Superexchange versus an intermediate BChl− mechanism in reaction centers of photosynthetic bacteria

Kinetic and singlet-triplet data are used to treat the mechanism of electron transfer for BChl^*₂-BChl-BPh in bacterial photosynthetic reaction centers. The data favor a two-step transfer rather than a superexchange single step.     

Magnetische Kernresonanzuntersuchungen an Ti−C−H-Legierungen

Ohne ZusammenfassungMit 4 Abbildungen     

Effects of an applied magnetic field on the anodic dissolution of nickel in HNO3 + Cl− solution

All types of the magnetic field effects on the anodic dissolution of metallic materials have been found in one electrochemcial system: the Ni/0.40 M HNO₃ + 5.0 mM NaCl system. The effects are similar to those of a stirring on all occasions. With the presence of the magnetic field, the current decreases in the active region. However, the current oscillations are changed to active dissolution in the prepassive region and induced in the transitive potential from the prepassive region to the passive region by the magnetic field. In the passive region, the magnetic field has little influence. Those effects are discussed with different rate-determining steps. The study of the effects of the magnetic field on this system may help us understand why the magnetic field enhances the corrosion rates in some conditions while suppressing them in others.     

Facile synthesis of an optical sensor for CO32− and HCO3− detection

A novel fluorogenic signalling probe (E)-3-(4-methoxyphenyl)-4-[(4-nitrobenzylidene)amino]-1H-1,2,4-triazole-5(4H)-thione (6) for the carbonate and bicarbonate ions has been developed through microwave assisted Schiff base formation reaction. The anion recognition occurs through hydrogen bonding assessed by ¹H NMR titration experiments. The photophysical results of probe 6 corroborates its applicability as an optical sensing platform for carbonate as well as bicarbonate ions in mixed aqueous organic media depending on pH of reaction solution. The fluorescence emission signal enhancement at 424 nm and considerable shift in the signal position as well as molar absorptivity to the probe absorption bands upon CO₃^2? and HCO₃^? addition suggest the affinity of probe 6 towards these ions in comparison to a variety of competitive ions in aqueous/ethanol (7:3, v/v) at neutral pH and ambient temperature. From the fluorescence titration experiment, the limit of detection was calculated to be 1.91 μM.     

Preparation of an extremely dense BaCe0.8Sm0.2O3−δ thin membrane based on an in situ reaction

The thin membrane of BaCe_0.8Sm_0.2O_3−δ (BCS) with high quality was successfully fabricated on porous NiO–BCS anode substrate through a novel in situ reaction method. The key part of this method is to directly spray well-mixed suspension of BaCO₃, CeO₂ and Sm₂O₃ instead of pre-synthesized BCS ceramic powder on the anode substrate. After sintering at 1400 °C for 5 h, the extremely dense electrolyte membrane in the thickness of 10 μm is obtained. A single cell was assembled with La_0.7Sr_0.3FeO_3−σ as cathode and tested with humidified hydrogen as fuel at 650 °C. The open circuit voltage (OCV) and maximum power density respectively reach 1.04 V and 535 mW/cm². Interface resistance of cell under open circuit condition was also investigated.     

Recent Advance in the Development of Singlet−Fission−Capable Polymeric Materials

Singlet fission (SF) is a spin–allowed process in which a higher–energy singlet exciton is converted into two lower-energy triplet excitons via a triplet pair intermediate state. Implementing SF in photovoltaic devices holds the potential to exceed the Shockley–Queisser limit of conventional single-junction solar cells. Although great progress has been made in exploiting the underlying mechanism of SF over the past decades, the scope of materials capable of SF, particularly polymeric materials, remains poor. SF–capable polymer is one of the most potential candidates in the implementation of SF into devices due to their distinct superiorities in flexibility, solution processability and self-assembly behavior. Notably, recent advancements have demonstrated high-performance SF in isolated donor-acceptor (D-A) copolymer chains. This review provides an overview of recent progress in the development of SF-capable polymeric materials, with a significant focus on elucidating the mechanisms of SF in polymers and optimizing the design strategies for SF-capable polymers. Additionally, the paper discusses the challenges encountered in this field and presents future perspectives. It is expected that this comprehensive review will offer valuable insights into the design of novel SF-capable polymeric materials, further advancing the potential for SF implementation in photovoltaic devices.     

Electropolymerization of O-Phenylenediamine in an Ionic Liquid

Ionic liquid like 1-ethyl-3-methylimidazolium bromine ([EMIM]Br) has been used as electrolyte for the electropolymerization of O-phenylenediamine at glassy carbon electrode by cyclic voltammetry. It is found that poly (O-phenylenediamine) film modified electrode has favorable electrochemical activity in acid solution.     

Structural and Electronic Influences on Rates of Tertpyridine−Amine CoIII−H Formation During Catalytic H2 Evolution in an Aqueous Environment

In this work, the differences in catalytic performance for a series of Co hydrogen evolution catalysts with different pentadentate polypyridyl ligands (L), have been rationalized by examining elementary steps of the catalytic cycle using a combination of electrochemical and transient pulse radiolysis (PR) studies in aqueous solution. Solvolysis of the [Co^II−Cl]⁺ species results in the formation of [Co^II(κ⁴-L)(OH₂)]²⁺. Further reduction produces [Co^I(κ⁴-L)(OH₂)]⁺, which undergoes a rate-limiting structural rearrangement to [Co^I(κ⁵-L)]⁺ before being protonated to form [Co^III−H]²⁺. The rate of [Co^III−H]²⁺ formation is similar for all complexes in the series. Using E_1/2 values of various Co species and pK_a values of [Co^III−H]²⁺ estimated from PR experiments, we found that while the protonation of [Co^III−H]²⁺ is unfavorable, [Co^II−H]⁺ reacts with protons to produce H₂. The catalytic activity for H₂ evolution tracks the hydricity of the [Co^II−H]⁺ intermediate.     

Photolysis of Fe(CO)42− in an aqueous NaOH glass at 77 K. formation of solvated electrons

The photolysis of [Fe(CO)₄]²⁻ in 10 M NaOH glass at 77 K leads to the formation of solvated electrons with θ = 0.03 at λ_irr = 254 nm. The solvated electrons, which are stable under these conditions, are identified by their characteristic absorption band at λ_max = 588 nm.     

Medium effects on HSO 4 − formation in a mixture of isomolar solutions of hydrochloric acid and an alkali metal chloride

The strontium sulfate solubility has been studied in mixtures of isomolar MCl and HCl solutions (M = Li, Na, K, Cs) with ionic strengths of I = 0.5, 1.0, 2.0, 3.0, and 4.0 at 25°C. At I ≥ 2, the SrSO₄ solubility as a function of hydrogen ion concentration passes through a maximum in all systems but (Li,H)Cl. The position of this maximum depends only slightly on the nature and ionic strength of the medium. The presence of the maximum is unambiguous evidence that there are secondary effects of the medium associated with the substitution of H⁺ for M⁺. These effects oppose the ordinary shift of the HSO ₄ ^? formation equilibria. A method is suggested for separating these effects. The standard values of pSP⁰ and logβ⁰, determined by extrapolation to zero ionic strength, are in satisfactory agreement with the literature. The parameter α₁, which characterizes the secondary effects of the medium on one of the basic equilibrium constants (log K _S1 ^O ), increases in the order (Li,H)Cl < (Na,H)Cl < (K,H)Cl < (Cs,H)Cl.     

Electrochemical Synthesis of Polythiophene in an Ionic Liquid

Polythiophene(PTh) was prepared by the direct electrochemical synthesis in an ionic liquid ([BMIM]PF6) containing 0.1mol/L thiophene by cyclic voltammetry,constant potential and constant current techniques. It is found that smooth and blue-green PTh films can be obtained at a potential of ca. 1.75V(vs. Ag/AgCl) or a current of ca. 1.5mA cm^-2 in the ionic liquid.     

Cholesterol-based simple supramolecular gelators: an approach to selective sensing of CN− ion with application in dye adsorption

Cholesterol-linked simple supramolecular gelators 1–3 with functional diversity have been designed on 4-hydroxybenzaldehyde backbone for anion sensing through gel-to-sol methodology. Change in functional group in the gelators of common structural feature has significant impact on gelation, gel properties, morphology and anion sensing behavior. The dicyanovinyl derivative 3 has been established as superior gelator among the three as it forms gel from varieties of solvents with lowest concentration. All the three gels are applied in anion recognition. The gel state of 1 remains virtually intact in presence of all the anions tested. The oxime derivative 2 interacts with basic anions like CN^?, F^? and AcO^? and displays no selectivity in gel phase anion sensing. On contrary, the dicyanovinylated analogue 3 shows gel-to-sol transition selectively in presence of CN^? and validates its visual sensing. Additionally, the gel of 3 as explored in dye adsorption works well in rapid removal of crystal violet, a cationic dye from waste water.     

Coumarin-based urea-amide scaffold in ratiometric fluorescence sensing of CN−

Coumarin-based urea and urea–amide scaffolds 1–3 have been designed and synthesized for the selective and naked eye detection of cyanide ion. Of the three, compound 3 exhibits ratiometric fluorescence change selectively in the presence of CN^? and validates the rationality in designing anion receptor. Upon interaction with CN^?, the color of the solution of 3 in CH₃CN under UV exposure becomes bright yellow, which is beneficial for its naked eye detection. Addition of CN^? of ～10^?4 M brings nice color change from colourless to yellow in ordinary light. The sensing event is supposed to be due to nucleophilic addition of CN^? to the coumarin unit enabling intramolecular charge transfer (ICT) mechanism.     

Reversal of regiocontrol in the alkylation of an arene π-complex

Tricarbonyl(η⁶-1-methoxy-2,4-dimethylbenzene)manganese(1+) hexafluorophosphate(1−) was preferentially alkylated by vinyl Grignard reagents at C(5), When methymagnesium bromide was used, however, reaction occurred predominantly at C(3), the more hindered of the two sites meta to the methoxy substituent.     

Effect of EDTA on the diffusion behavior of 99TcO4 − and ReO4 − in GMZ bentonite

Polyaminopolycarboxylate EDTA with powerful metal-binding property, which often presents in low and intermediate-level waste, can enhance the radionuclide migration. The effect of EDTA on the diffusion behavior of ⁹⁹TcO₄ ^? and ReO₄ ^? in Gaomiaozi (GMZ) bentonite was investigated by using through-diffusion method. For ⁹⁹TcO₄ ^? in present of EDTA, the D _e values was (1.2 ± 0.1) × 10^?11 m²/s, which was 4 times higher than that in absent of EDTA. It can be explained that the complexation between ⁹⁹TcO₄ ^? and EDTA might be formed. By contrast, the D _e values of ReO₄ ^? remained unchanged in present or absent of EDTA, indicating that ReO₄ ^? could not complex with EDTA. However, the diffusion of ReO₄ ^? could be increased in present of EDTA, the D _a value was found to be increased from 1.8 × 10^?10 to 5.4 × 10^?10 m²/s. It demonstrated that ReO₄ ^? need more drastic conditions to form the Re(VII)–EDTA complexes than those used for ⁹⁹TcO₄ ^?. For both ReO₄ ^? and ⁹⁹TcO₄ ^?, the rock capacity factor α is less than the total porosity ε _tot, indicating that they has little retention/sorption on the surface of bentonite.     

Separation and preconcentration of131I− and131IO 3 − in a liquid-liquid system

The application of isotope exchange in a liquid-liquid system for the separation and preconcentration of¹³¹I^– and¹³¹IO^3/– from water is described. For this purpose a solution of elemental iodine in tri-n-butyl phosphate diluted with toluene was used. The influence of various factors on the separation efficiency of¹³¹I was investigated. These are: time of the exchange, concentration of a carrier in the aqueous phase, concentration of I₂ in the organic phase, volume ratio of the phases, pH, foreign ions, storage of the organic phase, etc. The method is quite rapid and the selective preconcentration of these chemical forms of radioiodine from water can be accomplished even in the presence of the most important fission products. This method makes also possible to separate these chemical forms from each other under controlled pH conditions. The activity of the separated radioiodine can be measured advantageously, e.g., by homogeneous liquid scintillation counting after decolourization of the organic phase.