Analysis of saccharides in beer samples by flow injection with electrospray mass spectrometry

Saccharides in foods play important roles, as they are essential substrates for fermentation processes. In brewing, the concentration of maltooligosaccharides influences the characteristics of beers and therefore their determination is of great practical interest. Electrospray ionization mass spectrometry (ESI-MS) was applied to identify and characterise maltooligosaccharides in beer samples. The effects due to different cation concentrations and dilution of samples were studied. Furthermore, quantitative analyses of maltooligosaccharides by means of flow-injection ESI-MS (FI/ESI-MS) of 1-microL beer samples (diluted 1000-fold) are described.     

Zinc(II) as an allosteric regulator of liposomal membrane permeability induced by synthetic template-assembled tripodal polypeptides

Three copies of peptide sequences from the peptaibol family, known to affect the permeability of the lipid bilayer of membranes, were connected to tris(2-aminoethyl)amine (TREN), a tripodal metal ion ligand, to prepare functional peptides capable of modifying the permeability of liposomal membranes. Some of the resulting tripodal polypeptide derivatives are very effective in promoting carboxyfluorescein (CF) leakage from CF-loaded unilamellar vesicles composed of a 70:30 phosphatidylcholine/cholesterol blend. The activity of these novel compounds was shown to be tunable upon metal ion coordination of the TREN subunit; the tripodal apopeptide was far more effective than its ZnII complex. Leakage experiments showed that a minimum number of five amino acids per peptide chain is required to form active systems. A mechanism is proposed in which the ZnII ion changes the conformation of the template from extended to globular and thus acts as an allosteric regulator of the activity of the systems. Molecular modeling studies indicate that when the three peptide chains are connected to the template in the extended conformation, the resulting tripodal polypeptide is able to span across the membrane, thus allowing the formation of permeable channels made of a cluster of molecules. The same change of conformation induces, to some extent, fusion of the membranes of different liposomes.     

Synthesis and thermal degradation of some ferrocene-containing polyazines and poly-schiff bases

A series of ferrocene-containing polymeric azines and polymeric Schiff bases have been synthesized by means of acid-catalyzed solution polycondensations. The molecular structures of the polymers synthesized have been determined, and information concerning their thermal behavior has been obtained. Comparative thermal stabilities of the products of polymerization of aliphatic and aromatic diamines with 1,1′-diformylferrocene and 1,1′-diacetylferrocene were investigated by thermogravimetric analysis both in air and in an inert atmosphere. In the inert atmosphere, initial weight loss due to thermal stress did not occur below 300°C in all cases, and in many cases 50–70% residue of polymer sample remained at 700°C. The use of a fluorinated diamine led to the synthesis of a polymer which did not exhibit any significant enhancement of thermal properties. Investigation of the polymer products by direct inlet mass spectroscopy led to the observation that several of the systems contained significant amounts of cyclic dimers, although linear polymers were the major products in most cases. Extraction of the cyclic dimers followed by molecular weight determination by vapor phase osmometry confirmed their molecular structures.     

Analytical methodologies for identifying a polypeptide antibiotic

This article discusses the development of various analytical methods for identification and quantification of residues of antibiotics in meeting international regulatory requirements, and, as an example, overviews the screening, purification, fractionation and analytical assays of bacitracin, a commonly applied polypeptide antibiotic mixture. Attention is focused on the development of chemical methods, as they provide extraordinary performance, in terms of sensitivity and selectivity, for measuring residual levels of the various components of bacitracin in food and other matrices; the non-compound specific biological assay is discussed only briefly. Because of its advantages, state-of-the-art high-performance liquid chromatography (HPLC) coupled with various detection techniques, in particular mass spectrometry (MS), has recently gained in popularity in confirming and quantifying drug residues. In this article, the authors also outline the latest results on the application of highly sensitive and selective LC-MS in analysis of bacitracin residues in milk and animal tissues. LC-MS is suggested as the technique of choice for confirmation of polar polypeptide antibiotics and the like at trace concentrations.     

Fluoropolyethers end‐capped by polar functional groups. III. Kinetics of the reactions of hydroxy‐terminated fluoropolyethers and model fluorinated alcohols with cyclohexyl isocyanate catalyzed by organotin compounds

The kinetics of the dibutyltin dilaurate (DBTDL)‐catalyzed urethane formation reactions of cyclohexyl isocyanate (CHI) with model monofunctional fluorinated alcohols and fluoropolyether diol Z‐DOL H‐1000 of various molecular weights (100–1084 g mol^?1) in different solvents were studied. IR spectroscopy and chemical titration methods were used for measuring the rate of the total NCO disappearance at 30–60 °C. The effects of the reagents and DBTDL catalyst concentrations, the solvent and hydroxyl‐containing compound nature, and the temperature on the reaction rate and mechanism were investigated. Depending on the initial reagent concentration and solvent, the reactions could be well described by zero‐order, first‐order, second‐order, or more complex equations. The reaction mechanism, including the formation of intermediate ternary or binary complexes of reagents with the tin catalyst, could vary with the concentration and solvent and even during the reaction. The results were treated with a rate expression analogous to those used for enzymatic reactions. Under the explored conditions, the rate of the uncatalyzed reaction of fluorinated alcohols with CHI was negligible. Moreover, there was no allophanate formation, nor were there other side reactions, catalysis by urethane in the absence of DBTDL, or a synergetic effect in the presence of the tin catalyst. © 2002 Wiley Periodicals, Inc. J Polym Sci Part A: Polym Chem 40: 3771–3795, 2002     

Synthesis of 4H-3,1-benzoxazines, quinazolin-2-ones, and quinoline-4-ones by palladium-catalyzed oxidative carbonylation of 2-ethynylaniline derivatives

An effective and straightforward approach to the synthesis of 4H-3,1-benzoxazines 3 and 4, quinazolin-2-ones 5, and quinoline-4-one derivatives 6 and 7 is provided by palladium-catalyzed cyclization-alkoxycarbonylation of variously substituted 2-(trimethylsilanyl)ethynylaniline amide or urea derivatives 2. Reactions are carried out in 7:1 MeCN/MeOH at 65 or 75 degrees C in the presence of catalytic amounts of 10% Pd/C in conjunction with Bu(4)NI and KF and under 2.4 MPa of a 3:1 mixture of CO and air. Anti and syn 6-exo-dig cyclization modes account for the formation of the two stereoisomers. Isomerization of the vinylpalladium intermediate may occur as well. Formation of a double carbonylation product 7r and of a gem-dimethoxycarbonylation product 6s, whose structures have been determined by X-ray diffraction analysis, is justified through an unusual type of rearrangement.     

Extraction of humic acids from a natural matrix by alkaline pyrophosphate. Evaluation of the molecular weight of fractions obtained by ultrafiltration

 Fractions of humic acids, resolved by ultrafiltration of extracts from a sample of peat treated with alkaline pyrophosphate solution, have been submitted to high-performance size-exclusion chromatography, with the aim of determining the molecular weight distributions. Anomalous peaks, located at retention volumes higher than those corresponding to the main signal, are present in the elution profiles relative to the lightest fractions. These peaks are more intense when using a refractive index detector rather than a UV detector. Elemental analysis data for the lightest fractions suggested that the spurious peaks are due to the presence of inorganic material. The hypothesis that pyrophosphate interacts with humic acids in the course of the extraction has been confirmed by colorimetric determination of the phosphorus content in the different fractions. As a consequence, the extraction procedure has been modified by using 0.1 mol/L NaOH as extractant. The average molecular weights of the various fractions, following NaOH extraction, result in substantial agreement with those obtained following pyrophosphate solution extraction (if the ‘pyrophosphate peaks’ present in the chromatographic profile are discarded in the calculations). Received: 18 November 1996 / Revised: 18 February 1997 / Accepted: 23 February 1997     

Can the pi-facial selectivity of solvation be predicted by atomistic simulation?

This work is concerned with the rationalization and prediction of solvent and temperature effects in nucleophilic addition to alpha-chiral carbonyl compounds leading to facial diastereoselectivity. We study, using molecular dynamics simulations, the facial solvation of (R)-2-phenyl-propionaldehyde in n-pentane and n-octane at a number of temperatures and compare it with experimental selectivity data for the nBuLi addition leading to syn- and anti-(2R)-2-phenyl-3-heptanol, which give nonlinear Eyring plots with the presence of inversion temperatures. We have found from simulations that the facial solvation changes with temperature and alkane. Moreover, by introducing a suitable molecular chirality index we have been able to predict break temperatures (T(CI)) for the two solvents within less than 20 degrees of the inversion temperatures experimentally observed in the diastereoselective nBuLi addition. We believe this could lead to a viable approach for predicting inversion temperatures and other subtle solvent effects in a number of stereoselective reactions.     

Complexes self‐associate by hydrogen bonding and metallophilic attraction: Theoretical study

Hydrogen bonding and metallophilic attractions are studied in the model systems: [(AuNH₃Cl)₂], [(AuNH(CH₃)₂Cl)₂], [{Au₂(μ‐SH)(PH₂O)(PH₂OH)}₂], [(CuNH₃Cl)₂], and [{Cu(NH₃)Cl}₄] at the Hartree–Fock (HF) and second‐order Møller–Plesset (MP2) levels. The two interactions are found to be comparable and prevailing in the final structure. It is determined that the aurophilic contact has a same magnitude that the hydrogen bonding, and is stronger than the cuprophilic interaction. The presence of hydrogen bond directs the growth of the crystal. © 2005 Wiley Periodicals, Inc. Int J Quantum Chem, 2006     

Formation of a nanostructured layer on bioglass particles of different sizes immersed in tris-buffered solution. N2 adsorption and HR-TEM/EDS analysis

Morphological and structural variations of particles of Bioglass with two different grain sizes reacted in Tris-buffered solution were analyzed by means of N(2) adsorption/desorption at 77 K and HR-TEM/EDS. A remarkable increase in specific surface area (ssa) was observed after the first hour of dissolution. A plateau value corresponding to an increase of at least 2 orders of magnitude was reached after 2 days of dissolution. The ssa increase was faster for the smaller particle size sample, and the ratio between the ssa of the starting samples was not maintained during dissolution. Both micro- and mesopores were formed at different stages of the reaction for the two samples. Increasing ssa was also connected to the formation of a microcrystalline structure rich in Ca and P, as shown by TEM images. The segregation of both a SiO(2)-rich amorphous phase and a Ca/P-rich crystalline phase was observed after the first hour of dissolution. After 2 days of reaction, Ca/P-rich particles made of fine aciculate crystals were found either in close contact with SiO(2) particles or deposited on a small SiO(2)-rich core. A preliminary analysis of TEM data showed the formation, together with hydroxy carbonate apatite, of different types of calcium phosphates not detectable by powder X-ray diffraction.