Equilibrium Constants For Formation Research Articles

Electrodeposition of Fe-Ni Alloy Films having Invar Compositions with Fe3+ as the Sole Iron Source

Fe-Ni alloy films with invar alloy compositions were electrodeposited from a stable citrate bath containing trivalent iron ions (Fe3+) as the sole iron source. This bath was prepared based on determining the equilibrium constants for acid dissociation, complex formation and precipitation reactions. Electrodeposition was conducted under galvanostatic conditions at 25 °C without agitation and an investigation was carried out into the effects of pH and current density on the composition and microstructure of the films. The results showed that ferric hydroxide (Fe(OH)3), which is normally poorly soluble, did not precipitate after electrodeposition. Fe-Ni alloy films containing 31‒42 mass% Ni (including Fe-36 mass% Ni) were formed with a current efficiency of approximately 70%. The films were smooth and were made up of grains with sub-micron sizes, although some cracks were observed. Fe and Ni were distributed homogeneously throughout the films and the Fe-Ni solid solutions exhibited both face-centered cubic and body-centered cubic structures.

Impact of the Warhead of Dipeptidyl Keto Michael Acceptors on the Inhibition Mechanism of Cysteine Protease Cathepsin L.

Cathepsin L (CatL) is a lysosomal cysteine protease whose activity has been related to several human pathologies. However, although preclinical trials using CatL inhibitors were promising, clinical trials have been unsuccessful up to now. We are presenting a study of two designed dipeptidyl keto Michael acceptor potential inhibitors of CatL with either a keto vinyl ester or a keto vinyl sulfone (KVS) warhead. The compounds were synthesized and experimentally assayed in vitro, and their inhibition molecular mechanism was explored based on molecular dynamics simulations at the density functional theory/molecular mechanics level. The results confirm that both compounds inhibit CatL in the nanomolar range and show a time-dependent inhibition. Interestingly, despite both presenting almost equivalent equilibrium constants for the reversible formation of the noncovalent enzyme/inhibitor complex, differences are observed in the chemical step corresponding to the enzyme-inhibitor covalent bond formation, results that are mirrored by the computer simulations. Theoretically determined kinetic and thermodynamic results, which are in very good agreement with the experiments, afford a detailed explanation of the relevance of the different structural features of both compounds having a significant impact on enzyme inhibition. The unprecedented binding interactions of both inhibitors in the P1' site of CatL represent valuable information for the design of inhibitors. In particular, the peptidyl KVS can be used as a starting lead compound in the development of drugs with medical applications for the treatment of cancerous pathologies since sulfone warheads have previously shown promising cell stability compared to other functions such as carboxylic esters. Future improvements can be guided by the atomistic description of the enzyme-inhibitor interactions established along the inhibition reaction derived from computer simulations.

Permittivity Threshold and Thermodynamics of Integer Charge-Transfer Complexation for an Organic Donor–Acceptor Pair

Molecular charge doping involves the formation of donor-acceptor charge-transfer complexes (CTCs) through integer or partial electron transfer; understanding how local chemical environment impacts complexation is important for controlling the properties of organic materials. We present steady-state and temperature-dependent spectroscopic investigations of the p-dopant 2,3,5,6-tetrafluoro-7,7,8,8-tetracyanoquinodimethane (F4TCNQ) complexed with the electron donor and hole transport material N,N'-diphenyl-N,N'-di-p-tolylbenzene-1,4-diamine (MPDA). Equilibrium formation constants (KCT) were determined for donor-acceptor pairs dissolved in a series of solvents covering a range of values of permittivity. A threshold for highly favorable complex formation was observed to occur at ϵ ∼ 8-9, with large (>104) and small (<103) values of KCT obtained in solvents of higher and lower permittivity, respectively, but with chloroform (ϵ = 4.81) exhibiting an anomalously high formation constant. Temperature-dependent formation constants were determined in order to evaluate the thermodynamics of complex formation. In 1,2-dichloroethane (ϵ = 10.36) and chlorobenzene (ϵ = 5.62), complex formation is both enthalpically and entropically favorable, with higher enthalpic and entropic stabilization in the solvent with higher permittivity. Complexation in chloroform is exothermic and entropically disfavored, indicating that specific, inner-shell solvent-solute interactions stabilize the charge-separated complex and result in a net increase in local solution structure. Our results provide insight into how modification to the chemical environment may be utilized to support stable integer charge transfer for molecular doping applications and requiring only modest changes in local permittivity.

Rate and equilibrium constants for the addition of triazolium salt derived N-heterocyclic carbenes to heteroaromatic aldehydes.

Heteroaromatic aldehydes are often used preferentially or exclusively in a range of NHC-catalysed processes that proceed through the generation of a reactive diaminoenol or Breslow Intermediate (BI), with the reason for their unique reactivity currently underexplored. This manuscript reports measurement of rate and equilibrium constants for the reaction between N-aryl triazolium NHCs and heteroaromatic aldehydes, providing insight into the effect of the NHC and heteroaromatic aldehyde structure up to formation of the BI. Variation in NHC catalyst and heteroaromatic aldehyde structure markedly affect the observed kinetic parameters of adduct formation, decay to starting materials and onward reaction to BI. In particular, large effects are observed with both 3-halogen (Br, F) and 3-methyl substituted pyridine-2-carboxaldehyde derivatives which substantially favour formation of the tetrahedral intermediate relative to benzaldehyde derivatives. Key observations indicate that increased steric hindrance leads to a reduction in both k 2 and k -1 for large (2,6-disubstituted)-N-Ar groups within the triazolium scaffold, and sterically demanding aldehyde substituents in the 3-position, but not in the 6-position of the pyridine-2-carboxaldehyde derivatives. As part of this study, the isolation and characterisation of twenty tetrahedral adducts formed upon addition of N-aryl triazolium derived NHCs into heteroaromatic aldehydes are described. These adducts are key intermediates in NHC-catalysed umpolung addition of heteroaromatic aldehydes and are BI precursors.

Thermodynamic and kinetic aspects of the solvent-free liquid–liquid synthesis of tailor-made glyceride esters

Direct esterification between glycerol and carboxylic acids allows the design of different glycerides according to predetermined applications. Five carboxylic acids (caprylic, capric, lauric, stearic and oleic) which formed a bi-phasic system with glycerol were tested for esterification in a 1:1 M proportion. Two strategies were pursued: on one hand, homogeneous acid catalysis using sulfuric acid or p-toluenesulfonic acid at 100 °C and on the other hand, reactions catalyzed by immobilized lipase B from Candida antarctica at 65 °C. The selectivity and yield for MG was higher at lower temperature and with the use of the enzyme. Lauric acid was the carboxylic acid with the higher yield and selectivity to MG despite the catalyst used. The decrease in the mutual solubility between the carboxylic acid and glycerol seems to favor MG formation. The rate of reaction decreased with the increase in the molecular weight of the carboxylic acid used and the introduction of one unsaturation. From caprylic to lauric acid, the catalyst performance was: p-toluenesulfonic acid > lipase > sulfuric acid whereas for stearic and oleic acids the lipase was superior. Reactant accumulation at the interface is proposed to explain these results. The thermodynamic UNIFAC model was applied to calculate the initial activity coefficients and molar fractions in each phase. It was demonstrated that the thermodynamic activity of the species is a more convenient representation of the effective concentration for kinetic description of a liquid–liquid system. The equilibrium constant of lipase reaction was calculated with an expression based on the activity of compounds. The equilibrium constant for diglycerides formation decreased with the carbon chain length.

Reaction of Cl Atom with c-C5F8 and c-C5HF7: Relative and Absolute Measurements of Rate Coefficients and Identification of Degradation Products.

Partially and fully fluorinated olefins are a class of compounds with relatively short atmospheric lifetimes and low 100-year global warming potentials, compared to their saturated predecessors, which are used or considered as refrigerants, propellants, solvents, and other end-uses. The cyclic unsaturated compounds c-C5F8 and c-C5HF7 are currently under consideration as etching agents for the semiconductor industry. In this study, we expand on our previous work on the reaction of the OH radical with c-C5F8 and c-C5HF7 and report the rate coefficients, k, for the gas-phase reaction of the Cl atom with c-C5F8 and c-C5HF7 over a range of temperature (245-367 K) and pressure (100-200 Torr of He or N2 and 0 to 4.8 Torr O2) using a pulsed laser photolysis-resonance fluorescence (PLP-RF) technique. In addition, a relative rate (RR) technique, employing multiple reference compounds, was used to study the Cl atom reactions at 296 K, 100 and 630 Torr (N2 or air) total pressure. Reaction rate coefficients, k1, of the Cl atom reaction with c-C5F8 were found to be independent of pressure, over the pressure range used in this work, with k1(296 K), derived as an average of results from the PLP-RF and RR techniques being (1.07 ± 0.02) × 10-12 cm3 molecule-1 s-1 and k1(T) = (7.76 ± 0.73) × 10-13 × (exp[(98 ± 26)/T]) cm3 molecule-1 s-1, where the quoted error limits represent the 2σ data precision. Rate coefficients, k2, for the Cl atom + c-C5HF7 reaction were measured to be k2(296 K) = (4.61 ± 0.10) × 10-12 cm3 molecule-1 s-1 and k2(T) = (7.42 ± 0.89) × 10-13 × (exp[(540 ± 32)/T]) cm3 molecule-1 s-1. The Cl atom temporal profiles, observed with the PLP-RF technique, indicate that the Cl atom with c-C5F8 and c-C5HF7 reactions lead to adduct formation. The equilibrium constants for adduct formation were derived in this work, and a second-law analysis was used to obtain ΔH and ΔS values of -18.5 ± 0.4 kcal mol-1, -30.9 ± 1.2 cal K-1 mol-1, and -13.9 ± 0.5 kcal mol-1, -27.6 ± 1.1 cal K-1 mol-1 for the c-C5F8 and c-C5HF7 reactions, respectively. The Cl-initiated degradation of c-C5F8 and c-C5HF7 in the presence of O2 was studied and stable products were identified via infrared spectroscopy using experimental or theoretically derived spectra from our previous OH reaction work. For c-C5F8, FC(O)CF2CF2CF2C(O)F and FC(O)C(O)F were observed with molar yields of 0.80 and 0.10, respectively. For c-C5HF7, we observed the formation of HC(O)CF2CF2CF2C(O)F and HC(O)C(O)F with a combined molar yield of 0.72. Carbonyl difluoride, F2CO, was also a major product in the decomposition of c-C5F8 and c-C5HF7. The oxidation mechanism of the Cl-initiated degradation of c-C5F8 and c-C5HF7 is discussed. Based on the combined findings from this and our previous work, the atmospheric implications from the use of c-C5F8 and c-C5HF7 are presented.

Synthesis of Methylal and Poly(oxymethylene) Dimethyl Ethers from Dimethyl Ether and Trioxane

Poly(oxymethylene) dimethyl ethers (OME) are interesting synthetic fuels that could replace fossil diesel fuel. Therefore, economic routes for OME production have to be developed. One particularly interesting route is the synthesis of OME from dimethyl ether (DME) and formaldehyde. The principal feasibility of this route is established, but the physico-chemical information on essential steps is still lacking. In particular, there is no data on the first step in this synthesis, which is the formation of methylal (MAL) from DME and formaldehyde. Kinetic batch experiments were carried out in a stirred batch autoclave with a commercially available acidic ion-exchange resin as a catalyst in the temperature range of 353–373 K for up to 200 h. Trioxane was used as a water-free source of formaldehyde. Due to the volatility of DME, the experiments were carried out under pressure; high-pressure magnetic resonance (NMR) spectroscopy was applied for the analysis. During the reaction, not only MAL but also OME are formed, as well as a side product, methyl formate (MeFo). Therefore, the equilibrium constant of the MAL formation had to be determined based on a reaction kinetic model of the entire reaction network. The formation of MAL was found to have a larger equilibrium constant than the subsequent oligomerization reactions leading to OME, but it is also much slower than these reactions.

Quantitating the Binding Energy of Metal Ions to Langmuir-Blodgett Monolayers: The Copper(II)-Octadecylphosphonic Acid System.

We report on the formation and organization of a Cu2+-complexed octadecylphosphonic acid (ODPA) monolayer formed by Langmuir-Blodgett deposition. The formation of the Cu-complexed monolayer is seen to depend sensitively on the subphase pH and Cu2+ concentration, and it is possible to form a monolayer containing the regions of complexed and free ODPA. From the pressure-area isotherm data for these monolayers, we determine the equilibrium constant and free energy of formation for the Cu2+-ODPA complex, ΔG = -22.5 kJ/mol.

Ion Complexation Explains Orders of Magnitude Changes in the Equilibrium Constant of Biochemical Reactions in Buffers Crowded by Nonionic Compounds

The equilibrium constant (K) of biochemical complex formation in aqueous buffers with high concentration (>20 wt %) of nonionic compounds can vary by orders of magnitude in comparison with the K in a pure buffer. The precise molecular mechanisms of these profound changes are not known. Herein, we show up to a 1000-fold decrease of the K value of DNA hybridization (at nM concentration) in standard molecular crowder systems such as PEG, dextrans, Ficoll, and glycerol. The effect responsible for the decrease of K is the complexation of positively charged ions from a buffer by nonionic polymers/small molecules. We determined the average equilibrium constant for the complexation of ions per monomer (∼0.49 M–1). We retrieve K’s original value for a pure buffer if we properly increase the ionic strength of the buffer crowded by the polymers, compensating for the loss of complexed ions.

The Delplot kinetic method applied to systems with adsorbates: Hydrodeoxygenation of benzofuran on a bimetallic CoPd phosphide catalyst supported on KUSY

The Delplot method provides a means of analyzing conversion and selectivity data to derive a reaction sequence and has been applied so far to gas-phase or liquid-phase species. This study analyses the applicability of the method for catalytic reactions and considers for the first time adsorbed intermediates. The method is applied to a contact time study of the hydrodeoxygenation (HDO) of benzofuran at 0.5 MPa and 350 °C over a catalyst consisting of bimetallic CoPd phosphide supported on a potassium ion-exchanged ultra-stable Y (KUSY) zeolite. Both simple and detailed reaction networks were derived. The simple networks considered only gas-phase species and were modeled by a first-order sequence of steps, whereas the detailed network took into account adsorbed intermediates and was simulated using a rake mechanism. The networks were compared using F-statistics, which accounted for the differences in the number of fitting parameters. The detailed network gave a better fit to the experimental data because it represented a more realistic description of the transformation. A suggested sequence from the Delplot method was consistent with the simple network but not with the detailed network. The lack of applicability of the Delplot analysis to the network with adsorbates was linked to overly large equilibrium constants, a determination supported by Delplot fitting for a model sequence. This study indicated the inapplicability of the Delplot method in determining reaction sequences that involve adsorbed species with large equilibrium constants for formation.

Monitoring Silver(I)-Insulin Complexes with Electrospray Ionization Quadrupole Ion Trap Mass Spectrometry.

Ag(I)-insulin complex formation was investigated using electrospray quadrupole ion trap mass spectrometry (ESI-QIT-MS), and Ag(I) ion binding to an insulin molecule was evaluated. The Ag(I) binding ratios were measured in the range of pH 3-8. The highest binding ratio of the Ag(I) ions was obtained at pH 7. Spectrometric titration was carried out at varied molar ratios of Ag(I) ions to insulin from 20/1 to 250/1. It was observed that four Ag(I) ions were bound effectively to an insulin molecule to form Ag(I)1-4-insulin complexes. The formation equilibrium constants of Ag(I)1-4-insulin complexes were calculated from the ESI-QIT-MS peak intensities. The equilibrium constants were found as Kf1 = (2.92 ± 0.18) × 104 M-1, Kf2 = (1.03 ± 0.07) × 104 M-1, Kf3 = (6.67 ± 0.46) × 103 M-1, and Kf4 = (2.00 ± 0.16) × 103 M-1. The tandem MS/MS spectroscopies were studied to evaluate the stability of the Ag(I) complexes. The different flow rates with nano-ESI were performed to determine the binding of Ag(I) ions in solution or gas phase. In conclusion, it was observed that the Ag(I) ion forms stable Ag(I)1-4-complexes with high formation equilibrium constants.

Design and synthesis of ferrocene‐tethered pyrazolines and pyrazoles: Photophysical studies, protein‐binding behavior with bovine serum albumin, and antiproliferative activity against MDA‐MB‐231 triple negative breast cancer cells

We report synthesis and characterization of a series of ferrocene‐pyrazoline and pyrazole hybrids and demonstrate their biomedical applications. All new compounds were identified with the help of spectroscopic techniques and single‐crystal X‐ray analysis. The compounds from both the series show fluorescent activity. The effect of C5 aryl substituent on the luminescent behavior of the parent system was followed by studying their absorption and emission behavior. The binding affinity of a selected ferrocenyl pyrazoline with C5 2‐naphthyl substituent (4g) to bovine serum albumin (BSA) was examined through fluorescence quenching experiments using excitation wavelength 290 nm. The ligand 4g quenched the intrinsic fluorescence of BSA. Strong binding between 4g and BSA was observed with equilibrium constant for the complex formation of the order of 105 M‐1. In vitro anticancer activity of a series of ferrocenyl‐pyrazolines and pyrazoles (4f, 4g, 4h, 5f, 5g, and 5h) was tested against hormone‐independent triple negative breast cancer cells MDA‐MB‐231 in which maximum inhibition potency was noted for 4h with IC50 value of 3.61 mg ml−1.

Synthesis of Mn(II)-containing paratungstate B from aqueous solutions acidified by acetic acid

The method of pH-potentiometric titration and mathematical simulation were used to study the equilibrium processes in aqueous solutions of the WO42––CH3COOH–H2O system in the acidity range Z=(CH3COOH)/(Na2WO4)=0.8–1.7 at СW=0.01 mol L–1 and T=2980.1 K, a constant ionic strength being maintained by sodium nitrate as a background electrolyte ((NaNO3)=0.10 mol L–1). We developed the models of polyoxotungstate anions formation and the equilibrium transformation processes, which adequately describe experimental pH vs. Z dependences. It was found that acetic acid using to create the solution acidity that is necessary for the formation of isopoly tungstate anion contributes only to the formation of protonated paratungstate B anions Нх[W12O40(ОН)2](10–х)– (where x=0–4). We calculated the logarithms of the concentration equilibrium constants of the polyanion formation and plotted the distribution diagrams. Double sodium-manganese(II) paratungstate B Na8(H2O)28Mn(H2O)2[H2W12O42]4H2O was synthesized at Z=1.00 to confirm the results of the mathematical modeling. The chemical composition of the prepared salt was established by chemical elemental analysis, thermal analysis, FTIR spectroscopy, and single crystal X-ray analysis. The stepwise process of salt dehydration was studied by means of differential thermal analysis.

Interplay of Acidity and Ionic Liquid Structure on the Outcome of a Heterocyclic Rearrangement Reaction.

The study of suitable probe reactions is a powerful tool to investigate the properties of nonconventional solvents such ionic liquids (ILs). In particular, we studied the acid-catalyzed mononuclear rearrangement of heterocycles (MHR) of the Z-phenylhydrazone of 5-amino-3-benzoyl-1,2,4-oxadiazole into the relevant 1,2,3-triazole, in solution of ILs by means of kinetic measurements. We chose as solvents six ILs differing both in the cation and anion, in the presence of five carboxylic and sulfonic acids as catalysts. For a useful comparison, the reaction was also performed in 1,4-dioxane and methanol. In general, the reaction occurs faster in ILs, compared to conventional solvents, according to the weaker solvation interactions operating in the former media. The effect of IL anion and cation on the reactivity and on the acidic strength of the catalysts was analyzed. To this aim, we measured the acidic strength of the sulfonic acids in each IL, estimated by the equilibrium formation constant of each acid with 4-nitroaniline. We found that the trend of reactivity as a function of the IL anion mainly reflects the larger difference in acidic strengths of the catalyst. Conversely, acidic strength spans a narrower range as a function of the IL cation. As a result, other factors come into play, such as the π-π interactions involving aromatic IL cations, substrate, and transition states, leading to a more articulate trend.

Interaction of Salicylamide and Salicylic Acid with Iron and Cobalt and their Comparative Study by IR and NMR

The complexes formed by salicylic acid and several substituted derivatives of salicylic acid (Salicylamide) with essential metal ions of the soil (iron and cobalt) have been investigated at 25° and in a medium of variable ionic strength using pH. The equilibrium constants of complex formation of the 1 : 1 , 1 : 2 and1 : 3 mole ratio metal–acid complexes formed are discussed with reference to the activity degradation of substituents. Salicylic acid and Salicylamide after disposal can also react with the various metal ions present in the soil to form complexes. The rate at which these complexes are formed is done with the help of UV-vis. Spectroscopy. The complexes formed are characterized by various Spectroscopic technique viz. FTIR and NMR.

Non-unity stoichiometric reversible electrode reactions. The effect of coupled kinetics and the oxidation of bromide

We explore via simulation, the cyclic voltammetry of the following mechanism involving a reversible electrode process coupled with a follow up reaction in which the product (B) of the electrode reaction reacts chemically with the reactant, A, to form a species C:2A−2e−⇄BB+A⇌kbkfC Such a mechanism is shown, under certain critical combinations of rate constant and reactant concentration to give rise to two voltammetric peaks despite the assumption of a single redox couple (A/B). This results from the formation of C during the first peak whilst the second peak, seen at more oxidizing potentials, reflects the dissociation of C releasing A. A mechanism of the type investigated may hold during the oxidation of bromide(Br−, A) in solution to form bromine(Br2, B) and tribromide (Br3−,C). Simulations are used to explore the conditions for which two peaks are expected in the bromide oxidation system in aqueous solution and for which the two following limiting cases operate3Br−−2e−⇄Br3− and2Br−−2e−⇄Br2 We report experimental data for the bromide oxidation in aqueous solution. These are interpreted via simulations using independent literature values for the rate and equilibrium constants for tribromide formation.

Thermodynamics of antibiotics: natural cyclodextrin inclusion complex formation and covering of nano-metric calcite with these substances

Isothermal titration calorimetry (ITC) has been used to characterize inclusion complex formation of natural (α-, β-, γ-)cyclodextrins with antibiotics (ampicillin—sodium, penicillin G—sodium, streptomycin sulfate) in aqueous solutions. ITC measurements were taken at 298.15 K on Isothermal Titration Calorimeter Nano ITC. The experimental data were analyzed on the basis of the independent site model. Based on the experimental values of equilibrium constant (K) and enthalpy of complex formation (ΔH), the Gibbs energy of complex formation (ΔG) and the entropy of complex formation (ΔS) have been calculated. The analysis of the obtained inclusion complexes show that independently of the kind of cyclodextrin and antibiotics the obtained equilibrium constants are almost the same, but it is a difference between the changes in enthalpies of complex formation for the investigated systems. The stoichiometry of complexes formed both by ampicillin—sodium and by penicillin G—sodium with all the natural cyclodextrins is the same and equal to 1:1 and the complex formation is entropy driven. Three antibiotics (ampicillin—sodium, penicillin G—sodium and streptomycin sulfate) have been used further for covering of the monodisperse calcium carbonate nanoparticles obtained in the reactor (three-phase reaction) with rotating disks. Three series of experiments have been performed. First was connected with adsorption of the antibiotics on the surface on nano-calcite and two others with intercalation of the drugs into nano-metric CaCO3 structure (aggregates). An intercalation has been performed in two ways: one where the antibiotic was added to the reactor chamber at the beginning of the precipitation reaction and second where it was added just after the end of the reaction. Both pure CaCO3 nanoparticle and antibiotic-coated CaCO3 powders were deeply analyzed by the use of the thermogravimetric and the differential scanning calorimetry method. The performed investigations showed that all the antibiotics used can be both adsorbed and intercalated into the nano-metric CaCO3 obtained in the reactor with rotating disks. The different adsorption obtained by different antibiotics was caused by the different interaction between them and nano-calcite, caused by their different structure. The experimental data have allowed also for distinction between the antibiotics molecules present on calcite surface (adsorption) or antibiotics molecules intercalated into the nano-calcite structure. The conducted research shows that both approaches, i.e., formation of inclusion complexes with natural cyclodextrins and covering (adsorption and intercalation) of nano-metric CaCO3, can be successfully implemented for their pharmaceutical applications.

A voltammetric study on drug-DNA interactions: Kinetic and thermodynamic aspects of the relations between the anticancer agent dasatinib and ds-DNA using a pencil lead graphite electrode

The interaction of anticancer drug dasatinib (DSB) with double-stranded calf thymus DNA (ds-DNA) was investigated by using voltammetric techniques on a single-use pencil graphite electrode (PGE). Free DSB displayed a single oxidation peak in acetate buffer solution (pH 4.80). The changes in the anodic CV and DPV peak currents of DSB were investigated in the absence and presence of DNA in aqueous media. Some kinetic parameters, such as diffusion coefficient (D), heterogeneous rate constants (ks), and electrode surface concentration (Γ) of free DSB and DSB-DNA complex, were calculated using CV data. The DSB-DNA complex formation constant (K) and Gibbs free energy (ΔGº) were determined to be 2.51×104 M−1 and 25.10 kJ mol−1, respectively. The results obtained show that there is an interaction between DSB and ds-DNA, and DSB binds to DNA through intercalation interaction. The formation equilibrium constant (K) was found to compare well with similar data reported in the literature. Besides, the thermodynamic parameters (K and ΔGº) obtained by voltammetric measurements were compared with UV spectroscopic data and were found to be approximately of the same order (4.49×104 M−1).

Sensing Zn2+ in Aqueous Solution with a Fluorescent Scorpiand Macrocyclic Ligand Decorated with an Anthracene Bearing Tail.

Synthesis of the new scorpiand ligand L composed of a [9]aneN3 macrocyclic ring bearing a CH2CH2NHCH2-anthracene tail is reported. L forms both cation (Zn2+) and anion (phosphate, benzoate) complexes. In addition, the zinc complexes of L bind these anions. The equilibrium constants for ligand protonation and complex formation were determined in 0.1 M NaCl aqueous solution at 298.1 ± 0.1 K by means of potentiometric (pH-metric) titrations. pH Controlled coordination/detachment of the ligand tail to Zn2+ switch on and off the fluorescence emission from the anthracene fluorophore. Accordingly, L is able to sense Zn2+ in the pH range 6–10 down to nM concentrations of the metal ion. L can efficiently sense Zn2+ even in the presence of large excess of coordinating anions, such as cyanide, sulphide, phosphate and benzoate, despite their ability to bind the metal ion.

Antioxidant Properties of Adrenaline in the Presence of Ge‐132

Using cyclic voltammetry, UV and 1H NMR spectroscopy, we have investigated the effect of 2‐carboxyethylgermanium (Ge‐132), the most common germanium‐containing dietary supplement, on the antioxidant activity of adrenaline in aqueous solutions. The complex formed by adrenaline and Ge‐132 is oxidizable at 400 mV more positive potentials compared to non‐coordinated adrenaline which corresponds to its 9 kcal/mol more difficult oxidation. An equilibrium constant of the complex formation was estimated (1300 m–1). It was shown that at the concentrations &lt;10–3 m the complex Ge‐132‐adrenaline is mostly dissociated to the initial compounds, and the influence of Ge‐132 on the antioxidant properties of adrenaline becomes significant only when the former is in excess. Considering that such concentrations are typical for physiological conditions, this fact can be significant in identifying the mechanism of the biological action of Ge‐132 and its interference with the biological catechols.