The Spin‐Forbidden Reaction of Ground‐State Sulfur Atoms with Ethylene

Ground‐state S‐atoms (³P_J) were generated by pulsed laser photolysis of carbonyl sulfide (OCS) precursor and monitored by time‐resolved resonance fluorescence. The kinetics were studied over the temperature range of 291–1052 K. Below 900 K, the effective bimolecular rate constant k₁ was found to be independent of pressure and also to be in good accord with prior measurements made at 442 K and below. At higher temperatures, fall‐off curves were characterized. These demonstrate that the reaction is dominated by addition. The high‐pressure limit is summarized as k_∞ = 1.5 × 10^?11 exp(?8.4 kJ mol^?1/RT) cm³ molecule^?1 s^?1. The low‐pressure limiting rate constant is also obtained. The observation of formation of one or more adducts even at ～1000 K constrains their thermochemistry, and comparison with the computed reaction enthalpies for various candidates in the literature shows the addition products can only be accessed via intersystem crossing. Estimated Rice–Ramsperger–Kassel–Marcus (RRKM) addition rate constants at the low‐pressure limit for formation of vinylthiol and ethanethial are in accord with the observed kinetics assuming that the collisional efficiency near 1000 K is about 0.1.     

Electrospray ionization-voltage sweep-Ion mobility spectrometry for biomolecules and complex samples

Voltage Sweep Ion Mobility Spectrometry (VSIMS) has been applied to complex samples using electrospray ionization (ESI). The usable range of VSIMS has been extended from that obtained in previous studies where only volatile compounds were investigated. Using ESI, VSIMS was evaluated with compounds with reduced mobility values as low as 0.3 V²cm^?1 s^?1. The primary advantage of VSIMS is to enable a drift time ion mobility spectrometer (DTIMS) to detect both fast and slow moving ions at optimal resolving power, thus improving the peak capacity. In this work ESI-VSIMS was applied to a series of small peptides and drugs spanning a large range of reduced mobility values in order to demonstrate ESI-VSIMS to separation. To demonstrate improved peak capacity of IMS with voltage scan operation, oligomers of silicone oil provided a series of evenly-spaced peaks, ranging in reduced mobility values from 0.85 to 0.3 V²cm^?1 s^?1. The peak capacity of 61 for a standard IMS was improved to 102 when voltage sweep operation was employed. In addition, VSIMS increased the average resolving power of the DTIMS from 66 to 106 for silicone oil.     

Influence of fluorination on the microstructure and performance of diketopyrrolopyrrole‐based polymer solar cells

The solar cell performance and microstructure of DPP‐based polymers with different degrees of fluorination are reported. DPP‐based polymers with thiophene–phenyl–thiophene comonomer and thiophene flanking units are studied, with the degree of fluorination of the phenyl unit varied. With bifluorination of the phenyl ring, a higher open circuit voltage is achieved whilst maintaining or even improving the overall solar cell efficiency. While tetrafluorination leads to a further 0.1 V increase in V_OC, reaching a high photo voltage of 0.81 V, overall solar cell performance significantly drops. Microstructural studies using AFM, TEM, Grazing incidence wide‐angle X‐ray scattering (GIWAXS), and Resonant soft X‐ray scattering (R‐SoXS) reveal that bifluorination largely preserves the microstructure of the nonfluorinated system, whereas tetrafluorination results in coarse phase separation between the polymer donor and the fullerene acceptor. Our results demonstrate that the use of an extended comonomer is a promising strategy for optimizing the beneficial effects of fluorination for DPP‐based polymer solar cells, especially in improving the open circuit voltage. © 2016 Wiley Periodicals, Inc. J. Polym. Sci., Part B: Polym. Phys. 2017 , 55, 49–59     

Trifluoroacetic Acid in 2,2,2‐Trifluoroethanol Facilitates SNAr Reactions of Heterocycles with Arylamines

Small‐molecule drug discovery requires reliable synthetic methods for attaching amino compounds to heterocyclic scaffolds. Trifluoroacetic acid‐2,2,2‐trifluoroethanol (TFA‐TFE) is as an effective combination for achieving S_NAr reactions between anilines and heterocycles (e.g., purines and pyrimidines) substituted with a leaving group (fluoro‐, chloro‐, bromo‐ or alkylsulfonyl). This method provides a variety of compounds containing a “kinase‐privileged fragment” associated with potent inhibition of kinases. TFE is an advantageous solvent because of its low nucleophilicity, ease of removal and ability to solubilise polar substrates. Furthermore, TFE may assist the breakdown of the Meisenheimer–Jackson intermediate by solvating the leaving group. TFA is a necessary and effective acidic catalyst, which activates the heterocycle by N‐protonation without deactivating the aniline by conversion into an anilinium species. The TFA‐TFE methodology is compatible with a variety of functional groups and complements organometallic alternatives, which are often disadvantageous because of the expense of reagents, the frequent need to explore diverse sets of reaction conditions, and problems with product purification. In contrast, product isolation from TFA‐TFE reactions is straightforward: evaporation of the reaction mixture, basification and chromatography affords analytically pure material. A total of 45 examples are described with seven discrete heterocyclic scaffolds and 2‐, 3‐ and 4‐substituted anilines giving product yields that are normally in the range 50–90 %. Reactions can be performed with either conventional heating or microwave irradiation, with the latter often giving improved yields.     

Three-dimensional point cloud registration by matching surface features with relaxation labeling method

Automated approaches for the conversion of multiple overlapped three-dimensional (3D) point clouds into an integrated surface shape measurement in the form of a complete polygon surface are important in the general field of reverse engineering. Traditionally, the conversion process is achieved in a semi-automated manner that requires extensive user interaction. In this work, automated methods for point set registration are developed and experimentally validated using polygon surface reconstruction to represent raw, 3D point clouds obtained from non-contacting measurement systems. Using local differential properties extracted from the polygon surface representation for a measurement data set, a robust sculpture surface feature-matching method is described for automatically obtaining the initial orientation and mismatch estimates for each overlapped data set. Using both simulated and measured experimental data to quantify the performance of the method, it is shown that differential local surface features are appropriate metrics for identifying common features and initializing the relative positions of individual point clouds, thereby providing the basis for automating the registration and integration processes while improving the speed of the surface distance minimization method developed for the initial registration process.     

Rigidity for Nonnegatively Curved Metrics on S 2 × R3

We address the question: how large is the family of complete metricswith nonnegative sectional curvature on S ² × R³? We classify theconnection metrics, and give several examples of nonconnection metrics.We provide evidence that the family is small by proving some rigidityresults for metrics more general than connection metrics.

     

MALDI ionization mechanisms investigated by comparison of isomers of dihydroxybenzoic acid

Matrix‐assisted laser desorption/ionization (MALDI) ion formation mechanisms were investigated by comparison of isomers of dihydroxybenzoic acid (DHB). These exhibit substantially different MALDI performance, the basis for which was not previously understood. Luminescence decay curves are used here to estimate excited electronic state properties relevant for the coupled chemical and physical dynamics (CPCD) model. With these estimates, the CPCD predictions for relative total ion and analyte ion yields are in good agreement with the data for the DHB isomers. Predictions of a thermal equilibrium model were also compared and found to be incompatible with the data. Copyright © 2015 John Wiley & Sons, Ltd.     

Click chemistry in mesoporous materials: functionalization of porous silicon rugate filters

In this paper we report the use of the optical properties of porous silicon photonic crystals, combined with the chemical versatility of acetylene-terminated SAMs, to demonstrate the applicability of "click" chemistry to mesoporous materials. Cu(I)-catalyzed alkyne-azide cycloaddition reactions were employed to modify the internal pore surfaces through a two-step hydrosilylation/cycloaddition procedure. A positive outcome of this catalytic process, here performed in a spatially confined environment, was only observed in the presence of a ligand-stabilized Cu(I) species. Detailed characterization using Fourier transform infrared spectroscopy and optical reflectivity measurements demonstrated that the surface acetylenes had reacted in moderate to high yield to afford surfaces exposing chemical functionalities of interest. The porous silicon photonic crystals modified by the two-step strategy, and exposing oligoether moieties, displayed improved resistance toward the nonspecific adsorption of proteins as determined with fluorescently labeled bovine serum albumin. These results demonstrate that "click" immobilization offers a versatile, experimentally simple, and modular approach to produce functionalized porous silicon surfaces for applications as diverse as porous silicon-based sensing devices and implantable biomaterials.     

Highly luminescent Eu3+ chelate nanoparticles prepared by a reprecipitation-encapsulation method

Aqueous suspensions of highly luminescent Eu3+ chelate nanoparticles are prepared by a novel reprecipitation-encapsulation method. An alkyl alkoxysilane encapsulation agent is included during the nanoparticle formation process, forming a nanoparticle encapsulation layer that inhibits aggregation as evidenced by UV-vis spectroscopy and atomic force microscopy. In addition, the encapsulated nanoparticles exhibit a small size (10 nm), intense luminescence, and excellent photostability. We estimate that the molar extinction coefficients of the approximately 10 nm particles are approximately 5.0x10(7) M-1 cm-1 with a luminescence quantum yield of 6%, indicating a luminescence brightness many times larger than that of conventional fluorescent dyes and comparable to that of colloidal semiconductor quantum dots. The small size, high brightness, highly red-shifted luminescence, and long luminescence lifetimes of the nanoparticles are of interest for luminescence labeling and sensing applications.     

51V solid-state NMR and density functional theory studies of vanadium environments in V(V)O2 dipicolinic acid complexes

(51)V solid-state NMR and density functional theory (DFT) investigations are reported for a series of pentacoordinate dioxovanadium(V)-dipicolinate [V(V)O(2)-dipicolinate] and heptacoordinate aquahydroxylamidooxovanadium(V)-dipicolinate [V(V)O-dipicolinate] complexes. These compounds are of interest because of their potency as phosphatase inhibitors as well as their insulin enhancing properties and potential for the treatment of diabetes. Experimental solid-state NMR results show that the electric field gradient tensors in the V(V)O(2)-dipicolinate derivatives are affected significantly by substitution on the dipicolinate ring and range from 5.8 to 8.3 MHz. The chemical shift anisotropies show less dramatic variations with respect to the ligand changes and range between -550 and -600 ppm. To gain insights on the origins of the NMR parameters, DFT calculations were conducted for an extensive series of the V(V)O(2)- and V(V)O-dipicolinate complexes. To assess the level of theory required for the accurate calculation of the (51)V NMR parameters, different functionals, basis sets, and structural models were explored in the DFT study. It is shown that the original x-ray crystallographic geometries, including all counterions and solvation water molecules within 5 A of the vanadium, lead to the most accurate results. The choice of the functional and the basis set at a high level of theory has a relatively minor impact on the outcome of the chemical shift anisotropy calculations; however, the use of large basis sets is necessary for accurate calculations of the quadrupole coupling constants for several compounds of the V(V)O(2) series. These studies demonstrate that even though the vanadium compounds under investigations exhibit distorted trigonal bipyramidal coordination geometry, they have a "perfect" trigonal bipyramidal electronic environment. This observation could potentially explain why vanadate and vanadium(V) adducts are often recognized as potent transition state analogs.