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151.
Manning GS 《The European physical journal. E, Soft matter》2011,34(12):132-18
There is abundant experimental evidence suggesting the existence of attractive interactions among identically charged polyelectrolytes
in ordinary salt solutions. The presence of multivalent counterions is not required. We review the relevant literature in
detail and conclude that it merits more attention than it has received. We discuss also some recent observations of a low
ionic strength attraction of negatively charged DNA to the region of a negatively charged glass nanoslit where the floor of
the nanoslit meets the walls, again in the absence of multivalent ions. On the theoretical side, it has become clear that
purely electrostatic interactions require the presence of multivalent counterions if they are to generate like-charge attraction.
Any theory of like-charge attraction in the absence of multivalent counterions must therefore contain a non-electrostatic
component. We point out that counterion condensation theory, which has predicted like-charge polyelectrolyte attraction in
an intermediate range of distances in ordinary 1:1 salt conditions, contains both electrostatic and non-electrostatic elements.
The non-electrostatic component of the theory is the modeling constraint that the counterions fall into two explicit populations,
condensed and uncondensed. As reviewed in the paper, this physically motivated constraint is supported by strong experimental
evidence. We proceed to offer an explanation of the nanoslit observations by showing in an idealized model that the line of
intersection of two intersecting planes is a virtual polyelectrolyte. Since we have previously developed a counterion condensation
theory of attraction of two like-charged polyelectrolytes, our suggestion is that the DNA is attracted to the virtual polyelectrolytes
that may be located in the nanoslit where floor meets walls. We present the detailed calculations needed to document this
suggestion: an extension of previous theory to the case of polyelectrolytes with like but not identical charges; the demonstration
of counterion condensation on a plane with bare charge density greater than an explicitly exhibited critical value; a calculation
of the free energy of the plane; a calculation of the interaction of a line charge polyelectrolyte with a like-charged plane;
and the detailed demonstration that the line of intersection of two planes is a virtual polyelectrolyte. 相似文献
152.
The feasibility of constructing carbocycles through the metal-halogen exchange-initiated cyclization reactions of iodoketones and other carboxyl derivatives has been studied. With saturated primary iodides, cyclization predominates when deactivated ketones are employed. 相似文献
153.
154.
155.
Wayne B. Manning 《Tetrahedron letters》1981,22(17):1571-1574
No regiochemical directing effects could be attributed to methoxy styrene ring substituents in the cycloaddition of substituted styrene to juglone and its methyl ether. Control of quinone electron distributions, however, led to higher regioselectivity. 相似文献
156.
157.
David Wilbur Wayne B. Manning Bruce D. Hilton Gary M. Muschik 《Magnetic resonance in chemistry : MRC》1982,18(2):63-67
Benz[a]anthracene-7, 12-dione, eight monomethoxybenz[a]anthracene-7, 12-diones and two dimethoxybenz[a]anthracene-7, 12-diones were analyzed by 13C and 1H NMR. All 13C and 1H resonances have been assigned. Substituent effects on the 13C chemical shifts are discussed. 相似文献
158.
159.
Development and characterization of high performance solid propellants containing nano-sized energetic ingredients 总被引:7,自引:0,他引:7
J.R. Luman B. Wehrman K.K. Kuo R.A. Yetter N.M. Masoud T.G. Manning L.E. Harris H.A. Bruck 《Proceedings of the Combustion Institute》2007,31(2):2089-2096
This paper addresses the development of a pair of layered solid propellants suitable for use in a fast-core gun-propellant charge application. A baseline propellant combination was formulated using RDX particles and thermoplastic-elastomer binder as the major ingredients and CL-20 and nitroguanadine as separate additives for high- and low-energy propellants. The propellant’s burning rate was characterized and insufficient burning-rate ratio between the fast and slow baseline propellants was found. Impetus obtained from the combustion of the combined baseline propellants was also found to be far from the demanded value of 1300 J/g. Several modifications were made by introducing nano-sized aluminum particles and ultra-fine boron particles as well as high-energy oxidizer HNF into the propellant formulation. It was found that the addition of nano-sized aluminum particles can enhance the propellant burning rate only when the propellant contains oxidizers with a positive oxygen balance. Without the presence of positive oxygen balance oxidizer, the exothermic reaction of aluminum and boron particles occurs at a large distance from the burning surface introducing an energy-sink effect. The results obtained from the combustion of the advanced propellants show that an average impetus of 1299 J/g, a flame temperature of 3380 K with a burn rate ratio around 3 between the fast- and the slow-burning layers can be achieved. These conditions are desired for fast-core layered propellant applications. The impact sensitivities of the baseline, intermediate and advanced propellants were measured. The results show that addition of HNF and nano-sized aluminum exhibited improved impact sensitivity at levels that can be considered acceptable for deployment. 相似文献
160.