Effects of Modified β-Cyclodextrins on the Hydrolysis Reaction of p-Nitrophenyl α-Methoxyphenylacetate

Effects of -cyclodextrin (-CD) 1and its derivatives 2–7 on the deacylationreaction of p-nitrophenyl (R or S)--methoxyphenylacetatewere studied. The-CD derivatives used were6--D-glucosyl--CD 2, sulfated-CD (7–11 sulfate groups/CD ring) 3,dimethylated -CD 4, carboxymethylated-CD (3.5 carboxymethyl groups/CD ring) 5,2-tri(2-hydroxypropyl)--CD 6, and-CD appended on poly(allylamine) 7. Therate constant (k ^CD) of thesubstrate/-CD complexes and the formationconstants (K) of the complexes were determinedfrom the dependence of the pseudo-first order rateconstants of the deacylation reaction on theconcentration of -CDs. The order ofk ^CD for the R-enantiomer at pH8.0 is 45H₂O3 6 1 2 7, whilethat for the S-enantiomer is 4 5 6H₂O 1 2 3 7: H₂O denotes the rate in theabsence of -CDs. The order of K values is3 7 6 2 1 4 5. This work indicates that, though thesecondary hydroxyl groups of -CD play criticalroles in the deacylation reactions of the esterscomplexed with -CDs, the reactivity of theester/-CD complexes depends highly on thenature of the substituents at the secondary face of-CD. It also suggests that the substratesinserted from the secondary side as well as theprimary side of -CD of poly(allylamine)-bound-CD undergo the reaction by attack of aminogroups on the polymer chain.     

Enantioselective Fluorination Reaction of β-Ketoester–Catalyzed Chiral Primary Amine–Based Multifunctional Catalyst Systems

The fluorination reaction is an important organic transformation for asymmetric synthesis. In this article, we reported the determination of chiral primary amine–based multicatalyst systems for enantioselective fluorination of β-ketoester. Studies on the enantioselective organocatalytic fluorination promoted by cinchona alkaloid–derived chiral primary amines in the absence of various co catalysts revealed that the combined metal salts and organocatalysts resulted in poor conversion and enantioselectivities, whereas the combinational use of L-leucine and QN-NH₂ as dual primary amine catalysts led to the determination of a novel dual organocatalyst with promising catalytic activity. On the basis of these results, we revealed that the steric environment of the chiral enamine intermediate formed by the condensation of β-ketoester with the chiral primary amine is most responsible for the observed enantioselectivity.

[Supplementary materials are available for this article. Go to the publisher's online edition of Synthetic Communications® for the following free supplemental resource(s): Full experimental and spectral details.]     

Characterization of Super‐Absorbent Material Based on Carboxymethylcellulose Sodium Salt Prepared by Electron Beam Irradiation

Crosslinked CMC‐N/PAAm hydrogel were prepared using electron beam irradiation. The factors affecting the degree of crosslinking and swelling behavior of the prepared copolymer were determined. As the irradiation dose and/or PAAm concentration increase, the gel content increases. Preparation of super‐porous hydrogel was attained by the addition of ammonium carbonate as a gas‐blowing agent during the irradiation process. The surface morphology and pore structure of such a prepared hydrogel were examined using scanning electron microscopy. The ability of the prepared hydrogel to absorb and retain large amount of water and as simulating urine was measured. The results suggested the possible use of CMC‐Na/PAAm hydrogels in the personal care product industry.     

Modified Coumarins. 12. Synthesis of 3,4-Cycloannelated Coumarin β-D-Glucopyranosides

O--D-Glucopyranosides were synthesized using 3,4-cycloannelated hydroxycoumarins as aglycons. Phenolic hydroxyls were O-glycosylated via condensation of coumarin potassium salts with acetobromoglucose in homogeneous medium and in a liquid-liquid system using a phase-transfer catalyst.     

Influence of α-Tocopherol Load and Annealing Treatment on the Wear Resistance of Biomedical UHMWPE Irradiated with Electron Beam

A biomedical UHMWPE electron beam irradiated in air with doses raging between 25 and 100 KGy was doped with different amounts of α-tocopherol (0.1–0.7 wt.%) to prevent oxidative degradation. The polymer was annealed just after the irradiation at 110° for 24 h. Physical and mechanical tests were performed on the UHMWPE before and after the irradiation and on neat or doped material. Results showed that heat treatment after irradiation improves cross-links in the UHMWPE and α-tocopherol has good antioxidant action. The UHMWPE blended with 0.7% of antioxidant became harder and more wear resistant (+52%) after the irradiation with 100 KGy.     

Theoretical Study of the Inclusion Processes of Ibuprofen Enantiomers with Native and Modified β-CDs

PM3 calculations in vacuum were performedon the inclusion complexation of-cyclodextrin (-CD),heptakis-(2-O-methyl)--cyclodextrin(2-Me--CD) and heptakis-(6-O-methyl)--cyclodextrin(6-Me--CD) withibuprofen (IB) enantiomers. Inclusion processpathways are described and the most probablestructure of the 1:1 complex are sought througha potential energy scan. The energy differencesbetween the inclusion complexes and the hosts(native and modified CDs) by calculation show thatmodified CDs have much more interaction sites withIB and enhance van der Waals interaction andhydrophobic interaction between them, form morestable complexes than native CD does.Stabilization energies of S-IB complexes arehigher than that of R-IB complexes both for nativeand modified CDs.     

Electron momentum density and band structure calculations of α- and β-GeTe

We have measured isotropic experimental Compton profile of α-GeTe by employing high energy (662 keV) γ-radiation from a ¹³⁷Cs isotope. To compare our experiment, we have also computed energy bands, density of states, electron momentum densities and Compton profiles of α- and β-phases of GeTe using the linear combination of atomic orbitals method. The electron momentum density is found to play a major role in understanding the topology of bands in the vicinity of the Fermi level. It is seen that the density functional theory (DFT) with generalised gradient approximation is relatively in better agreement with the experiment than the local density approximation and hybrid Hartree–Fock/DFT.     

Complexation of the Non-steroidal Anti-inflammatory Drug Loxoprofen with Modified and Unmodified β-Cyclodextrins

The inclusion complex of the anti-inflammatory drug, loxoprofen, with -cyclodextrin-(CD), sulfated -CD, and glycerol ether -CD was studied by UV-VIS absorption and ¹H-NMR spectroscopy in solution. The inclusion complex of loxoprofen with -CDs was prepared by freeze-drying, and then characterized in the solid state by thermal analysis, X-ray diffraction, FT-IR and FT-Raman spectroscopy, and scanning electron microscopy (SEM). Furthermore, a physical mixture of loxoprofen/-CD (1/1, mol-%) in the solid state was also characterized. The solubility of the loxoprofen increased on addition of -CDs. The solubility enhancement of the loxoprofen with -CDs is in the following order: glycerol ether -CD > sulfated -CD > -CD.     

Synthesis of Modified Methylaluminoxane

Methylaluminoxane (MAO) is one of the most important cocatalysts of metallocene catalysts. The yield and activity of MAO is low when using Al2(SO4)3 nH2O and other inorganic hydrates to synthesize methylaluminoxane. The repeatability of this reaction is not good. The product cost is very high because one of the raw materials (Trimethylaluminium, TMA) to prepare MAO is very expensive. In addition, on standing, MAO toluene solution tends to gel. Gelled MAO can not be used to prepare su…     

Impact of Electron–Electron Collisions on the Spatial Electron Relaxation in Non-Isothermal Plasmas

The impact of electron–electron collisions on the spatial relaxation of electrons in the column-anode plasma of a glow discharge, acted upon by a space-independent electric field and initiated by a constant influx at the cathode side of the plasma, is investigated in inert gas plasmas. The investigations are based on a new method for numerically solving the one-dimensional inhomogeneous Boltzmann equation of the electrons including electron–electron interaction in weakly ionized, collision-dominated plasmas. A detailed analysis of the spatial behaviour of the velocity distribution function and relevant macroscopic properties of the electrons is given for various degrees of ionization and electric field strengths. A significant impact of the electron–electron collisions on the relaxation structure and the resultant relaxation length already at relatively low ionization degrees has been found for low to medium electric fields.     

Enantioselective Aldol Reaction of α-Ketoester and Cyclopentaone Catalyzed by L-Proline

A concise and enantioselective synthesis of (S)‐ethyl 2‐cyclopentyl‐2‐hydroxy‐2‐arylacetate, a key intermediate for the muscarinic receptor, is reported. The tertiary stereogenic center was constructed with good stereoselectivity through the L‐proline‐catalyzed direct asymmetric aldol reaction of ethyl arylglyoxylate and cyclopentanone. The carbonyl of the condensation product was reduced using a modified Clemmensen reaction which provided an easier workup and was more environmentally acceptable. The enantioselectivity of the aldol reactions was between 58.3%–93.2%, which means that the stereoselective is efficient in controlling configuration of reaction product.     

Complexation of Monosulfonated Triphenylphosphine with Chemically Modified β-Cyclodextrins: Effect of Substituents on the Stability of Inclusion Complexes

Interactions between the meta-substituted monosulfonated triphenylphosphine and chemically modified β-cyclodextrins were investigated in aqueous solution by NMR and UV–vis spectroscopy. Titration and continuous variation plots obtained from ³¹P NMR data indicate that the monosulfonated triphenylphosphine forms 1:1 inclusion complexes with the 2-hydroxypropylated β-cyclodextrin, the methylated β-cyclodextrin and the (2-hydroxy-3-trimethylammoniopropyl)-β-cyclodextrin chloride. These inclusion complexes are more stable that those formed with native β-cyclodextrin, confirming that poisoning of the chemically modified β-cyclodextrins by the hydrosoluble phosphine occurs when modified cyclodextrins are used as mass transfer promoters in aqueous-phase organometallic catalysis.This revised version was published online in July 2005 with a corrected issue number.     

Preparation of β-Cyclodextrin Modified FusedSilica Capillary and Its Application inCapillary Electrophoresis Enantiom eric Separation

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Performance Evaluation on a Modified β-Cyclodextrin Crosslinking Acid System

Russian Journal of Applied Chemistry - Maleic anhydride (MAH) and β-cyclodextrin (β-CD) were chosen to synthetize vinyl β-cyclodextrins monomer (MAH-β-CD) by alcoholysis...     

Electron magnetic resonance and density functional theory study of room temperature X-irradiated β-D-fructose single crystals

Stable free radical formation in fructose single crystals X-irradiated at room temperature was investigated using Q-band electron paramagnetic resonance (EPR), electron nuclear double resonance (ENDOR), and ENDOR induced EPR (EIE) techniques. ENDOR angular variations in the three main crystallographic planes allowed an unambiguous determination of 12 proton HFC tensors. From the EIE studies, these hyperfine interactions were assigned to six different radical species, labeled F1-F6. Two of the radicals (F1 and F2) were studied previously by Vanhaelewyn et al. [Vanhaelewyn, G. C. A. M.; Pauwels, E.; Callens, F. J.; Waroquier, M.; Sagstuen, E.; Matthys, P. J. Phys. Chem. A 2006, 110, 2147.] and Tarpan et al. [Tarpan, M. A.; Vrielinck, H.; De Cooman, H.; Callens, F. J. J. Phys. Chem. A 2009, 113, 7994.]. The other four radicals are reported here for the first time and periodic density functional theory (DFT) calculations were used to aid their structural identification. For the radical F3 a C3 carbon centered radical with a carbonyl group at the C4 position is proposed. The close similarity in HFC tensors suggests that F4 and F5 originate from the same type of radical stabilized in two slightly different conformations. For these radicals a C2 carbon centered radical model with a carbonyl group situated at the C3 position is proposed. A rather exotic C2 centered radical model is proposed for F6.     

Steric Considerations in Supramolecular Inclusion of Modified β-cyclodextrins with Triton X-100 and α-bromonaphthalene

Supramolecular inclusion of modified β-cyclodextrin (β-CD) with Triton X-100 (TX) and α-bromonaphthalene (BN) was studied by fluorescence and phosphorescence measurements. Major differences were observed in the magnitude of the apparent stability constants and quenching constants of the inclusion complexes. Methyl substitution on the rims of β-CD increased the binding of TX with β-CD but was unfavorable to the protection of the phenyl group of TX from fluorescence quenching and further accommodation of BN for steric considerations. According to the overall molecular size of β-CD, TX and BN, further inclusion of BN in the cavity of β-CD occupied by TX may force the flexible tert-octyl chain of TX to deform to a greater extent and close packing complexes were obtained. Phosphorescence of BN arising from intermolecular energy transfer between BN and the phenyl group of TX was observed when the phenyl group of TX was irradiated. In the case of heptakis(2,6-di-O-methyl)-β-CD, BN failed to penetrate into the cavity because of the steric hindrance of the methyl substituents at the rim of the β-CD cavity.     

Correlation between Thermodynamic Behavior and Structure in the Complexation of Modified β-Cyclodextrins and Bile Salts

Complex stability constants (K _S), standard molar enthalpy changes (ΔH ⁰) and entropy changes (ΔS ⁰) for the inclusion complexation of two cyclodextrin dimers, 6,6′-{2,2′-diselenobis[2-(benzoylamino)ethylamino]}-bridged bis(β-cyclodextrin) (1) and o-phenylenediseleno bridged bis(β-cyclodextrin)s (3), and their monomer analogs, 6-deoxy-6-{[2-(2,3-dihydro-3-oxo-1,2-benzisoselenazol-2-yl)ethyl]amino}-β-cyclodextrin (2) and mono[6-(phenylseleno)-6-deoxy]-β-cyclodextrin (4), with two bile salt guests, sodium cholate (CA) and sodium deoxycholate (DCA), were determined at 25°C in Tris buffer solutions (pH 7.4) at 298.15?K by means of isothermal titration microcalorimetry (ITC). The interactions and binding modes between the host cyclodextrins and the guest bile salts were further studied by ROESY spectroscopy. The thermodynamic parameters obtained, together with the ROESY spectra, were used to examine the correlations between thermodynamic behavior and binding modes of the host–guest complexation. The results indicate that the length, structure and conformation of the tethers linked to the cyclodextrins determine the binding modes and the binding abilities between hosts and guests to a great extent, leading to a reversion in binding ability when comparing the corresponding dimer and its monomer analog.     

Multiwalled Carbon Nanotubes β-Cyclodextrin Modified Electrode for Electrochemical Determination of Bisphenol S in Water Samples

Russian Journal of Electrochemistry - A voltammetric sensor for the determination of bisphenol S (BPS) in aqueous samples was fabricated by immobilization of β-cyclodextrin/multiwalled carbon...     

The Adsorption of NOx on Magnesium Aluminium Hydrotalcite

Magnesium aluminium hydrotalcite (Mg-Al-HT) with molar ratio of Mg-to-Al of 3 to 1 was prepared and characterized by X-ray diffraction (XRD) and infrared spectra (IR). The performances of Mg-Al-HT for the adsorption and desorption of NOx were studied. The results indicated that the adsorption capacity of the hydrotalcite for NOx was 1398.2mg/g, and it was higher than the acticarbon‘s. The adsorption capacities depended on adsorption time and temperature.Mg-Al-HT could be regenerated by thermal decomposition, and the adsorption efficiency had not changed markedly after three cycles.