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71.
Tam-Chang SW Iverson IK Helbley J 《Langmuir : the ACS journal of surfaces and colloids》2004,20(2):342-347
The chromonic liquid-crystalline properties of bis-(N,N-diethylaminoethyl)perylene-3,4,9,10-tetracarboxylic diimide dihydrochloride in an aqueous solution were investigated by polarized light microscopy and 2H NMR spectroscopy. Both techniques indicate a narrow I + N biphasic region and a broad N phase region at concentrations ranging from approximately 6.9 to approximately 30 wt % at room temperature. Optical microscopy indicates that a hexagonal M phase exists at higher concentrations. The variation of the I --> N + I and N + I --> N transition temperatures with concentration was studied by 2H NMR spectroscopy. Finally, the effects of temperature and concentration on the order parameter of the N phase were investigated by 2H NMR using a tetra-deuterated derivative. A value of 0.97 was obtained for the N phase at its upper concentration limit. 相似文献
72.
Kidney stones are heterogeneous polycrystalline aggregates that can consist of several different building blocks. A significant number of human stones contain uric acid crystals as a crystalline component, though the molecular-level growth of this important biomaterial has not been previously well-characterized. In the present study, in situ atomic force microscopy (AFM) is used to investigate the real-time growth on the (100) surface of uric acid (UA) single crystals as a function of fundamental solution parameters. Layer-by-layer growth on UA (100) was found to be initiated at screw dislocation sites and to proceed via highly anisotropic rates which depend on the crystallographic direction. The smallest b-steps exhibited minimum heights corresponding to two molecular layers, while fast-moving c-steps more commonly showed monolayer heights. Growth kinetics measured under a range of flow rates, supersaturation levels, and pH values reveal linear trends in the growth kinetics, with faster growth attained in solutions with higher supersaturation and/or pH. The calculated kinetic parameters for UA growth derived from these experiments are in good agreement with the values reported for other crystal systems. 相似文献
73.
Handley LL Johnston AM Hallett PD Scrimgeour CM Wheatley RE 《Rapid communications in mass spectrometry : RCM》2001,15(15):1274-1278
New evidence, obtained using a robust method for measuring the delta(15)N of NO(3)(-)-N in soil, is consistent with denitrification being the major determinant in the vertical distribution of NO(3)(-)-delta(15)N in soil profiles. These data also suggest that varying moisture regimes result in different effects of soil NO(3)(-)-N leaching on residual whole soil delta(15)N. 相似文献
74.
Hill RT Lyon JL Allen R Stevenson KJ Shear JB 《Journal of the American Chemical Society》2005,127(30):10707-10711
The functionality and structural diversity of biological macromolecules has motivated efforts to exploit proteins and DNA as templates for synthesis of electronic architectures. Although such materials offer promise for numerous applications in the fabrication of cellular interfaces, biosensors, and nanoelectronics, identification of techniques for positioning and ordering bioelectronic components into useful patterns capable of sophisticated function has presented a major challenge. Here, we describe the fabrication of electronic materials using biomolecular scaffolds that can be constructed with precisely defined topographies. In this approach, a tightly focused pulsed laser beam capable of promoting protein photo-cross-linking in specified femtoliter volume elements is scanned within a protein solution, creating biomolecular matrices that either remain in integral contact with a support surface or extend as free-standing structures through solution, tethered at their ends. Once fabricated, specific protein scaffolds can be selectively metallized via targeted deposition and growth of metal nanoparticles, yielding high-conductivity bioelectronic materials. This aqueous fabrication strategy opens new opportunities for creating electronic materials in chemically sensitive environments and may offer a general approach for creating microscopically defined inorganic landscapes. 相似文献
75.
The treatment of cutaneous vascular lesions (port wine stains etc.) using lasers has been guided by theories based on the “cold” or room‐temperature optical properties of the hemoglobin target chromophore. We have recently presented evidence showing that under the influence of laser irradiation, the optical properties of blood in vitro are time and temperature dependent. Such complications are not currently subsumed into the in vivo theory. Here, we study the time‐domain optical properties of blood undergoing photocoagulation in vitro using two newly developed time‐resolved techniques. We also study the asymptotic effect of laser photocoagulation on the chemical and structural properties of the components of the blood matrix. We present evidence showing that the photocoagulation process involves significant changes in the optical absorption and scattering properties of blood, coupled with photothermally induced chemical and structural changes. We demonstrate the first use of a laser to deliberately generate magnetic resonance imaging contrast in vitro. We show that this technique offers significant potential advantages to in vivo intravenous chemical contrast agent injection. 相似文献
76.
Williams JR Smalley AL Sellinschegg H Daniels-Hafer C Harris J Johnson MB Johnson DC 《Journal of the American Chemical Society》2003,125(34):10335-10341
A series of samples ((AB)(x)(CD)(y))(z) were prepared containing both short repeat units (AB and CD) and long repeat units ((AB)(x)(CD)(y)), where the short repeat units were designed to have the composition appropriate to form square M(4)Sb(12) skutterudites (M = Fe, Co, or Ir; square = vacancy, La, or Y). X-ray diffraction and reflectivity were used to follow the evolution of the films from amorphous, layered materials to crystalline skutterudite superlattices as a function of annealing temperature and time. In all cases, the short repeat units interdiffused and crystallized the expected skutterudite, while the long repeat period persisted after annealing. The skutterudites crystallize with random crystallographic orientation with respect to the substrate. The observed splitting of the peaks in the high-angle diffraction data from the IrSb(3)/CoSb(3) sample indicates the formation of a novel superlattice structure with each grain having a random crystallographic orientation of the skutterudite lattice with respect to the superlattice direction. 相似文献
77.
Capon RJ Skene C Liu EH Lacey E Gill JH Heiland K Friedel T 《Natural product research》2004,18(4):305-309
Bioassay directed fractionation of a Raspailia (Raspailia) sp. (Order Poecilosclerida; Family Raspailiidae) collected during scientific trawling operations off the Northern Rottnest Shelf yielded as nematocidal agents the known metabolites, phorboxazoles A (1) and B (2). Further examination revealed the new natural product but known synthetic compound, esmodil (3). The structure for 3 was confirmed by spectroscopic analysis and total synthesis. 相似文献
78.
[reaction: see text] The convergent total synthesis of (+)-okaramine J was achieved in a longest linear sequence of 12 steps from l-tryptophan tert-butyl ester. A key reaction was the acid-catalyzed room-temperature aza-Claisen rearrangement of a N-reverse-prenylated hexahydro[2,3-b]pyrroloindole to a C-prenylated derivative. 相似文献
79.
Zhang J Brodbelt JS Wang J 《Journal of the American Society for Mass Spectrometry》2005,16(2):139-151
The relative threshold dissociation energies of a series of flavonoid/transition metal/auxiliary ligand complexes of the type [MII (flavonoid - H) auxiliary ligand]+ formed by electrospray ionization (ESI) were measured by energy-variable collisionally activated dissociation (CAD) in a quadrupole ion trap (QIT). For each of the isomeric flavonoid diglycoside pairs, the rutinoside (with a 1-6 inter-saccharide linkage) requires a greater CAD energy and thus has a higher dissociation threshold than its neohesperidoside (with a 1-2 inter-saccharide linkage) isomer. Likewise, the threshold energies of complexes containing flavones are higher than those containing flavanones. The monoglycoside isomers also have characteristic threshold energies. The flavonoids that are glycosylated at the 3-O- position tend to have lower threshold energies than those glycosylated at the 7-O- or 4'-O- position, and those that are C- bonded have lower threshold energies than the O- bonded isomers. The structural features that substantially influence the threshold energies include the aglycon type (flavanone versus flavone), the type of disaccharide (rutinose versus neohesperidose), and the linkage type (O- bonded versus C- bonded). Various computational means were applied to probe the structures and conformations of the complexes and to rationalize the differences in threshold energies of isomeric flavonoids. The most favorable coordination geometry of the complexes has a plane-angle of about 62 degrees , which means that the deprotonated flavonoid and 2,2'-bipyridine within a complex do not reside on the same plane. Stable conformations of five cobalt complexes and five deprotonated flavonoids were identified. The conformations were combined with the point charges and helium accessible surface areas to explain qualitatively the differences in threshold energies for isomeric flavonoids. 相似文献
80.
J.E. Greedan Chai-Ling Chien Richard G. Johnston 《Journal of solid state chemistry》1976,19(2):155-160
The magnetic properties of a series of cubic perovskite materials, Eu(Al0.5Ta0.5)O3, Eu(Mg0.5W0.5)O3, and Eu(Lu0.5Ta0.5)O3 have been investigated using bulk magnetic and Mössbauer techniques. Eu(Al0.5Ta0.5)O3 is a ferromagnet (Tc ~ 5°K, θc = + 8°K), Eu(Lu0.5Ta0.5)O3 is an antiferromagnet (TN = 4.0, θc = ?8°K), while Eu(Mg0.5W0.5)O3 is probably antiferromagnetic (TN = 2.8°K, θc = ? 1°K). These data are compared with the known properties of EuLiH3 and EuTiO3 and a sharp drop in θc as a function of increasing lattice constant is noted. A molecular field theory analysis of the data yields two possible sets of nn (J1) and nnn (J2) exchange constants for each compound which are compared with existing theories. 相似文献