HS-SPME-GC×GC-qMS volatile metabolite profiling of Chrysolina herbacea frass and Mentha spp. leaves

Headspace solid-phase microextraction (HS-SPME) comprehensive two-dimensional (2D) gas chromatography combined with quadrupole-mass spectrometry (GC×GC-qMS) with dedicated comparative data elaboration was applied to separate chemical patterns arising from the interaction between some Mentha species and the herbivore Chrysolina herbacea, also known as the mint bug. Upon feeding on different Mentha species (Mentha spicata L., Mentha × piperita L. and Mentha longifolia L.), C. herbacea produced frass (faeces) which were characterized by a typical volatile fraction. HS-SPME GC×GC-qMS analysis of the complex volatile fraction of both mint leaf and C. herbacea frass was submitted to advanced fingerprinting analysis of 2D chromatographic data. 1,8-Cineole, found in the leaves of all the Mentha species examined, was oxidized, and C. herbacea frass yielded high rates of several hydroxy-1,8-cineoles, including 2α-hydroxy-, 3α-hydroxy-, 3β-hydroxy- and 9-hydroxy-1,8-cineole. Upon insect feeding, several unknown oxidized monoterpenes, a p-menthane diol and three unknown phenylpropanoids were also detected in the frass volatiles. In M. longifolia, the occurrence of the monoterpene piperitenone oxide was found to be toxic and associated with insect death. The results of this work show that high throughput techniques such as HS-SPME and GC×GC-qMS fingerprint analysis are ideal tools to analyze complex volatile matrices, and provide a sensitive method for the direct comparison and chemical visualization of plant and insect emitted volatile components.     

New artificial receptors from selectively functionalized calix[4]arenes

Abstract

The development of new synthetic methods for the monoalkylation of calix[4]arenes at the lower rim allows the synthesis of a new class of trihydroxamate siderophores. Three chelating hydroxamic acid units are introduced through a sequence of reactions which blocks the macrocycle in the cone conformation. The new ligands obtained form neutral 1:1 complexes (FeL) with iron (III), which are stable in EtOH/H₂O 9:1 at pH 2–7. Calix[4]arene bis-crown ethers are prepared by exploiting the selective 1,2-(proximal) functionalization of calix[4]arenes at the lower rim. These ligands are, however, less effective in complexing alkali metal cations compared with the 1,3-calix[4]arene crown-ethers which, in their partial cone structure, offer a better shielding for the complexed cations. Rigid upper rim-bridged calix[4]arenes potentially useful for the inclusion of neutral molecules are prepared by exploiting the selective 1,3-diformylation of calix[4]arene at the upper rim. Finally a new chloromethylation method for calix[4]arenes blocked in the cone conformation is described together with the synthesis of new cavitands.     

A versatile strategy for tuning the color of electrochemiluminescence using silica nanoparticles

Colour emission of core-shell silica-PEG nanoparticles in water is tuned with an electrochemically induced energy transfer approach. The lack of solubility problems, side electrochemical reactions involving donors and acceptors within the nanoparticle, and the possibility of using many classes of dyes in ECL applications confirm the validity of this strategy.     

Solvent-Free Microwave-Assisted Organic Reactions Preparation of β-Keto Esters

Microwave technique has been utilised in the preparation of β-keto esters. Two different procedures are described: transesterification of β-keto esters and ring opening of 2,2,6-trimethyl-1,3-dioxin-4-one.     

A Practical Synthesis of 1,4,7,10-Tetraaza-Cyclododecane,A Pivotal Precursor for MRI Contrast Agents

A practical preparation of the versatile macrocycle 1,4,7,10-tetraazacyclododecane (cyclen) was developed starting from cheap and easily available starting materials as ethylenediamine and glyoxal.     

Discrimination between ethanol inhibition models in a continuous alcoholic fermentation process using flocculating yeast

Discrimination between different rival models for describing the inhibitory effect of ethanol both on yeast growth and on fermentation was studied for a continuous process of alcoholic fermentation in a tower reactor with recycling of flocculating cells. Models tested include linear, parabolic, hyperbolic, exponential, and generalized nonlinear power-law types. The best expressions were identified under the criteria that all the kinetic parameters should assume acceptable values in a feasible range and should result in the best fit of the experimental data. The kinetic parameters were estimated from steady-state data of several sugar concentrations in feeding stream (S₀ = 160, 170, 180, 190, 200 g/L), constant dilution rate (D = 0.2 h^-1), recycle ratio (α = 13.6), and temperature (T = 30°C). The best model for the yeast growth was of power-law type, whereas for the product formation the best model was of linear type. These models were able to reproduce the trends of the process variables satisfactorily.     

Generation and reactivity of ketyl radicals with lignin related structures. On the importance of the ketyl pathway in the photoyellowing of lignin containing pulps and papers

[reaction: see text] Ketyl radicals with lignin related structures have been generated by means of radiation chemical and photochemical techniques. In the former studies ketyl radicals are produced by reaction of alpha-carbonyl-beta-aryl ether lignin models with the solvated electron produced by pulse radiolysis of an aqueous solution at pH 6.0. The UV-vis spectra of ketyl radicals are characterized by three main absorption bands. The shape and position of these bands slightly change when the spectra are recorded in alkaline solution (pH 11.0) being now assigned to the ketyl radical anions and a pKa = 9.5 is determined for the 1-(3,4,5-trimethoxyphenyl)-2-phenoxyethanol-1-yl radical. Decay rates of ketyl radicals are found to be dose dependent and, at low doses, lie in the range (1.7-2.7) x 10(3) s(-1). In the presence of oxygen a fast decay of the ketyl radicals is observed (k2 = 1.8-2.7 x 10(9) M(-1) s(-1)) that is accompanied by the formation of stable products, i.e., the starting ketones. In the photochemical studies ketyl radicals have been produced by charge-transfer (CT) photoactivation of the electron donor-acceptor salts of methyl viologen (MV2+) with alpha-hydroxy-alpha-phenoxymethyl-aryl acetates. This process leads to the instantaneous formation of the reduced acceptor (methyl viologen radical cation, MV+*), as is clearly shown in a laser flash photolysis experiment by the two absorption bands centered at 390 and 605 nm, and an acyloxyl radical [ArC(CO2*))(OH)CH2(OC6H5)], which undergoes a very fast decarboxylation with formation of the ketyl radicals. Steady-state photoirradiation of the CT ion pairs indicates that 1-aryl-2-phenoxyethanones are formed as primary photoproducts by oxidation of ketyl radicals by MV2+ (under argon) or by molecular oxygen. Small amounts of acetophenones are formed by further photolysis of 1-aryl-2-phenoxyethanones and not by beta-fragmentation of the ketyl radicals. The high reactivity of ketyl radicals with oxygen coupled with the low rates of beta-fragmentation of the same species have an important bearing in the context of the photoyellowing of lignin containing pulps and papers.     

The ring-opening reaction of chromenes: a photochemical mode-dependent transformation

The efficiency of the photochemical ring-opening of chromenes (or benzopyrans) depends on the vibronic transition selected by the chosen excitation wavelength. In the present work, ab initio CASPT2//CASSCF calculations are used to determine the excited-state ring-opening reaction coordinate for 2H-chromene (C) and 2,2-diethyl-2H-chromene (DEC) and provide an explanation for such an unusual mode-dependent behavior. It is shown that excited-state relaxation and decay occur via a multimodal and barrierless (or nearly barrierless) reaction coordinate. In particular, the relaxation out of the Franck-Condon involves a combination of in-plane skeletal stretching and out-of-plane modes, while the second part of the reaction coordinate is dominated exclusively by a different out-of-plane mode. Population of this last mode is shown to be preparatory with respect to both C-O bond breaking and decay via an S(1)/S(0) conical intersection. The observed mode-dependent ring-opening efficiency is explained by showing that the vibrational mode corresponding to the most efficient vibronic transition has the largest projection onto the out-of-plane mode of the reaction coordinate. To support the computationally derived mechanism, we provide experimental evidence that the photochemical ring-opening reaction of 2,2-dimethyl-7,8-benzo(2H)chromene, that similarly to DEC exhibits a mode-dependent photoreaction, has a low ( approximately 1 kcal mol(-1)) activation energy barrier.