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331.
Infrared absorption spectra of co-crystalline CO(2)·C(2)H(2) aerosol particles were modeled using a combination of two methods. Density functional theory was used to model several bulk CO(2)·C(2)H(2) co-crystal structures and to calculate their lattice energies and frequency-dependent dielectric tensors. This was necessary as there currently exists no crystallographic or refractive index data on co-crystalline CO(2)·C(2)H(2)due to its metastability. The discrete dipole approximation was then used to calculate infrared absorption spectra of different model particles using the dielectric tensors calculated using density functional theory. Results from these simulations were compared to the experimental spectrum of co-crystalline CO(2)·C(2)H(2) aerosol particles. The aerosol particles after the decomposition of the co-crystalline phase were studied in Part I. 相似文献
332.
FP Binder K Lemme RC Preston B Ernst 《Angewandte Chemie (International ed. in English)》2012,51(29):7327-7331
Organized and released: Sialyl Lewis(x) (sLe(x)) represents a "pre-organized water oligomer", that is, a surrogate for clustered water molecules attached to a scaffold. The impetus for sLe(x) binding to E-selectin is shown to be the high degree of pre-organization allowing an array of directed hydrogen bonds, and the entropic benefit of the release of water molecules from the large binding interface to bulk water (see picture). 相似文献
333.
Landon PB Ramachandran S Gillman A Gidron T Yoon D Lal R 《Langmuir : the ACS journal of surfaces and colloids》2012,28(1):534-540
Here we report the design and development of DNA zippers and tweezers. Essentially a zipper system consists of a normal strand (N), a weak strand (W), and an opening strand (O). N strand is made up of normal DNA bases, while W is engineered to have inosine substituting for guanine. By altering the number and order of inosine, W is engineered to provide less than natural bonding affinities to N in forming the [N:W] helix. When O is introduced (a natural complement of N), it competitively displaces W from [N:W] and forms [N:O]. This principle is incorporated in the development of a molecular device that can perform the functions of tweezers (sense, hold, and release). Tweezers were constructed by holding N and W together using a hinge at one end. Thus, when the tweezers open, N and W remain in the same vicinity. This allows the tweezers to cycle among open and close positions by their opening and closing strands. Control over their opening and closing kinetics is demonstrated. In contrast to the previously reported DNA tweezers, the zipper mechanism makes it possible to operate them with opening strands that do not contain single-stranded DNA overhangs. Our approach yields a robust, compact, and regenerative tweezer system that could potentially be integrated into complex nanomachines. 相似文献
334.
Sensitive methods to measure protein synthetic rate in vivo are required to assess changes in protein expression, especially when comparing healthy with infirm subjects. We have previously applied a ‘flooding dose’ procedure using 2H5‐phenylalanine (2H5‐phe) and 2H8‐phe isotopomers as tracers, which has proven successful in measuring albumin and fibrinogen synthesis in response to feeding in cancer patients. Using tert‐butyldimethylsilyl derivatives, we have observed that 2H7‐phe is formed with time in vivo from 2H8‐phe, probably during transamination. This increases errors when estimating the fractional synthetic rate (FSR) using the 2H8‐phe isotopomer compared with the 2H5‐phe isotopomer. We sought to improve this situation by use of an alternative derivative that overcomes this problem whilst also streamlining sample preparation. When using N‐ethoxycarbonyltrifluoroethyl (ECTFE) amino acid esters, 2H8‐phe is effectively converted into 2H7‐phe through fragmentation under electron ionisation (EI), allowing both 2H8‐phe and 2H7‐phe isotopomers to be measured as a single intense CH fragment at 98 Th. To illustrate the improved situation, the mean RMS residual was calculated for all albumin data, for each isotopomer and for each derivative. Albumin‐bound Phe was analysed as ECTFE‐phe with improved precision, independent of the isotopomer used, confirming that the new derivative is superior. Copyright © 2010 John Wiley & Sons, Ltd. 相似文献
335.
Stephen C. Preston 《Annals of Global Analysis and Geometry》2012,41(3):281-305
In this article, we study geometric aspects of the space of arcs parameterized by unit speed in the L
2 metric. Physically, this corresponds to the motion of a whip, and it also arises in studying shape recognition. The geodesic
equation is the nonlinear, nonlocal wave equation η
tt
= ∂
s
(σ η
s
), with
\lvert hs\rvert o 1{\lvert \eta_{s}\rvert\equiv 1} and σ given by
sss- \lvert hss\rvert2 s = -\lvert hst\rvert2{\sigma_{ss}- \lvert \eta_{ss}\rvert^2 \sigma = -\lvert \eta_{st}\rvert^2}, with boundary conditions σ(t, 1) = σ(t, −1) = 0 and η(t, 0) = 0. We prove that the space of arcs is a submanifold of the space of all curves, that the orthogonal projection exists
but is not smooth, and as a consequence we get a Riemannian exponential map that is continuous and even differentiable but
not C
1. This is related to the fact that the curvature is positive but unbounded above, so that there are conjugate points at arbitrarily
short times along any geodesic. 相似文献
336.
A chemical vapor deposition method has been developed for the synthesis of both solvent-free Co[TCNE]2 and VyCo1−y[TCNE]2 thin films. Both materials have been previously synthesized by solution methods, but contain solvent. The Co[TCNE]2 thin films were characterized by infrared spectroscopy and magnetic studies, and albeit solvent-free were determined to be similar to the analogous solution-prepared samples as they are paramagnetic with slight antiferromagnetic coupling. In contrast to the solution-based synthesis, VyCo1−y-[TCNE]2 showed no dependence of coercive field based on the composition of the films, even though infrared spectroscopic data indicates formation of a solid-solution thin film, and not a physical mixture. 相似文献
337.
We demonstrate a new class of passively temperature stabilized resonant silicon electro-optic modulators. The modulators consist of a ring resonator coupled to a Mach-Zehnder interferometer with tailored thermal properties. We demonstrate 2 GHz continuous modulation over a temperature range of 35 °C and describe the scalability and design rules for such a device. 相似文献
338.
339.
Morrison DJ Dodson B Slater C Preston T 《Rapid communications in mass spectrometry : RCM》2000,14(15):1321-1324
Surprisingly little information is available on the natural abundance of the minor isotope of carbon, (13)C, in common foodstuffs in the British diet. This study therefore aimed to examine the (13)C natural abundance of foodstuffs from a small cross-section of the British diet. The isotopic abundance, delta per mil, was calculated by measurement of the isotope ratio (13)C:(12)C by isotope ratio mass spectrometry. Results from this study were also compared with results from a North American study to highlight the difference in isotopic abundance between Northern European foodstuffs and North American foodstuffs. Such data should prove useful to those planning tracer studies using the stable isotope (13)C where enrichment is measured against a large and variable natural abundance in the body. Minimisation of this basal variation, for example in breath CO(2), can be achieved by controlling dietary intake of foods naturally abundant in (13)C. 相似文献
340.
J. Asrar J. Preston A. Ciferri W. R. Krigbaum 《Journal of polymer science. Part A, Polymer chemistry》1982,20(2):373-381
A novel extension of the Yamazaki reaction is used to prepare block copolymers having rigid blocks of poly-(p-benzamide) (PBA) and semiflexible blocks of polyamide-hydrazide. A PBA prepolymer having M ? 10,000 was synthesized by the usual Yamazaki reaction using triphenylphosphite. As previously reported, higher-molecular-weight PBA could be obtained using 4-N-(4′-aminobenzamido)benzoic acid containing a preformed amide linkage. Addition of p-aminobenzhydrazide and terephthalic acid then led to formation of the polyamide-hydrazide blocks using as the active reactant the diphenylphosphite formed as a by-product in the first polymerization. Evidence that a block copolymer is produced includes an increase in inherent viscosity during the second step, differences in the solubility of the copolymer compared to the homopolymers, and comparison of the phase diagram of the block copolymer in N-methylpyrrolidone having 4% added LiCl with those of a random copolymer, and of mixtures of the two homopolymers. The critical concentration required to form a nematic phase in solutions of the block copolymers is correlated with the length (or axial ratio) of the rigid block, and with its proportion in the copolymer. 相似文献