Deoxy-nitrosugars. 10th Communication. Synthesis of Isosteric Phosphonate Analogues of Ulose-1-Phosphates

A general approach to isosteric phosphonate analogues of ulose-l-phosphates is described. A base-catalysed chain elongation via a Michael addition of 1-deoxy-1-nitro-sugars 4, 8 , and 16 to the vinylphosphonate 18 followed by hydrolysis of the nitro adducts gave the analogues of D -ribulose-1-phosphate, D -fructose-1-phosphate, and D -sedoheptulose-1,7-diphosphate 21, 23 , and 27 , respectively, in high yields.     

First-language phonotactics in second-language listening

Highly proficient German users of English as a second language, and native speakers of American English, listened to nonsense sequences and responded whenever they detected an embedded English word. The responses of both groups were equivalently facilitated by preceding context that both by English and by German phonotactic constraints forced a boundary at word onset (e.g., lecture was easier to detect in moinlecture than in gorklecture, and wish in yarlwish than in plookwish). The American L1 speakers' responses were strongly facilitated, and the German listeners' responses almost as strongly facilitated, by contexts that forced a boundary in English but not in German (thrarshlecture, glarshwish). The German listeners' responses were significantly facilitated also by contexts that forced a boundary in German but not in English (moycelecture, loitwish), while L1 listeners were sensitive to acoustic boundary cues in these materials but not to the phonotactic sequences. The pattern of results suggests that proficient L2 listeners can acquire the phonotactic probabilities of an L2 and use them to good effect in segmenting continuous speech, but at the same time they may not be able to prevent interference from L1 constraints in their L2 listening.     

Kinetic and equilibrium studies on the polyazamacrocycle neotetren: metal-complex formation and DNA interaction

The macrocyclic polyamine 2,5,8,11,14-pentaaza[15]-[15](2,9)[1,10]phenanthrolinophane (neotetren) is studied in its ability to coordinate Cu(ii) even at very low pH values and to interact, as a metal complex, with DNA. The kinetics and equilibria for 1 : 1 and 2 : 1 metal-ligand complexes formation are studied by the stopped-flow method and UV spectrophotometry. Differently protonated complexes are formed, with rate constants much lower than that of water exchange at copper(II) and other Cu(II)/amine systems, this behaviour being ascribed to ring effects and intra-molecular hydrogen bonds. Concerning the DNA/copper(II)-neotetren complexes interaction, analysis of data suggests an intercalative mode of binding. The kinetic results for both DNA/CuL and DNA/Cu(2)L systems agree with the sequence D + S <-->D,S <-->DS where the metal complexes (D) react with the DNA sites (S) leading to fast formation of an externally bound form (D,S) which is converted into an intercalated complex (DS). A very slow process is also detected and ascribed to a conformational change in the polynucleotide secondary structure where the metal centre plays a crucial role. Chromatographic experiments demonstrate that both the investigated Cu(II)/L complexes are able to cleave DNA, but only in the presence of hydrogen peroxide.     

The influence of ligand field effects on the magnetic exchange of high-spin Co(II)-semiquinonate complexes

[Co(Me(4)cyclam)(tropolonate)](PF(6)) was synthesised and structurally characterised. Its electronic and W-band EPR spectra have been analysed by means of the angular overlap calculation of the Spin Hamiltonian parameters that provided also a satisfactory reproduction of the temperature dependence of the magnetic susceptibility. The present results can be interpreted assuming a pseudo-octahedral character for the Co(II) center. This prompted us to reconsider the model formerly used for the analysis of the magnetic coupling between hs-Co(II) and the paramagnetic o-semiquinonate ligand in the corresponding derivatives [Co(Me(4)cyclam)(PhenSQ)](PF(6)) and [Co(Me(4)cyclam)(DTBSQ)](PF(6)). These results indicate that the effect of the magnetic coupling is active only below 50 K and that a more refined model of exchange coupling between Co(II) and semiquinonato ligands is needed to quantitatively analyze the magnetic behaviour of this class of systems.     

A new 2-carboxylate-substituted 4,4'-bipyridine ligand: coordination chemistry of 4,4'-bipyridine-2-carboxylic acid and its synthetic intermediate 2-methyl-4,4'-bipyridine

The first monocarboxylate-substituted 4,4'-bipyridine ligand, 4,4'-bipyridine-2-carboxylic acid (4-(pyridin-4-yl)pyridine-2-carboxylic acid (PPCAH)), has been successfully synthesized from 4,4'-bipyridine. Reactions with transition metals zinc and manganese were used to establish the coordination characteristics of the product, 4,4'-bipyridine-2-carboxylic acid, and of the synthetic intermediate, 2-methyl-4,4'-bipyridine, by single-crystal X-ray diffraction. The ligand PPCAH is useful for the formation of metal-containing building blocks that can be used in the assembly of mixed-metal framework materials. The synthesis and structure of one such mixed-metal coordination polymer, Cu(PPCA)(2)HgI(2), is also presented.     

Matrix isolation and low temperature solid state FTIR spectroscopic study of alpha-furil

Alpha-furil [C(4)H(3)O-C(=O)-C(=O)-C(4)H(3)O] has been isolated in argon and xenon matrices and studied by FTIR spectroscopy, supported by DFT(B3LYP)/6-311++G(d,p) calculations. The obtained spectra were fully assigned and revealed the presence in the matrices of three different conformers, all of them exhibiting skewed conformations around the intercarbonyl bond with the two C(4)H(3)O-C(=O) fragments nearly planar. The three conformers differ in the orientation of the furan rings relative to the carbonyl groups: the most stable conformer, I (C(2) symmetry; O=C-C=O intercarbonyl dihedral equal to 153.1 degrees), has both furan rings orientated in such a way that one of their beta-hydrogen atoms approaches the oxygen atom of the most distant carbonyl group, forming two H-C=C-C-C=O six-membered rings; the second most stable conformer, II (C(1) symmetry; O=C-C=O intercarbonyl dihedral equal to 126.9 degrees ), has one furan ring orientated as in I, while the second furan group is rotated by ca. 180 degrees (resulting in an energetically less favourable H-C=C-C=O five-membered ring); in the third conformer, III (C(2) symmetry; O=C-C=O dihedral equal to 106.2 degrees ), both furan rings assume the latter orientation relative to the dicarbonyl group. The theoretical calculations predicted the two higher energy forms being 5.85 and 6.22 kJ mol(-1) higher in energy than the most stable form, respectively, and energy barriers for conformational interconversion higher than 40 kJ mol(-1). These barriers are high enough to prevent observation of conformational isomerization for the matrix isolated compound. The three possible conformers of alpha-furil were also found to be present in CCl(4) solution, as well as in a low temperature neat amorphous phase of the compound prepared from fast condensation of its vapour onto a suitable 10 K cooled substrate. On the other hand, in agreement with the available X-ray data [S. C. Biswas, S. Ray and A. Podder, Chem. Phys. Lett., 1987, 134, 541], the IR spectra obtained for the neat low temperature crystalline state reveals that, in this phase, alpha-furil exists uniquely in its most stable conformational state, I.     

Microwaves make hydroformylation a rapid and easy process

[reaction: see text] Hydroformylation of alkenes can be carried out in a few minutes under microwave activation at a relatively low pressure (40 psi) using commercially available catalysts and ligands. The 80 mL vial of a Discover microwave oven was connected to a cylinder of CO and H2, and after filling the reactor at 40 psi, a mixture of an alkene, the Wilkinson catalyst, and XANTPHOS was submitted to microwave irradiation giving, after 4 min, high conversion into the corresponding aldehyde without formation of the isomerized alkene.     

A comparative study on the application of hierarchical-agglomerative clustering approaches to organize outputs of reiterated docking runs

Reiterated runs of standard docking protocols usually provide a collection of possible binding modes rather than pinpoint a single solution. Usually, this ensemble is then ranked by means of an energy-based scoring function. However, since many degrees of approximation have to be introduced in the computation of the binding free energy, scoring functions cannot always rank the experimental pose among the top scorers. Cluster analysis might help to overcome this limit, provided that data clusterability has been earlier assessed. In this paper, first, we present a modified version of a test earlier developed by Hopkins to assess whether or not docking outputs show the natural tendency to be grouped in clusters. Then, we report the results of a comparative study on the application of different hierarchical-agglomerative cluster rules to partition docking outputs. The rule that was able to best manage the observed data was finally applied to the whole ensemble of poses collected from several docking tools. The combination of the average linkage rule with the cutting function developed by Sutcliffe and co-workers turned out to be an approach that meets all of the criteria required for a robust clustering protocol. Furthermore, a consensus clustering allowed us to identify the pose closest to the experimental one within a statistically significant cluster, whose number was always of few units.