN groups when the amount of Hg2+ was above 1.0 equiv.

Spectroscopic, electrochemical and X-ray crystallographic properties of a novel palladium(II) complex of thioamide deprotonated di-2-pyridyl ketone thiosemicarbazone (dpktsc-H)−

The reaction between di-2-pyridyl ketone thiosemicarbazone (dpktsc) and PdCl2(CH3CN)2, generated in situ from the reaction between PdCl2 and CH3CN, gave the unprecedented [Pd2Cl3(κ5-Npy,Nim,S,Npy,Nam-dpktsc-H)]·2CH3CN (1) complex (py = pyridine, im = imine and am = amide). The identity of 1 was confirmed via its elemental analysis and spectroscopic properties. Infrared and 1H-NMR spectra confirmed the coordination of (dpktsc-H)− to the palladium ions. The electronic absorption spectra measured in dmso and dmf and density functional theory (DFT) calculations revealed metal-to-ligand charge-transfer (MLCT), d–d and intra-ligand charge-transfer (ILCT) electronic transitions. X-ray structural analysis on a crystal of [Pd2Cl3(κ5-Npy,Nim,S,Npy,Nam-dpktsc-H)]·H2O (2) grown from dmf solution of 1 confirmed its formulation and showed the solid-state structure contains a web of molecules locked via a network of non-covalent interactions. Electrochemical measurements on 1 in dmf revealed metal- and ligand-based redox processes. In contrast to the electrochemical decomposition of uncoordinated dpktsc, coordinated (dpktsc-H)− in 1 does not undergo electrochemical decomposition. Electrochemical titrations of 1 with p-toluenesulfonic acid monohydrate (p-TSOH) revealed electro-catalytic proton reduction. Over-potential (η) of 180 mV for the H2 evolution was observed and is comparable to several molecular electro-catalysts for proton reduction. Controlled-potential electrolysis confirmed the electro-catalytic proton reduction by the Pd-complex. Electrochemical reactions of CO2 in the presence of 1 exhibited a proton dependence, and metal- and ligand-based electrochemical reaction.

Electrolyte Influence in Developing a High-Capacity, Reversible Lithium-Oxygen (Lithium-Air) Battery

The nonaqueous lithium-oxygen (also called lithium-air) electrochemistry has an extraordinarily high theoretical specific energy, but critical electrochemical challenges prevent the realization of a high-capacity, reversible battery. Consisting of a lithium-metal negative electrode, an anhydrous, organic solvent-based lithium electrolyte, and a gaseous oxygen-saturated porous carbon positive electrode, the battery operates via the formation and decomposition of lithium peroxide (Li2O2). Unfortunately, in the most stable, ether-based electrolytes studied to-date, Li2O2 forms as a thin film on the carbon surface. As Li2O2 is an insulator, the thin film quickly leads to a large increase in the surface overpotential, effectively shutting off the battery before a high capacity can be achieved. Additionally, both the most stable electrolytes and porous carbons studied to-date still exhibit electrochemical decomposition in the presence of Li2O2 in operating cells, leading to parasitic products and poor cyclability. In this work, we present electrolyte salt and solvent considerations toward addressing these challenges. We will particularly focus on recent reports that the introduction of lithium iodide (LiI) salt to a water-contaminated ether-based electrolyte induces a 4e- per O2 reduction reaction forming lithium hydroxide (LiOH) rather than the typical 2e- per O2 reduction reaction forming Li2O2.1,2 This could potentially mitigate both charge transport and instability issues related to Li2O2 by entirely changing the discharge electrochemistry. We present our recent quantitative analysis of the influence of LiI and H2O on the electrochemistry in a typical ether-based Li-O2 battery via differential electrochemical mass spectrometry and titrations of extracted cathodes.3 We confirm that LiI and H2O promote the efficient production of LiOH on discharge, but we find that LiOH is not reversibly oxidized to O2 on charge. Rather, the charge electrochemistry is a complicated mix of redox shuttling and side reactions. We hope to inspire further research toward understanding the complex chemistry involved upon the addition of redox mediators to lithium-oxygen batteries. (1) Liu, T.; Leskes, M.; Yu, W.; Moore, A. J.; Zhou, L.; Bayley, P. M.; Kim, G.; Grey, C. P. Science 2015, 350, 530. (2) Kwak, W.-J.; Hirshberg, D.; Sharon, D.; Shin, H.-J.; Afri, M.; Park, J.-B.; Garsuch, A.; Chesneau, F. F.; Frimer, A. A.; Aurbach, D.; Sun, Y.-K. J. Mater. Chem. A 2015, 3, 8855. (3) Burke, C. M.; Black, R.; Kochetkov, I. R.; Giordani, V.; Addison, D.; Nazar, L. F.; McCloskey, B. D. ACS Energy Letters 2016, 1, 747.

Colorimetric and electrochemical sensing for fluoride anion by ferrocenyl-based imidazole compound with electron donor–acceptor structure

In this paper, a new ferrocenylimidazole compound L was designed and synthesized. L could selectively sense a fluoride anion among test anions such as F−, AcO−, Cl−, Br−, I− and HSO4 −, accompanied by obvious color or electrochemical changes. The detection limit in a DMSO solution was calculated as 5.94 × 10−6 M−1. From the Uv–vis, NMR and electrochemical titrations, it was indicated that L and fluoride anions formed a 1:1 complex with hydrogen bonding and anion–π interactions.

Water oxidation catalysis by Co(II) impurities in Co(III)4O4 cubanes.

The observed water oxidation activity of the compound class Co4O4(OAc)4(Py–X)4 emanates from a Co(II) impurity. This impurity is oxidized to produce the well-known Co-OEC heterogeneous cobaltate catalyst, which is an active water oxidation catalyst. We present results from electron paramagnetic resonance spectroscopy, nuclear magnetic resonance line broadening analysis, and electrochemical titrations to establish the existence of the Co(II) impurity as the major source of water oxidation activity that has been reported for Co4O4 molecular cubanes. Differential electrochemical mass spectrometry is used to characterize the fate of glassy carbon at water oxidizing potentials and demonstrate that such electrode materials should be used with caution for the study of water oxidation catalysis.

Spectroscopic, electrochemical and theoretical studies on anion recognition by receptors with redox active ferrocene and quinone centers bridged by imidazole

Two chromogenic sensors possessing two redox-active centers (quinone and ferrocene) bridged by imidazole anion recognition group have been synthesized and screened for their anion sensing properties. Both the receptors exhibited dramatic color change upon the addition of fluoride and cyanide ions so that we could finish anion recognition by visual detection without resorting to any spectroscopic instruments. The evaluation of the receptor interaction with anions was performed by UV–Vis titration experiments in DMSO. UV–Vis titrations revealed that receptor 1, wherein the imidazole moiety is directly attached to naphthoquinone unit, exhibited a relatively larger bathochromic shift of the intramolecular charge transfer (ICT) band than 2 in which the imidazole receptor unit is away from the quinone moiety. Receptor 1 displays a higher (Δδ = 0.269, 0.352 ppm) downfield shift of the imidazole N–H proton than 2 (Δδ = 0.070, 0.122 ppm) indicating that the anion binding pattern of these chemosensors was H-bond interaction. Also, the UV–Vis and 1H NMR results indicated that the receptor-CN− binding is relatively stronger than receptor-F− interaction. The redox activities of the quinone and ferrocenyl centers in 1 and 2 have been characterized by cyclic and differential pulse voltammetries. Electrochemical titrations revealed that the receptor 1 sensed CN− ions with an anodic shift of −198 mV in the oxidation potential of ferrocene moiety when compared to −188 mV with the receptor 2. Addition of incremental amounts of F− and CN− ions, to these two receptors, shifts the E1/2 of the quinone redox couple to less negative potentials. DFT (B3LYP/3-21G) calculations performed for both free receptor and receptor–anion complexes are in good agreement with the observed spectroscopic and electrochemical data.

Three-channel ferrocene-based chemosensors for Cu(II) and Hg(II) in aqueous environments

Ferrocene-based conjugated complexes, benzenediamine (A), benzidine (B) and disulfanediyldianiline (C) are synthesized and their spectroscopic, electrochemical and cation sensing properties are studied. Three complexes are high sensitive color systems for determination of Hg(II) and Cu(II) in DMSO-H2O (10:0.5) solution. The absorption spectral changes were observed upon the addition of either Hg(II) or Cu(II), with the dramatic naked eye detectable color changes from yellow to red or green respectively. Moreover, the addition of cations showed strong fluorescent quenching, while new redox peaks were observed during electrochemical titrations. The DFT calculations were carried out to investigate the electronic coupling between the ferrocene centers.

Synthesis, photophysical, electrochemical, and ion-binding properties of Ru(II) polypyridyl complexes containing benzo-15-crown-5

Two polypyridyl ligands, 5-(4′-ethynylbenzo-15-crown-5)-2,2′-bipyridine (L1) and 3-bromo-8-(4′-ethynylbenzo-15-crown-5)-1,10-phenanthroline (L2), and their Ru(II) complexes [(bpy)2RuL](PF6)2 have been prepared and characterized. Both complexes exhibit metal-to-ligand charge transfer absorption at around 452 nm and emission at around 640 nm in MeCN solution. Electrochemical studies of the complexes reveal a Ru(II)-centered oxidation at around 1.31 V and three ligand-centered reductions. The binding ability of the complexes with Na+ has been investigated by UV/Vis absorption, emission, and electrochemical titrations. Addition of Na+ to MeCN solutions of both complexes results in a progressive enhancement of the emission, a red-shift of the UV/Vis absorption, and a progressive cathodic shift of the Ru(II)-centered E1/2 couple. The stability constants for the 1:1 stoichiometry adducts of the complexes with Na+ have been obtained from the UV/Vis absorption titrations.

Spectral response to oxy-anions based on ferrocenylphalene

A series of ferrocenyl derivatives (1, 2, 3 and 4) containing phenol group, chemosensors for anions, have been synthesized and optimized. Their binding ability for various anions (F−, Cl−, Br−, I−, AcO− and H2PO4−) were evaluated by theoretical investigation, UV–Vis, 1H NMR titration and cyclic voltammetry experiments and these chemosensors showed strong binding ability for oxy-anions. Theoretical investigation analysis revealed the substituent was different, the space structure was different. And the intramolecular hydrogen bond existed between –OH and other atoms in the structure of these compounds. UV–Vis titrations indicated the anion binding abilities could be tuned by electron push–pull properties of the substituents on the phenyl ortho or para position. Electrochemical titrations showed the addition of anions led to the weak of redox response and the oxidation peak potential moved to more positive potential gradually. In addition, these chemosensors were sensitive to the AcO− detection without the interference of other anions studied, as well as chemosensor 4 was sensitive to the H2PO4− detection.

Preparation, Photophysical, Electrochemical, and Ion-Binding Properties of Ru(II) Polypyridyl Complexes Containing a Crown Ether Unit

Two polypyridyl ligands, 4`-(4,5-diazafluoren-9-ylimino)benzo-15-crown-5 (L1) and 4` -(4,5-diazafluoren- 9-ylimino)benzo-12-crown-4 (L2), and their Ru(II) complexes [(bpy)2RuL1](PF6)2 and [(bpy)2RuL2](PF6)2, respectively, have been synthesized and characterized. The two complexes display metal-to-ligand charge transfer absorptions at around 444 nm in CH3CN solution at r. t. and emission at around 573 nm in an EtOH-MeOH (4 : 1, v/v) glassy matrix at 77 K. Electrochemical studies of the complexes show one Ru(II)-centered oxidation at around 1.33 V and three ligandcentered reductions. The binding ability of the complexes with Na+ and Li+ has been investigated by UV/Vis absorption and emission spectroscopy and electrochemical titrations. Addition of Na+ and Li+ to solutions of the complexes results in a progressive quenching of the emission, a hyperchromic effect of the UV/Vis absorption, and a progressive cathodal shift of the Ru(II)-centered E1/2 potential. The stability constants for the stoichiometric 1 : 1 ratio of the complexes and the cations have been obtained by UV/Vis absorption titration.

Electrochemical titrations and reaction time courses monitored in situ by magnetic circular dichroism spectroscopy

Magnetic circular dichroism (MCD) spectra, at ultraviolet–visible or near-infrared wavelengths (185–2000 nm), contain the same transitions observed in conventional absorbance spectroscopy, but their bisignate nature and more stringent selection rules provide greatly enhanced resolution. Thus, they have proved to be invaluable in the study of many transition metal-containing proteins. For mainly technical reasons, MCD has been limited almost exclusively to the measurement of static samples. But the ability to employ the resolving power of MCD to follow changes at transition metal sites would be a potentially significant advance. We describe here the development of a cuvette holder that allows reagent injection and sample mixing within the 50-mm-diameter ambient temperature bore of an energized superconducting solenoid. This has allowed us, for the first time, to monitor time-resolved MCD resulting from in situ chemical manipulation of a metalloprotein sample. Furthermore, we report the parallel development of an electrochemical cell using a three-electrode configuration with physically separated working and counter electrodes, allowing true potentiometric titration to be performed within the bore of the MCD solenoid.

Dual chemosensing properties of new ferrocene-based receptors towards fluoride and copper(II) ions

The new ferrocene based receptors N-[4-ferrocenyl-2-methyl-4-oxobut-1-enyl]-N′-phenylthiourea ( 1 ), N-[4-ferrocenyl-2-methyl-4-oxobut-1-enyl]-N′-[4-nitrophenyl]thiourea ( 2 ) were synthesized and characterized. Fluorescence titrations of receptors 1 and 2 with various transition metal ions showed selective response to Cu 2+ ions and the emission intensities quenched significantly. Electrochemical titrations with anions revealed that receptors 1 and 2 sensed the F − anion in high selectivity with a cathodic shift of 100 mV. Two new colorimetric chemosensors 1 and 2 have been synthesized and characterized by different spectroscopic techniques like IR, Mass and NMR. Anion binding studies carried out using UV–visible spectrophotometric titrations revealed that these receptors exhibit selective recognition towards F − over other halide anions. Chromogenic receptors 1 and 2 undergo distinct color changes from yellow to green ( 1 ) and red to dark green ( 2 ) on gradual addition of Cu(II) and can be used as colorimetric probes for spectrophotometric and visual analysis of Cu(II) in the presence of other transition metal ions such as Mg 2+ , Ca 2+ , Cd 2+ , Ni 2+ , Co 2+ , Mn 2+ and Zn 2+ . Fluorescence titrations of receptors 1 and 2 with various transition metal ions showed selective response to Cu 2+ ions and the emission intensities quenched significantly. Electrochemical titrations with anions revealed that receptors 1 and 2 sensed the F − anion in high selectivity with a cathodic shift of 100 mV. ► Easy to synthesize 1 and 2 . ► Detectable by using colorimetric, optical (UV–vis and fluorescence) and electrochemical methods. ► Both sensors highly sensitive at low analyte concentration. ► These receptors can also be used to detect copper ions.

Control of Proton and Electron Transfer in de Novo Designed, Biomimetic β Hairpins

Tyrosine side chains are involved in proton coupled electron transfer reactions (PCET) in many complex proteins, including photosystem II (PSII) and ribonucleotide reductase. For example, PSII contains two redox-active tyrosines, TyrD (Y160D2) and TyrZ (Y161D1), which have different protein environments, midpoint potentials, and roles in catalysis. TyrD has a midpoint potential lower than that of TyrZ, and its protein environment is distinguished by potential π-cation interactions with arginine residues. Designed biomimetic peptides provide a system that can be used to investigate how the protein matrix controls PCET reactions. As a model for the redox-active tyrosines in PSII, we are employing a designed, 18 amino acid β hairpin peptide in which PCET reactions occur between a tyrosine (Tyr5) and a cross-strand histidine (His14). In this peptide, the single tyrosine is hydrogen-bonded to an arginine residue, Arg16, and a second arginine, Arg12, has a π-cation interaction with Tyr5. In this report, the effect of these hydrogen bonding and electrostatic interactions on the PCET reactions is investigated. Electrochemical titrations show that histidine substitutions change the nature of PCET reactions, and optical titrations show that Arg16 substitution changes the pK of Tyr5. Removal of Arg16 or Arg12 increases the midpoint potential for tyrosine oxidation. The effects of Arg12 substitution are consistent with the midpoint potential difference, which is observed for the PSII redox-active tyrosine residues. Our results demonstrate that a π-cation interaction, hydrogen bonding, and PCET reactions alter redox-active tyrosine function. These interactions can contribute equally to the control of midpoint potential and reaction rate.

TTFAQ-cored D/A ensembles: synthesis, electronic properties, and redox responses to transition metal ions

Two anthraquinone-type π-extended tetrathiafulvalene (TTFAQ)-cored D/A triads were synthesized and characterized by UV–vis absorption and cyclic voltammetric analyses. Electronic substituent effects were unraveled by making a comparison with analogous TTFAQ derivatives previously reported. Electrochemical titrations of the two TTFAQ D/A triads with selected transition metal cations (Ag+ and Cu2+) were examined by cyclic voltammetry, and the results suggest potential application of such TTFAQ derivatives as electrochemical sensors for transition metal ions.