Automated headspace solid-phase dynamic extraction to analyse the volatile fraction of food matrices

High concentration capacity headspace techniques (headspace solid-phase microextraction (HS-SPME) and headspace sorptive extraction (HSSE)) are a bridge between static and dynamic headspace, since they give high concentration factors as does dynamic headspace (D-HS), and are as easy to apply and as reproducible as static headspace (S-HS). In 2000, Chromtech (Idstein, Germany) introduced an inside-needle technique for vapour and liquid sampling, solid-phase dynamic extraction (SPDE), also known as "the magic needle". In SPDE, analytes are concentrated on a 50 microm film of polydimethylsiloxane (PDMS) and activated carbon (10%) coated onto the inside wall of the stainless steel needle (5 cm) of a 2.5 ml gas tight syringe. When SPDE is used for headspace sampling (HS-SPDE), a fixed volume of the headspace of the sample under investigation is sucked up an appropriate number of times with the gas tight syringe and an analyte amount suitable for a reliable GC or GC-MS analysis accumulates in the polymer coating the needle wall. This article describes the preliminary results of both a study on the optimisation of sampling parameters conditioning HS-SPDE recovery, through the analysis of a standard mixture of highly volatile compounds (beta-pinene, isoamyl acetate and linalool) and of the HS-SPDE-GC-MS analyses of aromatic plants and food matrices. This study shows that HS-SPDE is a successful technique for HS-sampling with high concentration capability, good repeatability and intermediate precision, also when it is compared to HS-SPME.     

Selective recognition of G-qQuadruplex telomeric DNA by a bis(quinacridine) macrocycle

The interaction of G-quadruplex DNA with the macrocyclic compound BOQ1, which possesses two dibenzophenanthroline (quinacridine) subunits, has been investigated by a variety of methods. The oligonucleotide 5'-A(GGGT(2)A)(3)G(3), which mimics the human telomeric repeat sequence and forms an intramolecular quadruplex, was used as one model system. Equilibrium binding constants measured by biosensor surface plasmon resonance (SPR) methods indicate a high affinity of the macrocycle for the quadruplex conformation (K > 1 x 10(7) M(-)(1)) with two equivalent binding sites. The affinity of BOQ1 for DNA duplexes is at least 1 order of magnitude lower. In addition, the macrocycle is more selective than the monomeric control compound (MOQ2), which is not able to discriminate between the two DNA structures (K(duplex) approximately K(quadruplex) approximately 10(6) M(-)(1)). Strong binding of BOQ1 to G4 DNA sequences was confirmed by fluorometric titrations with a tetraplex-forming oligonucleotide. Competition dialysis experiments with a panel of different DNA structures, from single strands to quadruplexes, clearly established the quadruplex binding specificity of BOQ1. Fluorescence resonance energy transfer (FRET) T(m) experiments with a doubly labeled oligonucleotide also revealed a strong stabilization of the G4 conformation in the presence of BOQ1 (DeltaT(m) = +28 degrees C). This DeltaT(m) value is one of the highest values measured for a G-quadruplex ligand and is significantly higher than observed for the monomer control compounds (DeltaT(m) = +10-12 degrees C). Gel mobility shift assays indicated that the macrocycle efficiently induces the formation of G-tetraplexes. Strong inhibition of telomerase was observed in the submicromolar range (IC(50) = 0.13 microM). These results indicate that macrocycles represent an exciting new development opportunity for targeting DNA quadruplexes.     

Organometallic chemistry and homogeneous catalysis of Rh and Rh-Co mixed metal carbonyl clusters

The reactions of hydrosilane and/or alkyne as well as isonitriles with rhodium and rhodium cobalt mixed metal carbonyl clusters, e.g., Rh₄(CO)₁₂ and Co₂Rh₂(CO)₁₂, are studied. Novel mixed metal complexes, e.g., CoRh(CO)₅ (HCCBu ⁿ ), (R₃Si)₂Rh(CO) _n Co(CO)₄, Rh(R–NC)₄Co(CO)₄, Co₂Rh₂(CO)₁₀(HCCR), and Co₂Rh₂(CO)₉(HCCBu ⁿ ), are synthesized and identified. The catalytic activities of these rhodium and rhodium-cobalt mixed metal complexes are examined in hydrosilyation, silylformylation, and novel silylcarbocyclization reactions. Possible mechanisms for these reactions are proposed and discussed.     

A Determination of Standard Potentials and Related Primary pH Standards in the 50 Mass Percent (N-Methyl-2-Pyrrolidinone + Water) Mixture at Various Temperatures

Following the IUPAC-endorsed procedure, the primary pH standards offered by the equimolal phosphate buffer (Na₂HPO₄ (0.01 mol⋅kg⁻¹) + KH₂PO₄ (0.01 mol⋅kg⁻¹)) in the (N-methyl-2-pyrrolidinone + water) solvent mixture of 50 mass percent composition at various temperatures have been determined from potential difference measurements with the reversible Harned cell. Since the essential prerequisite of the above procedure is the knowledge of the (hitherto unknown) standard potential difference of Harned’s cell, a parallel supplementary series of potential difference measurements has been carried out with the reversible cell, Pt|H₂|HCl(m)|AgCl|Ag|Pt according to the classical thermodynamic procedure. The problem of comparability of the pH scale in the (N-methyl-2-pyrrolidinone + water) solvent with that in the pure water solvent is duly discussed in terms of primary medium effects.     

Bifurcation of fixed points from a manifold of trivial fixed points in the infinite-dimensional case

We obtain a necessary as well as a sufficient condition for the existence of bifurcation points of a coincidence equation, and, in particular, of a parametrized fixed point problem. In both cases the trivial solutions are assumed to form a finite-dimensional submanifold of a Banach manifold. An application is given to a delay differential equation on a manifold: we detect periodic solutions that rotate close to an equilibrium point. To Albrecht Dold and Edward Fadell, superb mathematicians and first rate friends     

Lipase-Catalyzed Regio- and Stereoselective Acylation of Hydroxy Groups in Steroid Side Chains

 Lipase from Pseudomonas cepacia (PCL) catalyzes the regio- and stereoselective acylation of primary and secondary hydroxy groups in steroid side chains under irreversible transesterification conditions with vinyl acetate in organic solvents.     

Quasilinear elliptic inequalities on complete Riemannian manifolds

We prove maximum and comparison principles for weak distributional solutions of quasilinear, possibly singular or degenerate, elliptic differential inequalities in divergence form on complete Riemannian manifolds. A new definition of ellipticity for nonlinear operators on Riemannian manifolds is introduced, covering the standard important examples. As an application, uniqueness results for some related boundary value problems are presented.     

Existence,non-existence and regularity of radial ground states for p-Laplacian equations with singular weights

By the Mountain Pass Theorem and the constrained minimization method existence of positive or compactly supported radial ground states for quasilinear singular elliptic equations with weights are established. The paper also includes the discussion of regularity and the validity of useful qualitative properties of the solutions, which seems of independent interest. Finally, a Pohozaev type identity is produced to deduce some non-existence results.     

Global branches of periodic solutions for forced delay differential equations on compact manifolds

We prove a global bifurcation result for T-periodic solutions of the T-periodic delay differential equation x^′(t)=λf(t,x(t),x(t−1)) depending on a real parameter λ?0. The approach is based on the fixed point index theory for maps on ANRs.