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41.
We prove that any graph with maximum degree sufficiently large, has a proper vertex colouring using +1 colours such that each colour class appears at most log8 times in the neighbourhood of any vertex. We also show that for 1, the minimum number of colours required to colour any such graph so that each vertex appears at most times in the neighbourhood of any vertex is (+1+1//), showing in particular that when =log/loglog, such a colouring cannot always be achieved with O() colours. We also provide a polynomial time algorithm to find such a colouring. This has applications to the total chromatic number of a graph.The second two authors were supported by NATO Collaborative Research Grant #CRG950235. 相似文献
42.
Eight derivatives of 2-oxazolidone,, have been synthesized by the Homeyer method and purified by fractional freezing or fractional distillation to obtain low-conducting liquids. Dielectric constants, viscosities, densities, and refractive indices of these 2-oxazolidones have been determined at several temperatures within the range 25 to 75°C. Values for activation energies of viscous flow also have been calculated. The isomeric 3-methyl and 5-methyl derivatives of 2-oxazolidone have high dielectric constants which differ only slightly from that of water. The 3-substituted (or N-substituted) 2-oxazolidones exhibit the most favorable combination of physical properties, stability, and ease of purification and appear to have excellent potential as new nonaqueous solvents.Based on a portion of the Ph. D. dissertation of H. L. Huffman, Jr., University of Kentucky, 1972. Presented in major part at the 21 st Southeastern Regional Meeting of the American Chemical Society, Richmond, Virginia, 1969. 相似文献
43.
44.
Abstract The knowledge of water exchange reaction mechanism in aqueous solutions of Gd3+ polyaminocarboxylates is important for the understanding of the relatively slow water exchange rates measured for these complexes. Variable ressure measurements show a change of mechanism from associatively activated on [Gd(H2O)8]3+ and [Gd(PDTA)(H2O2)2]? to probably limiting dissociative on the MRI contrast agents [Gd(DOTA)(H2O)]?, [Gd(DTPA)(H2O)]2? and [Gd(DTPA-BMA)(H2O)]. 相似文献
45.
The study of the interaction of anticancer drugs with mammalian cells in vitro is important to elucidate the mechanisms of action of the drug on its biological targets. In this context, Raman spectroscopy is a potential candidate for high throughput, non-invasive analysis. To explore this potential, the interaction of cis-diamminedichloroplatinum(II) (cisplatin) with a human lung adenocarcinoma cell line (A549) was investigated using Raman microspectroscopy. The results were correlated with parallel measurements from the MTT cytotoxicity assay, which yielded an IC(50) value of 1.2 ± 0.2 μM. To further confirm the spectral results, Raman spectra were also acquired from DNA extracted from A549 cells exposed to cisplatin and from unexposed controls. Partial least squares (PLS) multivariate regression and PLS Jackknifing were employed to highlight spectral regions which varied in a statistically significant manner with exposure to cisplatin and with the resultant changes in cellular physiology measured by the MTT assay. The results demonstrate the potential of the cellular Raman spectrum to non-invasively elucidate spectral changes that have their origin either in the biochemical interaction of external agents with the cell or its physiological response, allowing the prediction of the cellular response and the identification of the origin of the chemotherapeutic response at a molecular level in the cell. 相似文献
46.
Resolution and uniqueness of estimated parameters of a model of thin filament regulation in solution
Srboljub M. Mijailovich Xiaochuan Li Juan C. del Álamo R. Hugh Griffiths Vojislav Kecman Michael A. Geeves 《Computational Biology and Chemistry》2010,34(1):19-33
The estimation of chemical kinetic rate constants for any non-trivial model is complex due to the nonlinear effects of second order chemical reactions. We developed an algorithm to accomplish this goal based on the Damped Least Squares (DLS) inversion method and then tested the effectiveness of this method on the McKillop–Geeves (MG) model of thin filament regulation. The kinetics of MG model is defined by a set of nonlinear ordinary differential equations (ODEs) that predict the evolution of troponin–tropomyosin–actin and actin–myosin states. The values of the rate constants are estimated by integrating these ODEs numerically and fitting them to a series of stopped-flow pyrene fluorescence transients of myosin-S1 fragment binding to regulated actin in solution. The accuracy and robustness of the estimated rate constants are evaluated for DLS and two other methods, namely quasi-Newton (QN) and simulated annealing (SA). The comparison of these methods revealed that SA provides the best estimates of the model parameters because of its global optimization scheme. However it converges slowly and does quantify the uniqueness of the estimated parameters. On the other hand the QN method converges rapidly but only if the initial guess of the parameters is close to the optimum values, otherwise it diverges. Overall, the DLS method proves to be the most convenient method. It converges fast and was able to provide excellent estimates of kinetic parameters. Furthermore, DLS provides the model resolution matrix, which quantifies the interdependence of model parameters thereby evaluating the uniqueness of their estimated values. This property is essential for estimating of the dependence of the model parameters on experimental conditions (e.g. Ca2+ concentration) when it is assessed from noisy experimental data such as pyrene fluorescence from stopped-flow transients. The advantages of the DLS method observed in this study should be further examined in other physicochemical systems to firmly establish the observed effectiveness of DSL vs. the other parameter estimation methods. 相似文献
47.
Pereira RF Valente AJ Fernandes M Burrows HD 《Physical chemistry chemical physics : PCCP》2012,14(20):7517-7527
The interaction of sodium octanoate, decanoate or dodecanoate with calcium(ii) in aqueous solutions has been studied using turbidity, conductivity and potentiometric measurements. These show a marked alkyl chain length dependence on the behaviour. At the calcium concentration used (1.0 mM), there is little interaction with the octanoate, the decanoate shows initially formation of a 1:1 complex, followed by precipitation, while the dodecanoate precipitates at low surfactant concentrations. The solid calcium carboxylates were prepared, and show lamellar, bilayer structures with planes of calcium(II) ions coordinated to carboxylate groups through bidentate chelate linkages. Thermogravimetry and elemental analyses indicate the presence of coordinated water with the calcium decanoate but not with longer chain carboxylates. The results of both the solution and solid state studies suggest that precipitation of long-chain carboxylates depends on a balance between hydration effects and hydrophobic (largely van der Waals') interactions. Electrostatic effects make little energetic contribution but play the important structural role of ordering the carboxylate anions before precipitation. Differences are observed in the interactions between calcium(II) and long chain alkylcarboxylates and alkylsulfates, and are interpreted in terms of stronger binding to the metal of the carboxylate group. A general mechanism is proposed for calcium carboxylate precipitation from aqueous solution based on this and previous studies. 相似文献
48.
Chung‐Der Chen Andrew P. J. Brunskill Stan S. Hall Roger A. Lalancette Hugh W. Thompson 《Acta Crystallographica. Section C, Structural Chemistry》2000,56(9):1148-1151
α‐Oxobenzeneacetic (phenylglyoxylic) acid, C8H6O3, adopts a transoid dicarbonyl conformation in the solid state, with the carboxyl group rotated 44.4 (1)° from the nearly planar benzoyl moiety. The heterochiral acid‐to‐ketone catemers [O?O = 2.686 (3) and H?O = 1.78 (4) Å] have a second, longer, intermolecular O—H?O contact to a carboxyl sp3 O atom [O?O = 3.274 (2) and H?O = 2.72 (4) Å], with each flat ribbon‐like chain lying in the bc plane and extending in the c direction. In α‐oxo‐2,4,6‐trimethylbenzeneacetic (mesitylglyoxylic) acid, C11H12O3, the ketone is rotated 49.1 (7)° from planarity with the aryl ring and the carboxyl group is rotated a further 31.2 (7)° from the ketone plane. The solid consists of chiral conformers of a single handedness, aggregating in hydrogen‐bonding chains whose units are related by a 31 screw axis, producing hydrogen‐bonding helices that extend in the c direction. The hydrogen bonding is of the acid‐to‐acid type [O?O = 2.709 (6) and H?O = 1.87 (5) Å] and does not formally involve the ketone; however, the ketone O atom in the acceptor molecule has a close polar contact with the same donor carboxyl group [O?O = 3.005 (6) and H?O = 2.50 (5) Å]. This secondary hydrogen bond is probably a major factor in stabilizing the observed cisoid dicarbonyl conformation. Several intermolecular C—H?O close contacts were found for the latter compound. 相似文献
49.
Sharma SK Lucey PG Ghosh M Hubble HW Horton KA 《Spectrochimica acta. Part A, Molecular and biomolecular spectroscopy》2003,59(10):2391-2407
We have designed and developed two breadboard versions of stand-off Raman spectroscopic systems for landers based on a 5-in. Maksutov-Cassegrain telescope and a small (4-in. diameter) Newtonian telescope receiver. These systems are capable of measuring the Raman spectra of minerals located at a distance of 4.5-66 m from the telescope. Both continuous wave (CW) Ar-ion and frequency doubled Nd:YAG (532 nm) pulsed (20 Hz) lasers are used as excitation sources for measuring remote Raman spectra of rocks and minerals. We have also made complementary measurements on the same rock samples with a micro-Raman system in 180 and 135 degrees geometry for evaluating the system performance and for estimating effect of grain size and laser-induced heating on the spectra of minerals using alpha-quartz as a model mineral. A field portable remote pulsed Raman spectroscopic system based on the 5-in. telescope and an f/2.2 spectrograph has been developed and tested. We have also demonstrated a prototype of a combined Raman and laser-induced breakdown spectroscopy (LIBS) system, capable of providing major element composition and mineralogical information on both biogenic and inorganic minerals at a distance of 10 m from the receiver. 相似文献
50.
Synthesis and Biological Evaluation of a Class of Mitochondrially‐Targeted Gadolinium(III) Agents 下载免费PDF全文
Dr. Daniel E. Morrison Dr. Jade B. Aitken Dr. Martin D. de Jonge Dr. Fatiah Issa Prof. Hugh H. Harris Prof. Louis M. Rendina 《Chemistry (Weinheim an der Bergstrasse, Germany)》2014,20(50):16602-16612
A structure–activity relationship study of a library of novel bifunctional GdIII complexes covalently linked to arylphosphonium cations is reported. Such complexes have been designed for potential application in binary cancer therapies such as neutron capture therapy and photon activation therapy. A positive correlation was found between lipophilicity and cytotoxicity of the complexes. Mitochondria uptake was determined by means of inductively coupled plasma mass spectrometry (ICP‐MS), and Gd uptake was determined by means of quantification using synchrotron X‐ray fluorescence (XRF) imaging. A negative correlation between lipophilicity and tumour selectivity of the GdIII complexes was demonstrated. This study highlights the delicate balance required to minimise in vitro cytotoxicity and optimise in vitro tumour selectivity and mitochondrial localisation for this new class of mitochondrially‐targeted binary therapy agents. We also report the highest in vitro tumour selectivity for any Gd agent reported to date, with a T/N (tumour/normal cell) ratio of up to 23.5±6.6. 相似文献