Mechanism of 1,4,5,8-naphthalene tetracarboxylic acid dianhydride hydrolysis and formation in aqueous solution

The study of highly conjugated, carbonyl-containing molecules such as 1,4,5,8-naphthalene tetracarboxylic dianhydride, III, is of interest since reactivity differences and transmission of electronic effects through the conjugated framework can be evidenced. The kinetics of hydrolysis of III in aqueous solution were determined from 5 M acid to pH 10. In basic solution hydrolysis of III yields, sequentially, 1,4,5,8-naphthalene diacid monoanhydride, II, and 1,4,5,8-naphthalene tetracarboxylic acid, I. The second order rate constant for alkaline hydrolysis is 200 fold higher for the first ring opening. The water-catalyzed hydrolysis of III yields a pH-dependent mixture of ionic forms of I and II. The rate constant for water-catalyzed hydrolysis of III is 25 fold higher than that for II. In concentrated acid the rates for reaching equilibrium (I, II and III) increase and III is the major product. The pK(a)s of I (3.24, 5.13 and 6.25) and II (3.05, 5.90) were determined by potentiometric, fluorescence and UV spectroscopy titrations and by quantitative fit of the kinetic and equilibrium data. The apparent, pH-dependent, equilibrium constants, K(EqII), for anhydride formation between I and II were obtained from the UV spectra. The quantitative fit of kinetic and equilibrium data are consistent with the assumption that anhydride formation only proceeds with the fully protonated species for both I and II and permitted the estimation of the equilibrium constants for anhydride formation, K(EqII). The value of K(EqII) (I <==> II) between pH 1 and 6 was ca. 5. Geometry optimization calculations in the gas phase of the reactions of III in alkaline, neutral and acid conditions, at the DFT level of theory, gave electronic distributions that were qualitatively consistent with the experimental results.     

Novel quinoxalinophenanthrophenazine-based molecules as sensors for anions: synthesis and binding investigations

The design and synthesis of two novel quinoxalinophenanthrophenazine-based anion sensors are reported. Binding studies of these sensors with an array of mono- and polyatomic anions using UV-vis, fluorescence, and NMR titrations have shown 1:1 and 1:2 sensor-to-anion ratios. Binding constants were calculated for anions, which exhibited high affinity for the sensors, including acetate, benzoate, cyanide, and fluoride ions.     

Phosphonium-mediated cyclization of N-(2-aminophenyl)thioureas: efficient synthesis of 2-aminobenzimidazoles

BOP efficiently promoted the phosphonium-mediated cyclization of thioureas, leading to a convenient synthesis of 2-aminobenzimidazoles. Compared to conventional methods, the reactions were complete at room temperature with times ranging from a few minutes to 1 h in near quantitative yields. This method is also applicable to the synthesis of more challenging structures such as 2-akylaminobenzimidazoles and 2-(N-acyl)-aminobenzimidazoles. The methodology described herein represents a mild and efficient route to a variety of 2-aminobenzimidazoles.     

Viologen‐Templated Arrays of Cucurbit[7]uril‐Modified Iron‐Oxide Nanoparticles

Magnetic and fluorescent assemblies of iron‐oxide nanoparticles (NPs) were constructed by threading a viologen‐based ditopic ligand, DPV²⁺, into the cavity of cucurbituril (CB[7]) macrocycles adsorbed on the surface of the NPs. Evidence for the formation of 1:2 inclusion complexes that involve DPV²⁺ and two CB[7] macrocycles was first obtained in solution by ¹H NMR and emission spectroscopy. DPV²⁺ was found to induce self‐assembly of nanoparticle arrays (DPV²⁺?CB[7]NPs) by bridging CB[7] molecules on different NPs. The resulting viologen‐crosslinked iron‐oxide nanoparticles exhibited increased saturation magnetization and emission properties. This facile supramolecular approach to NP self‐assembly provides a platform for the synthesis of smart and innovative materials that can achieve a high degree of functionality and complexity and that are needed for a wide range of applications.     

水介质中药物-AOT混合物的温度依赖的混合胶束化行为(英文)

The mixed micellization behavior of an amphiphilic antidepressant drug amitriptyline hydrochloride(AMT)in the presence of the conventional anionic surfactant sodium bis(2-ethylhexyl)sulfosuccinate(AOT)was studied at five different temperatures and compositions by the conductometric technique.The critical micelle concentration(cmc)and critical micelle concentration at the ideal state(cmcid)values show mixed micelle formation between the components(i.e.,drug and AOT).The micellar mole fractions of the AOT(X1)values calculated using the Rubingh,Motomura,and Rodenas models show a higher contribution of AOT in the mixed micelles.The interaction parameter(β)is negative at all temperatures and the compositions show attractive interactions between the components.The activity coefficients(f1and f2)calculated using the different proposed models are always less than unity indicating non-ideality in the systems.TheΔGmΘ values were found to be negative for all the binary mixed systems.However,ΔHmΘ values for the pure drug as well as the drug-AOT mixed systems are negative at lower temperatures(293.15-303.15 K)and positive at higher temperatures(308.15 K and above).TheΔSmΘ values are positive at all temperatures but their magnitude was higher at T=308.15 K and above.The excess free energy of mixing(ΔGex)determined using the different proposed models also explains the stability of the mixed micelles compared to the pure drug(AMT)and surfactant micelles.     

Co-extraction and separation of zirconium and hafnium by long-chain amines from sulphate media

The extraction of Zr and Hf from sulphuric acid systems by solutions of Primene JMT (a long-chain primary amine) in kerosene, is described. The effect of contact time, free acidity, solvent concentration and temperature, has been thoroughly examined. A rapid improved method for HfZr separation is suggested.     

Selection of Microalgae and Cyanobacteria Strains for Bicarbonate-Based Integrated Carbon Capture and Algae Production System

Using microalgae to capture CO₂ from flue gas is an ideal way to reduce CO₂ emission, but this is challenged by the high cost of carbon capture and transportation. To address this problem, a bicarbonate-based integrated carbon capture and algae production system (BICCAPS) has been proposed, in which bicarbonate is used for algae culture, and the regenerated carbonate from this process can be used to capture more CO₂. High-concentration bicarbonate is obligate for the BICCAPS. Thus, different strains of microalgae and cyanobacteria were tested in this study for their capability to grow in high-concentration NaHCO₃. The highest NaHCO₃ concentrations they are tolerant to were determined as 0.30 M for Synechocystis sp. PCC6803, 0.60 M for Cyanothece sp., 0.10 M for Chlorella sorokiniana, 0.60 M for Dunaliella salina, and 0.30 M for Dunaliella viridis and Dunaliella primolecta. In further study, biomass production from culture of D. primolecta in an Erlenmeyer flask with either 0.30 M NaHCO₃ or 2 % CO₂ bubbling was compared, and no significant difference was detected. This indicates BICCAPS can reach the same biomass productivity as regular CO₂ bubbling culture, and it is promising for future application.