No abstract

Dielectrophoresis is an electronic analogue1,2 of optical tweezers3 based on the same physical principle: an ac electric field induces a dipole moment on an object in solution, which then experiences a force proportional to the gradient of the field intensity. For both types of tweezers, this force must compete with thermal Brownian4 motion to be effective, which becomes increasingly difficult as the particle size approaches the nanometer scale. Here we show that this restriction can be overcome by using the large electric field gradient in the vicinity of a carbon nanotube to electronically manipulate nanoparticles down to 2 nm in diameter.

Using the tools of modern molecular biology, we probe the interaction of nanotubes on silicon chips with proteins via combinatorial phage display methods. By screening against a large library of random peptides, we find that over half of the single-walled carbon nanotube (SWNT)-binding peptides show a motif of SXWWXXW, where S is serine, W is tryptophan, and X is anything. In a helical wheel diagram, this peptide is amphiphilic, where the hydrophobic and aromatic tryptophan side groups are concentrated on one face of an R-helix. This theme is robust and occurs in all of the SWNT-binding peptides. Surprisingly, the other aromatic amino acids seem less likely to show up in the screen, indicating a special role of tryptophan in binding to SWNTs. By elucidating the physical principles underlying the interaction between SWNTs and peptides and proteins, this work lays the foundation for the eventual human (or computer) nanoengineered, precise, and economical manipulation of nanotubes using peptides and proteins for nanotube sorting, assembly into electronic components, and understanding the effect of biological function.

No abstract

No abstract

No abstract

Single-molecule enzymology allows scientists to examine the distributions of kinetic rates among members of a population. We describe a simple method for the analysis of single-molecule enzymatic kinetics and provide comparisons to ensemble-averaged kinetics. To isolate our model enzyme, alpha-chymotrypsin, into single molecules, we use an array of cylindrical poly(dimethylsiloxane) wells 2 microm in diameter and 1.35 microm in height. Inside the wells, a protease assay with a profluorescent substrate detects alpha-chymotrypsin activity. We hold the concentration of alpha-chymotrypsin at 0.39 nM in a given well with an enzyme-to-substrate ratio of 1:6,666 molecules. Fluorescence emitted by the substrate is proportional to enzyme activity and detectable by a charge-coupled device. This method allows for the simultaneous real-time characterization of hundreds of individual enzymes. We analyze single-molecule kinetics by recording and observing their intensity trajectories over time. By testing our method with our current instruments, we confirm that our methodology is useful for the analysis of single enzymes for extracting static inhomogeneity.

Mn-corrolazine-catalyzed CH 4 oxidation, as well as the regulation of its oriented external electric fields (OEEFs), is systematically studied using the first-principle calculations. Extensive density functional calculations show that the activation energy of CH 4 oxidation catalyzed by Mn-corrolazine is up to 38.5 kcal/mol in the field-free condition. However, when the OEEF is applied, the reactant and the transition state of the oxidation reaction are stabilized, originating from an attractive interaction between the increased dipole moment and the applied fields. Furthermore, when the field is negative, the activation energy decreases as the field increases. Especially for the negative field along the intrinsic Mn O reaction axis perpendicular to the corrolazine ring, of which the orientation is easily aligned in practical applications, when its intensity reaches −0.015 a.u., the activation energy of CH 4 oxidation is reduced to 25.0 kcal/mol. K E Y W O R D S catalysis, CH 4 oxidation, density functional theory calculations, Mn-corrolazine, oriented external electric field 1 | INTRODUCTION Searching for novel and efficient catalysts has always been the most important subject in chemical research. Traditionally, the common catalysts are molecules and the surfaces or interface in homogeneous and heterogeneous systems, [1-6] respectively. However, in recent years, many new technologies, such as ultrasound, [7] microwaves, [8] mechanical stress, [9] and nanoreactors, [10] have been used to control various reaction processes as novel catalysts. Electrostatic forces play an extremely important role in chemical reactions involving the arrangement of nuclei and electrons. [11-13] A typical example is the electrostatic catalysis of enzymes in nature. [10,14-16] The polar environment originating from the subtle arrangement of atoms around the active site produces the electric field that can efficiently and selectively catalyze various biochemical reactions. Using the same idea, research is increasingly focused on regulating the stability of the reactants and transition states, as well as products, using artificial external electric fields through dipole-field interaction, thereby manipulating the chemical reaction process. [17-44] Very recently, Shaik et al. performed a much computational research to explore the effect of oriented external electric fields (OEEFs) on organic reactions. [17-23] Their research results show that OFFEs along the reaction axis involving the electron transfer can significantly catalyze the organic reactions, while the OFFEs along other directions can control the regioselectivity and stereoselectivity, and some results are confirmed by experimental evidence provided by Aragonès et al. [18] However, although great progress has been made in both the experimental and theoretical research, [17-24,27,30] a major problem in using the OFFEs to manipulate reaction processes is to deliver the external electric fields and orient the molecules within the applied fields simultaneously. The corrole, a porph...