DFT Study of the Molybdenum‐Catalyzed Deoxydehydration of Vicinal Diols

The mechanism of the molybdenum‐catalyzed deoxydehydration (DODH) of vicinal diols has been investigated using density functional theory. The proposed catalytic cycle involves condensation of the diol with an Mo^VI oxo complex, oxidative cleavage of the diol resulting in an Mo^IV complex, and extrusion of the alkene. We have compared the proposed pathway with several alternatives, and the results have been corroborated by comparison with the molybdenum‐catalyzed sulfoxide reduction recently published by Sanz et al. and with experimental observations for the DODH itself. Improved understanding of the mechanism should expedite future optimization of molybdenum‐catalyzed biomass transformations.     

RAFT polymerization of alternating styrene‐pentafluorostyrene copolymers

Reversible addition‐fragmentation chain‐transfer (RAFT) polymerization was used to control the alternating copolymerization of styrene and 2,3,4,5,6‐pentaflurostyrene. The RAFT polymerization yields a high degree of control over the molecular weight of the polymers and does not significantly influence the reactivity ratios of the monomers. The controlled free‐radical polymerization could be initiated using AIBN at elevated temperatures or using a redox couple (benzoyl peroxide/N,N‐dimethylaniline) at room temperature, while maintaining control over molecular weight and dispersity. The influence of temperature and solvent on the molecular weight distribution and reactivity ratios were investigated. © 2014 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2014 , 52, 1555–1559     

Optimal control in NMR spectroscopy: Numerical implementation in SIMPSON

We present the implementation of optimal control into the open source simulation package SIMPSON for development and optimization of nuclear magnetic resonance experiments for a wide range of applications, including liquid- and solid-state NMR, magnetic resonance imaging, quantum computation, and combinations between NMR and other spectroscopies. Optimal control enables efficient optimization of NMR experiments in terms of amplitudes, phases, offsets etc. for hundreds-to-thousands of pulses to fully exploit the experimentally available high degree of freedom in pulse sequences to combat variations/limitations in experimental or spin system parameters or design experiments with specific properties typically not covered as easily by standard design procedures. This facilitates straightforward optimization of experiments under consideration of rf and static field inhomogeneities, limitations in available or desired rf field strengths (e.g., for reduction of sample heating), spread in resonance offsets or coupling parameters, variations in spin systems etc. to meet the actual experimental conditions as close as possible. The paper provides a brief account on the relevant theory and in particular the computational interface relevant for optimization of state-to-state transfer (on the density operator level) and the effective Hamiltonian on the level of propagators along with several representative examples within liquid- and solid-state NMR spectroscopy.     

Determination of liposome–buffer distribution coefficients of charged drugs by capillary electrophoresis frontal analysis

The potential of using CE frontal analysis (CE‐FA) to study the interactions between a range of charged low molecular weight drug substances and liposomes was evaluated. The liposomes used were net negatively charged and consisted of 2‐oleoyl‐1‐palmitoyl‐sn‐glycero‐3‐phosphocholine and 1,2‐dipalmitoyl‐sn‐glycero‐3‐phosphate monosodium salt in a ratio of 80/20 mol%. Apparent distribution coefficients (D_mem), defined as the molar concentration of drug substance in the membrane phase divided by the molar concentration of drug substance in the aqueous phase, were successfully determined for six positively and eight negatively charged drug substances with log D_mem ranging from 1.35 to 3.63. The extent of liposome–buffer distribution was found to be dependent on the drug concentration. The results obtained with the developed CE‐FA method were in good agreement with results obtained by equilibrium dialysis. Furthermore, the CE‐FA method was faster, less labor intensive and required smaller sample volumes (～50 μL) compared with equilibrium dialysis. Thus, CE‐FA is an efficient and useful tool for the characterization of interactions between liposomes and low molecular weight drug substances.     

Structural Tracking of a Bimolecular Reaction in Solution by Time‐Resolved X‐Ray Scattering

Molecular movies : Time‐resolved X‐ray scattering provides direct structural information on an electronically excited complex while it is formed in the bimolecular reaction between excited octahydrogen[tetrakis‐μ‐diphosphito‐1κP:2κP′‐diplatinate](4‐) (PtPOP*) and thallium ions. In the exciplex one thallium(I) and two platinum(II) ions are found to be collinear.

     

The maximum of a Lévy process reflected at a general barrier

We investigate the reflection of a Lévy process at a deterministic, time-dependent barrier and in particular properties of the global maximum of the reflected Lévy process. Under the assumption of a finite Laplace exponent, ψ(θ)$\psi \left(\theta \right)$, and the existence of a solution θ^∗>0${\theta }^{\ast }>0$ to ψ(θ)=0$\psi \left(\theta \right)=0$ we derive conditions in terms of the barrier for almost sure finiteness of the maximum. If the maximum is finite almost surely, we show that the tail of its distribution decays like Kexp(−θ^∗x)$Kexp(-{\theta }^{\ast }x)$. The constant K$K$ can be completely characterized, and we present several possible representations. Some special cases where the constant can be computed explicitly are treated in greater detail, for instance Brownian motion with a linear or a piecewise linear barrier. In the context of queuing and storage models the barrier has an interpretation as a time-dependent maximal capacity. In risk theory the barrier can be interpreted as a time-dependent strategy for (continuous) dividend pay out.     

Dimensional asymptotics of determinants on <Emphasis Type="Italic">S</Emphasis><Superscript><Emphasis Type="Italic">n</Emphasis></Superscript>, and proof of Bär–Schopka’s conjecture

We study the dimensional asymptotics of the effective actions, or functional determinants, for the Dirac operator D and Laplacians \({\Delta +\beta R}\) on round S ⁿ . For Laplacians the behavior depends on “the coupling strength” β, and one cannot in general expect a finite limit of \({\zeta'(0)}\) , and for the ordinary Laplacian, \({\beta=0}\) , we prove it to be \({+\infty}\) , for odd dimensions. For the Dirac operator, Bär and Schopka conjectured a limit of unity for the determinant (Bär and Schopka, Geometric Analysis and Nonlinear PDEs, pp. 39–67, 2003), i.e.

$\lim_{n\to\infty} {\rm{det}}(D, S^n_{\rm{can}})=1.$

We prove their conjecture rigorously, giving asymptotics, as well as a pattern of inequalities satisfied by the determinants. The limiting value of unity is a virtue of having “enough scalar curvature” and no kernel. Thus, for the important (conformally covariant) Yamabe operator, \({\beta=(n-2)/(4(n-1))}\) , the determinant tends to unity. For the ordinary Laplacian it is natural to rescale spheres to unit volume, since

$\lim_{k\to\infty} {\rm{det}}(\Delta,S^{2k+1}_{\rm rescaled})=\frac{1}{2\pi e}$

.

     

Binding of Ca2+, Mg2+, and heparin by human serum amyloid P component in affinity capillary electrophoresis

Human serum amyloid P component (SAP) is a glycoprotein circulating in the blood and found in association with all types of amyloid (malfolded potein aggregates) examined so far. Despite uncertainties regarding the precise function of SAP in vivo, the lectin-like properties of this Ca(2+)-activated protein with affinity for anionic saccharides and malfolded proteins are well known. The propensity to form homomeric penta- or decamers in solution and the selfaggregation in the presence of Ca(2+) as well as the tendency of SAP to attach to uncoated fused silica have precluded the analysis of SAP by microelectrophoretic methods. We now work out conditions to characterize the binding of Ca(2+) and Mg(2+) and the binding of heparin to SAP in the presence of divalent metal ions by ACE. The results show a strong binding of heparin (sub-muM apparent dissociation constants) even in the abscence of Ca(2+) at low ionic strength, pH 8.2. Also, a selective interaction with Ca(2+) compared with Mg(2+) is demonstrated. The approach will further the use of microelectrophoretic methods to examine the interactions of SAP with ligands of putative pathophysiological relevance such as lipopolysaccharides and misfolded proteins.