Kinetics of the thermal dehydrations and decompositions of some mixed metal oxalates

Both isothermal and programmed temperature experiments have been used to obtain kinetic parameters for the dehydrations and the decompositions in nitrogen of the mixed metal oxalates: FeCu(ox)₂·3H₂O, CoCu(ox)₂·3H₂O and NiCu(ox)₂·3.5H₂O, [ox=C₂O₄]. Results are compared with those reported for the thermal decompositions of the individual metal oxalates, Cuox, Coox·2H₂O, Niox·2H₂O and Feox·2H₂O. X-ray photoelectron spectroscopy (XPS) was also used to examinee the individual and the mixed oxalates. Dehydrations of the mixed oxalates were mainly deceleratory processes with activation energies (80 to 90 kJ·mol⁻¹), similar to those reported for the individual hydrated oxalates. Temperature ranges for dehydration were broadly similar for all the hydrates studied here (130 to 180°C). Decompositions of the mixed oxalates were all complex endothermic processes with no obvious resemblance to the exothermic reaction of Cuox, or the reactions of physical mixtures of the corresponding individual oxalates. The order of decreasing stability, as indicated by the temperature ranges giving comparable decomposition rates, was NiCu(ox)₂>CoCu(ox)₂>FeCu(ox)₂, which also corresponds to the order of increasing covalency of the Cu−O bonds as shown by XPS. In celebration of the 60^th birthday of Dr. Andrew K. Galwey     

KINETIC BEHAVIOR OF EPR SIGNAL I: INDUCTION EFFECTS IN INTACT ALGAE

Abstract— There is considerable evidence that the light-induced narrow EPR signal I at g = 2·0025 in green algae is a reflection of the turnover of the photosynthetic reaction center, P700. A lag period or induction effect of the formation of this signal, subsequent to a dark period in whole fresh cells, is similar to induction effects for the bleaching of P700. The rate of formation of the signal is slower the longer the preceding dark period. DCMU does not much affect the induction phenomenon, but heating the cells to 60° abolishes it. Some substance or process which exists in the intact cell is altered by light and is detectable by its effect on signal I and on the rate of light-induced oxidation of P700 and cytochrome.     

Solid-state polymerization of vinylpyridine coordination compounds

A survey of the solid-state polymerizability of 2- and 4-vinylpyridine (Vpy) complexes of divalent cobalt, nickel, copper, and zinc chlorides has been carried out. The influence of metal ion, ligand, coordination stereochemistry, and crystal structure is discussed. The tetrahedral modification of the complex Co(4-Vpy)₂Cl₂ has been found to undergo a particularly facile thermal polymerization below its melting point to yield high molecular weight poly-4-vinylpyridine. The polymer is shown to be conventional atactic head-to-tail poly-4-vinylpyridine. Thermogravimetric methods and optical microscopy have been used to study the thermal polymerization of single crystals of the complex. Results indicate a diffusion-controlled mechanism in which defective regions in the crystal act as nuclei for the polymerization.     

Cyclopentadiene annulated polycyclic aromatic hydrocarbons: investigations of electron affinities

The adiabatic electron affinities of cyclopentadiene and 10 associated benzannelated derivatives have been predicted with both density functional and Hartree-Fock theory. These systems can also be regarded as benzenoid polycyclic aromatic hydrocarbons (PAHs) augmented with five-membered rings. Like the PAHs, the electron affinities of the present systems generally increase with the number of rings. To unequivocally bind an electron, cyclopentadiene must have at least two conventionally fused benzene rings. 1H-Benz[f]indene, a naphthalene-annulated cyclopentadiene, is predicted to have a zero-point energy corrected adiabatic electron affinity of 0.13 eV. Since the experimental E(A) of naphthalene is negative (-0.19 eV), the five-membered ring appendage contributes to the stability of the naphthalene-derived 1H-benz[f]indene radical anion significantly. The key to binding the electron is a contiguous sequence of fused benzenes, since fluorene, the isomer of 1H-benz[f]indene, with separated six-membered rings, has an electron affinity of -0.07 eV. Each additional benzene ring in the sequence fused to cyclopentadiene increases the electron affinity by 0.15-0.65 eV: the most reliable predictions are cyclopentadiene (-0.63 eV), indene (-0.49 eV), fluorene (-0.07 eV), 1H-benz[f]indene (0.13 eV), 1,2-benzofluorene (0.25 eV), 2,3-benzofluorene (0.26 eV), 12H-dibenzo[b,h]fluorene (0.65 eV), 13H-indeno[1,2-b]anthracene (0.82 eV), and 1H-cyclopenta[b]naphthacene (1.10 eV). In contrast, if the six-membered ring-fusion is across the C(2)-C(3) cyclopentadiene single bond, only a single benzene is needed to bind an electron. The theoretical electron affinity of the resulting molecule, isoindene, is 0.49 eV, and this increases to 1.22 eV for 2H-benz[f]indene. The degree of aromaticity is responsible for this behavior. While the radical anions are stabilized by conjugation, which increases with the size of the system, the regular indenes, like PAHs in general, suffer from the loss of aromatic stabilization in forming their radical anions. While indene is 21 kcal mol(-1) more stable than isoindene, the corresponding radical anion isomers have almost the same energy. Nucleus-independent chemical shift calculations show that the highly aromatic molecules lose almost all aromaticity when an extra electron is present. The radical anions of cyclopentadiene and all of its annulated derivatives have remarkably low C-H bond dissociation energies (only 18-34 kcal mol(-1) for the mono-, bi-, and tricyclics considered). Hydrogen atom loss leads to the restoration of aromaticity in the highly stabilized cyclopentadienyl anion congeners.     

Are 1,5-disubstituted semibullvalenes that have C2v equilibrium geometries necessarily bishomoaromatic?

Unrestricted density functional theory (UB3LYP), CASSCF, and CASPT2 calculations have been employed to compute the relative energies of the C(s) and C(2v) geometries of several 1,5-disubstituted semibullvalenes. Substitution at these positions with R = F, -CH(2)-, or -O- affords semibullvalenes that are predicted to have C(2v) equilibrium geometries. Calculated singlet-triplet energy splittings and the energies of isodesmic reactions are used to assess the amount of bishomoaromatic character at these geometries. The results of these calculations show that employing strain to destabilize the C(s) geometries of semibullvalenes can lead to a significant decrease in the amount of bishomoaromatic stabilization of the C(2v) geometries, due to reduced through-space interaction between the two allyl groups. However, the C(2v) equilibrium geometries of the 1,5-disubstituted semibullvalenes with R = F and -RR- = -O- do benefit from stabilizing through-bond interactions between the two allyl groups. These interactions involve mixing of the bisallyl HOMO with the low-lying C-F or C-O sigma orbital combinations of the same symmetry. In contrast, for -RR- = -CH(2)-, through-bond interactions destabilize the bisallyl HOMO and are predicted to make the ground state of this semibullvalene a triplet.     

Electron spin echo envelope modulation from trapped electrons in a glassy medium

An amplitude modulation of the electron spin echo envelope has been observed for radiation-produced trapped electrons in 10 M NaOD/D₂O at 77°K but not in 10 M N₂OH/H₂O. The modulation has been simulated theoretically by generalizing the single crystal model of Rowan et al. to disordered systems. The modulation has been interpreted as due to dipolar interactions with deuterons in molecules of the second solvation shell around the trapped electrons.     

Identification of diethylene glycol monobutyl ether as a source of contamination in an ion trap mass spectrometer

Tandem liquid chromatography-mass spectrometry coupled to online radioactive material detection (LC/RAM/MS/MS) is a technique that is used routinely for in vivo and in vitro drug metabolism studies and allows for a simultaneous correlation between radiochemical peaks and mass spectral data. The compound diethylene glycol monobutyl ether (DGBE), a component of a commercially available scintillation cocktail for RAM analysis, was identified as a source of overwhelming chemical noise in a mass spectrometer which was used in an LC/RAM/MS/MS configuration. In this report, we describe the identification of DGBE as the source of the chemical noise and the methods that were used to minimize the exposure of the mass spectrometer to volatile components of the scintillation cocktail.