Liquid chromatography of synthetic polymers under critical conditions of enthalpic interactions 4: Sample recovery

Reduced sample recovery is a frequent feature of LC of macromolecules under critical conditions of enthalpic interactions (LC CC). Several methods of assessment of LC CC sample recovery are compared. A novel approach is based on an online combination of the. The LC CC column with a noninteractive SEC column. It provides not only the amount but also the molar mass of the eluted/withheld polymer. The procedure was tested with poly(methyl methacrylate), bare silica gel column packings, and “critical eluent” tetrahydrofuran/toluene. It was shown that macromolecules with higher molar masses were preferentially trapped within the LC CC column packing so that the eluted part of the sample was no longer representative. The incomplete polymer elution can make the LC CC polymer analyses susceptible to significant experimental errors.     

Tetramethyl(perfluoroalkyl)cyclopentadienyl rhodium(I) complexes with ethylene or diene ligands. Crystal structure of [(η-C5Me4C6F13)Rh(CO)2]

Tetramethyl(perfluoroalkyl)cyclopentadienyl rhodium(I) complexes with ethylene or diene (norbornadiene, cycloocta-1,5-diene, 2,3-dimethylbuta-1,3-diene, cyclohexa-1,3-diene) ligands were obtained by reduction of tetramethyl(perfluoroalkyl)rhodium(III) dichloro dimers by zinc in THF or by propan-2-ol/sodium carbonate in the presence of the ligands. Reduction in the presence of cycloocta-1,3-diene gave a different product, an η³-cyclooctenyl complex, which was not reduced further. During the reduction in the presence of ethylene, a new tetramethyl(perfluoroalkyl)-η⁴-cyclopentadiene complex was observed by NMR. This compound, formed by hydrogen transfer from the metal to the ligand, is probably in an equilibrium with the parent hydridocyclopentadienyl complex. Crystal and molecular structure of dicarbonyltetramethyl(perfluorohexyl)cyclopentadienylrhodium(I) complex was determined by X-ray diffraction. The structure shows a moderate ring slippage of the rhodium atom which was not observed in the only other known structure of a complex with the same ligand, the rhodium(III) dichloro dimer.     

Modulation of Uptake and Reactivity of Nitrogen Dioxide in Metal-Organic Framework Materials

We report the modulation of reactivity of nitrogen dioxide (NO₂) in a charged metal–organic framework (MOF) material, MFM-305-CH₃ in which unbound N-centres are methylated and the cationic charge counter-balanced by Cl⁻ ions in the pores. Uptake of NO₂ into MFM-305-CH₃ leads to reaction between NO₂ and Cl⁻ to give nitrosyl chloride (NOCl) and NO₃⁻ anions. A high dynamic uptake of 6.58 mmol g⁻¹ at 298 K is observed for MFM-305-CH₃ as measured using a flow of 500 ppm NO₂ in He. In contrast, the analogous neutral material, MFM-305, shows a much lower uptake of 2.38 mmol g⁻¹. The binding domains and reactivity of adsorbed NO₂ molecules within MFM-305-CH₃ and MFM-305 have been probed using in situ synchrotron X-ray diffraction, inelastic neutron scattering and by electron paramagnetic resonance, high-field solid-state nuclear magnetic resonance and UV/Vis spectroscopies. The design of charged porous sorbents provides a new platform to control the reactivity of corrosive air pollutants.     

Identification of regioisomers and enantiomers of triacylglycerols in different yeasts using reversed‐ and chiral‐phase LC–MS

LC with atmospheric pressure chemical ionization (ACPI) MS with RP and chiral phase was used for separation of triacylglycerols (TAGs) from yeasts of the genera Candida, Kluyveromyces, Rhodotorula, Saccharomyces, Torulospora, Trichosporon, and Yarrowia. Chiral LC–APCI‐MS is based on using two columns in series packed with a 3,5‐dimethylphenyl carbamate modified β‐cyclodextrin chiral phase. All regioisomers and enantiomers of TAGs containing one to five double bonds were separated. Molecular species of TAGs, i.e. regioisomers and enantiomers, were identified and quantified by MS/MS. Among the 94 identified TAGs, the most abundant were triolein, oleopalmitoleoolein, and dipalmitoleoolein. In strains producing palmitoleic acid in amounts >25% of total fatty acids (FAs), this acid, or unsaturated FA is bound in sn‐1. In strains containing palmitoleic acid at 10–25% total FAs this acid is mainly bound in sn‐3, saturated FA being bound in sn‐1. Strains containing <10% palmitoleic acid form preferentially symmetrical TAGs.     

p-tert-Butyl thiacalix[4]arenes functionalized at the lower rim by amide, hydroxyl and ester groups as anion receptors

New p-tert-butyl thiacalix[4]arenes differently substituted at the lower rim with amide, hydroxyl and ester groups were synthesized. Binding properties of the compounds toward some tetrabutylammonium salts n-Bu(4)NX (X = F(-), Cl(-), Br(-), I(-), CH(3)CO(2)(-), H(2)PO(4)(-), NO(3)(-)) were studied by UV spectroscopy. It was found that the stoichiometry of the complexes, generally, is 1 : 1, and the association constants are in the range of 10(3)-10(5) M(-1). The p-tert-butyl thiacalix[4]arenes containing secondary amide groups trisubstituted at the lower rim bind the studied anions most effectively. Selective receptors for fluoride and dihydrogen phosphate salts of tetrabutylammonium were found.     

Using nutritional and oxidative stress to increase content of healthbeneficial fatty acids in oleaginous and non-oleaginous yeasts

Yeast responses to stress conditions include an increase in lipid content and concomitant changes in content of saturated and unsaturated fatty acids. Some fatty acids are among the dietetically important fatty acids and new possibilities are sought for their biotechnological production in addition to those already exploited from marine organisms, nuts and other sources. The possibility of the production of palmitoleic and linoleic acids resulting from new approaches to traditional biotechnologically useful yeast species (Kluyveromyces polysporus, Saccharomyces cerevisiae, Torulospora delbrueckii) and species capable of high accumulation of lipids (Rhodotorula glutinis, Trichosporon cutaneum, Candida sp., Yarrowia lipolytica) was explored. The most promising was the combination of two stress factors: limitation of N-sources (C/N mass ratio of 70: 1) and oxidative stress induced by zero- valent iron nanoparticles. These conditions were conducive to the production of palmitoleic acid commonly used in cosmetics and medicine and ω-6-linoleic acid, a precursor of thromboxanes, prostaglandins and leucotrienes. The yield of these two fatty acids in T. cutaneum was more than 500 mg g^?1 (dry mass) and in Candida sp. more than 600 mg g-1 (dry mass).     

Two Tags in One Probe: Combining Fluorescence- and Biotin-based Detection of the Trypanosomal Cysteine Protease Rhodesain

Rhodesain is the major cysteine protease of the protozoan parasite Trypanosoma brucei and a therapeutic target for sleeping sickness, a fatal neglected tropical disease. We designed, synthesized and characterized a bimodal activity-based probe that binds to and inactivates rhodesain. This probe exhibited an irreversible mode of action and extraordinary potency for the target protease with a k_inac/K_i value of 37,000 M⁻¹s⁻¹. Two reporter tags, a fluorescent coumarin moiety and a biotin affinity label, were incorporated into the probe and enabled highly sensitive detection of rhodesain in a complex proteome by in-gel fluorescence and on-blot chemiluminescence. Furthermore, the probe was employed for microseparation and quantification of rhodesain and for inhibitor screening using a competition assay. The developed bimodal rhodesain probe represents a new proteomic tool for studying Trypanosoma pathobiochemistry and antitrypanosomal drug discovery.     

Dinuclear copper(II) perchlorate complexes with 6-(benzylamino)purine derivatives: Synthesis,X-ray structure,magnetism and antiradical activity

The reactions of Cu(ClO₄)₂·6H₂O with 6-(benzylamino)purine derivatives in a stoichiometric 1:2 metal-to-ligand ratio led to the formation of penta-coordinated dinuclear complexes of the formula [Cu₂(μ-L^1–8)₄(ClO₄)₂](ClO₄)₂·nsolv, where L¹ = 6-(2-fluorobenzylamino)purine (complex 1), L² = 6-(3-fluorobenzylamino)purine (2), L³ = 6-(4-fluorobenzylamino)purine (3), L⁴ = 6-(2-chlorobenzylamino)purine (4), L⁵ = 6-(3-chlorobenzylamino)purine (5), L⁶ = 6-(4-chlorobenzylamino)purine (6), L⁷ = 6-(3-methoxybenzylamino)purine (7) and L⁸ = 6-(4-methoxybenzylamino)purine (8); n = 0–4 and solv = H₂O, EtOH or MeOH. All the complexes have been fully characterized by elemental analysis, FTIR, UV–Vis and EPR spectroscopy, and by magnetic and conductivity measurements. Variable temperature (80–300 K) magnetic susceptibility data of 1–8 showed the presence of a strong antiferromagnetic exchange interaction between two Cu(II) (S = 1/2) atoms with J ranging from −150.0(1) to −160.3(2) cm⁻¹. The compound 6·4EtOH·H₂O was structurally characterized by single crystal X-ray analysis. The Cu?Cu separation has been found to be 2.9092(8) Å. The antiradical activity of the prepared compounds was tested by in vitro SOD-mimic assay with IC₅₀ in the range 8.67–41.45 μM. The results of an in vivo antidiabetic activity assay were inconclusive and the glycaemia in pre-treated animals did not differ significantly from the positive control.