Determination of benzotrifluoride derivative compounds in groundwater

Two simple analytical methods for the simultaneous determination and quantification of benzotrifluoride and eight chlorinated, amino and nitro benzotrifluoride derivatives in groundwater are proposed. Benzotrifluoride, 4-chlorobenzotrifluoride, 2,4-dichlorobenzotrifluoride and 3,4-dichlorobenzotrifluoride, were extracted by Purge-and-Trap on the basis of their volatile properties, while 3-aminobenzotrifluoride, 4-nitrobenzotrifluoride, 3-amino-4-chlorobenzotrifluoride, 3-nitro-4-chlorobenzotrifluoride and 4-chloro-3,5-dinitrobenzotrifluoride extractions were done with an automated SPE system. The analytical separations and detections were performed with two different GC systems, both equipped with single quadrupole mass spectrometer as detector. The LOD ranges for the two methods were 0.002–0.005 μg L⁻¹ and 0.01–0.07 μg L⁻¹, respectively. Both extraction methods were developed using spiked Milli-Q water and were then demonstrated with groundwater samples collected during autumn 2008. The areas of groundwater collection were polluted due to an episode of improper industrial soil disposal and consequent leakage of aliphatic and aromatic, fluorinated chemicals into the groundwater. This work eventually revealed the presence of several benzotrifluoride compounds most of them, like dichloro- and amino-derivatives, never been reported as environmental contaminants.     

Evaluation of different polymerase chain reaction methods for the identification of Vibrio parahaemolyticus strains isolated by cultural methods

Control of contamination by Vibrio parahaemolyticus in fishery products is often hampered by the lack of standardized methods and by the uncertainty associated with biochemical identification of the isolates. In this study, 5 polymerase chain reaction (PCR) methods for the identification of V. parahaemolyticus to the species level were evaluated by using 25 Vibrio reference strains and 163 isolates from fishery products, environmental sources, and clinical samples. Sequence targets of the methods were toxR, gyrB, and tlh genes (tested with 2 protocols), and the fragment pR72H. Isolate identification was confirmed by sequencing of the 16S rRNA gene and by PCR protocols for the identification of other Vibrio species. The PCR assay targeting the toxR gene achieved the highest performance (100% inclusivity and exclusivity). The 2 PCR protocols based on tlh gene detection, although showing the same inclusivity (100%), differed in the exclusivity (50 and 91%, respectively). Finally, the results provided by the PCR assays targeting the gyrB gene and pR72H fragment were less reliable and, in some cases, difficult to assess. According to the results of this study, the characteristics of accuracy expressed by the toxR identification method make it a suitable candidate as a reference method for the molecular identification of V. parahaemolyticus strains.     

Synthesis, structure and conformation of partially-modified retro- and retro-inverso psi[NHCH(CF3)]Gly peptides

Partially modified retro- (PMR) and retro-inverso (PMRI) psi[NHCH(CF(3))]Gly peptides, a conceptually new class of peptidomimetics, have been synthesized in wide structural diversity and variable length by aza-Michael reaction of enantiomerically pure alpha-amino esters and peptides with enantiomerically and geometrically pure N-4,4,4-trifluorocrotonoyl-oxazolidin-2-ones. The factors underlying the observed moderate to good diastereocontrol have been investigated. The conformations of model PMR-psi[NHCH(CF(3))]Gly tripeptides have been studied in solution by (1)H NMR spectroscopy supported by MD calculations, as well as in the solid-state by X-ray diffraction. Remarkable stability of turn-like conformations, comparable to that of parent malonyl-based retropeptides, was evidenced, as a likely consequence of two main factors: 1) severe torsional restrictions about sp(3) bonds in the [CO-CH(2)-CH(CF(3))-NH-CH(R)-CO] module, which is biased by the stereoelectronically demanding CF(3) group and the R side chain; 2) formation of nine-membered intramolecularly hydrogen-bonded rings, which have been clearly detected both in CHCl(3) solution and in some crystal structures. The former factor seems to be more important, as turn-like conformations were found in the solid-state even in the absence of intramolecular hydrogen bonding. The relative configuration of the -C*H(CF(3))NHC*H(R)- stereogenic centers has a major effect on the stability of the turn-like conformation, which seems to require a syn stereochemistry. X-ray diffraction and ab initio computational studies showed that the [-CH(CF(3))NH-] group can be seen as a sort of hybrid between a peptide bond mimic and a proteolytic transition state analogue, as it combines some of the properties of a peptidyl -CONH- group (low NH basicity, CH(CF(3))-NH-CH backbone angle close to 120 degrees, C-CF(3) bond substantially isopolar with the C=O) with some others of the tetrahedral intermediate [-C(OX)(O(-))NH-] involved in the protease-mediated hydrolysis reaction of a peptide bond (high electron density on the CF(3) group, tetrahedral backbone carbon).     

Enzyme-Mediated Preparation of (+)- and (–)-cis-α-Irone and (+)- and (–)-trans-α-Irone

The preparation of (−)- and (+)-trans-α-irone ( 1a and 1b , resp.) and of (+)- and (−)-cis-α-irone ( 1c and 1d , resp.) from commercially available Irone alpha ^® is reported. The relevant step in the synthetic sequence is the initial chromatographic separation of crystalline (±)-4,5-epoxy-4,5-dihydro-cis-α-irone ((±)- 5 ) from oily (±)-4,5-epoxy-4,5-dihydro-trans-α-irone ((±)- 4 ). The latter was subsequently converted, after NaBH₄ reduction, into the crystalline 3,5-dinitrobenzoate ester (±)- 8 , thus allowing a complete separation of the two corresponding diastereoisomeric alcohol derivatives. Suitable enantiomerically pure precursors of the desired products 1a – d were obtained by kinetic resolution of the racemic allylic alcohols derived from (±)- 5 and (±)- 8 , mediated by lipase PS (Amano). The last steps consisted of MnO₂ oxidation and removal of the epoxy moiety with Me₃SiCl/NaI in MeCN. External panel olfactory evaluation showed that (−)-cis-α-irone ( 1d ) has the finest and most distinct `orris butter' character.     

First total synthesis of (±)-floribundane B: An approach based on Johnson-Claisen rearrangement of a Morita-Baylis-Hillman adduct

The first total synthesis of (±)-floribundane B is reported. Johnson-Claisen rearrangement of a Morita-Baylis-Hillman adduct assembled all of the stereochemical features of this secoiridoid. The formal synthesis of (±)-oleocanthal and the synthesis of a chemical constituent of olive press juice is also reported.     

Study of non-covalent interactions of luotonin A derivatives and the DNA minor groove as a first step in the study of their analytical potential as DNA probes

The interaction between DNA and several newly synthesized derivatives of the natural anticancer compound luotonin A has been studied. The results from our work reveal an effective and selective alkaloid/double-stranded DNA (ds-DNA) interaction. In the presence of increasing amounts of ds-DNA, a noticeable fluorescence quenching of the luotonin A derivatives under study was observed. However, this effect did not take place when single-stranded DNA (ss-DNA) was employed. The association constant alkaloids/ds-DNA was calculated by quantitation of such a quenching effect. The influence of other quenchers, namely Co²⁺ and Br⁻ on the native fluorescence of luotonin A and derivatives was also studied, and a remarkable quenching effect was observed for both ions. We have also investigated how by binding DNA the alkaloids could get protected from the external Co²⁺ and Br⁻ quenchers. The Stern–Volmer constants (K _SV) for Co²⁺ and Br⁻ quenching effect on the studied alkaloids were considerably reduced (10–50%) after incubation of the compounds in the presence of DNA with regard to the K _SV values in absence of DNA. An increase in the fluorescence anisotropy values of luotonins was also produced only in the presence of ds-DNA but not in the case of ss-DNA. To better characterize the nature of that interaction, viscosimetry assays and ethidium bromide displacement studies were conducted. With regard to DNA reference solutions, the viscosity of solutions containing DNA and luotonin A derivatives was reduced or not significantly increased. It was also observed that the studied compounds were unable to displace the intercalating agent ethidium bromide. All of these results, together with the obtained association constants values (K _ass = 2.2 × 10² – 1.3 × 10³), support that neither covalent nor intercalating interactions luotonin A derivatives/ds-DNA are produced, leading to the conclusion that these alkaloids bind ds-DNA through the minor groove. The specific changes in the fluorescence behavior of luotonin A and derivatives distinguishing between ss-DNA and ds-DNA binding, lead us to propose these compounds as attractive turn-off probes to detect DNA hybridization.     

Spirofungins A and B: a reassignment of Kiyota’s spiroketals

In this letter, we present our results obtained in attempts to synthesize the initially proposed structure of the spiroketal core of spirofungin B. Based on these results, we propose a reassignment for the structures of the spiroketals obtained by Kiyota’s group.     

Info-quantifiers’ map-characterization revisited

We highlight the potentiality of a special Information Theory (IT) approach in order to unravel the intricacies of nonlinear dynamics, the methodology being illustrated with reference to the logistic map. A rather surprising dynamic feature→plane-topography map becomes available.