Electrochemical procedure for constructing poly(phenylene sulfide) brushes on glassy carbon and stainless steel

A simple electrochemical approach based on potential sweeping has been developed for growing poly(phenylene sulfide) (PPS) brushes from 4,4’‐disulfanediyldibenzenediazonium salt on glassy carbon and stainless steel. First, the diazonium salt becomes reduced at the substrate on the initial part of the sweep carried out in a negative direction to form a covalently bonded diphenyl disulfide film. Once sufficiently extreme potentials are reached the disulfide bridges are reductively cleaved to form a thin layer of covalently attached thiophenolates. These are prone to be involved in fast coupling reactions with the diazonium salt to form PPS brushes in a repetitive growth process. In this manner linear PPS brushes with thicknesses up to 150 nm are easily formed. In addition, exact control on the brush length may be exerted through the switching potential selected or the number of sweeps applied. The films are characterized by time‐of‐flight secondary ion mass spectrometry which shows that the film growth is accompanied by an increase in the intensity ratio of S^?/ in line with the proposed PPS structure. This structure was further supported by Raman spectra, exhibiting a high‐intensity C?S stretch band and no S?S stretch band. © 2015 Wiley Periodicals, Inc. J. Polym. Sci., Part A: Polym. Chem. 2016 , 54, 91–98     

Diazophosphonates: Effective Surrogates for Diazoalkanes in Pyrazole Synthesis

Diazophosphonates, readily prepared from α-ketophosphonates by oxidation of the corresponding hydrazones in batch or in flow, are useful partners in 1,3-dipolar cycloaddition reactions to alkynes to give N-H pyrazoles, including the first intramolecular examples of such a process. The phosphoryl group imbues a number of desirable properties into the diazo 1,3-dipole. The electron-withdrawing nature of the phosphoryl stabilizes the diazo compound making it easier to handle, whilst the ability of the phosphoryl group to migrate readily in a [1,5]-sigmatropic rearrangement enables its transfer from C to N to aromatize the initial cycloadduct, and hence its facile removal from the final pyrazole product. Overall, the diazophosphonate acts as a surrogate for the much less stable diazoalkane in cycloadditions, with the phosphoryl group playing a vital, but traceless, role. The cycloaddition proceeds more readily with alkynes bearing electron-withdrawing groups, and is regiospecific with asymmetrical alkynes. The potential of diazophosphonates for use in bioorthogonal cycloadditions is demonstrated by their facile addition to strained alkynes.     

Towards fully multivariate algorithmics: Parameter ecology and the deconstruction of computational complexity

The aim of this article is to motivate and describe the parameter ecology program, which studies how different parameters contribute to the difficulty of classical problems. We call for a new type of race in parameterized analysis, with the purpose of uncovering the boundaries of tractability by finding the smallest possible parameterizations which admit FPT-algorithms or polynomial kernels. An extensive overview of recent advances on this front is presented for the Vertex Cover problem. Moving even beyond the parameter ecology program we advocate the principle of model enrichment, which raises the challenge of generalizing positive results to problem definitions with greater modeling power. The computational intractability which inevitably emerges can be deconstructed by introducing additional parameters, leading towards a theory of fully multivariate algorithmics.     

Interkingdom signaling: integration, conformation, and orientation of N-acyl-L-homoserine lactones in supported lipid bilayers

N-Acyl-L-homoserine lactones (AHLs) are small cell-to-cell signaling molecules involved in the regulation of population density and local gene expression in microbial communities. Recent evidence shows that contact of this signaling system, usually referred to as quorum sensing, to living eukaryotes results in interactions of AHL with host cells in a process termed "interkingdom signaling". So far details of this process and the binding site of the AHLs remain unknown; both an intracellular and a membrane-bound receptor seem possible, the first of which requires passage through the cell membrane. Here, we used sum-frequency-generation (SFG) spectroscopy to investigate the integration, conformation, orientation, and translocation of deuterated N-acyl-L-homoserine lactones (AHL-d(n)) with varying chain length (8, 12, and 14 C atoms) in lipid bilayers consisting of a 1:1 mixture of POPC:POPG supported on SiO(2) substrates (prepared by vesicle fusion). We found that all AHL-d(n) derivatives are well-ordered within the supported lipid bilayer (SLB) in a preferentially all-trans conformation of the deuterated alkyl chain and integrated into the upper leaflet of the SLB with the methyl terminal groups pointing downward. For the bilayer system described above, no flip-flop of AHL-d(n) from the upper leaflet to the lower one could be observed. Spectral assignments and interpretations were further supported by Fourier transform infrared and Raman spectroscopy.     

Weighted compound integration rules with higher order convergence for all N

Quasi-Monte Carlo integration rules, which are equal-weight sample averages of function values, have been popular for approximating multivariate integrals due to their superior convergence rate of order close to 1/N or better, compared to the order 1/?N1/\sqrt{N} of simple Monte Carlo algorithms. For practical applications, it is desirable to be able to increase the total number of sampling points N one or several at a time until a desired accuracy is met, while keeping all existing evaluations. We show that although a convergence rate of order close to 1/N can be achieved for all values of N (e.g., by using a good lattice sequence), it is impossible to get better than order 1/N convergence for all values of N by adding equally-weighted sampling points in this manner. We then prove that a convergence of order N ^− α for α > 1 can be achieved by weighting the sampling points, that is, by using a weighted compound integration rule. We apply our theory to lattice sequences and present some numerical results. The same theory also applies to digital sequences.     

Computational elucidation of mechanisms of alkaline hydrolysis of nitrocellulose: dimer and trimer models with comparison to the corresponding monomer

Density functional theory (DFT) investigation has been undertaken to explore alkaline hydrolysis mechanisms for nitrocellulose in the gas phase and in bulk water solution by considering the dimer and trimer forms of 2,3,6-trinitro-β-d-glucopyranose in the (4)C(1) chair conformation and by comparing the computed results with the monomer. Ground and transition state geometries were optimized using the B3LYP functional and the 6-311G(d,p) basis set both in the gas phase and in the bulk water solution. The nature of respective potential energy surfaces was ascertained through harmonic vibrational frequency analysis. Intrinsic reaction coordinate calculations were performed to ensure that computed transition state connects to the respective reactants and products. Single-point energy calculations were also performed using the recently developed M06-2X functional and the cc-pVTZ basis set using the B3LYP/6-311G(d,p) optimized geometries. Effect of the bulk water solution was modeled using the polarizable continuum model (PCM) approach. It has been suggested that the dimeric form of 2,3,6-trinitro-β-d-glucopyranose can be considered as the smallest model to study the nitrocellulose system regarding the alkaline hydrolysis reaction. It was predicted that the peeling-off reaction will start after the denitration of various sites, which will follow a C3 → C6 → C2 denitration route. Further, it was determined that the peeling-off reaction will be more preferred than the ring cleavage through the ring CO bond.     

Gauss-Hermite quadratures for functions from Hilbert spaces with Gaussian reproducing kernels

We study univariate integration with the Gaussian weight for a positive variance α. This is done for the reproducing kernel Hilbert space with the Gaussian kernel for a positive shape parameter γ. We study Gauss-Hermite quadratures, although this choice of quadratures may be questionable since polynomials do not belong to this space of functions. Nevertheless, we provide the explicit formula for the error of the Gauss-Hermite quadrature using n function values. In particular, for 2αγ ²<1 we have an exponential rate of convergence, and for 2αγ ²=1 we have no convergence, whereas for 2αγ ²>1 we have an exponential divergence.     

Enantioselective alpha-hydroxylation of 2-arylacetic acid derivatives and buspirone catalyzed by engineered cytochrome P450 BM-3

Here we report that an engineered microbial cytochrome P450 BM-3 (CYP102A subfamily) efficiently catalyzes the alpha-hydroxylation of phenylacetic acid esters. This P450 BM-3 variant also produces the authentic human metabolite of buspirone, R-6-hydroxybuspirone, with 99.5% ee.