Gel permeation chromatographic study of the molecular weight distribution of tannins in the wood,bark and leaves ofEucalyptus spp.

Summary The molecular weight distribution of tannins from the wood, bark and leaves ofEucalyptus camaldulensis, E. globulus andE. rudis from two different Spanish provenances has been studied by high performance gel permeation chromatography, using the compounds' acetylated derivatives. The MW distribution profiles showed important variability depending on the type of vegetal tissue, the species and, in some cases, on the geographical provenance of the samples. Bark was the vegetal tissue that yielded tannins with the highest molecular weight, followed by wood and leaves. Tannins from wood and bark ofE. camaldulensis were of higher molecular size than those fromE. globulus andE. rudis; those in the leaves ofE. globulus andE. camaldulensis were similar in molecular size and larger than those in the leaves ofE. rudis.     

An efficient procedure for the preparation of (1S,3R)- and (1S,3S)-1-amino-3-(hydroxymethyl)cyclopentanes

Enantiomerically pure (1S,3S)- and (1S,3R)-1-amino-3-(hydroxymethyl)cyclopentanes have been efficiently synthesized from L-aspartic acid. The title compounds are isosteres of ribose and may be used to construct nucleoside analogs with important antiviral and antineoplastic activities as demonstrated by a concise total synthesis of (+)-4'-deoxycarbapentostatin nucleoside.     

Hydrogen atom vs electron transfer in catecholase-mimetic oxidations by superoxometal complexes. Deuterium kinetic isotope effects

Dioximato-cobalt(II), -iron(II) and -manganese(II) complexes (1)-(6), acting as functional catecholase and phenoxazinone synthase models, exhibit a deuterium kinetic isotope effect predicted by theory (k4H/k4D < or = 3) in the catalytic oxidative dehydrogenation of 3,5-di-tert-butylcatechol and 2-aminophenol by O2. KIEs in the range of (k4H/k4D approximately 1.79-3.51) are observed with (1) and (2) as catalysts, pointing to hydrogen atom transfer in the rate-determining step from the substrate hydroxy group to the metal-bound superoxo ligand. Less significant KIEs (1.06-1.20) are exhibited by catalysts systems (3)-(6), indicating that proton-coupled electron transfer is the preferred route in those cases.     

Asymmetric Induction by β-Cyclodextrins in NaBH4 Reduction of Ketones

Asymmetric reduction of various prochiral ketones was achieved with sodium borohydride utilizing -CD or its derivative, mono-6-deoxy-6-[N-(2-aminoethyl)]amino--CD (-CD-en) as a chiral template. It was found that pre-equilibrium between ketone and -CD derivative and low reaction temperature increase asymmetric induction. The extent of asymmetric induction and the absolute configuration of the resulting secondary alcohols are highly dependent upon the nature of the ketones and also -CD derivatives. A mechanistic scheme is suggested to explain the dependency.     

Chromium adsorption in olive stone activated carbon

In this work, Cr(III) adsorption on activated carbon obtained from olive stones in an upflow fixed-bed column at 30^∘C was studied. The flow rate influence on the breakthrough curves at a feed concentration of 0.87 meq/L was investigated in an attempt to minimize the diffusional resistances. Breakthrough curves for a flow range of 2–8 mL/min were obtained at 10.5 cm bed height and inlet diameter of 0.9 cm. The mass transfer parameters indicated that the bed minimal resistance was attained at 2 mL/min. Therefore, the data equilibrium was carried out until the bed was saturated at 2 mL/min. The dynamic system generated a favorable isotherm with a maximum chromium uptake of 0.45 meq/g. A column sorption mathematical model was created considering the axial dispersion in the column and the intraparticle diffusion rate-controlling steps. The isotherm was successfully modeled by the Langmuir equation and the mathematical model described the experimental dynamic data adequately for feed concentrations from 0.26 to 3.29 meq/L.     

Chiral capillary electrophoresis-mass spectrometry of amino acids in foods

In this work, the development of a new chiral capillary electrophoresis-mass spectrometry (CE-MS) method to separate D- and L-amino acids is shown. On-line coupling between CE and MS is established through an electrospray-coaxial sheath flow interface. Enantiomer separation is achieved by using a cheap, nonvolatile, chiral selector as beta-cyclodextrin in the background electrolyte (BGE) together with a physically coated capillary that is aimed to prevent contamination of the electrospray. The capillary coating is simple and easy to obtain as it only requires flushing of the capillary with a polymer aqueous solution for 3 min. Optimization of CE parameters (pH of BGE, type and concentration of chiral selector, and capillary inner diameter) and electrospray-MS parameters (nature and flow rate of the sheath liquid, nebulizer pressure) is carried out. Two different derivatization protocols of amino acids using dansyl chloride (DNS) and fluorescein isothiocyanate (FITC) are compared in terms of MS sensitivity and chiral resolution. Under optimum CE-MS conditions it is observed that the MS sensitivity obtained for FITC- and DNS-amino acids is similar (with limit of detection (LOD) in the microM range, corresponding to amounts injected in the fmol range) while chiral resolution is better for FITC-amino acids. The optimized method is demonstrated to provide the simultaneous analysis of 15 selected amino acids (i.e., FITC-D/L-Asp, -Glu, -Ser, -Asn, -Ala, -Pro, -Arg, and FITC-gamma-aminobutyric acid (GABA) in a single chiral CE-MS run, corresponding to the main amino acids that can be found in orange. Moreover, as a result of the high resolution achieved, it is possible to detect down to 2% of D-Asp in the presence of 98% of L-Asp. The good possibilities of chiral CE-MS in food analysis are corroborated through the detection of the main amino acids in a commercial orange juice (i.e., FITC-L-Asp, -Glu, -Ser, -Asn, -Pro, -Arg, and the nonchiral FITC-GABA) as well as the determination of the fraudulent addition of synthetic amino acids (containing D- and L-forms) to a fresh orange juice.     

Coumarin-strapped calix[4]pyrrole: a fluorogenic anion receptor modulated by cation and anion binding

A new strapped calix[4]pyrrole containing a fluorophore as part of the strap has been synthesized and characterized. Association constants with various anions have been determined using both fluorescence titration and isothermal titrations calorimetry (ITC). The two sets of association constants were found to be in good agreement with one another. The fluorescence emission properties of this new receptor could be controlled by addition of Na+ (or H2O) and anions. However, the fluorescence quenching by anions is only observed in the presence of Na+ (or H2O). All the experimental evidence is consistent with the notion that independent PET processes are modulated by separate cation and anion recognition events. As such, this system operates as an elementary logic gate wherein anion and cation concentrations serve as the input and fluorescence intensity changes provide the output.     

Metal complexes of 2-acetylpyridine N(4)-dihexyl- and N(4)-dicyclohexylthiosemicarbazones

Summary 2-Acetylpyridine N(4)-dihexyl- and N(4)-dicyclohexylthiosemicarbazone, HAc4DHex and HAc4DCHex, respectively, and Fe^III, Co^II, Co^III, Ni^II, Cu^II and Zn^II complexes have been prepared and characterized by molar conductivities, magnetic susceptibilities and spectroscopic techniques. For many of the complexes, loss of the N(2)H hydrogen occurs, and the ligands coordinate to the metal centres as NNS monoanionic, tridentate ligands, e.g., [M(NNS)X] (M = Co^II, Ni^II, Cu^II, NNS = Ac4DHex or Ac4DCHex and X = Cl or Br), [Fe(NNS)₂]ClO₄, [Co(NNS)₂]BF₄, [Cu(NNS)NO₃] and [Zn(NNS)OAc]. Zn^II ion is also chelated by neutral ligands in [Zn(HNNS)X₂] (X = Cl, Br). In addition, [Ni(Ac4DHex)-(HAc4DHex)]X (X = BF₄, ClO₄) and [Ni(HAc4DCHex)₂]-(BF₄)₂ are reported where the neutral thiosemicarbazone is coordinated via the pyridyl nitrogen, azomethine nitrogen and thione sulfur. Crystal structure determinations of HAc4DCHex and [Cu(Ac4DHex)Br] show the former to contain the bifurcated hydrogen bonded form and the latter to be planar with no significant interaction between neighbouring centres.     

Capillary zone electrophoretic studies of interactions of some quaternary isoquinoline alkaloids with DNA constituents and DNA

Capillary zone electrophoresis was applied for the investigation of interactions of some quaternary isoquinoline alkaloids, namely sanguinarine, chelerythrine, berberine, and jatrorrhizine, with DNA constituents and with DNA. None of these alkaloids attach covalently to nucleotides or to the whole DNA under physiological conditions. The interaction with DNA constituents is a noncovalent complexation based on weak intermolecular forces. Electrostatic attraction participates in the interaction but other types of intermolecular forces are involved as well. Cations were identified as the most probable interacting forms of the alkaloids. The interaction with compounds derived from purine was always stronger than those derived from pyrimidine. All alkaloids behaved analogously and similarly to ethidium bromide, the classic DNA intercalator. Stability constants K (in l.mol(-1)) for sanguinarine and chelerythrine in phosphate buffer of pH 7.4 (I(S) = 30 mM) ranged from tens to hundreds.