Enantiomerically pure phosphaalkene-oxazolines (PhAk-Ox): synthesis, scope and copolymerization with styrene

The design of a synthetic route to a class of enantiomerically pure phosphaalkene-oxazolines (PhAk-Ox) is presented. The condensation of a lithium silylphosphide and a ketone (the phospha-Peterson reaction) was used as the P=C bond-forming step. Attempted condensation of PhC(=O)Ox (Ox = CNOCH(iPr)CH(2)) and MesP(SiMe(3))Li gave the unusual heterocycle (MesP)(2)C(Ph)=CN-(S)-CH(iPr)CH(2)O (3). However, PhAk-Ox (S,E)-MesP=C(Ph)CMe(2)Ox (1?a) was successfully prepared by treating MesP(SiMe(3))Li with PhC(=O)CMe(2)Ox (52?%). To demonstrate the modularity and tunability of the phospha-Peterson synthesis several other phosphaalkene-oxazolines were prepared in an analogous manner to 1?a: TripP=C(Ph)CMe(2)Ox (1?b; Trip = 2,4,6-triisopropylphenyl), 2-iPrC(6)H(4)P=C(Ph)CMe(2)Ox (1?c), 2-tBuC(6)H(4)P=C(Ph)CMe(2)Ox (1?d), MesP=C(4-MeOC(6)H(4))CMe(2)Ox (1?e), MesP=C(Ph)C(CH(2))(4)Ox (1?f), and MesP=C(3,5-(CF(3))(2)C(6)H(3))C(CH(2))(4)Ox (1?g). To evaluate the PhAk-Ox compounds as prospective precursors to chiral phosphine polymers, monomer 1?a and styrene were subjected to radical-initiated copolymerization conditions to afford [{MesPC(Ph)(CMe(2)Ox)}(x){CH(2)CHPh}(y)](n) (9?a: x = 0.13n, y = 0.87n; GPC: M(w) = 7400?g mol(-1) , PDI = 1.15).     

Electro-oxidation of CO(chem) on Pt nanosurfaces: solution of the peak multiplicity puzzle

An understanding of the oxidation of chemisorbed CO (CO(chem)) on Pt nanoparticle surfaces is of major importance to fuel cell technology. Here, we report on the relation between Pt nanoparticle surface structure and CO(chem) oxidative stripping behavior. Oxidative stripping voltammograms are obtained for CO(chem) preadsorbed on cubic, octahedral, and cuboctahedral Pt nanoparticles that possess preferentially oriented and atomically flat domains. They are compared to those obtained for etched and thermally treated Pt(poly) electrodes that possess atomically flat, ordered surface domains separated by grain boundaries as well as those obtained for spherical Pt nanoparticles. A detailed analysis of the results reveals for the first time the presence of up to four voltammetric features in CO(chem) oxidative stripping transients, a prepeak and three peaks, that are assigned to the presence of surface domains that are either preferentially oriented or disordered. The interpretation reported in this article allows one to explain all features within the voltammograms for CO(chem) oxidative stripping unambiguously.     

Structure and hydrolysis of the U(IV), U(V), and U(VI) aqua ions from ab initio molecular simulations

Ab initio molecular dynamics simulations at 300 K, based on density functional theory, are performed to study the hydration shell geometries, solvent dipole, and first hydrolysis reaction of the uranium(IV) (U(4+)) and uranyl(V) (UO(2)(+)) ions in aqueous solution. The solvent dipole and first hydrolysis reaction of aqueous uranyl(VI) (UO(2)(2+)) are also probed. The first shell of U(4+) is coordinated by 8-9 water ligands, with an average U-O distance of 2.42 ?. The average first shell coordination number and distance are in agreement with experimental estimates of 8-11 and 2.40-2.44 ?, respectively. The simulated EXAFS of U(4+) matches well with recent experimental data. The first shell of UO(2)(+) is coordinated by five water ligands in the equatorial plane, with the average U═O(ax) and U-O distances being 1.85 ? and 2.54 ?, respectively. Overall, the hydration shell structure of UO(2)(+) closely matches that of UO(2)(2+), except for small expansions in the average U═O(ax) and U-O distances. Each ion strongly polarizes their respective first-shell water ligands. The computed acidity constants (pK(a)) of U(4+) and UO(2)(2+) are 0.93 and 4.95, in good agreement with the experimental values of 0.54 and 5.24, respectively. The predicted pK(a) value of UO(2)(+) is 8.5.     

The effect of point mutation on the equilibrium structural fluctuations of ferric Myoglobin

The ultrafast equilibrium fluctuations of the Fe(III)-NO complex of a single point mutation of Myoglobin (H64Q) have been studied using Fourier Transform 2D-IR spectroscopy. Comparison with data from wild type Myoglobin (wt-Mb) shows the presence of two conformational substates of the mutant haem pocket where only one exists in the wild type form. One of the substates of the mutant exhibits an almost identical NO stretching frequency and spectral diffusion dynamics to wt-Mb while the other is distinctly different in both respects. The remarkably contrasting dynamics are largely attributable to interactions between the NO ligand and a nearby distal side chain which provides a basis for understanding the roles of these side chains in other ferric haem proteins.     

Formation of high-capacity protein-adsorbing membranes through simple adsorption of poly(acrylic acid)-containing films at low pH

Layer-by-layer polyelectrolyte adsorption is a simple, convenient method for introducing ion-exchange sites in porous membranes. This study demonstrates that adsorption of poly(acrylic acid) (PAA)-containing films at pH 3 rather than pH 5 increases the protein-binding capacity of such polyelectrolyte-modified membranes 3-6-fold. The low adsorption pH generates a high density of -COOH groups that function as either ion-exchange sites or points for covalent immobilization of metal-ion complexes that selectively bind tagged proteins. When functionalized with nitrilotriacetate (NTA)-Ni(2+) complexes, membranes containing PAA/polyethylenimine (PEI)/PAA films bind 93 mg of histidine(6)-tagged (His-tagged) ubiquitin per cm(3) of membrane. Additionally these membranes isolate His-tagged COP9 signalosome complex subunit 8 from cell extracts and show >90% recovery of His-tagged ubiquitin. Although modification with polyelectrolyte films occurs by simply passing polyelectrolyte solutions through the membrane for as little as 5 min, with low-pH deposition the protein binding capacities of such membranes are as high as for membranes modified with polymer brushes and 2-3-fold higher than for commercially available immobilized metal affinity chromatography (IMAC) resins. Moreover, the buffer permeabilities of polyelectrolyte-modified membranes that bind His-tagged protein are ~30% of the corresponding permeabilities of unmodified membranes, so protein capture can occur rapidly with low-pressure drops. Even at a solution linear velocity of 570 cm/h, membranes modified with PAA/PEI/PAA exhibit a lysozyme dynamic binding capacity (capacity at 10% breakthrough) of ~40 mg/cm(3). Preliminary studies suggest that these membranes are stable under depyrogenation conditions (1 M NaOH).     

Preparation of Nitriles by Dehydration of Primary Carboxawides with a Supported phosphorus pentoxide reagent

The use of a supported phosphorus pentoxide reagent in the synthesis of selected nitriles is discussed.     

2-Butyl-4-iodoimidazole-5-carboxaldehyde: A Versatile Intermediate for the Synthesis of Highly Functionalized Imidazoles

The facile preparation of 2-butyl-4-iodoimidazole-5-carboxaldehyde 1 is described. The versatility of this intermediate in the synthesis of highly tunctionalized imidazoles is demonstrated with the synthesis of two potent and selective angiotensin II receptor antagonists.     

Vibrational energy relaxation dynamics of Si---H stretching modes on stepped H/Si(111) 1×1 surfaces

The vibrational energy relaxation rates of excited Si---H stretching modes on the monohydride steps of miscut H/Si(111) 1×1 surfaces are calculated using Bloch-Redfield theory combined with classical molecular dynamics (MD) simulation. The structure and vibrational frequencies of the surface are first investigated using the Car-Parrinello ab initio MD method. The calculated Si---Si---H bending frequencies and relaxed structures are then used to refine the empirical potential for the classical MD simulations. The lifetime of the excited Si---H stretching mode at the step is found to be shorter than the modes on the terrace. Both the magnitude and the trend of the calculated results agree well with the experimental measurement on the 9° monohydride stepped surface. The vibrational relaxation rate of the Si---H stretching modes on the 15° monohydride stepped surface are also calculated and predicted to have a slightly shorter lifetime than for the 9° surface.