“Binding” of water by ions

Summary We confirmed the inadequacy of the correction for, binding of water by ions for explaining the discrepancy between the electrostatic theory in [2] and experiment.     

Synthesis of β-aminovinylphosphonates by organocatalytic nucleophilic displacement of acetate with amines

The synthesis of diethyl β-aminovinylphosphonates 2 from acetoxy phosphonate 1 is described. The reaction entails an organocatalyzed substitution of the acetoxy group by primary or secondary amines. The use of a catalytic amount of DABCO is necessary if the amine is not nucleophilic enough, otherwise a strong nucleophilic amine can react without organocatalyst. The reaction led to a series of functionalized title compounds in good to excellent yields.     

Crystalline alignment of metal ions templated by β-chitin ester

The highly crystalline β-chitin from diatom Thalassiosira weissflogii was esterified via intercalation with succinic anhydride followed by simple heating, maintaining the original crystalline order. Due to the introduced free carboxyl groups, the chitin ester crystal showed ion exchange ability for metal cations in aq. solution. Heavy metal cations such as Pb²⁺ bound to the β-chitin succinate gave characteristic X-ray diffraction patterns, indicating regular alignment of metal ions. Such materials represent a new type of organometallic architecture, possibly leading to novel functionalities.     

Versatile synthesis of α, β-acetylenic ketones by oxidative nucleophilic addition of vanadium acetylides

Treatment of aldehydes with vanadium acetylides generated from equimolar amounts of vanadium trichloride and acetylenic Grignard or lithium compounds gave α,β-acetylenic ketones via oxidative nucleophilic addition.     

Enantioselective trapping of oxonium ylide intermediates by N-benzhydryl-α-imino ester:Synthesis of β-tetrasubstituted α-amino acids

A synergistic rhodium(Ⅱ)/phosphoric acid catalyzed three component reaction of 3-diazooxindoles,alcohols and N-benzhydryl-α-imino ester is developed for the efficient construction of chiral β-alkoxy C~β-tetrasubstituted α-amino acid derivatives in good yields and with excellent diastereoselectivities and high enantioselectivities.The synthetic application of the resulting products was illustrated by reducing with Pd/C under H_2 atmosphere followed reacting with CSCl_2 at room temperature to rapid afford 3-spirocyclic oxindole in a good yield with a chirality retainment.The three-component reaction is proposed to proceed through an electrophilic trapping of the oxonium ylides by N-benzhydryl-α-imino ester.     

Interfacial activity of metal β-diketonato complexes: in situ generation of amphiphiles by water coordination

Symmetric transition metal complexes of 2,4-pentanedione (acetyl acetone) are interfacially active: Spinning drop tensiometry reveals lowering of the interfacial tension at the water-organic interface, most pronounced for [Cr(acac)(3)], [Fe(acac)(3)], [Zr(acac)(4)], and [Hf(acac)(4)]. The interfacial activity is explained by the in situ generation of amphiphilic species. Based on tensiometry and (1)H and diffusion-ordered NMR spectroscopy (DOSY NMR), hydrogen bonding of the organically dissolved complexes with water, in some cases in combination with inner-sphere hydrolytic coordination, is identified as the primary origin of this amphiphilicity. The complexes are a rare example of symmetric molecules that turn amphiphilic only upon interfacial interaction with water.     

Enantioselective trapping of an α-chiral carbanion of acyclic nitrile by a carbon electrophile

An α-chiral nitrile carbanion generated by deprotonation of enantioenriched O-carbamoyl cyanohydrin was trapped in situ with ethyl cyanoformate to give the corresponding ester derivative in 92% yield and 90?:?10 er, providing the first example of trapping of an α-chiral acyclic nitrile carbanion that has been considered to be very configurationally labile.     

Removal of organic micro-pollutants from water by β-cyclodextrin triazine polymers

β-Cyclodextrin (CD) polymers were synthesized by nucleophilic substitutions between β-CD with cyanuric chloride. Insoluble polymers were obtained. Polymers were characterized by DSC, TGA, FTIR, SS-¹³CNMR. Polymers and activated carbon (AC-Darco) were used to remove model micro-pollutants of bisphenol-A (BPA), 2-naphthol, 2-cholor-biphenyl (PCBNO1), benzene and dibutyl phthalate from water. The results showed that β-CD-triazine polymers showed better performance to adsorb BPA compared with activated carbon; β-CD-triazine polymer showed similar performance to activated carbon on removing benzene from water; however, it showed worse performance for removing 2-naphthol, PCBNO1 and dibutylphthalate by comparison with activated carbon. β-CD-triazine polymers with varying ratio of β-CD to cyanuric chloride were synthesized and their performance on model micro-pollutants were evaluated. Removal efficiency of micro-pollutants from water for β-CD-triazine polymers correlated with their CD concentration except for removing benzene which showed similar performance.     

Theoretical investigations of β-trimethylsilyl-substituted iminium ions

Calculated reaction energies, NBO analyses, and natural charge distributions show that a trimethylsilyl group at the β carbon atom stabilizes the positive charge of an iminium cation more effectively than a tert-butyl group in the same position. Different from the classical β-silicon effect, where theoretical studies suggest that the positive charge is stabilized hyperconjugatively by interaction of the Si-C σ-bond with a formally empty 2p-orbital of suitable symmetry at the carbonium carbon, the stabilization in the case of iminium ions occurs by interaction of the Si-C σ-bond with the π^∗ orbital of the CN double bond. Stabilization of the silyl-substituted derivatives by hyperconjugation might be enhanced by interaction of the positive charge with a neighboring induced dipole.     

Modulation of animal and human hematopoiesis by β-glucans: a review

β-glucans are cell wall constituents of bacteria, yeast, fungi, and plants. They are not expressed in mammalian cells, but they are recognized by mammalian cells as pathogen-associated molecular patterns by pattern recognition receptors and thus act as biological response modifiers. This review summarizes data on the hematopoiesis-stimulating effects of β-glucans, as well as on their ability to enhance bone marrow recovery after an injury. β-glucans have been shown to support murine hematopoiesis suppressed by ionizing radiation or cytotoxic anti-cancer therapy. They also enhance stem cell homing and engraftment. Basically, two forms of β-glucan preparations have been investigated, namely particulate and soluble ones. β-glucans are generally well tolerated, the particulate forms showing a higher incidence of undesirable side effects. Taken together, the hematopoiesis-stimulating properties of β-glucans predetermine these biological response modifiers to ever increasing use in human medicinal practice.     

An intramolecular oxa-Michael addition on prebuilt β-lactam tethered α, β-unsaturated ester: A remarkable synthesis of a unique scaffold of 2,3-fused β-lactam-1,4-dioxepane

An expeditious base assisted highly diastereoselective intramolecular oxy-Michael addition reaction in the synthesis of enantiomerically pure 1,4-dioxepane fused β-lactam has been described. This present study has been portrayed a rapid intramolecular 7-exo-trig oxy-Michael reaction involving chemoselective nucleophilic addition of 2⁰ alcohol of the vic-diols to an α β-unsaturated ester. Furthermore, the developed methodology elaborates an extremely atom-economical approach in constructing the C–O bond in stereoselective fashion under mild reaction conditions.     

Synergistic extraction of metal ions involving mixed adduct formation by β-diketone-neutral donor mixtures

Synergistic solvent extraction of metal ions by β-diketone-neutral donor(S) solutions sometimes involves the formation of mixed adducts with the anions from the aqueous medium participating in adduct formation. A curve-fitting method for the study of such systems is described. The utility of the method was demonstrated with results on the extraction of Pu(IV) from a nitric acid medium by solutions of HTTA-TBP and HTTA-DBBP mixtures. The mixed adducts involved in the extraction were identified as Pu(NO₃)₃(TTA)·2S, Pu(NO₃)₂(TTA)₂·S and Pu(NO₃)(TTA)₃·S. Equilibrium constants for several equilibria involved were determined.     

Conversion of isoxazole derivatives into β-aminoenones by pentacarbonyliron,water and photoirradiation

3,5-Disubstituted isoxazole derivatives, when irradiated in the presence of pentacarbonyliron and water undergo reductive cleavage of the NO bond to give β-aminoenones in good yields.     

Asymmetric sulfoxidation of a β-carbonyl sulfide series by chloroperoxidase

The chloroperoxidase (CPO)-catalyzed oxidation of a series of β-carbonyl sulfides to sulfoxides has been studied at room temperature in aqueous citrate buffer. For dialkyl β-carbonyl sulfides, the products with methyl and ethyl substituents are obtained in ca. 100% yield. However when the alkyl group is n-propyl or i-propyl the yield drops dramatically (25%). An aryl sulfide derivative afforded product in very low yield (4%), but when the phenyl group bears a carbonyl, and the sulfur substituents are methyl or ethyl, the oxidation occurs with high yields (91–95%). Steric control of the sulfoxidation reaction is also confirmed with cyclohexanone derivatives, where a low product yield is observed even at high enzyme concentrations. Noteworthy are the yields obtained with cyclopentanone sulfide (65%) and an unexpected quantitative yield obtained with the γ-butyrolactone sulfide.     

Chemistry of nitrosyliron complexes supported by a β-diketiminate ligand

Several nitrosyl complexes of Fe and Co have been prepared using the sterically hindered Ar-nacnac ligand (Ar-nacnac = anion of [(2,6-diisopropylphenyl)NC(Me)](2)CH). The dinitrosyliron complexes [Fe(NO)(2)(Ar-nacnac)] (1) and (Bu(4)N)[Fe(NO)(2)(Ar-nacnac)] (2) react with [Fe(III)(TPP)Cl] (TPP = tetraphenylporphine dianion) to generate [Fe(II)(NO)(TPP)] and the corresponding mononitrosyliron complexes. The factors governing NO transfer with dinitrosyliron complexes (DNICs) 1 and 2 are evaluated, together with the chemistry of the related mononitrosyliron complex, [Fe(NO)Br(Ar-nacnac)] (4). The synthesis and properties of the related cobalt dinitrosyl [Co(NO)(2)(Ar-nacnac)] (3) is also discussed for comparison to DNICs 1 and 2. The solid-state structures of several of these compounds as determined by X-ray crystallography are reported.     

Cars spectrum of O2− formed by the trapping of photo-generated electrons on a ZnO surface

Using the planar optical waveguide geometry, two-photon absorption in ZnO generates electrons which are trapped by physisorbed O₂. The CARS spectrum of transient O₂⁻ on a ZnO surface indicates the presence of at least three bound species with vibrational frequencies of 1121, 1133 and 1142 cm⁻¹. The required CARS sensitivity in a UHV environment was achieved by establishing an interference condition within a ZnO waveguide to eliminate the contribution from the non-resonant susceptibility of the ZnO.