New small γ-turn type N-primary amino terminal tripeptide organocatalyst for solvent-free asymmetric aldol reaction of various ketones with aldehydes

New small γ-turn type N-primary amino terminal tripeptides were synthesized and their functionality as an organocatalyst was examined in the asymmetric aldol reaction of various ketones with different aromatic aldehydes under solvent-free neat conditions to afford the desired chiral anti-aldol products in good to excellent chemical yields, diastereoselectivities and enantioselectivities (up to 99%, up to syn : anti/13 : 87 dr, up to 99% ee).

New small γ-turn type N-primary amino terminal tripeptides were applied for the asymmetric aldol reaction of ketones with aldehydes under neat conditions to afford the chiral aldol products (up to 99%, up to syn : anti/13 : 87 dr, up to 99% ee).     

A novel substrate directed multicomponent reaction for the syntheses of tetrahydro-spiro[pyrazolo[4,3-f]quinoline]-8,5′-pyrimidines and tetrahydro-pyrazolo[4,3-f]pyrimido[4,5-b]quinolines via selective multiple C–C bond formation under metal-free conditions

A versatile and substrate oriented multicomponent reaction for the syntheses of novel highly diastereoselective tetrahydro-1′H-spiro[pyrazolo[4,3-f]quinoline-8,5′-pyrimidine]-2′,4′,6′(3′H)-triones (d.r. up to 20 : 1 (syn : anti)) and tetrahydro-8H-pyrazolo[4,3-f]pyrimido[4,5-b]quinoline-8,10(9H)-diones via formation of selective multiple C–C bonds under identical reaction conditions (viz. ethanol as a reaction medium and deep eutectic mixture as a catalyst) is demonstrated. Both approaches involve mild reaction conditions, use of non-hazardous solvents, and facilitate good to excellent reaction yields of the target compounds.

Substrate selectivity in the novel multi-component reaction of 5-aminoindazole, barbituric acid derivatives and aldehyde is explored.     

A combined crystallography and DFT study on ring-shaped Cucurbit[n]urils: structures,surface character,and host–guest recognition

A combined crystallography and DFT study of cucurbit[n]urils (n = 5–8, 10) was carried out, and PBE0 was certified to be the most rational density functional method for optimization task. Steric hindrance and electronic effect of the hindered lone pair electrons in cucurbit[n]urils were qualitatively measured by bond order analysis, lone pair electron (LP) visualization and electrostatic potential (ESP) study. Together with energy decomposition analysis of some selected host–guest systems, we quantitatively verified the effect of size/cavity and noncovalent interaction in host–guest recognition. This solid study revealed that lone pairs electrons affect not only on host–guest identification mode but also on geometry stability, which pave the avenue for further sophisticated applications.

A combined crystallography and DFT study of CB[n]s (n = 5–8, 10) was carried out. Through wavefunction analysis, how the hindered lone pair electrons affect on structures, electrostatics potential distribution and host–guest recognition were disclosed.     

Betaine host–guest complexation with a calixarene receptor: enhanced in vitro anticancer effect

p-Sulfonatocalix[n]arenes have shown excellent potential for accommodating chemotherapeutic drugs through host–guest complexation and enhancing their anticancer activity. Betaine has been reported to exert an anticancer effect at high concentrations. In order to increase its concentration in cancer cells, we have complexed it with p-SC4, which releases its content in an acidic environment typical of cancer tissue. In this work, a host–guest complex of the chemically stable, natural, and safe active methyl donor (betaine) and p-sulfonatocalix[4]arenes (p-SC4) was designed and characterized using ¹H NMR, UV, Job''s plot analysis, DFT calculations, and molecular modeling for use in cancer therapeutics. The peak amplitude of the prepared host–guest complexes was linearly proportional to the concentration of betaine in the range of 1.0 × 10⁻⁵ M⁻¹ to 2.5 × 10⁻⁴ M⁻¹. The reaction stoichiometry between p-SC4 and betaine in the formed complex was 1 : 1. The stability constant for the complex is 8.9 × 10⁴ M⁻¹ which corresponds to a complexation free energy of −6.74 kcal mol⁻¹. Complexation between betaine and p-SC4 was found to involve the insertion of the trimethylammonium group of betaine into the p-SC4 cavity, as supported by the experimental data. The complex displayed enhanced cytotoxic activities against breast adenocarcinoma cells (MCF-7) and cervical cancer cells (HeLa) compared to free betaine. In conclusion, the host–guest complexation of betaine with p-SC4 increases its concentration in cancer cells, which warrants further investigation for cancer therapy.

The complexation between p-SC4 and betaine was thoroughly investigated experimentally and computationally. A remarkable enhancement of the cytotoxic activities of betaine/p-SC4 complex was observed as compared to free betaine.     

A novel self-healing power cable insulating material based on host–guest interactions

The insulating materials used in power cables are susceptible to damage and cracks during installation and operation. To solve this problem, we have prepared a self-healing material PVP/p(HEMA-co-BA), which is synthesized by radical polymerization using HEMA, BA, PVP and a host–guest assembly. The host–guest assembly is constructed through interactions between host and guest molecules (CD–Al₂O₃ NPs act as the host, and HEMA–Ad acts as the guest). The characterization results of the materials show that there are two kinds of supramolecular interactions, namely, the host–guest interaction and the hydrogen bonding. The material possesses good thermal stability (heat-resisting temperature can reach 200 °C) and good electrical performance. The storage modulus of the material can be increased up to 432 MPa using a cross-linking agent at 20 °C. Furthermore, the material exhibits self-healing property, and it can self-heal several times; its self-healing efficiency is relative to the dosage of the cross-linking agent.

The insulating materials used in power cables are susceptible to damage and cracks during installation and operation.     

An efficient access to β-ketosulfones via β-sulfonylvinylamines: metal–organic framework catalysis for the direct C–S coupling of sodium sulfinates with oxime acetates

A copper-based framework Cu₂(OBA)₂(BPY) was synthesized and used as a recyclable heterogeneous catalyst for the synthesis of β-sulfonylvinylamines from sodium sulfinates and oxime acetates via direct C–S coupling reaction. The transformation was remarkably affected by the solvent, and chlorobenzene emerged as the best option. This Cu-MOF displayed higher activity than numerous conventional homogeneous and MOF-based catalysts. The catalyst was reutilized many times in the synthesis of β-sulfonylvinylamines without considerably deteriorating in catalytic efficiency. These β-sulfonylvinylamines were readily converted to the corresponding β-ketosulfones via a hydrolysis step with aqueous HCl solution. To the best of our knowledge, this direct C–S coupling reaction to achieve β-sulfonylvinylamines was not previously conducted with a heterogeneous catalyst.

Cu₂(OBA)₂(BPY) was used as catalyst for the synthesis of β-sulfonylvinylamines from sodium sulfinates and oxime acetates. These β-sulfonylvinylamines were readily converted to corresponding β-ketosulfones via a hydrolysis step.     

[3+2] regioselective annulation reaction of 2-arylidene-1,3-indandiones towards synthesis of spirocyclopentenes: understanding the mechanism of γ-attack vs. α-attack using DFT studies

A regioselective [3+2] cyclisation reaction between 2-arylidene-1,3-indanedione and ethyl 2,3-butadienoate catalysed by triphenylphosphine has been demonstrated to synthesize functionalised spirocyclic cyclopentenes. The reaction tolerated various electron-rich and electron-deficient aryl substituted 2-arylidene-1,3-indanediones with high to excellent chemical yields (up to 99%) and moderate to good regioselectivity (up to 5 : 1). DFT studies have also been carried out to understand the regioselective nature of this reaction. The results of Frontier molecular orbital calculations and the activation energy (E_a) favour the formation of compound 3avia γ-attack compared to that of 4avia α-attack.

A [3+2] annulation protocol for the construction of functionalized spirocyclopentenes utilizing 1,3-indanedione derived benzylidene-1,3-indanedione and ethyl-2,3-butadienoate at room temperature was developed.     

Sulfonated biochar catalyst derived from eucalyptus tree shed bark: synthesis,characterization and its evaluation in oleic acid esterification

Herein, fatty acid (oleic acid, OA) was upgraded to fatty acid methyl ester (FAME) via esterification reaction using sulfonated biochar obtained from eucalyptus tree shed bark as solid acid catalyst. Under the optimal esterification conditions (i.e., at 65 °C for 2 h using a methanol/OA molar ratio of 10 : 1 with a catalyst dosage of 4 wt%), the FAME yield was 97.05 ± 0.28% when a solid acid catalyst prepared by loading 6 g of p-Toluenesulfonic acid (p-TSA) on 2 g of activated biochar (p-TSA₃/ABC) was used. The remarkable performance of the p-TSA₃/ABC could be attributed to its high acidity (468.8 μmol g⁻¹) and dominance of the SO₃H acid site on the catalyst surface. Experimental findings showed that the p-TSA₃/ABC was relatively stable due to its highly functionalized structure. The catalyst was recycled for five successive cycles and exhibited no dramatic decrease in catalytic activity.

Herein, fatty acid (oleic acid, OA) was upgraded to fatty acid methyl ester (FAME) via esterification reaction using sulfonated biochar obtained from eucalyptus tree shed bark as solid acid catalyst.     

Pillararene-functionalised graphene nanomaterials

Pillararene-modified graphene materials integrate the advantages of both graphene and pillararenes; e.g., the cavity of pillararenes can recognise suitably sized electron-deficient and hydrophobic guest molecules via host–guest interactions, while the graphene composite is able to exhibit unique physiochemical properties including inertness, nanoscale, electrical and thermal structural properties. Those novel organic–inorganic hybrid composites can be efficiently prepared via both covalent and noncovalent bonds by classic organic reactions and supramolecular interactions, respectively. Pillararene-functionalised graphene materials have been used in various applications, such as electrochemical sensing guest molecules, performing as the platform for fluorescent probes, carrying out fluorescence quenching as the sensor, biosensing toxic molecules in cells, Raman and fluorescence bioimaging of cancer cells, photoacoustic and ultrasound imaging, as well as storage materials and reactors in energy fields.

The current research progress on diverse pillararene derivative functionalised graphene materials, including different synthesis strategies and various applications, is reviewed.     

Novel oxygen-generation from electrospun nanofibrous scaffolds with anticancer properties: synthesis of PMMA-conjugate PVP–H2O2 nanofibers,characterization, and in vitro bio-evaluation tests

Released oxygen plays a critical role in reducing destructive tumor behavior. This study aims to utilize decomposed hydrogen peroxide as an oxygen source by conjugating it with polyvinylpyrrolidone (PVP). PVP–hydrogen peroxide complex (PHP) composed of different ratios of (PVP : H₂O₂) (0.5 : 1, 1 : 1, 1 : 1.5, 1 : 5, and 1 : 10) were successfully synthesized. PHP complex with a ratio of 1 : 1.5 was chosen as the optimized ratio, and it was incorporated into the polymethyl methacrylate (PMMA) nanofibrous scaffold via the electrospinning technique. Results have revealed that the PMMA–10% PHP complex provided a significant morphological structure of nanofibrous scaffolds. The mechanical properties of PMMA–10% PHP nanofibers showed the most suitable mechanical features such as Young''s modulus, elongation-at-break (%), and maximum strength, in addition to the highest degree of swelling. All PHP complex scaffolds released oxygen in a sustained manner. However, the PMMA–10% PHP complex gave the highest concentration of released-oxygen with (∼8.9 mg L⁻¹, after 2.5 h). PMMA–10% PHP nanofibers provided an ideal model for released-oxygen scaffold with anti-cancer effect and high selectivity for cancer cells, especially for breast cancer cells. Nanofibrous scaffolds with different composition revealed high cell viability for normal cells. Such outcomes support the suitability of using synthesized nanofibrous scaffolds as released-oxygen biomaterials to enhance cancer cells'' sensitivity and maximize the treatment effect.

Released oxygen plays a critical role in reducing destructive tumor behavior.     

Gram-scale carbasugar synthesis via intramolecular seleno-Michael/aldol reaction

Carbasugars represent an important category of natural products possessing a broad spectrum of biological activities. Lots of effort has been done to develop gram scale synthesis. We are presenting a new approach to gram scale synthesis of the carbasugar skeleton via intramolecular seleno-Michael/aldol reaction. The proposed strategy gave gram amounts of 6-hydroxy shikimic ester in a tandem process in 36% overall yield starting from d-lyxose. We have attempted to demonstrate the synthetic utility of 6-hydroxyshikimic acid derivatives by covering the important synthetic modifications and related applications, namely synthesis of protected (−)-gabosine E, (−)-MK7606, (−)-valienamine and finally unprotected methyl (−)-shikimate.

A new approach to gram scale synthesis of carbasugar derivatives via intramolecular seleno-Michael/aldol reaction.     

Synthesis of bodinieric acids A and B,both C-18 and C-19-functionalized abietane diterpenoids: DFT study of the key aldol reaction

The first synthesis of C-18- and C-19-bifunctionalized abietane diterpenoids, bodinieric (or callicapoic) acids, via an aldol reaction has been developed. This key aldol reaction was very sensitive to steric hindrance. This fact has been studied by deuterium exchange experiments and DFT methods. Optimization of this reaction led to the synthesis of anti-inflammatory bodinieric acids A and B, starting from abietic acid.

The first synthesis of C-18- and C-19-bifunctionalized abietane diterpenoids, bodinieric (or callicapoic) acids, via an aldol reaction has been developed.     

Catechin or quercetin guests in an intrinsically microporous polyamine (PIM-EA-TB) host: accumulation,reactivity, and release

Microporous polymer materials based on molecularly “stiff” structures provide intrinsic microporosity, typical micropore sizes of 0.5 nm to 1.5 nm, and the ability to bind guest species. The polyamine PIM-EA-TB contains abundant tertiary amine sites to interact via hydrogen bonding to guest species in micropores. Here, quercetin and catechin are demonstrated to bind and accumulate into PIM-EA-TB. Voltammetric data suggest apparent Langmuirian binding constants for catechin of 550 (±50) × 10³ M⁻¹ in acidic solution at pH 2 (PIM-EA-TB is protonated) and 130 (±13) × 10³ M⁻¹ in neutral solution at pH 6 (PIM-EA-TB is not protonated). The binding capacity is typically 1 : 1 (guest : host polymer repeat unit), but higher loadings are readily achieved by host/guest co-deposition from tetrahydrofuran solution. In the rigid polymer environment, bound ortho-quinol guest species exhibit 2-electron 2-proton redox transformation to the corresponding quinones, but only in a thin mono-layer film close to the electrode surface. Release of guest molecules occurs depending on the level of loading and on the type of guest either spontaneously or with electrochemical stimuli.

Microporous polymer materials based on molecularly “stiff” structures provide intrinsic microporosity, typical micropore sizes of 0.5 nm to 1.5 nm, and the ability to bind guest species.     

Pyranopyrazole based Schiff base for rapid colorimetric detection of arginine in aqueous and real samples

A novel pyranopyrazole-based Schiff base PPS has been synthesized via a condensation reaction between aldehyde and hydrazide derivatives of pyranopyrazole. The probe acted as a selective and sensitive chemosensor for the colorimetric detection of arginine under aqueous conditions with a detection limit of 1.8 × 10⁻⁵ M. The 1 : 1 binding stoichiometry was established using various UV-vis spectroscopic methods. A plausible binding mechanism of PPS towards arginine was established via¹H NMR titration techniques and the results were further validated using DFT studies. Moreover, PPS provided a reasonable response for arginine in dietary supplements and human blood plasma which demonstrates its potential application in real sample analysis as well.

A novel pyranopyrazole-based Schiff base PPS has been synthesized via a condensation reaction between aldehyde and hydrazide derivatives of pyranopyrazole.     

Synthesis of Pd–Ru solid-solution nanoparticles by pulsed plasma in liquid method

We have synthesized solid-solution nanoparticles (Pd : Ru = 1 : 3, 1 : 1 and 3 : 1) in an immiscible Pd–Ru system by the pulsed plasma in liquid method using Pd–Ru mixture bulk electrodes. The particle sizes of the floated and sedimented samples were measured to be <10 and <20 nm, respectively, via high-resolution transmission electron microscopy (HR-TEM). The lattice parameters of nanoparticles followed the Vegard''s law, and the energy-dispersive X-ray spectroscopy (EDX) results almost coincided with those obtained for the starting bulk mixtures. The solid-solution structures and local structure were confirmed via HR-TEM, X-ray photoelectron spectroscopy (XPS) and X-ray absorption fine structure spectroscopy (XAFS).

We have synthesized solid-solution nanoparticles (Pd : Ru = 1 : 3, 1 : 1 and 3 : 1) in an immiscible Pd–Ru system by the pulsed plasma in liquid method using Pd–Ru mixture bulk electrodes.     

Optimization of biodiesel synthesis from Jatropha curcas oil using kaolin derived zeolite Na–X as a catalyst

Biodiesel is an alternative renewable green fuel obtainable from the reaction of plant or animal oil with a low molecular weight alcohol in the presence of a catalyst. However, the cost of its production remains high due to costly feedstock, the majority of which is competitively also used as food, and the use of homogeneous catalysts, which pose difficulties in product purification and resulting environmental pollution. The aim of this study was to explore the production of biodiesel through transesterification of non-edible and cheap Jatropha curcas (JC) oil using a zeolite Na–X catalyst obtained from naturally occurring kaolin clay. The transesterification parameters, namely reaction temperature, reaction time, catalyst loading and methanol to oil molar ratio were optimized using the L₁₆(4⁴) Taguchi orthogonal array approach. The catalyst loading was found to be the most influential parameter at 93.79%. The optimum conditions for the conversion of JC oil, with a biodiesel yield of up to 93.94%, were found to be a methanol to oil molar ratio of 10 : 1, catalyst loading of 8%, reaction temperature of 70 °C and reaction time of 5 h. Fuel characterization parameters were within the European Norm (EN) 14214:2019 biodiesel specifications. Our findings offer insights into the ideal parametric conditions for the cost-effective synthesis of biodiesel from JC oil via zeolite-catalyzed esterification.

Zeolite Na–X derived from inexpensive kaolin clay is an effective catalyst (up to 94% yield) for Jatropha curcas oil conversion to biodiesel; Taguchi optimization shows methanol/oil ratio of 10, with 8% catalyst loading at 70 °C for 5 h as optimum.     

Rh(iii)-catalyzed synthesis of tetracyclic isoquinolinium salts via C–H activation and [4+2] annulation of 1-phenyl-3,4-dihydroisoquinolines and alkynes in ethanol

An efficient and convenient method to construct tetracyclic isoquinolinium salts via [Cp*RhCl₂]₂ catalyzed C–H activation and [4 + 2] annulation reactions in ethanol is described. This reaction is very fast and highly efficient in the green solvent ethanol. The reaction works with a broad substrate scope affording the products in good to excellent yields in a short time. Moreover, a ratio of S/C up to 10 000 could be achieved with gram scale synthesis.

An efficient method to construct tetracyclic isoquinolinium salts via C–H activation and [4 + 2] annulation reactions in ethanol is described.     

Optimization of synthetic parameters of high-purity trifunctional mercaptoesters and their curing behavior for the thiol–epoxy click reaction

The direct esterification reaction between 3-mercaptopropionic acid (3-MPA) and trimethylolpropane (TMP) was conducted in the presence of various catalyst concentrations of p-toluenesulfonic acid (p-TSA) to examine the optimized synthetic conditions needed to produce high-purity trimethylolpropane-tris(3-mercaptopropionate) (TMPMP). The purity of the desired TMPMP and uncompleted side-product reduced as the acid catalyst concentration in this esterification reaction increased while the generation of thioester-based side-product increased. The equivalent ratio between epoxy and the manufactured TMPMP was maintained at 1 : 1 to monitor the curing behavior of the thiol–epoxy click reaction using the DSC technique. The thermal features of the base-catalyzed TMPMP-cured epoxy resin were assessed according to the purity of the TMPMP curing agent.

The direct esterification reaction between 3-mercaptopropionic acid and trimethylolpropane was conducted in the presence of various catalyst concentrations to find a synthetic route for high-purity trimethylolpropane-tris(3-mercaptopropionate).     

pH-responsive molecular assemblies of pyridylbutadiene derivative with cucurbit[7]uril

The interaction between red-emitting pyridinium derivative [4-((1E,3E)-4-(4-(dimethylamino)phenyl)buta-1,3-dien-1-yl)-1-methylpyridin-1-ium] (DABP) and cucurbit[7]uril was investigated using optical absorption, steady-state and time-resolved fluorescence and anisotropy measurements. The changes in the UV/Vis absorption, fluorescence spectral characteristics and lifetime, with a change in pH, reveal efficient binding of CB7 to the dye molecule. The cucurbit[7]uril encapsulated DABP brings ∼1.5 units upward pK_a shift. The formation of supramolecular assemblies with 1 : 1 and 2 : 1 host–guest stoichiometries with CB7 at different pH conditions have been verified from ¹H NMR, isothermal titration calorimetric studies and geometry optimization calculations. CB7-dye complexation and the ensuing morphological changes were revealed by SEM, AFM and optical microscopy images. This pH-responsive supramolecular assemblies of red-emitting DABP dye can find potential applications in biological imaging, optical pH-sensor and the construction of building blocks for the supramolecular architectures.

pH-responsive emission behavior of supramolecular complexes between pyridylbutadiene with CB7 and formation of molecular assemblies is described.      

Oxidatively induced exposure of active surface area during microwave assisted formation of Pt3Co nanoparticles for oxygen reduction reaction

The oxygen reduction reaction (ORR), the rate-limiting reaction in proton exchange membrane fuel cells, can efficiently be facilitated by properly manufactured platinum catalysts alloyed with late 3d transition metals. Herein we synthesize a platinum : cobalt nanoparticulate catalyst with a 3 : 1 atomic ratio by reduction of a dry metalorganic precursor blend within a commercial household microwave oven. The formed nanoparticles are simultaneously anchored to a carbon black support that enables large Pt surface area. Two separate microwave treatment steps were employed, where step one constitutes a fast oxidative treatment for revealing active surface area while a reductive secondary annealing treatment promotes a Pt rich surface. The resulting Pt₃Co/C catalyst (∼3.4 nm) demonstrates an enhanced ORR activity directly attributed to incorporated Co with a specific and mass activity of 704 μA cm_Pt⁻² and 352 A g_Pt⁻¹ corresponding to an increase by 279% and 66% respectively compared to a commercial Pt/C (∼1.8 nm) catalyst measured under identical conditions. The method''s simplicity, scalability and novelty is expected to further assist in Pt–Co development and bring the catalyst one step closer toward commercialization and utility in fuel cells.

The oxygen reduction reaction (ORR) is efficiently facilitated platinum catalysts alloyed with Co and reveal high electrochemically active surface area via rapid microwave synthesis.