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51.
Benedict JB Cohen DE Lovell S Rohl AL Kahr B 《Journal of the American Chemical Society》2006,128(16):5548-5559
The concept of syncrystallization was reinvestigated by focusing on phthalic acid (PA) grown with methyl red (MR). Crystals are alternately red and yellow in adjacent growth sectors. X-ray structures of MR and its cocrystals, revealing MR in the neutral, zwitterionic, and protonated states, as well as measurements of linear birefringence and linear dichroism of mixed crystals, were used to investigate mechanisms of PA coloring. These experiments were complemented by force field calculations of the lowest energy stable surfaces of expressed facets and energies of MR on and in crystals, as well as molecular orbital calculations of MR. Two MR species were detected in PA having distinct energies, polarizations, and face selectivities. Assignments of structures to these MRs, previously thought to be neutral and protonated, required a nuanced analysis of hydrogen bonds. The essential difference between yellow and red species is whether the MR carboxylic acid proton is inter- or intramolecularly hydrogen bound. Inferences about mixed crystal structure drawn from an examination of cocrystals of PA and MR are inconsistent with polarization spectroscopy signaling caution when using stoichiometric compounds as models of dilute solid solutions. Upon heating mixed crystals, linear dichroism diminishes and oriented, elongated pools of MR separate and pass through the bulk in directions perpendicular to the direction of elongation. These batonnets subsequently crystallize leaving macroscopic oriented crystals of a MR-rich phase within PA. No evidence was found for the simultaneous crystallization of MR and PA; however, the MR reorientation on heating as well as the separation and recrystallization of a MR-rich phase are distinct processes that could be embraced by the literal meaning of syncrystallization. 相似文献
52.
Igor V. Mastikhin Aidin Arbabi Benedict Newling Abdelhaq Hamza Alexander Adair 《Experiments in fluids》2012,52(1):95-104
In acoustic cavitation, the relationship between the bubble dynamics on the microscale and the flow properties on the macroscale
is critical in determining sonochemical reaction kinetics. A new technique was developed to measure the void fraction and
estimate water mobility in the vicinity of cavitating bubbles using phase-encoded magnetic resonance imaging with short characteristic
measurement timescales (0.1–1 ms). The exponential behavior of the NMR signal decay indicated the fast diffusion regime, with
the relationship between local mechanical dispersion D
mix and the average bubble radius R,
Dmix >> \frac2R210-4s, D_{\rm mix}\gg \frac{2R^2}{10^{-4}\hbox{s}}, resulting in dispersion of orders of magnitude greater than diffusion in quiescent water. For two different samples (water
and a surfactant solution), the independent measurements of three-dimensional void fraction and velocity fields permitted
the calculation of compressibility, divergence and vorticity of the cavitating medium. The measured dynamics of the dissolved
gas, compared with that of the surrounding liquid, reflected the difference in the bubble coalescence and lifetimes and correlated
with the macroscopic flow parameters. 相似文献
53.
Makal A Benedict J Trzop E Sokolow J Fournier B Chen Y Kalinowski JA Graber T Henning R Coppens P 《The journal of physical chemistry. A》2012,116(13):3359-3365
The excited-state structure of [Cu(I)[(1,10-phenanthroline-N,N') bis(triphenylphosphine)] cations in their crystalline [BF(4)] salt has been determined at both 180 and 90 K by single-pulse time-resolved synchrotron experiments with the modified polychromatic Laue method. The two independent molecules in the crystal show distortions on MLCT excitation that differ in magnitude and direction, a difference attributed to a pronounced difference in the molecular environment of the two complexes. As the excited states differ, the decay of the emission is biexponential with two strongly different lifetimes, the longer lifetime, assigned to the more restricted molecule, becoming more prevalent as the temperature increases. Standard deviations in the current Laue study are very much lower than those achieved in a previous monochromatic study of a Cu(I) 2,9-dimethylphenanthroline substituted complex ( J. Am. Chem. Soc. 2009 , 131 , 6566 ), but the magnitudes of the shifts on excitation are similar, indicating that lattice restrictions dominate over the steric effect of the methyl substitution. Above all, the study illustrates emphatically that molecules in solids have physical properties different from those of isolated molecules and that their properties depend on the specific molecular environment. This conclusion is relevant for the understanding of the properties of molecular solid-state devices, which are increasingly used in current technology. 相似文献
54.
We complete the classification of positive rank gradings on Lie algebras of simple algebraic groups over an algebraically closed field k whose characteristic is zero or not too small, and we determine the little Weyl groups in each case. We also classify the stable gradings and prove Popov’s conjecture on the existence of a Kostant section. 相似文献
55.
In this paper, we study an exceptional theta correspondence, obtained by restricting the minimal automorphic representation of the adjoint group of type E7 and rank 3 over Q to the dual pair GxPGSp6. Here G is the anisotropic form of G2 over Q; using the correspondence, we lift certain automorphic forms on G to holomorphic cusp forms on PGSp6. This lifting provides the first step in a project to construct motives of rank 7 and weight O over Q with Galois group of type G2. 相似文献
56.
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58.
-2-Cyano-3,3-dimethylcyclopropanecarboxylic acid was obtained in >50% overall yield starting with ethyl 3,3-dimethylacrylate. The key step involved a tandem Michael reaction - intramolecular displacement to afford stereoselectively a cyclopropanoid precursor of -pyrethroids. 相似文献
59.
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