Phosphorus pentoxide as a cost-effective,metal-free catalyst for ring opening polymerization of ε-caprolactone

The ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) using phosphorus pentoxide (P₂O₅) as a metal-free catalyst and isopropanol (iPrOH) as initiator resulted in the preparation of poly(ε-caprolactone) with narrow weight distribution. NMR spectroscopy analyses of the prepared PCL indicated the presence of the initiator residue at the end of the polymer chain, implying the occurrence of the ε-CL-catalysis ROP through a monomer activation mechanism. Kinetic experiments confirmed the controlled/living nature of ε-CL ring-opening catalyzed by phosphorus pentoxide. The commercial availability of phosphorus pentoxide and its easy-handling provide additional opportunities for polymer synthesis and nanocomposite manufacturing.

The ring-opening polymerization (ROP) of ε-caprolactone (ε-CL) using phosphorus pentoxide (P₂O₅) as a metal-free catalyst and isopropanol (iPrOH) as initiator resulted in the preparation of poly(ε-caprolactone) with narrow weight distribution.     

Copolyesters of ε-caprolactone and l-lactide catalyzed by a tetrabutylammonium phthalimide-N-oxyl organocatalyst

Aliphatic polyesters are biocompatible materials that can be used in biomedical applications. We report here the use of tetrabutylammonium phthalimide-N-oxyl catalyst (TBAPINO), as a thermally stable organocatalyst for the ring-opening polymerization (ROP) of cyclic esters under mild conditions. In the solution ROP of ε-caprolactone (ε-CL), quantitative conversion and M_n of ∼20 000 g mol⁻¹ are achieved in a wide temperature range from −15 to 60 °C. Under bulk condition, the conversion of ε-CL reaches over 85% at 120 °C within 2 h. The living ROP character of l-lactide (l-LA) catalyzed over TBAPINO is proved by multiple additions of monomer in the bulk polymerization. The catalyst shows comparable selectivity towards the ring-opening polymerization of l-LA and ε-CL. Their copolymerization over TBAPINO is carried out in one-pot bulk condition in terms of the reaction time, monomer feed ratio, and sequence of addition. The colorless poly(ε-caprolactone-co-lactide) (PCLA) is obtained with considerable conversion of both monomers with the M_n over 22 000 g mol⁻¹.

By utilizing tetrabutylammonium phthalimide-N-oxyl organocatalyst, copolymer PCLA with M_n over 20 000 g mol⁻¹ was synthesized by sequential ring-opening polymerization of ε-caprolactone and l-lactide under bulk conditions.     

Preparation of functionalized poly(1-butene) from 1,2-polybutadiene via sequential thiol-ene click reaction and ring-opening polymerization

Poly(1-butene) is a kind of unique poly(α-olefin) material that displays exceptional creep resistance and environmental stress cracking resistance, and therefore currently finds wide application in the fields of packaging, films, pipes, etc. However, very few current researchers are paying attention to functional poly(1-butene) despite its great research significance, perhaps due to the general paucity of catalytic systems for synthesizing this material. Therefore, in the present study, we set out to develop an alternative method to prepare polar poly(1-butene)s. Specifically, 1,2-enriched poly(1,3-butadiene), used as a starting material, was partially hydrogenated to afford a quasi-poly(1-butene) polymer containing C C double bonds. These double bonds were further modified by subjecting the quasi-poly(1-butene) polymer to a thiol-ene reaction in the presence of thiol compounds, and a series of polar poly(1-butene)s that bore significantly improved surface properties were obtained. By using hydroxyl-containing thiol compounds, ring-opening polymerization (ROP) of ε-caprolactone was further implemented. Here, polar poly(ε-caprolactone) was incorporated as side chains, and we were able to control the chain length by adjusting the feeding ratio. The water contact angles of the resultant polymers, i.e., those containing the poly(ε-caprolactone) side chains, were as low as 59.4°, indicating a greater hydrophilicity resulting from the incorporation of these side chains.

An alternative method for preparing functionalized poly(1-butene) from 1,2-polybutadiene via sequential thiol-ene click reaction and ring-opening polymerization is reported.     

Photo-responsive polymeric micelles and prodrugs: synthesis and characterization

Bio-recognizable and photocleavable amphiphilic glycopolymers and prodrugs containing photodegradable linkers (i.e. 5-hydroxy-2-nitrobenzyl alcohol) as junction points between bio-recognizable hydrophilic glucose (or maltose) and hydrophobic poly(α-azo-ε-caprolactone)-grafted alkyne or drug chains were synthesized by combining ring-opening polymerization, nucleophilic substitution, and “click” post-functionalization with alkynyl-pyrene and 2-nitrobenzyl-functionalized indomethacin (IMC). The block-grafted glycocopolymers could self-assemble into spherical photoresponsive micelles with hydrodynamic sizes of <200 nm. Fluorescence emission measurements indicated the release of Nile red, a hydrophobic dye, encapsulated by the Glyco-ONB-P(αN₃CL-g-alkyne)_n micelles, in response to irradiation caused by micelle disruption. Light-triggered bursts were observed for IMC-loaded or -conjugated micelles during the first 5 h. Following light irradiation, the drug release rate of IMC-conjugated micelles was faster than that of IMC-loaded micelles. Selective lectin binding experiments confirmed that glycosylated Glyco-ONB-P(αN₃CL-g-alkyne)_n could be used in bio-recognition applications. The nano-prodrug with and without UV irradiation was associated with negligible levels of toxicity at concentrations of less than 30 μg mL⁻¹. The confocal microscopy and flow cytometry results indicated that the uptake of doxorubicin (DOX)-loaded micelles with UV irradiation by HeLa cells was faster than without UV irradiation. The DOX-loaded Gluco-ONB-P(αN₃CL-g-PONBIMC)₁₀ micelles effectively inhibited HeLa cells'' proliferation with a half-maximal inhibitory concentration of 8.8 μg mL⁻¹.

Bio-recognizable and photocleavable amphiphilic glycopolymers and prodrugs containing photodegradable linkers as junction points between hydrophilic glycose and hydrophobic poly(α-azo-ε-caprolactone)-grafted alkyne or drug chains were synthesized.     

Synthesis,characterization and olefin polymerization behaviors of phenylene-bridged bis-β-carbonylenamine binuclear titanium complexes

Binuclear and multinuclear complexes have attracted much attention due to their unique catalytic performances for olefin polymerization compared with their mononuclear counterparts. In this work, a series of phenyl-bridged bis-β-carbonylenamine [O⁻NS^R] (R = alkyl or phenyl) tridentate ligands and their binuclear titanium complexes (Ti²L₁–Ti²L₅) were synthesized and characterized by ¹H NMR, ¹³C NMR, FTIR and elemental analysis. The molecular structure of ligand L₂ (R = ⁿPr) and its corresponding Ti complex Ti²L₂ were further investigated by single-crystal X-ray diffraction, which showed that each titanium coordinated with six atoms to form a distorted octahedral configuration along with the conversion of the ligand from β-carbonylenamine to β-imino enol form. Under the activation of MMAO, these complexes catalyzed ethylene polymerization and ethylene/α-olefin copolymerization with extremely high activity (over 10⁶ g mol (Ti)⁻¹ h⁻¹ atm⁻¹) to produce high molecular weight polyethylene. At the same time, wider polydispersity as compared with the mononuclear counterpart TiL₆ was observed, indicating that two active catalytic centers may be present, consistent with the asymmetrical crystal structure of the binuclear titanium complex. Furthermore, these complexes possessed better thermal stability than their mononuclear analogues. Compared with the complexes bearing alkylthio sidearms, the complex Ti²L₅ bearing a phenylthio sidearm exhibited higher catalytic activity towards ethylene polymerization and produced polyethylene with much higher molecular weight, but with an appreciably lower 1-hexene incorporation ratio. Nevertheless, these bis-β-carbonylenamine-derived binuclear titanium complexes showed much higher ethylene/1-hexene copolymerization activity and 1-hexene incorporation ratios as compared with the methylene-bridged bis-salicylaldiminato binuclear titanium complexes, and the molecular weight and 1-hexene incorporation ratio could be flexibly tuned by the initial feed of α-olefin commoners and catalyst structures.

Phenyl-bridged bis-β-carbonylenamine binuclear titanium complexes were synthesized, characterized and used to catalyze ethylene (co)polymerization with extremely high activity.     

Synthesis of copolyesters based on substituted and non-substituted lactones towards the control of their crystallinity and their potential effect on hydrolytic degradation in the design of soft medical devices

A series of copolymers based on ε-caprolactone (ε-CL) in combination with lactone monomers substituted with alkyl groups (4 and 6 carbon atoms), specifically δ-decalactone (δ-DL), ε-decalactone (ε-DL) and δ-dodecalactone (δ-DD), as well as a copolymer using two substituted lactone monomers with alkyl groups (ε-DL and δ-DD) were synthesized in different molar ratios. The objective of the synthesis of these copolymers was to evaluate the effects of branching in the polymer backbone on the crystallinity and the thermal properties of the synthesized materials. All copolymers were obtained via ring-opening polymerization with high conversion values for both comonomers using neodymium isopropoxide (Nd(i-Pr)₃) as the initiator, and their compositions were determined by ¹H NMR and ¹³C NMR. The molar masses (M_n and M_w) and distributions were obtained by GPC measurements. Such measurements showed that a majority of the copolymers exhibited dispersities (Ɖ) in the range of 1.2–1.6 and M_n in the range of 15–40 kDa. First- and second-order transitions such as melting, crystallization and glass transition, as well as the crystallization degree (melting enthalpy), were determined by DSC analysis. Copolymers based on ε-CL developed interesting behaviors, wherein the copolymers with higher percentages of this monomer exhibited semicrystalline behavior, while the copolymers with a higher percentage of the comonomers ε-DL, δ-DL or δ-DD showed amorphous behavior. In contrast, the copolymers synthesized using both monomers from the alkyl group-substituted lactone developed fully amorphous features, regardless of their composition. These changes in the crystalline features of the synthesized copolymers suggest that the content of short branchings on the copolymer backbone will significantly modify their rates of hydrolytic degradation and their potential use in the development of different soft medical devices.

ROP synthesis of polyesters at different molar ratios of monomers ε-caprolactone (ε-CL) in combination with alkyl substituted lactones δ-decalactone (δ-DL), ε-decalactone (ε-DL) and δ-dodecalactone (δ-DD), as well copolymers based on ε-DL and δ-DD.     

Binary catalytic system for homo- and block copolymerization of ε-caprolactone with δ-valerolactone

The combined interaction of 2,3,6,7-tetrahydro-5H-thiazolo[3,2-a] pyrimidine (ITU) as the organocatalytic nucleophile with YCl₃ as Lewis acid cocatalyst, generating ITU/YCl₃, was employed for homo- and copolymerization of ε-caprolactone (CL) with δ-valerolactone (VL). Poly(caprolactone) (PCL) and poly(caprolactone)–poly(ethylene glycol)–poly(caprolactone) (PCL–PEG–PCL) triblock copolymer and poly(valerolactone)–poly(caprolactone)–poly(ethylene glycol)–poly(caprolactone)–poly(valerolactone) (PVL–PCL–PEG–PCL–PVL) pentablock copolymer were successfully prepared by ring-opening polymerization (ROP) of CL employing ITU/YCl₃ as catalyst in the presence of benzyl alcohol (BnOH) or poly(ethylene glycol) (PEG) as initiator, respectively. The reaction was systematically optimized, and the architecture, molecular weight and thermal properties of the polymers were characterized by NMR, FTIR, SEC and DSC analyses. Finally, a plausible polymerization mechanism was proposed.

The combined interaction of 2,3,6,7-tetrahydro-5H-thiazolo[3,2-a] pyrimidine (ITU) as the organocatalytic nucleophile with YCl₃ as Lewis acid cocatalyst, generating ITU/YCl₃, was employed for homo- and copolymerization of CL with VL.     

N α-arylsulfonyl histamines as selective β-glucosidase inhibitors

N ^α-benzenesulfonylhistamine, a new semi-synthetic β-glucosidase inhibitor, was obtained by bioactivity-guided isolation from a chemically engineered extract of Urtica urens L. prepared by reaction with benzenesulfonyl chloride. In order to identify better β-glucosidase inhibitors, a new series of N^α,N^τ-di-arylsulfonyl and N^α-arylsulfonyl histamine derivatives was prepared. Biological studies revealed that the β-glucosidase inhibition was in a micromolar range for several N^α-arylsulfonyl histamine compounds of the series, N^α-4-fluorobenzenesulfonyl histamine being the most powerful compound. Besides, this reversible and competitive inhibitor presented a good selectivity for β-glucosidase with respect to other target enzymes including α-glucosidase.

A selective β-glucosidase inhibitor was discovered using the chemically engineered extracts approach.     

Tailor-made block copolymers of l-, d- and rac-lactides and ε-caprolactone via one-pot sequential ring opening polymerization by pyridylamidozinc(ii) catalysts

Three-coordinated Zn(ii) complexes bearing sterically encumbered bidentate monoanionic [N,N⁻] pyridylamido ligands efficiently catalyze the ring opening polymerization of lactide (LA) and ε-caprolactone (CL). Owing to the polymerization controlled nature and high rate, precise stereodiblock poly(LLA-b-DLA) with different block lengths can be easily produced by one-pot sequential monomer addition at room temperature in short reaction times. NMR, SEC and DSC analyses confirm the production of highly isotactic diblock copolymers which crystallize in the high melting stereocomplex phase. Stereo-triblock and tetrablock copolymers of l-LA, d-LA and rac-LA have been synthesized similarly. Finally, a diblock poly(CL-b-LA) has been easily obtained by sequential addition of ε-caprolactone and lactide under mild conditions.

New 3-coordinated Zn ROP catalysts afford lactide stereo-block copolymers with variable block lengths and steric structures and diblock ε-caprolactone-lactide copolymers at room temperature and in short reaction times.     

Aluminium alkyl complexes supported by imino-phosphanamide ligand as precursors for catalytic guanylation reactions of carbodiimides

Herein, we report the synthesis, characterisation, and application of three aluminium alkyl complexes, [κ²-{NHI^RP(Ph)NDipp}AlMe₂] (R = Dipp (2a), Mes (2b); tBu (2c), Dipp = 2,6-diisopropylphenyl, Mes = mesityl, and tBu = tert-butyl), supported by unsymmetrical imino-phosphanamide [NHI^RP(Ph)NDipp]⁻ [R = Dipp (1a), Mes (1b), tBu (1c)] ligands as molecular precursors for the catalytic synthesis of guanidines using carbodiimides and primary amines. All the imino-phosphanamide ligands 1a, 1b and 1c were prepared in good yield from the corresponding N-heterocyclic imine (NHI) with phenylchloro-2,6-diisopropylphenylphosphanamine, PhP(Cl)NHDipp. The aluminium alkyl complexes 2a, 2b and 2c were obtained in good yield upon completion of the reaction between trimethyl aluminium and the protic ligands 1a, 1b and 1c in a 1 : 1 molar ratio in toluene via the elimination of methane, respectively. The molecular structures of the protic ligands 1b and 1c and the aluminium complexes 2a, 2b and 2c were established via single-crystal X-ray diffraction analysis. Complexes 2a, 2b and 2c were tested as pre-catalysts for the hydroamination/guanylation reaction of carbodiimides with aryl amines to afford guanidines at ambient temperature. All the aluminium complexes exhibited a high conversion with 1.5 mol% catalyst loading and broad substrate scope with a wide functional group tolerance during the guanylation reaction. We also proposed the most plausible mechanism, involving the formation of catalytically active three-coordinate Al species as the active pre-catalyst.

Three aluminium alkyl complexes, [κ²-{Im^RNP(Ph)NDipp}AlMe₂] (2a–2c), supported by unsymmetrical imino-phosphanamide were synthesised and utilised as competent precatalysts for the hydroamination of carbodiimides under ambient conditions.     

Asymmetric amination of α,α-dialkyl substituted aldehydes catalyzed by a simple chiral primary amino acid and its application to the preparation of a S1P1 agonist

The chiral catalytic amination of an α,α-dialkyl substituted aldehyde usually proceeds with low enantioselectivity. We selected naphthyl-l-alanine as the catalyst and observed improved enantioselectivity for the amination. Using this method, racemic α-methyl-α-benzyloxypropanal was aminated to give chiral serine derivatives in 74% ee, which was further increased to >99% ee after recrystallization. Moreover, we also successfully synthesized a chiral phosphonium salt 9 for the preparation of one α-substituted alaninol compound 14 as an S1P₁ agonist in high overall yield.

The chiral catalytic amination of an α,α-dialkyl substituted aldehyde usually proceeds with low enantioselectivity.     

μ-Oxo-bridged diiron(iii) complexes of tripodal 4N ligands as catalysts for alkane hydroxylation reaction using m-CPBA as an oxidant: substrate vs. self hydroxylation

A series of non-heme μ-oxo-bridged dinuclear iron(iii) complexes of the type [Fe₂(μ-O)(L1–L6)₂Cl₂]Cl₂1–6 have been isolated and their catalytic activity towards oxidative transformation of alkanes into alcohols has been studied using m-choloroperbenzoic acid (m-CPBA) as an oxidant. All the complexes were characterized by CHN, electrochemical, and UV-visible spectroscopic techniques. The molecular structures of 2 and 5 have been determined successfully by single crystal X-ray diffraction analysis and both possesses octahedral coordination geometry and each iron atom is coordinated by four nitrogen atoms of the 4N ligand and a bridging oxygen. The sixth position of each octahedron is coordinated by a chloride ion. The (μ-oxo)diiron(iii) core is linear in 2 (Fe–O–Fe, 180.0°), whereas it is non-linear (Fe–O–Fe, 161°) in 5. All the diiron(iii) complexes show quasi-reversible one electron transfer in the cyclic voltammagram and catalyze the hydroxylation of alkanes like cyclohexane, adamantane with m-CPBA as an oxidant. In acetonitrile solution, adding excess m-CPBA to the diiron(iii) complex 2 without chloride ions leads to intramolecular hydroxylation reaction of the oxidant. Interestingly, 2 catalyzes alkane hydroxylation in the presence of chloride ions, but intramolecular hydroxylation in the absence of chloride ions. The observed selectivity for cyclohexane (A/K, 5–7) and adamantane (3°/2°, 9–18) suggests the involvement of high-valent iron–oxo species rather than freely diffusing radicals in the catalytic reaction. Moreover, 4 oxidizes (A/K, 7) cyclohexane very efficiently up to 513 TON while 5 oxidizes adamantane with good selectivity (3°/2°, 18) using m-CPBA as an oxidant. The electronic effects of ligand donors dictate the efficiency and selectivity of catalytic hydroxylation of alkanes.

The ligand stereoelectronic effect of diiron(iii) complexes determines the efficiency and selectivity of catalytic alkane hydroxylation with m-CPBA as an oxidant.     

Photostability and antioxidant activity studies on the inclusion complexes of trans-polydatin with β-cyclodextrin and derivatives

The inclusion complexes of trans-polydatin and three cyclodextrins (CDs), namely β-cyclodextrin (β-CD), methyl-β-cyclodextrin (Me-β-CD) and (2-hydroxy) propyl-β-cyclodextrin (HP-β-CD) were prepared. The effects of the inclusion behavior of trans-polydatin with three kinds of CDs were investigated in both solution and the solid state with the following methods: phase-solubility, X-ray diffraction (XRD), thermogravimetric analysis (TG), differential scanning calorimetry (DSC), and scanning electron microscopy (SEM), proton nuclear magnetic resonance (¹H-NMR) and two-dimensional rotational frame nuclear overhauser effect spectroscopy (2D ROESY). The results indicated that trans-polydatin formed a 1 : 1 stoichiometric inclusion complex with CDs. Meanwhile, the solubility and thermal stability of the inclusion complexes were improved after encapsulating by CDs. Furthermore, the photostability of trans-polydatin was enhanced after forming the inclusion complexes. The antioxidant activities results showed that the antioxidant performance of the inclusion complexes was enhanced in comparison to the native trans-polydatin. Therefore, it can be a potentially promising way to promote its drug bioavailability or phytochemical preparations.

The inclusion complexes of trans-polydatin and three cyclodextrins (CDs), namely β-cyclodextrin (β-CD), methyl-β-cyclodextrin (Me-β-CD) and (2-hydroxy) propyl-β-cyclodextrin (HP-β-CD) were prepared.     

High-pressure synthesis of ε-FeOOH from β-FeOOH and its application to the water oxidation catalyst

Research on materials under extreme conditions such as high pressures provides new insights into the evolution and dynamics of the earth and space sciences, but recently, this research has focused on applications as functional materials. In this contribution, we examined high-pressure/high-temperature phases of β-FeO_1−x(OH)_1+xCl_x with x = 0.12 (β-FeOOH) and their catalytic activities of water oxidation, i.e., oxygen evolution reaction (OER). Under pressures above 6 GPa and temperatures of 100–700 °C, β-FeOOH transformed into ε-FeOOH, as in the case of α-FeOOH. However, the established pressure–temperature phase diagram of β-FeOOH differs from that of α-FeOOH, probably owing to its open framework structure and partial occupation of Cl⁻ ions. The OER activities of ε-FeOOH strongly depended on the FeOOH sources, synthesis conditions, and composite electrodes. Nevertheless, one of the ε-FeOOH samples exhibited a low OER overpotential compared with α-FeOOH and its parent β-FeOOH, which are widely used as OER catalysts. Hence, ε-FeOOH is a potential candidate as a next-generation earth-abundant OER catalyst.

Research on materials under extreme conditions such as high pressures provides new insights into the evolution and dynamics of the earth and space sciences, but recently, this research has focused on applications as functional materials.     

Al-doped α-MnO2 coated by lignin for high-performance rechargeable aqueous zinc-ion batteries

Zn/MnO₂ batteries, one of the most widely studied rechargeable aqueous zinc-ion batteries, suffer from poor cyclability because the structure of MnO₂ is labile with cycling. Herein, the structural stability of α-MnO₂ is enhanced by simultaneous Al³⁺ doping and lignin coating during the formation of α-MnO₂ crystals in a hydrothermal process. Al³⁺ enters the [MnO₆] octahedron accompanied by producing oxygen vacancies, and lignin further stabilizes the doped Al³⁺via strong interaction in the prepared material, Al-doped α-MnO₂ coated by lignin (L + Al@α-MnO₂). Meanwhile, the conductivity of L + Al@α-MnO₂ improves due to Al³⁺ doping, and the surface area of L + Al@α-MnO₂ increases because of the production of nanorod structures after Al³⁺ doping and lignin coating. Compared with the reference α-MnO₂ cathode, the L + Al@α-MnO₂ cathode achieves superior performance with durably high reversible capacity (∼180 mA h g⁻¹ at 1.5 A g⁻¹) and good cycle stability. In addition, ex situ X-ray diffraction characterization of the cathode at different voltages in the first cycle is employed to study the related mechanism on improving battery performance. This study may provide ideas of designing advanced cathode materials for other aqueous metal-ion batteries.

Al³⁺ doping combined with lignin coating improves the structural stability and electrochemical performance of the modified α-MnO₂, L + Al@α-MnO₂.     

Controlled self-assembly into diverse stimuli-responsive microstructures: from microspheres to branched cylindrical micelles and vesicles

A series of amphiphilic PDMAEMA–SS–PCL chains with variable ratios of hydrophilic poly(2-(dimethylamino)ethyl methacrylate) (PDMAEMA) to hydrophobic poly(ε-caprolactone) (PCL) were prepared via ring-opening polymerization, in which the two different moieties were linked via a disulfide bond with reduction responsiveness. After cross-linking by the photodegradable o-nitrobenzyl linkage, the amphiphilic chains could self-assemble into microspheres, branched cylindrical micelles and vesicles, which were responsive to the reduction agent dl-dithiothreitol and UV light irradiation through different mechanisms.

A series of cross-linked amphiphilic PDMAEMA–SS–PCL were prepared, which could self-assemble into diverse microstructures with reduction and light responsiveness.     

Synthesis of different crystallographic FeOOH catalysts for peroxymonosulfate activation towards organic matter degradation

In this study, different crystalline structures of FeOOH have been prepared. α-FeOOH was synthesized through a hydrothermal method, whereas β-FeOOH was synthesized via a direct hydrolysis method. Moreover, γ- and δ-FeOOH were prepared by precipitation methods through slow and quick oxidation, respectively. On this basis, their crystal structure, morphology, and surface area were measured. Then, all the synthesized materials were applied to activate peroxymonosulfate (PMS) to generate sulfate radicals (SO₄⁻˙) for acid orange 7(AO7) degradation. Compared with α-FeOOH, β-FeOOH, and γ-FeOOH, δ-FeOOH showed more efficient decolorization of AO7 in the catalytic system because of its abundant surface area and crystalline structure. The effects of several parameters in the δ-FeOOH/PMS/AO7 system were investigated. The results show that the initial pH, which is related to the features of surface hydroxyl groups, is the decisive factor, and excellent catalytic activity is maintained in the pH range 5–8. The increase of catalyst dosage and appropriate increase of PMS concentration contributed to promote the degradation effect. However, self-quenching was observed in a high PMS concentration system. Moreover, δ-FeOOH was stable after six consecutive cycles, and the leaching of iron ions was negligible. According to the quenching test and electron spin resonance analysis, both SO₄⁻˙ and ˙OH were the dominant radicals for AO7 degradation.

In this study, different crystalline structures of FeOOH have been prepared.     

Total synthesis of Palmarumycin BGs,C1 and Guignardin E

The first total synthesis of Palmarumycin BG1–3, BG5–6, C₁ and Guignardin E (1–7) were achieved by the same intermediate Palmarumycin C₂ through a N-benzyl cinchoninium chloride-catalyzed epoxidation, an organoselenium-mediated reduction, and a cerium(iii) chloride hydrate-promoted regioselective ring-opening and elimination of cyclic α,β-epoxy ketone as the key steps via6–7 step routes using 1,8-dihydroxynaphthalene (DHN) and 5-methoxytetralone as the starting materials in overall yields of 1.0–17.4%, respectively. Their structures and absolute configurations were characterized and determined by ¹H, ¹³C NMR, IR, HR-ESI-MS and X-ray diffraction data. These compounds displayed significant inhibition activities against HCT116, U87-MG, HepG2, BGC823 and PC9 cell lines.

The first total syntheses of Palmarumycin BG1–3, BG5–6, C₁ and Guignardin E were achieved. These compounds displayed significant inhibition activities against HCT116, U87-MG, HepG2, BGC823 and PC9 cell lines.     

Ratiometric fluorescence sensing of d-allulose using an inclusion complex of γ-cyclodextrin with a benzoxaborole-based probe

Because d-allulose has been attracting attention as a zero-calorie sugar, the selective sensing of d-allulose is desired to investigate its health benefits. We report herein a novel fluorescence chemosensor that is based on an inclusion complex of γ-cyclodextrin (γ-CyD) with a benzoxaborole-based probe. Two inclusion complexes, 1/γCyD and 2/γCyD, were prepared by mixing γ-CyD with their corresponding probes in a water-rich solvent, where γ-CyD encapsulates two molecules of the probes inside its cavity to form a pyrene dimer. Both 1/γCyD and 2/γCyD exhibit monomeric and dimeric fluorescence from the pyrene moieties. By the reaction of 1/γCyD with saccharides, the intensities of monomeric and dimeric fluorescence remained unchanged and decreased, respectively. We have demonstrated that 1/γCyD has much higher affinity for d-allulose than for the other saccharides (d-fructose, d-glucose, and d-galactose). The conditional equilibrium constants for the reaction systems were determined to be 498 ± 35 M⁻¹ for d-fructose, 48.4 ± 25.3 M⁻¹ for d-glucose, 15.0 ± 3.3 M⁻¹ for d-galactose, and (8.05 ± 0.59) × 10³ M⁻¹ for d-allulose. These features of 1/γCyD enable ratiometric fluorescence sensing with high sensitivity and selectivity for d-allulose. The limits of detection and quantification of 1/γCyD for d-allulose at pH 8.0 were determined to be 6.9 and 21 μM, respectively. Induced circular dichroism spectral study has shown that the reaction of 1/γCyD with d-allulose causes the monomerisation of the dimer of probe 1 that is encapsulated by γ-CyD, which leads to the diminishment of the dimeric fluorescence.

We proposed an inclusion complex of γ-cyclodextrin with a benzoxaborole-based fluorescent probe as a highly sensitive and selective chemosensor for d-allulose.     

Synthesis and characterization of 4-arm star-shaped amphiphilic block copolymers consisting of poly(ethylene oxide) and poly(ε-caprolactone)

Star-shaped polymers exhibit lower hydrodynamic volume, glass transition temperature, critical micelles concentration (CMC), and higher viscosity and drug-loading capacity compared to their linear counterparts. In the present study, amphiphilic biodegradable 4-arm star-shaped block copolymers, based on poly(ethylene oxide) (PEO) as a hydrophilic part and poly(ε-caprolactone) (PCL) as a hydrophobic segment, are synthesized by ring-opening polymerization of ε-caprolactone employing pentaerythritol as an initiator and stannous octoate as a catalyst, followed by the coupling reaction with carboxyl-functionalized monomethoxy poly(ethylene oxide) (MeO-PEO-COOH). The structures of intermediates were deduced through ¹H-NMR and FT-IR spectroscopy. Average chemical composition of the star block copolymer is determined by proton NMR. Information related to molar mass distribution of targeted products and their precursors is obtained by size exclusion chromatography (SEC). However, due to its inherent poor resolution SEC could not reveal whether all the parent homopolymers are coupled to each other or remained unattached to the other segment. In order to comprehensively characterize the synthesized star-block copolymers, liquid chromatography at critical conditions of both blocks is employed. The study allowed for separation of homopolymer precursors from targeted star-block copolymers. The study exposed heterogeneity of star block copolymers that was not possible by conventional techniques.

LCCC on RP columns proves to be efficient for separation of precursors from targeted star block copolymers in a single run.