Fluorescent and Electrochemical Sensing of Polyphosphate Nucleotides by Ferrocene Functionalised with Two ZnII(TACN)(pyrene) Complexes

The [Fc? bis{Zn^II(TACN)(Py)}] complex, comprising two Zn^II(TACN) ligands (Fc=ferrocene; Py=pyrene; TACN=1,4,7‐triazacyclononane) bearing fluorescent pyrene chromophores linked by an electrochemically active ferrocene molecule has been synthesised in high yield through a multistep procedure. In the absence of the polyphosphate guest molecules, very weak excimer emission was observed, indicating that the two pyrene‐bearing Zn^II(TACN) units are arranged in a trans‐like configuration with respect to the ferrocene bridging unit. Binding of a variety of polyphosphate anionic guests (PPi and nucleotides di‐ and triphosphate) promotes the interaction between pyrene units and results in an enhancement in excimer emission. Investigations of phosphate binding by ³¹P NMR spectroscopy, fluorescence and electrochemical techniques confirmed a 1:1 stoichiometry for the binding of PPi and nucleotide polyphosphate anions to the bis(Zn^II(TACN)) moiety of [Fc? bis{Zn^II(TACN)(Py)}] and indicated that binding induces a trans to cis configuration rearrangement of the bis(Zn^II(TACN)) complexes that is responsible for the enhancement of the pyrene excimer emission. Pyrophosphate was concluded to have the strongest affinity to [Fc? bis{Zn^II(TACN)(Py)}] among the anions tested based on a six‐fold fluorescence enhancement and 0.1 V negative shift in the potential of the ferrocene/ferrocenium couple. The binding constant for a variety of polyphosphate anions was determined from the change in the intensity of pyrene excimer emission with polyphosphate concentration, measured at 475 nm in CH₃CN/Tris‐HCl (1:9) buffer solution (10.0 mM , pH 7.4). These measurements confirmed that pyrophosphate binds more strongly (K_b=(4.45±0.41)×10⁶ M ^?1) than the other nucleotide di‐ and triphosphates (K_b=1–50×10⁵ M ^?1) tested.     

Lignin Chemistry: Biosynthetic Study and Structural Characterisation of Coniferyl Alcohol Oligomers Formed In Vitro in a Micellar Environment

Model coniferyl alcohol lignin (the so‐called dehydrogenative polymerisate, DHP) was produced in water under homogeneous conditions guaranteed by the presence of a micellised cationic surfactant. A complete study of the activity of the enzymatic system peroxidase/H₂O₂ under our reaction conditions was reported and all the reaction products up to the pentamer were characterised by ¹H NMR spectroscopy and ESI mass spectrometry. Our system, and the molecules that have been generated in it, represent a closer mimicry of the natural microenvironment since an enzyme, under micellar conditions, reproduces the cell system better than in buffer alone. On the basis of the oligomers structures a new biosynthetic perspective was proposed that focused attention on a coniferyl alcohol dimeric quinone methide as the key intermediate of the reaction. A formal, strictly alternate sequence of a radical and an ionic step underlines the reaction, thus generating ordered oligolignols structures. Alternatively to other model lignins, our olignols present a lower degree of radical coupling between oligomeric units. This offers a closer biosynthetic situation to the observation of a low rate of radical generation in the cell wall.     

A B3LYP investigation of the conformational and environmental sensitivity of carbon�Cdeuterium frequencies of aryl-perdeuterated phenylalanine and tryptophan

Carbon?Cdeuterium labeled amino acids can serve as sensitive probes for biophysical characterization. Although multiple research groups have used infrared spectroscopy in conjunction with alkyl backbone or side-chain deuterated amino acids for the biophysical characterization of conformational and/or environmental changes, it was not entirely clear to the authors that perdeuterated aryl rings would demonstrate a similar sensitivity toward conformational or environmental changes. In an effort to evaluate the sensitivity of aryl carbon?Cdeuterium (C?CD) IR frequencies, a B3LYP investigation of the sensitivity of aryl C?CD frequencies toward conformational and environmental changes was conducted for phenylalanine (Phe) and tryptophan (Trp). To compensate for the low molar absorptivity of C?CD frequencies, perdeuterated aryl rings were investigated, which are commercially available and can be readily compared to experimental data. B3LYP results suggest that aryl-deuterated Phe and Trp will exhibit moderate sensitivities toward conformational and environmental changes with frequency shifts upward of 13 and 26?cm^?1 for Phe and Trp, respectively. B3LYP predicts that conformational sensitivity arises from dipole changes and not orbital alignment changes. In an effort to mimic what might be observed experimentally, simulated IR spectra were created and show absorption band changes with conformational and environmental changes, which indicate that IR characterization of perdeuterated aryl rings in amino acids could serve as a biophysical tool.     

Application of the Tris(acetylacetonato)iron(III)/(II) Redox Couple in p‐Type Dye‐Sensitized Solar Cells

An electrolyte based on the tris(acetylacetonato)iron(III)/(II) redox couple ([Fe(acac)₃]^0/1?) was developed for p‐type dye‐sensitized solar cells (DSSCs). Introduction of a NiO blocking layer on the working electrode and the use of chenodeoxycholic acid in the electrolyte enhanced device performance by improving the photocurrent. Devices containing [Fe(acac)₃]^0/1? and a perylene–thiophene–triphenylamine sensitizer (PMI–6T–TPA) have the highest reported short‐circuit current (J_SC=7.65 mA cm^?2), and energy conversion efficiency (2.51 %) for p‐type DSSCs coupled with a fill factor of 0.51 and an open‐circuit voltage V_OC=645 mV. Measurement of the kinetics of dye regeneration by the redox mediator revealed that the process is diffusion limited as the dye‐regeneration rate constant (1.7×10⁸ M ^?1 s^?1) is very close to the maximum theoretical rate constant of 3.3×10⁸ M ^?1 s^?1. Consequently, a very high dye‐regeneration yield (>99 %) could be calculated for these devices.     

Fungistatic activity of Zanthoxylum rhoifolium Lam. bark extracts against fungal plant pathogens and investigation on mechanism of action in Botrytis cinerea

Plant-derived compounds are emerging as an alternative choice to synthetic fungicides. Chloroform–methanol extract, obtained from the bark of Zanthoxylum rhoifolium, a member of Rutaceae, showed a fungistatic effect on Botrytis cinerea, Sclerotinia sclerotiorum, Alternaria alternata, Colletotrichum gloeosporioides and Clonostachys rosea, when added to the growth medium at different concentrations. A fraction obtained by gel separation and containing the alkaloid O-Methylcapaurine showed significant fungistatic effect against B. cinerea and S. sclerotiorum, two of the most destructive phytopathogenic fungi. The underlying mechanism of such an inhibition was further investigated in B. cinerea, a fungus highly prone to develop fungicide resistance, by analysing the expression levels of a set of genes (BcatrB, P450, CYP51 and TOR). O-Methylcapaurine inhibited the expression of all the analysed genes. In particular, the expression of BcatrB gene, encoding a membrane drug transporter involved in the resistance to a wide range of xenobiotic compounds, was strongly inhibited (91%).     

On a stability condition for elastic plastic structures

Summary The paper considers discrete or discretized elastic-plastic structures subjected to conservative external forces and given imposed strains. Material flow laws are assumed to be associated; the plasticity condition and the hardening rule are piecewise linearized.For a given equilibrium configuration of such systems, a necessary and sufficient condition for the positivity of second order plastic work is proved. It is shown that this work is positive if and only if a certain matrix is positive definite. Connections with the kinematic stability of the configuration are discussed.The interest of the statement is two-fold. Firstly it provides a deeper understanding on the assumptions on which some techniques for elastic-plastic analysis are based. Secondly, it leads to operative procedures for stability analysis which may prove efficient in some cases, as it is illustrated with reference to the evaluation of the collapse load for elastic-perfectly plastic frames in the presence of second order geometrical effects.

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Sommario Si considerano strutture elasto-plastiche discrete e discretizzate, soggette a carichi esterni di tipo conservativo e a distorsioni assegnate. Si suppone che il legame costitutivo del materiale sia associato e la condizione di plasticità e le leggi di incrudimento vengano linearizzate a tratti.Per un'assegnata configurazione di equilibrio di un sistema di questo tipo, si dimostra una condizione necessaria e sufficiente per la positività del lavoro plastico del second'ordine; si mostra che esso è positivo se e solo se una certa matrice risulta positiva definita. Le implicazioni di questo evento con la stabilità della configurazione sono brevemente discusse.L'asserto dimostrato ha un duplice interesse. In primo luogo approfondisce il significato di alcune ipotesi alla base di certe tecniche numeriche per l'analisi elasto-plastica; in secondo luogo porta a procedimenti operativi per l'analisi della stabilità che possono rivelarsi utili in alcuni casi, come è illustrato con riferimento alla determinazione del carico di collasso di telai elasto-plastici in presenza di effetti del II ordine.

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Research sponsored by the C.N.R.     

Volatile fingerprints of artemisinin-rich Artemisia annua cultivars by headspace solid-phase microextraction gas chromatography/ mass spectrometry

The cultivar Anamed (A3) is a hybrid of Artemisia annua with a high content of the secondary metabolite artemisinin, a well-known antimalarial drug. Here we report for the first time the volatile profile of fresh leaves of this hybrid in comparison with that of Artemisia annua L. wild-type species. Evaluation and comparison of the volatile profiles of A. annua genotypes with different content in artemisinin were carried out by headspace solid-phase microextraction (HS-SPME) coupled with gas chromatography/mass spectrometry (GC/MS) that was performed on fresh leaves of the plants under investigation using a polydimethylsiloxane (PDMS) fiber. The chromatograms obtained from hybrids with a high content of artemisinin (A. annua cv. Anamed A3 and A. annua cv. Artemis F2) reveal the total absence of artemisia ketone, one of the major and characteristic compounds of the wild-type A. annua L., along with a significantly lower variety of volatile compounds. In conclusion, HS-SPME coupled with GC/MS is a very useful, non-destructive and efficient method to describe the volatile pattern of Artemisia annua cultivars. It represents a rapid screening method for the evaluation of volatile biomarkers like artemisia ketone, whose absence is typical of artemisinin-rich A. annua cultivars.