Light and heavy dansyl reporter groups in food chemistry: amino acid assay in beverages

5‐Dimethylamino‐1‐sulfonyl naphthalene (DNS, commonly referred as dansyl) is a functionality, bearing well‐established properties in directing the fragmentation, by mass spectrometry (MS), of the corresponding ionized sulfonylated derivatives. This property is shared also by its labeled analogs. The use of d₀/d₆ DNS derivatives is now exploited in the application of the well‐established isotope dilution mass spectrometric approach in the assay of complex mixtures. A new method for the quantitation of amino acids (AAs) in beverages is therefore presented, which relies on liquid chromatographic separation of their N‐dansylated derivatives followed by comparative electrospray tandem MS/MS of the d₀/d₆ isobaric mixtures. Labeled and unlabeled DNS derivatives of the selected AAs are readily available by microwave‐assisted synthetic protocols. The novelty of the method is represented by the use of heavy and light DNS‐isotopologue providing suitable reporter groups. Multiple‐reaction monitoring has been applied in the assay of AAs in wine, pineapple juice and bergamot juice with good‐to‐excellent results as proved by both relative standard deviation, lower than 15%, and by the accuracy values in the range 90–110%. Copyright © 2012 John Wiley & Sons, Ltd.     

Invariant measures for skew products and uniformly distributed sequences

??Almost all?? sequences (r ₁, . . . , r _n , . . . ) of positive integers have the following ??universal?? property: Whenever (X,???) is a Borel probability compact metric space, and ?? ₁, ?? ₂, . . . , ?? _n , . . . a sequence of commuting measure preserving continuous maps on (X,???), such that the action (by composition) on (X,???) of the semigroup with generators ?? ₁, . . . ,?? _n , . . . is uniquely ergodic and equicontinuous, then for every ${x \in X}$ the sequence w ₁,w ₂, . . . , w _n , . . . where $$w_n:=\varPhi_{r_n}(\varPhi_{r_{n-1}}(\ldots(\varPhi_{r_2}(\varPhi_{r_1}(x)))\ldots))$$ is uniformly distributed for???. This is a contribution to Problem 116 of Schreier and Ulam in the Scottish Book.     

Diagnosis of magnetoresponsive aromatic and antiaromatic zones in three‐membered rings of d‐ and f‐block elements

Magnetoresponsive three‐membered rings of d‐ and f‐block elements have been thoroughly investigated with the help of electronic structure calculation methods. The magnetic response of the clusters was evaluated by the Nucleus Independent Chemical Shifts (NICS)_zz‐scan curves, which in conjunction with symmetry‐based selection rules for the most significant translationally and rotationally allowed transitions helped rationalize and predict the orbital‐type of aromaticity/antiaromaticity of the clusters. The magnetoresponsive early (Groups 3, 4, and 5) transition metal M₃ rings exhibit successive aromatic and antiaromatic zones separated by a nodal plane. The magnetoresponsive late (Groups 11 and 12) transition metal M₃ rings exhibit long‐range aromatic zone with the NICS_zz(R) values decaying rapidly and monotonically with respect to R. The magnetic response of Group 10 transition metal M₃ rings is similar to that of the early transition metal M₃ rings, but it is long‐range antiaromatic only for the [c‐Ni₃] cluster. The NICS_zz‐scan curve of the [(H_tLa)₃(μ₂‐H)₆] cluster is indicative of weak pure σ‐aromaticity due to the induced diatropic ring current from the translationally allowed a → e′ and e′ → a transitions. The aromatic–antiaromatic behavior of the [(H_tCe)₃(μ₂‐H)₆]⁺ and [(H_tTm)₃(μ₂‐H)₆]²⁻ clusters is similar to that of the early d‐block elements. The magnetic response of [(H_tYb)₃(μ₂‐H)₆]³⁻ is similar to that of [c‐Hg₃]²⁻. The [(H_tLu)₃(μ₂‐H)₆] cluster can be considered as a doubly (σ + π) aromatic system, with the σ‐aromatic component being much stronger than the π‐aromatic one. Finally, the [(X_tRe)₃(μ₂‐X)₆] and [(X_tRu)₃(μ₂‐X)₆]⁺ (X = Cl, Br, I) clusters exhibit significant aromatic character with the greatest contribution to the induced diatropic ring currents coming from π‐type transitions. © 2009 Wiley Periodicals, Inc. J Comput Chem 2010     

Triangular Ni(II) complexes from the use of 2-pyridyl oximes

The reactions of representative 2-pyridyl oximes with Ni^II salts in the presence of a base have been investigated. The synthetic study has led to the new triangular complexes [Νi₃(ppko)₆]·2H₂O·0.5EtOH·MeOH (1·2H₂O·0.5EtOH·MeOH), [Νi₃(mpko)₃(HCO₂)₂(mpkoH)₂](ClO₄) (2) and [Νi₃(ppko)₃(HCO₂)₂(ppkoH)₂](ClO₄) (3), where ppko⁻ is the anion of phenyl(2-pyridyl)ketone oxime and mpko⁻ is the anion of methyl(2-pyridyl)ketone oxime. The structures of compounds 1 and 2 have been determined by single crystal X-ray diffraction. The ppko⁻ ligand in 1 adopts four different coordination modes including the unique N_pyridylO_oximate chelating one which gives rise to a 6-membered chelating ring, while the neutral and the deprotonated oxime ligands in 2 adopt three different coordination modes. The magnetic properties of 1 and 2 have been studied by variable-temperature dc magnetic susceptibility techniques which indicate antiferromagnetic interactions.     

Modeling cell membrane transport: interaction of guanidinylated poly(propylene imine) dendrimers with a liposomal membrane consisting of phosphate-based lipids

Mixed anionic liposomes consisting of dihexadecyl phosphate, phosphatidylcholine, and cholesterol were employed as model systems for assessing the ability of a series of functionalized dendrimers, bearing a varying number of guanidinium groups at their surface, to translocate across the liposomal bilayers. At low guanidinium/phosphate molar ratios or when weakly guanidinylated dendrimeric derivatives were employed, the dendrimeric derivative acted as a kind of "molecular glue" leading to a simple adhesion of the liposomes. Liposomal fusion occurred to a certain extent at high guanidinium/phosphate molar ratios or when highly guanidinylated dendrimeric derivatives were employed. Furthermore, translocation of these dendrimeric derivatives to the liposomal core was observed for low to medium guanidinylation and at low guanidinium/phosphate molar ratios which was, however, enhanced when the lipid bilayer was in its fluid liquid-crystalline phase. Thus, an optimum balance is required between the binding strength of guanidinium with the phosphate groups and the degree of hydrophilicity of the guanidinylated dendrimers for the transport of the latter to the liposomal core to occur.     

Synthesis and structures of Se analogues of the antithyroid drug 6-n-propyl-2-thiouracil and its alkyl derivatives: formation of dimeric Se-Se compounds and deselenation reactions of charge-transfer adducts of diiodine

Four selenium analogues of the antithyroid drug 6-n-propyl-2-thiouracil (PTU), of formulae RSeU, (R = methyl (Me) (1), ethyl (Et) (2), n-propyl (nPr) (3), and isopropyl (iPr) 4), have been synthesized. Reaction of 1-4 with diiodine in a 1:1 molar ratio in dichloromethane results in the formation of [(RSeU)I(2)] (R = methyl (5), ethyl (6), n-propyl (7) and isopropyl (8)). All compounds have been characterized by elemental analysis, FT-Raman, FT-IR, UV/Vis, (1)H-, (13)C-, (77)Se-1D and -2D NMR spectroscopy, and ESI-MS spectrometric techniques. Recrystallization of 4 from dichloromethane afforded (4CH(2)Cl(2)). Crystals of [(nPrSeU)I(2)] (7), a charge-transfer complex, were obtained from chloroform solutions, while crystallization of 6 and 7 from acetone afforded the diselenides [N-(6-Et-4-pyrimidone)(6-EtSeU)(2)] (92 H(2)O) and [N-(6-nPr-4-pyrimidone)(6-nPrSeU)(2)] (10) as oxidation products. Recrystallization of 7 from methanol/acetonitrile solutions led to deselenation with the formation of 6-n-propyl-2-uracil (nPrU) (11). [(nPrSeU)I(2)] (7) was found to be a charge-transfer complex with a Se--I bond. These results are discussed in relation to the mechanism of action of antithyroid drugs.     

Estimation of type I error probability from experimental Dixon's "Q" parameter on testing for outliers within small size data sets

Common significance tests carried out using statistical software packages usually return to the user the probability p of type I error as the result. Based on p and the preset confidence level the user will decide on the acceptance or the rejection of the associated null hypothesis. Dixon's test (Q-test) is commonly used for the detection of an outlier within a set of N observations (typically: N = 3–12). Q-test can only be applied by comparing the experimental value of the statistic Q with tabulated critical Q-values corresponding to some standard values of p. Hence, for a given value of Q and a number of observations, N, the user knows only the range and not the value of the associated probability p of type I error (erroneous rejection). This is due to the lack of explicit expressions of the form p = F(Q,N). In this work, a simple stochastic (Monte Carlo) approach is presented for the estimation of p corresponding to a given experimental value of Q and size N of the data set. In addition, based on Dixon's equations, explicit expressions of p are given for N = 3 and 4.     

Synthesis and antioxidative/anti-inflammatory activity of novel fullerene–polyamine conjugates

(E)-4-(Fullerenopyrrolidin-1-yl)-3-methylbut-2-enoic acid and its corresponding succinimidyl ester, readily obtained through Prato-type modification of C₆₀, were used for the selective N-acylation of polyamines. The thus obtained conjugates were evaluated for their antioxidative and anti-inflammatory activity and their cytotoxicity was determined. Members of this family of compounds showed interesting anti-lipid peroxidation, anti-lipoxygenase and anti-inflammatory activity and comparable cytocompatibility to spermidine.     

Homoclinic bifurcations in radiating diffusion flames

We analyse the dynamics of a model describing a planar diffusion flame with radiative heat losses incorporating a single step kinetic using timestepping techniques for Lewis number equal to one. We construct the full bifurcation diagram with respect to the Damköhler number including the branches of oscillating solutions. Based on this analysis we found, for the first time, homoclinic bifurcations that mark the abrupt disappearance of the nonlinear oscillations near extinction as reported in experiments.     

Measuring the fundamental frequency and the harmonic properties of the wingbeat of a large number of mosquitoes in flight using 2D optoacoustic sensors

Mosquito flight tones occur during locomotion and courtship and are mostly analyzed using microphones. The use of microphones is impractical for analyzing the wingbeat of non-tethered insects especially if one is interested in studying the frequency content of wingbeats of a large number of insects. In this study we present a practical setting based on a novel 2D optical sensor that we embed inside insectary cages to record the wingbeats of three mosquito species belonging to three different genera, namely Culex pipiens molestus, Anopheles gambiae and Aedes albopictus. We show that this setting allows to automatically create distributions of parameters related to wingbeat frequency and harmonic properties derived from many non-tethered wingbeats and therefore characterize the wingbeat properties of a whole species with increased confidence. Implications for potential applications are discussed.