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101.
Kovacs JM Mant CT Kwok SC Osguthorpe DJ Hodges RS 《Journal of chromatography. A》2006,1123(2):212-224
Side-chain backbone interactions (or "effects") between nearest neighbours may severely restrict the conformations accessible to a polypeptide chain and thus represent the first step in protein folding. We have quantified nearest-neighbour effects (i to i+1) in peptides through reversed-phase liquid chromatography (RP-HPLC) of model synthetic peptides, where L- and D-amino acids were substituted at the N-terminal end of the peptide sequence, adjacent to a L-Leu residue. These nearest-neighbour effects (expressed as the difference in retention times of L- and D-peptide diastereomers at pHs 2 and 7) were frequently dramatic, depending on the type of side-chain adjacent to the L-Leu residue, albeit such effects were independent of mobile phase conditions. No nearest-neighbour effects were observed when residue i is adjacent to a Gly residue. Calculation of minimum energy conformations of selected peptides supported the view that, whether a L- or D-amino acid is substituted adjacent to L-Leu, its orientation relative to this bulky Leu side-chain represents the most energetically favourable configuration. We believe that such energetically favourable, and different, configurations of L- and D-peptide diastereomers affect their respective interactions with a hydrophobic stationary phase, which are thus quantified by different RP-HPLC retention times. Side-chain hydrophilicity/hydrophobicity coefficients were generated in the presence of these nearest-neighbour effects and, despite the relative difference in such coefficients generated from peptides substituted with L- or D-amino acids, the relative difference in hydrophilicity/hydrophobicity between different amino acids in the L- or D-series is maintained. Overall, our results demonstrate that such nearest-neighbour effects can clearly restrict conformational space of an amino acid side-chain in a polypeptide chain. 相似文献
102.
Guo Q Brodzeli Z Pozhidaev EP Fan F Chigrinov VG Kwok HS Silvestri L Ladouceur F 《Optics letters》2012,37(12):2343-2345
The electro-optical behavior of deformed helix ferroelectric liquid crystal in reflective mode is described in this paper. The electrically controlled reflectance has been measured at subkilohertz driving voltage frequency for different polarizations of the incident light and compared quite successfully with the simulation results. 相似文献
103.
104.
We report on a novel concept of sample loading for microfluidic devices using a benchtop centrifuge and a magnetically actuated circular closed-loop PCR microchip as a model system. The PCR mixture and the ferrofluid were loaded into a specially designed microchip. The microchip was then placed in an off-the-shelf 50-mL tube and centrifuged. The strong centrifugal force drives the PCR mixture and the ferrofluid into the microchannels of the microchip, and simultaneously expels any trapped microbubbles. PCR was successfully carried out on single and parallel closed-loop PCR microchips. The addition of a few off-chip handling steps allows great simplification of the device design. This new loading concept may be useful for designing robust and low-cost lab-on-a-chip devices because benchtop centrifuges are quite common in most laboratories. Figure
This paper reports a novel concept of sample loading for microfluidic devices using a benchtop centrifuge. The addition of a few simple off-chip handling steps allows designing robust and low-cost lab-on-a-chip devices. 相似文献
105.
This work examines the cooperative motion of a group of autonomous vehicles in a fast flow environment. The magnitude of the flow velocity is assumed to be greater than the available actuation to each agent. Collectively, the agents wish to maximize total coverage area defined as the set of points reachable by any agent within T time. The reachable set of an agent in a fast flow is characterized using optimal control techniques. Specifically, this work addresses the complementary cases where the static flow field is smooth, and where the flow field is piecewise constant. The latter case arises as a proposed approximation of a smooth flow that remains analytically tractable. Furthermore, the techniques used in the piecewise constant flow case enable treatment for obstacles in the environment. In both cases, a gradient ascent method is derived to maximize the total coverage area in a distributed fashion. Simulations show that such a network is able to maximize the coverage area in a fast flow. 相似文献
106.
We analyze a least-squares asymmetric radial basis function
collocation method for solving the modified Helmholtz equations. In
the theoretical part, we proved the convergence of the proposed
method providing that the collocation points are sufficiently dense.
For numerical verification, direct solver and a subspace selection
process for the trial space (the so-called adaptive greedy
algorithm) is employed, respectively, for small and large scale
problems. 相似文献
107.
Recent studies have revealed that the fractional derivative can behave as a dissipative term. The analysis of a simple fractional oscillator has supported this point of view. However, other physical aspects related to fractional derivative are also important to be explored. For this purpose, in this work, we employ the fractional approach and guide ourselves by the above property to investigate the falling body problem. We show that the velocity of a falling body, in the fractional approach, can be greater (t<1) or less (t>1) than that velocity of free-fall obtained by the usual approach. Moreover, we show that the fractional derivative alone is not sufficient to attain a terminal speed. In order to provide a terminal speed into the fractional system a term, proportional to velocity, must be introduced. 相似文献
108.
Wei‐Yu Bi Xing‐Qiang Lü Wen‐Li Chai Ji‐Rong Song Wai‐Kwok Wong Xiao‐Ping Yang Richard A. Jones 《无机化学与普通化学杂志》2008,634(10):1795-1800
Two heterobimetallic Zn‐Nd phenylene‐bridged Schiff‐base ligands complexes [ZnNd L1 (Py)(NO3)3] ( 1 ) and [Zn L2 Nd(Py)(NO3)3]·MeCN ( 2 ) (Py = pyridine, H2L1 = N,N′‐bis‐ (3‐methoxy‐salicylidene)phenylene‐1,2‐diamine, H2L2 = N,N′‐bis‐5‐bromo‐3‐methoxy‐salicylidene)phenylene‐1,2‐diamine) were obtained. Both 1 and 2 were structurally characterized by X‐ray crystallography, and their near‐infrared (NIR) luminescent properties were determined. For the two complexes, the occupation of pyridine at the axial position of 3d Zn2+ ions could effectively prevent luminescent quenching arising from OH‐, NH‐ or CH oscillators of the solvates around the 4f Nd3+ ions, and the heavy‐atom (Br) effect of the Schiff‐base ligands on their NIR luminescent properties is also discussed. 相似文献
109.
110.
Tze-Lock Chan Si-San Kwong Thomas C. W. Mak Russell Kwok Xiao-Ming Chen Kai-Liang Shi 《Journal of inclusion phenomena and macrocyclic chemistry》1988,6(5):507-513
C19H19NO3·x CH3CN (x=0.3),M
r=643.35, hexagonal, space groupP61 (No. 169),a=23.027(5),c=5.775(1) Å,V=2652(1) Å3,Z=6. The structure was solved by direct methods and refined toR=0.077 for 1562 observed MoK
reflections. The title heterocyclic carboxylic acid was established as thetrans isomer, with the phenyl and carboxyl substituents occupying pseudo-equatorial and equatorial positions, respectively, of the piperidin-2-one ring in a half-chair conformation. Acid host molecules related by the 61 screw operation are linked by intermolecular O–H...O (cyclic amide) hydrogen bonds to generate an open channel bounded by coaxial intertwined helices each having a pitch of 5c. Within each channel of free diameterca. 6.0 Å the acetonitrile molecules partially occupy highly disordered sites which do not lie on thec axis.
Supplementary Data relating to this article are deposited with the British Library as Supplementary Publication No. SUP 82067 (13 pages). 相似文献