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61.
Rabindra N. Roy Lakshmi N. Roy Kathleen A. Allen Casey J. Mehrhoff Isaac B. Henson Jessica M. Stegner Alexis L. Jenkins Ankita A. Shah Stephen D. Rocchio 《Journal of solution chemistry》2012,41(6):1044-1053
In this study, we report the pH values of two buffer solutions without chloride ion and eight buffer solutions with NaCl with an ionic strength I=0.16 mol?kg?1. Electromotive force (emf) techniques have been used to get the cell potentials at 12 temperatures from 5 to 55?°C, including 37?°C. An extended form of the Bates-Guggenheim convention is used in the entire ionic strength range, 0.04 to 0.16?mol?kg?1. The residual liquid junction potentials (??E j ) of the buffer solutions of MOBS have been estimated from previous measurements with a flowing junction cell. These values of ??E j have been used for correction in order to ascertain the operational pH values of four buffer solutions of MOBS at 25 and 37?°C. These solutions are recommended as pH standards for physiological application in the pH range 7.4 to 7.7. 相似文献
62.
63.
Jessica M. Torres Christopher M. Stafford David Uhrig Bryan D. Vogt 《Journal of Polymer Science.Polymer Physics》2012,50(5):370-377
The modulus and glass transition temperature (Tg) of ultrathin films of polystyrene (PS) with different branching architectures are examined via surface wrinkling and the discontinuity in the thermal expansion as determined from spectroscopic ellipsometry, respectively. Branching of the PS is systematically varied using multifunctional monomers to create comb, centipede, and star architectures with similar molecular masses. The bulk‐like (thick film) Tg for these polymers is 103 ± 2 °C and independent of branching and all films thinner than 40 nm exhibit reductions in Tg. There are subtle differences between the architectures with reductions in Tg for linear (25 °C), centipede (40 °C), comb (9 °C), and 4 armed star (9 °C) PS for ≈ 5 nm films. Interestingly, the room temperature modulus of the thick films is dependent upon the chain architecture with the star and comb polymers being the most compliant (≈2 GPa) whereas the centipede PS is most rigid (≈4 GPa). The comb PS exhibits no thickness dependence in moduli, whereas all other PS architectures examined show a decrease in modulus as the film thickness is decreased below ~40 nm. We hypothesize that the chain conformation leads to the apparent susceptibility of the polymer to reductions in moduli in thin films. These results provide insight into potential origins for thickness dependent properties of polymer thin films. © 2011 Wiley Periodicals, Inc. J Polym Sci Part B: Polym Phys, 2012 相似文献
64.
A solid state metathesis (SSM) reaction was investigated with respect to the formation of rare‐earth carbodiimides, the role of the co‐produced salt (LiCl), and the eutectic flux medium (LiCl/KCl). A SSM reaction is characterized by an exothermic reaction in which a salt (often LiCl) is coproduced. When the salt melts, it can serve as a useful medium for the crystallization of a desired product. An improved crystal growth can be observed by using an eutectic flux. However, the composition of an eutectic LiCl/KCl flux is altered when LiCl is produced during the reaction. The thermal effects concerning the endothermic melting of the flux and the exothermic ingnition of the SSM reaction may compensate each other, which is not necessarily a drawback for the reaction to proceed. 相似文献
65.
Bennett N. Walker Jessica A. Stolee Deanna L. Pickel Scott T. Retterer Akos Vertes 《Applied Physics A: Materials Science & Processing》2010,101(3):539-544
Experimental assessment of the thermal load induced by fast laser pulses on micro- and nanostructures through IR imaging is
currently too slow and lacks the spatial resolution to be useful. In this paper, we introduce a method based on measuring
the laser-induced yields of ions to compare the thermal loads on nanofabricated silicon structures, when exposed to nanosecond
laser pulses. The laser fluences at which the ion yields of, for example, sodiated and potassiated peptides ions are equal
for two different structures correspond to equivalent thermal loads. Using alkalinated peptides is a convenient choice because
the corresponding ion intensities are easily measured up to the melting point of silicon. As an example, we compare the nanosecond
laser heating of silicon nanopost arrays with diverse post diameters and periodicities. Assessment of the thermal load through
ion yield measurements can also be used to verify model assumptions for heat transport regimes in nanostructures. 相似文献
66.
Moser DF Bosse T Olson J Moser JL Guzei IA West R 《Journal of the American Chemical Society》2002,124(16):4186-4187
A number of disilanes have been synthesized from a stable silylene, 1 (N,N'-di-tert-butyl-1,3-diaza-2-silacyclopent-4-en-2-ylidene), and a variety of halocarbons. It is proposed that disilane formation is a result of an initial halophilic interaction between the silylene and halocarbon. Formation of disilanes from 1 and CCl4, 2a, CHCl3, 2b, CH2Cl2, 2c, benzyl chloride, 2d, and bromobenzene, 5, are described here. An X-ray crystal structure of 2b was determined. 相似文献
67.
Many recent advances in Poisson-Boltzmann and generalized Born implicit solvent models have used atom-centered polynomial or Gaussian functions to define the boundary separating low and high dielectric regions. In contrast to the Lee and Richards molecular surface, atom-centered surfaces result in interatomic crevices and buried pockets of high dielectric which are too small for a solvent molecule to occupy. We show that these interstitial high dielectric regions are of significant magnitude in globular proteins, that they artificially increase solvation energies, and that they distort the free energy surface of nonbonded interactions. These results suggest that implicit solvent dielectric functions must exclude interstitial high dielectric regions in order to yield physically meaningful results. 相似文献
68.
Mohd Mustapa MF Harris R Esposito D Chubb NA Mould J Schultz D Driscoll PC Tabor AB 《The Journal of organic chemistry》2003,68(21):8193-8198
Two diastereomeric analogues of ring C of nisin incorporating a novel norlanthionine residue have been synthesized via a triply orthogonal protecting group strategy. A full structural study was carried out by NMR, which elucidated the conformational properties of the two peptides and enabled the identity of each diastereoisomer to be proposed. 相似文献
69.
Kerckhoffs JM Ishi-i T Paraschiv V Timmerman P Crego-Calama M Shinkai S Reinhoudt DN 《Organic & biomolecular chemistry》2003,1(14):2596-2603
This article describes the complexation of phenol derivatives by hydrogen-bonded receptors. These phenol receptors are formed by self-assembly of calix[4]arene dimelamine or tetramelamine derivatives with 5,5-diethylbarbiturate (DEB) or cyanurate derivatives (CYA). The double rosette assemblies 3(3).(DEB)6/(CYA)6 have their phenol-binding functionalities (ureido groups) at the top and at the bottom of the double rosette (exo-receptors). The tetrarosette assemblies 4(3).(DEB)12/(CYA)12 form a cavity with binding sites between the two double rosettes for guest encapsulation (endo-receptors). An intrinsic binding constant Ka of 202 M-1 and 286 M-1 for the binding of 4-nitrophenol to the ureido functionalized exo- and endo-receptors, respectively, was observed. For the exo-receptor a 1:6 stoichiometry was observed while for the endo-receptor 1:4 binding stoichiometry was determined by Job plot and MALDI-TOF MS. The important role that the hydroxy group's acidity plays in the complexation of 4-nitrophenol is clarified by binding studies with different phenol derivatives. The hydrogen-bonded receptors showed a much smaller response towards less acidic phenol derivatives. 相似文献
70.