Simple preparation of multi-valent cyclodextrin–carbohydrate conjugates

Several β-cyclodextrin (CD) derivatives conjugated with carbohydrates via aminohexyl linkages have been prepared. These CD-conjugates were demonstrated to be multi-valent ligands by lectin-binding assay.     

The effect of the precursor structure on the catalytic properties of the nickel—chromium catalysts of hydrogenation reactions

The influence of the Ni²⁺/Cr³⁺ ratio in the precursor compound on the formation of the catalyst structure and its transformation upon the thermal treatment and reductive activation in hydrogen was studied. The precursors with the cation ratio Ni²⁺/Cr³⁺ = (2.3–3)/1 represent a homogeneous system of the stichtite-type structure. The treatment of the precursors at T ～400 °C in an inert atmosphere forms a nanosized phase of the NiO-type structure with the lattice parameter a = 4.186±0.005 Å. At 600 °C the lattice parameter of this phase decreases to the tabulated value (a = 4.177±0.005 Å). The phase of nickel chromite of the cubic spinel structure with the lattice parameter a = 8.320±0.005 Å is also observed. Hydrogen activation of the catalyst preheated at 300 °C in an inert gas leads to the formation of Ni⁰ crystallites with a size of ～5.5 nm and a specific surface area of ～7.0 m² g^?1. This catalyst exhibits high activity and selectivity in benzene hydrogenation and preferential CO hydrogenation in the presence of CO₂. The catalysts with the ratio Ni²⁺/Cr³⁺ = 1/(2?3) containing nickel and chromium hydroxocarbonates as precursors are less active in the hydrogenation of benzene to cyclohexane.     

The effect of UV irradiation on air/water interfacial activity of Tween 20–coumarin conjugates

In order to obtain photo-sensitive surfactants, coumarin derivatives were covalently attached, through either ester bond or ether bond, to hydroxyl groups located at the ends of PEO segments of Tween 20. The molar ratios of Tween 20 to coumarin residues in both Tween 20–coumarin conjugate having ester bond (TCES) and ether bond (TCET) were about 1:1 despite the excess coumarin in the reaction mixture. The photo-dimerization degree was in the order of TCET?>?TCES?>?a free coumarin derivative. And the air/water interfacial activity was in the order of TCET?>?Tween 20?>?TCES. The interfacial activities of TCES and TCET increased with the UV irradiation time. This is possibly because the coumarin residues of TCES and TCET are photo-dimerized to produce Gemini surfactant-like dimeric surfactants. The photo-induced change in the interfacial activity of TCES was slightly greater than that of TCET, probably due to the difference in the length, the polarity, and the flexibility of the linker between two monomeric conjugates of Gemini-like dimeric surfactants.     

Synthesis of cyclodextrin–pyrrole conjugates possessing tuneable carbon linkers

Cyclodextrins are naturally occurring cyclic oligosaccharides consisting of glucose units. The main feature of cyclodextrins is the ability to accommodate various lipophilic compounds in their interior, which determines them to be popular helpers to the mankind. However, there is still a demand for new derivatives for advanced applications. Herein, we report the synthesis of β-cyclodextrin–pyrrole conjugates. Their preparation is based on an amide bond formation or copper(I)-catalysed azide-alkyne cycloaddition between β-cyclodextrin and pyrrole derivatives. The main advantage of the synthetic approach lies in the possibility to attach the substituent in β-position, because polypyrroles possessing a substituent in this position are generally more conductive than the N-substituted ones. Moreover, the presented synthetic route is general and allows tuning the properties (various types of connections and lengths) of a linker. The presented cyclodextrin–pyrrole derivatives thus open the door for new applications in the field of sensors or tissue engineering.     

Study on the structure–activity of dihydromyricetin and its new production

Myricetin (MY) was firstly synthesized from dihydromyricetin (DMY), and its antioxidant activity was analyzed. FTIR, NMR, and TG measurements confirmed that the DMY turned to MY. Scanning electron microscope observation showed that the 2,3-single bond offered great flexibility on the stage of crystallization to form imperfect crystalline regions; hence, DMY tends to form larger columnar crystals than MY. It has been found that the antioxidative efficiency of DMY was superior to MY, based on the measurement of radical scavenging activity by DPPH and the oxidation induction time of PP-antioxidant samples. The 2,3-double bond in MY structure, known as one of the characteristic determinants, was not an important requirement for antioxidant capacity or even negative correlation observed. Such a deduction was further supported by UV–Vis absorption spectra change when the pH was raised to pH 9. It was concluded that the ortho-trihydroxyl group in the B ring provides an antioxidant defense, and the 2,3-single band of C ring provides the structural stability.     

The effect of framework functionality on the catalytic activation of supported Pd nanoparticles in the Mizoroki–Heck coupling reaction

Palladium nanoparticles (Pd-NPs) were supported on functional and nonfunctional Co-coordination polymers (Pd/CoBDCNH₂ and Pd/CoBDC). Advanced analytical techniques revealed that Pd-NPs are supported on the external surface of the polymer framework and the functionalized framework possesses effective influence to prevent Pd-NP aggregation. Supported Pd-NPs were effectively applied as heterogeneous recyclable catalysts in the Mizoroki–Heck C–C cross coupling reactions of iodobenzene and either aromatic or aliphatic terminal alkenes. Catalytic results exhibited that highly dispersed Pd-NPs with low loading (1%) on the functional polymer (Pd/CoBDCNH₂) are more effective than aggregated Pd-NPs with high loading (9%) on the nonfunctional polymer (Pd/CoBDC). Both catalysts can simultaneously provide high activity and selectivity to E-coupled products, high efficiency in low amounts, easy separation of heterogeneous catalyst and appropriate performance in the recycling reaction without addition of a reducing agent.     

Influence of the synthesis conditions on the structure and composition of the titanium–magnesium nanocatalyst and on its activity in isoprene polymerization

Synthesis of titanium–magnesium nanocatalyst in a high-pressure reactor under the conditions modeling the industrial conditions was studied. A laboratory scale plant including the units for the product synthesis, washing, and filtration was developed. The effect of elevated pressure (10–90 atm) on the process course, on the properties of the catalyst formed, and on the isoprene polymerization was studied for the first time. An increase in pressure leads to an increase in titanium incorporation into the catalyst from 1.52 to 2–2.3 wt % and simultaneously to an increase in the trivalent titanium content to 81 wt %. The titanium–magnesium nanocatalyst with such properties exhibits enhanced performance in isoprene polymerization without deteriorating the polymer microstructure. The development of the catalyst synthesis procedure on the laboratory scale plant will allow pilot-scale modeling of this process in the future.     

New chiral phosphine–phosphites: a convenient synthesis based on the demethylation of o-anisyl phosphines and application in highly enantioselective catalytic hydrogenations

An easy demethylation of o-anisyl phosphines provides a convenient access to a series of new chiral phosphine–phosphites. The screening of these derivatives as ligands in rhodium-catalyzed asymmetric hydrogenation of dimethyl itaconate has shown a profound influence of ligand structure on the enantioselectivity of the process.     

Effect of cobalt weight content on the structure and catalytic properties of Co/CNT catalysts in the fischer–tropsch synthesis

Cobalt-based Fischer–Tropsch synthesis (FTS) catalysts containing 1 to 40 wt % cobalt supported on multi-walled carbon nanotubes (CNTs) have been investigated. The CNTs have been characterized by low-temperature nitrogen adsorption, scanning electron microscopy, and X-ray photoelectron spectroscopy. All catalysts have been prepared by impregnating, with an ethanolic solution of cobalt nitrate, the CNTs preoxidized with concentrated nitric acid and have been tested in the FTS at 220°C and atmospheric pressure. Correlations have been established between the cobalt weight content of the catalyst and the Co particle size determined by transmission electron microscopy and X-ray diffraction. The Co content and particle size have an effect on the activity and selectivity of the catalyst and on the target fraction (C₅₊) yield in the FTS. The highest CO conversion is observed for the catalyst containing 20 wt % Co; the highest selectivity and activity, for the catalyst containing 5 wt % Co; the highest C₅₊ yield, for the catalyst containing 10 wt % Co.     

Proline–cyclodextrin conjugates: synthesis and evaluation as catalysts for aldol reaction in water

The synthesis of six conjugates of l-proline and β-cyclodextrin and their evaluation as catalysts of aldol reaction in water are described. The results indicated that the nature of the linker between proline and β-cyclodextrin is important for catalytic activity; the one with the most flexible linker gave the best results. Inhibition experiments showed that the cavity of β-cyclodextrin plays a role in the catalysis. Permethylation of the cyclodextrin hydroxyl groups led to higher conversion rates.     

Influence of photodynamic effect on biological activity of PBR–PP complexes

The aim of this study was to examine the influence of photodynamic effect on biological activity of PBR–PP complexes. These measurements were performed in pH dependent environment. Constant concentration of solubilized receptor was titrated with increasing concentration of porphyrins (PPIX, Hp, PP(Arg)₂, Hp(Arg)₂, PP(Gly)₂, PP(Ala)₂, PP(Ser)₂, PP(Phe)₂) and binding constants were calculated. PBP–PP mixtures were illuminated with 3 J, 5 J or 10 J of blue light and changes in protein fluorescence was recorded. Experimental data were fitted to weak and strong binding models. As a result for all derivatives weak binding model was the best fitted. The strongest binding showed PPIX in pH 7.4 and with pH drop binding constants showed greater values for all examined derivatives. Out of amino acid derivatives the strongest binding was noticed for PP(Gly)₂ and PP(Phe)₂ and for the last one pH influence was not observed.     

Synthesis of immobilized nanopalladium on polymer-supported Schiff base, and study of its catalytic activity in the Suzuki–Miyaura reaction

Abstract  

Nanopalladium particles immobilized on a matrix of poly(vinyl chloride) (PVC)-supported Schiff base were prepared from PVC with sequential attachment of ethylenediamine and salicylaldehyde, followed by treatment with an ethanolic solution of palladium chloride. The as-prepared catalyst was found to be air and moisture-stable and to have significant catalytic activity in Suzuki–Miyaura reactions under mild operating conditions. Various phenyl halides were coupled with phenylboronic acid in aqueous ethanol, under air, to afford the corresponding cross-coupled products in good yields. Furthermore, the catalyst can be easily recovered by simple filtration and reused for up to five cycles without losing its activity.     

Further study on the synthesis of F-containing porphyrins and their catalytic activity on oxidation of cyclohexene

Reaction of tetrakis(p-allyloxyphenyl)porphyrin and perfluoroalkanesulfonyl bromides givestetrakis(p-polyfluoroalkoxylphenyl)substituted porphyrins.The yields are over 90%.The synthesis ofthe metal ion complexes of these F-containing porphyrins is also reported.Preliminary results on thestudy of the catalytic activity of the manganese(Ⅲ)complexes of various fluorinated porphyrins onoxidation of cyclohexene indicate that the introduction of R_F group into porphyrin contributes to thestability of the catalysts.     

Reactivity of 2-methylene-1,3-dicarbonyl compounds: catalytic enantioselective Diels–Alder reaction

The catalytic enantioselective Diels–Alder reaction of 1,1-dicarbonylethenes 3 with cyclopentadiene in the presence of Ti-TADDOLs, Mg–Ph-box and Mg–Ph-mox complexes was investigated. Although both exo- and enantioselectivity with Ti-TADDOL catalysts were poor, they were much improved using Mg–Ph-box or Mg–Ph-mox complexes as chiral catalysts. Thus, 3 was an efficient two-point binding dienophile and the non-C₂-symmetric Ph-mox 8 could be used as a chiral ligand.     

Homologous series of novel adamantane–colchicine conjugates: synthesis and cytotoxic effect on human cancer cells

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Effect of the functionalizing of carbon nanotubes on the electrodeposited catalysts’ structure and catalytic properties

The structure and hydrophilic-hydrophobic properties of functionalized single-wall carbon nanotubes are studied by the standard porosimetry method. It is shown that the functionalized nanotubes have highly hydrophilic surface; at that the summary surface area measured “by octane” decreased, as a result of the functionalizing, due to the blocking of the nanotubes’ inner channels by the functional groups located at the nanotubes’ ends. The nanotubes’ capacitive properties are studied; their charging-discharging curves appeared being highly reversible, unlike those of other carbonaceous materials. Catalytic properties of the functionalized nanotubes are studied, with particular tendency toward their using as a carrier of platinum catalysts for the methanol oxidation and oxygen electroreduction reactions. When minor amounts (5–10 μg cm⁻²) of platinum or platinum-ruthenium alloy are deposited onto the nanotubes’ hydrophilic surface, uniform layer of the catalyst is formed, with specific surface area up to 150–300 m² g⁻¹; high current of the methanol oxidation or oxygen electroreduction is observed at these catalysts. When the catalyst deposit mass increased, its specific surface area decreased, as well as the specific current of the reactions occurring thereon. When the current is related to the electrochemically active unit surface, the catalytic activity is nearly the same both for different catalyst mass deposited onto the nanotubes and the same catalyst mass at different carbonaceous carriers.     

Structural characterization of nitro-substituted phenoxyiminato nickel complexes; inter-molecular π-π interactions in the solid states and effect of the electron drawing groups on catalytic activity

Three phenoxyiminato nickel complexes [(L)Ni(PPh₃)(Ph)] have been prepared by the introduction of the electron drawing nitro substitutes on ortho or para-position of phenoxy and characterized by X-ray crystallography. Experimental and theory calculation suggested that the ortho and para nitro groups may be equally responsible for the small net charge on the central metal atoms because the interplanar angles between o-nitro planes and aromatic rings (28.7-37.3°) are much higher than those between p-nitro planes and aromatic rings (8.2-13.8°). In the solid states of these nickel complexes there exist the short inter-molecular π-π stacking interactions with the distances of 3.5828 Å (ortho-nitro), 3.5844 Å (para-nitro), and 3.0929 Å (ortho- and para-nitro) between two neighboring nitro-phenyl moieties.