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991.
992.
Salmon DJ Torres de Holding CL Thomas L Peterson KV Goodman GP Saavedra JE Srinivasan A Davies KM Keefer LK Miranda KM 《Inorganic chemistry》2011,50(8):3262-3270
The growing evidence that nitroxyl (HNO) has a rich pharmacological potential that differs from that of nitric oxide (NO) has intensified interest in HNO donors. Recently, the diazeniumdiolate (NONOate) based on isopropylamine (IPA/NO; Na[(CH(3))(2)CHNH(N(O)NO)]) was demonstrated to function under physiological conditions as an organic analogue to the commonly used HNO donor Angeli's salt (Na(2)N(2)O(3)). The decomposition mechanism of Angeli's salt is dependent on pH, with transition from an HNO to an NO donor occurring abruptly near pH 3. Here, pH is shown to also affect product formation from IPA/NO. Chemical analysis of HNO and NO production led to refinement of an earlier, quantum mechanically based prediction of the pH-dependent decomposition mechanisms of primary amine NONOates such as IPA/NO. Under basic conditions, the amine proton of IPA/NO is able to initiate decomposition to HNO by tautomerization to the nitroso nitrogen (N(2)). At lower pH, protonation activates a competing pathway to NO production. At pH 8, the donor properties of IPA/NO and Angeli's salt are demonstrated to be comparable, suggesting that at or above this pH, IPA/NO is primarily an HNO donor. Below pH 5, NO is the major product, while IPA/NO functions as a dual donor of HNO and NO at intermediate pH. This pH-dependent variability in product formation may prove useful in examination of the chemistry of NO and HNO. Furthermore, primary amine NONOates may serve as a tunable class of nitrogen oxide donor. 相似文献
993.
The first enantioselective total syntheses of indole alkaloids of the condylocarpine type are reported. (+)-Condylocarpine, (+)-isocondylocarpine, and (+)-tubotaiwine were prepared in high enantiomeric purity (er > 99:1) from (1S,5R)-hexahydro-1,5-methano-1H-azocino[4,3-b]indole-12-one 7b by way of five or six isolated intermediates. 相似文献
994.
Tyler K. Allred Andr P. Dieskau Peng Zhao Gregory L. Lackner Larry E. Overman 《Angewandte Chemie (International ed. in English)》2020,59(15):6268-6272
The enantioselective total synthesis of the rearranged spongian diterpenoid (?)‐macfarlandin C is reported. This is the first synthesis of a rearranged spongian diterpenoid in which the bulky hydrocarbon fragment is joined via a quaternary carbon to the highly hindered concave face of the cis‐2,8‐dioxabicyclo[3.3.0]octan‐3‐one moiety. The strategy involves a late‐stage fragment coupling between a tertiary carbon radical and an electrophilic butenolide resulting in the stereoselective formation of vicinal quaternary and tertiary stereocenters. A stereoselective Mukaiyama hydration that orients a pendant carboxymethyl side chain cis to the bulky octahydronapthalene substituent was pivotal in fashioning the challenging concave‐substituted cis‐dioxabicyclo[3.3.0]octanone fragment. 相似文献
995.
Larry W. Mc Laughlin 《Phosphorus, sulfur, and silicon and the related elements》2013,188(3-4):579-580
Abstract T4 RNA ligase can be used efficiently for the synthesis of 3′-5′ phosphodiester linkages between oligo-nucleotide blocks if the intermediate adenylated donor oligo-nucleotide is used. These adenylated oligonucleotides can be prepared using phosphorylating reagents activated by 1-hydroxybenzotriazole. 相似文献
996.
Abrahamyan S Ahmed Z Allada K Anez D Averett T Barbieri A Bartlett K Beacham J Bono J Boyce JR Brindza P Camsonne A Cranmer K Dalton MM de Jager CW Donaghy J Essig R Field C Folts E Gasparian A Goeckner-Wald N Gomez J Graham M Hansen JO Higinbotham DW Holmstrom T Huang J Iqbal S Jaros J Jensen E Kelleher A Khandaker M LeRose JJ Lindgren R Liyanage N Long E Mammei J Markowitz P Maruyama T Maxwell V Mayilyan S McDonald J Michaels R Moffeit K Nelyubin V Odian A Oriunno M Partridge R Paolone M 《Physical review letters》2011,107(19):191804
We present a search at the Jefferson Laboratory for new forces mediated by sub-GeV vector bosons with weak coupling α' to electrons. Such a particle A' can be produced in electron-nucleus fixed-target scattering and then decay to an e + e- pair, producing a narrow resonance in the QED trident spectrum. Using APEX test run data, we searched in the mass range 175-250 MeV, found no evidence for an A'→ e+ e- reaction, and set an upper limit of α'/α ~/= 10(-6). Our findings demonstrate that fixed-target searches can explore a new, wide, and important range of masses and couplings for sub-GeV forces. 相似文献
997.
Dewi P. Go Dalton J. E. Harvie Nicolin Tirtaatmadja Sally L. Gras Andrea J. O'Connor 《Particle & Particle Systems Characterization》2014,31(6):685-698
Porous microspheres capable of delivering high payloads of biomolecules with suitable biodegradability and biocompatibility would be valuable in delivery systems to aid tissue regeneration. This study describes a facile, scalable technique to produce biodegradable porous microspheres by combining continuous ink‐jetting through a piezoelectric nozzle with thermally induced phase separation (TIPS). A selection of biomaterials is investigated to suit delivery in tissue engineering, the synthetic polyesters poly(lactic‐co‐glycolic acid) (PLGA), and poly caprolactone (PCL) and a natural polymer, gelatin. The parameters governing the microsphere production are determined experimentally and compared to theoretical predictions derived from the fluid mechanics and heat transfer during the ink‐jetting process. The microspheres produced have open interconnected pores with mean particle diameters of 80–200 μm and no significant skin region. The physical properties, such as the mean particle diameter, pore size, and surface area could be controlled by varying production parameters including the ink‐jetting pressure, nozzle height, and the size and oscillation frequency of the nozzle. The technique is demonstrated to successfully encapsulate a model hydrophobic molecule during microsphere production with uniform distribution. Porous PLGA microspheres are also used to achieve much higher adsorption capacities of a short peptide than non‐porous microspheres of the same material. 相似文献
998.
A. Petri A. Baldassarri F. Dalton G. Pontuale L. Pietronero S. Zapperi 《The European Physical Journal B - Condensed Matter and Complex Systems》2008,64(3-4):531-535
We experimentally investigate the response of a sheared granular medium in a Couette geometry. The apparatus exhibits the expected stick-slip motion and we probe it in the very intermittent regime resulting from low driving. Statistical analysis of the dynamic fluctuations reveals notable regularities. We observe a possible stability property for the torque distribution, reminiscent of the stability of Gaussian independent variables. In this case, however, the variables are correlated and the distribution is skewed. Moreover, the whole dynamical intermittent regime can be described with a simple stochastic model, finding good quantitative agreement with the experimental data. Interestingly, a similar model has been previously introduced in the study of magnetic domain wall motion, a source of Barkhausen noise. Our study suggests interesting connections between different complex phenomena and reveals some unexpected features that remain to be explained. 相似文献
999.
Günther Nürnberger Vera Rayevskaya Larry L. Schumaker Frank Zeilfelder 《Constructive Approximation》2005,23(1):33-59
We describe a method which can be used to interpolate
function values at a set of scattered points
in a planar domain using bivariate polynomial splines
of any prescribed smoothness.
The method starts with an arbitrary given triangulation
of the data points, and involves refining some of the
triangles with Clough-Tocher splits.
The construction of the interpolating splines requires
some additional function values at selected points in
the domain, but no derivatives are needed at any point.
Given n data points and a corresponding
initial triangulation, the interpolating spline can be
computed in just O(n) operations.
The interpolation method is local
and stable, and provides optimal order approximation of smooth
functions. 相似文献
1000.