Catalysis design for ring-opening polymerization of cyclic esters: 1. Group 1 metal and thallium(I) trispyrazolylborate complexes with hemilabile ligands

The synthesis of 3-(2-methoxy-1,1-dimethylethyl)pyrazole, pz*H is described together with its reactions with the borohydrides MBH(4), where M = Li, Na, and K, under melt conditions. At 180 degrees C, this procedure leads to a mixture of products for M = Li, and at higher temperatures, a derivative LiTp'pz*H, 1, is isolated, wherein a B-H bond and a methyl group have been eliminated and a B-O bond has been formed. For M = Na, the reaction proceeds to give the tris-pyrazolylborate derivative NaTp*, 2, but at higher temperatures the tetra-pyrazolylborate complex NaB(pz*)(4), 3, is obtained. The reactions involving KBH4 and pz*H yield the dinuclear complex K(2)(Tp*)(2)pz*H, 4. The reaction between NaTp* and TlOAc in CH(2)Cl(2) at room temperature leads to the formation of TlTp*, 5, along with NaOAc. Thallium 5 reacts with methyllithium in diethylether to give LiTp*, 6, and thallium metal, and, similarly, 5 and KH react in tetrahydrofuran to give KTp*, 7 and Tl(0). 1-7 have been characterized by elemental analysis, NMR spectroscopy, and by single-crystal X-ray studies, the latter of which reveal the versatile modes of binding for this new ligand bearing hemilabile ether appendages.     

Interactions between cellulose nanocrystals and anionic and neutral polymers in aqueous solutions

Physical structures of aqueous cellulose nanocrystal (CNC) suspensions in anionic polyelectrolyte carboxymethyl cellulose (CMC) and non-ionic poly(ethylene oxide) (PEO) were investigated by studying their cross polarized, polarized optical microscope (POM) images and dynamic light scattering, zeta potential, ¹H spin–lattice relaxation nuclear magnetic resonance (NMR) data. The presence of anionic CMC and nonionic PEO in CNC suspensions led to two different kind of interactions. Semi-dilute CNC suspensions showed first gel-like behavior then phase separation by adding only semi-dilute un-entangled CMC polymer solutions, whereas the addition of PEO didn’t cause any significant change. POM images showed the phase transitions of CNC suspensions in the presence of CMC solutions from the isotropic state to nematic and chiral nematic phases. Dynamic light scattering, zeta potential and ¹H spin–lattice relaxation NMR data presented further arguments to explain polymer-CNC interactions in CMC and PEO solutions. ¹H NMR solvent relaxation technique determined the adsorption and depletion interactions between polymers and CNC. The minima in spin–spin specific relaxation rate constant showed the depletion of CNC nanoparticles in CMC. It is believed that the depletion flocculation was the case for the effects of CMC polymer chains in CNC suspensions. PEO was adsorbed on CNC surfaces and caused only weak depletion interactions due to the presence of soft particles.     

Ionizing radiation and its effects on pharmaceuticals

Journal of Radioanalytical and Nuclear Chemistry - In this work, a total of twenty samples selected for investigation originate from South Africa and Namibia uranium mines. The aim of this study...     

Synthesis and functionalization of dendron‐polymer conjugate based hydrogels via sequential thiol‐ene “click” reactions

Fabrication and functionalization of hydrogels from well‐defined dendron‐polymer‐dendron conjugates is accomplished using sequential radical thiol‐ene “click” reactions. The dendron‐polymer conjugates were synthesized using an azide‐alkyne “click” reaction of alkene‐containing polyester dendrons bearing an alkyne group at their focal point with linear poly(ethylene glycol)‐bisazides. Thiol‐ene “click” reaction was used for crosslinking these alkene functionalized dendron‐polymer conjugates using a tetrathiol‐based crosslinker to provide clear and transparent hydrogels. Hydrogels with residual alkene groups at crosslinking sites were obtained by tuning the alkene‐thiol stoichiometry. The residual alkene groups allow efficient postfunctionalization of these hydrogel matrices with thiol‐containing molecules via a subsequent radical thiol‐ene reaction. The photochemical nature of radical thiol‐ene reaction was exploited to fabricate micropatterned hydrogels. Tunability of functionalization of these hydrogels, by varying dendron generation and polymer chain length was demonstrated by conjugation of a thiol‐containing fluorescent dye. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 926–934     

Identification of Chemical Forms of Lead, Cadmium and Nickel in Sewage Sludge of Waste Water Treatment Facilities

 Lead, cadmium and nickel levels in sewage sludge of a waste water treatment facility were determined by slotted tube atom trap (STAT)-flame atomic absorption spectrometry after using different extraction reagents. In addition, a sequential extraction procedure was applied to the same samples and the results were compared. It was found that Pb and Cd were relatively mobile as organically bound, carbonate or adsorbed on the Fe–Mn oxides and the concentrations in the extracts were higher than 50%. However, the percentage of Ni bound to these phases was found to be very low. Received October 23, 2001; accepted August 2, 2002     

Intracellular Modulation of Excited‐State Dynamics in a Chromophore Dyad: Differential Enhancement of Photocytotoxicity Targeting Cancer Cells

The photosensitized generation of reactive oxygen species, and particularly of singlet oxygen [O₂(a¹Δ_g)], is the essence of photodynamic action exploited in photodynamic therapy. The ability to switch singlet oxygen generation on/off would be highly valuable, especially when it is linked to a cancer‐related cellular parameter. Building on recent findings related to intersystem crossing efficiency, we designed a dimeric BODIPY dye with reduced symmetry, which is ineffective as a photosensitizer unless it is activated by a reaction with intracellular glutathione (GSH). The reaction alters the properties of both the ground and excited states, consequently enabling the efficient generation of singlet oxygen. Remarkably, the designed photosensitizer can discriminate between different concentrations of GSH in normal and cancer cells and thus remains inefficient as a photosensitizer inside a normal cell while being transformed into a lethal singlet oxygen source in cancer cells. This is the first demonstration of such a difference in the intracellular activity of a photosensitizer.     

Sensitivity enhancement in flame atomic absorption spectrometry for determination of copper in human thyroid tissues.

Various designs of quartz tube in a slotted tube atom trap were examined for improving the sensitivity of flame AAS. A 3.5-fold enhancement in the sensitivity was obtained by using the optimized method. The method was applied to the determination of Cu in cancerous and non-cancerous human thyroid tissues. The Cu concentrations of the cancerous samples tended to increase compared with the non-cancerous samples. Zn concentrations of the same tissues were also determined.     

Acid–base interactions and swelling of cellulose fibers in organic liquids

Drago’s acid–base approach was used to quantify the hydrogen bonding interactions in solvent swelling of cellulose fibers. The fiber swelling was correlated with acid–base, dispersive interactions and solvent molar volume. The acid–base interaction potentials of solvents were expressed in terms of their electron pair donor and acceptor numbers. The acid–base interaction terms of cellulosic materials were determined by using: (1) Flory–Huggins; (2) multiple regression models. We have used the swelling data of Mantanis and coworkers, which were based on the equilibrium liquid holding capacities of various compressed fibers in water and series of organic solvents. According to our interpretations, acid–base interactions and molar volume parameters were the major contributors to the overall solubility parameter. Acid–base interaction terms were balanced in alpha-cellulose sample. However spruce wood and sulfite pulp samples were more acidic than basic and therefore swollen better in organic basic solvents. For a good swelling behavior solvent must have high electron pair donor number/acceptor number ratio and high electron pair donor number–acceptor number difference.     

Pentacarbonyl(2-ferrocenylpyridine)metal(0) complexes of Group 6 elements. Synthesis and characterization

2-Ferrocenylpyridine (2-Fcpy) was prepared according to the literature procedure. 1,1-Dipyridylferrocene was also obtained as a minor product and characterized by ¹H- and ¹³C-n.m.r. spectroscopy. Prolonged irradiation of Cr(CO)₆ in the presence of 2-Fcpy in n-hexane gave Cr(CO)₅(2-Fcpy) which could not be isolated due to its instability even at low temperature, but was detected in solution by i.r. spectroscopy. The preparation of Mo(CO)₆(2-Fcpy) from direct photolysis of Mo(CO)₅ with 2-Fcpy could not be achieved. However, the reaction of Mo(CO)₅ (THF) with 2-Fcpy gave Mo(CO)₅ (2-Fcpy) which was isolated and characterized by i.r., ¹H- and ¹³C-n.m.r. spectroscopic techniques. W(CO)₅ (2-Fcpy) was prepared by irradiation of W(CO)₆ in the presence of 2-Fcpy in n-hexane. The complex was isolated and characterized by i.r., ¹H-, ¹³C-n.m.r. spectroscopic techniques. W(CO)₅ (2-Fcpy) thus appears to be more stable than the Mo and Cr analogues. The main reason for the general instability of the M(CO)₅ (2-Fcpy) complexes is assigned to the weak -accepting ability of 2-ferrocenylpyridine.