Unexpected retention of electrostatically adsorbed cytochrome c in high ionic strength solutions

Redox inactivation, but not removal, of electrostatically adsorbed cytochrome c(cyt-c) on an alkanethiol modified gold surface was observed after exposure of the electrode to 1.0 M aqueous NaCl, NaClO4, KCl, or KClO4 solutions.     

Assessing synthetic strategies: total syntheses of (+/-)-neodolabellane-type diterpenoids

Two strategies, namely a cross-metathesis/ring-closing metathesis and Pd-catalyzed Stille allylation/Nozaki-Hiyama-Kishi coupling, are examined for the preparation of neodolabellane-type diterpenoids 1 and 2. Whereas the first approach possessed synthetic limitations, the latter was successfully employed to provide compounds 1 and 2 in 8.8% (14 steps) and 8% (15 steps) overall yields, respectively.     

Conjugate addition/Ireland-Claisen rearrangements of allyl fumarates: simple access to terminally differentiated succinates

The conjugate addition of dialkylzinc reagents to allyl fumarates with subsequent Ireland-Claisen rearrangement has been accomplished yielding substituted unsymmetrical succinic acid derivatives. This one-pot reaction creates two new carbon-carbon bonds at contiguous stereogenic centers. The reaction proceeds for several alkylzinc reagents and substituted allyl fumarates. The products contain distinguishable functional handles for further manipulation.     

Alpha-particle-induced luminescence of rare-earth-doped Y2O3 nanophosphors

The feasibility of utilizing Y₂O₃:Tb³⁺ and Y₂O₃:Eu³⁺ as radioluminescent nanophosphors under alpha-particle excitation is investigated. Materials synthesized by the urea homogeneous precipitation method were characterized using scanning electron microscopy (SEM), transmission electron microscopy (TEM), and X-ray diffraction (XRD). The XRD analysis of as-produced precipitates and nanophosphors fired at temperatures ranging from 950 to 1100 °C indicated the presence of highly crystalline cubic Y₂O₃ with crystallite sizes of ∼40 nm. SEM and TEM analysis revealed that particles with average diameters of ∼200 nm and comprised of ∼40 nm grains were obtained. High-resolution radioluminescence and photoluminescence spectra were used to investigate the unwanted radioluminescence saturation effects associated with the high ionization rate of alpha-particles. Additionally, the radioluminescence intensity as a function of rare-earth ion dopant concentration is investigated for these materials under alpha-particle excitation. The prospect for utilizing these materials as intermediate absorbers in indirect-conversion radioisotope batteries is discussed.     

Bifunctional CD22 ligands use multimeric immunoglobulins as protein scaffolds in assembly of immune complexes on B cells

CD22 is a B cell-specific sialic acid-binding immunoglobulin-like lectin (Siglec) whose function as a regulator of B cell signaling is modulated by its interaction with glycan ligands bearing the sequence NeuAc alpha2-6Gal. To date, only highly multivalent polymeric ligands (n = 450) have achieved sufficient avidity to bind to CD22 on native B cells. Here we demonstrate that a synthetic bifunctional molecule comprising a ligand of CD22 linked to an antigen (nitrophenol; NP) can use a monoclonal anti-NP IgM as a decavalent protein scaffold to efficiently drive assembly of IgM-CD22 complexes on the surface of native B cells. Surprisingly, anti-NP antibodies of lower valency, IgA (n = 4) and IgG (n = 2), were also found to drive complex formation, though with lower avidity. Ligands bearing alternate linkers of variable length and structure were constructed to establish the importance of a minimal length requirement, and versatility in the structural requirement. We show that the ligand drives assembly of IgM complexes exclusively on the surface of B cells and not other classes of white blood cells that do not express CD22, which lends itself to the possibility of targeting B cells in certain hematopoietic malignancies.     

Evolution of the total syntheses of ustiloxin natural products and their analogues

Ustiloxins A-F are antimitotic heterodetic cyclopeptides containing a 13-membered cyclic core structure with a synthetically challenging chiral tertiary alkyl-aryl ether linkage. The first total synthesis of ustiloxin D was achieved in 31 linear steps using an S(N)Ar reaction. An NOE study of this synthetic product showed that ustiloxin D existed as a single atropisomer. Subsequently, highly concise and convergent syntheses of ustiloxins D and F were developed by utilizing a newly discovered ethynyl aziridine ring-opening reaction in a longest linear sequence of 15 steps. The approach was further optimized to achieve a better macrolactamization strategy. Ustiloxins D, F, and eight analogues (14-MeO-ustiloxin D, four analogues with different amino acid residues at the C-6 position, and three (9R,10S)-epi-ustiloxin analogues) were prepared via the second-generation route. Evaluation of these compounds as inhibitors of tubulin polymerization demonstrated that variation at the C-6 position is tolerated to a certain extent. In contrast, the S configuration of the C-9 methylamino group and a free phenolic hydroxyl group are essential for inhibition of tubulin polymerization.     

A Comparison of Primary and Secondary Hydrogen Abstraction from Organophosphates by Hydroxyl Radical

To compare the effect of primary and secondary C? H bonds on hydrogen?atom abstraction by hydroxyl radical, rate constants for the reactions of OH radicals with trimethyl phosphate [TMPO, (CH₃O)₃P(O)] and triethyl phosphate [TEPO, (CH₃CH₂O)₃P(O)] have been calculated using the semiclassical flux–flux autocorrelation function (SCFFAF) method and compared with experimental measurements over the temperature range 250–350 K. SCFFAF specifies that structures be obtained at the CCSD/6?31++G** level of chemical theory and the height of the activation barrier be determined using an energy extrapolation, here a variant of the G2MP2 method. Dynamics are generated in the SCFFAF method from forces computed with a transfer Hamiltonian, which provides information about the curvature of the potential energy surface in the neighborhood of the transition state (TS), as well as the required internal forces. The temperature?dependent reaction rate constants are calculated for the various possible abstraction pathways, primary hydrogen atom abstraction in the case of TMPO, and primary and secondary in the case of TEPO. Since two energetically favorable parent structures for each system are included in the model, the activation energy is calculated with respect to the conformer that connects to a given TS and the total rate constant at a given temperature is Boltzmann weighted with respect to the parent conformer. The computed temperature?dependent rate curves are consistent with published experimental data in both magnitude and temperature dependence. © 2013 Wiley Periodicals, Inc. Int J Chem Kinet 45: 187–201, 2013