The first pure LambdaHT rotamer of a complex with a cis-[metal(nucleotide)2] unit: a cis-[Pt(amine)2(nucleotide)2] LambdaHT rotamer with unique molecular structural features

cis-[PtA2(nucleotide)2] complexes (A2 stands for two amines or a diamine) have been extensively investigated as model compounds for key cisplatin-DNA adducts. All cis-[metal(nucleotide/nucleoside)2] complexes with guanine and related purines characterized in the solid state thus far have the DeltaHT conformation (head-to-tail orientation of the two bases and right-handed chirality). In sharp contrast, the LambdaHT conformation (left-handed chirality) dominates in acidic and neutral aqueous solutions of cis-[PtA2(5'-GMP)2] complexes. Molecular models and solution experiments indicate that the LambdaHT conformer is stabilized by 5'-phosphate/N1H hydrogen-bond interactions between cis nucleotides with the normal anti conformation. However, this evidence, while compelling, is indirect. At last, conditions have been defined to allow crystallization of this elusive conformer. The structure obtained reveals three unique features not present in all other cis-[PtA2(nucleotide)2] solid-state structures: a LambdaHT conformation, very strong hydrogen-bond interactions between the phosphate and N1H of cis nucleotides, and a very small dihedral angle between the planes of the two guanines lying nearly perpendicular to the coordination plane. These new results indicate that, because there are no local base-base repulsions precluding the LambdaHT conformer, global forces rather than local interactions account for the predominance of the DeltaHT conformer over the LambdaHT conformer in the solid state and in both inter- and intrastrand HT crosslinks of oligonucleotides and DNA.     

Ionization and tautomerization of 2-nitrocyclohexanone in aqueous solution

The keto-enol tautomerism of 2-nitrocyclohexanone (2-NCH) was studied in aqueous solution under different experimental conditions. Ketonization rate constants were measured spectrophotometrically at 25 degrees C at an ionic strength of 0.4 mol dm-3 (NaCl) in diluted hydrochloric acid, in diluted sodium hydroxide, and in several buffers by using NaHSO3 as the scavenger of the keto form. A value of pK(a)(EH) = 4.78 for the enol form was obtained from the rate-pH profile of the reaction. A value of pK(a)(KH) = 5.97 for the keto form was directly obtained from the UV-vis spectra of 2-NCH recorded at different pHs. The equilibrium constant for the keto-enol tautomerism, pK(T) = -log([enol]/[ketone]) = 1.19, was obtained by combining the two pKa values (pK(T) = pK(a)(KH) - pK(a)(EH)). A comparison of these results with the corresponding values (Keefe, J. R.; Kresge, A. J. In The Chemistry of Enols; Rappoport, Z., Ed.; Wiley & Sons: New York, 1990; pp 399-480) for cyclohexanone shows the dramatic effects of an alpha-nitro substituent on the keto-enol acidities and the tautomerization constant of alicyclic ketones. Rates and equilibria were discussed in the light of the Br?nsted equation, the principle of nonperfect synchronization, and the Marcus theory. It turns out that, on passing from nitroalkanes to nitroketones, the resonance contribution to pKa and deprotonation rate decreases, being overwhelmed by steric and inductive effects.     

Chemical and Mechanical Characterization of Licorice Root and Palm Leaf Waste Incorporated into Poly(urethane-acrylate) (PUA)

A poly(urethane-acrylate) polymer (PUA) was synthesized, and a sufficiently high molecular weight starting from urethane-acrylate oligomer (UAO) was obtained. PUA was then loaded with two types of powdered ligno-cellulosic waste, namely from licorice root and palm leaf, in amounts of 1, 5 and 10%, and the obtained composites were chemically and mechanically characterized. FTIR analysis of final PUA synthesized used for the composite production confirmed the new bonds formed during the polymerization process. The degradation temperatures of the two types of waste used were in line with what observed in most common natural fibers with an onset at 270 °C for licorice waste, and at 290 °C for palm leaf one. The former was more abundant in cellulose (44% vs. 12% lignin), whilst the latter was richer in lignin (30% vs. 26% cellulose). In the composites, only a limited reduction of degradation temperature was observed for palm leaf waste addition and some dispersion issues are observed for licorice root, leading to fluctuating results. Tensile performance of the composites indicates some reduction with respect to the pure polymer in terms of tensile strength, though stabilizing between data with 5 and 10% filler. In contrast, Shore A hardness of both composites slightly increases with higher filler content, while in stiffness-driven applications licorice-based composites showed potential due to an increase up to 50% compared to neat PUA. In general terms, the fracture surfaces tend to become rougher with filler introduction, which indicates the need for optimizing interfacial adhesion.     

A New Dimeric Copper(II) Complex of Hexyl Bis(pyrazolyl)acetate Ligand as an Efficient Catalyst for Allylic Oxidations

A new dimeric copper(II) bromide complex, [Cu(L^OHex)Br(μ-Br)]₂ (1), was prepared by a reaction of CuBr₂ with the hexyl bis(pyrazol-1-yl)acetate ligand (L^OHex) in acetonitrile solution and fully characterized in the solid state and in solution. The crystal structure of 1 was also determined: the complex is interlinked by two bridging bromide ligands and possesses terminal bromide ligands on each copper atom. The two pyrazolyl ligands in 1 coordinate with the nitrogen atoms to complete the Cu coordination sphere, resulting in a five-coordinated geometry—away from idealized trigonal bipyramidal and square pyramidal geometries—which can better be described as distorted square pyramidal, as measured by the τ and χ structural parameters. The pendant hexyloxy chain is disordered over two arrangements, with final site occupancies refined to 0.705 and 0.295. The newly synthesized complex was evaluated as a catalyst in copper-catalyzed C–H oxidation for allylic functionalization through a Kharasch–Sosnovsky reaction without any external reducing agent. Using 0.5 mol% of this catalyst, and tert-butyl peroxybenzoate (Luperox) as an oxidant, allylic benzoates were obtained with up to 90% yield. The general reaction time was only slightly decreased to 24 h but a very significant decrease in the alkene:Luperox ratio to 3:1 was achieved. These factors show relevant improvements with respect to classical Kharasch–Sosnovsky reactions in terms of rate and amount of reagents. The present study highlights the potential of copper(II) complexes containing functionalized bis(pyrazol-1-yl)acetate ligands as efficient catalysts for allylic oxidations.     

Content and Nutritional Evaluation of Zinc in PDO and Traditional Italian Cheeses

Zinc is an essential mineral which plays a key role in several important biological processes in the human body. The determination of its level in food matrices can contribute to the food quality characterization and to the adequacy of the diet. Animal food products generally have a higher zinc content compared to vegetables. Among them, dairy products consumption can provide a great contribution to the zinc reference intakes. In this study, different Italian cheeses (38 Protected Denomination of Origin and 9 Traditional) were evaluated for their zinc content. Cow cheeses generally showed the highest zinc content (1.83–7.75 mg/100 g cheese), followed by sheep cheeses (1.34–3.69 mg/100 g), and cheeses from mixed milk (0.39–4.54 mg/100 g). The only cheese from buffalo milk (Mozzarella di Bufala Campana PDO) showed a zinc content of 2.14 mg/100 g. The great variability in the zinc content observed among the samples is the result of the influence of several factors, such as the feeding system, the species (cow, sheep, goat, and buffalo), and the cheese-making. Most of the samples resulted in a great contribution (>10%) to the zinc Daily Reference Intake set by EU (10 mg/day), with only two samples contributing to less than 4%.     

Proteomic strategies for the identification of proteinaceous binders in paintings

The identification of proteinaceous components in paintings remains a challenging task for several reasons. In addition to the minute amount of sample available, complex and variable chemical composition of the paints themselves, possible simultaneous presence of several binders and contaminants, and degradation of the original materials due to aging and pollution are complicating factors. We proposed proteomic strategies for the identification of proteins in binders of paintings that can be adapted to overcome the requirements and difficulties presented by specific samples. In particular, we worked on (1) the development of a minimally invasive method based on the direct tryptic cleavage of the sample without protein extraction; (2) the use of microwave to enhance the enzymatic digestion yield, followed by the analysis of the peptide mixtures by nanoLC-MS/MS with electrospray ionization (ESI). Moreover, as an additional tool to tackle the problem of contaminating proteins, we exploited the possibility of generating an exclusion list of the mass signals that in a first run had been fragmented and that the mass spectrometer had to ignore for fragmentation in a subsequent run. The methods, tested on model samples, allowed the identification of milk proteins in a sample from paintings attributed to Cimabue and Giotto, thirteenth-century Italian masters, decorating the vaults of the upper church in the Basilica of St. Francis in Assisi, Italy.     

X‐ray structure and density functional theory studies of an unexpected product: trans‐bis{2‐[(2‐cyanoethyl)iminomethyl]phenolato}copper(II)

The title compound, [Cu(C₁₀H₉N₂O)₂] or [Cu^II(CYMB)₂], (I), was obtained in an attempt to reduce trans‐bis(2‐{[3,5‐bis(trifluoromethyl)phenyl]iminomethyl}phenolato)copper(II), [Cu(TIMB)₂], (II), with bis(pentamethylcyclopentadienyl)cobalt(II) [decamethylcobaltocene, Cp*₂Co, (III)]. The molecular structure of (I) has the Cu^II centre located on an inversion centre of the C2/c space group. A density functional theory (DFT) analysis at the B3LYP/Lanl2dz(CuF);6‐31G**(CHNO) level performed in order to optimize the structures of the free ligands CYMB⁻ and TIMB⁻, and the metal complexes [Cu^I/II(CYMB)₂]^−/0 and [Cu^I/II(TIMB)₂]^−/0, reproduced well the X‐ray diffraction structure and allowed us to infer the insertion of the cyanomethide anion on the 3,5‐bis(trifluoromethyl)phenyl system from an evaluation of the Mulliken atomic charges and the electronic energies.     

Corrigendum to “Morita theory for coring extensions and cleft bicomodules” [Adv. Math. 209 (2) (2007) 611-648]

The results in our paper heavily rely on the journal version of [T. Brzeziński, A note on coring extensions, Ann. Univ. Ferrara Sez. VII (N.S.) 51 (2005) 15-27; a corrected version is available at http://arxiv.org/abs/math/0410020v3, Theorem 2.6]. Since it turned out recently that in the proof of the quoted theorem there are some assumptions missing, our derived results are not expected to hold at the stated level of generality either. Here we supplement the constructions in our article with the missing assumptions and show that they hold in most of our examples. In order to handle also the non-fitting case of cleft extensions by arbitrary Hopf algebroids, Morita contexts are constructed that do not necessarily correspond to coring extensions. They are used to prove a Strong Structure Theorem for cleft extensions by arbitrary Hopf algebroids. In this way we obtain in particular a corrected form of the journal version of [G. Böhm, Integral theory for Hopf algebroids, Algebr. Represent. Theory 8 (4) (2005) 563-599; Corrigendum, to be published; see also http://arxiv.org/abs/math/0403195v4, Theorem 4.2], whose original proof contains a similar error.     

Corrigendum to Cleft Extensions of Hopf Algebroids

Theorem 2.2 stated a monoidal isomorphism between the comodule categories of two bialgebroids in a Hopf algebroid. The proof of Theorem 2.2 was based on the journal version of Brzeziński (Ann Univ Ferrara Sez VII (NS) 51:15–27, 2005, Theorem 2.6), whose proof turned out to contain an unjustified step. Here we show that all other results in our paper remain valid if we drop unverified Theorem 2.2, and return to an earlier definition of a comodule of a Hopf algebroid that distinguishes between comodules of the two constituent bialgebroids.