Aqueous-Phase Synthesis of α-Hydroxyphosphonates Catalyzed by β-Cyclodextrin

α-Hydroxyphosphonates were synthesized from aromatic/heteroaromatic aldehydes with triethyl phosphite in the presence of β-cyclodextrin in an aqueous medium. The β-cyclodextrin can be recovered and reused without loss of catalytic activity.     

A Study on the Inclusion of α-Cyclodextrin with Mono-and 1,4-Disubstituted Benzenes by Neural Networks

Itiswellknownthatthecycledextrin(CD)isonekind0ftheidealenzyrnemedels.ThestudiesofcycboextrininmoIecularrmpition,mimeticenzyTneandseParationscienceandtechnolOgyhavebenexPeriencedanenormousinterestintherecentyears.l-5Inspite0fafewdrivingforceshavebenprohof0rtheinclusionofCDwithavarietyofgUestco~nds,therestillrernainsnoclearagreeInent0nthemechanisrnf0rCDinclusioncomPlexation.Daviesetal"'estabIishedamedelfortheinclusionofQ-CDwithl,4-disubstitutedbenzenesbased0naregress1onanalysis.According…     

Synthesis of α-Aminophospiionic Esters by Solid-Liquid Phase Transfer Catalysis

Abstract

(1-aminoalkyl)phosphonic acids are important amino acids with interesting biological properties (1). They are available by various procedures (2). However, a potentially efficient and direct route not very well documented is the use of schiff bases derived from diethyl-aminomethylphosphonate. These substrates have been used to prepare a-alkylated phosphonic aminoacids using strong bases under anhydrous conditions (3). We report here a simple method using solid-liquid phase transfer catalysis (PTC) as wel1 as solid-liquid PTC without solvent:     

Enantioselective Synthesis of α-Alkoxy-Phosphonates by Chiral Phase Transfer Catalysis

Abstract

Enantioselective PTC phosphorylation of aldehydes performed in a two phase (aq. NaOH/toluene) system mediated by chiral crown ether incorporating one or two sugar units. To avoid the rearrangement of hydroxy phosphonate 3 to nonchiral mixed phosphate ester 4 the hydroxy phosphonate was trapped by alkylation to give 5.     

Amine-Borane Dehydrogenation and Transfer Hydrogenation Catalyzed by α-Diimine Cobaltates

Anionic α-diimine cobalt complexes, such as [K(thf)_1.5{(^DippBIAN)Co(η⁴-cod)}] ( 1 ; Dipp=2,6-diisopropylphenyl, cod=1,5-cyclooctadiene), catalyze the dehydrogenation of several amine-boranes. Based on the excellent catalytic properties, an especially effective transfer hydrogenation protocol for challenging olefins, imines, and N-heteroarenes was developed. NH₃BH₃ was used as a dihydrogen surrogate, which transferred up to two equivalents of H₂ per NH₃BH₃. Detailed spectroscopic and mechanistic studies are presented, which document the rate determination by acidic protons in the amine-borane.     

Inclusion Behavior of α-Cyclodextrin with 2-Methylnaphthalene in Aqueous Solutions

By means of absorption and fluorescence spectroscopy, 2-methylnaphthalene (2MN) was found to be incorporated into the cavity of -cyclodextrin (-CD) to form a 1 : 1 inclusion complex. The 1 : 1 inclusion complex further associated with another -CD molecule, resulting in the formation of a 2 : 1 -CD-2MN inclusion complex. The equilibrium constants for the formation of the 1 : 1 and 2 : 1 inclusion complexes were estimated to be 44.6 and 376 mol-1 dm3, respectively, on the basis of a simulation of the observed 2MN fluorescence intensities. The induced circular dichroism spectra suggested that 2MN, buried within the -CD inclusion complexes, resided in a different orientation relative to the CD symmetry axis, as compared to 2MN within a -CD inclusion complex.     

Association Constant Prediction for the Inclusion of α-Cyclodextrin with Benzene Derivatives by an Artificial Neural Network

The association constants (K_a) for the inclusion complexation of -cyclodextrin (-CD) with 72 mono- and 1,4-disubstituted benzenes were predicted successfully by an artificial neural network (ANN) with molar refraction (R_m) and hydrophobic constant () as input parameters, which reflect the volume and hydrophobicity of the substituents respectively. The predictions strongly suggested that the inclusion complexation of -CD with guest molecules was mainly driven by van der Waals forces and hydrophobic interactions     

Interactions of Nabumetone with γ-Cyclodextrin Studied by Fluorescence Measurements

The inclusion of the anti-inflammatory drug, Nabumetone (NAB), in γ-cyclodextrin (γ-CD) was studied by fluorescence measurements. The emission fluorescence spectrum, of NAB reveals a maximum whose intensity increases with the different γ-CD’s growing concentrations. The stoichiometery (1:1) and binding constants of the complexes at 15, 25, 35, and 45 °C were extracted from the analysis of the emission spectra of NAB. The thermodynamic parameters ΔH ° and ΔS ° for the formation of the complex were calculated from the temperature dependence of the binding constants and compared with previous results for similar complexes of NAB with α- and β-CDs. The location of NAB in the complex was determined using the fluorescence quenching method. Our results indicate that NAB is completely penetrated into the cavity of γ-CD.This revised version was published online in July 2005 with a corrected issue number.     

Iodination of α-Cyclodextrin with N-Iodosuccinimide and Triphenylphosphine in N,N-Dimethylformamide

Abstract

α-Cyclodextrin mainly underwent monoiodo substitution on treatment with N-iodosuccinimide and triphenylphosphine in DMF, giving 6-monodeoxy-6-monoiodo-α-cyclodextrin. A small amount of 6,6′-dideoxy-6,6′-diiodo-α-cyclodextrin was also obtained as a by-product. The structures of these compounds were elucidated from their elemental analyses and ¹³C NMR spectra.     

Thermodynamics of α-Cyclodextrin Complexation with Bases of Nucleic Acids and Their Derivatives

The interactions of -cyclodextrin with adenine, thymine, uracil, cytosine, and caffeine in water at 298.15 K have been studied by the calorimetric method. -Cyclodextrin is found to interact selectively with nucleic bases and their derivatives to form complexes with uracil, cytosine, and caffeine only. The influence of the structure and solvation of the reactants on the thermodynamic characteristics of their complexation in a solution has been examined.     

Investigation of Inclusion Complexes Between α-Cyclodextrin and Ferrocene by ESI-MSn and Cyclic Voltammetry

The inclusion complexes of α-cyclodextrin(α-CD) and FcCO2(CH2)18 (FcSH) and their self-assembled monolayers(SAMs) on gold surface were investigated by electrospray tandem ionization mass spectrometry(ESI-MSn) and cyclic voltammetry, respectively. The interfacial electrochemical response of the SAMs is related to the way in which the inclusion complexes formed.     

Selective Formation of Methyl α-Methylsulfanyl Dimethylphosphonothioacetate and Thiopropanoate by Phase Transfer Catalysis

The sulfanylation of methyl dimethylphosphonothioacetate was investigated by a phase transfer catalysis procedure which was shown to be superior to the noncatalytic method. The possibility of electrophilic substitution of the α-sulfanylated phosphonothioacetate to give a quaternary α-carbon atom is shown by the reaction with methyl iodide.

     

Investigation of Inclusion Complexes Between α-Cyclodextrin and Ferrocene by ESI-MSn and Cyclic Voltammetry

The inclusion complexes of α-cyclodextrin (α-CD) and FcCO2 (CH2)18(FcSH) and their self-as-sembled monolayers (SAMs) on gold surface were investigated by electrospray tandem ionization mass spectrometry (ESI-MS″) and cyclic voltammetry, respectively. The interfacial electrochemical response of the SAMs is related to the way in which the inclusion complexes formed.     

Effect of Temperature-responsive Solution Behavior of PNIPAM-bPPEOMA-b-PNIPAM on Its Inclusion Complexation with α-Cyclodextrin

The effect of temperature-responsive solution behavior of PNIPAM-b-PPEOMA-b-PNIPAM on its inclusion complexation with α-cyclodextrin was studied. The triblock polymer was prepared by reversible addition-fragmentation chain transfer(RAFT) polymerization and formed inclusion complexes(ICs) after selective threading of the PEO segment of the triblock polymer through the cavities of α-CD units. For comparison, PPEOMA homopolymer was prepared and the inclusion complexation with α-CD was also studied. The ICs were prepared with α-CD when the polymer was in different conformations by changing the temperature, and the formed ICs were characterized by XRD, 1H-NMR, TGA and DSC. The solutions of the ICs show temperature-responsive clear/turbid transition or fluidic emulsion/gel transition depending on the concentration of the α-CD added, and the stoichiometry determined by 1H-NMR and TGA indicates that the stoichiometry of EO to α-CD of the resulted ICs increases with increasing of temperature.     

Derivatives Of α-Cyclodextrin and the Synthesis of 6-O-α-D-Glucopyranosyl-α-Cyclodextrin

Abstract

Regioselective silylation of α-cyclodextrin with tert-butyl-dimethylsilyl chloride in N, N-dimethylformamide in the presence of imidazole gave, in 75% yield, the hexakis(6-O-tert-butyldimethylsilyl) derivative 2, which was transformed into the hexakis(2,3-di-O-methyl, 6-O-methyl, 2,3-di-O-propyl, and 2,3-di-O-acetyl) derivatives. On methanesulfonylation and p-toluenesulfonylation, the hexakis(2,3-di-O-acetyl) derivative 16 afforded the hexakis(2,3-di-O-acetyl-6-O-methylsulfonyl 17 and 2,3-di-O-acetyl-6-O-p -tolylsulfonyl 18) derivatives, respectively. Nucleophilic displacement of 17 and 18 with iodide, bromide, chloride, and azide ions afforded the hexakis(6-deoxy-6-iodo 19, 6-bromo-6-deoxy, 6-chloro-6-deoxy, and 6-azido-6-deoxy) derivatives, respectively, of α-cyclodextrin dodeca-acetate. The hexakis (2, 3-di-O-acetyl-6-deoxy) derivative was prepared from 19. Selective glucosylation of 16 with 2,3,4,6-tetra-O-benzyl-α-D-glucopyranosyl bromide under catalysis by halide ion, followed by removal of protecting groups, furnished 6-O-α-D-glucopyranosyl-α-cyclodextrin.     

A Study on the Driving Force for Binding of Benzene Derivatives by α-and β-Cyclodextrin

WehavedemonstTatedthattheassociationconstantsfortheinclusioncomplexationofa-and6-cyclodextrin(a-and9-CD)withsubstitutedbenzene(PhX)arecorrelatedwithpropertiessuchasmolarrefraction(R.),hydrophobicity(n.)andeIectroniceffect(a.)ofsubstitUentsintheguestcompounds.Uponapplicationofanariificialneuralnetwork(ANN),theassociationconstants(Ka)fortheinclusionofa-CDand6-CDwithsubstitutedbenzenewerepredictedfromR.,rrxandG.withsatisfactoryresultSl'2.Furthermore,theeffectsofsubstituentsinbenzenederivat…     

Hydrogen Production System by Light-Induced α-FeOOH Coupled with Photoreduction

Solar-driven catalysts on semiconductors to produce hydrogen are considered as a means to solve environmental issues. In this study, H₂ production coupling with oxygen consumption by noble metal-free α-FeOOH was demonstrated even though the conduction band edge was lower than the reduction potential of H⁺ to H₂. For activation of α-FeOOH, an electron donor, Hg-Xe irradiation, and low pH (ca. 5) were indispensable factors. The H₂ production from H₂O was confirmed by GC-MS using isotope-labeled water (D₂O) and deuterated methanol. The α-FeOOH synthesized by coprecipitation method showed 25 times more active than TiO₂. The photocatalytic activity was stable for over 400 h. Our study suggests that α-FeOOH known as rust can produce H₂ by light induction.     

Synthesis and Chromatographic Properties of New β-Cyclodextrin Derivatives with α-Schiff Base Groups for HPLC

β-Cyclodextrin 1 was directly oxidized to the corresponding monoaldehyde 2 on their primary faces by cyclized 2-iodoxybenzoic acid(IBX) in DMSO, followed by the synthesis of β-cyclodextrin derivatives bearing Schiff-base group 3. A new chiral stationary phase(BCDS 6) was then prepared by immobilization of β-cyclodextrin derivative with α-Schiff base group onto the surface of sillica gel. A series of compounds with amino groups were readily separated using this CSE Methanol and acetonitrile were tested as the mobile phase while the influence of temperature and the addition of aqueous triethylammonium acetate buffer to the mobile phase was also innvestigated. Ferrocene ligand with Schiff-based groups have been separated satisfactorilly on BCDS column.