Titanium and zirconium ketimide complexes: synthesis and ethylene polymerisation catalysis

The syntheses of ketimide titanium complexes of the type Ti(NC^tBu₂)₃X (X = Cl, Cp, Ind), Ti(NC^tBu₂)₄ and the zirconium complex CpZr(NC^tBu₂)₂Cl are described. When activated by MAO, all compounds are ethylene polymerisation catalysts. In the conditions studied, the most active catalyst is CpZr(NC^tBu₂)₂Cl, with an activity of 2.7 × 10⁵ kg/(molZr [E] h). Titanium complexes are less active by about two orders of magnitude. The polyethylene produced is linear, as determined by NMR spectroscopy. Molecular structures of Ti(NC^tBu₂)₃X (X = Cl, Cp, Ind) and Ti(NC^tBu₂)₄ were determined by X-ray single crystal diffraction.     

A theoretical study of nonlinearity in heterocyclic hydrogen-bonded complexes

Ab initio calculations are performed at the MP2/6-311++G(d,p) and DFT/B3LYP/6-311++G(d,p) theoretical levels to obtain geometries, H-bond energies and harmonic infrared vibrational properties for the Cs symmetry structures of heterocyclic hydrogen-bonded complexes, CnHmY-HX. The H-bond lengths in DFT/B3LYP calculation level are in better agreement with the experimental values than the MP2 results. The geometry optimization are interpreted in terms of hydrogen bond nonlinearity represented by theta; and phi angles, once the hydrogen bond is formed among n-electrons pairs of the heteroatom in heterocyclic and the hydrogen atom in HX. The hydrogen bond energy after of the zero-point vibrational energy (ZPE) and basis set superposition error (BSSE) corrections are overestimated at DFT/B3LYP, whereas the MP2 BSSE corrections are very large than corresponding DFT/B3LYP. For example, the BSSE corrections for the C2H4S-HNC complex are 7.60 and 0.09 kJ mol(-1) in MP2 and DFT/B3LYP calculations levels, respectively. The new vibrational modes in infrared harmonic spectrum arising from complexation show several interesting features, especially the intermolecular stretching mode.     

Spectroscopic study of the water-soluble organic matter isolated from atmospheric aerosols collected under different atmospheric conditions

The composition of the water-soluble organic matter from fine aerosols collected in a rural location during two different meteorological conditions (summer and autumn) was investigated by UV-vis, synchronous fluorescence (with Δλ = 20 nm), FT-IR and CPMAS-¹³C NMR spectroscopies. A seasonal variation in the concentration of total carbon, organic carbon and water-soluble organic carbon was confirmed, with higher values during the autumn and lower values during the summer season. The chemical characterisation of the water-soluble organic matter showed that both samples are dominated by a high content of aliphatic structures, carboxyl groups and aliphatic carbons single bonded to one oxygen or nitrogen atom. However, the autumn sample exhibits a higher aromatic content than the summer sample, plus signals due to carbons of phenol, ketones and methoxyl groups. These signals were attributed to lignin breakdown products which are likely to be released during wood combustion processes. The obtained results put into evidence the major contribution of biomass burning processes in domestic fireplaces during low temperature conditions into both the concentration and the bulk chemical properties of the WSOC from fine aerosols.     

Treatment of long‐term stored DNA—Comparison between different methods to obtain high‐quality material

Long‐term stored DNA can be sometimes the only source of genetic material of an organism that does not exist anymore, but a research interest still persists. However, there is a lack of information about useful methods to improve quality from such type of material. In this study, we compared four different protocols using DNA samples collected in 1998. Fresh DNA was also tested aiming to check the differences between these two material types. Sixteen samples of each DNA type treated with phenol‐chloroform with PEG 5.0%, silica‐gel membrane spin column, PEG 7.5%, and glass‐fiber matrix spin column were submitted to spectrophotometer measurements, electrophoresis, PCR, and RFLP‐PCR to assess the best method concerning yield, quality, and purity. Based on the results, purification with PEG 7.5% was considered the best method to treat aged DNA samples. In addition to the efficiency, this protocol has low cost. Analyzing the data, we also conclude that long‐term stored DNA may be considered a reliable and potential resource for future molecular studies.     

Synthesis and structural characterization of silver(I) complexes with moon-shaped benzo[1,2-b;4,3-b′]dithiophene phosphine derivative ligands

New silver complexes of general formula [Ag(O₃SCF₃)(PPh₂{bzt})_n] (n = 1–3, bzt = benzo[1,2-b;4,3-b′]dithiophene) have been synthesized and characterized. Spectroscopic studies shown neutral ligand fluxionallity, typical of silver(I) complexes. The solid state structure of the complexes was determined by X-ray crystallographic studies, showing a decrease in structure complexity with increasing number of neutral ligands in silver coordination sphere: [Ag(O₃SCF₃)(PPh₂{bzt})] is a dimer with two bridging triflate anions, further linked into polymeric bidimensional chains along bc plane, through Ag?Ph close contacts; Ag(O₃SCF₃)(PPh₂{bzt})₂] is also a dimmer with two bridging triflate anions, displaying an interesting packing feature, with zig-zag alignment of bzt groups along direction b; [Ag(O₃SCF₃)(PPh₂{bzt})₃] is a monomer.     

trans‐Chlorido(phenyl)bis(triphenylphosphine)nickel(II) and its 1:1 cocrystal with chloridobis(triphenylphosphine)nickel(I)

Two conformational polymorphs of trans‐chlorido(phenyl)bis(triphenylphosphine)nickel(II), [Ni(C₆H₅)Cl(C₁₈H₁₅P)₂], (1), viz. orange needle‐shaped crystals (form I) and brown prism‐shaped crystals (form II), were obtained under different crystallization conditions from a mixture of toluene and n‐hexane, and characterized by single‐crystal X‐ray diffraction at low temperature. These two forms were compared with that published previously [Zeller, Herdtweck & Strassner (2003). Eur. J. Inorg. Chem. pp. 1802–1806], characterized at room temperature. Additionally, blue–green prisms of a 1:1 cocrystal of complex (1) with chloridobis(triphenylphosphine)nickel(I), (2), viz.trans‐chlorido(phenyl)bis(triphenylphosphine)nickel(II)–chloridobis(triphenylphosphine)nickel(I) (1/1), [Ni(C₆H₅)Cl(C₁₈H₁₅P)₂]·[NiCl(C₁₈H₁₅P)₂], (3), were obtained concomitantly with form I. In forms I and II, as well as in the cocrystal, the overall crystal packings are determined by an energetic interplay between intramolecular torsions and weak intermolecular C—H...π and C—H...Cl interactions.     

High stereocontrol in aldol reaction with ketones: enantioselective synthesis of beta-hydroxy gamma-ketoesters by ester enolate aldol reactions with 2-acyl-2-alkyl-1,3-dithiane 1-oxides

The asymmetric aldol reaction of 1,2-diketones, masked as nonracemic 2-acyl dithiane oxides, with lithium enolates derived from several esters and lactones, proceeds with a high degree of stereocontrol at both carbonyl and enolate prochiral centers, the stereocontrol mainly determined by the configuration of the sulfoxide sulfur atom. The sense of induced stereochemistry observed for ester enolates is different from that seen for lactone enolates. Hydrolysis of the dithiane oxide units of the major diastereoisomerically pure aldol products affords enantiomerically pure tertiary alpha-substituted beta-hydroxy-gamma-ketoesters.     

New N-acylamino acids and derivatives from renewable fatty acids: gelation of hydrocarbons and thermal properties

This work reports the synthesis of new fatty N-acylamino acids and N-acylamino esters from the C16:0, C18:0, C18:1, and C18:1(OH) fatty acid families and demonstrates the activity of these compounds as organogel agents. Compounds were heated and dissolved in various solvents (n-hexane, toluene, and gasoline). Only saturated C16:0 and C18:0 derived from alanine were able to form gels in toluene, and saturated C16:0 derived from phenylalanine showed gelation in n-hexane. This is the first evidence that fatty N-acylamino esters and N-acylamino acid derivatives of l-serine and fatty acids C16:0, C18:0, and C18:1 are able to form gels with hexane. This observation confirms the importance of the hydroxyl group in the segment derivative of l-serine in forming good gels.