A theoretical study on the on–off phosphorescence of novel Pt(ii)/Pt(iv)–bisphenylpyridinylmethane complexes

An in-depth theoretical study on the Pt(ii)/Pt(iv)–bisphenylpyridinylmethane complexes was carried out, which focused on the geometric/electronic structures, excitation procedures, on–off phosphorescence mechanisms, and structure–optical performance relationships. The key roles of the linkages (LK) connected in the middle of phenylpyridines were carefully investigated using multiple wavefunction analysis methods, such as non-covalent interaction (NCI) visualizations and natural bond orbital (NBO) studies. The phosphorescence-off phenomenon was considered by hole–electron analysis and visualizations, spin–orbit coupling (SOC) studies, and NBO analysis. Through these investigations, the relationship of the substituents in LK and the optical performances were revealed, as well as the fundamental principles of the phosphorescence-quenching mechanism in Pt(iv) complexes, which pave the way for further performance/structural renovation works. In addition, an intuitive visualization method was developed using a heatmap to quantitatively express the SOC matrix elementary (SOCME), which is helpful for big data simplification for phosphorescence analysis.

An in-depth theoretical study on the Pt(ii)/Pt(iv)–bisphenylpyridinylmethane complexes was carried out, which focused on the structures, excitation procedures, on–off phosphorescence mechanisms, and structure–optical performance relationships.     

Effect of anion in carboxylate-based ionic liquids on catalytic activity of transesterification with vinyl esters and the solubility of cellulose

The role of 1-ethyl-3-methylimidazolium (Emim) carboxylate-type ionic liquid (IL) as the solvent and organocatalyst for transesterification reaction of cellulose was investigated. The reported method using Emim acetate and vinyl ester caused an undesired side reaction: the acetate anion derived from EmimOAc was introduced into cellulose ester. To improve the reaction system, ILs with a high cellulose solubility, a high degree of substitution (DS) value, and low side-reaction were systematically explored. Newly synthesized Emim p-anisate and a mixed solvent system achieved the transesterification reaction of cellulose with a high DS value derived from the employed vinyl esters (DS > 2.9), and a low DS value derived from side reaction (selectivity > 99%).

The role of 1-ethyl-3-methylimidazolium carboxylate-type ionic liquid as the solvent and organocatalyst for transesterification reaction of cellulose was investigated.     

Mechanical and self-recovery properties of supramolecular ionic liquid elastomers based on host–guest interactions and correlation with ionic liquid content

Supramolecular materials have received considerable attention due to their higher fracture energy and self-recovery capability compared to conventional chemically cross-linked materials. Herein, we focus on the mechanical properties and self-recovery behaviours of supramolecular polymeric elastomers swollen with ionic liquid. We also gained insight into the correlation between ionic liquid content and mechanical properties. These supramolecular polymers with ionic liquid can be easily prepared from bulk copolymerization of the host–guest complex (peracetylated cyclodextrin and adamantane derivatives) and alkyl acrylates and subsequent immersion in ionic liquid such as 1-ethyl-3-methylimidazolium bis(trifluoromethylsulfonyl)imide. The supramolecular polymeric elastomers showed a self-recovery ability, which the conventional chemically cross-linked elastomers with ionic liquid cannot achieve.

Supramolecular ionic liquid elastomers showed higher fracture energy than chemically cross-linked ionic liquid elastomers and also self-recovery ability.     

Palladium supported on mixed-metal–organic framework (Co–Mn-MOF-74) for efficient catalytic oxidation of CO

Successful monometallic and bimetallic metal–organic frameworks with different Co/Mn ratios have been synthesized under solvothermal conditions. The as-synthesized MOFs followed by deposition of Pd nanoparticles with 0.5 to 7 wt%. The XRD, BET, SEM, TEM, EDAX and FT-IR characterization results reveal that bimetallic MOFs and Pd nanoparticles were finely dispersed on the prepared MOFs surfaces. XRD results confirm the formation of the desire MOFs and show the high degree of dispersion of Pd nanoparticles. TEM images show that Pd nanoparticles are nano-sized with almost uniform shape. EDAX shows that Pd nanoparticles successfully loaded on Co_0.5–Mn_0.5-MOF-74 catalyst. CO oxidation as a model reaction was then used to assess the catalytic performance of the prepared catalysts. The catalytic activity results show enhancement in the catalytic activities of monometallic MOFs after introducing another metal in the same framework and show an excellent improvement in CO conversion after loading with Pd nanoparticles. Furthermore, the samples that contain Pd nanoparticles exhibits higher catalytic activities which raised with increasing the content of Pd nanoparticles.

Pd nanoparticles were loaded on Co_x–Mn_(1−x)-MOF-74. 5 wt% Pd@Co_0.5–Mn_0.5-MOF-74 was the most effective catalyst for CO oxidation. The prepared catalysts displayed excellent stability during CO oxidation without significant decrease in catalytic performance.     

Nonstoichiometric oxygen in Mn–Ga–O spinels: reduction features of the oxides and their catalytic activity

The subject of this study was the content of oxygen in mixed oxides with the spinel structure Mn_1.7Ga_1.3O₄ that were synthesized by coprecipitation and thermal treatment in argon at 600–1200 °C. The study revealed the presence of excess oxygen in “low-temperature” oxides synthesized at 600–800 °C. The occurrence of superstoichiometric oxygen in the structure of Mn_1.7Ga_1.3O_4+δ oxide indicates the formation of cationic vacancies, which shows up as a decreased lattice parameter in comparison with “high-temperature” oxides synthesized at 1000–1200 °C; the additional negative charge is compensated by an increased content of Mn³⁺ cations according to XPS. The low-temperature oxides containing excess oxygen show a higher catalytic activity in CO oxidation as compared to the high-temperature oxides, the reaction temperature was 275 °C. For oxides prepared at 600 and 800 °C, catalytic activity was 0.0278 and 0.0048 cm³ (CO) per g per s, and further increase in synthesis temperature leads to a drop in activity to zero. The process of oxygen loss by Mn_1.7Ga_1.3O_4+δ was studied in detail by TPR, in situ XRD and XPS. It was found that the hydrogen reduction of Mn_1.7Ga_1.3O_4+δ proceeds in two steps. In the first step, excess oxygen is removed, Mn_1.7Ga_1.3O_4+δ → Mn_1.7Ga_1.3O₄. In the second step, Mn³⁺ cations are reduced to Mn²⁺ in the spinel structure with a release of manganese oxide as a single crystal phase, Mn_1.7Ga_1.3O₄ → Mn₂Ga₁O₄ + MnO.

The hydrogen reduction of Mn_1.7Ga_1.3O_4+δ proceeds in two steps. In the first step, excess oxygen is removed, Mn_1.7Ga_1.3O_4+δ → Mn_1.7Ga_1.3O₄. In the second step, Mn³⁺ cations are reduced to Mn²⁺ in the spinel structure and formation of MnO, Mn_1.7Ga_1.3O₄ → Mn₂Ga₁O₄ + MnO.     

Understanding liquid–liquid equilibria in binary mixtures of hydrocarbons with a thermally robust perarylphosphonium-based ionic liquid

Binary mixtures of hydrocarbons and a thermally robust ionic liquid (IL) incorporating a perarylphosphonium-based cation are investigated experimentally and computationally. Experimentally, it is seen that excess toluene added to the IL forms two distinct liquid phases, an “ion-rich” phase of fixed composition and a phase that is nearly pure toluene. Conversely, n-heptane is observed to be essentially immiscible in the neat IL. Molecular dynamics simulations capture both of these behaviours. Furthermore, the simulated composition of the toluene-rich IL phase is within 10% of the experimentally determined composition. Additional simulations are performed on the binary mixtures of the IL and ten other small hydrocarbons having mixed aromatic/aliphatic character. It is found that hydrocarbons with a predominant aliphatic character are largely immiscible with the IL, while those with a predominant aromatic character readily mix with the IL. A detailed analysis of the structure and energetic changes that occur on mixing reveals the nature of the ion-rich phase. The simulations show a bicontinuous phase with hydrocarbon uptake akin to absorption and swelling by a porous absorbent. Aromatic hydrocarbons are driven into the neat IL via dispersion forces with the IL cations and, to a lesser extent, the IL anions. The ion–ion network expands to accommodate the hydrocarbons, yet maintains a core connective structure. At a certain loading, this network becomes stretched to its limit. The energetic penalty associated with breaking the core connective network outweighs the gain from new hydrocarbon–IL interactions, leaving additional hydrocarbons in the neat phase. The spatially alternating charge of the expanded IL network is shown to interact favourably with the stacked aromatic subphase, something not possible for aliphatic hydrocarbons.

Binary mixtures of hydrocarbons and a thermally robust ionic liquid (IL) incorporating a perarylphosphonium-based cation are investigated experimentally and computationally.     

Synthesis of Zn-based metal–organic frameworks in ionic liquid microemulsions at room temperature

For the first time, Zn-metal–organic frameworks (Zn-MOFs) were prepared using Zn²⁺ and the aromatic ligand 1,3,5-benzenetricarboxylic acid (BTC) in ionic liquid microemulsions stabilized by the surfactant TX-100. This proposed environmentally friendly approach to synthesize Zn-MOFs is simple, requires no energy input, and operates at room temperature. The synthesized Zn-MOFs were characterized by scanning electron microscopy (SEM), transmission electron microscopy (TEM), single crystal X-ray diffraction and powder X-ray diffraction (XRD), thermal gravimetric analysis (TGA), and Fourier transform infrared spectroscopy (FT-IR). The results showed that two different Zn-MOF crystals had been successfully synthesized and that [NaZn(C₉H₃O₆)(H₂O)₄]·1.5H₂O was prepared by using this method for the first time. The influence of different parameters such as the pH value, the ratio of reactants, and reaction time on the morphology and size of the Zn-MOFs was studied. Long rod Zn-MOFs with an average size of ∼25 μm could be obtained in the ionic liquid microemulsions with a molar ratio (organic ligand to metal ion) of 1 : 1 at pH 5.98 for 24 h. The crystal type and morphology of the Zn-MOFs could be controlled by the ionic liquid microemulsions at room temperature. This green synthesis method can be used to study their industrial production.

For the first time, Zn-metal–organic frameworks (Zn-MOFs) were prepared using Zn²⁺ and the aromatic ligand 1,3,5-benzenetricarboxylic acid (BTC) in ionic liquid microemulsions stabilized by the surfactant TX-100.     

Iridium-catalyzed ortho-selective carbon–hydrogen amidation of benzamides with sulfonyl azides in ionic liquid

An efficient and convenient iridium(iii) catalyzed ortho-C–H bond amidation of weakly coordinating benzamides treated with readily available sulfonyl azides as the amino source has been described. In this transformation, ionic liquids represents an ideal reaction medium, giving rise to a broad range of amidation products under mild conditions in the open air. This protocol offers moderate to excellent chemical yields, exclusive regioselectivities, and good functional group tolerance.

Ir-catalyzed ortho-C–H amidation of benzamides with sulfonyl azides has been conducted effectively in ionic liquid reaction medium.     

High catalytic performance of Al–Pd–(Ru,Fe) icosahedral approximants for acetylene semi-hydrogenation

Three cubic crystalline icosahedral approximants (C phase: Al_72.0Pd_16.4Fe_11.6, P₄₀ phase: Al_72.0Pd_16.4Ru_11.6, P₂₀ phase: Al_70.0Pd_22.3Ru_7.7) exhibit high ethylene selectivity of over 90% for hydrogenating acetylene at 150 °C. Moreover, the powdered P₂₀ also demonstrates a high catalytic performance under an industry-like ethylene feed containing 0.5% acetylene as an impurity. Overall, icosahedral approximants in the Al–Pd–(Ru, Fe) systems are promising as a novel class of alloy catalysts.

The Al–Pd–(Ru, Fe) icosahedral approximants exhibited high catalytic ethylene selectivity and stability for semi-hydrogenation of acetylene.     

Structural investigation of ternary PdRuM (M = Pt,Rh, or Ir) nanoparticles using first-principles calculations

We perform first-principles calculations and Monte Carlo sampling to investigate the structures of ternary PdRuM (M = Pt, Rh, or Ir) nanoparticles (NPs) with respect to three different spherical shapes. The morphologies include hexagonal close-packed (hcp), truncated-octahedral (fcc), and icosahedral (Ih, fcc) shapes with 57, 55, and 55 atoms, respectively. The calculations show that the atomic position is dominant in determining the stability of the ternary NPs. For bare ternary NPs, Pd and Ru atoms favor a location on the vertex sites and the core, respectively, which can be understood by the surface energy of the corresponding slab models. For single-crystalline NPs, the binary shell could be either a solid solution or a segregation alloy depending on composition and morphology. However, polycrystalline Ih NPs only form segregated binary shells surrounding the Ru core. Such configurations tend to minimize the surface lattice to gain more energy from the d orbital of the transition metals. In addition to the bare NPs, we study the oxidized ternary NPs. The results show that the Ru atoms penetrate outwards from the core to the surface reducing the oxidation formation energy. Furthermore, oxygen adsorption facilitates Pt, Pd, and Pd penetration into the PdRuPt, PdRuRh, and PdRuIr NPs, respectively. Most of the oxide shells are a solid solution, except for the PdRuRh NP with an Ih shape, which is found to be in a segregation shell. The free energy calculation reveals that the pure hcp NPs are thermodynamically unstable under oxygen-rich conditions. This work clearly demonstrates the structural trends of small ternary NPs and their oxidation, unveiling that the structural trends can be understood by the surface formation energy and the interplay between adsorbent and adsorbing oxygen atoms.

First-principles calculations and Monte Carlo sampling was used to investigate the structures of PdRuM (M = Pt, Rh, or Ir) nanoparticles with three different spherical shapes. Oxygen adsorption facilitates Ru penetration from core to surface sites.     

Air-assisted ionic liquid dispersive liquid–liquid microextraction based on solidification of the aqueous phase for the determination of triazole fungicides in water samples by high-performance liquid chromatography

A simple, rapid, and environmentally friendly approach was introduced to determine triazole fungicides in water samples by air-assisted ionic liquid dispersive liquid–liquid microextraction based on solidification of the aqueous phase using high-performance liquid chromatography-diode array detection. Ionic liquid was applied as the extraction solvent rather than a high-toxicity extraction solvent. The air-assisted dispersion method induced a trace amount of the ionic liquid to disperse as small droplets in the water sample, which significantly increased the contact area between the organic phase and the aqueous phase for the rapid transfer of target fungicides without using a dispersion solvent or auxiliary extraction devices. The solidification of the aqueous phase facilitated the collection of extraction solvent. The type of extraction solvent, the volume ratio of the extraction solvent to the water sample, the number of extraction cycles, the addition of NaCl, and pH values were evaluated. The recoveries were 72.65–100.13% with a relative standard deviation of 0.92% to 5.99%. The limits of quantification varied from 0.65 ng mL⁻¹ to 1.83 ng mL⁻¹. This approach can be used to determine fungicides in ground, river, and lake water samples.

A simple, rapid, and environmentally friendly approach was introduced to determine triazole fungicides in water samples by air-assisted ionic liquid dispersive liquid–liquid microextraction based on solidification of the aqueous phase by HPLC-DAD.     

Heteropolyacid ionic liquid heterogeneously catalyzed synthesis of isochromans via oxa-Pictet–Spengler cyclization in dimethyl carbonate

A recyclable and efficient heterogeneous, green catalyst based on the synthesis of Keggin-type polyoxometalate (H₃PMo₁₂O₄₀) and vitamin B1 analogue 3-ethyl-5-(2-hydroxyethyl)-4-methylthiazol-3-ium (HEMT), i.e., [HEMTH]H₂[PMo₁₂O₄₀] was prepared. Oxa-Pictet–Spengler cyclization of arylethanols and aldehydes were catalyzed to afford various substituted isochromans in moderate conditions with excellent yields using dimethyl carbonate (DMC) as a green solvent. Furthermore, this protocol was applicable in a gram-scale reaction, and the catalyst could be recycled eight times without significant loss of activity.

An efficient heterogeneous and green catalyst [HEMTH]H₂[PMo₁₂O₄₀] was prepared to catalysis the oxa-Pictet–Spengler cyclization of arylethanols and aldehydes to afford isochromans with excellent yields using dimethyl carbonate as a green solvent.     

The influence of the polymerization approach on the catalytic performance of novel porous poly (ionic liquid)s for green synthesis of pharmaceutical spiro-4-thiazolidinones

Although poly (ionic liquids) (PILs) have attracted great research interest owing to their various applications, the performance of nanoporous PILs has been rarely developed in the catalysis field. To this end, a micro–mesoporous PIL with acid–base bifunctional active sites was designed and fabricated by two different polymerization protocols including hydrothermal and classical precipitation polymerization in this paper. Based on our observations, hydrothermal conditions (high temperature and pressure) enabled the proposed sonocatalyst to possess a great porous structure with a high specific surface area (S_BET: 315 m² g⁻¹) and thermal stability (around 450 °C for 45% weight loss) through strengthening cross-linking. In a comparative study, the preferred nanoporous PIL was selected and utilized as the sonocatalyst in a multicomponent reaction of isatins, primary amines, and thioglycolic acid. In the following, a variety of new and known pharmaceutical spiro-4-thiazolidinone derivatives were synthesized at room temperature and obtained excellent yields (>90%) within short reaction times (4–12 min) owing to the substantial synergistic effect between ultrasound irradiation and magnetically separable catalyst.

Sustainable synthesize of a new mesoporous poly (ionic liquid) as acid–base bifunctional catalyst for environmental being preparation of monospiro derivatives has been developed.     

Rh(iii)-catalyzed C-7 arylation of indolines with arylsilanes via C–H activation

Site-selective synthesis of C-7 arylated indolines has been achieved via oxidative arylation of indolines with arylsilanes under Rh(iii)-catalyzed C–H activation of indolines by using CuSO₄ as a co-oxidant. This transformation has been explored for a wide range of substrates under mild conditions.

Site-selective synthesis of C-7 arylated indolines has been achieved via oxidative arylation of indolines with arylsilanes under Rh(iii)-catalyzed C–H activation of indolines.

The indole and indoline ring systems represent ubiquitous structural motifs as natural alkaloids and biologically active compounds as well as in functional materials.^1,2 With the development of C–H bond functionalization,³ a great deal of effort has been devoted to the formation C-2 and C-3 functionalized indoles.⁴ Nevertheless, only a few methods have been explored for the direct C–H bond functionalization of indoles at the C-7 position,⁵ in which the unique work for the direct Pd-catalyzed C–H arylation of indoles with arylboronic acids at the C-7 position was developed by the Shi group using a designed di-tert-butylphosphine oxide (TBPO) directing-group.^5b In general, the C-7 arylated indolines can be conveniently oxidized to transform into C-7 arylated indoles. So far, transition metals such as Pd,⁶ Rh,⁷ Ru,⁸ Ir,⁹etc.,¹⁰ have been employed as catalysts for the C-7 C–H bond functionalization of indolines, among which the C–H arylation in the C-7 position of indoline was mainly established by using Pd complexes as catalysts (Scheme 1a).¹¹ In 2016, we also reported the Pd-catalyzed C-7 arylation of indolines with arylsilanes via C–H bond activation.¹² Recently, the Punniyamurthy group developed the site-selective C-7-arylation of indolines with arylboronic acids by using low-cost and earth-abundant cobalt(ii)-PCy₃ as a catalyst.¹³ Even so, in view of the importance of indole and indoline scaffolds, it is still highly desirable to develop more convenient and efficient approaches for the synthesis of C-7 arylated indolines and C-7 arylated indoles.Open in a separate windowScheme 1C-2 arylation of indoles with arylsilanes and C-7 arylation of indolines.Meanwhile, recent years have witnessed tremendous developments in the area of Rh(iii)-catalyzed C–H bond functionalization,¹⁴ which has allowed effective construction of various C–C bonds. The major advantages of Rh(iii) catalysis are (i) high functional-group tolerance, (ii) broad substrate scope, (iii) low catalyst loading, high activity, and high catalytic efficiency.Since the Hiyama cross-coupling reaction had been first reported in 1988,¹⁵ as one of the most useful and reliable synthetic methods for the construction C–C bonds, the Hiyama cross-coupling reaction has drawn increasing attention.¹⁶ As attractive organometallic coupling partners with many unique advantages such as low toxicity, high stability and environmental benignity, organosilicon reagents were used as coupling partners for the C–H arylation of indoles and indolines (Scheme 1b).¹⁷ Zhang group reported the Pd-catalyzed C-2 arylation of indoles with arylsilanes in acidic medium in 2010. In 2014, Loh group developed the Rh(iii) catalyzed C-2 C–H arylation of indoles with arylsilanes in aqueous media.¹⁸ Very recently, Szostak group developed the Ru(ii) catalyzed arylation of indoles with arylsilanes via C–H activation,¹⁹ it is worth noting that the reaction was carried out in water. However, the methods for the synthesis of C-7 arylated indolines and C-7 arylated indoles are very limited by using arylsilanes as the coupling partners. To the best of our knowledge, the Rh(iii) catalyzed C-7 arylation of indolines with arylsilanes has not been achieved. Due to our continuous interest in the arylsilanes-based coupling reaction,^12,20 we herein would like to report a Rh(iii)-catalyzed regioselective C-7 arylation of indolines with arylsilanes via C–H activation (Scheme 1c), the reaction provides a facile access to C-7 arylated indolines.At the outset of the investigation, various N-protecting indolines (iii)-catalyzed C-7 arylation of indolines with arylsilane^a

Entry	Substrates	Co-oxidant	F source	Solvent	Yieldb (%)
1	1a–1d	Ag2CO3	AgF	Dioxane	0
2	1e	Ag2CO3	AgF	Dioxane	0
3	1f	Ag2CO3	AgF	Dioxane	81
4	1f	Ag2CO3	CsF	Dioxane	0
5	1f	Ag2CO3	KF	Dioxane	0
6	1f	Ag2CO3	TBAF	Dioxane	0
7	1f	—	AgF	Dioxane	72
8	1f	AgOAc	AgF	Dioxane	89
9	1f	Cu(OAc)2	AgF	Dioxane	85
10	1f	CuSO4	AgF	Dioxane	98
11	1f	CuSO4	AgF	DMF	62
12	1f	CuSO4	AgF	DMSO	0
13	1f	CuSO4	AgF	iPrOH	81
14	1f	CuSO4	AgF	H2O	Messy
15	1f	CuSO4	AgF	Dioxane/H2O = 1/10	47
16c	1f	CuSO4	AgF	Dioxane	87

Open in a separate window^aUnless otherwise noted, the reaction conditions are as follows: 1 (0.3 mmol), 2a (0.9 mmol), [Cp*Rh(iii)Cl₂]₂ (1 mol%), Co-oxidant (0.6 mmol), F resource (0.9 mmol), solvent (3.0 mL).^bIsolated yield after purification by flash column chromatography on silica gel, n.d.p or trace product was determined by TLC.^cThe reaction temperature was 60 °C.With the optimized reaction conditions in hand, we then proceeded to explore the scope of the direct C-7 C–H arylation of N-(2-pyrimidyl)-indoline with a series of arylsilanes (iii)-catalyzed the direct C-7 arylation of indoline 1f with various phenyltriethoxysilane 2^a,bOpen in a separate window^aUnless otherwise noted, the reaction conditions are as follows: 1f (0.3 mmol), 2 (0.9 mmol), dioxane (3.0 mL).^bAll the yields refer to isolated yields.^cPhenyltrimethoxysilane was used.To further evaluate the substrate scope, various substituted N-(2-pyrimidyl)-indolines were used to test the reaction with the phenyltriethoxysilane 2a under the optimized reaction conditions. The results are summarized in iii)-catalyzed the direct C-7 arylation of various indolines 1 with phenyltriethoxysilane 2a^a,bOpen in a separate window^aUnless otherwise noted, the reaction conditions are as follows: 1 (0.3 mmol), 2a (0.9 mmol), dioxane (3.0 mL).^bAll the yields refer to isolated yields.To explore the utility of this transformation, we tried to explore direct C-8 C–H arylation with N-(2-pyrimidyl)-tetrahydroquinoline 5 and phenyltrimethoxy-silane 2a under the standard condition, to our delight, the desired C-8 C–H arylated product was obtained in 48% yield (Scheme 2).Open in a separate windowScheme 2Rh(iii)-catalyzed the direct C-8 arylation of N-(2-pyrimidyl)-tetrahydroquinoline 5 with phenyltriethoxysilane 2a.To further demonstrate the synthetic utility of the method, the transformation of C-7 arylated indoline into C-7 arylated indole was studied.^13,21 As shown in Scheme 3, the transformation was begun with the oxidation of C-7 arylated N-(2-pyrimidyl)-indoline 3fa by the use of DDQ (2,3-dicyano-5,6-dichlorobenzoquinone), followed by removing pyrimidyl group in the present of base. Finally, 83% yield of the C-7arylated indole product 7a was successfully obtained.Open in a separate windowScheme 3Transformation of C-7-arylated indoline 3fa to the corresponding indole 7a.To gain some preliminary mechanistic insights, kinetic isotope experiments were conducted. The parallel reactions of 1f and deuterio-1f with 2a resulted k_H/K_D = 0.80 (Scheme 4), which suggested that the C–H cleavage was not the rate-determining step in the catalytic cycle. On the basis of previous literatures, ^18,22,23 a plausible mechanism is proposed as shown Scheme 5. The process is likely to be initiated by the coordination of the nitrogen atom of 2-pyrimidyl group of 1f to the rhodium catalyst, leading directly to cyclometalation process via C–H bond activation to afford the five-membered rhodacycle A.²⁴ The Ph–Ag species can be generated via the C–Si activation by the nucleophilic attack of a fluoride ion on silicon,^20c,25 followed by the transmetalation with intermediate A to afford the Rh(iii) intermediate B, from which reductive elimination would provide C-7 arylated indolines 3fa and regenerate the Rh(i) catalyst, which is reoxidized to Rh(iii) species by Ag(i) or Cu(ii) salts to complete the catalytic cycle.Open in a separate windowScheme 4Parallel kinetic isotope experiment.Open in a separate windowScheme 5Plausible catalytic cycle for Rh(iii)-catalyzed the direct C-7 arylation of indolines with phenyltriethoxysilane.In summary, we have demonstrated a Rh(iii)-catalyzed oxidative arylation of indolines with arylsilanes via C–H activation by using CuSO₄ as an co-oxidant. This general transformation exhibits excellent reactivity and broad substrate scopes, various functional groups are well tolerated under the mild reaction conditions. This reaction constitutes a complement method for the synthesis the desired C-7 arylated indolines up to excellent yields, which can be conveniently transformed into C-7 arylated indoles.     

Conformational dynamics of amyloid-β (16–22) peptide in aqueous ionic liquids

Molecular dynamics simulations of amyloid-β (16–22) peptide dimer in water as well as at two different experimentally studied concentrations of hydrated ionic liquids (ILs), ethylammonium mesylate (EAM), ethylammonium nitrate (EAN), and triethylammonium mesylate (TEAM), were carried out employing an umbrella sampling method. We used the average Ψ angle of the peptide backbone as the reaction coordinate to observe the conformational changes of a peptide dimer. Secondary structural element values were calculated for the peptide dimer along the reaction coordinate to see the transition of the peptide dimer between β-sheet and α-helix conformations. We observe the β-sheet conformation as the global minimum on the free energy surfaces in both EAM and EAN ILs at both the concentrations and at a low concentration of TEAM. However, we observe α-helix conformation as the global minimum at a high concentration of TEAM. Our results are in good correlation with the experimental findings. We calculated the average number of intramolecular and intermolecular hydrogen bonds of α-helix and β-sheet conformations in all solutions, and they are in correlation with the secondary structure element values. To understand the peptide–IL interactions, atom–atom radial distribution functions of cation, anion, and water around amide oxygen and hydrogen atoms were calculated. The solvent-accessible surface area of the peptide dimer was calculated to understand the exposure of the peptide towards the solvent during conformational changes. Finally, van der Waals (vdW) and Coulomb interaction energies were calculated between peptide–cation, peptide–anion, and peptide–water to understand the stability of conformations in different concentrations. We find that the TEA cation has more vdW interaction energy compared to Coulomb interaction energy with peptide in 70% (w/w) TEAM, which mimics a membrane-like environment to induce α-helix conformation rather than β-sheet conformation.

Molecular dynamics simulations of amyloid-β (16–22) peptide dimer at two different experimentally studied concentrations of hydrated ethylammonium mesylate, ethylammonium nitrate, and triethylammonium mesylate were carried out employing an umbrella sampling method.     

Influence of the acid–base stoichiometry and residual water on the transport mechanism in a highly-Brønsted-acidic proton-conducting ionic liquid

In this study, Brønsted-acidic proton conducting ionic liquids are considered as potential new electrolytes for polymer membrane fuel cells with operating temperatures above 100 °C. N-Methyltaurine and trifluoromethanesulfonic acid (TfOH) were mixed at various stoichiometric ratios in order to investigate the influence of an acid or base excess. The proton conductivity and self-diffusion of the “neat” and with 6 wt% water samples were investigated by following electrochemical and NMR methods. The composition change in the complete species and the relative proton transport mechanism based on the NMR results are discussed in detail. During fuel cell operation, the presence of significant amounts of residual water is unavoidable. In PEFC electrolytes, the predominating proton transfer process depends on the cooperative mechanism, when PILs are fixed on the polymer matrix within the membrane. Due to the comparable acidity of the cation [2-Sema]⁺ and the hydroxonium cation, with excess N-methyltaurine or H₂O in the compositions, fast proton exchange reactions between the protonated [2-Sema]⁺ cation, N-methyltaurine and H₂O can be envisaged. Thus, an increasing ratio of cooperative proton transport could be observed. Therefore, for polymer membrane fuel cells operating at elevated temperatures, the highly acidic PILs with excess bases are promising candidates for future use as electrolytes.

There is a transition between prevailing vehicular and cooperative transport mechanism in base-excess Brønsted-acidic proton-conducting ionic liquids depending on stoichiometry.     

Solvent-tuned charge-transfer properties of chiral Pt(ii) complex and TCNQ˙− anion adducts

A new pair of adducts comprising one chiral Pt(ii) complex cation, [Pt((−)-L₁)(Dmpi)]⁺ ((−)-1) or [Pt((+)-L₁)(Dmpi)]⁺ ((+)-1) [(−)-L₁ = (−)-4,5-pinene-6′-phenyl-2,2′-bipyridine, (+)-L₁ = (+)-4,5-pinene-6′-phenyl-2,2′-bipyridine, Dmpi = 2,6-dimethylphenylisocyanide], together with one TCNQ˙⁻ anion have been obtained, and the structures have been confirmed via single-crystal X-ray crystallography and infrared (IR) spectroscopy. The chiral Pt(ii) cation and TCNQ˙⁻ anion are dissociated in MeOH solution, while charge transfer adducts are formed in H₂O solution, leading to perturbation of the electronic structure and alteration of the chiral environment, as evidenced by the differences in the UV-vis absorption and electronic circular dichroism spectra. The solvent-tuned charge-transfer properties also have been validated through emission and resonance light scattering spectra. The interesting findings may have potential applications in the development of black absorbers and wide band gap semiconductors.

A new couple of charge transfer adducts comprising of one chiral Pt(ii) complex cation together with one TCNQ˙⁻ anion have been prepared, and solvent-induced variances of absorption, luminescence as well as chiral spectra have been investigated.     

The effect of octahedral distortions on the electronic properties and magnetic interactions in O3 NaTMO2 compounds (TM = Ti–Ni & Zr–Pd)

The interplay between the coordination environment and magnetic properties in O3 layered sodium transition metal oxides (NaTMO₂) is a fascinating and complex problem. Through detailed and comprehensive density functional investigations on O3 NaTMO₂ compounds, we demonstrate that the TM ions in O3 NaMnO₂, NaFeO₂ and NaCoO₂ adopt a high spin state. Structurally, NaMnO₂ and NaPdO₂ undergo Jahn–Teller distortions while NaNbO₂ undergoes puckering distortion. Furthermore, in addition to Jahn–Teller distortion, NaPdO₂ exhibits charge disproportionation as it contains Pd²⁺, Pd³⁺ and Pd⁴⁺ species. These distortions stabilize the inter-plane ferromagnetism. Additionally, the inter-plane ferromagnetic coupling is stabilized by kinetic p–d exchange mechanism in undistorted NaCoO₂, NaNiO₂ and NaTcO₂. The intra-plane coupling in this family of compounds on the other hand was found to be generally weak. Only NaMnO₂, NaNiO₂ and NaTcO₂ are predicted to show bulk ferromagnetism with estimated Curie temperatures below ∼50 K.

Although O3 sodium transition metal oxides (NaTMO₂) share many similarities, they still differ from one another by some fine structural details.     

A facile and general approach for the direct fabrication of N-rGO–metal(metal oxides)–Pt composites as electrocatalyst for oxygen reduction reactions

Nitrogen-doped reduced graphene oxide–metal(metal oxides) nanoparticle (N-rGO–M(MO) NPs, M = Fe, MO: M = Co, Mn) composites were prepared through a facile and general method at high temperature (800 °C). M(MO) were well-dispersed and tightly anchored on graphene sheets, which were doped with nitrogen simultaneously and further loaded with Pt nanoparticles. Those results showed a more positive onset potential, higher cathodic density, and higher electron transfer number for the ORR in alkaline media. Furthermore, N-rGO–metal(metal oxides)–Pt (N-rGO–M(MO)–Pt) nanoparticles show better durability than the commercial Pt/C catalyst, and can be used as promising potential materials in practical applications.

We developed a facile, yet general approach to prepare N-rGO–M(MO)–Pt (M = Co, Fe and Mn) composites, which showed excellent electrocatalytic activity for the ORR in alkaline electrolytes.     

Lecithin–chitosan–TPGS nanoparticles as nanocarriers of (−)-epicatechin enhanced its anticancer activity in breast cancer cells

Natural compounds such as (−)-epicatechin show a variety of biological properties including anticancer activity. Nonetheless, (−)-epicatechin''s therapeutic application is limited due to its low water solubility and sensitivity to oxygen and light. Additionally, previous studies have reported that the encapsulation of flavonoids in nanoparticles might generate stable deliverable forms, which improves the availability and solubility of the bioactive compounds. The aims of this study were to generate (−)-epicatechin-loaded lecithin–chitosan nanoparticles (EC-LCT-NPs) by molecular self-assembly and to assess their cytotoxic potential against breast cancer cells. Various parameters were measured to characterize the EC-LCT-NPs including size, polydispersity index (PdI), zeta potential, morphology and entrapment efficiency. The results showed that the mean particle size of the EC-CLT-NPs was 159 ± 2.23 nm (PdI, 0.189), and the loading and entrapment efficiencies of (−)-epicatechin were 3.42 ± 0.85% and 56.1 ± 3.9%, respectively. The cytotoxic effect of the EC-CLT-NPs was greater than that of free (−)-epicatechin on breast cancer cell lines (MCF-7, MDA-MB-231, MDA-MB-436 and SK-Br3). Indeed, EC-LCT-NPs showed an IC₅₀ that was four-fold lower (85 μM) than free (−)-epicatechin (350 μM) and showed selectivity to cancerous cells. This study demonstrated that encapsulating (−)-epicatechin into lecithin–chitosan nanoparticles opens new options for breast cancer treatment.

Natural compounds such as (−)-epicatechin show a variety of biological properties including anticancer activity.