Synthesis and structure of isopropyldimethylsilyl-substituted octamethyltitanocene

Reduction of isopropyldimethylsilyl-substituted titanocene dichloride [TiCl₂(η⁵-C₅Me₄SiMe₂Prⁱ)₂] (1) by excess magnesium in the presence of excess bis(trimethylsilyl)ethyne (btmse) in tetrahydrofuran at 60 °C yielded a mixture of products amongst them only the trinuclear Ti-Mg-Ti hydrido-bridged complex Mg[Ti(μ-H)₂(η⁵-C₅Me₄SiMe₂Prⁱ)]₂ (3) was isolated and characterized. The precursor of titanocene, [Ti(η⁵-C₅Me₄SiMe₂Prⁱ)₂(η²-btmse)] (6), was obtained from the identical system which, after initial formation of [TiCl(η⁵-C₅Me₄SiMe₂Prⁱ)₂] (2), reacted at −18 °C overnight and then the solution was rapidly separated from the remaining magnesium. Titanocene [Ti(η⁵-C₅Me₄SiMe₂Prⁱ)₂] (7) was obtained by thermolysis of 6 at 75 °C in vacuum. Crystal structures of 1, 2, 3, 6, and 7 were determined.     

Direct determination of acrylamide in food by gas chromatography-high-resolution time-of-flight mass spectrometry

Simple and rapid gas chromatographic (GC) method employing a high-resolution time-of-flight mass analyzer that enables direct analysis (no derivatization) of acrylamide in various heat-processed foodstuffs has been developed and validated. Co-isolation of acrylamide precursors such as sugars and asparagine, constituting the risk of results overestimation due to additional formation of analyte in hot GC injector, is avoided by the extraction with n-propanol followed by solvent exchange to acetonitrile (MeCN). Introduction of a novel purification strategy, dispersive solid phase extraction, based on addition of primary-secondary amine (PSA) sorbent into deffated extract in MeCN, provides a significant reduction of some abundant matrix co-extracts (mainly free fatty acids). Isotope dilution technique (d₃-acrylamide as an internal standard) is employed for compensation of potential target analyte losses and/or matrix-inducted chromatographic response enhancement. Limits of quantifications (LOQs) ranged between 15 and 40 μg kg⁻¹ and recoveries were between 97 and 108% depending on the examined food matrix. The repeatability of measurements (expressed as relative standard deviation, R.S.D.) was as low as 1.9% for potato crisps containing acrylamide at a level of 1 mg kg⁻¹. Slightly higher values (R.S.D. < 4.0%) were achieved for breakfast cereals and crisp bread with approximately 10 times lower content of this processing contaminant. Trueness of results generated by this new method was demonstrated via FAPAS^® (Food Analysis Performance Assessment Scheme) interlaboratory proficiency tests.     

An evaluation of GC-MS and HPLC-FD methods for analysis of protein binders in paintings

Two chromatographic methods have been compared for analysis of protein-binding media used in paintings, namely, HPLC with fluorescence detection and GC-MS. The proteins were hydrolyzed to the corresponding amino acids (AAs) by gaseous HCl and the AAs were derivatized with methyl chloroformate, followed by GC-MS or by HPLC after derivatization with the AccQ fluorescence reagent. The hydrolysis, derivatization reactions and the chromatographic procedures have been optimized and applied to standard binding media, model and real samples of paintings. The methods have been compared and critically evaluated.     

Functionalization Conditions of PLGA-PEG-PLGA Copolymer with Itaconic Anhydride

Summary: Biodegradable thermosensitive triblock copolymers based on poly(ethylene glycol) and poly(lactic-co-glycolic acid) (PLGA-PEG-PLGA) prepared via ring opening polymerization were modified by itaconic anhydride (ITA), which gives copolymer both reactive double bonds and functional carboxylic acid groups essential for the reaction with biological active material. Functionalization conditions comprising ITA purification, temperature, time and presence of solvent were optimized with the respect to amount of end-capped ITA. Maximum of 76.6 mol. % of bonded ITA were reached via “one pot” reaction in a bulk at 110 °C after 1.5 h. ITA functionalization thermally stabilized the original copolymer by increasing the initial degradation temperature T_d from 284 °C to 294 °C and changing the negative glass transition temperature (T_g = -1.8 °C) to positive one up to 2.4 °C. The novel functionalized macromonomer can be cross-linked either chemically or physically in order to produce new functionalized hydrogel network applicable as biomedical material in tissue engineering.     

Parabolic symmetric spaces

We study here systems of symmetries on |1|-graded parabolic geometries. We are interested in smooth systems of symmetries, and we discuss non-flat homogeneous |1|-graded geometries. We show the existence of an invariant admissible affine connection under quite weak condition on the system.     

NMR determination of pKa values of indoloquinoline alkaloids

Malaria is one of the most serious global health problems. Isolating new therapeutic agents with potential antimalarial activity from natural sources or preparing such agents either semisynthetically or synthetically is one strategy for solving the problem of resistance constantly evolving to the drugs currently in use. For alkaloids, the acid–base dissociation constant, pK_a, is an important characteristic, thought to be associated with biological activity. In this contribution, pK_a values for several indoloquinoline alkaloids were determined by using ¹H NMR spectroscopy in a mixture of solvents. The data were recalculated for water solutions using the correction factors reported previously. The structural dependence of the pK_a values for cryptolepine and its isomers neocryptolepine, isocryptolepine and isoneocryptolepine as well as some substituted neocryptolepine derivatives is discussed. Copyright © 2009 John Wiley & Sons, Ltd.     

Vinyl polymerization initiated by peroxydiphosphate

Colloid and Polymer Science - The kinetics of aqueous polymerization of acrylamide and methacrylamide initiated by potassium peroxydiphosphate has been investigated. The kinetic orders with respect...