Determination of hydroxycarbamates in aqueous matrices by direct derivatization and GC-MS analysis in chemical ionization mode

A rapid and effective procedure, developed for the determination of polar compounds in water, has been applied to hydroxycarbamates. In few minutes, it is possible to perform a catalyzed derivatization of such compounds directly in the aqueous medium, using n-hexyl chloroformate. Extraction with n-hexane and injection into a benchtop GC-MS system are the only two further steps to complete the analysis. Chemical ionization proved to be more effective than electron impact to produce valuable mass spectra in terms of selectivity and sensitivity. Linear quantitative responses were demonstrated over a two-order-of-magnitude range. The minimum detectable concentration was 3 ppb for acetohydroxamic acid and 10 ppb for hydroxyurethane, obtained from Po river water samples spiked with the two hydroxycarbamate standards.     

Enthalpic determinations of aliphatic ester-solvent systems with correlations

Calorimetric measurements were carried out on ester-solvent systems where the esters were H(CH₂)_xCOO(CH₂)_yH, with x and y varying from 1 to 5, and the solvents were n-hexane and 1,2-dichloroethane. Calculation of the enthalpies of cavity formation enabled the enthalpies of interaction to be determined. Both enthalpies correlated with number of carbon atoms N, equal to x+y in the esters, giving for 1,2-dichloroethane

Electronic and Steric Influence of Axial and Equatorial Ligands in Vitamin B12 Model Complexes Derived from Cobaloxime: Electrochemical and 59Co-NMR Studies

In four series of strictly related organocobalt complexes, derived from cobaloximes by replacement of the O…H…O with O…-BF₂…O and/or (CH₂)₃ groups, the trends of ⁵⁹Co-NMR shielding and electrochemical data are discussed. A largely parallel behaviour of the plots of E_1/2(I) values for the first Co(III)/Co(II) electron transfer vs. the ₅₉Co chemical shifts reflects the similar sensitivity of the two parameters to a change in electron affinity of the central metal ion due to a variation of the organic group R. E_1/2(II) values for the second Co(II)/CO(I) electron transfer are less sensitive to the change of R, but the trend of the plot vs. δ(₅₉Co) is still parallel in the four series. Consistent deviations from a roughly linear dependence of E_1/2(I) on pK_a of the hydrocarbon acid corresponding to R, on Taft constant s?_* and on ⁵⁹Co shielding are noticed for the isopropyl derivatives and attributed to a steric effect. This was confirmed in a series of R? Co(DMG)pyridine complexes in which ⁵⁹Co shielding decreases steadily with increasing steric parameter E_s (Taft) of the alkyl group. There is experimental evidence from X-ray data that δ(⁵⁹Co) decreases with an increase of the Co? C bond length, illustrating steric hindrance in alkyl coordination to be responsible for the decreased shielding of the ⁵⁹Co nucleus. The relative displacements of the graphic displays for the different series reflect the effect of changes in electron affinity of the redox center, due to the equatorial ligand, which, in turn, is caused by variations in the electron-withdrawing power due to the introduction of the BF₂ group and by the change from ?2 to ?1 valence of the (CH₂)₃-capped ligands.     

Metal Catalyzed Polymerization: From Stereoregular Poly(α-olefins) to Tailor-Made Biodegradable/Biorenewable Polymers and Copolymers

Metal catalyzed polymerizations are among the most important chemical reactions, accounting for the production of about 400 million tons per year of polymeric materials, 50 % of which are polyolefins. The CIRCC research units at the University of Salerno, founded by the late Professor Adolfo Zambelli, a coworker of Giulio Natta and a pioneer in the studies of stereospecific polymerization catalysts, has a consolidated expertise in this field. Although often considered a “mature” area of research, olefin polymerization catalysis continues to drive great interest of both industrial and academic scientists. On the other hand, strong political and economic pressure toward the development of “green” and possibly biodegradable alternatives to olefin-based polymers stimulated our group to direct increasing research efforts in the area of sustainable polymers. In this perspective, we focus on the most recent work from the CIRCC research units involved in homogeneous catalysis for polymerization of a variety of monomers, with the aim to address how the concepts and the expertise developed for olefin polymerization can be applied to the development of different metal-catalyzed polymerizations and copolymerizations. Of course, although the results are discussed in the frame of the most important literature contributions, a comprehensive review of such a wide and diversified topic is out of the scope of the paper. References to reviews covering the different types of metal catalyzed polymerizations are provided in each chapter.     

FLUORESCENCE QUANTUM YIELDS OF 124-kDa PHYTOCHROME FROM OAT UPON EXCITATION WITHIN DIFFERENT ABSORPTION BANDS

Abstract— A fluorescence quantum yield (emission at650–850 nm) of π= (2.3 ± 0.3)10⁻³ was measured for the red-absorbing form (Pr) of 124-kDa phytochrome from etiolated oat seedlings ( Avena sativa ) upon excitation in the Soret band at Λ^exc= 380 nm. The small difference between this value and the previously determined quantum yield with Λ^exc= 640 nm, π= (3.5 ± 0.4)10⁻³is attributed to a blue-absorbing emitter responsible for the "anomalous" or "blue" emission of the chromoprotein in the region from ca. 400 to 550 nm. The absorption of Pr at 380 nm is consequently somewhat lower than that measured directly from the spectrum. Processes from upper excited states of the Pr phytochromobilin-derived chromophore other than rapid relaxation to the emitting state are not important. A quantum yield of Φ ' 1.2 times 10⁻³ is estimated for the blue fluorescence. The proportion of the blue emitters relative to Pr appears to be relatively high.     

Polar effects in free-radical reactions. New synthetic developments in the functionalization of heteroaromatic bases by nucleophilic radicals

The synthetic interest of the direct substitution of protonated heteroaromatic bases by nucleophilic carbon-centered radicals is furtheron developed by the following new achievements: i) utilization of the redoc system

in several solvents; ii) utilization of benzoyl peroxide in alcohols; iii) carbamoylation by HCONH₂ and H₂O₂ in the presence of catalytic amounts of Fe(II). These systems allow to obtain either substitution till now tried without success or reactions of industrial interest. Polar effects play a dominant role in determining reactivity, selectivity and synthetic applications; in particular the role of the strongly nucleophilic intermediate radicals of pyridinyl type in the rearomatization step is emphasized.     

Structural flexibility and role of vicinal 2-thienyl rings in 2,3-dicyano-5,6-di(2-thienyl)-1,4-pyrazine, [(CN)2Th2Pyz], its palladium(II) complex [(CN)2Th2Pyz(PdCl2)2], and the related pentametallic pyrazinoporphyrazines [(PdCl2)4Th8TPyzPzM] (M = Mg(II)(H2O), Zn(II))

The solid state and solution structure of 2,3-dicyano-5,6-di(2-thienyl)-1,4-pyrazine, [(CN)(2)Th(2)Pyz], and its Pd(II) derivative, [(CN)(2)Th(2)Pyz(PdCl(2))(2)]·H(2)O, formed by reaction of [(CN)(2)Th(2)Pyz] with [(C(6)H(5)CN)(2)PdCl(2)] were characterized by X-ray, UV-visible, (1)H and (13)C NMR, and extended X-ray absorption fine structure (EXAFS) spectral measurements. The X-ray crystal structure of [(CN)(2)Th(2)Pyz] shows the presence of one thienyl ring positioned orthogonal to the rest of the molecule, with the two vicinal thienyl rings lying orthogonal to each other in a rare arrangement. NMR studies of [(CN)(2)Th(2)Pyz] in the solid state and in solutions of dimethylformamide or dimethyl sulfoxide confirm a nonequivalence of the thienyl rings in the solid state and also in solution. EXAFS results indicate that two distinct Pd(II) coordination sites are formed at the di(2-thienyl)pyrazino moiety of [(CN)(2)Th(2)Pyz(PdCl(2))(2)]·H(2)O, with identical Pd-N(pyz) (2.03(3) ?) and Pd-Cl (2.36(3) ?) bond lengths but with different Pd-S1 (2.25(4) ?) and Pd-S2 (3.21(5) ?) bond distances in an overall asymmetric molecular framework. Density functional theory (DFT) and time-dependent DFT (TDDFT) theoretical studies also provide information about the structure and spectral behavior of the precursor and its metalated Pd(II) derivative. (1)H/(13)C NMR and UV-visible spectral measurements were also carried out on two heteropentametallic porphyrazine macrocycles which were prepared by a reaction of PdCl(2) with [Th(8)TPyzPzM] where Th(8)TPyzPz = tetrakis-2,3-[5,6-di-(2-thienyl)-pyrazino]porphyrazinato dianion and M = Mg(II)(H(2)O) or Zn(II). Spectroscopic data on the newly synthesized [(PdCl(2))(4)Th(8)TPyzPzM] compounds suggest that the binding of PdCl(2) involves coordination sites of the type S(2(th))PdCl(2) with the two thienyl rings of each di(2-thienyl)pyrazino fragment bound to Pd(II) in an equivalent manner ("th-th" coordination). This is similar to what was found for the corresponding octapyridinated analogues ("py-py" coordination).     

Compatible blends of biorelated polyesters through catalytic transesterification in the melt

The transesterification during the melt blending of polylactide (PLA) and poly(butylene adipate-co-terephthalate) (PBAT) was investigated in presence of Ti(OBu)₄ as a catalyst. Both the effect of catalyst concentration and reaction duration was considered. The process was studied by analyzing the molecular weight of the polyesters by size exclusion chromatography (SEC). The rheological, thermal and morphological properties of the blends were investigated by melt flow rate, DSC and SEM analyses, respectively. Evidences about the formation of PBAT-PLA copolymers were obtained and discussed. The tensile properties of compression moulded films were also determined and correlated to the structure and phase morphology development of the blends. In particular, the use of Ti(OBu)₄ resulted in the improvement of compatibility. Moreover, the decrease in stiffness and the increase in elongation at break with the increase of mixing time was observed, in good agreement with the improved compatibility of the modified blend.     

Potent 5-nitrofuran derivatives inhibitors of Trypanosoma cruzi growth: electrochemical, spectroscopic and biological studies

Cyclic voltammetry and electron spin resonance techniques were used in the investigation of several potential antiprotozoal containing thiosemicarbazone and carbamate nitrofurans. In the electrochemical behaviour, a self-protonation process involving the nitro group was observed. The reactivity of the nitro anion radical for these derivatives with glutathione, a biological relevant thiol, was also studied in means of cyclic voltammetry. These studies demonstrated that glutathione could react with radical species from 5-nitrofuryl system. Furthermore, from the voltammetric results, some parameters of biological significance as E(7)(1) (indicative of the biological nitro anion radical formation), and [Formula: see text] (thermodynamic indicator the of oxygen redox cycling) have been calculated. We also evaluated the stability of the nitro anion radical in terms of the dimerization constant (k(d)). The nitrofuran-free radicals from cyclic voltammetry were characterized by electron spin resonance. A clear dependence between both the thiosemicarbazone or carbamate substructure and the length of the linker, furyl- or furylpropenyl-spacer, and the delocalization of the unpaired electron was observed. Through of biological assays we obtained important parameters that account for the selective anti-trypanosomal activity of these derivatives. The trypomastigote viability study showed that all derivatives are as active as in the epimastigote form of the parasite in a doses dependent manner.