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71.
Dou RF Ma XC Xi L Yip HL Wong KY Lau WM Jia JF Xue QK Yang WS Ma H Jen AK 《Langmuir : the ACS journal of surfaces and colloids》2006,22(7):3049-3056
Parallel-displaced pi-pi stacking interactions have been known to be the dominant force in stabilizing the double helical structure of DNA and the tertiary structure of proteins. However, little is known about their roles in self-assembled monolayers of other large pi molecules such as aromatic thiols. Here we report on a systematic study of the self-assembled monolayers of four kinds of anthracene-based thiols, 9-mercaptoanthracene (MA), (4-mercaptophenyl) (9-anthryl) acetylene (MPAA), (4-mercaptophenyl) (10-nitro-9-anthryl) acetylene (MPNAA), and (4-mercaptophenyl) (10-carboxyl-9-anthryl) acetylene (MPCAA) on Au(111), in which a spacer and different functional groups (NO2 and COOH) are intentionally designed to introduce and thus allow the investigation of various intermolecular interactions, in addition to pi-pi interactions in the base molecules. We find that all molecules form long-range-ordered monolayers and, more interestingly, that these assembled monolayers exhibit essentially the same fundamental packing structure. On the basis of high-resolution scanning tunneling microscopy observations, we propose the space-filling models for the observed superstructures and demonstrate that all superstructures can be understood in terms of the parallel-displaced pi-pi stacking interactions, despite the presence of competing dipole-dipole and H-bonding interactions associated with these specially designed functional groups. 相似文献
72.
Tavana H Yang G Yip CM Appelhans D Zschoche S Grundke K Hair ML Neumann AW 《Langmuir : the ACS journal of surfaces and colloids》2006,22(2):628-636
Contact angles of a series of n-alkanes (i.e., n-heptane to n-hexadecane) are studied on two functionalized maleimide copolymers (i.e., poly(ethene-alt-N-(4-(perfluoroheptylcarbonyl)aminobutyl)maleimide) (ETMF) and poly(octadecene-alt-N-(4-(perfluoroheptylcarbonyl)aminobutyl)maleimide) (ODMF)). On the homogeneous ETMF films, all liquids show a smooth motion of the three-phase line. In contrast, on ODMF surfaces that are found to consist of mainly fluorocarbons and small patches of hydrocarbons, short-chain n-alkanes show a stick-slip pattern. By increasing the chain length of the probe liquids, stick-slip is reduced significantly. The phenomenon is discussed in the framework of the Cassie equation. It is found that the upper limit of contact angles in the stick-slip pattern is given by the advancing angle that would be obtained on the pure fluorocarbon surface, whereas the lower limit of the stick-slip pattern is given by the Cassie angle. 相似文献
73.
Ye?Mei Caiyi?Wei Yew?Mun?Yip Chun?Ying?Ho John?Z.?H.?Zhang Dawei?ZhangEmail author 《Theoretical chemistry accounts》2012,131(3):1168
Two replica exchange molecular dynamics (REMD) simulations were carried out to study the thermodynamics of a 20-residue Trp-cage
folding based on a newly developed polarized protein-specific charge (PPC). Starting from a fully extended conformation, Trp-cage
native conformation was successfully sampled using REMD based on a 3-step PPC update. Next, the obtained Trp-cage folded conformation
was then used to calculate the PPC in which another REMD was performed to explore the thermodynamic stability of Trp-cage.
The theoretical melting temperature T
m of ≈325 K was found to be in close agreement with experimental melting temperature, T
m of 315 K. This indicates that the PPC was correctly predicting the temperature dependence. The current study provides a direct
proof of how electrostatic polarization affects protein folding. 相似文献
74.
75.
Pensini E Yip CM O'Carroll DM Sleep BE 《Langmuir : the ACS journal of surfaces and colloids》2012,28(28):10453-10463
The transport of particles through groundwater systems is governed by a complex interplay of mechanical and chemical forces that are ultimately responsible for binding to geological substrates. To understand these forces in the context of zero valent iron particles used in the remediation of groundwater, atomic force microscopy (AFM)-based force spectroscopy was employed to characterize the interactions between AFM tips modified with either carbonyl iron particles (CIP) or electrodeposited Fe as a function of counterion valency, temperature, particle morphology, and age. The measured interaction forces were always attractive for both fresh and aged CIP and electrodeposited iron, except in 100 mM NaCl, as a consequence of electrostatic attraction between the negatively charged mica and positively charged iron. In 100 mM NaCl, repulsive hydration forces appeared to dominate. Good agreement was found between the experimental data and predictions based on the extended DLVO (XDLVO) theory. The effect of aging on iron particle composition and morphology was assessed by X-ray photoelectron spectroscopy (XPS), scanning electron microscopy (SEM), and energy dispersive spectroscopy (EDS) revealing that the aged particles comprising a zero valent iron core passivated by a mixture of iron oxides and hydroxides. Force spectroscopy showed that aging caused variations in the adhesive force due to the changes in particle morphology and contact area. 相似文献
76.
Martha Yip 《Mathematische Zeitschrift》2012,272(3-4):1259-1290
Macdonald polynomials are orthogonal polynomials associated to root systems, and in the type A case, the symmetric Macdonald polynomials are a common generalization of Schur functions, Macdonald spherical functions, and Jack polynomials. We use the combinatorics of alcove walks to calculate products of monomials and intertwining operators of the double affine Hecke algebra. From this, we obtain a product formula for Macdonald polynomials of general Lie type. 相似文献
77.
In this paper, the problems of estimating the covariance matrix in a Wishart distribution (refer as one-sample problem) and the scale matrix in a multi-variate F distribution (which arise naturally from a two-sample setting) are considered. A new class of estimators which shrink the eigenvalues towards their harmonic mean is proposed. It is shown that the new estimator dominates the best linear estimator under two scale invariant loss functions. 相似文献
78.
79.
The phonon dispersion in semiconductor superlattices is studied in the adiabatic bond-charge model. The complex phonon dispersion relations of the constituent bulk materials are obtained via the eigenvalue method in a zeroth-order calculation, which includes only short range forces and Coulomb interactions between ions and bond charges in the same and neighboring layers. The eigenmode displacements of the superlattice are obtained by matching the eigenvectors associated with complex phonon branches at the interfaces. The effect of the remaining Coulomb interactions are then included in the first-order approximation. The results for the superlattice phonon frequencies compare favorably with the existing experimental data. 相似文献
80.