Adenosylcobinamide plus exogenous, sterically hindered, putative axial bases: a reinvestigation into the cause of record levels of Co-C heterolysis

A reinvestigation of an earlier Ph.D. thesis (Sirovatka, J. M. Ph.D. Thesis, Colorado State University, Fort Collins, CO, 1999) is reported herein. That thesis examined the thermolysis reaction of AdoCbi(+)BF(4)(-) in ethylene glycol solution with exogenous bases, N-methylimidazole (N-Me-Im) and the sterically hindered 1,2-dimethylimidazole, (1,2-Me(2)-Im), 2-methylpyridine (2-Me-py), and 2,6-dimethylpyridine (2,6-Me(2)-py). In the present work, multiple purities of each base have been utilized as a check to see if impurities in the nitrogenous bases are causing the observed homolysis and heterolysis product distributions as others have implied (Trommel, J. S.; Warncke, K.; Marzilli, L. G. J. Am. Chem. Soc. 2001, 123, 3358). The "impurity hypothesis" is disproven by a series of results, including the following: N-Me-Im displays an invariant 52 +/- 10% heterolysis and the 1,2-Me(2)-Im system displays an invariant 83 +/- 7% heterolysis as a function of different base purification methods. Moreover, 2-Me-py and 2,6-Me(2)-py also display an invariant approximately 16 +/- 5% heterolysis as a function of different purification methods. What is responsible for the high levels of Co-C heterolysis in the AdoCbi(+) plus sterically bulky base thermolyses was uncovered via a revisitation of our four, earlier alternative hypotheses for the enhanced Co-C heterolysis (Sirovatka, J. M.; Finke, R. G. Inorg. Chem. 1999, 38, 1697). Our prior number one alternative hypothesis is shown to be correct: the added bases simply deprotonate the ethylene glycol solvent, forming ethylene glycolate anion and base-H(+)() as the key agents behind the previously ill-understood Co-C heterolyses. Also reported are Co(II)Cbi(+) titrations with five bases (1,2-Me(2)-Im, N-Me-Im, pyridine, 2-MePy, and 2,6-Me(2)-py). These experiments confirm Marzilli and co-workers' (op. cit.) results by showing that sterically hindered bases do not bind to Co(II)Cbi(+); therefore, Co(II)Cbi(+) EPR literature showing binding of bulky pyridines is erroneous as is the previously reported binding of bulky pyridine bases to Co(II)Cbi(+) by UV-vis spectroscopy (Sirovatka, J. Ph.D. Thesis, op. cit.). Also reported is our current best synthesis and purification of AdoCbi(+)BF(4)(-), work that builds off our 1987 synthesis of AdoCbi(+)BF(4)(-) (Hay, B. P.; Finke, R. G. J. Am. Chem. Soc. 1987, 109, 8012). Finally, the multiple, compounding errors which have caused problems in this project are listed, notably errors in the protein X-ray crystallography literature, the EXAFS literature, the Co(II)Cbi(+) plus bulky-bases EPR literature, the misleading B(12)-model literature, the erroneous experimental work (Sirovatka, op. cit.) and thus incorrect conclusions in one of our prior papers, as well as the erroneous implications in parts of the Marzilli and co-workers paper (op. cit.). It is hoped that a forthright reporting of these errors will help others avoid similar mistakes in the future when studying complex, bioinorganic systems.     

Superlattice Turing structures in a photosensitive reaction-diffusion system

Families of complex superlattice structures, consisting of combinations of basic hexagonal or square patterns, are found in a photosensitive reaction-diffusion system. The structures are induced by simple illumination patterns whose wavelengths are appropriately related to that of the system's intrinsic Turing pattern. Computer simulations agree with the structures and their stability. The technique offers a general approach to generating superlattices for use in information storage and other applications.     

Nanofilm Low Cost Oxygen Sensors

The resitivity change of ultra thin metals under air exposure is used for vacuum or inert gas packaging control. In order to reach low cost, single use applications, few nm thin Aluminum layers were deposited on PET substrates and combined with wireless electronic readout circuitry.The sensor respose is characterized by resistance changes and explained in terms of multiphase diffusion mechanisms which are very sensitive to technological parameters.     

Density functional study of the adsorption of K on the Cu(111) surface

The adsorption of potassium on the Cu(111) surface in a (2×2) pattern has been simulated with all-electron full-potential density functional calculations. The top site is found to be the preferred adsorption site, with the other highly symmetric adsorption sites being nearly degenerate. The bond length from potassium to the nearest copper atom is computed to be 2.83 ?. Population analysis and density of states indicate that there is no evidence for covalent bonding so that the binding mechanism appears to be a metallic bond. Received 11 April 2001     

Bestimmung von Blei in Erzen

Ohne ZusammenfassungAus dem Englischen übersetzt von der Redaction.     

A simplified [11C]phosgene synthesis

A new flow-through system for the production of [¹¹C]phosgene, a versatile labelling agent in radiochemistry for PET, is described. Cyclotron-produced [¹¹C]CH₄ is mixed with Cl₂ and converted into [¹¹C]CCl₄ by passing the mixture through an empty quartz tube at 510 °C. The outflow is directed through a Sb-filled guard that takes out Cl₂ and then, without intentional O₂ addition, through a second empty quartz tube at 750 °C, giving rise to [¹¹C]phosgene in 30–35% radiochemical yield.     

Ambipolar hexa-peri-hexabenzocoronene-fullerene hybrid materials

A new class of self-assembling hexa-peri-hexbenzocoronene (HBC)-fullerene hybrid materials has been synthesized and characterized. Photoluminescence experiments indicate that energy transfer processes can be tuned in these donor-acceptor systems by varying the length and nature of the linker group. In preliminary device testing, ambipolar charge transport behavior is observed in organic field effect transistors, while single active component organic photovoltaic devices consisting of these materials achieved a maximum external quantum efficiency of 30%.     

Visualization of Protein‐Specific Glycosylation inside Living Cells

Protein glycosylation is a ubiquitous post‐translational modification that is involved in the regulation of many aspects of protein function. In order to uncover the biological roles of this modification, imaging the glycosylation state of specific proteins within living cells would be of fundamental importance. To date, however, this has not been achieved. Herein, we demonstrate protein‐specific detection of the glycosylation of the intracellular proteins OGT, Foxo1, p53, and Akt1 in living cells. Our generally applicable approach relies on Diels–Alder chemistry to fluorescently label intracellular carbohydrates through metabolic engineering. The target proteins are tagged with enhanced green fluorescent protein (EGFP). Förster resonance energy transfer (FRET) between the EGFP and the glycan‐anchored fluorophore is detected with high contrast even in presence of a large excess of acceptor fluorophores by fluorescence lifetime imaging microscopy (FLIM).