Daniele Dondi

Improving selectivity in gas chromatography by using chemically modified multi-walled carbon nanotubes as stationary phase.

Amino-terminated alkyl MWCNTs (MWCNTs-R-NH2), synthesized by chemical modification of the nanotube skeleton by nucleophilic substitution with 2,2′-(ethylenedioxy)diethylamine, were successfully used as stationary phases for gas chromatographic separation of esters and chloroaromatics. The presence of alkyl chains with polar embedded groups made the functionalized MWCNTs (f-MWCNTs) a mixed-mode GC separation material able to interact in different ways with the analytes. Compared with non-functionalized MWCNTs (nf-MWCNTs), MWCNTs-R-NH2 had higher selectivity, enhanced resolution, and optimum retention behaviour, and they were proved to perform better than the commercial stationary phase Porapak QS (PQS), claimed to be suitable for similar applications. The so-prepared stationary phase was used for analysis of a synthetic mixture containing different classes of analytes, viz. esters, ketones, alcohols, alkanes, and aromatic hydrocarbons, and finally used for investigation of similar real matrices. In particular, the constituents of a commercial paint thinner were determined by direct injection of the sample, with good reproducibility (inter-day precision RSDs from 5 to 19%). Two unknown samples of commercial white spirit were also analysed for determination of the aromatic hydrocarbon content, and their composition was profiled on the basis of the different compounds identified.

Photochemistry in synthesis: Where, when, and why

A series of photochemical reactions are assessed under the environmental aspect by using Eissen and Metzgers EATOS (environmental assessment tool for organic syntheses) method and are compared with strictly analogous thermal processes. These include C-C bond-forming reactions (arylation and alkylation) and selective oxidation and reduction reactions. In most cases, the photochemical method is experimentally simpler and less expensive than the thermal alternative. A disadvantage is that photochemical reactions are carried out in rather dilute solution, and this factor gives by far the main contribution to the assessment. However, if the solvent is recovered, the photochemical reaction is more environment-friendly.

Knockout of pgdS and ggt genes improves γ-PGA yield in B. subtilis.

One of the emerging biopolymers that are currently under active investigation is bacterial poly(γ‐glutamic acid) (γ‐PGA). However, before its full industrial exploitation, a substantial increase in microbial productivity is required. γ‐PGA obtained from the Bacillus subtilis laboratory strain 168 offers the advantage of a producer characterized by a well defined genetic framework and simple manipulation techniques. In this strain, the knockout of genes for the major γ‐PGA degrading enzymes, pgdS and ggt, leads to a considerable improvement in polymer yield, which attains levels analogous to the top wild γ‐PGA producer strains. This study highlights the convenience of using the laboratory strain of B. subtilis over wild isolates in designing strain improvement strategies aimed at increasing γ‐PGA productivity. Biotechnol. Bioeng. 2013; 110: 2006–2012.

Structurally-variable, rigid and optically-active D2 and D3 macrocycles possessing recognition properties towards C60.

The reactivity of aromatic dicarboxylic acids, in combination with an axially-chiral, suitable dibenzylic alcohol, derived from BINOL, has been exploited in one-pot esterification reactions for the direct formation of several rigid, homochiral macrocycles. Cyclic adducts possessing, respectively, average molecular D(2) and D(3) symmetries, have been characterized in pure forms, with isolated yields and selectivities which are substantially different from those rising from purely statistical arguments. NMR and CD spectroscopies detect the structural and shape variability in the scaffolds, reflected both in terms of large changes in chemical shifts of selected proton resonances, and in terms of the variation of the CD signature related to the dihedral angle defined by the binaphthyl units embedded in the rigid cyclic skeleton. The crystal structure of two homochiral D(2) macrocycles show the formation of ordered nanostructures in the solid state, with the naphthyl rings of the binaphthyl units packing intermolecularly in an eclipsed-like conformation to yield nonhelical tubular arrangements. The larger D(3) cyclic adducts are able to afford stable complexes with C(60) in toluene solution, with comparable binding strengths, yet whose stoichiometries are dependent on small variations in the spacing units and therefore in the shapes of the internal cavities of the cyclic structures.

Titanium dioxide photocatalysis of adamantane

Abstract TiO 2 photocatalysis of adamantane in oxygen equilibrated MeCN yields 1- and 2-adamantanol and adamantanone with limited degradation and preference for functionalization at the 1 position, particularly in the presence of silver salts. Oxidation in CH 2 Cl 2 is less selective. The oxidation of cyclohexane and cyclododecane is slower. In N 2 -flushed solutions with Ag + as a sacrificial acceptor, products from the trapping of both 1-adamantyl radical (adamantyl methyl ketone) and cation ( N -adamantylacetamide) are obtained. Furthermore, alkylation of an electrophilic alkene (isopropylydenmalononitrile) has been obtained, though in a low yield.

Selectivity in the reaction of triplet phenyl cations.

A DFT study of the reaction of phenyl cation and some 4-substituted derivatives (cyano, methyl, methoxy, amino) with a pi nucleophile (ethylene) as well as with representative n nucleophiles (NH(3), MeOH, and MeCN) reveals a multiform behavior depending on both the cation multiplicity and the trap used. A straightforward addition takes place with the singlet (pi(6)sigma(0) structure) both with ethylene, where a spiro[2,5]octa-4,7-dienyl (phenonium) cation is formed, and with n nucleophiles, where the corresponding onium cations result. On the contrary, with the triplet (pi(5)sigma(1) structure) the reaction depends on the nature of the nucleophile, as indicated by MO correlation diagrams. Thus, with ethylene a bonding interaction occurs between the singly occupied sigma(sp(2)) orbital of the cation and the alkene pi orbital and leads to a planar distonic diradical cation. On the contrary, no addition takes place with n nucleophiles, which interact only with the phenyl cations pi MO, leading to weakly bonded, face-to-face complexes. An electron-withdrawing substituent such as CN allows the formation of a stabilized adduct cation also from the triplet, but only with a good nucleophile, such as ammonia. The spin-dependent dichotomy in the chemical behavior rationalizes recent experimental findings and fits with the prediction formulated by Taft 45 years ago. The unusual combination of a carbocation nature and of triplet multiplicity originates the peculiar chemistry of phenyl cations that appear to be promising intermediates in synthesis.

Synthesis of γ-lactols, γ-lactones and 1,4-monoprotected succinaldehydes under moderately concentrated sunlight

The usefulness of solar light for carrying out photocatalytic reactions involving the formation of a carbon–carbon bond has been explored. Thus, some radical alkylations of α,β-unsaturated acids or aldehydes have been carried out in a mixed aqueous solution. Under these conditions, alkyl radicals are generated from i-PrOH and 1,3-dioxolane by photocatalyzed hydrogen abstraction. A water soluble photocatalyst (disodium benzophenondisulfonate, BPSS) was used, which greatly simplifies work up. With reasonably efficient radical traps (e.g. maleic acid), the syntheses could be carried out up to completion on a 10 gram scale within 10–15 hours exposure to sunlight in a solar concentrator (SOLFIN apparatus) in November in Almeria (Spain). The alkylation of some α,β-unsaturated aldehydes have been likewise performed under the same conditions.

Predicting the UV spectrum of polyoxometalates by TD-DFT.

UV absorption spectra of the Lindqvist polyoxometalate [W6O19]2− were predicted by relativistic time‐dependent density functional theory with several combinations of density functional and basis set. Hybrid functionals with frozen‐core Slater basis sets were found to provide the best agreement with experiment while keeping reasonable computational demand. The approach was extended to [W10O32]4− and [PW12O40]3−, suggesting that it can be applied to the polyoxometalates family.

Regio- and Stereoselectivity in the Decatungstate Photocatalyzed Alkylation of Alkenes by Alkylcyclohexanes

Tetrabutylammonium decatungstate (WO) photocatalyzes radical alkylation reactions starting directly from alkanes. When using tert-butylcyclohexane and methylcyclohexane as the radical precursors, the addition to electrophilic alkenes (beta,beta-dialkylmethylenemalononitriles, acrylonitrile, methyl acrylate, methyl vinyl ketone) is regioselective and exclusively gives 3- and 4-substituted cyclohexyl adducts, with no significant functionalization of the other positions. Furthermore, when a beta,beta-disubstituted alkene is used, the reaction is stereoselective (cis stereochemistry for the 1,3-cyclohexane derivatives and trans for the 1,4 isomers). Some of the reactions have also been carried out by using benzophenone as the photocatalyst, giving the same product distribution. However, the decatungstate anion is a superior catalyst from a preparative point of view, because it is efficient at low concentrations (0.002 m, 2 mol %) and allows for a simple work up. From a mechanistic point of view, the role of both the alkyl radicals and the radical adducts has been assessed by trapping experiments in the presence of suitable additives (alpha-phenyl-N-tert-butylnitrone, PBN, and 2-methyl-2-nitrosopropane, MNP) and by EPR spectroscopic detection of the resulting nitroxides in solution. Furthermore, trapping by the nitroxide TEMPO (TEMPO = 2,2,6,6-tetramethylpiperidine N-oxide) gives O-(tert-butylcyclohexyl)hydroxylamines, again as only the 3- and the 4-substituted isomers. We conclude that the observed regioselective activation originates from the initial hydrogen abstraction step (the statistically corrected ratio for positions 3 and 4 ranges from 1.1 to 1.35 for all of the trapping products). The selectivity is mainly due to steric hinderence.

Physical Methods for Seed Invigoration: Advantages and Challenges in Seed Technology.

In the context of seed technology, the use of physical methods for increasing plant production offers advantages over conventional treatments based on chemical substances. The effects of physical invigoration treatments in seeds can be now addressed at multiple levels, ranging from morpho-structural aspects to changes in gene expression and protein or metabolite accumulation. Among the physical methods available, “magneto-priming” and irradiation with microwaves (MWs) or ionizing radiations (IRs) are the most promising pre-sowing seed treatments. “Magneto-priming” is based on the application of magnetic fields and described as an eco-friendly, cheap, non-invasive technique with proved beneficial effects on seed germination, vigor and crop yield. IRs, as γ-rays and X-rays, have been widely regarded as a powerful tool in agricultural sciences and food technology. Gamma-rays delivered at low dose have showed to enhance germination percentage and seedling establishment, acting as an actual ‘priming’ treatment. Different biological effects have been observed in seeds subjected to MWs and X-rays but knowledge about their impact as seed invigoration agent or stimulatory effects on germination need to be further extended. Ultraviolet (UV) radiations, namely UV-A and UV-C have shown to stimulate positive impacts on seed health, germination, and seedling vigor. For all mentioned physical treatments, extensive fundamental and applied research is still needed to define the optimal dose, exposition time, genotype- and environment-dependent irradiation conditions. Electron paramagnetic resonance has an enormous potential in seed technology not fully explored to monitor seed invigoration treatments and/or identifying the best suitable irradiation dose or time-point to stop the treatment. The present manuscript describes the use of physical methods for seed invigoration, while providing a critical discussion on the constraints and advantages. The future perspectives related to the use of these approaches to address the need of seed technologists, producers and trade markers will be also highlighted.