Role Of Charge Distribution Research Articles

The role of charge distribution on the friction coefficients of epitaxial graphene grown on the Si-terminated and C-terminated faces of SiC

The friction coefficients of single-layer epitaxial graphene grown on the Si-terminated and C-terminated faces of Silicon Carbide (SiC) substrate were measured under ambient conditions using Friction Force Microscope (FFM). The lateral friction force measurements acquired in the applied normal force range between 4.0 and 16.0 nN showed that the friction coefficient of graphene on the C-terminated face of SiC is about two times smaller than the one grown on its Si-terminated face. The lateral friction was found to be decreased as the average of root mean square roughness increases suggesting the observed difference in the friction coefficients cannot be related to the roughness of the graphene layers. DFT calculations demonstrated that the altered periodicity of charge distribution on graphene due to the specific interactions with two distinct polar faces of SiC substrate might explain the observed difference in the friction coefficients.

Peptide Dendrimer-Lipid Conjugates as DNA and siRNA Transfection Reagents: Role of Charge Distribution Across Generations.

Transfection reagents are used to deliver DNA and siRNA into cells to achieve genetic manipulations, and may ultimately enable nonviral gene therapy. Progress in transfection reagents is limited by the fact that such reagents cannot be easily optimized due to their polymeric nature and/or difficult synthesis. We have developed a new class of well-defined and easily modifiable transfection reagents in the form of peptide dendrimers. These dendrimers self-assemble with DNA or siRNA and lipofectin to form nanoparticles which efficiently enter mammalian cells and liberate their nucleic acid cargo. By systematically modifying the amino acid sequence of our dendrimers we have found that their transfection efficiency depends on the distribution of positive charges and hydrophobic residues across the dendrimer branches. Positive charges present in all three generations lead to efficient DNA delivery, whereas siRNA delivery requires charges in the outer two generations combined with a hydrophobic dendrimer core.

Role of charge distribution in a flexible loop on bioluminescence color of firefly luciferase: a lesson from nature

The presence of Arg353 in PhRE luciferase, which corresponds to the deleted residue in green emitter luciferases, is an important distinctive structural feature of it. Insertion and substitution of positively‐charged amino acids in a flexible loop (352TPEGDDKP359) of firefly luciferase brought about with change of bioluminescence color. Insertion of Arg356 in a green‐emitter luciferase (Lampyris turkestanicus), that is corresponding to Arg353 in P. hirtus, changed the emitted light from green to red. In order to further clarification of the effect of this position in the light shift, residues with positive side‐chain (Arg356 and Lys356) were inserted in Photinus pyralis luciferase which changed the light color to red, while insertion of a residue with negative side‐chain (Glu356) had little effect and a neutral residue (Gln356) had not any effect on color. On the other hand, by insertion and substitution of positive‐charged residues, in the same loop of Lampyris turkestanicus luciferase, different mutation (E354R/Arg356, E354k/Arg356, E354R, E354K) lead to changes of the bioluminescence color. Bioluminescence emission spectra indicate that substitution of E354 by R along with insertion of Arg356 produces a luciferase that emit red light with a single peak bioluminescence spectrum.

Charge distribution effects in polyatomic reactants involved in simple electron transfer reactions

The role of charge distribution in a polyatomic reactant in determining its effective charge in the double layer is discussed. It is shown that the use of a corrected Tafel plot (cTp) requires knowledge of the effective charge on both the reactant and product of a simple electron transfer process. This leads to the use of so called apparent corrected Tafel plots. Data obtained in this laboratory for six different simple electron transfer reactions involving transition metal ions are reviewed, and discussed in terms of their kinetic parameters, namely, the effective charge on the reactant and the apparent Tafel coefficient.

The Role of Charge Distribution on the Antimalarial Activity of Artemisinin Analogues.

In this work the calculated nuclear quadrupole coupling constants (NQCC; Χ) of 1 7 O in artemisinin and some of its derivatives and the effects of charge density due to the nature of ligands on NQCC of 1 7 O were investigated. All calculations were performed at the HF/3-21G level using the Gaussian 98 program. The results show that the O-O linkage has a characteristic role in the antimalarial activity of artemisinin. In addition, various substitutions on C4 change the charge density on these oxygens and consequently change the pharmaceutical effect of artemisinin. Our results suggest that due to a larger charge density on O1, the heme iron approaches the endoperoxide moiety at the O1 position with preference to the 02 position.

The Role of Charge Distribution on the Antimalarial Activity of Artemisinin Analogues

In this work the calculated nuclear quadrupole coupling constants (NQCC; chi) of 17O in artemisinin and some of its derivatives and the effects of charge density due to the nature of ligands on NQCC of 17O were investigated. All calculations were performed at the HF/3-21G level using the Gaussian 98 program. The results show that the O-O linkage has a characteristic role in the antimalarial activity of artemisinin. In addition, various substitutions on C4 change the charge density on these oxygens and consequently change the pharmaceutical effect of artemisinin. Our results suggest that due to a larger charge density on O1, the heme iron approaches the endoperoxide moiety at the O1 position with preference to the O2 position.

Role of Charge Distribution in the Reactant and Product in Double Layer Effects: Construction of Corrected Tafel Plots

The effect of charge distribution within Cr(III) and Eu(III) aquacomplexes on the kinetics of simple electron-transfer reactions at electrodes is considered. The construction of corrected Tafel plots using noninteger effective charges for the reactant and product estimated on the basis of quantum-chemical data was shown to be more reasonable than the traditional approach in which integer charges are assumed. The potential distribution near the electrode has been estimated both by the Gouy-Chapman model and from Monte Carlo simulations for 1-1 supporting electrolytes. Kinetic parameters obtained using the two approaches are compared.

The role of charge distribution in the reactant and product in double layer effects for simple heterogeneous redox reactions

The role of charge distribution in transition metal complexes is considered for simple heterogeneous electron transfer reactions. On the basis of quantum chemical calculations for the couples [Co(NH3)6]3+/2+, [Fe(H2O)6]3+/2+, and Fe(CN)63−/4−, and a simple model for the double layer, it is shown that the double layer effect for these reactions depends more on the charge on the ligands than on that on the central metal ion. The results of calculations based on the double layer model are discussed with respect to experimental data obtained at mercury and single crystal gold electrodes.

Electrostatic Effects on Partitioning of Proteins in Aqueous Two-Phase Systems: I. pH and Charge Equilibria

The charge on a protein molecule is obviously an average, and here the role of charge distribution is accounted for by using Hill's small system thermodynamics. The conventional equation of protein charging is obtained in a very simple manner, and with a more accurate description of the electrostatic effects some insight into anomalous effects is also obtained. The importance of straightening out the charge effects becomes obvious in treating the more complicated system of partitioning proteins in an aqueous two-polymer two-phase system. Correct dependence of the partition coefficient on the charge is obtained. This takes the form that the logarithm of the partition coefficient is proportional to the square of the charge at low charges and only to the charge at large values, in keeping with the experimental data. However, it is only easy to get some form of upper limit and difficult to quantify individual cases because of the large number of variables involved and because detailed data are unavailable. An explanation has been given as to why the logarithm of the partition coefficient versus charge (z p or z 2 p) plots have varying slopes and intercepts. This explanation lies in the asymmetry of the polymer distribution and thus provides an explanation as to why the protein partitions unequally, in that the asymmetrically distributed polymers affect the charge and ion equilibria in proteins differently and thus partition proteins differently into the two phases. Obviously, the polymer molecular weight distribution is a key feature in determining this asymmetry and, with one polymer bimodally distributed, it is possible to show that if some amount of the same polymer of a larger molecular weight is added it steepens the partitioning, but a lower molecular weight fraction has no effect.

Superconductivity near 70 K in a new family of layered copper oxides

A new family of high-temperature superconductors is described, with the general formula Pb2Sr2ACu3O8+δ. Although they have the planes of CuO5 square pyramids characteristic of the other copper-oxide superconductors, the new compounds belong to a distinct structural series, with wide scope for elemental substitution. Their unusual electronic configuration also gives new insight into the role of charge distribution among the structural building blocks in controlling superconductivity.