L2 Mol Research Articles

A reactive transport model for in-situ leaching of weathered crust elution-deposited rare earth ores using ammonium sulfate

This study presents a reactive transport model for the in-situ recovery of weathered crust elution-deposited rare earth ores and aims to provide predictive and optimization techniques for rare earth recovery. The model integrates Kerr's selection coefficient, dynamic reversible shrinking core model, and transport model to capture the dynamics of leaching fraction, rare earth elements (REEs), and exchangeable ions during in-situ leaching. The proposed model was validated through bench-scale equilibrium, kinetic, and column experiments, as well as numerical simulation. The results indicate that the deviation from using a single selection coefficient (referred to as 4.26 L2 mol−2 in this study) for modeling is acceptable. Both Darcy velocity and concentration of leaching solution mainly affect the peak value and bending degree of the post-peak leaching curve. Optimal cessation of leaching solution injection, such as substituting water after the peak of the leaching curve, enables effective conservation of leaching solution and reduction of environmental pollution. Differences of at least two orders of magnitude were observed between dynamic parameters derived from kinetic experiments (1.46 and 4.34 L mol−1 min−1) and those obtained from column experiments (2.60 × 10−3 and 1.71 × 10−2 L mol−1 min−1). This finding carries substantial implications for in-situ recovery and mineralization processes, highlighting the need for further investigation at the pore scale.

Spectral Studies of Coordination of 1-Methyl-2-(pyridin-4-yl)-3,4-fullero[60]pyrrolidine by Highly Substituted Cobalt(II) Porphyrin

A new dendrimeric cobalt(II) complex CoP has been obtained when reacting (5,15-bis[3,5-bis(tert-butyl)phenyl]-10,20-bis{4,6-bis[3,5-bis(3,6-di-tert-butylcarbazole-9-yl)phenoxy]pyrimidin-5-yl}porphine with Co(AcO)2·4H2O. The process of two-step two-way coordination of 1-methyl-2-(pyridin-4'-yl)-3,4-fullero[60]pyrrolidine (PyC60) with cobalt(II) porphyrin ends with the formation of a stable 1 : 2 complex, a triad of composition (PyC60)2CoP. The process has been completely kinetically described using UV-vis and fluorescent spectroscopy data. The stability constant (K) of the coordination complex is (9.9 ± 2.4) × 108 L2 mol–2 (log K = 9.0). The chemical structure of the triad has been determined by UV-vis, 1H NMR, and IR spectroscopy. The effect of PyC60 fluorescence quenching in the triad has been found and studied, and the static mechanism of the quenching process has been substantiated. The result can be used in optoelectronics to optimize the structures of donor–acceptor systems with the property of photoinduced electron transfer.

Kinetics of Catalytic Oxidation of Oleic Acid Methyl Ester

The results of studying the kinetics of the reaction of catalytic oxidation of oleic acid methyl ester with hydrogen peroxide in a two-phase system (aqueous phase-organic phase) in the presence of a bifunctional catalyst of the composition [(Octn)3NMe]3{PO4[WO(O2)2]4} are presented. For the selected reaction conditions, the first orders of catalyst, substrate and oxidizer are established. The value of the activation energy for the temperature range 313–353 K is 47 ± 3 kJ/mol, and the pre-exponential multiplier is (6.0 ± 0.3) × 107 L2 mol–2 min–1.

Binding behavior and in vitro cytotoxicity of inclusion complexes between aminopterin and cucurbit[7]uril

Aminopterin (AMT) is a kind of universal antineoplastic drugs, but it has severe toxic and side effects, leaving it rarely used in clinic. Herein, we found that cucurbit[7]uril (CB[7]) and AMT can form stable inclusion complexes, and the formation of CB[7]-AMT 2:1 supramolecular inclusion complex was confirmed by UV-visible absorption spectra, fluorescence spectra, 1H NMR, and molecular modeling calculations in aqueous solution. Binding stability constants (Ks) were determined by UV-visible and fluorescence spectra method, with 3.88 × 1010 L2 mol–2 and 5.24 × 1010 L2 mol–2, respectively. The binding energy was calculated to be 102.6 kcal mol–1 for the CB[7]-AMT complex. And then, through a series of cell experiments of CCK8 assay, DAPI staining and hoechst33342/PI double staining, we fully proved that the CB[7]-AMT complex can reduce the toxicity of AMT to normal cells such as hepatocyte line LO2, and improve its anticancer effect on cancer cells overexpressing spermine, typically like human colon cancer cell line HCT116. It confirmed that the CB[7]-AMT complex had the effect of reducing toxicity and increasing efficiency. These results indicated that CB[7]-AMT inclusion complex might be a promising novel formulation of AMT for its clinical development.

Process intensification of thumba methyl ester (Biodiesel) production using hydrodynamic cavitation

The development of clean and sustainable biofuel generation from sustainable feedstock using an integrated process intensification approach like hydrodynamic cavitation (HC) is essential now. The current research is a 'first of its kind' where hydrodynamic cavitation is integrated with heterogeneous catalyst, i.e. TiO2, to prepare thumba methyl esters (TME). So far, no studies on biodiesel production using heterogeneous catalysts using HC are reported in the literature. Experiments were performed with an optimized orifice plate to investigate the effects of operating parameters viz., Thumba oil to methanol molar ratio (1:4–1:8), TiO2 concentration (1–1.4% by weight of oil), and operating temperature (50 °C to 70 °C). Maximum triglyceride conversion (71.8%) was obtained at thumba oil to methanol ratio of 1:6, TiO2 concentration of 1.2% weight percentage and operating temperature of 60 °C in hydrodynamic cavitation reactor within 1 h at 5 bar. The cavitational yield for HC was found to be 9.3 × 10−6 moles L/J, which was almost 27% higher than the value for the conventional approach (3.37 × 10−7 moles L/J). The experimental data fitted second-order reaction kinetics w.r.t limiting reactant, i.e., thumba oil and first-order w.r.t excess reactant, i.e., methanol. The pre-exponential factor (k0) and activation energy (E) of the alcoholysis reaction was found to be 82.26 L2 mol−2 min−1 and 15.44 kJ/mol, respectively. The thermodynamic analysis suggested that the alcoholysis of the thumba oil followed the endergonic reaction pathway. Thumba methyl ester (TME) synthesized via this intensified approach is a novel and energy-efficient method compared to the conventional method.

Degradation of Organic Carbon in Pharmaceutical Wastewater: a Kinetic Approach

This study aimed to investigate the degradation kinetics of the total organic carbon (TOC) in real pharmaceutical wastewater. Because of the complexity of real wastewaters and the lack of knowledge on all reactions involved in their chemical degradation, the use of a kinetic approach becomes difficult. To overcome this difficulty, we adopted a kinetic model based on chemical equations validated for mechanisms of free radical generation. Photo-Fenton reactions were performed in a 1-L tubular reactor. The developed model satisfactorily described the degradation kinetics of TOC in wastewater, with an R2 of 0.9997. The TOC degradation rate constant (kd) was estimated at 1 × 1011 L2 mol2 s−1, in agreement with literature values for the degradation kinetics of organic compounds. UV radiation had a positive effect on degradation, contributing to HO• formation. The adopted mathematical approach was highly sensitive to the formation rate constant of HO• from H2O2 (k4). By assuming the reaction to follow variable order kinetics (β = 1 and β = 2), it was possible to improve the goodness of fit of the model. Our results suggest, albeit in an incipient way, that the approach used in this study can be extended to the kinetic understanding of other complex wastewaters.

Reduction of p-nitrophenol in an airlift electrochemical reactor with iron electrodes

Kinetic experiments of removal of p-nitrophenol (p-NP) from aqueous solution were performed in an airlift electrochemical reactor at 19.3 ± 0.5 °C and 1 atm. It was demonstrated that a simple and low-cost electrochemical reacting system with iron electrodes is able to reduce efficiently p-NP to a more friendly environment product. The rate limiting step of p-NP reduction and production of p-aminophenol at apparent rate constants between 6.03 ± 0.22 × 10–5 and 9.85 ± 0.45 × 10–5 s−1 was the one-electron transfer reaction at the liquid-cathode interface. The reaction involved the substituent nitro group as electron withdrawer with p-NP adsorbed on the cathode in a quasi-equilibrium condition. The residual amount of soluble ferrous ion, the major product of electrolytic oxidation of zero valent iron at the anode, was lower than the allowable limit of 2.68 × 10–4 mol L−1. The kinetics of oxidation of Fe2+ to ferric ion and the hydrolysis of Fe3+ to iron hydroxides was properly described by a reaction rate that was proportional to the partial pressure of oxygen, first- and nth-order in Fe2+ and hydroxyl anion, respectively. The rate constant of the overall oxidation/hydrolysis reaction of Fe2+ was 6.31 ± 0.63 × 1014 L2 mol−2 atm−1 s−1 for pH from ∼5.2–6.6 (n = 2) and 3.75 ± 0.88 × 10–8 mol L−1 atm−1 s−1 for pH from ∼6.9–8.8 (n = −1).

Self-organizing donor-acceptor assemblies of cobalt(II) porphyrin ligated with gold(III) porphyrin or fullero[60]pyrrolidine in liquid medium

This work provides the results of the spectroscopic, electrochemical, and photoelectrochemical study of the self-assembly in the systems consisting of (2,3,7,8,12,13,17,18-octaethylporphinato)cobalt(II) (CoOEP), (2,3,7,8,12,18-hexamethyl,13,17-diethyl,5-(4-pyridyl)porphinato)gold(III) chloride (ClAuP)/1′-N-methyl-2′-(pyridin-4-yl)pyrrolidino[3′,4′:1,2][60]fullerene (PyC60), and 1,2-dichlorobenzene/toluene as an electron donor, an acceptor, and a liquid medium, respectively. The results indicate axial coordination of electron acceptor functionalized by the pyridine units by cobalt(II) porphyrin with the donor-acceptor (ClAuP)2CoOEP/(PyC60)2CoOEP triad formation. The thermodynamic stability constant is (4.91 ± 1.10)×109 L2 mol−2 and (4.10 ± 1.14) ×1010 L2 mol−2 for ClAuP and PyC60, respectively. The formation of supramolecules was confirmed by UV, visible, IR, 1H NMR spectroscopy and cyclic voltammetry. DFT calculations (B3LYP+def2-SVP) detect octahedral geometry of the coordination center with the trans configuration of the axial ligands in the triads as well as the excited state calculations establish photoinduced electron transfer (PET). The jphavg value 266 μA cm−2 for the Ti|(ClAuP)2CoOEP|0.5 M Na2SO4|Pt system being 2–2.5 times higher compared with the precursors and slightly higher compared with (PyC60)2CoOEP shows that gold(III) porphyrin as an electron acceptor can be successfully used. The development of donor/acceptor platform selection strategy for the obtaining of photoactive supramolecules is an urgent task for future deriving of photovoltaic devices.

A new N-methylhydrazinecarbothioamide incorporated “naked-eye” and “turn-off” chemosensor for selective and low detection of Cu2+ ions and computation study

The rising concentration of Cu2+ ions in the environment is dangerous and showed adverse effects on the environment and human health. To concern this issue in this work, we designed N-methylhydrazinecarbothioamidebased (E)-2-(2-methoxy-4-(3-(2-methoxy-4-((E)-(2-(methylcarbamothioyl) hydrazono)methyl)phenoxy)propoxy)benzylidene)-N-methylhydrazinecarbothioamide (PMPMMHC) new chemosensor for selective and rapid detection of Cu2+ ions with quenching in luminescence or “turn-off” response among various cations and anions in semi-aqueous medium DMSO/H2O (1/1 v/v). The addition of Cu2+ ions to the solution of PMPMMHC showed remarkable changes in color, UV–vis, fluorescence spectra, and redox potential. The insight spectroscopic titrations result in the binding stoichiometry 1:2 (PMPMMHC:Cu2+) with a limit of detection (LOD) 15 Nm showing good binding constant 1.37 × 107 L2 mol−2 as determined by the Benesi–Hildebrand Equation in the linear range of detection 20–200 μM. In computational studies, chemosensor reveals unique interaction with Cu2+ as a result of metal-pi acceptor (2.33 Å and 2.77 Å) interactions as well as the non-classical intra-hydrogen bonding. In mechanistic studies, the photoinduced electron transfer (PET) inhibits and signal changes arise due to the electronic transition of higher-energy orbitals (HOMO) to lower energy orbitals (LUMO) as a result of PMPMMHC:Cu2+ binding.

Using High-Temporal-Resolution Ambient Data to Investigate Gas-Particle Partitioning of Ammonium over Different Seasons.

Ammonium is one of the dominant inorganic water-soluble ions in fine particulate matter (PM2.5). In this study, source apportionment and thermodynamic equilibrium models were used to analyze the relationship between pH and the partitioning of ammonium (ε(NH4+)) using hourly ambient samples collected from Tianjin, China. We found a "Reversed-S curve" between pH and ε(NH4+) from the ambient hourly aerosol dataset when the theoretical ε(NO3-)* (an index identified in this work) was within specific ranges. A Boltzmann function was then used to fit the Reversed-S curve. For the summer data set, when ε(NO3-)* was between 0.7 and 0.8, the fitted R2 was 0.88. Through thermodynamic analysis, we found that the values of k[H+]2 (k = 3.08 × 104 L2 mol-2) and ε(NO3-)* can influence the pH-ε(NH4+) curve. Under certain situations, the values of k[H+]2 and ε(NO3-)* are similar to each other, and ε(NH4+) is sensitive to pH, suggesting that ε(NO3-)* plays an important role in affecting the ε(NH4+). During summer, winter, and spring seasons, when the relative humidity was greater than 0.36 and ε(NO3-)* was between 0.8 and 0.95, there was an obvious Reversed-S curve, with R2 = 0.60. The theoretical k[H+]2 and ε(NO3-)* developed in this work can be used to analyze the gas-particle partitioning of ammonia-ammonium and nitrate-nitric acid in the ambient atmosphere. Also, it is the first time that we created the joint source-NH3/HNO3 maps to integrate sources, aerosol pH and liquid water content, and ions (altogether in one map), which can provide useful information for designing effective strategies to control particulate matter pollution.

Glycerol acetylation catalyzed by an acidic styrene-co-dimethacrylate resin: experiments and kinetic modeling

This work reports an experimental study and a kinetic model for glycerol acetylation. A sulfonated resin of styrene cross-linked with ethylene glycol dimethacrylate (EGDMA) was synthesized and applied as a catalyst in the referred reaction. Furthermore, the commercial sulfonated styrene–divinylbenzene resin Amberlyst 36® was also tested in the glycerol acetylation and the results were compared to those obtained with the synthesized resin. The reactions were carried out at two different temperatures: 80 and 90 °C. The experimental data were collected and compared to predictions of a homogeneous kinetic model of a second-order reaction using the Scilab software. The blank experiments had lower conversions than the catalyzed reaction. The difference found between the ion exchange capacities for PSEGDMA (3.45 mmol g−1) and Amberlyst 36 (5.45 mmol g−1) did not produce significant differences in the catalysis results. The average R2 obtained for the model fitting was 0.89733 and the rate constants of the catalyzed portion were found to be in the ranges: 0.01 × 10–5–1.30 × 10–5 L2 mol−2 min−1 for Amberlyst 36 and 0.01 × 10–5–2.74 × 10–5 L2 mol−2 min−1 for PSEGDMA. According to the rate constants obtained herein, it is concluded that PSEGDMA resins has a higher efficiency for application in the referred reaction. This conclusion can be verified by calculating the efficiency per catalytic sites, which were 51.78 and 104.24 for Amberlyst 36 and PSEGDMA, respectively. This calculation can be used because it is the same catalyst but supported in different structures, proven by calculating the swelling index of the resins, which are shown in the “Results” section.

The development of analytical methods to determine metoclopramide-hydrochloric acid in the standard raw and it compared with pharmaceuticals

The three novel easy, to the prepare and sensitive spectral methods, were used to estimate metoclopramide in both standard and pharmaceuticals. The effective double–electron, was present in the metoclopramide compound helps to interact in an acidic medium with a reagent such as diazetide resorcinol and 8-hydroxyquinoline reagents. The present article was extended to find out three analytical methods with UV-V is the detector. In both A and B methods, two azo-dyes are formed, they are orange-red and red stable and have high water solubility, giving highest absorption values at 415 nm and 485 nm but the C method will depend on a complex colour configuration with the p-benzoquinone reagent, which has a maximum absorption at a wavelength of 285 nm. Beer's law was applied in a range of concentrations between 1 and 10 μg / ml, 2-20 μg / ml and 1-30 μg / ml. The values ​​of the molar absorption factors were (4.1224 × 104, 3.0229 × 104 and 1.7373 × 104) L mol-1cm-1 with a sensitivity of Sandell’s equal to 0.2606 × 10-4, 0.9834 × 10-4 and 0.2568 × 10 - 4 μg cm-2 to methods A, B respectively and LLOD values ​​were 0.255, 0.553 and 0.158 μg / ml to methods A, B and C. LLOQ 0.512, 0.898 and 0.455 μg / ml to methods A, B, C respectively. The constant fixed Kf configuration was also calculated for the colored outputs of the reaction where it was found to be equal to 43.6435 × 108, 54.6261 × 10-8 and 17.29099 × 106 L2 mol-2 to all methods A, B, C respectively. The values ​​of G were calculated based on -43.9293 KJ / mol, -44.3735 and -51.2019. G values, molar absorption factor, Sandell sensitivity, detection limit.

Turn-on fluorescence study of a highly selective acridine-based chemosensor for Zn2+ in aqueous solutions

4,5-Bis(aminomethyl)acridine (LN) was investigated as a chemosensor for metal ions in aqueous solutions and it is selective for Zn2+, through a linear fluorescence enhancement of 230% in the concentration range of 17.8–600 μmol L−1. Benesi-Hildebrand and Job method formalisms showed the formation of a very stable complex with one of the highest binding constant (2.43 × 1014 L2 mol−2) reported for zinc, and a 2:1 (metal ion/sensor) ratio. DFT and TD-DFT calculations could explain the fluorescence augmentation upon complexation between Zn2+ and LN. Limit of detection and limit of quantification (R2 = 0.9970, least squares method) were found to be 5.36 and 17.8 μmol L−1, respectively, and appropriate robustness was verified based on the variation of several analytical conditions. Practical application testes showed recovery results such as (92 ± 4)% (tap water) and (99 ± 1%) (mineral water), proving to be adequate to quantify Zn2+ in real water samples, showing no effect of interfering ions.

Kinetics of β-Carotene Oxidation in the Presence of Highly Active Forms of µ-Carbido Diiron(IV) Tetraphenylporphyrinate

The oxidative destruction of β-carotene in the presence of highly oxidized forms of µ-carbido-bis[(5,10,15,20-tetraphenyl-21H,23H-porphyrinato)iron(IV)] (1 → 3) or its analog with axially coordinated imidazole (2 → 4) obtained under the action of tert-butyl hydroperoxide tBuOOH was studied by spectrophotometry. It was found that compound 3 is the oxo form of compound 1 singly oxidized at the macrocyclic ligand (π radical cation) under the action of which β-carotene is oxidized with a rate constant k = 3.3 L2 mol–2 s–1. A conclusion is drawn that short-lived compound 4 has unique EAS and is capable of oxidizing tBuOOH to form O2, which makes it possible to consider it the model of peroxidase. The value of k for the reaction with the participation of β-carotene and compound 4 (k = 10.3 L2 mol–2 s–1) is three times higher than that with the participation of compound 3. If a new portion of β-carotene is added, the process of its oxidative destruction in the presence of compounds 3 or 4 occurs without additives of the dimeric complex and peroxide. A possible nature of compound 4 is discussed, as well as the influence of N-base in the coordination sphere of the complex on the nature of active intermediates and the rate of β-carotene decomposition.

Influence of formaldehyde on N-nitrosopiperazine formation from nitrite and piperazine in CO2 capture

Piperazine (PZ) based amine blends are promising solvents for post-combustion CO2 capture, but PZ can form potential carcinogenic nitrosamines from nitrite. In this work, the kinetics of the reaction between nitrite and PZ to form N-nitrosopiperazine (MNPZ) was determined in 0.1–0.5 mol L−1 PZ in the presence of 17–170 mmol L−1 formaldehyde at 60–135 °C. The nitrosation of PZ can be catalyzed by formaldehyde, a primary degradation product of PZ. And the reaction involving nitrite and PZ is first order in nitrite, formaldehyde, and hydronium ion. A kinetic model was established, and the activation energy is 33.6 ± 1.8 kJ mol−1 with a rate constant of 2.3 × 103 ± 0.4 × 103 L2 mol−2 s−1 at 100 °C. The kinetics will be helpful to develop strategies to reduce nitrosamine formation and accumulation in PZ based CO2 capture systems.

Ratiometric Fluorescence Detection of Phosphorylated Amino Acids Through Excited-State Proton Transfer by Using Molecularly Imprinted Polymer (MIP) Recognition Nanolayers.

A 2,3-diaminophenazine bis-urea fluorescent probe monomer (1) was developed. It responds to phenylphosphate and phosphorylated amino acids in a ratiometric fashion with enhanced fluorescence accompanied by the development of a redshifted emission band arising from an excited-state proton transfer (ESPT) process in the hydrogen-bonded probe/analyte complex. The two urea groups of 1 form a cleft-like binding pocket (Kb >1010 L2 mol-2 for 1:2 complex). Imprinting of 1 in presence of ethyl ester- and fluorenylmethyloxycarbonyl (Fmoc)-protected phosphorylated tyrosine (Fmoc-pTyr-OEt) as the template, methacrylamide as co-monomer, and ethyleneglycol dimethacrylate as cross-linker gave few-nanometer-thick molecularly imprinted polymer (MIP) shells on silica core microparticles with excellent selectivity for the template in a buffered biphasic assay. The supramolecular recognition features were established by spectroscopic and NMR studies. Rational screening of co-monomers and cross-linkers allowed to single out the best performing MIP components, giving significant imprinting factors (IF>3.5) while retaining ESPT emission and the ratiometric response in the thin polymer shell. Combination of the bead-based detection scheme with the phase-transfer assay dramatically improved the IF to 15.9, allowing sensitive determination of the analyte directly in aqueous media.

Cobalt(II) porphyrin axially coordinated with 2′-(pyridin-4-yl)-5′-(pyridin-2-yl)-1′-(pyridin-2-ylmethyl)-2′,4′-dihydro-1′H-pyrrolo[3′,4′ : 1,2](C60-Ih)[5,6]fullerene: formation, chemical structure, and spectroscopic properties

Construction of new effective photovoltaic devices based on organic dyes has important implications for modern and future technologies. In this article, we studied the equilibrium, the rate, and the spectral manifestation of the reaction of [(2,3,7,8,12,18-hexamethyl,13,17-diethyl,5-(2-pyridyl)porphyrinato)cobalt(II)]–[2′-(pyridin-4-yl)-5′-(pyridin-2-yl)-1′-(pyridin-2-ylmethyl)-2′,4′-dihydro-1′H-pyrrolo[3′,4′ : 1,2](C60-Ih)[5,6]fullerene] triad formation as well as its spectral properties and photo electrochemical behavior. The cobalt porphyrin–pyridyl-substituted fullerene mixtures in toluene are self-assembling systems due to axial donor–acceptor binding between Co of the porphyrin complex and N-pyridyl of the substituted fullerene. The formation rate constant, k298K, and the stability constant, K298K, of donor–acceptor triad formed by coordination of two substituted fullerene molecules to Co porphyrin are (44.4 ± 0.8) mol L−1 s−1 and (56 ± 16)×107 L2 mol−2, respectively. Modification of the titanium electrode coated with the natural oxide film was carried out using the porphyrin–fullerene triad and its individual components. Photopotential and photocurrent density of the system with modified electrode were studied. The obtained results are of interest for creating porphyrin-based donor–acceptor systems as components in organic photovoltaics.

Kinetics and mechanism of the chain reaction of N,N′-diphenyl-1,4-benzoquinone diimine with thiophenol in chlorobenzene

The regularities of the reaction of N,N′-diphenyl-1,4-benzoquinone diimine with thiophenol in chlorobenzene at 343 K were studied by kinetic spectrophotometry. The reaction orders were determined for the components under the conditions when the concentration of thiophenol considerably exceeded that of quinone diimine: nQDI = 1.5 for quinone diimine and nPhSH = 1.0 for thiophenol. The initiators (azo-bis-isobutyronitrile and tetraphenylhydrazine) were found to considerably accelerate the reaction, which suggests that the reaction proceeded by the chain mechanism. The reaction chain length changed from one dozen to several dozens of units depending on the experimental conditions. The chain mechanism (kinetic scheme) of the reaction was suggested; it agrees with the experimental data, according to which the chains are initiated simultaneously by the second and third order reactions between quinone diimine and thiophenol. The rate constants of these stages at 343 K were determined: kbi = 0.014 ± 0.002 L mol−1s−1; ktri = 22.8 ± 1.8 L2 mol−2s−1. The limiting stage of chain propagation was concluded to be the reaction of the thiyl radical with quinone diimine; the rate constant of this stage was evaluated: kpr ∼ 1.3 × 106 L mol−1 s−1 at 343 K.

Supramolecular assembler based on cucurbit[8]uril: Photodimerization of a styryl dye in water

Photolysis of aqueous solutions of styryl dye 1 in the presence of cucurbit[8]uril (CB[8]) has been studied by optical spectroscopic methods for the molar ratios n = c CB[8]/c 1 in the range of 0 ≤ n ≤ 6. It has been found that the inclusion complexes (1)2@CB[8] dominate in the solution at n ≤ 0.5, whereas the complexes 1@CB[8] dominate at n ≥ 1. The stability constants have been determined for the 1: 1 (log K 1 = 6.2 (L mol−1)) and 2: 1 (log β = 11.9 (L2 mol−2)) complexes. The fluorescence decay kinetics of dye 1 in the presence of CB[8] is two-exponential, with the average lifetime increasing substantially at n ≥ 1. It has been shown that the system can operate in the cyclic mode as an assembler (or supramolecular catalyst) in the photodimerization reaction of dye 1 to form cyclobutane derivative 2. The stability constant of the complex 2@CB[8] (log K 3 = 5.9 (L mol−1)) and the quantum yield of cycloaddition ( ≈ 0.07 at n ≈ 0.5) have been determined.

Host–guest interaction of hemicucurbiturils with phenazine hydrochloride salt

The host–guest interactions between phenazine hydrochloride salt (PheH+) and hemicucurbit[n]uril (n = 6 or 12) (HemiQ[6 or 12]) have been studied by 1H NMR, UV–vis, IR, mass spectrometry (MS) and quantum chemistry. In 1H NMR spectra, the broadening of proton resonances of the hosts suggests the interactions of PheH+ with HemiQs. The quantitative stabilities of the host–guest systems have been obtained by UV–vis titration experiments, that is, the stoichiometric interactions of PheH+ with HemiQ[6] have been observed with an association constant of Ka = (2.5 ± 1.2) × 106 L mol− 1, while the 2:1 ratio complexes of PheH+ with HemiQ[12] are formed with stepwise association constants of K1 = (9.2 ± 2.8) × 104 L mol− 1 and K2 = (6.4 ± 0.9) × 105 L mol− 1, respectively, which induce a total association constant of Ka = 5.9 × 1010 L2 mol− 2. Both the 1:1 and 2:1 complexes have been detected by MS. Quantum chemistry calculations have been used to understand the static structures and thermodynamic stabilities of the supramolecular assemblies.