Nanoparticle shape anisotropy dictates the collective behavior of surface-bound ligands

We report on the modification of the properties of surface-confined ligands in nanoparticle systems through the introduction of shape anisotropy. Specifically, triangular gold nanoprisms, densely functionalized with oligonucleotide ligands, hybridize to complementary particles with an affinity that is several million times higher than that of spherical nanoparticle conjugates functionalized with the same amount of DNA. In addition, they exhibit association rates that are 2 orders of magnitude greater than those of their spherical counterparts. This phenomenon stems from the ability of the flat, extended facets of nonspherical nanoparticles to (1) support more numerous ligand interactions through greater surface contact with complementary particles, (2) increase the effective local concentration of terminal DNA nucleotides that mediate hybridization, and (3) relieve the conformational stresses imposed on nanoparticle-bound ligands participating in interactions between curved surfaces. Finally, these same trends are observed for the pH-mediated association of nanoparticles functionalized with carboxylate ligands, demonstrating the generality of these findings.     

Selective enhancement of nucleases by polyvalent DNA-functionalized gold nanoparticles

We demonstrate that polyvalent DNA-functionalized gold nanoparticles (DNA-Au NPs) selectively enhance ribonuclease H (RNase H) activity while inhibiting most biologically relevant nucleases. This combination of properties is particularly interesting in the context of gene regulation, since high RNase H activity results in rapid mRNA degradation and general nuclease inhibition results in high biological stability. We have investigated the mechanism of selective RNase H activation and found that the high DNA density of DNA-Au NPs is responsible for this unusual behavior. This work adds to our understanding of polyvalent DNA-Au NPs as gene regulation agents and suggests a new model for selectively controlling protein-nanoparticle interactions.     

Nanoelectrodes for intracellular measurements of reactive oxygen and nitrogen species in single living cells

Reactive oxygen and nitrogen species (ROS and RNS) play important roles in various physiological processes (e.g. phagocytosis) and pathological conditions (e.g. cancer). The primary ROS/RNS, viz., hydrogen peroxide, peroxynitrite ion, nitric oxide, and nitrite ion, can be oxidized at different electrode potentials and therefore detected and quantified by electroanalytical techniques. Nanometer-sized electrochemical probes are especially suitable for measuring ROS/RNS in single cells and cellular organelles. In this article, we survey recent advances in the localized measurements of ROS/RNS inside single cells and discuss several methodological issues, including optimization of nanoelectrode geometry, precise positioning of an electrochemical probe inside a cell, and interpretation of electroanalytical data.     

离子声等离子体波的动力屏蔽

本文讨论了离子声等离子体波的激发条件和它们对荷电粒子间相互作用势的动力屏蔽效应.对一些具有两个未完全被充满的外层电子能带的金属,计算了这种屏蔽效应,并研究了此动力效应对金属钯中氘-氘聚变反应率的影响.     

Federations and transitive group choice

The following is a brief English summary of the paper Mirkin (1979), in which he discusses social welfare functions where the relations involved are solely assumed to be reflexive. Under axioms of independence and neutrality, monotonicity, and two domain assumptions the author shows that such a social welfare function is determined by a ‘federation’,i.e., the set of coalitions such that if that each member considers a not worse than b so does the group. The author then characterizes transitive, completeness, definiteness, (a sort of non-indifference assumption), and majority rule in this framework. He also characterizes those domains on which social welfare functions determined by federations F satisfying I ∈ F if and only if ī ? F, are transitive. We omit proofs, which are given in the Russian version, as well as the author's discussion of these results.     

Influence of elevated hydrostatic pressure on the diffusion constants of polymer materials

The authors give experimental results showing how the diffusion constants of various polymer materials depend on the (elevated) hydrostatic pressure.A. A. Zhdanov Leningrad State University. Translated from Mekhanika Polimerov, No. 2, pp. 344–346, March–April, 1974.     

The action of intense light beams on metal surfaces

Studies of the effect of lasers on metals have shown that the action of intense light beams leads to the formation of craters on metal surfaces. A considerable increase in hardness is often observed in the region of such craters; the hardness of low-carbon steels may reach 700 kg/mm², which is considerably higher than that produced by other heat and mechanical treatments.In conclusion, the authors would like to thank R. V. Khokhlov for providing the facilities for the experimental work, and G. I. Barenblatt and I. M. Gryuznov for their assistance in interpreting the results.     

Reversible CO-induced chloride shuttling in Rh(I) tweezer complexes containing urea-functionalized hemilabile ligands

The urea moiety, which acts as a good hydrogen-bond donor, has been incorporated into a hemilabile phosphinoalkyl thioether ligand. Upon reaction of the ligand with a Rh(I) precursor, a tweezer complex with near-parallel planar urea moieties 2 forms. The host-guest interaction of 2 with Cl(-) has been characterized in solution and in the solid state. Cl(-) binding with the urea groups in 2 is retained under CO in nonpolar solvents to give a five-coordinate CO adduct 3. In polar solvents, CO binding to Rh(I) results in a Cl(-) shift from the urea host site to the Rh(I) metal center with a concomitant breaking of the Rh-S bonds. This is an unusual example of how two types of different interactions important in molecular recognition (ligand coordination to a metal and hydrogen bonding) can be regulated within one molecule through small-molecule coordination chemistry.