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41.
John Asplund Kossi Edoh Ruth Haas Yulia Hristova Beth Novick Brett Werner 《Discrete Mathematics》2018,341(10):2938-2948
For a graph and, the shortest path reconfiguration graph of with respect to and is denoted by . The vertex set of is the set of all shortest paths between and in . Two vertices in are adjacent, if their corresponding paths in differ by exactly one vertex. This paper examines the properties of shortest path graphs. Results include establishing classes of graphs that appear as shortest path graphs, decompositions and sums involving shortest path graphs, and the complete classification of shortest path graphs with girth 5 or greater. We include an infinite family of well structured examples, showing that the shortest path graph of a grid graph is an induced subgraph of a lattice. 相似文献
42.
Bryte V. Kelly Joseph M. Tanski Mary Beth Anzovino Gerard Parkin 《Journal of chemical crystallography》2005,35(12):969-981
The molecular structures of N(o-C6H4OH)3, PhN(o-C6H4OH)2, andp-TolN(o-C6H4OMe)2 have been determined by X-ray diffraction, thereby indicating several structural differences. For example, whereas the nitrogen
in N(o-C6H4OH)3 is pyramidal with ΣC–N–C = 348.3∘, the nitrogen atoms in PhN(o-C6H4OH)2 andp-TolN(o-C6H4OMe)2 are trigonal planar with ΣC–N–C = 359.9∘ and ΣC–N–C = 360.0∘, respectively. The phenyl andp-tolyl groups of PhN(o-C6H4OH)2 andp-TolN(o-C6H4OMe)2 lie close to the trigonal plane, while theo-C6H4OH ando-C6H4OMe groups are almost orthogonal to this plane. The coplanar and orthogonal orientations of the aryl groups of PhN(o-C6H4OH)2 andp-TolN(o-C6H4OMe)2 are in marked contrast to those of the phenyl groups within Ph3N, which exhibit dihedral angles in the range 38–52∘ and approximateD3 symmetry. The observed structures of PhN(o-C6H4OH)2 andp-TolN(o-C6H4OMe)2 may be rationalized in terms of maximizing delocalization of the nitrogen lone pair into the phenyl andp-tolyl groups, while minimizing unfavorable overlap with theo-C6H4OH ando-C6H4OMe groups due to the presence of π-donatingortho-substituents; the orthogonal orientation of theo-C6H4OH ando-C6H4OMe groups is also one that minimizes unfavorable steric interactions between theortho-substituents. 相似文献
43.
Integrated within an appropriate theoretical framework, molecular dynamics (MD) simulations are a powerful tool to complement experimental studies of solvation dynamics. Together, experiment, theory, and simulation have provided substantial insight into the dynamic behavior of polar solvents. MD investigations of solvation dynamics are especially valuable when applied to the heterogeneous environments found in biological systems, where the calculated response of the environment to the electrostatic perturbation of the probe molecule can easily be decomposed by component (e.g., aqueous solvent, biomolecule, ions), greatly aiding the molecular-level interpretation of experiments. A comprehensive equilibrium and nonequilibrium MD study of the solvation dynamics of the fluorescent dye Hoechst 33258 (H33258) in aqueous solution is presented. Many fluorescent probes employed in experimental studies of solvation dynamics in biological systems, such as the DNA minor groove binder H33258, have inherently more conformational flexibility than prototypical fused-ring chromophores. The role of solute flexibility was investigated by developing a fully flexible force-field for the H33258 molecule and by simulating its solvation response. While the timescales for the total solvation response calculated using both rigid (0.16 and 1.3 ps) and flexible (0.17 and 1.4 ps) models of the probe closely matched the experimentally measured solvation response (0.2 and 1.2 ps), there were subtle differences in the response profiles, including the presence of significant oscillations for the flexible probe. A decomposition of the total response of the flexible probe revealed that the aqueous solvent was responsible for the overall decay, while the oscillations result from fluctuations in the electrostatic terms in the solute intramolecular potential energy. A comparison of equilibrium and nonequilibrium approaches for the calculation of the solvation response confirmed that the solvation dynamics of H33258 in water is well-described by linear response theory for both rigid and flexible models of the probe. 相似文献
44.
Yoon J Lee SW Choi S Heo K Jin KS Jin S Kim G Kim J Kim KW Kim H Ree M 《The journal of physical chemistry. B》2008,112(17):5338-5349
In this study, we report the first production of two-dimensionally well-ordered molecular multilayers (i.e., with a well-defined molecular lamellar structure) based on the antiparallel beta-sheet chain conformation in thin films of a brush polypeptide, poly(S-n-hexadecyl-dl-homocysteine) (PHHC), through the use of a simple spin-coating process and the quantitative structural and property analysis of the thin films using a grazing incidence X-ray scattering technique combined with Fourier transform infrared spectroscopy and differential scanning calorimetry. These analyses provide detailed information about the structure and molecular conformation of the self-assembled lamellae in the PHHC thin film, which is not easily obtained using conventional techniques. Moreover, we used the in situ measurements carried out at various temperatures and the data analyses to establish mechanisms for the evolution of the self-assembled lamellar structures in the film and for their melting. In addition, we propose molecular structure models of the PHHC polymer molecules in the thin film at various temperatures. 相似文献
45.
Chromophore systems consisting of one (compound 5) or two (compound 6) phenothiazine rings covalently attached to a bis-piperazinexylene chain were synthesized and evaluated as DNA photocleaving agents. In the presence of DNA, the compounds were shown to monointercalate in their deaggregated forms and to strongly absorb red wavelengths of light. Reactions containing micromolar concentrations of compound produced robust photocleavage of plasmid DNA under near-physiological conditions of temperature and pH (22 °C and pH 7.0). Phenothiazines 5 and 6 increased the Tm of calf thymus DNA by 17 and 19 °C, indicating that significant levels of duplex stabilization were produced. 相似文献
46.
The infrared (IR)-vacuum ultraviolet (VUV)-pulsed field ionization-photoelectron (IR-VUV-PFI-PE) spectrum for C2H4(X1A(g), v11 = 1, N'(Ka'Kc') = 3(03)) in the VUV range of 83,000-84,800 cm(-1) obtained using a single mode infrared laser revealed 24 rotationally resolved vibrational bands for the ion C2H4(+)(X2B(3u)) ground state. The frequencies and symmetry of the vibrational bands thus determined, together with the anharmonic frequency predictions calculated at the CCSD(T)/aug-cc-pVQZ level, have allowed the unambiguous assignment of these vibrational bands. These bands are mostly combination bands. The measured frequencies of these bands yield the fundamental frequencies for v8+ = 1103 +/- 10 cm(-1) and v10+ = 813 +/- 10 cm(-1) of C2H4(+)(X2B(3u)), which have not been determined previously. The present IR-VUV-PFI-PE study also provides truly rovibrationally selected and resolved state-to-state cross sections for the photoionization transitions C2H4(X1A(g); v11, N'(Ka'Kc')) --> C2H4(+)(X2B(3u); vi+, N+(Ka+Kc+)), where N'(Ka'Kc') denotes the rotational level of C2H4(X1A(g); v11), and vi+ and N+(Ka+Kc+) represent the vibrational and rotational states of the cation. 相似文献
47.
Standard JM Copack BA Johnson TK Przybyla DE Graham SR Steidl RJ 《The journal of physical chemistry. A》2008,112(2):336-341
Sulfur ylides are useful synthetic intermediates that are formed from the interaction between singlet carbenes and sulfur-containing molecules. Partial double-bond character frequently has been proposed as a key contributor to the stability of sulfur ylides. Calculations at the B3LYP, MP2, and CCSD(T) levels of theory employing various basis sets have been performed on the sulfur ylides H(2)S-CH(2) and (CH(3))(2)S-CH(2) in order to investigate the structure and bonding of these systems. The following general properties of sulfur ylides were observed from the computational studies: C-S bond distances that are close in length to that of a typical C-S double bond, high charge transfer from the sulfide to the carbene, and large torsional rotation barriers. Analysis of the sulfur ylide charge distribution indicates that the unusually short C-S bond distance can be attributed in part to the electrostatic attraction between highly oppositely charged carbon and sulfur atoms. Furthermore, n --> sigma* stabilization arising from donation of electron density from the carbon lone pair orbital into S-H or S-C antibonding orbitals leads to larger than expected torsional barriers. Finally, natural resonance theory analysis indicates that the bond order of the sulfur ylides H(2)S-CH(2) and (CH(3))(2)S-CH(2) is 1.4-1.5, intermediate between a single and double bond. 相似文献
48.
McNally BA Koulov AV Lambert TN Smith BD Joos JB Sisson AL Clare JP Sgarlata V Judd LW Magro G Davis AP 《Chemistry (Weinheim an der Bergstrasse, Germany)》2008,14(31):9599-9606
Chloride transport by a series of steroid-based "cholapod" receptors/carriers was studied in vesicles. The principal method involved preincorporation of the cholapods in the vesicle membranes, and the use of lucigenin fluorescence quenching to detect inward-transported Cl-. The results showed a partial correlation between anion affinity and transport activity, in that changes at the steroidal 7 and 12 positions affected both properties in concert. However, changes at the steroidal 3-position yielded irregular effects. Among the new steroids investigated the bis-p-nitrophenylthiourea 3 showed unprecedented activity, giving measurable transport through membranes with a transporter/lipid ratio of 1:250 000 (an average of <2 transporter molecules per vesicle). Increasing transporter lipophilicity had no effect, and positively charged steroids had low activity. The p-nitrophenyl monourea 25 showed modest but significant activity. Measurements using a second method, requiring the addition of transporters to preformed vesicle suspensions, implied that transporter delivery was problematic in some cases. A series of measurements employing membranes of different thicknesses provided further evidence that the cholapods act as mobile anion carriers. 相似文献
49.
Beth M. Campbell Hetrick Rhonda J. Hughes 《Journal of Mathematical Analysis and Applications》2007,331(1):342-357
We apply semigroup theory and other operator-theoretic methods to prove Hölder-continuous dependence on modeling for the inhomogeneous ill-posed Cauchy problem in Banach space. The inhomogeneous ill-posed Cauchy problem is given by , u(0)=χ, 0?t<T; where −A is the infinitesimal generator of a holomorphic semigroup on a Banach space X, χ∈X, and . For a suitable function f, the approximate problem is given by , v(0)=χ. Under certain stabilizing conditions, we prove that for a related norm, where and M are computable constants independent of β, 0<β<1, and ω(t) is a harmonic function. These results extend earlier work of Ames and Hughes on the homogeneous ill-posed problem. 相似文献
50.
The cracking reaction pathways and mechanisms of ethylcyclohexane and 1-cyclohexyloctane with a rare earth Y (REY) catalyst were studied. Experiments at 500°C indicated that the dominant reactions were ring opening with subsequent secondary cracking, cracking in the alkyl side chain, isomerization, and hydrogen transfer. A kinetic model of the catalytic cracking of 1-cyclohexyloctane was developed using a novel mechanism-based lumping scheme that exploits the chemical similarities within reaction families. The formal application of 17 reaction family matrices, which correspond to 13 reaction family classes, to the matrix representations of the reactants and derived products generated the model. The reaction family concept was further exploited to constrain the kinetics within each reaction family to follow a quantitative structure/reactivity Polanyi relationship. Ultimately, nine Polanyi relationship parameters and three coking/deactivation parameters were determined by optimizing the model fit to the experimental data. The resulting model correlations were excellent, as the overall parity between experimental and model values was yModel=−0.000470+0.986yExp with a correlation coefficient of 0.971. © 1997 John Wiley & Sons, Inc. Int J Chem Kinet 29: 545–560, 1997. 相似文献