Redox control of a ring-opening polymerization catalyst

The activity of an yttrium alkoxide complex supported by a ferrocene-based ligand was controlled using redox reagents during the ring-opening polymerization of L-lactide. The oxidized complex was characterized by X-ray crystallography and (1)H NMR, XANES, and M?ssbauer spectroscopy. Switching in situ between the oxidized and reduced yttrium complexes resulted in a change in the rate of polymerization of L-lactide. Synthesized polymers were analyzed by gel permeation chromatography. Polymerization of trimethylene carbonate was also performed with the reduced and oxidized forms of an indium alkoxide complex. The indium system showed the opposite behavior to that of yttrium, revealing a metal-based dependency on the rate of polymerization.     

Synthesis and characterization of cerium and yttrium alkoxide complexes supported by ferrocene-based chelating ligands

Two series of Schiff base metal complexes were investigated, where each series was supported by an ancillary ligand incorporating a ferrocene backbone and different N=X functionalities. One ligand is based on an imine, while the other is based on an iminophosphorane group. Cerium(IV), cerium(III), and yttrium(III) alkoxide complexes supported by the two ligands were synthesized. All metal complexes were characterized by cyclic voltammetry. Additionally, NMR, Mo?ssbauer, X-ray absorption near-edge structure (XANES), and absorption spectroscopies were used. The experimental data indicate that iron remains in the +2 oxidation state and that cerium(IV) does not engage in a redox behavior with the ancillary ligand.     

Product ion mobility as a promising tool for assignment of positional isomers of drug metabolites

Travelling wave ion mobility spectrometry - mass spectrometry (TWIMS-MS) was evaluated as a tool for structural identification of metabolites of small molecule drugs in cases where the exact position of the biotransformation could not be identified by conventional tandem mass spectrometry. Test sets of compounds containing biotransformations at aromatic positions were analyzed. These present a problem for traditional MS methods since an atomic level localization of the biotransformation cannot normally be determined from MS(n) spectra. In addition to ion mobility measurements of the intact metabolite ions, ion mobility measurements of product ions were also made and the results compared with calculated values. This approach reduces the complexity of the problem, making theoretical calculations easier and more predictable when a modeled collision cross section (CCS) is required. A good relative correspondence between theoretical and measured CCSs was obtained allowing the identification of the exact position of the biotransformation. It was also demonstrated that authentic standards with substructures identical to those in the unknown can be used to assign the exact position of the biotransformation. In this approach the identification was based on the comparison of the drift times or CCSs for product ions of the standard, with those of the same product ions in the unknown.     

Photoracemization-Based Viedma Ripening of a BINOL Derivative

Viedma ripening is a deracemization process that has been used to deracemize a range of chiral molecules. The method has two major requirements: the compound needs to crystallize as a conglomerate and it needs to be racemizable under the crystallization conditions. Although conglomerate formation can be induced in different ways, the number of racemization methods is still rather limited. To extend the scope of Viedma ripening, in the present research we applied UV-light-induced racemization in a Viedma ripening process, and report the successful deracemization of a BINOL derivative crystallizing as a conglomerate. Irradiation by UV light activates the target compound in combination with an organic base, required to promote the excited-state proton transfer (ESPT), leading thereafter to racemization. This offers a new tool towards the development of Viedma ripening processes, by using a cheap and “green” catalytic source like UV light to racemize suitable chiral compounds.     

The hematopoietic factor GM-CSF (Granulocyte-macrophage colony-stimulating factor) promotes neuronal differentiation of adult neural stem cells in vitro

Background  

Granulocyte-macrophage colony stimulating factor (GM-CSF) is a hematopoietic growth factor involved in the generation of granulocytes, macrophages, and dendritic cells from hematopoietic progenitor cells. We have recently demonstrated that GM-CSF has anti-apoptotic functions on neurons, and is neuroprotective in animal stroke models.     

An experimental and computer modelling study of the photochemical reaction of tert-butylguaiacylcarbinol sensitized by p-methoxypropiophenone in aerated dimethoxyethane solution

The kinetics of the photochemical reaction of tert-butylguaiacyl-carbinol sensitized by p-methoxypropiophenone in aerated dimethoxyethane solution were measured experimentally. In contrast with the same model system in oxygen-free solution, the concentration of the sensitizer in the presence of oxygen remained constant within the experimental error limits. This implies that a regenerative loop exists for the sensitizer which operates efficiently if oxygen is present. The efficiency of this regenerative loop seems to depend on the substrate concentration. The rate of substrate consumption was found to be considerably faster than the rate obtained previously for the oxygen-free system.

The kinetics of substrate and sensitizer consumption and product formation were also studied by computer modelling, employing a reaction set consisting of 91 elementary reactions and 58 different species. Using this reaction set the kinetics of the substrate consumption were simulated for 4 h with good agreement with the experimental results. The calculated yields of the various reaction products were in fairly good agreement with previous experimental results for a similar model system. For the sensitizer, however, a small disagreement with the experimental results still remains, implying that in our simulation the regenerative loop does not operate with sufficient efficiency. The most important pathways for substrate reaction are the different singlet oxygen channels and the hydrogen abstraction mode of reaction. The relative importance of these two pathways could not be determined quantitatively.     

A New Class of Task-Specific Imidazolium Salts and Ionic Liquids and Their Corresponding Transition-Metal Complexes for Immobilization on Electrochemically Active Surfaces

Adding to the versatile class of ionic liquids, we report the detailed structure and property analysis of a new class of asymmetrically substituted imidazolium salts, offering interesting thermal characteristics, such as liquid crystalline behavior, polymorphism or glass transitions. A scalable general synthetic procedure for N-polyaryl-N’-alkyl-functionalized imidazolium salts with para-substituted linker (L) moieties at the aryl chain, namely [LPh_mIm^HR]⁺ (L=Br, CN, SMe, CO₂Et, OH; m=2, 3; R=C₁₂, PEG_n; n=2, 3, 4), was developed. These imidazolium salts were studied by single-crystal X-ray diffraction (SC-XRD), NMR spectroscopy and thermochemical methods (DSC, TGA). Furthermore, these imidazolium salts were used as N-heterocyclic carbene (NHC) ligand precursors for mononuclear, first-row transition metal complexes (Mn^II, Fe^II, Co^II, Ni^II, Zn^II, Cu^I, Ag^I, Au^I) and for the dinuclear Ti-supported Fe-NHC complex [(OPy)₂Ti(OPh₂ImC₁₂)₂(FeI₂)] (OPy=pyridin-2-ylmethanolate). The complexes were studied concerning their structural and magnetic behavior via multi-nuclear NMR spectroscopy, SC-XRD analyses, variable temperature and field-dependent (VT-VF) SQUID magnetization methods, X-band EPR spectroscopy and, where appropriate, zero-field ⁵⁷Fe Mössbauer spectroscopy.