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171.
Janice L. Malouf 《Discrete Mathematics》1992,110(1-3):257-261
The sequence of numbers {ai} defined by the recurrence
for n>3 with initial values a0, a1, a2, a3=1 is shown to be integral. Other initial values are also considered. 相似文献
172.
K. Tojo A. Furukawa T. Araki A. Onuki 《The European physical journal. E, Soft matter》2009,30(1):55-64
We numerically study the orientation deformations in nematic liquid crystals around charged particles. We set up a Ginzburg-Landau
theory with inhomogeneous electric field. If the dielectric anisotropy e1 \varepsilon_{1}^{} is positive, Saturn-ring defects are formed around the particles. For e1 \varepsilon_{1}^{} < 0 , novel “ansa” defects appear, which are disclination lines with their ends on the particle surface. We find unique defect
structures around two charged particles. To lower the free energy, oppositely charged particle pairs tend to be aligned in
the parallel direction for e1 \varepsilon_{1}^{} > 0 and in the perpendicular plane for e1 \varepsilon_{1}^{} < 0 with respect to the background director. For identically charged pairs the preferred directions for e1 \varepsilon_{1}^{} > 0 and e1 \varepsilon_{1}^{} < 0 are exchanged. We also examine competition between the charge-induced anchoring and the short-range anchoring. If the
short-range anchoring is sufficiently strong, it can be effective in the vicinity of the surface, while the director orientation
is governed by the long-range electrostatic interaction far from the surface. 相似文献
173.
Yuanyuan Zhang Alex D. MacIntosh Janice L. Wong Elizabeth A. Bielinski Paul G. Williard Brandon Q. Mercado Nilay Hazari Wesley H. Bernskoetter 《Chemical science》2015,6(7):4291-4299
A family of iron(ii) carbonyl hydride complexes supported by either a bifunctional PNP ligand containing a secondary amine, or a PNP ligand with a tertiary amine that prevents metal–ligand cooperativity, were found to promote the catalytic hydrogenation of CO2 to formate in the presence of Brønsted base. In both cases a remarkable enhancement in catalytic activity was observed upon the addition of Lewis acid (LA) co-catalysts. For the secondary amine supported system, turnover numbers of approximately 9000 for formate production were achieved, while for catalysts supported by the tertiary amine ligand, nearly 60 000 turnovers were observed; the highest activity reported for an earth abundant catalyst to date. The LA co-catalysts raise the turnover number by more than an order of magnitude in each case. In the secondary amine system, mechanistic investigations implicated the LA in disrupting an intramolecular hydrogen bond between the PNP ligand N–H moiety and the carbonyl oxygen of a formate ligand in the catalytic resting state. This destabilization of the iron-bound formate accelerates product extrusion, the rate-limiting step in catalysis. In systems supported by ligands with the tertiary amine, it was demonstrated that the LA enhancement originates from cation assisted substitution of formate for dihydrogen during the slow step in catalysis. 相似文献
174.
Janice Tardiff Ralph M. Deal William L. Hase Da-hong Lu 《Journal of Cluster Science》1990,1(4):335-354
Classical trajectory simulations are used to study the intramolecular dynamics of isolated CF3H and the CF3H(H2O)3 cluster, by either exciting the CH stretch local mode to then=6 level or by adding an equivalent amount of energy to an OH stretch normal mode. Energy transfer from the CH local mode is statistically the same for CF3H(H2O)3 as for isolated CF3H, and agrees with previous experimental studies. Clusters excited with 6 quanta in the CH local mode are remarkably stable. Though the CF3H-(H2O)3 intermolecular potential is only 1.5 kcal/mol, only 1 of 26 clusters excited with 6 quanta in the CH local mode dissociate within 10 ps. The absorption linewidth for the CH local mode in CF3H(H2O)3 is related to IVR within CF3H and not to the unimolecular lifetime of the cluster. When an OH stretch normal mode of the cluster is excited, energy transfer to CF3H is negligible and nearly one half of the clusters dissociate within 10 ps. 相似文献
175.
The excited state properties of a series of singly bonded dirhodium compounds, consisting of Rh(0)(2), Rh(0)Rh(II)X(2), and Rh(II)(2)X(4) (X = Cl and Br) cores coordinated by three bis(difluorophosphino)methylamine ligands, have been investigated. The newly synthesized complexes with X = Br have been structurally characterized. The mixed-valence complex Rh(2)[&mgr;-CH(3)N(PF(2))(2)](3)Br(2)[(PF(2))CH(3)N(PF(2))] crystallizes in the orthorhombic space group P2(1)2(1)2(1) with a = 13.868(7) ?, b = 16.090(5) ?, c = 11.614(5) ?, V = 1591(3) ?(3), and Z = 4; the structure was refined to values of R = 0.052 and R(w) = 0.062. Orange crystals of Rh(2)[&mgr;-CH(3)N(PF(2))(2)](3)Br(4) are monoclinic with a C2/c space group: a = 14.62(6) ?, b = 12.20(2) ?, c = 14.33(1) ?; beta = 106.0(2) degrees; V = 2457(11) ?(3); Z = 4; and R = 0.058 and R(w) = 0.056. Crystalline solids and low-temperature glasses of each member of the chloride and bromide series exhibit long-lived red luminescence. Excitation profiles and temperature dependencies of the emission bandwidths and lifetimes for all complexes are characteristic of luminescence originating from a dsigma excited state. Efficient nonradiative decay is observed upon the thermal population of an excited state proximate to the lowest energy emissive excited state of these complexes. The nonradiative decay rate constant of the upper excited state is 10(2)-10(3) and 10(3)-10(4) greater than that of the emissive excited state for complexes with X = Cl and Br, respectively. 相似文献
176.
Brodie CR Collins JG Aldrich-Wright JR 《Dalton transactions (Cambridge, England : 2003)》2004,(8):1145-1152
This study documents the first detailed investigation into the relationship between molecular structure and biological activity of platinum(II) complexes containing methylated derivatives of 1,10-phenanthroline (phen). A series of square planar platinum(II) compounds incorporating methylated derivatives of phen, 4-methyl-1,10-phenanthroline (4-Mephen), 5-methyl-1,10-phenanthroline (5-Mephen), 4,7-dimethyl-1,10-phenanthroline (4,7-Me2phen), 5,6-dimethyl-1,10-phenanthroline (5,6-Me2phen) and 3,4,7,8-tetramethyl-1,10-phenanthroline (3,4,7,8-Me4phen) were synthesised and the relationship between their structure and biological activity investigated. The biological activity of these compounds was quantified using the in vitro cytotoxicity assay against the L1210 Murine leukaemia cell line. Large variation in cytotoxicities with different methylation was observed. The 5- and 5,6-methylated derivatives of phen displayed a greater biological activity, with IC50 values of 2.8 +/- 0.8 microM and 1.5 +/- 0.3 microM respectively, compared with the phen compound, with an IC50 value of 9.7 +/- 0.3 microM, while all the others were inactive with IC50 values over 50 microM. Binding constants were determined using circular dichroism spectroscopy (CD) and induced circular dichroism (ICD). ICD was used to highlight any differences in the spectra. Viscometry studies and linear dichroism (LD) experiments indicate that the platinum(II) complexes intercalate although for [Pt(en)(4-Mephen)]Cl2 and [Pt(en)(4,7-Me2phen)]Cl2 this mode of binding appears to be concentration dependent. The binding of the platinum(II) complexes to the oligonucleotide d(GTCGAC)2 was studied using two-dimensional 1H NMR spectroscopy. The addition of each metal complex to the hexamer d(GTCGAC)2 produced upfield shifts of the metal complex resonances, characteristic of intercalation. Through the observation of NOE cross-peaks, two-dimensional NMR studies provided insight into the site and groove preferences of these compounds when binding to DNA. 相似文献
177.
Dwight SJ Gaylord BS Hong JW Bazan GC 《Journal of the American Chemical Society》2004,126(51):16850-16859
The use of anionic water-soluble conjugated polymers (CPs) for sensing the presence of avidin by use of a biotin-modified fluorescence quencher was studied. The molecules involved in the study included poly[2-methoxy-5-(3'-propyloxysulfonate)-1,4-phenylenevinylene] with either lithium (Li+-MPS-PPV) or sodium (Na(+)-MPS-PPV) countercations, the well-defined oligomer pentasodium 1,4-bis(4'(2",4"-bis(butoxysulfonate)-styryl)-styryl)2-butoxysulfonate-5-methoxybenzene (5R5-), the quenchers N-methyl-4,4'-pyridylpyridinium iodide (mMV+) and [N-(biotinoyl)-N'-(acetyl 4,4'-pyridylpyridinium iodide)] ethylenediamine (BPP+), which contains a molecular recognition fragment (biotin) attached to a unit that accepts an electron from a CP excited state, and the proteins avidin, tau, BSA, and pepsin A. Fluorescence quenching experiments were examined in a variety of conditions. Experiments carried out in water and in ammonium carbonate buffer (which ensures avidin/biotin complexation) reveal that nonspecific interactions between the CP and the proteins cause substantial perturbations on the CP fluorescence. The overall findings are not consistent with a simple mechanism whereby avidin complexation of BPP+ leads to encapsulation of the quencher molecule and recovery of Li+-MPS-PPV fluorescence. Instead, we propose that binding of BPP+ to avidin results in the quenching unit attaching to a positively charged macromolecule. Electrostatic attraction to the negatively charged conjugated polymer results in closer proximity to the quencher. Therefore, more enhanced fluorescence quenching is observed. 相似文献
178.
New and higher yielding synthetic routes to N-protected N-methylpyrrole and N-methylimidazole amino acids are introduced to circumvent difficulties associated with established schemes. Key steps in each synthesis include copper-mediated cross-coupling reaction to directly install a carbamate-protected 4-amine in the N-methylpyrrole derivative and effective nitration followed by a one-pot reduction/Boc protection of the amine in the synthesis of the N-Me-imidazole amino acid. 相似文献
179.
Synthesis and NMR Spectroscopic Elucidation of Four Diastereoisomers of Oxygenated Bisabolane Side Chain 下载免费PDF全文
Misaki Hirai Rurina Miyazaki Kana Mitsui Kota Kiuchi Hiroyuki Onuki Hiroshi Hirota Chiaki Kuroda 《Helvetica chimica acta》2015,98(8):1035-1060
Four possible stereoisomers of a model compound of highly O‐bearing bisabolane sesquiterpenes were synthesized and their NMR spectra were compared. Starting from isopulegol, allylic oxidation and Grignard reaction afforded a mixture of alcohols at C(8), which was separated. After metathesis reaction, both α‐ and β‐epoxides were obtained via non‐stereoselective epoxidation, while VO(OiPr)3‐catalyzed epoxidation afforded a single diastereoisomer selectively. NMR Spectra of twelve synthesized compounds, four stereoisomers of acetates, isobutyrates, and tiglates, were measured. A difference between C(8α)‐ and C(8β)‐acyloxy isomers was observed in the δ‐values of H? C(8) in CDCl3. Within the 8β‐acyloxy compounds, the α‐ and the β‐epoxides were distinguished by either the J‐value of H? C(8) or the chemical shift of CH2(9). Within the 8α‐acyloxy compounds, two epoxide isomers were distinguished by the J‐value of H? C(10) in C6D6 or in CD3OD. 相似文献
180.
Janice Duy Laurie B. Connell Wolfgang Eck Scott D. Collins Rosemary L. Smith 《Journal of nanoparticle research》2010,12(7):2363-2369
A simple, two-step method of producing stable and functional peptide nucleic acid (PNA)-conjugated gold nanoparticles using a surfactant stabilization step is presented. PNA are DNA analogs with superior chemical stability and target discrimination, but their use in metallic nanoparticle systems has been limited by the difficulty of producing stable colloids of nanoparticle–PNA conjugates. In this work, the nonionic surfactant Tween 20 (polyoxyethylene (20) sorbitan monolaurate) was used to sterically shield gold surfaces prior to the addition of thiolated PNA, producing conjugates which remain dispersed in solution and retain the ability to hybridize to complementary nucleic acid sequences. The conjugates were characterized using transmission electron microscopy, dynamic light scattering, and UV–visible absorbance spectroscopy. PNA attachment to gold nanoparticles was confirmed with an enzyme-linked immunoassay, while the ability of nanoparticle-bound PNA to hybridize to its complement was demonstrated using labeled DNA. 相似文献