Efficient synthesis of alpha-C-galactosyl ceramide immunostimulants: use of ethylene-promoted olefin cross-metathesis

[reaction: see text] Olefin cross-metathesis has been used to prepare alpha-C-galactosylceramide derivatives. The metathesis process merged vinyl and propenyl glycosides with vinyl derivatives of phytosphingosine. The use of ethylene enhanced the yield of the methathesis step.     

Structure of States Which Satisfy Strong Subadditivity of Quantum Entropy with Equality

We give an explicit characterisation of the quantum states which saturate the strong subadditivity inequality for the von Neumann entropy. By combining a result of Petz characterising the equality case for the monotonicity of relative entropy with a recent theorem by Koashi and Imoto, we show that such states will have the form of a so–called short quantum Markov chain, which in turn implies that two of the systems are independent conditioned on the third, in a physically meaningful sense. This characterisation simultaneously generalises known necessary and sufficient entropic conditions for quantum error correction as well as the conditions for the achievability of the Holevo bound on accessible information.     

Synthesis of fused polycycles by 1,4-palladium migration chemistry

Novel palladium migration/arylation methodology for the synthesis of complex fused polycycles has been developed, in which one or more sequential Pd-catalyzed intramolecular migration processes involving C-H activation are employed. The chemistry works best with electron-rich aromatics, which is in agreement with the idea that these palladium-catalyzed C-H activation reactions parallel electrophilic aromatic substitution.     

Highly symmetric networks derived from cubane-related octametallic complexes of a new oxyanion of carbon, C4O7(4-), each molecule attached to eight neighbors by 24 equivalent hydrogen bonds

Aqueous reaction mixtures containing dihydroxyfumaric acid, M2+ (M = Zn, Co, Fe, and Mg) and acetate ion at room temperature give crystals, suitable for single-crystal X-ray diffraction studies, of composition [(MII)8(C4O7)4(H2O)12].24H2O, in which the C4O74- component is the alkoxide-tricarboxylate tetra-anionic species -OC(CO2-)3, a new oxyanion of carbon. All four compounds crystallize in the body-centered space group I3m with cell dimensions a approximately 15.0 A. Discrete electrically neutral [(MII)8(C4O7)4(H2O)12] molecules are present, with a cubane-like core consisting of four trigonal prismatic metal centers and four mu3-alkoxo bridges from separate -OC(CO2-)3 ligands. The octametallic molecule is highly symmetrical, with four fac tri-aqua octahedral metal centers tetrahedrally appended to the central cubane-based [(MII)8(C4O7)4 ]8- unit. The molecules assemble in the crystal in a body-centered cubic fashion, each being attached to its eight neighbors by 24 equivalent hydrogen bonds-an extreme example of self-complementarity.     

Claisen-type addition of glycine to pyridoxal in water

The reaction between 5'-deoxypyridoxal and glycine in D2O buffered at pD 7.0 does not result in significant formation of the expected products of pyridoxal-catalyzed transamination or deuterium exchange of the alpha-amino protons of glycine, but rather gives a quantitative yield of the two diastereomeric products of the formal Claisen-type addition of glycine to 5'-deoxypyridoxal. The unexpected extensive formation of these products reflects the extraordinary selectivity of the 5'-deoxypyridoxal-stabilized glycine enolate toward addition to the carbonyl group of 5'-deoxypyridoxal in the protic solvent water.     

Ray-tracing simulation of ionization-free filamentation

A new ray-tracing scheme is proposed to simulate the non-linear propagation of ultra-short pulses. The results are in good agreement with experimental data and numerical solving of the non-linear Schrödinger equation in both the self-focusing and the filamentation regions. In particular, they indicate a major contribution of the photon bath in the self-guided propagation of ultra-short pulses. The model suggests that a pure-Kerr self-guiding mode can allow filamentation without ionization. PACS 42.65.Jx; 42.15.Dp     

The effect of a concurrent cognitive task on cortical potentials evoked by unpredictable balance perturbations

Background  

Although previous studies suggest that postural control requires attention and other cognitive resources, the central mechanisms responsible for this relationship remain unclear. To address this issue, we examined the effects of altered attention on cortical activity and postural responses following mechanical perturbations to upright stance. We hypothesized that cortical activity would be attenuated but not delayed when mechanical perturbations were applied during a concurrent performance of a cognitive task (i.e. when attention was directed away from the perturbation). We also hypothesized that these cortical changes would be accompanied by alterations in the postural response, as evidenced by increases in the magnitude of anteroposterior (AP) centre of pressure (COP) peak displacements and tibialis anterior (TA) muscle activity. Healthy young adults (n = 7) were instructed to continuously track (cognitive task) or not track (control task) a randomly moving visual target using a hand-held joystick. During each of these conditions, unpredictable translations of a moving floor evoked cortical and postural responses. Scalp-recorded cortical activity, COP, and TA electromyographic (EMG) measures were collected.     

Quantitative determination of the 3D dipole orientation of single molecules

Recently, different approaches have been implemented to detect single molecules with an optical dipole out of the sample plane. Principles to solve this problem of general interest have been laid but no detailed analysis has been performed to date. This paper is devoted to a quantitative analysis of the dipole orientation of out of plane molecules that we have detected by amplitude and phase masking of the input beam. The accuracy of the orientation is discussed.Received: 22 July 2003, Published online: 2 December 2003PACS: 32.50. + d Fluorescence, phosphorescence (including quenching)     

Effect of the counterion on the rate of electron transfer in dendrimer films

The electrochemical behavior of a film composed of a redox-active dendrimer was studied as a function of the type of counterion available during its reduction and reoxidation. The rate of permeation/migration of counterions into the film appeared to be the bottleneck to electron transfer through the film. Because the dendrimer is rather hydrophobic, increasing the hydrophobicity of the counterion increased the rate and extent of electron hopping within the films.     

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.