Recycling of End-of-Life Poly(bisphenol A carbonate) via Alkali Metal Halide-Catalyzed Phenolysis

The chemical recycling of end-of-life plastic waste streams can contribute to a resource-conserving and sustainable society. This matter of recycling is composed of a sequence of depolymerization and subsequent polymerization reactions. In this regard, we have studied the chemical recycling of end-of-life poly(bisphenol A carbonate) applying phenol as depolymerization reagent. In the presence of catalytic amounts of alkali metal halides as products bisphenol A and diphenyl carbonate were obtained in excellent turnover frequencies of up to 1392 h⁻¹ and short reaction times. These depolymerization products offer the straightforward possibility to close the cycle by producing new poly(bisphenol A carbonate) and as second product phenol, which can be reused for further depolymerizations.     

Coherent delocalization of atomic wave packets in driven lattice potentials

Atomic wave packets loaded into a phase-modulated vertical optical-lattice potential exhibit a coherent delocalization dynamics arising from intraband transitions among Wannier-Stark levels. Wannier-Stark intraband transitions are here observed by monitoring the in situ wave-packet extent. By varying the modulation frequency, we find resonances at integer multiples of the Bloch frequency. The resonances show a Fourier-limited width for interrogation times up to 2 s. This can also be used to determine the gravity acceleration with ppm resolution.     

Exploring the Strength of the H‐Bond in Synthetic Models for Heme Proteins: The Importance of the N−H Acidity of the Distal Base

The distal hydrogen bond (H‐bond) in dioxygen‐binding proteins is crucial for the discrimination of O₂ with respect to CO or NO. We report the preparation and characterization of a series of Zn^II porphyrins, with one of three meso‐phenyl rings bearing both an alkyl‐tethered proximal imidazole ligand and a heterocyclic distal H‐bond donor connected by a rigid acetylene spacer. Previously, we had validated the corresponding Co^II complexes as synthetic model systems for dioxygen‐binding heme proteins and demonstrated the structural requirements for proper distal H‐bonding to Co^II‐bound dioxygen. Here, we systematically vary the H‐bond donor ability of the distal heterocycles, as predicted based on pK_a values. The H‐bond in the dioxygen adducts of the Co^II porphyrins was directly measured by Q‐band Davies‐ENDOR spectroscopy. It was shown that the strength of the hyperfine coupling between the dioxygen radical and the distal H‐atom increases with enhanced acidity of the H‐bond donor.     

Ionic conduction of γ-titanium phosphate in hydrogen and alkali metal salt forms

Impedances of compact discs of anhydrous γ-titanium phosphate and some ofits salt forms were measured in the temperature range of 100–300°C, while the corresponding hydrated forms were investigated between -20 and +25°C. Either at low or high temperature the impedance plots are consistent with a parallel combination of a conductance, a capacitance and a constant phase angle admittance. Anhydrous compounds have lower conductivities (σ_300°C=10^-4–10^-6ω^-1cm^-1) and higher activation energies (E_a = 13.9–20.7 kcal/mol) than those of the corresponding hydrated ones (σ_25°C = 10^-3–10^-5ω^-1cm^-1 and E_a = 2–10 kcal/mol); however, in both cases, the activation energy increases with increasing ionic radius. The values of the ion diffusion coefficients for hydrated forms (10^-8–10^-9 cm²/s), computed at 25°C by the Nernst-Einstein equation, are considerably higher than those obtained by self diffusion experiments. This seems to indicate that the conductivity is essentially due to hydrated cations present on the surface of the microcrystals.     

Regioselective addition reactions of group IVB organometallic radicals with p-diones. An ESR study

The group IVB organometallic radical adducts of a number of substituted p-diones and related compounds have been investigated by ESR spectroscopy. In the case of substrates with unequivalent carbonyl groups two distinct isomeric adducts have been detected, and the factors affecting the regioselectivity of the addition reaction are discussed.The magnitude of the hyperfine splitting constants at the metal atoms and the trend of the g-values are consistent with a conformation for the adducts where the organometallic substituent eclipses the pπ orbital on the radical centre.     

Influence of the size of the counter-ion on the conformational stability of the alkali metal complexes of 2,2'-dithienyl ketyl

The ratio between the trans—trans and cis—trans isomers has been measured in the 2,2'-dithienyl ketyl and in its Li, Na, K and Cs complexes. The stability of the trans—trans conformation was found to increase with increasing size of the alkali counter-ion. This trend has been interpreted in terms of steric interaction between the cation and the atoms adjacent to the binding site.     

On the usefulness of crown ethers in freezing out the intramolecular cation migration in radical ion pairs

The additon of stoichiometric amounts of dibenzo-18-crown-6 ether to solutions of the sodium ion pairs of pyrazine and therephthalonitrile has been found to reduce dramatically the rate constant for the intramolecular migration of the alkali cation. The proton and nitrogen hyperfine splitting in the slow exchange region, could be easily measured under these experimental conditions.     

A proteomic approach to rapidly elucidate oligodendrocyte-associated proteins expressed in the myelinating rat optic nerve

The lack of cDNA libraries derived from myelinating oligodendrocytes has hampered attempts to identify proteins associated with myelination during normal development or with remyelination after insult or disease. We, therefore, established a new method to elucidate such proteins by coupling the techniques of X-irradiation, two-dimensional (2-D) gel electrophoresis, and mass spectrometry. Specifically, 2-D gel protein profiles of normal optic nerves were compared with those of X-irradiated rat optic nerves, which were absent of oligodendrocytes, to elucidate oligodendrocyte-associated proteins. The subsequent identification of these oligodendrocyte-associated proteins was accomplished by mass spectrometry. The results presented in this paper demonstrate the potential of the X-irradiated optic nerve model system combined with proteomic techniques to rapidly elucidate oligodendrocyte-associated proteins expressed in vivo.     

Phosphoryl and thiophosphoryldithioformates as spin traps: from EPR studies to practical applications

This paper is aimed at providing an overview of our studies on the title compounds as spin trapping agents, and at emphasising the links between purely cognitive, academic research and industrial applications. Phosphoryl- and thiophosphoryl-dithioformates exhibit a comparable and interesting spin trapping ability, their efficiency being analogous to that of some aromatic thioketones. The spectral hyperfine structure may provide valuable information on the nature of the trapped radical but the phosphorus hfs constant cannot be used as an useful indicator. Thionformates are less efficient spin traps than the corresponding dithioformates, being inert towards stabilised radicals such as benzyl or relatively hindered radicals as tert-butoxyl. In no case could spin adducts to thiolformates be detected, this being an indication that their carbonyl group is significantly deactivated with respect to that of organic and organometallic ketones. Because of their ability in trapping either alkyl or alkoxy radicals both kind of dithioformates were exploited as stabilisers in the processing of such polymers as polypropylene, but their outstanding performance could not compensate for some organoleptic drawbacks that were intrinsic of the thiocarbonyl function. A much more promising application of dithioesters is instead their use as RAFT chain transfer agents in the controlled polymerisation of styrene. Preliminary experiments with benzyl diethoxyphosphoryldithioformate have afforded polystyrene with a polydispersity as low as 1.17, but further studies are needed to fully elucidate the RAFT-polymerisation mechanism and to optimise its outcome.