Manifestation of Extracoordination in the Resonance Raman Spectra of Water‐Soluble Cation Co‐Porphyrins

Resonance Raman spectra (RRS) of Co(II) and Co(III)5,10,15,20tetrakis(4Nmethylpyridinium)porphyrin ((Co^II(TmpyP4), and Co^III(TMPyP4)) in aqueous solutions at different pH as well as in organic solvents (methanol, ethanol, DMSO, DMF) are obtained. The increased sensitivity of the oscillation frequencies ₂, ₄, ₈, and ₆ — the markers of the oxidation state of a metal — to the nature of an axial ligand has been revealed. For Co^III(TmpyP4), the shifts of the indicated frequencies in extracoordination have turned out to be twofold larger than those for Co^II(TmpyP4). The spectral effects observed are related to different electron influence of the extraligands on the system of the porphyrin ring. In the case of Co(III)porphyrin, interaction of the d orbitals of the metal and the e _g ^*orbitals of the macrocycle is more efficient since its ionic radius is smaller than for the Co(II)complex. For Co^III(TmpyP4), a linear correlation between the oscillation frequencies ₂, ₄, ₈, and ₆ and the experimental Gutmann parameters characterizing the electronacceptor properties of solvents is found.     

Measurement of the spin parameters A and Ann in pp elastic scattering in the 1–3 GeV/c region

We have measured the asymmetry parameter A and the spin correlation parameter A_nn in pp elastic scattering, using the Argonne ZGS polarized proton beam and a polarized proton target. Angular distributions of A and A_nn for |t| ? 0.2 (GeV/c)²wereobtainedateightmomentabetween 1.10 and 2if2.75 GeV/c. We find significant structure in both the energy and t-dependence of A_nn at these energies. At p_lab ≈ 1.34 GeV/cA_nn reaches a very large value of about 0.8–0.9 near θ_cm = 90°.     

Bioinspired Oxidative Cyclization of the Geissoschizine Skeleton for Enantioselective Total Synthesis of Mavacuran Alkaloids

Reported is the enantioselective total syntheses of mavacuran alkaloids, (+)‐taberdivarine H, (+)‐16‐hydroxymethyl‐pleiocarpamine, and (+)‐16‐epi‐pleiocarpamine, and their postulated biosynthetic precursor 16‐formyl‐pleiocarpamine. This family of monoterpene indole alkaloids is a target of choice since some of its members are subunits of intricate bisindole alkaloids such as bipleiophylline. Inspired by the biosynthetic hypothesis, an oxidative coupling approach from the geissoschizine framework to form the N1?C16 bond was explored. Quaternization of the aliphatic nitrogen center was key to achieving the oxidative coupling induced by KHMDS/I₂ as it masks the nucleophilicity of the aliphatic nitrogen center and locks in the required cis conformation.     

Formation of SERS-active silver structures on the surface of mesoporous silicon

We have optimized the procedure for preparation of nanostructured silver films on the surface of mesoporous silicon (PSi) to use them as active substrates in surface-enhanced Raman scattering (SERS) spectroscopy. The greatest enhancement of the SERS signal was observed for samples obtained when the silver was deposited on PSi from an aqueous AgNO₃ solution with concentration 1⋅10^–2 M over a 10–15 minute period. The detection limit for rhodamine 6G on SERS-active substrates prepared by the optimized procedure was 1⋅10^–10 M. The enhancement factor for the SERS signal on these surfaces was estimated as ≈2⋅10⁸. We have shown that SERS-active substrates based on mesoporous silicon are promising for detection and study of complex organic compounds, in particular tetrapyrrole molecules. Translated from Zhurnal Prikladnoi Spektroskopii, Vol. 76, No. 2, pp. 298–306, March–April, 2009.     

Rearrangement of a mesylate tropane intermediate in nucleophilic substitution reactions. Synthesis of aza-bicyclo[3.2.1]octane and aza-bicyclo[3.2.2]nonane ethers,imides, and amines

Nucleophilic substitution of 2beta-mesyloxymethyl-N-methyl-3beta-p-tolyl-tropane intermediate with alkoxides, metal imides, or amines was found to lead not only to the expected bicyclo[3.2.1]octane (tropane) ether, imide, and amine derivatives but also to unexpected bicyclo[3.2.2]nonane derivatives. When alkoxides were used as nucleophile, only the rearranged bicyclo[3.2.2]nonane structure was obtained, whereas the use of amines or imides as nucleophile afforded a mixture of the two structures. The bicyclo[3.2.2]nonane structure was assigned by NMR analysis.     

The CellCard System: a novel approach to assessing compound selectivity for lead prioritization of G protein-coupled receptors

Advances in high throughput screening technologies have led to the identification of many small molecules, "hits", with activities toward the target of interest. And, as the screening technologies become faster and more robust, the rate at which the molecules are identified continues to increase. This evolution of high throughput screening technologies has generated a significant strain on the laboratories involved with the downstream profiling of these hits using cell-based assays. The CellCard System, by enabling multiple targets and/or cell lines to be assayed simultaneously within a single well, provides a platform on which selectivity screening can be quickly and robustly performed. Here we describe two case studies using the beta-lactamase and beta-galactosidase reporter gene systems to characterize G protein-coupled receptor agonist activity. Using these examples we demonstrate how the implementation of this technology enables assay miniaturization without micro-fluidic devices as well as how the inclusion of intra-well controls can provide a means of data quality assessment within each well.     

Manifestation of Peripheral NO2-Substitution in the Resonance Raman Scattering Spectra of Tetraarylporphyrins

The resonance Raman scattering (RS) spectra of a series of nitro-substituted derivatives of the free base of tetraphenyl porphyrin that were obtained on continuous excitation near the Soret band have been investigated. For the molecules in which the NO₂ group is located in the -position of pyrrole rings or in the para-position of meso-phenyl substituents, an intense line of the mode within the range 1340–1355 cm^–1 is discovered. Based on the obtained resonance RS spectra of the diprotonated derivatives of nitro-tetraarylporphyrins, it is assigned to symmetrical vibration of a nitro group ( _s NO₂). Activation of the _s NO₂ vibration is indicative of the existence of the -delocalization effect for a number of nitro-substituted porphyrins at which interaction between the molecular orbitals of the nitro-substituents and the porphyrin macrocycle occurs. Moreover, the -delocalization is typical of both direct addition of a nitro-substituent to the porphyrin ring and of its binding via a meso-phenyl group. The results obtained demonstrate the informative value of the resonance RS spectroscopy for creating and studying model donor–acceptor systems with the participation of porphyrins.     

Improvement in the predictivity of squeal simulations: Uncertainty and robustness

The objective of this paper is to improve the predictivity of squeal simulations by introducing uncertainty and robustness concepts during simulations. Complex eigenvalue analysis is a traditional way to detect numerically the unstable modes that can be associated with extensive vibration and noise pollution. This simulation, for which associated computational times are compatible with the design phase, is known to be insufficiently predictive. We first propose a complete strategy that relies on the integration of random fields into the contact interface, complex eigenvalue calculations, probabilistic analysis and a robustness criterion. Next, this strategy is applied to study the instabilities of a complete industrial brake system. Experimental comparisons highlight the efficiency of the improved squeal detection methodology.