Host–Guest Chemistry of Aromatic‐Amide‐Linked Bis‐ and Tris‐Calix[4]pyrroles with Bis‐Carboxylates and Citrate Anion

A small library of polytopic receptors has been synthesized from meso‐p‐ and meso‐m‐aminophenylcalix[4]pyrroles and p‐ or m‐phthaloyl or trimesic chloride. Selected bis‐carboxylates and the citrate anion, which either exhibit altered distribution profiles in cancerous tissues in comparison with healthy tissues or are metabolites of carcinogenic substances (for example, trans,trans‐muconic acid from benzene exposure in humans) were tested as ligands. Varied affinities and binding modes were observed as a function of the number of calix[4]pyrroles and the topology of amide units present in each of the polytopic receptors. The structures of the 1:1 complexes derived by molecular modeling are in excellent agreement with the results of ¹H NMR complexation studies.     

Multiple headspace-solid-phase microextraction: An application to quantification of mushroom volatiles

Multiple headspace-solid phase microextraction (MHS-SPME) followed by gas chromatography/mass spectrometry (GC–MS) and flame ionization detection (GC–FID) was applied to the identification and quantification of volatiles released by the mushroom Agaricus bisporus, also known as champignon. MHS-SPME allows to perform quantitative analysis of volatiles from solid matrices, free of matrix interferences. Samples analyzed were fresh mushrooms (chopped and homogenized) and mushroom-containing food dressings. 1-Octen-3-ol, 3-octanol, 3-octanone, 1-octen-3-one and benzaldehyde were common constituents of the samples analyzed. Method performance has been tested through the evaluation of limit of detection (LoD, range 0.033–0.078 ng), limit of quantification (LoQ, range 0.111–0.259 ng) and analyte recovery (92.3–108.5%). The results obtained showed quantitative differences among the samples, which can be attributed to critical factors, such as the degree of cell damage upon sample preparation, that are here discussed. Considerations on the mushrooms biochemistry and on the basic principles of MHS analysis are also presented.     

Structural Characterization of a Zinc High‐affinity Binding Site in Rhodopsin†

For the first time to our knowledge, X‐ray absorption spectroscopy (XAS) has been used to investigate the environment of putative Zn²⁺ binding sites in rhodopsin. We studied native purified nondeionized rhodopsin without any further addition of Zn²⁺, as well as with 1.5 mol of Zn²⁺—as zinc chloride—per mole of protein. Three different binding sites in rhodopsin were considered based on computational chemistry studies, and a quantitative analysis of the XAS signal was performed by fitting the experimental data to their simulated XAS spectra. Our results demonstrate that Zn²⁺ is intrinsically bound to rhodopsin and are compatible with the existence of an octahedral coordination involving six oxygen atoms in the first shell (average Zn‐O distance of 2.08 Å), and with a second coordination shell containing one or two phosphorus or sulfur atoms at an average distance of 2.81 Å.     

Pulse EPR Methods for Studying Chemical and Biological Samples Containing Transition Metals

This review discusses the application of pulse EPR to the characterization of disordered systems, with an emphasis on samples containing transition metals. Electron nuclear double‐resonance (ENDOR), electron‐spin‐echo envelope‐modulation (ESEEM), and double electron–electron resonance (DEER) methodologies are outlined. The theory of field modulation is outlined, and its application is illustrated with DEER experiments. The simulation of powder spectra in EPR is discussed, and strategies for optimization are given. The implementation of this armory of techniques is demonstrated on a rich variety of chemical systems: several porphyrin derivatives that are found in proteins and used as model systems, otherwise highly reactive aminyl radicals stabilized with electron‐rich transition metals, and nitroxide–copper–nitroxide clusters. These examples show that multi‐frequency continuous‐wave (CW) and pulse EPR provides detailed information about disordered systems.     

Gap orders of rational functions on plane curves with few singular points

We prove that certain integers n cannot occur as degrees of linear series without base points on the normalization of a plane curve whose only singularities are a “small” number of nodes and ordinary cusps. As a consequence we compute the gonality of such a curve. Work done with financial support of M.U.R.S.T. while the authors were members of C.N.R.     

Two remarks on integral morphisms of affinek-varieties

Il lavoro prosegue lo studio dei morfismi interi di varietà algebriche su corpi non algebricamente chiusi iniziato, in collaborazione con M. Raimondo, su «Integral morphisms and homeomorphisms of affine varieties». Qui si provano due proprietà che chiariscono le analogia e differenze col caso in cui le varietà siano definite su un corpo algebricamente chiuso.     

A mechanical saffron flower harvesting system

This work is concerned with a mechanical system designed to harvest Crocus sativus L. (saffron) flowers. The system is conceived as a shoulder portable device with two main parts: the former is specifically designed to detach the flower containing three stigmas, which are the costly final product, while the second one collects the detached flower through a vacuum collector. This paper describes the operating principle of the device that imitates one of the procedures followed by the pickers but with the peculiarity that it harvests the flower without separating it from its leaves, which is a significant advantage since it simplifies the mechanical detachment of the flower. Experimental laboratory tests were carried out on the gripper prototype in order to investigate the dynamic behaviour of the detaching and harvesting device. The experimental activity is described in the paper and the experimental results are discussed to know the gripper prototype performances and to define the future work.